Aerodynamics analysis has become a mindset for high performance vehicles. This is because it provides valuable insight on a vehicle motion during different phases. There are vast varieties of software available like A...Aerodynamics analysis has become a mindset for high performance vehicles. This is because it provides valuable insight on a vehicle motion during different phases. There are vast varieties of software available like ANSYS Workbench, Star CCM+, Autodesk Simulation, SimFlow, FeatFlow, Autodesk Inventor etc. Amongst these softwares, Star CCM+ and ANSYS Workbench are the most widely used. Normally, it is observed that considerable users are confused in choosing the right software for CFD simulation because of a large variety of commercially available softwares. The present study provides comparative results to users of Computational Fluid Dynamics (CFD) with the driven case study. In the present case, authors chose the most commonly used CFD softwares, the ANSYS Workbench Fluent and the Star CCM+. Polyhedral meshing was applied on computer aided model of a car in both of these softwares. It has been found that coefficients of drag and lift achieved by aerodynamic analysis of a car are in a small marginal approximation between both ANSYS Workbench Fluent and Star CCM+ softwares. In the case of Star CCM+, CD was around 0.261 and CL was 0.07;however, in the case of ANSYS Workbench Fluent approximations were found to be 0.271 for CD and 0.05 for CL.展开更多
An improved circular synthetic aperture radar（CSAR） imaging algorithm of omega-k（ω-k） type mainly for reconstructing an image on a cylindrical surface is proposed.In the typical CSAR ω-k algorithm,the rage traje...An improved circular synthetic aperture radar（CSAR） imaging algorithm of omega-k（ω-k） type mainly for reconstructing an image on a cylindrical surface is proposed.In the typical CSAR ω-k algorithm,the rage trajectory is approximated by Taylor series expansion to the quadratic terms,which limits the valid synthetic aperture length and the angular reconstruction range severely.Based on the model of the CSAR echo signal,the proposed algorithm directly transforms the signal to the two-dimensional（2D） wavenumber domain,not using approximation processing to the range trajectory.Based on form of the signal spectrum in the wavenumber domain,the formula for the wavenumber domain interpolation of the w-k algorithm is deduced,and the wavenumber spectrum of the reference point used for bulk compression is obtained from numerical method.The improved CSAR ω-k imaging algorithm increases the valid synthetic aperture length and the angular area greatly and hence improves the angular resolution of the cylindrical imaging.Additionally,the proposed algorithm can be repeated on different cylindrical surfaces to achieve three dimensional（3D） image reconstruction.The 3D spatial resolution of the CSAR system is discussed,and the simulation results validate the correctness of the analysis and the feasibility of the algorithm.展开更多
With appropriate geometry configuration, helicopter- borne rotating synthetic aperture radar （ROSAR） can break through the limitations of monostatic synthetic aperture radar （SAR） on forward-looking imaging. With ...With appropriate geometry configuration, helicopter- borne rotating synthetic aperture radar （ROSAR） can break through the limitations of monostatic synthetic aperture radar （SAR） on forward-looking imaging. With this capability, ROSAR has extensive potential applications, such as self-navigation and self-landing. Moreover, it has many advantages if combined with the frequency modulated continuous wave （FMCW） technology. A novel geometric configuration and an imaging algorithm for helicopter-borne FMCW-ROSAR are proposed. Firstly, by per- forming the equivalent phase center principle, the separated trans- mitting and receiving antenna system is equalized to the case of system configuration with antenna for both transmitting and receiving signals. Based on this, the accurate two-dimensional spectrum is obtained and the Doppler frequency shift effect in- duced by the continuous motion of the platform during the long pulse duration is compensated. Next, the impacts of the velocity approximation error on the imaging algorithm are analyzed in de- tail, and the system parameters selection and resolution analysis are presented. The well-focused SAR image is then obtained by using the improved Omega-K algorithm incorporating the accurate compensation method for the velocity approximation error. FJnally, correctness of the analysis and effectiveness of the proposed al- gorithm are demonstrated through simulation results.展开更多
Knotless polyethylene(PE)netting is widely used in fisheries because of its excellent hydrodynamic performance and low cost.Netting deformation and the surrounding flow field distribution play an important role in det...Knotless polyethylene(PE)netting is widely used in fisheries because of its excellent hydrodynamic performance and low cost.Netting deformation and the surrounding flow field distribution play an important role in determining the hydrodynamic characteristics of netting in moving water.In order to investigate the effect of solidity ratio and attack angle on drag,netting deformation,and flow field distribution through the netting,a fluid-structure interaction(FSI)model based on a one-way coupling combining the shear stress turbulent(SST)k-omega model and the large deformation nonlinear structural finite element model was evaluated.Our results showed the difference between the parallel and normal drag forces found in the present numerical model and experimental flume tank data were 9.17%and 11.58%,respectively.The mean relative error in the inclined hydrodynamic drag for different flow velocities and attack angles was 8.35%,6.69%,and 5.37%for the nettings 1,2,and 3,respectively.These results show that the present numerical simulation based on FSI one-way coupling can be used to examine hydrodynamic forces on netting.The flow simulation results show that there is a noticeable flow velocity decrease through the netting and a rather large velocity reduction region downstream from the netting for different attack angles.These results reveal the existence of turbulent flow due to the netting wake.It was found that the equivalent stress and total deformation increase as the flow velocity increases and solidity ratio decreases.展开更多
文摘Aerodynamics analysis has become a mindset for high performance vehicles. This is because it provides valuable insight on a vehicle motion during different phases. There are vast varieties of software available like ANSYS Workbench, Star CCM+, Autodesk Simulation, SimFlow, FeatFlow, Autodesk Inventor etc. Amongst these softwares, Star CCM+ and ANSYS Workbench are the most widely used. Normally, it is observed that considerable users are confused in choosing the right software for CFD simulation because of a large variety of commercially available softwares. The present study provides comparative results to users of Computational Fluid Dynamics (CFD) with the driven case study. In the present case, authors chose the most commonly used CFD softwares, the ANSYS Workbench Fluent and the Star CCM+. Polyhedral meshing was applied on computer aided model of a car in both of these softwares. It has been found that coefficients of drag and lift achieved by aerodynamic analysis of a car are in a small marginal approximation between both ANSYS Workbench Fluent and Star CCM+ softwares. In the case of Star CCM+, CD was around 0.261 and CL was 0.07;however, in the case of ANSYS Workbench Fluent approximations were found to be 0.271 for CD and 0.05 for CL.
