基于代数重构思想,发展了一种新的双界面函数重构方法,并采用双正弦函数构造了双正弦界面重构方法(double sine interface capturing,DSINC).为验证不同界面函数对界面捕捉效果的影响,用数值方法求解了可压缩五方程模型,其中对流项的离...基于代数重构思想,发展了一种新的双界面函数重构方法,并采用双正弦函数构造了双正弦界面重构方法(double sine interface capturing,DSINC).为验证不同界面函数对界面捕捉效果的影响,用数值方法求解了可压缩五方程模型,其中对流项的离散采用五阶WENO(weighted essentially non-oscillatory method)格式,时间积分采用三阶Runge--Kutta方法,通量计算分别考虑了HLL和HLLC方法,而状态方程采用Mie-Gr¨uneisen状态方程.在数值计算中,在界面附近,采用DSINC来获得体积分数的重构,而在远离界面的区域采用WENO格式来获得高阶插值状态.相比采用单界面函数的方法,如双曲正切界面重构方法(tangent of hyperbola for interface capturing,THINC),DSINC方法同样具有界面重构算法简单,在程序中添加方便等特点,两者区别在于,DSINC方法在重构过程中未知函数更易于求解,而无需求解复杂的非线性超越方程,这就使其具有易于向多维扩展的能力.一些典型的两相流动问题,如圆形水柱对流问题,两相三波点问题和激波-界面不稳定性问题等被用作不同界面函数对界面捕捉效果的影响对比.对比分析发现,DSINC与THINC在界面捕捉效果上大致保持一致,并在计算中表现出了较好的稳定性.双界面函数重构思想可以为多相流动界面的代数重构提供了一种新的思路.展开更多
A constrained interpolation profile CIP-based numerical tank is developed to simulate violent free surface flows.The numerical simulation is performed by the CIP-based Cartesian grid method,which is described in the p...A constrained interpolation profile CIP-based numerical tank is developed to simulate violent free surface flows.The numerical simulation is performed by the CIP-based Cartesian grid method,which is described in the present paper.The tangent of hyperbola for interface capturing（THINC） scheme is applied for capturing complex free surfaces.The new model is capable of simulating a flow with violently varied free surface.A series of computations are conducted to assess the developed algorithm and its versatility.These tests include the collapse of water column with and without an obstacle,sloshing in a fixed tank,the generation of regular waves in a tank,the generation of extreme waves in a tank.Excellent agreements are obtained when numerical results are compared with available analytical,experimental,and other numerical results.展开更多
针对远程虚拟桌面系统存在的交互操作响应延时问题,参考VoIP技术中对语音数据包的传输控制方法,设计一种电信级的服务架构。以采用精简低级原语和映射机制的THINC(Thin Client Internet Computing)虚拟桌面为基础,引入SIP控制和RTP承载...针对远程虚拟桌面系统存在的交互操作响应延时问题,参考VoIP技术中对语音数据包的传输控制方法,设计一种电信级的服务架构。以采用精简低级原语和映射机制的THINC(Thin Client Internet Computing)虚拟桌面为基础,引入SIP控制和RTP承载手段,为实时交互数据提供有QoS保障的传输通道,给出了与实时会话业务类似的实时虚拟桌面系统RVDI(Real-time VDI)。通过一个简化的实验环境,验证了RVDI的可行性。测试结果表明,对于带宽较小的网络环境,RVDI可以有效改善虚拟桌面的操作响应性能。展开更多
While the recently proposed TENO(targeted essentially non-oscillatory)schemes[Fu et al.,Journal of Computational Physics 305(2016):333-359]exhibit better performance than the classical WENO(weighted essentially non-os...While the recently proposed TENO(targeted essentially non-oscillatory)schemes[Fu et al.,Journal of Computational Physics 305(2016):333-359]exhibit better performance than the classical WENO(weighted essentially non-oscillatory)schemes with the same accuracy order,there is still a room for further improvement,e.g.,the physical discontinuities may be significantly smeared by the excessive numerical dissipation due to the enforcement of the ENO property after a long-time advection.More recently,a new fifth-order TENO5-THINC scheme is proposed by coupling