Search

Currently, divers face significant safety risks when cleaning marine organisms from the steel structures of offshore underwater platform jackets. Consequently, utilizing robots instead of divers to carry out underwater biofouling removal operations will be an important development direction for the underwater maintenance of offshore platforms in the future. In this study, a wall-climbing robot was designed to clean marine organisms from the underwater surface of a platform jacket leg. The overall structure of the underwater cleaning wall-climbing robot is introduced, including the cleaning actuator and the variable curvature-adapted connecting rod mechanism. The corresponding relationship between the variable curvature-adapted connecting rod mechanism and the jacket leg is analyzed in detail. The variable curvature-adapted connecting rod mechanism was optimized using a genetic algorithm to ensure that the underwater cleaning wall-climbing robot can adapt to a minimum diameter of 1 m for the jacket leg. By drawing on Airy wave theory and random wave theory, the Airy wave parameters for waves were analyzed under different sea conditions, considering practical application scenarios. By using Fluent software 2022, a 2D numerical wave tank was constructed to simulate waves under various sea conditions, and the wave surface shapes for different sea states were determined. By building on the Morison equation, a method for calculating the horizontal wave forces on the underwater cleaning wall-climbing robot using the equivalent area and equivalent volume is proposed. By using the two aforementioned methods, the horizontal wave forces on the underwater cleaning wall-climbing robot under specific sea states were determined. The horizontal wave forces of the underwater cleaning wall-climbing robot under different sea conditions were analyzed and simulated in a 3D numerical wave tank. By comparing the theoretical analysis results with the numerical simulation results, where the maximum difference at the extreme points is approximately 11%, the feasibility of the proposed horizontal wave force estimation method was verified. [ABSTRACT FROM AUTHOR]

Currently, divers face significant safety risks when cleaning marine organisms from the steel structures of offshore underwater platform jackets. Consequently, utilizing robots instead of divers to carry out underwater biofouling removal operations will be an important development direction for the underwater maintenance of offshore platforms in the future. In this study, a wall-climbing robot was designed to clean marine organisms from the underwater surface of a platform jacket leg. The overall structure of the underwater cleaning wall-climbing robot is introduced, including the cleaning actuator and the variable curvature-adapted connecting rod mechanism. The corresponding relationship between the variable curvature-adapted connecting rod mechanism and the jacket leg is analyzed in detail. The variable curvature-adapted connecting rod mechanism was optimized using a genetic algorithm to ensure that the underwater cleaning wall-climbing robot can adapt to a minimum diameter of 1 m for the jacket leg. By drawing on Airy wave theory and random wave theory, the Airy wave parameters for waves were analyzed under different sea conditions, considering practical application scenarios. By using Fluent software 2022, a 2D numerical wave tank was constructed to simulate waves under various sea conditions, and the wave surface shapes for different sea states were determined. By building on the Morison equation, a method for calculating the horizontal wave forces on the underwater cleaning wall-climbing robot using the equivalent area and equivalent volume is proposed. By using the two aforementioned methods, the horizontal wave forces on the underwater cleaning wall-climbing robot under specific sea states were determined. The horizontal wave forces of the underwater cleaning wall-climbing robot under different sea conditions were analyzed and simulated in a 3D numerical wave tank. By comparing the theoretical analysis results with the numerical simulation results, where the maximum difference at the extreme points is approximately 11%, the feasibility of the proposed horizontal wave force estimation method was verified.

The Olympic Games (OG) are renowned for their prestige and socio-economic benefits; however, they have suffered criticism for their environmental practices. Unlike existing studies on the matter, which adopt top-down approaches, the purpose of this exploratory study is to conduct bottom-up research to understand Olympians’ perspectives of environmental sustainability within the OG. Data collected through semi-structured interviews with eight Olympians are used in this study to uncover an initial indication of their valuable yet previously undisclosed perspectives. Through the data, the Olympians’ awareness of the symbiotic relationship between sport and the environment is shown, alongside the factors that influence it. Uncovering Olympians’ perspectives allows for their call for change and collaboration with the International Olympic Committee (IOC) to be highlighted, while indicating that existing obstacles might be limiting the athletes and the Olympics in their efforts, progress and internalisation of environmental sustainability. [ABSTRACT FROM AUTHOR]

