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In this paper, an intelligent adaptive algorithm based on the integrated Inertial Navigation System (INS) is presented for estimating the velocity of an Autonomous Underwater Vehicle (AUV). The most common algorithm for incorporating the navigation data is Kalman Filter (KF). In the conventional KF algorithm, the covariance matrix of measurement noise is considered as a constant through running time. The noise covariance in the Adaptive Kalman Filter (AKF), is estimated through processing the innovation sequence inside a window of constant length. In actual conditions, the correct window length to achieve the best estimation, depends on the operational conditions. In this paper, proper window length in the adaptive algorithm is estimated by processing the probability density function of the innovation sequence at each time step; so the window length in the proposed algorithm is variable due to condition changes. The proposed integrated navigation system consists of a three-axis Inertial Measurement Unit (IMU) and a three-axis Doppler Velocity Log (DVL). The performance of the proposed system is evaluated through four sea tests using an AUV. Experimental results show that the proposed system has superior performance than the conventional KF algorithm and is similar to the optimum AKF(AKF with the best window length). [ABSTRACT FROM AUTHOR]

Maneuverability is one of the most important performance characteristics of submarines. Hydrodynamic model is increasingly relied on as a design approach to determine the inherent motion behavior of a proposed submarine before construction. Standard submarine motion equations are the most used hydrodynamic model, in which more than 100 coefficients need to be estimated. These coefficients have to be determined by captive model tests, semi-empirical method and potential flow method on the basis of existing approach. The separately determining approach makes it difficult to assess model reliability. This paper proposes a time-efficient approach for the estimation of hydrodynamic coefficients using computational fluid dynamics (CFD) method. Instead of a repetitive and time-consuming process, the proposed spatial captive motion could provide all necessary information for determination of all required coefficients in only one simulation. Linear regression, based on the least square method, is employed to determine coefficients in hydrodynamic model. Statistical investigation, correlation and significance analysis, indicates that the standard submarine motion equations can be further simplified when submarine moving forward with small perturbations along other directions. The final simplified motion equations have much fewer components than the original model while fitting accuracy remained. Validation results prove that spatial captive motion simulation and the simplification approach employed in this paper are effective and reliable. It should have a large scope in further maneuverability research. [ABSTRACT FROM AUTHOR]

Many papers in the literature present studies of the interaction of sea waves, structures, and soil; however, most of these studies focus on the pore pressures and stresses in the soil around structures. Very little knowledge has been obtained regarding the impedance of a foundation considering the coupling of the water wave pressure effect (WPE) and dynamic soil-structure interaction (DSSI), as classical impedance functions are obtained based on a foundation on an elastic half-space with a stress-free surface. Impedance functions can be used to study the dynamic responses of a structure using the substructure method during the serviceability limit state design. This paper studies the forced vertical vibration of a strip foundation on a poro-elastic seabed with surface subjected to water wave pressures. The strip foundation on the seabed is simultaneously excited by water wave and other external forces at the same frequencies as water waves (with WPE-DSSI coupled). Three new impedance functions for foundations in ocean engineering are defined. Selected results for the new impedance functions are examined based on different water depth, wave height, wave frequency, and poroelastic material. The results show that for a rigid strip foundation in ocean engineering, both its total impedance and effective impedance are displacement dependent. [ABSTRACT FROM AUTHOR]

The principal construction-area of offshore wind farm (OWF) in China has shifted from the soil-based seabed area to the weathered rock-based area. The current studies about construction materials of OWF mainly focus on the submarine soft-clay or sandy soil seabed, resulting in the design and construction of OWF in rock-based area cannot directly refer to the existing research conclusions and results recommended in standards. Therefore, this paper concentrates on the investigation of cyclic behavior of submarine completely weathered granite of offshore wind farms in rock-based sea area under cyclic loadings. The experiments analyze the cyclic stress-strain and stress path behavior, revealing two unique development modes under different dynamic loadings, i.e., the stable development mode and the destructive development mode. A unified forecasting model of pore water pressure with different development modes is established, and further research investigates insight critical failure stage by concentrating on pore water pressure. More critical, the unique mechanical properties and microscopic characteristics of completely weathered granite are clearly expounded by comparing with submarine soft clay and sandy soil. This gives the engineering suggestion of design value of OWT foundation in completely weathered granite seabed, and is a helpful reference for the construction of OWF in rock-based sea area. • Two unique development modes of completely weathered granite under different dynamic loading are put forward. • A new discrimination method of critical failure stage is proposed based on development of pore water pressure under different cyclic loading. • The unique mechanical properties and microscopic characteristics of submarine completely weathered granite are clearly revealed by comparing with submarine soft clay and sandy soil. [ABSTRACT FROM AUTHOR]

