[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for imp...[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for improving the engineering design and application of marine structures.[Method] This study utilized the computational fluid dynamics(CFD) approach and the Reynolds Averaged NavierStokes(RANS) method and considered the effects of viscosity and free surface interactions on the hydrodynamic behavior of floating structures.By employing the dynamic mesh technique,this study simulated the periodic movements of simplified three-dimensional(3D)shapes:spheres,cylinders,and cubes,which were representative of complex marine structures.The volume of fluid(VOF) method was leveraged to accurately track the nonlinear behavior of the free surface.In this analysis,the added mass and damping coefficients for the fundamental modes of motion(surge,heave,and roll) were calculated across a spectrum of frequencies,facilitating the fast determination of hydrodynamic forces and moments exerted on floating structures.[Result] The results of this study are not only consistent with the results of the 3D potential flow theory but also further reflect the role of viscosity.This method can be used for precise calculation of the hydrodynamic coefficients of floating structures and for describing the flow field of such structures in motion on a free surface.[Conclusion] The methodology presented goes beyond the traditional potential flow approach.展开更多
The detection of foreign object intrusion is crucial for ensuring the safety of railway operations.To address challenges such as low efficiency,suboptimal detection accuracy,and slow detection speed inherent in conven...The detection of foreign object intrusion is crucial for ensuring the safety of railway operations.To address challenges such as low efficiency,suboptimal detection accuracy,and slow detection speed inherent in conventional comprehensive video monitoring systems for railways,a railway foreign object intrusion recognition and detection system is conceived and implemented using edge computing and deep learning technologies.In a bid to raise detection accuracy,the convolutional block attention module(CBAM),including spatial and channel attention modules,is seamlessly integrated into the YOLOv5 model,giving rise to the CBAM-YOLOv5 model.Furthermore,the distance intersection-over-union_non-maximum suppression(DIo U_NMS)algorithm is employed in lieu of the weighted nonmaximum suppression algorithm,resulting in improved detection performance for intrusive targets.To accelerate detection speed,the model undergoes pruning based on the batch normalization(BN)layer,and Tensor RT inference acceleration techniques are employed,culminating in the successful deployment of the algorithm on edge devices.The CBAM-YOLOv5 model exhibits a notable 2.1%enhancement in detection accuracy when evaluated on a selfconstructed railway dataset,achieving 95.0%for mean average precision(m AP).Furthermore,the inference speed on edge devices attains a commendable 15 frame/s.展开更多
A discontinuous Galerkin finite element method （DG-FEM） is developed for solving the axisymmetric Euler equations based on two-dimensional conservation laws. The method is used to simulate the unsteady-state underex...A discontinuous Galerkin finite element method （DG-FEM） is developed for solving the axisymmetric Euler equations based on two-dimensional conservation laws. The method is used to simulate the unsteady-state underexpanded axisymmetric jet. Several flow property distributions along the jet axis, including density, pres- sure and Mach number are obtained and the qualitative flowfield structures of interest are well captured using the proposed method, including shock waves, slipstreams, traveling vortex ring and multiple Mach disks. Two Mach disk locations agree well with computational and experimental measurement results. It indicates that the method is robust and efficient for solving the unsteady-state underexpanded axisymmetric jet.展开更多
The data information transfer and time marching strategies between computational fluid dynamics （CFD） and computational structural dynamics （CSD） play crucial roles on the aeroelastic analysis in a time domain. An...The data information transfer and time marching strategies between computational fluid dynamics （CFD） and computational structural dynamics （CSD） play crucial roles on the aeroelastic analysis in a time domain. An improved CFD/CSD coupled system is designed, including an interpolation method and an improved loosely coupled algorithm. The interpolation method based on boundary element method （BEM） is developed to transfer aerodynamic loads and structural displacements between CFD and CSD grid systems, it can be universally used in fluid structural interaction solution by keeping energy conservation. The improved loosely coupled algo-rithm is designed, thus it improves the computational accuracy and efficiency. The new interface is performed on the two-dimensional （2-D） extrapolation and the aeroelastie response of AGARD445.6 wing. Results show that the improved interface has a superior accuracy.展开更多
Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the...Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the 2-D conservation laws.Comparisons between the numerical results and the experimental measurements show excellent agreements.The computed results are in good agreement with the numerical solutions obtained by using third order accurate RKDG finite element method.The results show larger gradient at discontinuous points compared with those obtained by second order accurate TVD schemes.It indicates that the presented method is efficient and reliable for solving the axisymmetric jet with external freestream flows,and shows that the method captures shocks well without numerical noise.展开更多