the TENO5 scheme with a non-polynomial THINC(tangent of hyperbola for interface capturing)scheme based on a parameter-free discontinuity indicator.The novelty originates from the fact that the new strategy locates the discontinuities accurately and deploys the jump-like THINC reconstruction scheme for resolving the discontinuities with a sub-cell resolution,instead of enforcing the ENO property.The new scheme successfully leverages the excellent wave-resolution property of standard TENO schemes for smooth and under-resolved continuous scales and the discontinuity-resolving capability of THINC for reconstructing genuine discontinuities.In this work,we further develop the low-dissipation discontinuity-resolving very-high-order TENO-THINC reconstruction schemes for hyperbolic conservation laws by proposing tailored coupling strategies.Without loss of generality,the six-and eight-point TENO-THINC schemes are developed,and the explicit formulas are given as well as the built-in parameters.Based on a set of critical benchmark simulations,the newly proposed schemes show S.Takagi,H.Wakimura,L.Fu and F.Xiao/Commun.Comput.Phys.,34(2023),pp.1043-1078 significantly lower numerical dissipation when compared to the counterpart TENO schemes without sacrificing numerical robustness.The presented numerical results represent the state-of-the-art in the literature and can serve as references for future algorithm development.展开更多
水气二相流与诸多领域的实际工程问题密切相关.对二相流运动进行高精度的数值模拟是计算流体力学研究的难点和热点.针对开敞水域的自由表面流运动问题,将水和空气均视为不可压缩流体,采用五阶加权基本无震荡(weighted essentially non-o...水气二相流与诸多领域的实际工程问题密切相关.对二相流运动进行高精度的数值模拟是计算流体力学研究的难点和热点.针对开敞水域的自由表面流运动问题,将水和空气均视为不可压缩流体,采用五阶加权基本无震荡(weighted essentially non-oscillatory,WENO)格式求解描述流体运动的纳维斯托克斯(Navier–Stokes,NS)方程,利用以加权线性界面算法改进的多维双曲正切函数界面捕捉法(tangent of hyperbola for interface capturing with weighed line interface calculation,THINC/WLIC)追踪水气界面,建立WENO–THINC/WLIC水气二相流运动数值模型.模型采用分步计算法离散求解控制方程,通过压力投影法求解压强场,并利用三阶总变差递减(total variation diminishing,TVD)龙格库塔(Runge–Kutta,RK)法对时间项进行离散求解.通过对环境速度场下Zalesak’s disk和shearing vortex界面运动问题,线性液舱晃荡问题以及溃坝问题的模拟结果与理论分析或试验结果的比较,对所建立的水气二相流数值模型的适用性及模拟精度进行了验证.结果表明,本模型的模拟结果与物理模型或理论分析结果吻合良好,能较为准确地再现不可压缩水气二相流运动现象.鉴于WENO格式和THINC法本身在算法及应用等方面仍在不断改进,本研究提出的WENO–THINC耦合模型为后续更高精度的二相流计算模型开发提供了一种研究思路.展开更多
入水问题涉及到军事、航空等领域,如子弹入水、船舶砰击等,具有很强的应用背景。物体入水的过程涉及到固、液、气三相流动和相互作用,并伴随水花飞溅、空泡形成等复杂的物理现象。该文基于紧致插值CIP(constrained interpolation profi...入水问题涉及到军事、航空等领域,如子弹入水、船舶砰击等,具有很强的应用背景。物体入水的过程涉及到固、液、气三相流动和相互作用,并伴随水花飞溅、空泡形成等复杂的物理现象。该文基于紧致插值CIP(constrained interpolation profile)数学模型,分步求解Navier-Stokes(N-S)方程,并通过多相流理论描述固-液-气之间的相互作用,采用Volume of Fluid(VOF)类型的高精度紧致tangent of hyperbola for interface capturing(THINC)方法重构自由面。模拟了刚性圆柱和方柱的入水过程,结果与实验数据吻合较好。展开更多
为实现波浪的超长距离传播和调制演变过程,该文提出一种高保真基于黏性流理论的数值波浪水槽。分别采用包含单元均值和点值(VPM, volume-average and point-value method)的有限体积法求解纳维斯托克斯方程及具有二次曲面性质和高斯积...为实现波浪的超长距离传播和调制演变过程,该文提出一种高保真基于黏性流理论的数值波浪水槽。分别采用包含单元均值和点值(VPM, volume-average and point-value method)的有限体积法求解纳维斯托克斯方程及具有二次曲面性质和高斯积分的双曲正切函数(THINC/QQ, the tangent of hyperbola for interface capturing with quadratic surface representation and Gaussian quadrature)方法来重构自由面,建立以OpenFOAM底层函数库为基础的VPM-THINC/QQ模型。依据推板造波理论,在VPM-THINC/QQ模型中实现了波浪产生功能。在300 m的超长水槽中对深水波列进行模拟,得到波群的长时间非线性演化过程,并与文献结果进行了对比,结果表明:所开发的高精度数值波浪水槽可有效模拟深水波列的长时间传播和演变过程。展开更多
