Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuver...Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuverability.Additionally,they can perform shallow dives,offering low visual and acoustic detectability.Therefore,the hydrodynamic design of a semisubmersible naval ship should address at-surface and submerged conditions.In this study,Numerical analyses were performed using a semisubmersible hull form to analyze its hydrodynamic features,including resistance,powering,and maneuvering.The simulations were conducted with Star CCM+version 2302,a commercial package program that solves URANS equations using the SST k-ωturbulence model.The flow analysis was divided into two parts:at-surface simulations and shallowly submerged simulations.At-surface simulations cover the resistance,powering,trim,and sinkage at transition and planing regimes,with corresponding Froude numbers ranging from 0.42 to 1.69.Shallowly submerged simulations were performed at seven different submergence depths,ranging from D/LOA=0.0635 to D/LOA=0.635,and at two different speeds with Froude numbers of 0.21 and 0.33.The behaviors of the hydrodynamic forces and pitching moment for different operation depths were comprehensively analyzed.The results of the numerical analyses provide valuable insights into the hydrodynamic performance of semisubmersible naval ships,highlighting the critical factors influencing their resistance,powering,and maneuvering capabilities in both at-surface and submerged conditions.展开更多
Combined with naval vessel practical antisubmarine equipment of towed linear array sonar,a mathematical model of naval vessel localization for submarine based on bearing measurement was built,and localization algorith...Combined with naval vessel practical antisubmarine equipment of towed linear array sonar,a mathematical model of naval vessel localization for submarine based on bearing measurement was built,and localization algorithm was given to solve submarine movement parameters.Localizaiton errors were analyzed.Based on localization model and algorithm,simulations were done to study the effect of factors such as initial distance between submarine and the naval vessel,submarine initial bearing angle measured by the naval vessel and submarine course on localization performance,and then simulation results were given and analyzed.The results have practical value to instruct real antisubmarine.Simulation results show that different target movement situations have great influence on sonar detection and localization performance,so the reasonable choice of sonar position and detection bearing according to the target movement situation can improve sonar detection and localization performance to some degree.展开更多
This study presents a thorough and holistic review of various studies focusing on the structural analysis of Oil and Gas(O&G)pipelines,with an emphasis on various defect modes.The study appraised pipeline-related ...This study presents a thorough and holistic review of various studies focusing on the structural analysis of Oil and Gas(O&G)pipelines,with an emphasis on various defect modes.The study appraised pipeline-related articles from the empirical,semi-empirical,analytical,and numerical studies.However,the study’s core objective remains to address the persistent challenge that often leads to Burst Pressure Loss(BPL)in a pipeline.These mechanical-associated damages,which can result in BPL,may include pipe scratches,dents,or cracks.Therefore,training a large volume of datasets in neural network architectures or the finite element domain is crucial in this context.The study further explores previous research to gain a deeper insight into how many modes of damage enhance loss in Burst Pressure(BP).The study further synthesises significant reasons why pipeline Structural Health Failures(SHFs)occur,as drawn from existing literature.Failure scenarios in pipeline dent,crack,fracture,buckling,fatigue,corrosion,BPL,and Third-Party Damage(TPD)could result from mechanical deformation,ageing,insufficient real-time monitoring,and TPD influences.Many of the assessed articles conclude that the experimental approach and Finite Element Method(FEM)are valid and can accurately validate one another in the analysis and prediction of pipeline failures.However,this study offers valuable and comprehensive resources for pipeline engineers,academic researchers,and industry professionals.Again,the study is crucial for pipeline fabricators,installers,and operators to keep up with maintenance,repairs,and predictions.展开更多
The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultane...The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultaneously simulating both vehicle and propeller holds several computational challenges.While during operation,this propellant device must face several forces like gravity,hydrodynamic load,and centrifugal force,which cause different problems like cavitation and structural failure,etc.Since these issues affect performance,it necessitates comprehensive analysis.In this study,hydrodynamic analysis is performed by using commercial software STAR CCM+.In hydrodynamic analysis,the effect of the rake angles–5°,5°,10°and 15°on hydrodynamic coeffiicients and effiiciency of the DTMB 4119 in the open water is analyzed using Computational Fluid Dynamics(CFD)and the control volume approach.The Shear Stress Transport(SST)k‑ωturbulence model is used in Computational Fluid Dynamics(CFD)simulation.Hydrodynamic analysis reveals that the rake angles 5°and 10°cause the open water effiiciency of David Taylor Model Basin(DTMB)4119 to improve by 0.4 to 1.32%with exception of the rake angles–5°and 15°,which possess different effects on effiiciency.The angle–5°causes a decrease in propeller effiiciency under heavy loading situations(low advance coeffiicient)apart from a minorfiluctuation at light loading conditions(high advance coeffiicient),while the angle 15°produces a drop in effiiciency by higher advance ratios but little variation at lower advance ratios.展开更多