In order to accurately describe the axial forced vibration law of horizontal well drill string, the equivalent viscous damping method was used to linearize the Coulomb damping and the dynamic analytical model of horizontal well drill string motion was established under the action of axial vibration tool after considering the continuous characteristics of drill string, Coulomb damping, viscous damping of drilling fluid and the displacement excitation of drill string by axial vibration tool, based on the continuous wave theory. The model was verified by the axial vibration tool test experiment. The influence of the frequency of the axial vibration tool and the friction coefficient between the drill string and the wellbore on the axial forced vibration of the horizontal well drill string was analyzed by numerical simulation. The results show that the axial forced vibration response of the drilling string in horizontal wells can be improved by increasing the oscillation frequency of the axial vibration tool in a certain range, and that the effect of friction coefficient between drill string and borehole wall on the axial forced vibration of horizontal well drill string decreases with the increase of drill string length. The research method and models described in this paper can be expected to provide theoretical guidance for improving the use of axial vibration tools in horizontal well operation. [ABSTRACT FROM AUTHOR]

The article solves the problem of theoretically determining the deformable characteristics of railway ballast, considering its condition through mathematical modeling. Different tasks require mathematical models with different levels of detail of certain elements. After a certain limit, excessive detailing only worsens the quality of the model. Therefore, for many problems of the interaction between the track and the rolling stock, it is sufficient to describe the ballast as a homogeneous isotropic layer with a vertical elastic deformation. The elastic deformation of the ballast is formed by the deviation of individual elements; the ballast may have pollutants, the ballast may have places with different levels of compaction, etc. To be able to determine the general characteristics of the layer, a dynamic model of the stress–strain state of the system based on the dynamic problem of the theory of elasticity is applied. The reaction of the ballast to the dynamic load is modeled through the passage of elastic deformation waves. The given results can be applied in the models of the railway track in the other direction as initial data regarding the ballast layer.

Passive multispectral imaging and active bathymetric lidar make a great achievement for bathymetry in optically shallow waters. However, due to the attenuation of the water column precludes deep penetration of the light, accurately obtaining the underwater topography in turbid waters through remote sensing techniques, both passive and active, is still a challenging task. Airborne lidars can obtain water surface topography with high accuracy and resolution, which can further be used to derive the water depth based on wave theory. In this study, an “indirect” method to determine water depth is proposed using airborne lidar measured water surface points. As the wavelength and wave direction can be accurately tracked from the water surface topography, a $20\times20$ m underwater topography near Ganquan Island, South China Sea, is generated with a root mean square error (RMSE) of 0.91 m and a mean absolute percent error (MAPE) of 7.1%. The basic theory of deriving water depths is totally different from airborne lidar bathymetry (ALB), i.e., this method is independent of water clarity and can be used in turbid waters or even works with near infrared airborne lidar that can only obtain water surface points. [ABSTRACT FROM AUTHOR]

The article solves the problem of theoretically determining the deformable characteristics of railway ballast, considering its condition through mathematical modeling. Different tasks require mathematical models with different levels of detail of certain elements. After a certain limit, excessive detailing only worsens the quality of the model. Therefore, for many problems of the interaction between the track and the rolling stock, it is sufficient to describe the ballast as a homogeneous isotropic layer with a vertical elastic deformation. The elastic deformation of the ballast is formed by the deviation of individual elements; the ballast may have pollutants, the ballast may have places with different levels of compaction, etc. To be able to determine the general characteristics of the layer, a dynamic model of the stress–strain state of the system based on the dynamic problem of the theory of elasticity is applied. The reaction of the ballast to the dynamic load is modeled through the passage of elastic deformation waves. The given results can be applied in the models of the railway track in the other direction as initial data regarding the ballast layer. [ABSTRACT FROM AUTHOR]

This paper introduces a new theory in temporal ontology, 'wave theory', and argues for its attractions over and above existing tensed theories of time. [ABSTRACT FROM AUTHOR]

The wave height is the most basic element of wave information, and accurate measurement of wave heights plays a crucial role in both understanding wave theory and verifying numerical models. An improved optical measurement system was proposed based on the principle of binocular stereo vision, which breaks through the limitations of traditional measurement devices such as wave gauges and other single-point measurements, and improves the commonly used optical measurement method relying solely on images by involving the water wave theory into the data post-processing procedure. Through the identification and reconstruction of the unidirectional regular wave surface in a towing tank and the comparison of the results with the wave gauges and theoretical incoming wave parameters for validation, the research shows that, the measuring system has an error of about 1% in the measurement of a wide-area wave surface. Finally, a preliminary attempt was made on the irregular wave surface identification. [ABSTRACT FROM AUTHOR]

