10,491 results
Search Results
2. Optimisation of mooring line parameters for offshore floating structures: A review paper
- Author
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Idris Ahmed Ja'e, Montasir Osman Ahmed Ali, Anurag Yenduri, Zafarullah Nizamani, and Akihiko Nakayama
- Subjects
Environmental Engineering ,Ocean Engineering - Published
- 2022
3. Research on flexible collapsible fluid-driven bionic robotic fish.
- Author
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Xia, Qingchao, Li, Hong, Song, Nan, Wu, Zeliang, Wang, Xiang, Sun, Xu, Zhang, Sheng, and Yang, Canjun
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BIONICS , *PAPER arts , *HYDRAULIC drive , *ROBOTICS , *DNA folding , *ENERGY consumption , *FISHERY products - Abstract
Hydraulic drive is one of the main driving methods of traditional bionic fish, which has the disadvantages of high driving pressure and significant radial expansion of the fishtail. In this research, two innovative structures are introduced in the fishtail design to overcome these drawbacks. Firstly, high-flexible origami technology is applied to the fishtail, significantly reducing the unwanted radial expansion of the fishtail and improving energy efficiency. Based on the experiments, the origami-structured fishtail can save up to 92.3% energy compared with the traditional fishtail. Secondly, according to the bionic principles, the hybrid neutral layer of the fishtail which is sandwich-structured with knitting methods was designed. The test results show that this novel hybrid neutral layer could save up to 56.7% energy compared to the fishtail with a rigid neutral layer. A bionic fish in BCF model (Body and/or Caudal Fin propulsion) is fabricated and tested in a water tank. The results prove that the new bionic fish with the innovative fishtail obtain a good straight-line swimming direction and turning ability. This study could provide an important reference for the bionic design to mimic real fish. • A new type of fishtail is designed with an origami-style driven structure and a neutral layer that mimics a real fish's bone. • The structure of the elastic fluid driver adopts the folding paper structure to expand and contract efficiently. • Inspired by traditional Chinese knot structure, the neutral layer of the original rigid body structure was scattered first and then connected by knot structure to form a whole structure. • The novel fishtail shows excellent energy efficiency in experiments. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Reply to Prof. Riggs’ discussion on paper “Investigation of Ship Hydroelasticity” by I. Senjanović, Š. Malenica, S. Tomašević
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Senjanovic, Ivo, primary
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- 2008
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5. Reply to Prof. Riggs’ discussion on paper 'Investigation of Ship Hydroelasticity' by I. Senjanović, Š. Malenica, S. Tomašević
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Ivo Senjanović
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Engineering ,Environmental Engineering ,Hydroelasticity ,business.industry ,Forensic engineering ,Ocean Engineering ,business - Published
- 2008
6. Leveraging digital twins for fault diagnosis in autonomous ships.
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Hasan, Agus, Asfihani, Tahiyatul, Osen, Ottar, and Bye, Robin T.
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FAULT diagnosis , *DIGITAL twins , *ELECTRONIC paper , *SHIP propulsion , *SENSOR arrays , *DRIVE shafts - Abstract
Autonomous ships are vulnerable to a spectrum of potential faults, including propeller damage, shaft-line failures, and electrical supply disruptions. Swift fault detection is critical to minimize the potentially catastrophic consequences of these issues. In this paper, we introduce an innovative digital twin-based method for diagnosing faults in autonomous ships. Our digital twin system collects data from the ship's sensor array, conducts comprehensive analysis, computes fault parameters, and provides real-time visualizations of the findings. To achieve this, we utilize the ship's dynamical model and employ a novel adaptive extended Kalman filter (AEKF) algorithm to estimate the severity of these faults. We evaluate the effectiveness of this approach through numerical simulations and practical implementation in an autonomous surface vehicle called the Otter, developed by Maritime Robotics. The experimental results, which consider both normal and faulty ship propulsion systems, underscore the significant potential of this novel approach to improve ship condition monitoring during operational activities. • This paper presents digital twin-based fault diagnosis architecture. • The fault diagnosis algorithm is based on a novel AEKF method. • The approach is demonstrated in a real-world scenario using a small autonomous vessel. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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7. Call for papers
- Published
- 1995
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8. Study on load characteristics and structural impact response propagation law of cabin internal explosion.
- Author
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Lin, Xin, Wang, Shiping, Zhang, Liang, Xu, Shaochen, and Hu, Yi
- Subjects
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IMPACT response , *SHOCK waves , *EXPLOSIONS , *VACATION homes , *NUMERICAL calculations - Abstract
Aiming at the problem that the distribution of explosion load in the cabin and the propagation law of structural impact response was unclear, this paper established the numerical calculation model of explosion in a closed cabin by ALE (Arbitrary Lagrangian Eulerian) method. There was an apparent convergence of shock waves at the cabin's corners, and the pressure relief hole's area and its position significantly affected the peak of quasi-static pressure. The peak acceleration of the deck structure decreased exponentially as the distance from the location of charge increased. Peak acceleration decreased by approximately 50% for each bulkhead crossing. There was a "paper window effect" during the cabin interior explosion on the whole ship. It meant there was a limit to the value for the energy generated by the explosion to be transmitted along the frame structure. When the charge was 150 kg, it reached the limit of the energy transferred by the structure in this paper. The response of the distant structure did not change significantly with the increase in the charge quality. The research revealed the impact response propagation mechanism in the structure and provided a reference for designing protective structures. • The shock wave shows noticeable convergence in the cabin corner, where the area and position of the pressure relief hole significantly affect the peak quasi-static pressure. • The existence of a bulkhead greatly affects the maximum acceleration, each additional bulkhead results in approximately a 50% reduction. • The investigation reveals a remarkable "paper window effect" during the localized explosion of the entire vessel. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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9. Control co-design optimization of nonlinear wave energy converters
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Abdulkadir, Habeebullah and Abdelkhalik, Ossama
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- 2024
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10. Drag reduction papers published
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- 1978
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11. Forthcoming papers
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- 1977
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12. Call for papers: 12th annual air cushion technology symposium
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- 1978
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13. Development of a wave-current model through coupling of FVCOM and SWAN
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Chao Ji, Jingsi Yang, Guangwei Liu, Tong-qing Chen, Yongsheng Wu, and Qinghe Zhang
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Environmental Engineering ,010504 meteorology & atmospheric sciences ,010505 oceanography ,Computer science ,Computation ,Ocean Engineering ,Paper based ,01 natural sciences ,Current (stream) ,Open source ,Coupling (computer programming) ,Coupling system ,0105 earth and related environmental sciences ,Marine engineering - Abstract
A coupled wave-current system has been developed in the present paper based on two open source community models, the Finite-Volume Community Ocean Model (FVCOM) and the Simulating WAves Nearshore (SWAN) using Model Coupling Toolkit (MCT). The coupled system runs on unstructured grids and multiple processors, and information, including water elevations and currents from FVCOM and wave parameters from SWAN, exchanges between FVCOM and SWAN in both on-line and two-way manners. The system was evaluated against laboratory experiments and the evaluation showed that the simulated results agree well with the measured data. Compared to the existing off-line coupling system based on FVCOM and SWAN, the system in the present study is able to accomplish the on-line, two-way coupling, and at the same time, is more efficient for computations and easier to use for the nearshore wave-current simulations.
- Published
- 2018
14. Optimization of heterogeneous arrays of wave energy converters
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Abdulkadir, Habeebullah and Abdelkhalik, Ossama
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- 2023
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15. Academic studies on fishing vessels in Turkey.