The study of submarine maneuverability is an important part in the overall design of submarines. The goal of this investigation is to study the hydrodynamic coefficients of SUBOFF AFF-8 in rotating arm maneuver. This paper consists of two parts, which deal with the test technology and test results, respectively. Part Ⅱ of this paper presents the angular velocity-dependent derivatives and spatial coupling coefficients of SUBOFF AFF-8 and investigates the forces and moments in steady turn. The forces and moments of SUBOFF AFF-8 are investigated and the hydrodynamic coefficients of SUBOFF AFF-8 are fitted. The results show the coefficients with r in the lower corner represent the linearity of hydrodynamic forces. In order to get more accurate nonlinear coefficients and coupling coefficients, the drift angle should not be too small in the rotating arm test. When SUBOFF AFF-8 has both drift angle and attack angle, the nonlinear degree of rotation increases sharply, which will bring great difficulties to the measurement of forces and moments. • The main contributions of this paper are the following: • The forces and moments of SUBOFF AFF-8 in steady turn are investigated. • The angular velocity-dependent derivatives and spatial coupling coefficients of SUBOFF AFF-8 are fitted. • The measuring and testing technique of the rotating arm test is discussed. [ABSTRACT FROM AUTHOR]

The study of submarine maneuverability is an important part in the overall design of submarines. The goal of this investigation is to study the hydrodynamic coefficients of SUBOFF AFF-8 in rotating arm maneuver. This paper consists of two parts, which deal with the test technology and test results, respectively. In Part I, the measuring and testing technique of the rotating arm test in rotating arm basin of Zhejiang University (ZJU) is presented. The connection between the model and the trailer is completed through a cylindrical strut. A steel base is pre-installed inside the model to connect one end of the strut. The detailed calibration of the six-component balance is presented. The linear hydrodynamic coefficients on the horizontal and vertical plane are obtained and compared with the results of DTRC. The results show that the ZJU test values is reliable. The difference between DTRC and ZJU is within 10%. Some technical details about the rotating arm test are discussed in the conclusion. Part Ⅱ of this paper presents the angular velocity-dependent derivatives and spatial coupling coefficients of SUBOFF AFF-8 and investigates the forces and moments in steady turn. • The main contributions of this paper are the following: • The measuring and testing technique of the rotating arm test is presented. • The detailed calibration of the six-component balance is introduced. • The linear hydrodynamic coefficients of SUBOFF AFF-8 on the horizontal and vertical plane are obtained. [ABSTRACT FROM AUTHOR]

The clarification of the pipe–soil interaction mechanism is a critical link in the design of the in-situ stability of shallow embedded pipes in subsea areas, and the in-situ embedment of pipelines is an important parameter in the pipe-soil interaction mechanism. A large-scale plane strain model test was performed for a shallow embedded pipeline with horizontal cyclic motion in sand. Additionally, a numerical analysis model that is applicable to multicycle submarine pipe–soil interactions in sand was constructed, which can consider the dynamic change in the pore ratio of sand during the motion of a shallow buried pipeline. The development law of dynamic embedment and factors influencing the pipeline after multiple horizontal cycles were studied. A method for calculating the dynamic embedment of pipelines in sandy soil was proposed. The results reveal that horizontal cyclic movement of the pipe in sandy soil increases the embedment depth, and dynamic embedment rises by 1.09–11.78 times depending on the initial state of the pipeline. Furthermore, a soil berm rises on both sides of the pipe following cycling, and the sand around the pipe is sheared and shrunken, causing a large increase in soil resistance during the horizontal movement of the shallow embedded pipe. • This paper outlines the change law of dynamic embedment during the cyclic movement of shallow embedded pipelines in sand. • Factors influencing the dynamic embedment of pipelines are analysed through a numerical model. • The empirical formulas for determining the dynamic embedment of pipelines in sand is provided based on numerical results. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a nonlinear parametric model and proof-of-concept motion control system for a scale model submarine undertaking an emergency ascent. An energy-based model is presented that represents the underactuated submarine in a non-neutrally buoyant state. This model is then used to synthesize a control law using Port-Hamiltonian theory and interconnection and damping assignment passivity-based control. Lyapunov analysis is used to demonstrate stability of the closed-loop system, and a simulation-based study is presented to demonstrate performance of the control law. The results demonstrate that a closed loop non-linear controller is able to improve the quality of emergency rise by automatically compensating for some parasitic effects in the hydrodynamics that can compromise ascent performance. Highlights •A control oriented nonlinear model of a non neutrally buoyant submarine can be developed. • A non linear control law can aid a submarine in emergency ascent. • By reducing ascent resistance, an automatic control strategy can reduce ascent resistance. [ABSTRACT FROM AUTHOR]