Shallow water infrastructure needs to support increased activity on the shores of Semarang.This study chooses several pontoons because of their good stability,rolling motion,and more expansive space.A coupled simulati...Shallow water infrastructure needs to support increased activity on the shores of Semarang.This study chooses several pontoons because of their good stability,rolling motion,and more expansive space.A coupled simulation method consisting of hydrodynamic and structural calculations has been used to evaluate a catamaran pontoon’s motion and structural integrity.Four different space sizes are set for the pontoon system:5 m,5.5 m,6 m,and 6.5 m.The frequency domain shows that the pontoon space affects the RAO in wave periods ranging from 3 s to 5 s.At wave periods of 3 s,4 s,and 5 s,the pontoon space significantly affects the maximum motion and chain tension parameter values,which are evaluated via time domain simulation.The critical stress of the pontoon is shown at a wave period of 5 s for 5 m and 5.5 m of pontoon space,which shows that the stress can reach 248 MPa.展开更多
In this study,an alternative modelling approach for absorbed hydrogen stress corrosion cracking(SCC)is proposed,with hydrogen-enhanced decohesion(HEDE)identified as the key failure mechanism.All analyses have been per...In this study,an alternative modelling approach for absorbed hydrogen stress corrosion cracking(SCC)is proposed,with hydrogen-enhanced decohesion(HEDE)identified as the key failure mechanism.All analyses have been performed by utilising only ABAQUS standard elements,COH2D4T and CPE4T,already available within the software and without the need to develop external subroutines.The study also tends to highlight the criticality of implementing a correct Traction Separation Law(TSL)curve to simulate the hydrogen diffusion within the specimen and using the concept of dynamic hydrogen penetration by continuously updating the hydrogen concentration boundary conditions as the crack propagates.In conclusion,this study successfully demonstrated that standard software elements(COH2D4T and CPE4T)can effectively model physical problems and crack velocity propagation without custom subroutines.It emphasized that while the specific shape of the Traction-Separation Law(TSL)is less critical,its correct implementation is vital for simulating dynamic hydrogen coverage.Crucially,excluding this dynamic coverage—a common practice—risks significantly underestimating crack propagation speed.Although results incorporating dynamic coverage aligned well with experimental data,minor discrepancies are likely due to unmodeled factors like material property variations,hydrogen trapping,temperature,and granular microstructure,which are proposed for future research.展开更多
The global discussion surrounding Functionally Graded Materials(FGMs)highlights their unique and diverse micro-material properties that result from varying two or more materials in a strategic combination profile.Thes...The global discussion surrounding Functionally Graded Materials(FGMs)highlights their unique and diverse micro-material properties that result from varying two or more materials in a strategic combination profile.These combinations produce distinct physical and chemical characteristics.Changes in these characteristics may occur continuously,referred to as a gradient function,or discontinuously as a stepwise function.The changes can appear within homogeneous or heterogeneous material geometries.The variation in material properties depends on the volume fraction index function.This variation can occur in 1D,2D,or 3D,either in the thickness or length direction within a material model.The vacuum in the review study on mechanically toughened and thermally resistant Functionally Graded(FG)pipelines prompted the current review study.This study addresses the absence of an appropriate variational function for FG cylindrical pipelines.It proposes a gradation function pattern to improve pipeline structural performance.An appraisal based on relevant FGM literature was conducted to improve the temperature differentials in traditional composite materials and stress-related issues in carbon steel pipelines.The review identifies specific FGM property variations that reduce failures that are possible in conventional materials.Reviewed articles and evaluation procedures followed the 2020 PRISMA guidelines.Literature was obtained from Scopus,Connected Papers,and other reputable sources.The study also discusses potential FG pipelines for gas and green energy transportation.The reviewed literature establishes the context for this research and addresses the gap in 3D FG model variation functions involving multiple materials.展开更多
Installing annular wave-energy converters(WECs)on the columns of floating wind platforms in the form of a coaxial-cylinder provides a convenient means of integration.Extant coaxial-cylinder-type wind-wave hybrid syste...Installing annular wave-energy converters(WECs)on the columns of floating wind platforms in the form of a coaxial-cylinder provides a convenient means of integration.Extant coaxial-cylinder-type wind-wave hybrid systems are mostly based on single-column platforms such as spars(single coaxial-cylinder hybrid system'hereafter).Systems based on multiple-column platforms such as semi-submersible platforms('multiple coaxial-cylinder hybrid systems'hereafter)are rarely seen or studied,despite their superiority in wave-power absorption due to the use of multiple WECs as well as in dynamic stability.This paper proposes a novel WindFloat-annular-WEC hybrid system,based on our study investigating its dynamic and power features,and optimizing the geometry and power take-off of the WECs.Our results show that the dynamic and power features of a multiple coaxial-cylinder hybrid system are different from those of a single coaxial-cylinder hybrid system,so the same optimization parameters cannot be directly applied.Flatter annular WECs absorb slightly more power in a wider wave-period range,but their geometry is confined by limitations in installation and structural strength.The overall effect of an oblique incident wave is greater intensity in the motions of the hybrid system in yaw and the direction perpendicular to propagation,although the difference is small and maybe negligible.展开更多