基金Supported in part by Elrha’s Humanitarian Innovation Fund programmethe National Natural Science Foundation of China(61771049)support of the Beijing Key Laboratory of Millimeter Wave and Terahertz Technology。
文摘An improved circular synthetic aperture radar（CSAR） imaging algorithm of omega-k（ω-k） type mainly for reconstructing an image on a cylindrical surface is proposed.In the typical CSAR ω-k algorithm,the rage trajectory is approximated by Taylor series expansion to the quadratic terms,which limits the valid synthetic aperture length and the angular reconstruction range severely.Based on the model of the CSAR echo signal,the proposed algorithm directly transforms the signal to the two-dimensional（2D） wavenumber domain,not using approximation processing to the range trajectory.Based on form of the signal spectrum in the wavenumber domain,the formula for the wavenumber domain interpolation of the w-k algorithm is deduced,and the wavenumber spectrum of the reference point used for bulk compression is obtained from numerical method.The improved CSAR ω-k imaging algorithm increases the valid synthetic aperture length and the angular area greatly and hence improves the angular resolution of the cylindrical imaging.Additionally,the proposed algorithm can be repeated on different cylindrical surfaces to achieve three dimensional（3D） image reconstruction.The 3D spatial resolution of the CSAR system is discussed,and the simulation results validate the correctness of the analysis and the feasibility of the algorithm.
基金supported by the National Basic Research Program of China(2011CB707001)the Fundamental Research Funds for the Central Universities(106112015CDJXY500001CDJZR165505)
文摘With appropriate geometry configuration, helicopter- borne rotating synthetic aperture radar （ROSAR） can break through the limitations of monostatic synthetic aperture radar （SAR） on forward-looking imaging. With this capability, ROSAR has extensive potential applications, such as self-navigation and self-landing. Moreover, it has many advantages if combined with the frequency modulated continuous wave （FMCW） technology. A novel geometric configuration and an imaging algorithm for helicopter-borne FMCW-ROSAR are proposed. Firstly, by per- forming the equivalent phase center principle, the separated trans- mitting and receiving antenna system is equalized to the case of system configuration with antenna for both transmitting and receiving signals. Based on this, the accurate two-dimensional spectrum is obtained and the Doppler frequency shift effect in- duced by the continuous motion of the platform during the long pulse duration is compensated. Next, the impacts of the velocity approximation error on the imaging algorithm are analyzed in de- tail, and the system parameters selection and resolution analysis are presented. The well-focused SAR image is then obtained by using the improved Omega-K algorithm incorporating the accurate compensation method for the velocity approximation error. FJnally, correctness of the analysis and effectiveness of the proposed al- gorithm are demonstrated through simulation results.
基金the National Natural Science Foundation of China(Grand No.31902426,41806110)Shanghai Sailing Program(19YF1419800),China Postdoctoral Science Foundation funded project(2018M630471)Special project for the exploitation and utilization of Antarctic biological resources of Ministry of Agriculture and Rural Affairs(D-8002-18-0097).
文摘Knotless polyethylene(PE)netting is widely used in fisheries because of its excellent hydrodynamic performance and low cost.Netting deformation and the surrounding flow field distribution play an important role in determining the hydrodynamic characteristics of netting in moving water.In order to investigate the effect of solidity ratio and attack angle on drag,netting deformation,and flow field distribution through the netting,a fluid-structure interaction(FSI)model based on a one-way coupling combining the shear stress turbulent(SST)k-omega model and the large deformation nonlinear structural finite element model was evaluated.Our results showed the difference between the parallel and normal drag forces found in the present numerical model and experimental flume tank data were 9.17%and 11.58%,respectively.The mean relative error in the inclined hydrodynamic drag for different flow velocities and attack angles was 8.35%,6.69%,and 5.37%for the nettings 1,2,and 3,respectively.These results show that the present numerical simulation based on FSI one-way coupling can be used to examine hydrodynamic forces on netting.The flow simulation results show that there is a noticeable flow velocity decrease through the netting and a rather large velocity reduction region downstream from the netting for different attack angles.These results reveal the existence of turbulent flow due to the netting wake.It was found that the equivalent stress and total deformation increase as the flow velocity increases and solidity ratio decreases.