To get a deeper understanding on the synergistic enhancement effect of low frequency artificial seismic wave on foam stability, a micro-kinetic model of enhanced foam stability under low frequency artificial seismic wave is established based on a vertical liquid film drainage model and elastic wave theory. The model is solved by non-dimensional transformation of the high order partial differential equations and a compound solution of implicit and explicit differences and is verified to be accurate. The foam film thickness, surfactant concentration distribution and drainage velocity under the action of low frequency artificial seismic wave are quantitatively analyzed. The research shows that low-frequency vibration can reduce the difference between the maximum and minimum concentrations of surfactant in the foam liquid film at the later stage of drainage, enhance the effect of Marangoni effect, and improve the stability of the foam liquid film. When the vibration frequency is close to the natural frequency of the foam liquid film, the vibration effect is the best, and the best vibration frequency is about 50 Hz. The higher the vibration acceleration, the faster the recovery rate of surfactant concentration in the foam liquid film is. The higher the vibration acceleration, the stronger the ability of Marangoni effect to delay the drainage of foam liquid film and the better the foam stability is. It is not the higher the vibration acceleration, the better. The best vibration acceleration is about 0.5 times of gravity acceleration. Reasonable vibration parameters would greatly enhance the effect of Marangoni effect. The smaller the initial concentration of surfactant, the better the vibration works in enhancing Marangoni effect.

Copyright of International Journal on Criminology is the property of Policy Studies Organization and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objectives]Resonance Changer (RC) is an effective vibration damping device,which receives much attention in the field of longitudinal vibration control of marine shafting. As the RC's damping effect is closely related to the internal structural parameters,[Methods]an analytical formula of sound pressure propagation in RC was derived based on the wave theory,and the physical relationship between the internal structural parameters and its vibration mechanism was constructed for engineering design. Then,the influence of design parameters of RC's external pipes and cavity on system insertion losses and sound pressure level in broad band as well as the sensitivity were analyzed.[Results]The results show that,RCs can control the resonance peak of the main system well at its natural frequency.[Conclusions]Attention should be paid to the external pipe size of RCs when considering the feature line spectrum suppression,and to the external cavity size when considering the overall control of sound pressure level in broad band.

Elastic parameters are important parameters in the study of shale anisotropy, exploration, and development, and their accuracy is of great significance. In this study, shale in the lower Silurian Longmaxi Formation of southeastern Chongqing was investigated by obtaining the acoustic velocity of the partial bedding angle through an acoustic transmission experiment based on the elastic wave theory of the VTI medium and the least squares method, thus establishing a shale elastic parameter inversion method for improved accuracy. Results found that (1) the stratification angle was negatively correlated with the wave velocity; (2) velocity results calculated using the inversion-obtained elastic parameter were consistent with the measured results, with a maximum relative error of less than 1.52%, demonstrating that elastic parameters obtained by the proposed inversion method are valid; and (3) Longmaxi Formation shale has strong anisotropy, with the most significant direction of shear wave splitting being the direction in which the bedding angle is 0°. The results of this study provide a working foundation for using acoustic logging data to more accurately obtain the elastic parameters of shale and to study shale anisotropy characteristics, which have important theoretical value and practical significance. [ABSTRACT FROM AUTHOR]

The paper analyzes the two theories of conducted light signal for Bragg fiber with high-index core, namely total internal reflection and photonic bandgap. From the perspective of the wave equation, the distribution of the electromagnetic field and the conditions for forming the guided mode when the optical signal is transmitted in the core of fiber are explained. The analysis of photonic bandgap adopts the band structure principle of natural crystals for analogy. Then, the formation process of the photonic bandgap is elaborated on.