For the solution of peridynamic equations of motion,a meshless approach is typically used instead of utilizing semi-analytical or mesh-based approaches.In contrast,the literature has limited analytical solutions.This ...For the solution of peridynamic equations of motion,a meshless approach is typically used instead of utilizing semi-analytical or mesh-based approaches.In contrast,the literature has limited analytical solutions.This study develops a novel analytical solution for one-dimensional peridynamic models,considering the effect of damping.After demonstrating the details of the analytical solution,various demonstration problems are presented.First,the free vibration of a damped system is considered for under-damped and critically damped conditions.Peridynamic solutions and results from the classical theory are compared against each other,and excellent agreement is observed between the two approaches.Next,forced vibration analyses of undamped and damped conditions are performed.In addition,the effect of horizon size is investigated.It is shown that for smaller horizon sizes,peridynamic results agree well with classical results,whereas results from these two approaches deviate from each other as the horizon size increases.展开更多
The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up consid...The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison’s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin’s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.展开更多
To address critical challenges in nighttime ship detection—high small-target missed detection(over 20%),insufficient lightweighting,and limited generalization due to scarce,low-quality datasets—this study proposes a...To address critical challenges in nighttime ship detection—high small-target missed detection(over 20%),insufficient lightweighting,and limited generalization due to scarce,low-quality datasets—this study proposes a systematic solution.First,a high-quality Night-Ships dataset is constructed via CycleGAN-based day-night transfer,combined with a dual-threshold cleaning strategy(Laplacian variance sharpness filtering and brightness-color deviation screening).Second,a Cross-stage Lightweight Fusion-You Only Look Once version 8(CLF-YOLOv8)is proposed with key improvements:the Neck network is reconstructed by replacing Cross Stage Partial(CSP)structure with the Cross Stage Partial Multi-Scale Convolutional Block(CSP-MSCB)and integrating Bidirectional Feature Pyramid Network(BiFPN)for weighted multi-scale fusion to enhance small-target detection;a Lightweight Shared Convolutional and Separated Batch Normalization Detection-Head(LSCSBD-Head)with shared convolutions and layer-wise Batch Normalization(BN)reduces parameters to 1.8M(42% fewer than YOLOv8n);and the FocalMinimum Point Distance Intersection over Union(Focal-MPDIoU)loss combines Minimum Point Distance Intersection over Union(MPDIoU)geometric constraints and Focal weighting to optimize low-overlap targets.Experiments show CLFYOLOv8 achieves 97.6%mAP@0.5(0.7% higher than YOLOv8n)with 1.8 M parameters,outperforming mainstream models in small-target detection,overlapping target discrimination,and adaptability to complex lighting.展开更多
The singularities, oscillatory performances and the contributing factors to the 3-＇D translating-pulsating source Green function of deep-water Havelock form which consists of a local disturbance part and a far-field ...The singularities, oscillatory performances and the contributing factors to the 3-＇D translating-pulsating source Green function of deep-water Havelock form which consists of a local disturbance part and a far-field wave-like part, are analyzed systematically. Relative numerical integral methods about the two parts are presented in this paper. An improved method based on LOBATTO rule is used to eliminate singularities caused respectively by infinite discontinuity and jump discontinuous node from the local disturbance part function, which makes the improvement of calculation efficiency and accuracy possible. And variable substitution is applied to remove the singularity existing at the end of the integral interval of the far-field wave-like part function. Two auxiliary techniques such as valid interval calculation and local refinement of integral steps technique in narrow zones near false singularities are applied so as to avoid unnecessary integration of invalid interval and improve integral accordance. Numerical test results have proved the efficiency and accuracy in these integral methods that thus can be applied to calculate hydrodynamic performance of floating structures moving in waves.展开更多
For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculatin...For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculating the forward-speed free-surface Green function are discussed and a computer program with this Green function is developed. According to the special rules, the wave loads under several typical design conditions of the platform are calculated. The maximum vertical bending moment, torsion moment and horizontal split force are determined from a series of contour maps of wave loads for the wave period of 5 to 18 seconds at a certain interval and the wave phase of 0degrees to 360degrees at a certain interval. The wave height is determined by the function of wave period with a given exceedance probability. The maximum wave loads under the combination of wave parameters are used as the input of hydrodynamic pressure in the three-dimensional finite element analysis process. The transfer functions of wave loads on the platform are used for the fatigue strength analysis of the K-tubular joint and the sub-model of the structure.展开更多