The lattice Boltzmann method （LBM） and the immersed boundary method （IBM） are alternative, com- putational techniques for solving complex fluid dynamics systems, and can take the place of the Navier-Stokes（N- S）...The lattice Boltzmann method （LBM） and the immersed boundary method （IBM） are alternative, com- putational techniques for solving complex fluid dynamics systems, and can take the place of the Navier-Stokes（N- S） equation. This paper proposes a novel immersed boundary-lattice Boltzmann method （IB-LBM） based on the feedback law. The method uses the immersed boundary concept in the LBM framework to capture the coupling between a body with complex geometry and a uniform fluid, Then, the flows around a stationary circular cylinder and two circular cylinders in a side by side arrangement are simulated by using the method. Results are agreed well with the benchmark data, so, the capability of the method for complex geometry is demonstrated. Different from the conventional IB-LBM, which uses the Hook＇s law or the direct forcing method to compute the interae- tion force, the method uses the feedback law--the feedback of velocity field and displacement information to calculate the force, thus ensuring the method has advantages of easy implementation and full parallelism.展开更多
A computational fluid dynamics (CFD) study was carried out on a four stroke air cooled DI diesel engine, F912Q manufactured by Beinei Company, by using the KIVA 3V code. A three dimensional mesh was set up to mode...A computational fluid dynamics (CFD) study was carried out on a four stroke air cooled DI diesel engine, F912Q manufactured by Beinei Company, by using the KIVA 3V code. A three dimensional mesh was set up to model the cylinder, intake passage and exhaust passage. The calculated in cylinder pressure history and emissions are compared with the engine test data. The results show reasonable agreement. The effects of swirl ratio and spray angle on fuel spray, evaporation and mixing are investigated. It is found that there are optimum swirl ratio and spray angle for better evaporation and combustion.展开更多
The computational fluid dynamics （CFD） method is used to investigate the aerodynamic characteristics of the seat/occupant with windblast protection devices. The upwind Osher scheme is used for the spatial discretisa...The computational fluid dynamics （CFD） method is used to investigate the aerodynamic characteristics of the seat/occupant with windblast protection devices. The upwind Osher scheme is used for the spatial discretisation. The detached-eddy simulation （DES） based on the Spalart-Allmaras one-equation turbulence model is ap- plied to the detached viscous flow simulation behind the seat/occupant, with Mach numbers 0.6 and 1.2 at attack angles between --10 and 30°, and at two sideslip angles of 0 and 15°, respectively. The aerodynamic characteristics of seat/occupants with and without windblast protection devices are calculated in cases of the freestream Mach numbers 0. 8 and 1.6, attack angles from 5 to 30°, and three sideslip angles of 0, --20 and --50°, respectively. Results show that simulation results agree well with experimental data. And the occupant is efficiently protected by windblast protection devices.展开更多
文摘0引言由于人工智能(artificial intelligence,AI)服务器需要对超大规模的数据量进行处理,需为视觉、交互等人工智能应用提供强大的计算力,促使印制电路板(printed circuit board,PCB)不断向高密度、高精度、高集成度方向发展[1]。AI服务器较通用服务器PCB设计有所区别,由传统金属化孔(plating through hole,PTH)跨入多阶高速高密度互连(high density interconnector,HDI)设计,除对材料的电性能有明确要求之外,材料还需要具有多次压合能力和高可靠性。
文摘[Introduction] Accurate calculation of the hydrodynamic coefficients for floating structures and the investigation of the flow field distribution around floating bodies on the marine free surface are essential for improving the engineering design and application of marine structures.[Method] This study utilized the computational fluid dynamics(CFD) approach and the Reynolds Averaged NavierStokes(RANS) method and considered the effects of viscosity and free surface interactions on the hydrodynamic behavior of floating structures.By employing the dynamic mesh technique,this study simulated the periodic movements of simplified three-dimensional(3D)shapes:spheres,cylinders,and cubes,which were representative of complex marine structures.The volume of fluid(VOF) method was leveraged to accurately track the nonlinear behavior of the free surface.In this analysis,the added mass and damping coefficients for the fundamental modes of motion(surge,heave,and roll) were calculated across a spectrum of frequencies,facilitating the fast determination of hydrodynamic forces and moments exerted on floating structures.[Result] The results of this study are not only consistent with the results of the 3D potential flow theory but also further reflect the role of viscosity.This method can be used for precise calculation of the hydrodynamic coefficients of floating structures and for describing the flow field of such structures in motion on a free surface.[Conclusion] The methodology presented goes beyond the traditional potential flow approach.
基金supported in part by the Science and Technology Innovation Project of CHN Energy Shuo Huang Railway Development Company Ltd(No.SHTL-22-28)the Beijing Natural Science Foundation Fengtai Urban Rail Transit Frontier Research Joint Fund(No.L231002)the Major Project of China State Railway Group Co.,Ltd.(No.K2023T003)。
文摘The detection of foreign object intrusion is crucial for ensuring the safety of railway operations.To address challenges such as low efficiency,suboptimal detection accuracy,and slow detection speed inherent in conventional comprehensive video monitoring systems for railways,a railway foreign object intrusion recognition and detection system is conceived and implemented using edge computing and deep learning technologies.In a bid to raise detection accuracy,the convolutional block attention module(CBAM),including spatial and channel attention modules,is seamlessly integrated into the YOLOv5 model,giving rise to the CBAM-YOLOv5 model.Furthermore,the distance intersection-over-union_non-maximum suppression(DIo U_NMS)algorithm is employed in lieu of the weighted nonmaximum suppression algorithm,resulting in improved detection performance for intrusive targets.To accelerate detection speed,the model undergoes pruning based on the batch normalization(BN)layer,and Tensor RT inference acceleration techniques are employed,culminating in the successful deployment of the algorithm on edge devices.The CBAM-YOLOv5 model exhibits a notable 2.1%enhancement in detection accuracy when evaluated on a selfconstructed railway dataset,achieving 95.0%for mean average precision(m AP).Furthermore,the inference speed on edge devices attains a commendable 15 frame/s.