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Saral, Dursun and Köse, Ercan
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SALTWATER fishing , *FISHING , *SHIP models , *RESEARCH vessels , *CONFERENCE papers , *FISHING boats - Abstract
Research on fishing vessels worldwide began in the 1850s and continues to increase to this day. In Turkey, academic studies on fishing vessels commenced with the establishment of the Ata Nutku Ship Model Experiment Laboratory in 1953. Academic studies on fishing vessels in Turkey can be divided into three periods: the early period studies, the İTU fishing vessel series studies, and the Black Sea type fishing vessels studies. The early period studies started in the 1950s and continued until the 1970s, focusing on Taka, Çektirme, and Alametro type fishing vessels. The İTU fishing vessel series studies began in 1979 under the leadership of Prof. Dr. Kemal KAFALI, in collaboration with İTU and TÜBİTAK, based on fishing vessel forms developed through model experiments, and have continued to the present day. The third period, the Black Sea type fishing vessels studies, started in the 1990s and research on these forms is still ongoing. These fishing vessels, generally built in the Black Sea region, are now used in all seas and oceans. This study examined master's and doctoral theses, articles, and conference papers from these three periods. The subjects were analyzed in a cause-and-effect relationship, and the information contained was summarized. • Academic studies on fishing vessels in Turkey. • Doctoral and master's theses, articles and conference papers from 1950 to the present. • Studies on Taka, Çektirme, Alametro. • Studies on ITU fishing boats series. • Studies on the Black Sea type fishing vessel. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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16. Lessons learned from accidents on some major European inland waterways
- Abstract
The collection of data on accidents in inland navigation is not mandatory in many European countries. The lack of a harmonized methodology or a centralized database of information on accidents makes it difficult to have a comprehensive picture of safety on European inland waterways. The problem becomes particularly evident in light of significant navigational challenges such as the introduction of autonomous shipping. To provide a better understanding of safety in inland navigation, the paper presents the results of an analysis of data on some 700 accidents which took place on the inland waterways in Austria and Serbia, over a 15-year period (2001/2002–2017). The analysis identifies the safety “hot spots” and the most important safety issues on examined waterways. Contrary to the widely-accepted belief, the results do not confirm that most of the accidents could be attributed to human failures and show that the removal of human operators from inland vessels could only have a limited positive impact on safety unless other aspects (primarily related to maintenance of the fleet and the waterway) are considered. Consequently, the paper outlines the fundamental conditions in which it would be possible to reduce the human presence or even remove the crew from inland ships.
- Published
- 2023
17. A comprehensive bibliometric analysis and assessment of high-impact research on the berth allocation problem.
- Author
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Dragović, Branislav, Zrnić, Nenad, Dragović, Andro, Tzannatos, Ernestos, and Dulebenets, Maxim A.
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BIBLIOMETRICS , *MOORING of ships , *SCIENTIFIC community , *RESEARCH personnel , *THEMATIC maps , *RESEARCH & development , *MARINE terminals - Abstract
This paper aims at the identification and assessment of High-Impact Research Papers (HIRPs) on the Berth Allocation Problem (BAP) research at marine terminals. The BAP objective is to optimally assign and schedule ships at berthing positions along a quay, as well as to determine the berthing times and positions of ships at a port. The purpose of this study is to facilitate the work of the relevant research community and ultimately promote the research quality in this area. In meeting this objective, the paper utilizes a systematic and fair method to determine HIRPs of the BAP, which is based on the h -index and the g -index. An in-depth bibliometric analysis of the identified studies reveals their key features and characteristics. The analysis was conducted using the VOSviewer and bibliometrix R-package software programs. The main findings provide many useful insights on the BAP research development. The adopted approach and associated analysis results present an up-to-date detailed picture of the BAP research and constitute a valuable tool for its applications into other relevant research areas. The common trends in the reviewed HIRPs and important future research needs are discussed in a comprehensive manner. This survey study can be viewed as the first attempt for a comprehensive bibliometric survey of the high-impact BAP literature, which will be of a great value to researchers and industry practitioners. Furthermore, the proposed methodology for the identification of HIRPs can be used not only for the BAP research but for the literature surveys in other domains as well. [Display omitted] • A comprehensive analysis is conducted for the Berth Allocation Problem (BAP) research. • High Impact Research Papers (HIRPs) in the BAP research are identified and analyzed. • The co-authorship relations among countries, institutes, and authors are investigated. • Trending models of HIRPs and their solution techniques are discussed. • The statistical techniques for mapping and network analysis of HIRPs are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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18. Active and passive heave compensation system based on feedback linearization sliding mode variable structure control
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Zhao, Fengshuo, Zhong, Yuguang, and Fu, Zeyu
- Published
- 2024
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19. Adaptive neural bounded formation tracking control of multiple autonomous surface vessels subject to actuator saturation and faults
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Wang, Wenxin, Wang, Tuotuo, and Qiao, Zheng
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- 2024
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20. A manipulator-assisted multiple UAV landing system for USV subject to disturbance
- Author
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Xu, Ruoyu, Liu, Chongfeng, Cao, Zhongzhong, Wang, Yuquan, and Qian, Huihuan
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- 2024
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21. Robust adaptive saturation-tolerance control for USVs formation via a novel L1-VS guidance
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Zhang, Guoqing, Bian, Wenzheng, Zhang, Xianku, and Li, Jiqiang
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- 2024
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22. Model-free adaptive predictive control with unscented Kalman filter for hovercraft speed and heading stabilization.
- Author
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Zhang, Weiqiu, Xu, Yujie, Fu, Mingyu, Zhang, Guorong, and Fan, Zhipeng
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ADAPTIVE control systems , *GROUND-effect machines , *NOISE measurement , *KALMAN filtering , *INTERFERENCE suppression , *NOISE control - Abstract
This paper develops a novel unscented Kalman filter-model free adaptive predictive control (UKF-MFAPC) method for an underactuated hovercraft speed and heading stabilization under the influence of measurement noise. First, the proposed method is based on the compact form dynamic linearization (CFLD) technique, which involves an analysis of the tight format dynamic linearization method. This approach specifically addresses the unique non-real-time scalability of the heading control subsystem, rendering the CFDL method unsuitable. Through redefining the linear combination of lateral velocity and heading as output to fulfill all assumptions of CFDL methods, this scheme effectively mitigates the lateral velocity vibration problem of the hovercraft. Secondly, this controller introduces the measurement noise during the data collection process into the optimization function and combines the unscented Kalman filtering method with data-driven models, the influence of error suppression noise on the controller is suppressed, ensuring that the output can still be controlled within a certain range of expected values. This paper also delves into the convergence of tracking errors and examines the stability of bounded inputs and outputs. Finally, the noise suppression effect and stability of the UKF-MFAPC scheme are demonstrated through a comparative analysis of simulation results with proposed model-free methods. • This paper proposes a UKF-MFAPC method for the complex modeling problem of hovercraft, which does not need to consider the mechanism model of the controlled system in the controller design process. In response to the issues of slow convergence speed of the MFAC method, and sensitivity of adaptive parameter changes to control effectiveness, the controller design of the MFAPC method introduces I/O information for future time when obtaining data from hovercraft. The simulation indicates that Compared with the PID method, it has a smaller overshoot and is less sensitive to the selection of adaptive coefficients, and faster convergence speed compared with the MFAC method. • The UKF-MFAPC proposed in this paper uses UT transformation to increase the accuracy of data sampling and the interference suppression ability of the hovercraft controller in response to the issues of process noise and measurement noise interference in the control process of hovercraft. The simulation indicates that the UKF-MFAPC approach has higher noise resistance and a faster response speed when compared to the TD-MFAC method. • This paper proposes a redefinition method to define longitudinal and transverse velocities as data-driven outputs for the lateral velocity oscillation problem of hovercraft under high speed and high turning, which satisfies the quasi linear assumption of data-driven methods and solves the lateral vibration problem of hovercraft. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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23. Quantitive HAZOP and D-S evidence theory-fault tree analysis approach to predict fire and explosion risk in inert gas system on-board tanker ship.