This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on...This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.展开更多
The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid ...The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.展开更多
How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was der...How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was derived for time-domain Green function and its gradients in this paper. A new efficient calculation method based on solving ODE is proposed. It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function. Numeiical research indicates that it is efficient to solve the hydrodynamic problems.展开更多
A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account.A free surface flow field is evaluated by solving Reynolds ...A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account.A free surface flow field is evaluated by solving Reynolds averaged Navier-Stokes(RANS) equations with volume of fluid(VoF) method.The sinkage and trim are computed by equating the vertical force and pitching moment to the hydrostatic restoring force and moment.The software Fluent,Maxsurf and MATLAB are used to implement this method.With dynamic mesh being used,the position of a ship is updated by the motion of "ship plus boundary layer" grid zone.The hull factors are introduced for fast calculating the running attitude of a ship.The method has been applied to the ship model INSEAN2340 for different Froude numbers and is found to be efficient for evaluating the flow field,resistance,sinkage and trim.展开更多
AA 6061 alloy and interstitial-free(IF)steel plates were joined by the friction stir welding(FSW)method,and the microstructure,mechanical properties,and biaxial stretch formability of the friction stir welded(FSWed)pa...AA 6061 alloy and interstitial-free(IF)steel plates were joined by the friction stir welding(FSW)method,and the microstructure,mechanical properties,and biaxial stretch formability of the friction stir welded(FSWed)parts were investigated.The results indicate that the FSWed parts showed optimum tensile strength during FSW with the 0.4-mm offset position of the tool.The Fe4Al13 intermetallic compound formed in the defect-free intersection of AA 6061 and IF-steel plates during FSW.The hardness of the IF-steel part of the FSWed region increased almost 90%relative to its initial hardness of HV0.2 105.The tensile and yield strengths of FSWed regions were approximately 170 MPa and 145 MPa,respectively.According to the formability tests,the Erichsen Index(EI)of the IF-steel,AA 6061,and the FSWed samples were determined to be 2.9 mm,1.9 mm,and 2.1 mm,respectively.The EI of the FSWed sample was almost the same as that of the AA 6061 alloy.However,it decreased compared with that of the IF-steel.The force at EI(FEI)was approximately 1180 N for the FSWed condition.This value is approximately 70%higher than that of AA 6061 alloy.展开更多
The lethality of a semi-preformed fragment warhead is closely related to the expand velocity and spatial distribution of the fragments from ruptured metal casing. The topic of how to improve the utilization of charge ...The lethality of a semi-preformed fragment warhead is closely related to the expand velocity and spatial distribution of the fragments from ruptured metal casing. The topic of how to improve the utilization of charge of have been drawing great attention from researchers and designer in this filed. In present paper,in order to investigate the influence of charge initiation manners on the scattering characteristics of semi-preformed fragment warhead, the numerical simulations and experimental test are conducted.Firstly, the influence of grid density on numerical results is investigated, and a proper numerical model with relatively high accuracy and effectiveness is determined. Then. numerical simulations of three kinds of different initiation position of a semi-preformed fragment warhead are carried out. An experimental test of the explosion of a semi-preformed fragment warhead is carried out. By comparing and analyzing the numerical results and experimental data, it is found that the initiation manners have great influence on scattering characteristics of semi-preformed fragment warhead. The researcher work of this paper would provide an effective alternative method to optimize the design of warhead.展开更多
文摘Semisubmersible naval ships are versatile military crafts that combine the advantageous features of high-speed planing crafts and submarines.At-surface,these ships are designed to provide sufficient speed and maneuverability.Additionally,they can perform shallow dives,offering low visual and acoustic detectability.Therefore,the hydrodynamic design of a semisubmersible naval ship should address at-surface and submerged conditions.In this study,Numerical analyses were performed using a semisubmersible hull form to analyze its hydrodynamic features,including resistance,powering,and maneuvering.The simulations were conducted with Star CCM+version 2302,a commercial package program that solves URANS equations using the SST k-ωturbulence model.The flow analysis was divided into two parts:at-surface simulations and shallowly submerged simulations.At-surface simulations cover the resistance,powering,trim,and sinkage at transition and planing regimes,with corresponding Froude numbers ranging from 0.42 to 1.69.Shallowly submerged simulations were performed at seven different submergence depths,ranging from D/LOA=0.0635 to D/LOA=0.635,and at two different speeds with Froude numbers of 0.21 and 0.33.The behaviors of the hydrodynamic forces and pitching moment for different operation depths were comprehensively analyzed.The results of the numerical analyses provide valuable insights into the hydrodynamic performance of semisubmersible naval ships,highlighting the critical factors influencing their resistance,powering,and maneuvering capabilities in both at-surface and submerged conditions.
