首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 156 毫秒
1.
一维定常泥石流的数学模型   总被引:3,自引:0,他引:3  
范椿 《力学与实践》1994,16(1):50-51
根据泥石流在山坡斜面的长度(L)远大于泥石流横截面的特征长度(H_0),对连续方程,运动方程和Bingham模型的本构方程进行量级比较,忽略H_0/L量级的量,推导出控制一维定常泥石流运动的微分方程。本文方法可应用于推导非定常一维泥石流的数学模型。  相似文献   

2.
本文把平面Poiseuille流的Navier-Stokes方程化为一非线性动力系统,用线性稳定性理论对其进行分析研究,得到一组特征方程,对离散后的特征方程施加一个矩阵变换,计算出不同波数下的临界雷诺数并与Orszay和Thmoas的计算结果进行比较,最后画出了Poiseuille流的中性稳定性曲线。  相似文献   

3.
通过动床试验,结合黄河下游细沙河床研究了大尺度缩窄河道时非恒定流桥墩的局部冲刷. 研究结果表明,非恒定流洪水过程中的桥墩局部冲刷与恒定流的情况相比,两者之间存在差 异而且有必然的联系. 通过影响因素和试验数据的分析,建立了两者之间的关系和相应的非 恒定流桥墩局部冲刷深度计算方法. 经与原型非恒定流洪水实测资料对比,结果合理且比较 符合实际情况.  相似文献   

4.
建立了模拟水电站水锤的一维LB模型.通过实例计算与特征线法进行了比较,结果表明LB方法效果很好,将之引入水电站流场模拟是可行的,值得进一步探讨.  相似文献   

5.
非牛顿体通用模型线接触弹流润滑的数值分析   总被引:3,自引:3,他引:0  
基于润滑剂在弹流润滑状态下表现为非牛顿体特性,根据弹流润滑理论,采用一种新的非牛顿体流变模型,建立了适用于非牛顿体的修正Reynolds方程,进行了等温弹流润滑的数值计算,并在等温解的基础地温度场分析。数值分析结果表明,由于滑滚比和模型参数对剪应力影响较大,因而在滑滚比和模型参数较大时应进行热弹流计算。通过温度场分析可证明:非牛顿体通过模型可用于等温弹流润滑和热弹流润滑计算。  相似文献   

6.
本文采用加权平均法成功地求解了由广义Reynolds方程(幂次型)和三维弹性方程组成的非牛顿体弹流模型,该方法较好的解决了大偏心率的弹流迭代收敛困难的问题。该方法具有收敛快,对初值要求松且计算精度高等优点,是一种解决弹流问题较好的迭代模式。  相似文献   

7.
本文采用加权平均法成功地求解了由广义Reynolds方程(幂次型)和三维弹性方程组成的非牛顿体弹流模型,该方法较好的解决了大偏心率下的弹流迭代收敛困难的问题。该方法具有收敛快,对初值要求松且计算精度高等优点,是一种解决弹流问题较好的迭代模式。  相似文献   

8.
用格子Boltzmann方程模拟浅水波问题   总被引:5,自引:0,他引:5  
提出了用格子Boltzmann方程(LBE)模拟浅水波问题的方法.通过无粘气体运动方程与浅水波方程的比较,确定了LBE方法中平衡态的形式,使宏观方程与浅水波方程一致.计算了二维浅水波的一个问题,数值结果与精确解做了比较.  相似文献   

9.
一阶非线性项、四阶色散项的Boussinesq类方程   总被引:1,自引:0,他引:1  
林建国  邱大洪 《力学学报》1998,30(5):531-539
推导了由一阶色散项O(β2)表示的Bousinesq类方程,方程中保留了一阶非线性项O(α)及四阶色散项O(β8),其中α=A/h0,β=h0/L,A为特征波高,L为特征波长,h0为特征水深从理论上证明了Bousinesq改善型方程对色散性精度的提高,阐明了此类方程对色散项所保留的精度为O(β8),而并非是此类方程推导之初的假设为O(β2)这一点,将改变人们传统的认识  相似文献   

10.
一类非线性奇异积分方程及其数值方法研究   总被引:1,自引:0,他引:1  
探讨了一类非线性奇异积分方程的数理性质以及在颗粒雷诺数Rep<1时此类方程解的存在条件,然后详细研究了该方程的数值计算方法并构造称之为P(EC)^k多步法的差分格式,分析了该格式的收敛性和代数精度,得到时域离散步长的约束关系。运用该格式计算了静止流场和均匀振荡流中球形小颗粒的非恒定运动,将计算结果与其解析解及有关实验数据的比较表明,上述数值方法具有良好的计算精度。  相似文献   

11.
刘宇陆 《力学季刊》1993,14(3):64-70
本文报告了明渠非定常水流垂向结构的实验研究,通过 LDV 激光测速,我们给出了非定常水流的速度削面,湍流度,Eulerian质量输运速度的垂向分布。实验结果表明:在非定常周期很长时非定常流动的速度剖面,湍流强度及其粗糙度的影响基本上与定常流动相一致,当非定常流动为纯往复流动时,存在一个逆时针方向的环流,这种环流有利于底部的质量输运。  相似文献   