- Author
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Durukan, Ozcan, Akyuz, Emre, Destanoğlu, Orhan, Arslanoğlu, Yasin, and Sezer, Sukru Ilke
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COLLISIONS at sea , *NOBLE gases , *TANKERS , *FAULT trees (Reliability engineering) , *FIRE risk assessment , *MARINE pollution , *EXPLOSIONS - Abstract
Tanker ships carry volatile cargo, presenting inherent risks of fire and explosion. Inert gas systems (IGS) are pivotal in mitigating risks by displacing oxygen in cargo tanks. However, failure of IGS components may lead to fatal consequences such as loss of life and marine pollution. This paper prompts a systematic approach integrating Quantitative Hazard and Operability (HAZOP) analysis under D-S (Dempster–Shafer) evidence theory and Fault Tree Analysis (FTA) to predict and quantify the fire and explosion risk associated with IGS malfunction on tanker ships. The methodology systematically evaluates failure probabilities, and consequences using HAZOP to identify critical scenarios. D-S evidence theory is employed to address uncertainties and incorporate expert knowledge into the analysis. FTA is applied to model fault propagation and assesses the likelihood of fire and explosion events based on the identified failure scenarios. A case study is presented to demonstrate the application of the proposed methodology, illustrating effectiveness in identifying high-risk scenarios and providing insights for enhancing operational safety minimising the risk of IGS on tanker ships. The findings show that the risk of fire and explosion in the inert gas system due to the high concentration of oxygen entering the tank was found to be 2.86E-01. Besides its robust theoretical background, the findings of the paper provide the utmost contribution to ship crew, ship inspectors, HSEQ managers and safety professionals for proactive risk mitigation strategies, contributing to the advancement of safety management practices in the maritime industry. • A systematic risk analysis for fire and explosion associated with IGS failure on tanker ships is conducted. • Quantitative Hazard and Operability (HAZOP) analysis under D-S (Dempster-Shafer) theory of evidence and Fault Tree Analysis (FTA) is proposed. • The risk of fire and explosion in the shielding gas system from the high concentration of oxygen entering the tank is 28%. • The most important root cause of this high risk of 28% is incorrect air and fuel line pressure measurement entering the boiler. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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24. Disturbance observer based adaptive trajectory tracking control for Unmanned Surface Vehicle with input and state quantization.
- Author
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Wang, Yu, Li, Wei, Ning, Jun, and Liu, Lu
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AUTONOMOUS vehicles , *TRACKING control systems , *CLOSED loop systems , *BACKSTEPPING control method , *SIGNAL quantization - Abstract
This paper explores the disturbance observer based adaptive trajectory tracking control strategy of Unmanned Surface Vehicle with input and state quantization. To devise the controller without prior knowledge of quantization parameters, a linear analytical model of input quantization is introduced, facilitating adaptive parameter estimation. Estimations of external disturbances and quantized states are obtained through the application of a disturbance observer. Additionally, the control law is constructed using a combination of backstepping control and dynamic surface techniques. By leveraging Lyapunov stability theory, this paper demonstrates the stability of the trajectory tracking control system for Unmanned Surface Vehicle with input and state quantization, as well as the boundedness of errors between quantized and non-quantized variables within the closed-loop control system. Finally, the effectiveness of the proposed tracking approach is validated through comprehensive simulation experiments. • This paper incorporates signal quantization into the USV trajectory tracking method. • Disturbance observer is used for estimating quantized states and external disturbances. • This paper introduces a linear analytical model of the input quantization. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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25. Wind speed forecasting by spatial-temporal data-driven models using atmospheric input variables.
- Author
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Wu, Mengning
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WIND speed , *ATMOSPHERIC models , *WEATHER , *WIND forecasting , *FEATURE selection , *DATA envelopment analysis , *MACHINE learning - Abstract
In this paper, data-driven models for wind speed forecasting are established by incorporating atmospheric variables, such as temperature, humidity divergence and etc. as input, and using forecasted wind speed as the output. Input data, statistics in every 3-h interval, utilized in this study are from CERA-20C within a period from the year 2001–2010. In the models, a feature selection technique is proposed to identify the relative dependence of each input to the output. Through a comparison between results with and without the selection technique, it is observed that the technique helps to select the most pertinent inputs, and thus further improve the forecast performance, accuracy and efficiency. In addition, three data-driven models are further revealed to acquire the best forecast accuracy, by including temporal effect, spatial effect, or coupled temporal and spatial effects on atmospheric conditions, which are named as temporal-based, spatial-based and hybrid data-driven models, respectively. By comparing the forecast performance among different models, it is revealed that the newly proposed hybrid data-driven model with feature selection technique is more suitable in dealing with wind speed forecasting. Moreover, an additional case study further reinforces the feasibility of the newly proposed hybrid data-driven model for forecasting of wind direction. The proposed date-driven models in the paper provide a high-cost efficiency alternative for wind speed forecast using machine learning instead of physical models. This approach can assist engineers in making prompt and informed decisions even when resources are constrained during emergency conditions. • Cost-efficiency wind speed forecast methods are developed by incorporating atmospheric variables into data-driven models. • Data-driven models are generated by considering temporal and spatial effects of atmospheric conditions on wind fields. • The feature selection is utilized to select the appropriate inputs and to enhance the accuracy of wind speed forecasts. • The important atmospheric variables that significantly affect wind fields are identified. • The feasibility of the newly proposed hybrid data-driven model for wind direction forecasting is demonstrated. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
26. Analysis of connection fault and service maintenance strategy for subsea horizontal clamp connector.
- Author
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Liu, Weifeng, Yun, Feihong, Ju, Ming, Yao, Shaoming, and Chen, Xi
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BAYESIAN analysis , *STATISTICAL errors , *MISSING data (Statistics) , *QUANTITATIVE research , *STATISTICAL models , *FAILURE mode & effects analysis , *RELIABILITY in engineering , *FAULT diagnosis - Abstract
The deep-sea environment restricts the collection of reliable data for subsea connectors, leading to a lack of available failure data to develop connection fault detection processes and maintenance strategies. Therefore, this paper proposes an FMECA-BN model. The model developed an algorithm for mapping Risk Priority Number (RPN) to Bayesian network (BN) parameters and enhanced the details for mapping BN structures to match the diversity of FMEA. This enables the establishment of a BN based on a given Failure Mode, Effects, and Criticality Analysis (FMECA). The model was applied to the development of the Subsea Horizontal Clamp Connector (SHCC) to quantify and evaluate failure modes during the connection stage, creating an effective detection process. Then, the system's reliability variations caused by component degradation were analyzed using transformed dynamic BN, offering information for maintenance strategies based on availability. The reliability analysis results of the FMECA-BN model demonstrate a statistical error of 4.5% compared to actual data samples, proving the model's efficacy in addressing issues of information asymmetry, incomplete reliability data, and uncertainty. The analysis revealed that the developed SHCC requires a maintenance cycle of 14,892 h to maintain a 0.99 reliability level, with a cumulative failure probability of 4.6% after 20 years. • This paper presents an FMECA-BN model that incorporates the functionality of mapping Risk Priority Number (RPN) to Bayesian network node parameters to address the challenge of insufficient prior data. • This paper is based on the engineering context and delves into the specific process and characteristics of failure modes occurring in the developed subsea horizontal clamp connector (SHCC). The conversion of static Bayesian networks to dynamic Bayesian networks has been employed to accomplish the reliability analysis and data update for the SHCC. • For the first time, a quantitative analysis of SHCC is conducted at both the system and component levels, effectively addressing the issues related to connection fault detection and formulating service and maintenance strategies based on availability. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
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27. Research on bearing capacity and stability of deep-water novel combined wellhead based on experimental methods.
- Author
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Xu, Dongsheng, Yang, Jin, Ma, Yongqi, Fan, Jianchun, Zhou, Yingfang, Sun, Ting, Liu, Xun, Zhao, Yuhang, and Zhu, Chunlin
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EXTERIOR walls , *EXPONENTIAL functions , *WATER well drilling - Abstract
The combined wellhead has the advantage of high bearing capacity and broad prospects for application in the construction of deep water surface wells; therefore, it is important to conduct relevant research to guide the construction of combined wellheads. The aim of this paper is to study the mechanical characteristics of the combined wellhead in the longitudinal direction and establish the method for real-time calculation of the bearing capacity of the combined wellhead taking into account the effects of installation. The variations of external wall pressure and internal soil pressure during installation and the waiting process of the combined wellhead were investigated by indoor experiments. The installation efficiency of the combined wellhead at different negative pressure conditions was also compared. The experimental results show that the pressure on the outer wall of the combined wellhead facility gradually increases as the depth of the combined wellhead facility increases, and the closer it is to the bottom, the greater the soil pressure. The pressure on the inner soil will increase rapidly during the installation process to almost the same level, while the pressure on the outer soil will increase slightly. During the waiting process of the combined wellhead, as the waiting time increases, the soil damaged during the installation process gradually recovers, and the external wall pressure gradually rises. Moreover, the pressure on the outer wall gradually increases, the pressure on the inner soil decreases slightly leveling off within about 24 h. An appropriate increase in suction pressure facilitates the installation of the combined wellhead, and approximately 2.0 L/min is the optimal option for installation. The computational model developed in this paper and the experimental measurements corroborate each other. These combined wellheads significantly improve the stability of deep water soft-soil well construction and provide a theoretical benchmark for developing oil, gas and hydration in deep water. • The pressure at the outside wall exhibited an exponential function during the installation of the combined wellhead. • During the installation of the combined wellhead, the pressure on the inner wall is slightly higher than that on the outer wall. • The combined wellhead is in place, the fluid from the outside gradually enters the combined wellhead inside. • Increasing the suction power appropriately can guarantee both the operating effect and the efficiency. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
28. Trajectory planning aided unmanned surface vehicle optimization communication method with hierarchical reinforcement learning.