Abstract Unburied submarine pipelines might buckle laterally under the conditions of high temperature and high pressure. As an important design parameter of submarine pipelines, the lateral buckling critical force (LBCF) is affected by the maximum amplitude, wavelength, shape of the initial imperfection, and etc. However, the exact relationship between the LBCF and the initial imperfection shape is not clear at present. In this paper, the lateral buckling behaviors of submarine pipelines with different initial imperfection shapes are studied using 3D finite element (FE) analysis. A parametric study is conducted and the characteristic parameter of the initial imperfection shape is found. It is the characteristic parameter that makes the LBCF greatly affected by the initial imperfection shape. A unified formula is proposed to reveal the exact relationship between the LBCF and the initial imperfection shape. An application of the unified formula is carried out and the results show the accuracy of the unified formula. Highlights • The effect of initial imperfection shape of a submarine pipeline on the critical force of lateral buckling is studied. • The lateral buckling behavior of a pipe with different initial imperfection shapes is studied. • A key parameter of initial imperfection shape that has a great influence on the critical force of lateral buckling is found. • A unified formula to determine the critical force of lateral buckling is proposed. • A case study is carried out to illustrate the application of the unified formula, showing the accuracy of the unified formula. [ABSTRACT FROM AUTHOR]

Submarine pipe-in-pipe flowline have become a common pipeline arrangement to achieve a significant thermal insulation capacity. A pipe-in-pipe system generally contains four structural components: jacket pipe, carrier pipe, spacers and bulkheads. Global response of the system depends on both the behaviour of each constituent part and interactions between them. Existing design approaches to consider this system are either too simplistic resulting in loss of accuracy or significantly complicated Finite Element Analysis demanding expensive highly skilled manpower. This paper proposes cost effective design methods which provide accurate prediction with minimum increase in modelling complexity through simplified Finite Element Analysis models. Pipe-in-pipe system S-lay, thermal expansion and spool arrangement design have been investigated. ABAQUS or AutoPIPE based methods have been proposed to cover each application and excellent performance has been observed. In addition to cost-effectiveness, ABAQUS based method for S-lay is able to capture twisting and residual stresses which are generally ignored by traditional approach but important in deep-water applications. [ABSTRACT FROM AUTHOR]

This paper presents a framework for the availability assessment of subsea distribution systems during the functional design (selection) phase. This framework, which also includes all interface elements, can be started at an early stage when the definition of the system architecture is coarse and generic failure data is available and can be refined as more information becomes available, then maintained as the system ages during the operational phase. The main objective is to present a decision tool for selecting the subsea distribution system with the highest advantage in terms of availability at a very early stage of the design. The Design Structure Matrix (DSM) mapping method is used to represent the system's components and their dependencies, which is then enriched with additional reliability data to calculate availability. A case study of an actual subsea distribution system is used to demonstrate the approach. [ABSTRACT FROM AUTHOR]

Numerical simulation is an effective method to study the global buckling of submarine pipelines under high temperature and high pressure. The length of the pipeline model has a significant effect on the global buckling during the numerical simulation. This paper outlines the global buckling regularity of different pipes of various lengths and proposes a method to determine the pipe model length for the numerical simulation of pipe buckling by using theoretical analysis and the FEA method. A method of calculating the pipeline's critical length and upper-limit critical length is proposed based on the characteristics of the short pipe and long pipe. The numerical analysis results indicate that the global buckling amplitude of the short pipe increases with the length of the pipeline model. Therefore, the model length of a short pipeline in the numerical simulation should be equal to the actual length of the research object. In contrast, the buckling amplitude of pipes with a length greater than the critical length does not vary with the pipe length. Thus, the model length only needs to be equal to or slightly larger than the critical length. A method to determine the length of the pipe model for the numerical simulation of pipe buckling is proposed for various pipelines with different laying modes in practical engineering. [ABSTRACT FROM AUTHOR]