Featured Application: Main gas and oil pipelines are critical elements of the world's infrastructure. The integrity of pipelines during earthquakes is a subject of intensive research. At present, underground pipelines' strength to the effect of seismic loads (seismic resistance) is calculated incorrectly. The existing methods do not consider seismic (dynamic) pressure, i.e., the stress normal to the pipeline's outer surface arising from the propagation of a seismic wave in the soil. This leads to an incorrect determination of the pipeline's stress; the longitudinal stress calculations leads to errors of 100% or more. A potential application of the results obtained is the calculation of seismic stability of underground pipelines. The object of the research is an underground straight horizontal pipeline subjected to seismic impact. The research method was analytical. The results were compared with the experimental results of other authors and computer calculations. It was shown that the main disadvantage of the dynamic theory of seismic resistance of underground pipelines is the neglect of the dynamic stress state in soil under seismic wave propagation. The next drawback of the dynamic theory is an inaccurate, approximate accounting for the displacement of the soil medium to which the underground pipeline is embedded. The complete interaction process includes the stages of nonlinear changes in the interaction force (the friction force) by manifesting its peak value and the Coulomb friction. The contact layer of soil undergoes shear deformations until complete structural destruction of the soil contact layer. The interaction force is the friction force, and its peak value does not appear. The seismic resistance of underground pipelines should be considered based on the theory of propagating seismic waves in a soil medium and the interaction of seismic waves with underground pipelines, i.e., based on the wave theory of seismic resistance of underground pipelines. A one-dimensional coupled problem of seismic resistance of underground pipelines under seismic impacts was posed based on the wave theory. An algorithm and a program for the numerical solution of the stated wave problems were developed using the method of characteristics and the method of finite differences. An analysis of the laws of interaction of underground pipelines with soil under seismic influences shows that it is necessary to use in the calculations the laws of interaction that account for the complete interaction processes observed in experiments. The analysis of the obtained numerical solutions and the posed coupled problems of the wave theory of seismic resistance of underground pipelines show the occurrence mechanisms of longitudinal stresses in underground pipelines under seismic influences. The results of calculations stated that an account for the dynamic stress normal to the underground pipeline's outer surface leads to multiple increases in longitudinal stress in the underground pipeline. This multiple increase is due to the transformation of the interaction force into an active frictional force, resulting from a greater strain in soil than the one in the underground pipeline. Based on the analysis results, a theory of the seismic wave propagation process in an underground pipeline and surrounding soil was proposed. [ABSTRACT FROM AUTHOR]

Under conditions when the particles' thermal gyro-radii are smaller than the Debye length λ D , the magnetic field influence on the collision dynamics and associated transport processes becomes significant and has to be considered. In this paper, derivation of the kinetic equation based on the Fokker–Planck approach is reviewed for uniform magnetized plasmas with ρ the < λ D < ρ thi , where ρ the and ρ thi are the electron and ion thermal gyro-radii, respectively. Generally speaking, current tokamak plasmas lie in the above studied parameter range. Serving as an example for the application of the derived magnetized kinetic equation and demonstrating the modifications to the transport coefficients from a strong magnetic field, the electron-ion temperature relaxation is reviewed. The relaxation time exhibits a noticeable magnetic field dependence. [ABSTRACT FROM AUTHOR]

Within Terrorism Studies, Rapoport, D. C.'s (2004. The Four Waves of Modern Terrorism. In A. Cronin, & J. Ludes (Eds.), Attacking Terrorism: Elements of a Grand Strategy (pp. 47–65). Washington, DC: Georgetown University Press.) Wave Theory is a theoretical landmark that covers modern terrorism since 1880. However, this masterpiece neglects Eco-Terrorism, a phenomenon starred by the Animal Liberation Front (ALF), the Earth Liberation Front (ELF) and some other ideologically similar organizations. Even though it has been catching authorities' attention around the world, such negligence towards the phenomenon has been replicated by others working on Rapoport's Wave Theory, leaving a question unaddressed: 'Was/Is there an 'Eco-Terrorist Wave'?' Methodologically built upon a Time Series analysis on the Global Terrorism Database (GTD) (1970–2017), the present research harmonizes Eco-Terrorism under Rapoport's Wave Theory. Based on the evidence collected, the phenomenon has been evolving in a Rapoportian 'Wave-Like' pattern since 1972. [ABSTRACT FROM AUTHOR]

• A modified model regarding the viscosity and cavitation criterion was proposed and validated by experimental results. • Various numerical models were evaluated and the turbulence stress should be considered. • Fluid network and wave theory were used to elucidate different modulation mechanism in self-sustained resonating jet. • Cavitation evolution dominates the oscillation frequency of LF nozzle via modifying disturbed volume. • Geometry resonance couples with cavitation collapse and growth to achieve frequency modulation in HF nozzle. Self-sustained oscillating jets are widely utilized in various industries, and their oscillation frequencies are closely related to their performance efficiencies. The oscillation frequency is affected by cavitation in practical situations, and cavitation effects vary with geometry. In the present study, the computation fluid dynamics (CFD)-aided method is used to investigate the different modulation mechanisms induced by cavitation in high-frequency (HF) and low-frequency (LF) nozzles. The results indicate that the modified numerical model can reproduce the cavitation evolution in different nozzles and provide information to aid theoretical and experimental analyses. Based on the wave theory, it is found that the cavitation structures determine the LF nozzle oscillation frequency by dominating the disturbed volume bounded by the shear layer and chamber walls. In the case of HF nozzle, the growth and collapse of cavitation are regarded as the major excitation sources affecting oscillation frequency. In addition, the frequency is predicted using the CFD-aided method at various cavitation numbers, which is beneficial to the utilization of self-sustained oscillating jets. [ABSTRACT FROM AUTHOR]