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Tang, Chengkai, Shi, Hanzhang, and Zhang, Lingling
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AUTONOMOUS vehicles , *RESCUE work , *MODULATION coding , *SUCCESSIVE approximation analog-to-digital converters , *RADARSAT satellites , *REMOTELY piloted vehicles , *REINFORCEMENT learning , *MARINE communication , *PROBLEM solving - Abstract
In maritime search and rescue (SAR), the boat swarm mode can greatly improve the success rate, but because of the influence of the curvature of the earth, the communication distance on the ground is short. Relay communication using unmanned surface vehicles (USVs) is the main means of maritime SAR, but communication speed and reliability are the core difficulties. To solve the problem, this paper proposes a trajectory planning aided unmanned surface vehicle optimization communication method with hierarchical reinforcement learning (TP–OC–HRL), which introduces relay USVs into the maritime SAR system and uses trajectory planning and the adaptive orthogonal frequency-division multiplexing (OFDM) technology as variables to optimize the communication rate of the SAR system. The paper proposes a communication optimization scheme based on hierarchical reinforcement learning, which divides the modulation coding scheme and the trajectory planning of the USVs into two hierarchical subproblems to improve the communication rate of the maritime SAR system through reinforcement learning. The experimental verification in the island area of the South China Sea shows that the TP–OC–HRL algorithm proposed in this paper has a faster convergence speed compared with that of the existing relay communication optimization methods, and can improve the communication rate of the maritime SAR system under the condition of meeting the reliability. • We established a high-speed maritime search and rescue communication method utilizing USV relays. • We established a surface USV communication optimization scheme based on hierarchical reinforcement learning. • Our method can adjust the MCS in real time based on the motion status of the USV, effectively improving the communication speed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
29. Numerical investigation of damping effect and flow characteristics induced by rigid vegetation in current-wave flows.
- Author
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Huang, Yuming, Chen, Ben, Jiao, Jian, Yang, Xiaoyu, Wang, Yifei, and Dou, Xiping
- Subjects
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KINETIC energy , *FREE surfaces , *LANDAU damping , *TURBULENCE , *TURBULENT flow , *THREE-dimensional modeling - Abstract
In the paper, a 3-D numerical model based on the olaFlow solver to study the vegetation effects on flow characteristics and turbulent structure as well as wave attenuation under combined regular wave-unidirectional current conditions. The results show that following currents can either promote or suppress wave attenuation within the velocity magnitude specified in the paper, whereas opposing currents always enhance wave damping. Moreover, the emergent canopy and a staggered configuration resulted in increased wave-height attenuation. The time-averaged velocity patterns are various for submerged and emergent scenarios with different configurations. Furthermore, the time-averaged velocity magnitude inside the canopy decreases as the wave height increases for following flow conditions, while it increases in opposing currents. The time-averaged turbulent kinetic energy (TKE) inside the canopy follows the same distribution pattern as that of time-averaged velocity, and the maximum values of time-averaged TKE for the submerged and emergent canopies appear at the free surface, and above, respectively. The flow field characteristics show different patterns for various wave-current combinations and vegetation configurations, which provides a microscopic perspective to understand the interaction of vegetation-wave-current. • A three-dimensional numerical model using cyclic boundary based on the OlaFlow solver was developed. • Time-averaged velocity and turbulent kinetic energy within submerged/emergent canopy present different patterns. • Microscopic flow fields characteristic within the vegetation in following and opposing currents are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
30. Human reliability analysis of offshore high integrity pressure protection system based on improved CREAM and HCR integration method.
- Author
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Yu, Yang, Wu, Shibo, Fu, Yiqin, Liu, Xiaowei, Zeng, Qingze, Ding, Hongyu, Pan, Yu, Wu, Yuke, Guo, Hao, and Yang, Yuheng
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ERROR probability , *HUMAN error , *COGNITIVE ability , *FAILURE (Psychology) , *HUMAN beings , *SYSTEM integration - Abstract
Control room operators on offshore platforms play an important role in realizing the safety instrumentation functions of the high integrity pressure protection system (HIPPS) during overpressure emergencies. Human reliability analysis is critical to the overpressure operation of offshore HIPPS, yet there are few studies. To remedy this gap, the paper proposes an integrated human reliability analysis method to analyse the impact of human intervention on offshore HIPPS safety. Considering the effects of context and cognitive performance on human reliability comprehensively, the improved cognitive reliability and error analysis model (CREAM) is established; The correction effect of external environmental factors on response failure probability is quantified, and the improved human cognitive reliability (HCR) model is developed; The two improved models are organically combined to form an integrated methodology. Based on the behaviour characteristics of personnel emergency response, human error probability is calculated in stages to analyse human reliability. The findings indicate that the overall human error probability for HIPPS overpressure operations is 0.124 and particular attention needs to be paid to observation and decision-making operations. Besides the theoretical background, the paper provides practical contributions to personnel training, mission planning, and risk management of HIPPS to minimize the possibility of human error. • An integrated human reliability analysis method for offshore HIPPS is proposed. • The cognitive performance correction coefficient is introduced to improve CREAM. • The modification effect of external environmental factors is quantified to improve the HCR model. • Human error probabilities are calculated in stages based on personnel task characteristics. [ABSTRACT FROM AUTHOR]
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- 2024
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31. Coupling a nonlinear finite element mooring model with an overset CFD solver for dynamic analysis of floating structures in waves.
- Author
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Long, Yuhong, Liu, Yuanchuan, Zhao, Zhixin, and Liu, Fushun
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FINITE element method , *STRUCTURAL frame models , *RESONANT vibration , *FLUID dynamics , *MOORING of ships , *TENSILE architecture - Abstract
An accurate prediction of motion responses of a moored floating structure requires high-fidelity coupled analysis between the structure and its mooring system in waves, which involves both mooring line dynamics and fluid dynamics. In this paper, we develop a nonlinear finite element dynamic mooring analysis module that allows large axial stretching of mooring lines under the open source CFD framework OpenFOAM, and couple it with an Overset CFD solver to establish a fully coupled finite element mooring-CFD analysis model for floating structures. The coupled model is advantageous over existing models in that it is able to deal with large axial mooring stretching and complex mesh motions induced by significant structure responses under severe operating conditions. The developed dynamic mooring analysis method is firstly validated against publicly available data. In order to validate the coupled model, a series of experimental tests were carried out for a semi-submersible platform moored by eight catenary lines under different operating conditions, including free decay, regular and irregular wave tests. The dynamic responses of the floating structure and mooring tension are analyzed and compared with experimental data. Results show that numerically predicted structure responses and mooring tension are generally in good agreement with experimental measurements. Meanwhile, the strongly nonlinear large-amplitude resonant motions generated by the interaction of irregular waves with the moored floating structure are also investigated. Comparisons reveal that the coupled model can accurately predict the resonant spectral peaks of the structure responses, indicating that the it is capable of simulating large-amplitude motions of moored floating structures. The coupled model developed in this paper can be further applied to study the survivability of moored floating structures under harsh sea conditions. • A finite element mooring dynamics module was developed in OpenFOAM. • The developed mooring module was coupled with an Overset CFD solver in OpenFOAM. • The coupled model was validated against model tests of a moored platform. • The coupled model can accurately predict large-amplitude motion responses. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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32. A novel analytical solution for horizontal vibration of partially embedded offshore piles considering the distribution effect of wave loads.