For pipelines on uneven seabed, upheaval buckling may occur if the axial compressive force reaches the critical force of upheaval buckling. The critical axial force is sensitive to the seabed undulation, However, the effect of the seabed undulation on the critical force has not been completely discussed. Moreover, effect of the initial stress which accumulates in the pipe wall when the pipeline conforms to the seabed undulation under self-weight has been rarely examined. This paper mainly focuses on the effect of the initial stress. Using numerical tools developed with the Vector Form Intrinsic Finite Element (VFIFE) method, effect of the initial stress is proved significant. Subsequently with the theory of dimensional analysis, a formula of the critical axial force is derived. This formula covers the dimensionless undulation length and the Out-of-Straight (OOS) of the seabed undulation. Considering three seabed undulation shapes, coefficients in the formulas are determined with numerical results from the VFIFE simulations. Finally, the proposed formulas are proved applicable for pipes with different properties and within the error range of ±10% for pipelines in continuous contact with the seabed in a large dimensionless scope. [ABSTRACT FROM AUTHOR]

Maneuvering abilities of underwater vehicles are one of the primary concerns for navies and in the civil field they provide great flexibility in working in confined environments. Numerical simulations of the motions of these vessels may be conducted via system-based or direct CFD approaches. In this study, we focus on direct CFD simulations of the benchmark DARPA Suboff AFF8 Configuration. The paper starts by showing the submarine's lack of course-keeping stability using the C-index. After validation of the numerical approach by self-propulsion tests (and the determination of the propeller rotation rate to achieve the required velocity), the results of an extensive set of standard maneuvering tests are presented. Turning circle, pullout and zig-zag tests confirm that the DARPA Suboff does not have course-keeping ability. The submarine leans to the starboard side at neutral rudder angle. The maneuvering indices are investigated with respect to changing rudder angle with turning circle tests. High residual yaw rates are found in both side turnings in the pullout tests and the zig-zag tests show the submarine's inadequacy in making sharp turns. Numerical simulations reveal that the DARPA Suboff has high turning ability but no course-keeping ability. • Maneuvering performance of a submerged hull (DARPA Suboff) was determined using standard maneuvering tests. • The effect of rudder angle (−35.0 ≤ δ ≤ 35.0) on the turning circle maneuver was investigated by direct CFD simulations. • Pullout tests revealed an excessive residual yaw rate indicating the lack of course-keeping stability. • The lack of course-keeping stability was also effective in zigzag maneuver as the ship barely managed to complete the tests. [ABSTRACT FROM AUTHOR]

This paper presents the effects of different scales on non-dimensional horizontal hydrodynamic derivatives of a generic underwater vehicle, DARPA Suboff. Thus, three different scales are created for fully appended submarine form. A numerical viscous solver is utilized to model the Planar Motion Mechanism (PMM) technique, numerically. Before presenting the scale effect, the numerical model is verified and validated with an appropriate method and available experimental data. Firstly, the sway forces and yaw moments are obtained under different scenarios, then the linear horizontal maneuvering derivatives of each scale are calculated and compared with each other. It is found that the sway forces obtained from pure yaw analyses are remarkably affected by the scale, while sway forces obtained from pure sway analyses are not affected reasonably. Yaw moment values are affected remarkably in neither pure sway nor pure yaw analyses. The scale effect appears also in a similar way in the linear maneuvering coefficients. • The horizontal maneuvering derivatives of the DARPA Suboff are obtained using a viscous solver, numerically. • The full-scale PMM analyses are conducted for the DARPA Suboff and the hydrodynamic derivatives are calculated. • The scale effect on the forces and moments acting on the submarine are investigated. • The scale effect on the horizontal hydrodynamic derivatives is presented by comparing the results with each other. [ABSTRACT FROM AUTHOR]