Based on the wave theory and propagation characteristics of Lamb wave in the thin plate, Lamb wave is excited by signal actuator in the thin plate and signal sensor is received in real time. Employing the superior features of dispersion curve produced the Lamb wave and combining the dichotomy iterative principle with MATLAB tools to solve Lamb wave dispersion equation, the propagation characteristics of the Lamb wave in the thin plate are plotted. It is verified that the excited Lamb wave has multimode characteristics in a certain thickness, and the different modes are related to the frequency-thickness. The wavelength-thickness ratio is defined to simplify the calculation and provide convenience for the frequency bandwidth interception of Lamb wave. The results of the theoretical analysis show that the propagation multimode of Lamb and the distribution characteristics of dispersion curve can effectively simulate the transmission information of damage signal-excited thin plate, and identify damage region and determine the damage degree by S 0 and A 0 mode. The experimental results indicate that the established method to determine damage degree of thin plate attached PZT transducers based on Lamb wave active monitoring technology can achieve a certain precision, and can make a rough quantitative recognition of damage position. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Following the 1st International Workshop on Waves, Storm Surges and Coastal Hazards, which incorporated the 15th session of the long-standing the International Workshop on Wave Hindcasting and Forecasting, in September 2017 in Liverpool, United Kingdom, a topical collection has appeared in recent issues of Ocean Dynamics. Here, we give a brief overview of the 15 papers published in this topical collection as well as an overview of the widening scope of the conference in recent years. The continuing trend towards closer integration between the wave and ocean modeling communities is reflected in this workshop, culminating in the renaming of the workshop, while maintaining the connection with the three-decade long history of the wave workshop. This is also seen in this topical collection, with several papers exploring wave-generated storm surge, wave-tide contributions to coastal flooding, forcing a global ocean model with fluxes from a wave model and interaction between surface waves and sea ice. [ABSTRACT FROM AUTHOR]

The object of the research is an underground straight horizontal pipeline subjected to seismic impact. The research method was analytical. The results were compared with the experimental results of other authors and computer calculations. It was shown that the main disadvantage of the dynamic theory of seismic resistance of underground pipelines is the neglect of the dynamic stress state in soil under seismic wave propagation. The next drawback of the dynamic theory is an inaccurate, approximate accounting for the displacement of the soil medium to which the underground pipeline is embedded. The complete interaction process includes the stages of nonlinear changes in the interaction force (the friction force) by manifesting its peak value and the Coulomb friction. The contact layer of soil undergoes shear deformations until complete structural destruction of the soil contact layer. The interaction force is the friction force, and its peak value does not appear. The seismic resistance of underground pipelines should be considered based on the theory of propagating seismic waves in a soil medium and the interaction of seismic waves with underground pipelines, i.e., based on the wave theory of seismic resistance of underground pipelines. A one-dimensional coupled problem of seismic resistance of underground pipelines under seismic impacts was posed based on the wave theory. An algorithm and a program for the numerical solution of the stated wave problems were developed using the method of characteristics and the method of finite differences. An analysis of the laws of interaction of underground pipelines with soil under seismic influences shows that it is necessary to use in the calculations the laws of interaction that account for the complete interaction processes observed in experiments. The analysis of the obtained numerical solutions and the posed coupled problems of the wave theory of seismic resistance of underground pipelines show the occurrence mechanisms of longitudinal stresses in underground pipelines under seismic influences. The results of calculations stated that an account for the dynamic stress normal to the underground pipeline’s outer surface leads to multiple increases in longitudinal stress in the underground pipeline. This multiple increase is due to the transformation of the interaction force into an active frictional force, resulting from a greater strain in soil than the one in the underground pipeline. Based on the analysis results, a theory of the seismic wave propagation process in an underground pipeline and surrounding soil was proposed.