- Author
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Wang, Benlong, Cui, Chunyi, Xu, Chengshun, Meng, Kun, Li, Jingbo, and Xu, Lina
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ANALYTICAL solutions , *FREQUENCY-domain analysis , *SEPARATION of variables , *WAVE diffraction , *WAVE forces , *WAVE equation - Abstract
According to the Novak's plane strain theory and Biot's wave equation, this paper proposes an analytical model for horizontal vibration of partially embedded offshore piles under distribution effect of wave loads (DEWL) incorporating the diffraction effects of waves. Firstly, for the pile above the mudline, the wave force acting on the pile is obtained through the method of separation of variables. Secondly, for the embedded section of offshore piles, the governing equations of the seabed are decoupled by introducing potential functions, and then the boundary condition of the seabed and the continuity condition at the soil-pile contact surface are combined to obtain the frequency domain analysis of the soil reaction forces. Furthermore, by applying the continuity condition of displacement at mudline and using the matrix transfer method, the analytical solution for the horizontal vibration characteristics (HVC) is derived. Finally, a comparison analysis with existing theoretical solutions is conducted to validate the rationality and accuracy of the analytical solution proposed in this paper. Based on this, a parametric analysis is conducted to discuss the effects of the parameters of the soil, the pile and the wave on the HVC of partially embedded offshore piles. • An analytical solution for the horizontal vibration of partially embedded offshore piles considering the distribution effect of wave loads is proposed. • The analytical solution is derived by the separation of variables technique and the transfer-matrix method. • The effect of wave load distribution on the horizontal vibration of partially embedded offshore piles is investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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33. A strategic fleet size and mix vehicle routing model to analyse the impact of demand fluctuation on river-sea liner shipping.
- Author
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Silva, L.M.R., Wang, Haiyan, and Guedes Soares, C.
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AUTOMOBILE size , *MIXED integer linear programming , *VEHICLE models , *MARITIME shipping , *INLAND navigation - Abstract
The paper proposes a fleet size and mix vehicle routing model to optimize the river-sea liner shipping service. A mixed integer linear programming model is adopted as a rapid screening tool for strategic fleet planning to determine the type and number of river-sea vessels to deal with the fluctuation of the demand over the year, guaranteeing the efficiency and effectiveness of the shipping service. Moreover, the model provides a better-informed decision on the logistic infrastructure design, demand allocation and fleet size and composition in scenarios of demand uncertainty. Thus, the quantified decision support model increases the service level of the shipping service, reducing the frequent mismatches between fleet capacity and demand. A verification step aiming to test the behaviour of the model solution in a realistic case study is presented to analyse the impact of the demand fluctuation on the fleet composition. In conclusion, river-sea vessels enable door-to-door transport via coastal and inland waterways without transhipment. This approach offers a reliable and cost-effective solution. The findings of the work may enhance the state of the art, expanding the narrow studies on river-sea liner shipping services and demonstrating the advantages of river-sea vessels. • The paper proposes a fleet size and mix vehicle routing model to optimize the river-sea liner shipping service. • A mixed integer linear programming is adopted as a tool for strategic fleet planning i.e. the type and number of vessels. • A decision support model increases the level of the shipping service reducing mismatches between fleet capacity and demand. • A verification step aiming to test the behaviour of the model solution in a realistic case study is presented. • The river-sea transport without transhipment was shown to be a sustainable, reliable, and cost-effective. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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34. Hydrodynamic performance of a water-air trans-media flying submersible vehicle.
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Lu, Deshun, Lin, Wei, Duan, Jinxiong, and Sun, Tiezhi
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OCEANOGRAPHIC submersibles , *OCEAN waves , *SUBMERSIBLES , *DEEP diving , *UNDERWATER navigation , *WATER depth - Abstract
Water-air trans-media flying submersible is a new type of unmanned vehicle with important engineering applications. This paper describes pool towing experiment and numerical calculation methods conducted to study the influence of the submersible's velocity on the free water-surface, the hydrodynamic characteristics, and the flow field structure. The working conditions researched in this paper include the water-surface navigation and underwater diving. The results show that the lift and drag of the submersible increase with velocity, but the trend and range are greatly affected by the water depth, especially those of the lift. The high-pressure area on the surface is mainly distributed in the bow and appendage structure inflow area, and the low-pressure area is distributed behind the high-pressure area and the back-flow area. The influence of the free water-surface causes the wake field to dissipate rapidly and become asymmetric when water-surface navigation. The free water-surface is a Kelvin wave system. The Kelvin angle decreases and the wavelength and amplitude increase with velocity. When navigating on the water-surface, the bow wave and tail wave form a double-row Kelvin wave. When diving underwater, a Bernoulli dome appears on the water-surface above the bow, and the surface forms a regular single-row Kelvin wave. • Hydrodynamic performance of a water–air trans-media flying submersible vehicle is studied. • The free water-surface evolution of the flying submersible vehicle at different velocities is analyzed. • The flow structure over the vehicle and the force of the vehicle are discussed. [ABSTRACT FROM AUTHOR]
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- 2024
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35. Distributed estimation of the pelagic scattering layer using multiple buoyancy controlled underwater vehicles.
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Wei, Cong, Berkenpas, Eric, and Paley, Derek A.
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SUBMERSIBLES , *DENSITOMETRY , *KALMAN filtering , *THREE-dimensional flow , *SHEAR flow , *SENSOR networks - Abstract
This paper introduces an adaptive sampling strategy for a multi-vehicle sensor network to explore an underwater biological system known as the pelagic scattering layer, which is a region in the water column with a high density of marine organisms that reflect sound. Ever-changing ocean flow presents a challenge to multi-vehicle coordination in this process. The presence of an ocean flow field may disrupt inter-vehicle spacing so that the group loses communication, strays from a desired formation, or ends up with reduced area of coverage, especially for robotic drifting vehicles whose motion is largely influenced by the ambient flow field. However, those vehicles may also take advantage of the vertical variation of the flow to form a desired cohesive configuration since they can tune their vertical position via depth control. A motion-control algorithm, therefore, is a key element of the adaptive sampling strategy. The paper derives a decentralized coordination algorithm to stabilize a cohesive formation in a two-dimensional flow field with an initial unknown vertical distribution. The algorithm works with a distributed extended Kalman filter that generates a local estimate of the flow from pairwise range measurements between vehicles. Another component of the sampling strategy is the modeling of organism density dynamics using estimation of the density with local optical measurements, such as from onboard cameras. The density evolution is estimated using an ensemble Kalman filter and the results are fed into the motion-coordination algorithm. Numerical simulations illustrate the efficacy of this strategy and motivate ongoing and future efforts to extend the result to a three-dimensional geophysical flow. • A decentralized depth control algorithm guides multiple drifting vehicles to varying depths, ensuring cohesive, collision-free formation in shear flow. • Buoyancy control extends to unknown shear flow using extended Kalman filter for parameter estimation, enabling formation. • Ensemble Kalman filter estimates scattering layer density from depth predictions using operator and local measurements. [ABSTRACT FROM AUTHOR]
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- 2024
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36. Experimental/numerical investigation on the hydrodynamic and noise characteristics of pump-jet propulsion.
- Author
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Weng, Kaiqiang, Sun, Cong, Han, Kang, Wang, Chao, Sun, Shuai, Li, Peng, and Hu, Jian
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- *
CAVITATION , *ACOUSTIC field , *SOUND pressure , *NOISE , *SONAR - Abstract
Pump-jet propulsion is a kind of propeller with excellent performance. Because of its high working efficiency and good anti-cavitation performance, it has been widely concerned and studied by scholars at home and abroad. This paper takes the self-designed pump-jet propulsion as the research object. The hydrodynamic and noise experiment of pump-jet propulsion was carried out based on the towing tank and the cavitation tunnel. It analyzes the mechanical characteristics and noise performance of pump-jet propulsion, compares and verifies the test results with CFD calculation results. The results show that the calculated values of hydrodynamic force and noise of pump-jet propulsion are in good agreement with the experimental test results, which further verifies the reliability of the calculation strategy in this paper. At the same time, it provides theoretical basis and data support for the performance forecast and optimization design of the subsequent pump-jet propulsion. • Hydrodynamic and noise experiment of pump-jet propulsion was carried out based on towing tank and cavitation tunnel in this paper. • The whole and rotor components in the axial and radial plane show obvious line spectrum characteristics at the axial frequency, blade frequency and their harmonic frequency. • The fluctuating range of the sound pressure level in the radial plane is approximately circular distribution, and there is no obvious sound field directivity. • The sound pressure directionality shows an approximate "8" shape distribution on the axial plane, showing the characteristics of the dipole sound source. [ABSTRACT FROM AUTHOR]
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- 2024
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37. Application of Bayesian networks based on Sequential Monte Carlo simulation and physical model in fault diagnosis of horizontal three-phase separator system.