文摘Combined with naval vessel practical antisubmarine equipment of towed linear array sonar,a mathematical model of naval vessel localization for submarine based on bearing measurement was built,and localization algorithm was given to solve submarine movement parameters.Localizaiton errors were analyzed.Based on localization model and algorithm,simulations were done to study the effect of factors such as initial distance between submarine and the naval vessel,submarine initial bearing angle measured by the naval vessel and submarine course on localization performance,and then simulation results were given and analyzed.The results have practical value to instruct real antisubmarine.Simulation results show that different target movement situations have great influence on sonar detection and localization performance,so the reasonable choice of sonar position and detection bearing according to the target movement situation can improve sonar detection and localization performance to some degree.
文摘This study presents a thorough and holistic review of various studies focusing on the structural analysis of Oil and Gas(O&G)pipelines,with an emphasis on various defect modes.The study appraised pipeline-related articles from the empirical,semi-empirical,analytical,and numerical studies.However,the study’s core objective remains to address the persistent challenge that often leads to Burst Pressure Loss(BPL)in a pipeline.These mechanical-associated damages,which can result in BPL,may include pipe scratches,dents,or cracks.Therefore,training a large volume of datasets in neural network architectures or the finite element domain is crucial in this context.The study further explores previous research to gain a deeper insight into how many modes of damage enhance loss in Burst Pressure(BP).The study further synthesises significant reasons why pipeline Structural Health Failures(SHFs)occur,as drawn from existing literature.Failure scenarios in pipeline dent,crack,fracture,buckling,fatigue,corrosion,BPL,and Third-Party Damage(TPD)could result from mechanical deformation,ageing,insufficient real-time monitoring,and TPD influences.Many of the assessed articles conclude that the experimental approach and Finite Element Method(FEM)are valid and can accurately validate one another in the analysis and prediction of pipeline failures.However,this study offers valuable and comprehensive resources for pipeline engineers,academic researchers,and industry professionals.Again,the study is crucial for pipeline fabricators,installers,and operators to keep up with maintenance,repairs,and predictions.
文摘The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultaneously simulating both vehicle and propeller holds several computational challenges.While during operation,this propellant device must face several forces like gravity,hydrodynamic load,and centrifugal force,which cause different problems like cavitation and structural failure,etc.Since these issues affect performance,it necessitates comprehensive analysis.In this study,hydrodynamic analysis is performed by using commercial software STAR CCM+.In hydrodynamic analysis,the effect of the rake angles–5°,5°,10°and 15°on hydrodynamic coeffiicients and effiiciency of the DTMB 4119 in the open water is analyzed using Computational Fluid Dynamics(CFD)and the control volume approach.The Shear Stress Transport(SST)k‑ωturbulence model is used in Computational Fluid Dynamics(CFD)simulation.Hydrodynamic analysis reveals that the rake angles 5°and 10°cause the open water effiiciency of David Taylor Model Basin(DTMB)4119 to improve by 0.4 to 1.32%with exception of the rake angles–5°and 15°,which possess different effects on effiiciency.The angle–5°causes a decrease in propeller effiiciency under heavy loading situations(low advance coeffiicient)apart from a minorfiluctuation at light loading conditions(high advance coeffiicient),while the angle 15°produces a drop in effiiciency by higher advance ratios but little variation at lower advance ratios.
基金financially supported by the Riset Pengembangan dan Penerapan(RPP),Diponegoro University 2023 research scheme with contract number 609-18/UN7.D2/PP/VIII/2023.