When a submarine with a large volume superstructure floats up, the water on the back of the superstructure is large. In order to ensure the safety of submarine floating, it is necessary to study the stability and attitude change of submarine floating. In the present study, STAR-CCM + software is used to construct a numerical wave pool based on the numerical wave making theory. Based on the overset grid, the calculation method for internal and external domains interaction is adopted, and the uncertainty of the numerical calculations is analyzed using the model floating test results. What's more, the numerical results of the hull longitudinal and vertical velocities, and heel and pitch angles are close to the test results, except for the peak values. Compared to the test results, the average error of the amplitude of the numerical results was within 10%.It can thus be concluded that the numerical simulations were credible, which confirmed that the proposed numerical method can be applied to simulating the emergency ascent of a submarine with flow holes. Finally, a numerical prediction method for submarine floating movement in waves considering the superstructure water hole is proposed. The characteristics of the submarine buoyancy and emergence in waves are explored for various wave directions, wave heights and wavelengths. The results indicate that beam waves have a greater impact on the lateral orientation of the submarine, while the head waves are more effective on the longitudinal direction. Furthermore, the heel angle of the submarine is higher in beam and oblique waves compared to that in head waves. The longitudinal displacement shows a descending trend as the wave height increases. As the submarine exits the water, the hull posture is affected by waves, and the heel and pitch angles tend to increase by the rise of wave height. Based on a given wavelength range of 1∼3L, the higher wavelengths increases the longitudinal and lateral displacements of the hull, and reduces its heel and yaw angles. For shorter wavelengths, the hull responds faster to variations induced by the wave disturbances. It can be concluded that submarines should avoid surfacing in shorter wavelengths as well as in beam waves. The proposed numerical methods and conclusions of the present study can be considered as a reference in the scope of submarine floating movement. • The present paper conducted a numerical simulation method to predict the submarine floating movement in waves in presence of an overflow induced by the water holes in the superstructure. • The method was verified based on the model floating test. • The effects of different wave orientations, heights and wavelengths were investigated when the submarine floated out of the water. • The relevant model test methods can lay a foundation for the study of submarine buoyancy. [ABSTRACT FROM AUTHOR]

This research investigates the short-distance hydrodynamic interaction of a squat submarine towed by a marine vessel. A one-tenth scaled captive model of a 0.625-m squat submarine is constructed along with a 1.5-m Fridsma ship to perform 69 unique experiments in a 4 × 6 × 400-m3 water tank located in a towing tank center. The submarine model is a new mini-submersible, Apam-Napat SMSD type, with an L/D ratio below four. The cable is specified, regarding its weight per unit length, using a scaling method introduced in this paper. The submarine-cable-ship system is tested for nine various relative lengths and depths at short-distance conditions. In each case, drag and heave forces are recorded and presented for the vessels using resistance tests at velocities of 0.5, 1.0, and 1.5-m/s. Finally, outputs are extended to develop 2-dimensional contours to estimate the interactional forces in the full domain. The results show a critical zone behind the ship around a depth of 0.75D where ship drag forces are increased by up to 177% compared to free-running conditions. In addition, comparing the towing mechanism to self-propelling operations shows that the towing effect dominates vessel interaction, increasing the drag forces by up to 240% when the ship tows the submarine. • Heave and drag forces are evaluated for the interaction of a submarine-cable-ship system. • Critical areas are identified where the magnitude, or variation, of interaction forces is significant. • A set of contours is presented to show interactional forces over the entire domain. • Investigation of the cable behavior according to Taut and Catenary mooring theories in different testing locations. • Towing a submarine makes larger interaction compared to self-propelling arrangement. [ABSTRACT FROM AUTHOR]

This paper empirically examines the hydrodynamic performances of squat submarines under the resistance and wave tests beside numerical investigation of pressure drag reduction techniques. Despite vast information about the operation of the streamlined fluid vessels, there is not much information about the geometries and hydrodynamic behaviors of squat vessels with L/D ratios below four. This study experimentally investigates the impacts of various relative depths and flow inclinations, intending to find drag, heave, and sway forces at the velocities of 0.5, 1.0, 1.5, 2.0, and 2.5-m/s. A one-tenth scaled model of a squat submarine is examined under the resistance and wave train scenarios as the captive model in the towing tank experiments via 110 unique testing scenarios. Then, different pressure drag reduction techniques on the full-scale submarine are evaluated numerically at one-phase fluid by developing stern geometric optimization, nose rod devices, water corridors, and surface patterns at the bow and stern. Results present drag forces increase up to 150% at the 0.5D level for the resistance and wave tests due to the influences of the free surface water. The drag coefficients at the fully submerged depth of 6D differ by up to 13.3% between the numerical and experimental evaluations. • The effects of the surface water create a critical zone on the 0.5D depth level. • The drag and heave forces decrease on the surface depth level. • The heave force variations generally show a higher reduction rate. • The output trends of the wave train tests are similar to the resistance tests. • The passive pressure drag reductions are functional for submarine. [ABSTRACT FROM AUTHOR]