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Liu, Daqian, Song, Shangfei, Huang, Ting, Shen, Siheng, Li, Xiaoping, and Gong, Jing
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- *
BAYESIAN analysis , *MONTE Carlo method , *CONVOLUTIONAL neural networks , *ARTIFICIAL neural networks , *HORIZONTAL wells , *FAULT diagnosis , *FAULT tolerance (Engineering) , *POLYMER networks - Abstract
In offshore production platforms, horizontal three-phase separator is common process equipment. Its main function is to complete the dehydration and degassing of crude oil. Separator system is more complex, and its failure may cause significant economic losses and disastrous consequences. Therefore, it is critical to accurately and quickly identify where and why faults occur in the separator system. In this study, separator fault diagnosis model based on Bayesian networks is developed. Moreover, Sequential Monte Carlo simulation and physical model are introduced to overcome field problems such as missing separator failure data and the inability of experts to provide accurate empirical knowledge. Using this model, 13 faults in a separator in an offshore crude oil processing system are successfully diagnosed. Meanwhile, the proposed model is compared with deep neural network, convolutional neural network, and deep residual network, with accuracy rates of 100%, 91.34%, 87.99%, and 94.62%, respectively. Then, the diagnostic accuracy of each model for different faults is also compared in this paper under various signal-to-noise ratios. The results show that the method proposed in this paper has better noise immunity compared to the other three models. Therefore, the accuracy and robustness of the proposed model is further demonstrated. Finally, to analyze the fault-tolerance of the proposed model, 2–3 error evidence is randomly entered. The results show that the proposed model has better fault tolerance compared to data-driven Bayesian networks. • A Bayesian network-based fault diagnosis method for separators is proposed. • Overcome the problem of lack of separator fault data in the field. • Overcome the inability of experts to provide expert experience for separator. • Use physical model instead of human expert to improve modelling efficiency. • Use physical model to compensate for the shortcomings of Sequential Monte Carlo. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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38. An efficient hybrid Laplace-time domain method for dynamic analysis of nonlinear floating systems.
- Author
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Tao, Wei, Wang, Shuqing, Sun, Jinwei, and Zhang, Linqiang
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- *
NONLINEAR systems , *NONLINEAR analysis , *HYBRID systems , *ANALYTICAL solutions , *WIND turbines - Abstract
The dynamic analysis for nonlinear floating systems has been traditionally conducted in the time domain. Although the time-domain method can obtain a sufficiently accurate result, it is usually time-consuming in computation. This paper proposes a novel hybrid Laplace-time domain method for computing the response of nonlinear floating systems. In the proposed method, the nonlinearities of the system are treated as an additional external load. The external excitation is then divided into a number of segments, of which the response of the floating structure under each segment is computed by the pole-residue method operated in the Laplace domain. Along with the pole-residue method in each segment computation, the iterative technique is employed for dealing with system nonlinearities in the time domain. As the pole-residue method computes the response through simple algebraic operations in the complex plane and obtains analytical solutions, the proposed hybrid Laplace-time domain method is more efficient and accurate. Two numerical examples are carried out in this paper, in which one is an analytical single-degree-of-freedom (SDOF) nonlinear floating system and the other is a semi-submersible floating offshore wind turbine (FOWT) foundation with nonlinear damping. Both computational accuracy and efficiency of the proposed method are demonstrated through these numerical examples, by comparing the responses with those obtained by traditional time-domain methods. • A novel hybrid Laplace-time domain method is proposed for nonlinear system responses. • Analytical solutions are obtained by pole-residue operations in the complex plane. • The proposed method is more efficient than traditional time methods. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
39. Responses analysis and structural optimization of a semisubmersible platform based on the Taguchi experiment method.
- Author
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Xie, Shuangyi, Kan, Yingzhe, Li, Yongran, Li, Yuxin, Jiang, Shuxin, and Song, Mengji
- Subjects
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TAGUCHI methods , *STRUCTURAL optimization , *WIND turbines , *WATER depth , *HYDRODYNAMICS - Abstract
Due to the early stage of development for floating offshore wind turbines (FOWTs), there's a scarcity of effective methods and procedures for determining the overall dimensions of floating foundation. Moreover, the comprehensive dynamic response features of various foundation configurations remain inadequately understood. To tackle these limitations, this paper presents a global design approach for semi-submersible platform used to support a large-scale wind turbine. In this paper, the distance between offset column and main column (R OI), the radius of offset column (R O), the height of heave plate (H HP), the total draft of platform (H dft), the ratio of heave plate radius to offset column radius (R HP), and the ratio of the horizontal distance from anchor to fairlead to the water depth (x M) were selected as the initial design variables of the platform. A design of experiment based on the Taguchi method was performed to construct various combinations of design variables. Then, the physical properties and hydrodynamics of the platform, and controller dynamics were determined for each combination. The correlations between the variables and key outputs were studied. Finally, the multi-objective optimization for the foundation dimensions was performed based on the Taguchi method. Compared to other experimental cases, the FOWT with optimal variables (R OI = 29 m, R HP = 2.0, R O = 7 m, H HP = 6.0 m, H dft = 21 m, and x M = 4.0) exhibits excellent comprehensive performance, particularly outperforming the OC4 model overall, with a 26% increase in platform mass (excluding ballast mass). This study offers an insight into the nature of the design variables and the response outputs, and provides a optimization framework to optimize the foundation dimensions, which can then serve as initial points for a more detailed design. • Natural frequency and output of a FOWT with various platform parameters were studied. • Taguchi method is used to perform the DOE. • The correlations between variables and key outputs were studied. • The multi-objective optimization of the platform structure was performed and validated. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
40. A review on design and analysis of floating bridges: Numerical simulations, model tests and field measurements.
- Author
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Wang, Chao, Cui, Minghao, Cheng, Zhengshun, and Moan, Torgeir
- Subjects
- *
COMPUTER simulation , *TWENTIETH century , *RESEARCH methodology , *FJORDS , *MEASUREMENT - Abstract
Floating bridges are economically attractive alternatives used for crossing wide and deep straits or fjords. They have played a crucial role in transportation since the early 20th century. Although several floating bridges are currently in operation worldwide, their design standards are not mature, especially associated with the dynamic response analysis. To this end, a review of the relevant advances and research directions of floating bridges is presented. In this paper, the development and types of floating bridges are briefly introduced. To evaluate the dynamic responses of floating bridges, research advances are reviewed from the perspectives of numerical simulations, model tests, and field measurements. It has shown that floating bridges are exposed to complex coastal environmental conditions in which combinations of various loads can induce significant load effects. Challenges can come from environmental inhomogeneity, structural flexibility, coupled effects, and multi-disasters. Besides, the existing research methods have more or less shortcomings, making it difficult to effectively analyze their dynamic responses. This paper summarizes the previous methods for the dynamic response analysis of floating bridges, with an emphasis on loads and load effects. Some recommendations and research opportunities for future work are also proposed. • Development and types of floating bridges are briefly summarized. • Relevant advances in design and analysis of floating bridges are reviewed. • Numerical simulations, model tests, and field measurements are addressed. • Challenges come from environmental modeling, load modeling, and response assessment. • Recommendations and research opportunities are identified. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