文摘Shallow water infrastructure needs to support increased activity on the shores of Semarang.This study chooses several pontoons because of their good stability,rolling motion,and more expansive space.A coupled simulation method consisting of hydrodynamic and structural calculations has been used to evaluate a catamaran pontoon’s motion and structural integrity.Four different space sizes are set for the pontoon system:5 m,5.5 m,6 m,and 6.5 m.The frequency domain shows that the pontoon space affects the RAO in wave periods ranging from 3 s to 5 s.At wave periods of 3 s,4 s,and 5 s,the pontoon space significantly affects the maximum motion and chain tension parameter values,which are evaluated via time domain simulation.The critical stress of the pontoon is shown at a wave period of 5 s for 5 m and 5.5 m of pontoon space,which shows that the stress can reach 248 MPa.
文摘In this study,an alternative modelling approach for absorbed hydrogen stress corrosion cracking(SCC)is proposed,with hydrogen-enhanced decohesion(HEDE)identified as the key failure mechanism.All analyses have been performed by utilising only ABAQUS standard elements,COH2D4T and CPE4T,already available within the software and without the need to develop external subroutines.The study also tends to highlight the criticality of implementing a correct Traction Separation Law(TSL)curve to simulate the hydrogen diffusion within the specimen and using the concept of dynamic hydrogen penetration by continuously updating the hydrogen concentration boundary conditions as the crack propagates.In conclusion,this study successfully demonstrated that standard software elements(COH2D4T and CPE4T)can effectively model physical problems and crack velocity propagation without custom subroutines.It emphasized that while the specific shape of the Traction-Separation Law(TSL)is less critical,its correct implementation is vital for simulating dynamic hydrogen coverage.Crucially,excluding this dynamic coverage—a common practice—risks significantly underestimating crack propagation speed.Although results incorporating dynamic coverage aligned well with experimental data,minor discrepancies are likely due to unmodeled factors like material property variations,hydrogen trapping,temperature,and granular microstructure,which are proposed for future research.
基金The Petroleum Training Development Fund(PTDF)is highly acknowledged for sponsorship.
文摘The global discussion surrounding Functionally Graded Materials(FGMs)highlights their unique and diverse micro-material properties that result from varying two or more materials in a strategic combination profile.These combinations produce distinct physical and chemical characteristics.Changes in these characteristics may occur continuously,referred to as a gradient function,or discontinuously as a stepwise function.The changes can appear within homogeneous or heterogeneous material geometries.The variation in material properties depends on the volume fraction index function.This variation can occur in 1D,2D,or 3D,either in the thickness or length direction within a material model.The vacuum in the review study on mechanically toughened and thermally resistant Functionally Graded(FG)pipelines prompted the current review study.This study addresses the absence of an appropriate variational function for FG cylindrical pipelines.It proposes a gradation function pattern to improve pipeline structural performance.An appraisal based on relevant FGM literature was conducted to improve the temperature differentials in traditional composite materials and stress-related issues in carbon steel pipelines.The review identifies specific FGM property variations that reduce failures that are possible in conventional materials.Reviewed articles and evaluation procedures followed the 2020 PRISMA guidelines.Literature was obtained from Scopus,Connected Papers,and other reputable sources.The study also discusses potential FG pipelines for gas and green energy transportation.The reviewed literature establishes the context for this research and addresses the gap in 3D FG model variation functions involving multiple materials.
基金supported by the National Natural Science Foundation of China(Nos.52201322,52222109,and 52071096)the Guangdong Basic and Applied Basic Research Foundation(Nos.2022B1515020036 and 2023A1515012144)the Natural Science Foundation of Guangzhou City(No.202201010055),China.
文摘Installing annular wave-energy converters(WECs)on the columns of floating wind platforms in the form of a coaxial-cylinder provides a convenient means of integration.Extant coaxial-cylinder-type wind-wave hybrid systems are mostly based on single-column platforms such as spars(single coaxial-cylinder hybrid system'hereafter).Systems based on multiple-column platforms such as semi-submersible platforms('multiple coaxial-cylinder hybrid systems'hereafter)are rarely seen or studied,despite their superiority in wave-power absorption due to the use of multiple WECs as well as in dynamic stability.This paper proposes a novel WindFloat-annular-WEC hybrid system,based on our study investigating its dynamic and power features,and optimizing the geometry and power take-off of the WECs.Our results show that the dynamic and power features of a multiple coaxial-cylinder hybrid system are different from those of a single coaxial-cylinder hybrid system,so the same optimization parameters cannot be directly applied.Flatter annular WECs absorb slightly more power in a wider wave-period range,but their geometry is confined by limitations in installation and structural strength.The overall effect of an oblique incident wave is greater intensity in the motions of the hybrid system in yaw and the direction perpendicular to propagation,although the difference is small and maybe negligible.