Divers commonly use buoyancy vests for maintenance and changing depth. They do this by manually actuating two pneumatic valves that cause the jacket's volume to expand or shrink, thus changing its buoyancy. Divers desire for a device that would automatically modify or maintain depth has been present since the beginning of modern diving using a buoyancy vest. The need arises mainly when diving: where poor visibility is present; when both hands are needed for the job; during amateur dives; where decompression procedures are needed; to limit the maximum ascending speed; during a safety stop procedure; automatic ascending when a diver's life functions are critical but nevertheless using the same technology for changing depth in small modern submarines and submarine-like vessels. A prerequisite for successful buoyancy control is definitely knowledge of the system's behaviour based on mathematical modelling. This paper proposes a detailed dynamic model of a diver with all its accessories. The accuracy of the model was validated by comparing simulation results with the measurement results of various experiments. [ABSTRACT FROM AUTHOR]

Inner substructures, which can be generally compartmentalized into axisymmetric and non-axisymmetric ones, are believed to significantly affect the vibro-acoustic characteristics of submarine hulls. In this paper, the vibro-acoustic behaviors of a submerged submarine hull coupled with multiple inner substructures are experimentally and analytically studied. The vibration of the stiffened hull is uniformly expressed by Flügge shell theory and power series method. The sound pressure is described by surface Helmhotlz integral. Diverse types of non-axisymmetric internal substructures are modeled by FEM. The analytical model of the hull and FE models of inner substructures are perfectly coupled in 6 DOFs through the matrix reduction technique. By assembling the generalized stiffness matrices of two types of subsystems, the final governing equation of the coupled model is established. To validate the reliability of the present method and examine the effects of non-axisymmetric inner substructures on vibro-acoustic behaviors of the hull, a large-scaled submarine hull with several axisymmetric and non-axisymmetric interior substructures is manufactured, and the underwater responses of the hull with and without non-axisymmetric substructures are tested and compared. Meanwhile, effects of non-axisymmetric inner substructures on vibro-acoustic characteristics of the hull are analytically discussed in wave domain and some significant phenomena are discovered. • A unified method is developed for vibro-acoustic analysis of submarine hull. • Multiple inner structures are considered in theoretical model. • Effects of non-axisymmetric structures are experimental and analytically studied. • A vibro-acoustic experiment of a large scaled hull is conducted. [ABSTRACT FROM AUTHOR]

Underwater explosion load can be divided into impact load and bubble action load, which can cause local or global damage to ship or submarine. The explosion-proof design of ship structure needs to consider the effect of underwater explosion impact load. Therefore, the measurement of underwater explosion load is very important. In this paper, the measurement methods of underwater explosion load are summarized, and the advantages and limitations of various measurement methods are expounded. In addition, due to the high pressure and strong nonlinearity of explosion and the lack of measurement means under large equivalent-weight charge and large impact factor, we put forward and simply expounded the measurement idea based on deep learning to provide research direction for the measurement of large equivalent-weight charge load and large impact factor. So as to provide a better choice for the study of underwater explosion load and measurement. • The research of underwater explosion load measurement methods in recent 20 years is reviewed. • The advantages and disadvantages of several sensor measurement methods are introduced. • The future development of underwater explosion is prospected. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the development, evaluation and validation of a finite element model for the simulation of the impact of a blank torpedo against a submarine pressure hull. A parametric, shell finite element model was generated and analysed using ANSYS Finite Element Package to explore the effects of different loading conditions and analysis types in the accuracy of the results. Results were compared to a series of drop tests conducted by the Australian Defence, Science and Technology Organisation (DSTO). Geometric and material non-linear models were compared against varying methods of load applications. A numerical model subjected to a concentrated load was found to provide a poor representation of the drop tests. A clear improvement in the accuracy of the results was achieved by implementing a distributed impact load case; however, a full nonlinear analysis involving large deflection, plasticity and contact was found to offer the best agreement with the experimental test results. [Copyright &y& Elsevier]