Hydroelastic behavior of an elastic wedge impacting on calm water surface was investigated. A partitioned approach by coupling finite difference method （FDM） and finite element method （FEM） was developed to analyz...Hydroelastic behavior of an elastic wedge impacting on calm water surface was investigated. A partitioned approach by coupling finite difference method （FDM） and finite element method （FEM） was developed to analyze the fluid structure interaction （FSI） problem. The FDM, in which the Constraint Interpolation Profile （CIP） method was applied, was used for solving the flow field in a fixed regular Cartesian grid system. Free surface was captured by the Tangent of Hyperbola for Interface Capturing with Slope Weighting （THINC/SW） scheme. The FEM was applied for calculating the structural deformation. A volume weighted method, which was based on the immersed boundary （IB） method, was adopted for coupling the FDM and the FEM together. An elastic wedge water entry problem was calculated by the coupled FDM-FEM method. Also a comparison between the current numerical results and the published results indicate that the coupled FDM-FEM method has reasonably good accuracy in predicting the impact force.展开更多
文摘基于代数重构思想,发展了一种新的双界面函数重构方法,并采用双正弦函数构造了双正弦界面重构方法(double sine interface capturing,DSINC).为验证不同界面函数对界面捕捉效果的影响,用数值方法求解了可压缩五方程模型,其中对流项的离散采用五阶WENO(weighted essentially non-oscillatory method)格式,时间积分采用三阶Runge--Kutta方法,通量计算分别考虑了HLL和HLLC方法,而状态方程采用Mie-Gr¨uneisen状态方程.在数值计算中,在界面附近,采用DSINC来获得体积分数的重构,而在远离界面的区域采用WENO格式来获得高阶插值状态.相比采用单界面函数的方法,如双曲正切界面重构方法(tangent of hyperbola for interface capturing,THINC),DSINC方法同样具有界面重构算法简单,在程序中添加方便等特点,两者区别在于,DSINC方法在重构过程中未知函数更易于求解,而无需求解复杂的非线性超越方程,这就使其具有易于向多维扩展的能力.一些典型的两相流动问题,如圆形水柱对流问题,两相三波点问题和激波-界面不稳定性问题等被用作不同界面函数对界面捕捉效果的影响对比.对比分析发现,DSINC与THINC在界面捕捉效果上大致保持一致,并在计算中表现出了较好的稳定性.双界面函数重构思想可以为多相流动界面的代数重构提供了一种新的思路.
基金supported by the Fundamental Research Funds for the Central Universities
文摘A constrained interpolation profile CIP-based numerical tank is developed to simulate violent free surface flows.The numerical simulation is performed by the CIP-based Cartesian grid method,which is described in the present paper.The tangent of hyperbola for interface capturing（THINC） scheme is applied for capturing complex free surfaces.The new model is capable of simulating a flow with violently varied free surface.A series of computations are conducted to assess the developed algorithm and its versatility.These tests include the collapse of water column with and without an obstacle,sloshing in a fixed tank,the generation of regular waves in a tank,the generation of extreme waves in a tank.Excellent agreements are obtained when numerical results are compared with available analytical,experimental,and other numerical results.