文摘For the solution of peridynamic equations of motion,a meshless approach is typically used instead of utilizing semi-analytical or mesh-based approaches.In contrast,the literature has limited analytical solutions.This study develops a novel analytical solution for one-dimensional peridynamic models,considering the effect of damping.After demonstrating the details of the analytical solution,various demonstration problems are presented.First,the free vibration of a damped system is considered for under-damped and critically damped conditions.Peridynamic solutions and results from the classical theory are compared against each other,and excellent agreement is observed between the two approaches.Next,forced vibration analyses of undamped and damped conditions are performed.In addition,the effect of horizon size is investigated.It is shown that for smaller horizon sizes,peridynamic results agree well with classical results,whereas results from these two approaches deviate from each other as the horizon size increases.
基金Project supported by the National Natural Science Foundation of China (No.50279026) andthe National985Engineering Project in China
文摘The vortex-induced nonlinear vibration of casing pipes in the deep water was studied considering the loads of current and combined wave-current. The vortex-induced vibration equation of a casing pipe was set up considering the beam mode and Morison’s nonlinear fluid loads as well as the vortex-excited loads. The approach of calculating vortex-excited nonlinear vibration by Galerkin’s method was proposed. The natural vibration frequencies and modes were obtained, and the response including primary resonance induced by current and the composite resonance under combined wave-current for the 170 m long casing pipe in the 160m depth of water were investigated. The results show that the dynamics response of casing pipe obviously increases, and the complicated response behaviors of casing pipe are described under combined wave-current.
基金the Shandong Provincial Key Research and Development Program(Grant No.2024SFGC0201).
文摘To address critical challenges in nighttime ship detection—high small-target missed detection(over 20%),insufficient lightweighting,and limited generalization due to scarce,low-quality datasets—this study proposes a systematic solution.First,a high-quality Night-Ships dataset is constructed via CycleGAN-based day-night transfer,combined with a dual-threshold cleaning strategy(Laplacian variance sharpness filtering and brightness-color deviation screening).Second,a Cross-stage Lightweight Fusion-You Only Look Once version 8(CLF-YOLOv8)is proposed with key improvements:the Neck network is reconstructed by replacing Cross Stage Partial(CSP)structure with the Cross Stage Partial Multi-Scale Convolutional Block(CSP-MSCB)and integrating Bidirectional Feature Pyramid Network(BiFPN)for weighted multi-scale fusion to enhance small-target detection;a Lightweight Shared Convolutional and Separated Batch Normalization Detection-Head(LSCSBD-Head)with shared convolutions and layer-wise Batch Normalization(BN)reduces parameters to 1.8M(42% fewer than YOLOv8n);and the FocalMinimum Point Distance Intersection over Union(Focal-MPDIoU)loss combines Minimum Point Distance Intersection over Union(MPDIoU)geometric constraints and Focal weighting to optimize low-overlap targets.Experiments show CLFYOLOv8 achieves 97.6%mAP@0.5(0.7% higher than YOLOv8n)with 1.8 M parameters,outperforming mainstream models in small-target detection,overlapping target discrimination,and adaptability to complex lighting.
基金supported by the National Natural Science Foundation of China (Grant No. 50879090)
文摘The singularities, oscillatory performances and the contributing factors to the 3-＇D translating-pulsating source Green function of deep-water Havelock form which consists of a local disturbance part and a far-field wave-like part, are analyzed systematically. Relative numerical integral methods about the two parts are presented in this paper. An improved method based on LOBATTO rule is used to eliminate singularities caused respectively by infinite discontinuity and jump discontinuous node from the local disturbance part function, which makes the improvement of calculation efficiency and accuracy possible. And variable substitution is applied to remove the singularity existing at the end of the integral interval of the far-field wave-like part function. Two auxiliary techniques such as valid interval calculation and local refinement of integral steps technique in narrow zones near false singularities are applied so as to avoid unnecessary integration of invalid interval and improve integral accordance. Numerical test results have proved the efficiency and accuracy in these integral methods that thus can be applied to calculate hydrodynamic performance of floating structures moving in waves.
文摘For the global and structural fatigue strength analysis of a semi-submersible platform, wave loads under design conditions are calculated by use of the three-dimensional boundary element method. Methods for calculating the forward-speed free-surface Green function are discussed and a computer program with this Green function is developed. According to the special rules, the wave loads under several typical design conditions of the platform are calculated. The maximum vertical bending moment, torsion moment and horizontal split force are determined from a series of contour maps of wave loads for the wave period of 5 to 18 seconds at a certain interval and the wave phase of 0degrees to 360degrees at a certain interval. The wave height is determined by the function of wave period with a given exceedance probability. The maximum wave loads under the combination of wave parameters are used as the input of hydrodynamic pressure in the three-dimensional finite element analysis process. The transfer functions of wave loads on the platform are used for the fatigue strength analysis of the K-tubular joint and the sub-model of the structure.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51579122,51609109,and 51622902)the Natural Science Found of Jiangsu Province(Grant No.BK20160556)+1 种基金the University Natural Science Research Project of Jiangsu Province(Grant No.16kjb70003)the Key Lab Foundation for Advanced Manufacturing Technology of Jiangsu Province(Grant No.CJ1506)
文摘This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics(CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom(3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step.The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes(sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.