Abstract: The breakout failure mechanism of un-trenched submarine pipelines subject to current-induced hydrodynamic loading involves complex interactions between the pipe and the surrounding soil. Methods commonly used in conventional stability analyses of pipelines do not adequately consider several important factors, such as the effects of seabed slope and pipe anchorages. In this paper, a self-evolving artificial neural network (SEANN) is used to develop an empirical relation between the coefficient of ultimate lateral soil resistance to breakout, the properties of the pipe, and the supporting seabed. Additional parameters such as the angle of inclination of the seabed to the horizontal and the pipe's rolling restraint condition are also included as variables affecting the resistance coefficient. The results of the model validation with previous experimental data demonstrate the abilities of the proposed SEANN. Its performance was found to surpass that of BPN networks with various types of activation functions. Compared with the method described in the DNV manual, the proposed model provides better predictions of the ultimate soil resistance. [Copyright &y& Elsevier]

In this paper, a generic submarine Joubert BB2 model travels both in the homogenous and linearly stratified fluid are simulated and investigated. The stable stratification of background density is achieved by specifying the linearly distributed temperature based on a thermocline model. Four main aspects are chosen to discuss the specialty of stratified fluid characteristics by comparing the drag force, downstream wakes, internal waves, and free surface signatures with those of the homogeneous condition. The results show that due to the density gradient and internal waves generation and propagation in the stratified flow, the resistance of the submarine increases. Because of the vertical confinement induced by buoyancy in the stratified environment, the velocity decays faster, thus leading to a broader spread range of wakes in the horizontal plane than the vertical plane. Furthermore, internal waves and anisotropic turbulence stimulated by the moving submarine result in specific signatures on the water surface. A noteworthy anisotropy of the surface wave crest and trough, and a larger influencing zone of the Kelvin waves are shown for the stratified case. • Proposed a thermocline model to achieve linear density and temperature stratification in STAR-CCM+. • Examined the effect of buoyancy when stratified flow past a submarine model with a relatively high Reynolds number. • Evaluated the effect of internal waves on the free surface characteristics. [ABSTRACT FROM AUTHOR]

Cavitation is accompanied by increased hull vibrations, reduced propulsion performance, and increased radiated noise. This can be particularly fatal for warships and submarines. Hence, navies worldwide introduced and managed a propeller performance index called cavitation inception speed (CIS). Among the many types of propeller cavitation, the first to occur is tip vortex cavitation (TVC). In this paper, the CIS decision procedure of TVC is presented via numerical analysis in terms of noise, which is the most prominent characteristic of cavitation inception. For the CIS decision, the cavitation noise from the propeller is obtained from bubble dynamics. Cavitation is simulated with cavitation nuclei, and the input data for nuclei is obtained from computational fluid dynamics (CFD) simulations. The noise from each nucleus was modeled with a monopole assumption. Additional impulse noise due to the bubble's implosion is used as the basis for the CIS decision. The usefulness of the proposed procedure is demonstrated by applying it to three propeller geometries with different skew and rake angles. Additionally, various aspects, such as propeller stern vortex and added mass, are analyzed; the results are consistent with the CIS simulation results for each propeller. • A numerical procedure that predicts the cavitation inception of propellers by noise. • Prediction of cavitation delay due to geometries in terms of noise by bubble dynamics. • Correlation between reduction of added mass acting on blade and cavitation delay. [ABSTRACT FROM AUTHOR]

Abstract: Computational fluid dynamics (CFD) approach was employed to simulate soil–pipe interaction behavior subjected to impact load. Numerical analysis is verified with results experimentally obtained in a geotechnical centrifuge. The physical experiments in centrifuge simulated the impact of soft to firm clay blocks (4 to 8kPa of undrained shear strengths) on two model pipes (0.19 and 0.29m in diameter), at velocities ranging between 0.04 and 1.3m/s in a direction normal to the pipe axis. The corresponding shear strain rates ranged from about 4 to 136s−1. In this paper, a relationship between shear stress and shear strain rate for the clay blocks is first established through re-analysis of the centrifuge experiments and then used to calibrate a CFD numerical model and to complement the physical test results. The present CFD analyses covered impact velocities up to 2m/s and investigated different pipe diameters (6.35 to 150mm) and clay strengths. The methodology and results of the CFD analyses are discussed and compared with the observations made from the physical experiments. The experimental results were combined with the results of the CFD analyses and a simple approach is proposed to estimate the drag force caused by a glide block or out-runner block impact on a suspended (free-span) pipeline. [Copyright &y& Elsevier]