41. Numerical simulation of wave-floater interactions using ISPH_GNN trained on data for wave-only cases.
- Author
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Zhang, Ningbo, Yan, Shiqiang, Ma, Qingwei, and Li, Qian
- Subjects
- *
GRAPH neural networks , *POISSON'S equation , *COMPUTATIONAL fluid dynamics , *COMPUTER simulation , *MACHINE learning - Abstract
As a mesh-free approach, the incompressible Smoothed Particle Hydrodynamics (ISPH) method has been often used for simulating wave-structure interaction problems. In the conventional ISPH method, the pressure-projection phase of solving the pressure Poisson's equation (PPE) is the most time-consuming. In recent years, the machine learning (ML) techniques has gradually shown their potential in accelerating the computational fluid dynamics. In this paper, the graph neural network (GNN) supported ISPH method (ISPH_GNN), in which the GNN replaces solving the PPE for the fluid pressure in the conventional ISPH, is adopted for numerical simulations of wave-floater interactions. To the best of the authors' knowledge, this is the first work to study the wave-floater interactions by using GNN supported ISPH method. More importantly, this paper demonstrates that the GNN trained only on data for simpler wave-only cases (i.e. no structure in the wave fields) can be satisfactorily applied to the cases for wave-floater interactions. More specifically, the paper will show this by using the ISPH_GNN with such trained GNN model to simulate various different cases, including the decay tests of a box, a floating box subjected to a wave, the interaction between wave and a moored floating breakwater and the violent green water impact on a floating structure. In most of the cases, the numerical results are validated by comparing with experimental data. Agreement between them is surprisingly satisfactory, being as good as those obtained by the conventional ISPH. The paper will also show that the ISPH_GNN requires much less computational time (97 times less for the cases concerned) than the conventional ISPH for estimating pressure involved in wave-floater interactions. This reveals a great potential that one can train the GNN using the datasets for simpler cases and then use the ISPH_GNN to simulate wave-floater interaction problems. • The first work to study the wave-floater interactions by using the graph neural network (GNN) supported ISPH method. • The GNN trained only on data for simpler wave-only cases can be applied to more complex cases for wave-floater interactions. • The ISPH_GNN can give satisfactory results for the relatively complex cases involving wave-floater interactions. • The ISPH_GNN takes much less computation time than the conventional ISPH for estimating pressure. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
42. Fixed-time trajectory tracking for autonomous surface vehicles via output feedback under various constraints.
- Author
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Luo, Peng, Wu, Defeng, and You, Zheng
- Subjects
- *
AUTONOMOUS vehicles , *ACTUATORS - Abstract
This paper proposes a novel fixed-time output feedback trajectory tracking control method suitable for autonomous surface vehicles (ASVs). Firstly, various complex uncertainty terms, such as unknown external disturbances, unmodeled errors, and actuator faults are considered in this paper. And these terms are uniformly converted into the total uncertainty terms through model transformation for convenience. Then, a fixed-time extended state observer (FTESO) with the newly expanded state is designed to observe and estimate the total uncertainty terms. Next, the saturation dynamic filter (SDF) is adopted to address the input saturation, and the saturation factors of SDF are incorporated into the trajectory error calculation to reduce the torque mutation caused by an excessive error in the control input. Finally, a fixed-time control law is proposed by taking into account the ASV system error and FTESO estimation state. Simulation experiments show that this method has excellent control performance, and this conclusion is validated through stability proof and case comparison. • A FTESO is designed to estimate the unknown states of ASVs. • A SDF is employed to address input saturation. • A novel FTOFC method is proposed for the stable and efficient operation of ASVs. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
43. Dynamic responses of the floatover system with nonstationary mating processes: An experimental study.
- Author
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Fang, Xukai, Li, Xinchao, Wang, Rongze, Chen, Yu, Hu, Changjun, Guo, Xiaoxian, Lu, Wenyue, Li, Xin, and Tian, Xinliang
- Subjects
- *
DYNAMIC loads , *NONLINEAR dynamical systems , *RELIABILITY in engineering , *HEAD waves - Abstract
Floatover method has been widely applied in the installation of both fixed and floating platforms, which has the advantages of high efficiency, economy, and large lifting capacity compared with other installation methods. Few studies could numerically and experimentally simulate the continuous load transfer process which shows significant nonstationary characteristics. This paper conducts experimental research on the nonstationary mating process of the floatover system. The ballasting system based on the control logic of feedback adjustment is developed to adjust the draft and inertia properties of the floatover vessel, and the validation tests are conducted to verify the feasibility and reliability of the system. The load buffer devices are designed carefully and the piecewise linear spring simulation method is applied to simulate the nonlinear stiffnesses of the elastic cushion. The stationary model for 0% and 100% load transfer stages and the nonstationary model for continuous load transfer process are established and tested in the model tests, and the dynamic responses are analyzed by using statistical and spectral methods respectively. Stationary model tests indicate that the spectral characteristics and distribution of LMU (Leg Mating Unit) dynamic loads in transverse symmetric positions are similar, and the statistical values are also relatively close under different wave heads. The nonstationary dynamic responses are segmented according to the physical process, time-frequency spectrum and piecewise statistics diagram to find the critical stage. The greatest dynamic load occurs in the intermediate stage of the mating process when the larger stiffness of the LMU acts and the steel-to-steel contact will also occur. • A brief introduction and the main procedures of the floatover installation operation are presented. • The paper reviews the numerical and experimental modeling of floatover installation systems. • The hydrodynamic analysis and the nonstationary nonlinear dynamical system of the floatover system are introduced. • The strength and weaknesses along with the challenges of each modeling and method are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
44. Research on optimal allocation of surface ship formation based on index method and multi-objective programming.
- Author
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Guo, Zilong, Hong, Mei, Shi, Jian, Zhang, Yongchui, Qian, Longxia, and Li, Hanlin
- Subjects
- *
MARINE engineers , *SHIPS , *SHIP models , *AIRCRAFT carriers , *MARINE engineering - Abstract
In recent times, marine engineers have progressively turned to collaborative efforts involving multiple ships to accomplish intricate tasks at sea and enhance the efficacy of maritime transportation. This trend is also observed in the context of surface ships, where coordinated actions among multiple vessels can enhance combat capabilities. Nevertheless, the assessment of ship formation coordination's effectiveness has emerged as a significant challenge. Consequently, this research paper presents a quantitative evaluation framework for ship performance indicators and develops a ship formation model grounded in multi-objective constraints that account for the complexities of the marine environment. This paper presents the establishment of a ship evaluation system that encompasses the impact of auxiliary equipment, the ship's platform, and trained personnel. The study utilizes aircraft carrier battle groups from four distinct countries as case examples to obtain quantitative evaluation results regarding combat performance. Furthermore, the analysis examines the effects of two extreme marine environments on surface ships. The organization of new surface ship formations is conducted based on a multi-objective planning model that is tailored to specific surface ship formations. All kinds of combat performance indexes are better than the formation of this particular surface ship. The experimental results show that the model can integrate different kinds of equipment performance parameters into a unified system and consider the comprehensive factors of equipment, platform and people. According to the requirements of task formation and the limitations of the actual Marine environment, a stable formation can be formed quickly, which can be superior to a specific formation in all aspects. Good results are obtained and the effectiveness of the model is verified. • We quantitatively assessed the operational effectiveness of the ship formation. • Different kinds of parameters are incorporated into a unified system. • The final result accords with the actual formation efficiency through comparative analysis. • Multi-objective programming model is used for autonomous formation research. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
45. Optimization of energy efficiency for offshore wind farms via wake modeling-free NMPC.
- Author
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Yao, Qi, Zhang, Yangming, Sun, Shanxun, Hu, Yang, Liu, Jizhen, and Fang, Fang
- Subjects
- *
OFFSHORE wind power plants , *ARTIFICIAL neural networks , *ENERGY consumption , *WIND turbines , *WIND power plants , *WIND power - Abstract
This paper presents an energy efficiency improvement scheme for offshore wind farms. This scheme uses learning-based nonlinear model predictive control (NMPC) and does not require wake modeling. The main feature is that each wind turbine can independently complete all optimal control, without the need for wind farm wake model calculation and iterative optimization. Specifically, this paper studies the critical factors for increasing the active power of wind farms and reducing the structural load of wind turbines, and reconstructs the optimal control objectives of wind turbines. Furthermore, combined with the nonlinear model of wind turbines containing uncertainty, a nonlinear model predictive control algorithm based on deep neural networks was designed, which can achieve multi-objective optimal control at the wind turbine level. The simulation results show that the uncertainty estimation method can effectively improve the nonlinear control performance, achieve an increase in the active power of the wind farm without wake iterative optimization, and at the same time suppress the structural loads of all wind turbines. • Propose a solution to improve wind farm energy efficiency without requiring wake modeling. • A nonlinear model of wind turbines considering uncertainty was established. • A deep neural network was used for uncertainty estimation. • Nonlinear model predictive control is used to achieve optimal control of wind turbines. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