基金the financial support provided by the Office of Naval Research(ONR) through grant number N00014-09-1-1204 (managed by Dr. Ki-Han Kim)supported in part by the National Research Foundation of Korea (NRF)grant funded by the Korea government (MEST) through the GCRC-SOP Grant No. 2012-0004783
文摘The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.
基金This work was financially supported by Key Program of the National Natural Science Foundation of China(No.50639020)the National High Technology Research and Development Program of China(863Program)(No.2006AA09Z332)
文摘How to evaluate time-domain Green function and its gradients efficiently is the key problem to analyze ship hydrodynamics in time domain. Based on the Bessel function, an Ordinary Differential Equation （ODE） was derived for time-domain Green function and its gradients in this paper. A new efficient calculation method based on solving ODE is proposed. It has been demonstrated by the numerical calculation that this method can improve the precision of the time-domain Green function. Numeiical research indicates that it is efficient to solve the hydrodynamic problems.
基金the National Natural Science Foundation of China (No.50879090)the Advanced Research Program of GAD of the P.L.A (No.7131005)
文摘A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account.A free surface flow field is evaluated by solving Reynolds averaged Navier-Stokes(RANS) equations with volume of fluid(VoF) method.The sinkage and trim are computed by equating the vertical force and pitching moment to the hydrostatic restoring force and moment.The software Fluent,Maxsurf and MATLAB are used to implement this method.With dynamic mesh being used,the position of a ship is updated by the motion of "ship plus boundary layer" grid zone.The hull factors are introduced for fast calculating the running attitude of a ship.The method has been applied to the ship model INSEAN2340 for different Froude numbers and is found to be efficient for evaluating the flow field,resistance,sinkage and trim.
基金supported by “The World Academy of Sciences(TWAS)under the Visiting Researchers program of TWAS-UNESCO Associateship Scheme(No.3240290077)”
文摘AA 6061 alloy and interstitial-free(IF)steel plates were joined by the friction stir welding(FSW)method,and the microstructure,mechanical properties,and biaxial stretch formability of the friction stir welded(FSWed)parts were investigated.The results indicate that the FSWed parts showed optimum tensile strength during FSW with the 0.4-mm offset position of the tool.The Fe4Al13 intermetallic compound formed in the defect-free intersection of AA 6061 and IF-steel plates during FSW.The hardness of the IF-steel part of the FSWed region increased almost 90%relative to its initial hardness of HV0.2 105.The tensile and yield strengths of FSWed regions were approximately 170 MPa and 145 MPa,respectively.According to the formability tests,the Erichsen Index(EI)of the IF-steel,AA 6061,and the FSWed samples were determined to be 2.9 mm,1.9 mm,and 2.1 mm,respectively.The EI of the FSWed sample was almost the same as that of the AA 6061 alloy.However,it decreased compared with that of the IF-steel.The force at EI(FEI)was approximately 1180 N for the FSWed condition.This value is approximately 70%higher than that of AA 6061 alloy.
基金supported by the Joint Foundation project for Young Scientists of Ministry of Education(6141A02033108)National Natural Science Foundation of China(11502180)
文摘The lethality of a semi-preformed fragment warhead is closely related to the expand velocity and spatial distribution of the fragments from ruptured metal casing. The topic of how to improve the utilization of charge of have been drawing great attention from researchers and designer in this filed. In present paper,in order to investigate the influence of charge initiation manners on the scattering characteristics of semi-preformed fragment warhead, the numerical simulations and experimental test are conducted.Firstly, the influence of grid density on numerical results is investigated, and a proper numerical model with relatively high accuracy and effectiveness is determined. Then. numerical simulations of three kinds of different initiation position of a semi-preformed fragment warhead are carried out. An experimental test of the explosion of a semi-preformed fragment warhead is carried out. By comparing and analyzing the numerical results and experimental data, it is found that the initiation manners have great influence on scattering characteristics of semi-preformed fragment warhead. The researcher work of this paper would provide an effective alternative method to optimize the design of warhead.