Abstract: Biofouling is a global problem in the marine industry though its effects on lift and drag are rarely discussed. This paper seeks to employ Computational Fluid Dynamics (CFD) method to quantify the effects of this problem based on the obtained flow field information. The simulation is carried out on a NACA 4424 airfoil and Defence Research Establishment Atlantic (DREA) Submarine Hull. Different levels of fouling are studied with quantified fouling height and density. As an extension, the effects of two common antifouling methods, i.e. tin-free Self-Polishing Copolymer (SPC) and Foul Release on the drag of NACA 4424 foil and the submarine hull is investigated. For NACA 4424 airfoil, fouling reduces lift–drag ratio (C L /C D ) by up to 80% in maximum and therefore result in the significant increase in fuel consumption. Predicted flow data shows this is related to the increased flow separation region caused by the fouling. It is found that pressure gradient gradually increases from the smallest fouling height to the largest but does not vary that much for fouling of varying densities. The general trend of C L /C D varies with angle of attack agrees well with others experimental data. Computed results also show good agreement with experimental data for the DREA bare hull. As to antifouling, Foul Release, despite being 30% more expensive than SPC, exhibits 10–40% higher C L /C D as compared to SPC for NACA foil and submarine hull. [Copyright &y& Elsevier]

Abstract: In this paper, a numerical model is established for simulating the wave forces on a submarine pipeline. A set of two-dimensional Navier–Stokes equations is discretized numerically with a finite volume method in a moving mesh system. After each time step, the mesh is modified according to the changed wave surface boundary. The deffered correction second-order upwind scheme (SUDC) is adopted here to discretize the convective fluxes. The effects of the clearance between the pipeline and the seabed, water depth and wave height on wave forces are studied, respectively. The results by the numerical simulation agree well with the experimental data and theory value. [Copyright &y& Elsevier]

Abstract: A three-dimensional modeling of multidirectional random-wave diffraction by a group of rectangular submarine pits is presented in this paper. The fluid domain is divided into N interior regions representing the pit area and an overall exterior region separated by the imaginary pit boundaries. In the interior region, the analytical expressions of the Fourier series expansion for velocity potentials in the pit regions have been derived with the unknown coefficients determined from a series of Green''s function based boundary integral equations. The boundary integral approach has also been applied to obtain the velocity potential and free-surface elevation in the exterior region. The Pierson–Moskowitz (P–M) frequency spectrum was selected for the random wave simulation using the superposition of solutions of a finite number of decomposed wave components. Numerical results for the cases of regular waves and random waves are presented to examine the influences of the pit geometry and incident wave condition on the overall wave field. The general diffraction pattern of alternate bands of increase and decrease of relative wave height in front of the pit system can be observed. It is found that, in the shadow region, the relative wave height is reduced. As the number of pit increases, the effectiveness of reducing the relative wave height behind the multiple-pit system increases. However, the relative wave height within the pit area and in front of the leading pit shows increasing trend. It is noticed that under the random-wave condition, the level of increase and decrease of the relative wave height due to the existence of submarine pits is less pronounced than that observed from results in regular-wave condition. [Copyright &y& Elsevier]

Large water tanks known as towing tanks, wave basins and cavitation tunnels, are used to determine the performance of ships, boats and submarines at model-scale. They may also be used for noise measurements but suffer from the effects of reverberation, which makes it difficult to capture the free field conditions necessary for complete characterisation of the noise. This paper describes an adapted Image Source Model and its use to understand these reverberation effects. It extends the conventional Image Source Model by the use of spherical wave reflection coefficients at the tank boundaries, in addition to the inclusion of volumetric absorption. Validation of the Image Source Model is undertaken by comparison with published transfer function measurements made in the depressurized wave basin at the Maritime Research Institute Netherlands (MARIN). The relative contribution to the tank response from the direct field and free surface is examined. The tank response is found to vary with three frequency-scales (periodicities) resulting from interactions with the free surface and axial modes. • Acoustic measurements in towing tanks suffer from the effects of reverberation. • Image source model developed with plane and spherical wave reflection coefficients. • Three Scales of reverberation where found due to Lloyds mirror interference and axial modes. [ABSTRACT FROM AUTHOR]