文摘A discontinuous Galerkin finite element method （DG-FEM） is developed for solving the axisymmetric Euler equations based on two-dimensional conservation laws. The method is used to simulate the unsteady-state underexpanded axisymmetric jet. Several flow property distributions along the jet axis, including density, pres- sure and Mach number are obtained and the qualitative flowfield structures of interest are well captured using the proposed method, including shock waves, slipstreams, traveling vortex ring and multiple Mach disks. Two Mach disk locations agree well with computational and experimental measurement results. It indicates that the method is robust and efficient for solving the unsteady-state underexpanded axisymmetric jet.
基金Supported by the Ph.D.Program Foundation of Ministry of Education of China (20070699054)~~
文摘The data information transfer and time marching strategies between computational fluid dynamics （CFD） and computational structural dynamics （CSD） play crucial roles on the aeroelastic analysis in a time domain. An improved CFD/CSD coupled system is designed, including an interpolation method and an improved loosely coupled algorithm. The interpolation method based on boundary element method （BEM） is developed to transfer aerodynamic loads and structural displacements between CFD and CSD grid systems, it can be universally used in fluid structural interaction solution by keeping energy conservation. The improved loosely coupled algo-rithm is designed, thus it improves the computational accuracy and efficiency. The new interface is performed on the two-dimensional （2-D） extrapolation and the aeroelastie response of AGARD445.6 wing. Results show that the improved interface has a superior accuracy.
基金Supported by the National Natural Defense Basic Scientific Research Program of China(A262006-1288)the Key Disciplines Program of Shanghai Municipal Commission of Education(J50501)~~
文摘Supersonic axisymmetric jet flow over a missile afterbody containing exhaust jet is simulated using the second order accurate positive schemes method developed for solving the axisymmetric Euler equations based on the 2-D conservation laws.Comparisons between the numerical results and the experimental measurements show excellent agreements.The computed results are in good agreement with the numerical solutions obtained by using third order accurate RKDG finite element method.The results show larger gradient at discontinuous points compared with those obtained by second order accurate TVD schemes.It indicates that the presented method is efficient and reliable for solving the axisymmetric jet with external freestream flows,and shows that the method captures shocks well without numerical noise.
基金Supported by the Aeronautical Science Foundation of China(20111453012)the National Defense Pre-Research Foundation of China(9140A13040111HK0329)~~
文摘The lattice Boltzmann method （LBM） and the immersed boundary method （IBM） are alternative, com- putational techniques for solving complex fluid dynamics systems, and can take the place of the Navier-Stokes（N- S） equation. This paper proposes a novel immersed boundary-lattice Boltzmann method （IB-LBM） based on the feedback law. The method uses the immersed boundary concept in the LBM framework to capture the coupling between a body with complex geometry and a uniform fluid, Then, the flows around a stationary circular cylinder and two circular cylinders in a side by side arrangement are simulated by using the method. Results are agreed well with the benchmark data, so, the capability of the method for complex geometry is demonstrated. Different from the conventional IB-LBM, which uses the Hook＇s law or the direct forcing method to compute the interae- tion force, the method uses the feedback law--the feedback of velocity field and displacement information to calculate the force, thus ensuring the method has advantages of easy implementation and full parallelism.
文摘A computational fluid dynamics (CFD) study was carried out on a four stroke air cooled DI diesel engine, F912Q manufactured by Beinei Company, by using the KIVA 3V code. A three dimensional mesh was set up to model the cylinder, intake passage and exhaust passage. The calculated in cylinder pressure history and emissions are compared with the engine test data. The results show reasonable agreement. The effects of swirl ratio and spray angle on fuel spray, evaporation and mixing are investigated. It is found that there are optimum swirl ratio and spray angle for better evaporation and combustion.
基金Supported by the Aeronautical Science Foundation of China(2008ZC52039)~~
文摘The computational fluid dynamics （CFD） method is used to investigate the aerodynamic characteristics of the seat/occupant with windblast protection devices. The upwind Osher scheme is used for the spatial discretisation. The detached-eddy simulation （DES） based on the Spalart-Allmaras one-equation turbulence model is ap- plied to the detached viscous flow simulation behind the seat/occupant, with Mach numbers 0.6 and 1.2 at attack angles between --10 and 30°, and at two sideslip angles of 0 and 15°, respectively. The aerodynamic characteristics of seat/occupants with and without windblast protection devices are calculated in cases of the freestream Mach numbers 0. 8 and 1.6, attack angles from 5 to 30°, and three sideslip angles of 0, --20 and --50°, respectively. Results show that simulation results agree well with experimental data. And the occupant is efficiently protected by windblast protection devices.