文摘针对远程虚拟桌面系统存在的交互操作响应延时问题,参考VoIP技术中对语音数据包的传输控制方法,设计一种电信级的服务架构。以采用精简低级原语和映射机制的THINC(Thin Client Internet Computing)虚拟桌面为基础,引入SIP控制和RTP承载手段,为实时交互数据提供有QoS保障的传输通道,给出了与实时会话业务类似的实时虚拟桌面系统RVDI(Real-time VDI)。通过一个简化的实验环境,验证了RVDI的可行性。测试结果表明,对于带宽较小的网络环境,RVDI可以有效改善虚拟桌面的操作响应性能。
基金supported by National Key R&D Program of China(No.2022YFA1004500)Lin Fu acknowledges the fund from the Research Grants Council(RGC)of the Government of Hong Kong Special Administrative Region(HKSAR)with RGC/ECS Project(No.26200222)+3 种基金the fund from Guangdong Basic and Applied Basic Research Foundation(No.2022A1515011779)the fund from Key Laboratory of Computational Aerodynamics,AVIC Aerodynamics Research Institute,and the fund from the Project of Hetao Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone(No.HZQB-KCZYB-2020083)Feng Xiao acknowledges the fund from JSPS(Japan Society for the Promotion of Science)under Grant Nos.18H01366 and 19H05613Hiro Wakimura acknowledges the fund from JSPS under Grant No.22KJ1331.
文摘While the recently proposed TENO(targeted essentially non-oscillatory)schemes[Fu et al.,Journal of Computational Physics 305(2016):333-359]exhibit better performance than the classical WENO(weighted essentially non-oscillatory)schemes with the same accuracy order,there is still a room for further improvement,e.g.,the physical discontinuities may be significantly smeared by the excessive numerical dissipation due to the enforcement of the ENO property after a long-time advection.More recently,a new fifth-order TENO5-THINC scheme is proposed by coupling the TENO5 scheme with a non-polynomial THINC(tangent of hyperbola for interface capturing)scheme based on a parameter-free discontinuity indicator.The novelty originates from the fact that the new strategy locates the discontinuities accurately and deploys the jump-like THINC reconstruction scheme for resolving the discontinuities with a sub-cell resolution,instead of enforcing the ENO property.The new scheme successfully leverages the excellent wave-resolution property of standard TENO schemes for smooth and under-resolved continuous scales and the discontinuity-resolving capability of THINC for reconstructing genuine discontinuities.In this work,we further develop the low-dissipation discontinuity-resolving very-high-order TENO-THINC reconstruction schemes for hyperbolic conservation laws by proposing tailored coupling strategies.Without loss of generality,the six-and eight-point TENO-THINC schemes are developed,and the explicit formulas are given as well as the built-in parameters.Based on a set of critical benchmark simulations,the newly proposed schemes show S.Takagi,H.Wakimura,L.Fu and F.Xiao/Commun.Comput.Phys.,34(2023),pp.1043-1078 significantly lower numerical dissipation when compared to the counterpart TENO schemes without sacrificing numerical robustness.The presented numerical results represent the state-of-the-art in the literature and can serve as references for future algorithm development.
文摘为实现波浪传播的高保真数值模拟,采用包含单元均值和点值(volume-average/point-value method,VPM)的有限体积法求解纳维-斯托克斯方程和具有二次曲面性质和高斯积分的双曲正切函数(THINC method with quadratic surface representation and Gaussian quadrature,THINC/QQ)方法来重构自由面,建立以开源求解库OpenFOAM底层函数库为基础的VPM-THINC/QQ模型.在本模型中添加推板造波法实现波浪的产生功能,采用松弛法实现消波功能,构建高精度黏性流数值波浪水槽.分别采用VPM-THINC/QQ模型和InterFoam求解器(OpenFOAM软件包中广泛使用的多相流求解器)开展规则波的数值模拟,重点探究网格大小和时间步长等因素对波浪传播过程的影响,定量地分析波高衰减程度;为验证本模型的适应性,对长短波进行模拟.结果表明,在相同网格大小或时间步长条件下,VPM-THINC/QQ模型的预测结果与参考值吻合较好,波高衰减较少,且无相位差,在波浪传播过程的模拟中呈现出良好的保真性.本文工作为波浪传播的模拟研究提供了一种高精度的黏性数值波浪水槽模型.