46. Research on cable dynamic response of a catenary anchor leg mooring system based on ANCF.
- Author
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Fan, Jihua, Bai, Honglin, Wang, Mingqiang, and Fang, Haifeng
- Subjects
- *
MOORING of ships , *CATENARY , *CABLE structures , *VALUE engineering , *VIRTUAL work , *CONTINUUM mechanics , *CABLES - Abstract
This paper presents a dynamic analysis model for a catenary anchor leg mooring (CALM) system based on the absolute nodal coordinate formulation (ANCF) method, combined with continuum mechanics and finite element theory. This model uses absolute slope coordinates instead of traditional angle coordinates to better describe the large deformation and large displacement of the cables. The paper derives the element mass matrix, generalized stiffness matrix, and the element external load matrix, including the Morison force transformed into the ANCF framework, based on the virtual work principle. The accuracy and reliability of the ANCF program are validated using static and dynamic beam models, as well as submerged tether models. Furthermore, a comparative analysis of the ANCF mooring cable model with OpenFAST and MoorDyn accentuates the program's practical value in real engineering applications. Finally, we systematically analyzed the dynamic characteristics of a CALM single-point mooring system, revealing that the mooring forces in the cables significantly influence the high-frequency motion of the buoy. Additionally, the reduction in the length of the mooring cables, to an appropriate extent, enhances the stability of the system, which further attests to the effectiveness and practicality of the ANCF model that has been developed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
47. Optimized design of multiple tuned mass dampers for vibration control of offshore wind turbines.
- Author
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McNamara, Donagh, Pandit, Amiya, and Malekjafarian, Abdollah
- Subjects
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TUNED mass dampers , *WIND turbines , *WIND waves , *ROOT-mean-squares , *TORQUE control , *TOWERS , *STRUCTURAL dynamics - Abstract
Offshore wind turbines (OWTs) are dynamically sensitive structures to low-frequency wind-wave loadings due to their low damping and high flexibility. This makes them vulnerable to unwanted vibrations in ocean environments. Therefore, there is a need to implement innovative vibration control devices to suppress undesired vibration and ensure their structural safety. A tuned mass damper (TMD) has been a promising solution to control excessive vibrations recently in OWTs due to higher efficiency and low installation cost. However, TMD performance in vibration mitigation of OWTs when placed at a nacelle is still challenging to investigate because the generator torque and pitch control may affect the dynamics of the overall system. In this paper, an optimal multiple TMD system is designed by placing TMDs at optimal locations along the tower, which are defined using the maximum amplitude of the displacements for the first three natural frequencies of the tower. In addition, extensive simulations are carried out with integrated OWT-TMD systems to find the optimal mass ratio values and quantity of the TMDs. The TMD system is also tuned for several scenarios, including operating, parked, and idling conditions under the combined wind-wave loadings. A numerical model of the 5 MW NREL OWT developed in OpenFAST is considered as the baseline in this study. The results show a root mean square (RMS) response reduction of 10.2% and 42% in fore-aft (FA) and side-side (SS) tower displacement with optimally designed multiple TMDs. Moreover, improved mitigation effects on tower base moment of RMS 43.6% and 20.8% are observed in orthogonal directions, respectively. The findings of this paper may have the potential for designing passive TMD systems for vibration reductions in OWT. • A novel bi-directional MTMD is proposed for vibration suppression of a 5 MW OWT. • The proposed MTMD shows a significant improvement in vibration control of the OWT compared to a single TMD. • Optimized MTMD distributed along the tower can effectively suppress the tower base moment. • The performance of the proposed MTMD is evaluated under parked, idling, and operational conditions. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
48. Energy efficient coverage path planning for USV-assisted inland bathymetry under current effects: An analysis on sweep direction.
- Author
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Zhao, Liang and Bai, Yong
- Subjects
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WATER currents , *ENERGY consumption , *WATER consumption , *CONSUMPTION (Economics) , *MAP design , *BATHYMETRY - Abstract
Effective coverage path planning for USVs is essential to optimize the performance of bathymetric surveys. Traditionally, it is well recognized that the best sweep direction for coverage path planning is the parallel direction that finds the minimum span of the region of interest (ROI). However, the results in this paper first reveals that it is not always the case when the water current is involved. In this paper, we first formulate an energy consumption estimation model for USV and introduce a novel coverage path planning strategy. Then, we investigate the relationship between sweep direction and USV energy consumption under the influence of water currents, referred to as the E - β curve. We then systematically analyze the variations of the E - β curve under different shapes of ROIs, various water current attacking angles, and different coverage strategies. Finally, the model is extended to more realistic scenarios involving non-convex ROIs. The practicality of the model is validated USV semi-physical model. The results indicate that, under water currents, our proposed model allows for an optimal sweep direction that minimizes the energy consumption of USVs. This contrasts with traditional methods, which fail to achieve the optimal energy cost. The results hold significant implications for the design of USV mapping strategies in inland river. • This paper is the first to unveil the relationship between sweep direction and USV energy consumption under water currents, referred to as E - β curve. • Systematical analysis has been conducted on the factors that may impact the E - β curve. • An energy consumption estimation model for USV is constructed. • The model is extended to realistic scenarios involving non-convex polygonal ROIs and semi-physical simulation. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
49. Application of fluctuations in the sound field in inversion of internal solitary wave phase speed.
- Author
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Zheng, Yingdong, Lin, Ju, and Chen, Xu
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ACOUSTIC field , *THEORY of wave motion , *SPEED of sound , *SOUND pressure , *ACOUSTIC wave propagation , *INTERNAL waves , *ION acoustic waves - Abstract
Internal solitary waves propagation perturbing the sound velocity field, causes fluctuations in the sound field. This paper proposes to process the sound pressure data by the Product of the Slope and the even square of the Difference between two points of the acoustic parameter-time curve (PSD). The PSD processed data are processed to time-frequency analysis to extract the frequencies of the fluctuations in sound field. In this paper, numerical simulations and laboratory experiments are carried out on the process of internal solitary wave propagation in the sound field, and the characteristics of the sound field perturbation by internal solitary waves of different amplitudes are investigated. Results are both showing that the method can extract the dominant frequency of fluctuations in the sound field caused by internal solitary waves in real conditions. The method can be applied to the inversion of internal solitary wave phase speed which related to other parameters such as amplitude and characteristic width by theory. It is anticipated that this method can help realize the monitoring of internal solitary waves using acoustic paths. • A Product of Slop and Difference (PSD) method used to extract the fluctuation of sound field. • Considering the effects on sound field with internal solitary wave propagating. • The method to extract fluctuations in the sound field is validated by experiments in the tank. • Both simulation and experiments results showed the method can be applied in inversion of internal solitary waves. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
50. Spectral statistics in bubble dynamics.
- Author
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Jalili, Amir, Saleki-Haselghoubi, Noureyeh, Rasouli, Sadegh, Saleki, Ziba, and Luo, Yan-An
- Subjects
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BUBBLE dynamics , *BOUNDARY element methods , *RANDOM matrices , *SPECTRAL theory - Abstract
The application of Random Matrix Theory to study the spectral statistics of bubble dynamics near a curved perforated plate in an infinite liquid domain is presented in this work. The simulation of bubble dynamics is conducted in the vicinity of a circular opening in the bilge. Empirical interpolation distribution is employed to quantify the chaoticity of the simulation results, while the boundary element method combined with RMT is utilized to evaluate the level spacing of different opening sizes and standoff distances. The objective of this study is to gain a deeper insight into the internal dynamics and to determine the presence of chaotic or regular behavior. The findings reveal that chaotic behavior emerges in the presence of jet formation in bubbles, while regular behavior dominates when jet formation is not observed. • The paper investigates the bubble dynamics by adopting simulation approaches and boundary element method. • The effects of the two key parameters including opening size and standoff distance, were numerically studied on the bubble dynamics near a curved perforated plate in an infinite liquid domain. • The results reveal the complexity of bubble dynamics and the capability of the boundary element method to predict the bubble dynamics. • The paper opens up new avenues to understand the chaos and regularity in the bubble dynamics. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
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