文摘水气二相流与诸多领域的实际工程问题密切相关.对二相流运动进行高精度的数值模拟是计算流体力学研究的难点和热点.针对开敞水域的自由表面流运动问题,将水和空气均视为不可压缩流体,采用五阶加权基本无震荡(weighted essentially non-oscillatory,WENO)格式求解描述流体运动的纳维斯托克斯(Navier–Stokes,NS)方程,利用以加权线性界面算法改进的多维双曲正切函数界面捕捉法(tangent of hyperbola for interface capturing with weighed line interface calculation,THINC/WLIC)追踪水气界面,建立WENO–THINC/WLIC水气二相流运动数值模型.模型采用分步计算法离散求解控制方程,通过压力投影法求解压强场,并利用三阶总变差递减(total variation diminishing,TVD)龙格库塔(Runge–Kutta,RK)法对时间项进行离散求解.通过对环境速度场下Zalesak’s disk和shearing vortex界面运动问题,线性液舱晃荡问题以及溃坝问题的模拟结果与理论分析或试验结果的比较,对所建立的水气二相流数值模型的适用性及模拟精度进行了验证.结果表明,本模型的模拟结果与物理模型或理论分析结果吻合良好,能较为准确地再现不可压缩水气二相流运动现象.鉴于WENO格式和THINC法本身在算法及应用等方面仍在不断改进,本研究提出的WENO–THINC耦合模型为后续更高精度的二相流计算模型开发提供了一种研究思路.
文摘入水问题涉及到军事、航空等领域,如子弹入水、船舶砰击等,具有很强的应用背景。物体入水的过程涉及到固、液、气三相流动和相互作用,并伴随水花飞溅、空泡形成等复杂的物理现象。该文基于紧致插值CIP(constrained interpolation profile)数学模型,分步求解Navier-Stokes(N-S)方程,并通过多相流理论描述固-液-气之间的相互作用,采用Volume of Fluid(VOF)类型的高精度紧致tangent of hyperbola for interface capturing(THINC)方法重构自由面。模拟了刚性圆柱和方柱的入水过程,结果与实验数据吻合较好。
文摘为实现波浪的超长距离传播和调制演变过程,该文提出一种高保真基于黏性流理论的数值波浪水槽。分别采用包含单元均值和点值(VPM, volume-average and point-value method)的有限体积法求解纳维斯托克斯方程及具有二次曲面性质和高斯积分的双曲正切函数(THINC/QQ, the tangent of hyperbola for interface capturing with quadratic surface representation and Gaussian quadrature)方法来重构自由面,建立以OpenFOAM底层函数库为基础的VPM-THINC/QQ模型。依据推板造波理论,在VPM-THINC/QQ模型中实现了波浪产生功能。在300 m的超长水槽中对深水波列进行模拟,得到波群的长时间非线性演化过程,并与文献结果进行了对比,结果表明:所开发的高精度数值波浪水槽可有效模拟深水波列的长时间传播和演变过程。
基金the support of Grants-in-Aid for Scientific Research (B), MEXT (No.24360358)
文摘Hydroelastic behavior of an elastic wedge impacting on calm water surface was investigated. A partitioned approach by coupling finite difference method （FDM） and finite element method （FEM） was developed to analyze the fluid structure interaction （FSI） problem. The FDM, in which the Constraint Interpolation Profile （CIP） method was applied, was used for solving the flow field in a fixed regular Cartesian grid system. Free surface was captured by the Tangent of Hyperbola for Interface Capturing with Slope Weighting （THINC/SW） scheme. The FEM was applied for calculating the structural deformation. A volume weighted method, which was based on the immersed boundary （IB） method, was adopted for coupling the FDM and the FEM together. An elastic wedge water entry problem was calculated by the coupled FDM-FEM method. Also a comparison between the current numerical results and the published results indicate that the coupled FDM-FEM method has reasonably good accuracy in predicting the impact force.