12.
IntroductionShallowwaterflowexistsverywidelyinhydraulicengineering .Pollutantdiffusionthatismainlycontrolledbytheshallowwaterflowhasbroughtincreasinglyattentioninenvironmentalengineering.Thetwo_dimensionalmodelfordescribingtheflowcharacteristicshasbee…  相似文献   

13.
A way of taking the effects of unsteady motion into consideration in boundary layer theory has been found recently [1]. In the meantime, in hydraulics ever-increasing interest is being shown in the application of the ideas and methods of boundary layer theory to the study channel flows. We have attempted here to apply this hydrodynamic approach in deriving the law of resistance for turbulent unsteady flows in open channels.  相似文献   

14.
The knowledge of the channel bed topography is paramount in modeling the hydrodynamics of open channel flows. Indeed, flow models based on the Shallow Water Approximation require prior information on the channel bed topography to accurately capture the flow features in natural rivers, estuaries, and flood plains. We present here a numerical technique for reconstructing the channel bed topography from given free surface elevation data for steep open channel flows for which the zero-inertia shallow water approximation holds. In this context, the shallow water equations are modified by neglecting inertia terms while retaining the effects of the bed slope and friction terms. We show in this work that by algebraic manipulation, we can recast the governing equations into a single first-order partial differential equation which describes the inverse problem which consists in finding the bed topography from known free surface elevation data. Interestingly, the analysis shows that the inverse problem does not require the knowledge of the bed roughness. The forward problem is solved using MacCormack’s explicit numerical scheme by considering unsteady modified shallow water equations. However, the inverse problem is solved using the method of characteristics. The results of the inverse and the forward problem are successfully tested against each other on two different test cases.  相似文献   

15.
An improved lattice Boltzmann (LB) model with a new scheme for the interparticle interaction force term is proposed in this paper. Based on the improved LB model, the equation-free method is implemented for simulating liquid–vapour phase change and multiphase flows. The details of phase separation are presented by numerical simulation results in terms of coexistence curves and spurious currents. Compared with existing models, the proposed model can give more accurate results in a wider temperature range with the spurious currents reduced and less time consumed. Characteristics of phase separation can be quickly and accurately reflected by the proposed method. Then, the contact angle of the solid surface is numerically investigated based on the proposed model. The proposed model is valid for steady flow with near zero velocity; unsteady cases will be investigated in further studies. This work will be helpful for our long-term aim of multi-scale modelling of convective boiling.  相似文献   

16.
The jet flows induced around a submerged channel due to the hot inner channel walls and the flow inside the channel are calculated. The formation of high-and low-density regions at the inlet and outlet of the channel is detected. The dependence of the flow rate on the channel orientation relative to the gravity force is analyzed. The onset of coherent flow structures results in the development of unsteady oscillating flows. Natural convection in the fluid is studied using the JoinCAD/FEM program package. The regularized Oberbeck-Boussinesq equations are solved using a finite-element method with the same order of the approximating functions.  相似文献   

17.
In the framework of the specified‐time‐interval scheme, the accuracy of the characteristic method is greatly related to the form of the interpolation. The linear interpolation was commonly used to couple the characteristics method (LI method) in open channel flow computation. The LI method is easy to implement, but it leads to an inevitable smoothing of the solution. The characteristics method with the Hermite cubic interpolation (HP method, originally developed by Holly and Preissmann, 1977) was then proposed to largely reduce the error induced by the LI method. In this paper, the cubic‐spline interpolation on the space line or on the time line is employed to integrate with characteristics method (CS method) for unsteady flow computation in open channel. Two hypothetical examples, including gradually and rapidly varied flows, are used to examine the applicability of the CS method as compared with the LI method, the HP method, and the analytical solutions. The simulated results show that the CS method is comparable to the HP method and more accurate than the LI method. Without tackling the additional equations for spatial or temporal derivatives, the CS method is easier to implement and more efficient than the HP method. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
19.
A hybrid unsteady Reynolds-averaged numerical simulation (U-RANS) and probability density function (PDF) method is developed for turbulent non-reactive and reactive flows. The resulting modeled equations are solved by a consistent hybrid finite volume and Lagrangian Monte-Carlo particle method. Both turbulent non-reactive and reactive flows in a rectangular channel containing a triangular-shaped bluff-body are simulated. One-step and two-step mechanisms for propane/air combustion are used for the reactive case. The time-averaged results are compared with both experimental data and numerical results from the literature using large eddy simulation (LES) and steady RANS. The results of the present method are in good agreement with the experimental data, and they improve the numerical results available in the literature.  相似文献   

20.
In this article we discuss the reduced basis method (RBM) for optimal control of unsteady viscous flows. RBM is a reduction method in which one can achieve the versatility of the finite element method or another for that matter and gain significant reduction in the number of degrees of freedom. The essential idea in this method is to define a reduced order subspace spanned by few basis elements and then obtain the solution via a Galerkin projection. We present several ways to define this subspace. Feasibility of the approach is demonstrated on two boundary control problems in cavity and wall bounded channel flows. Control action is effected through boundary surface movement on part of the solid wall. Application of RBM to the control problems leads to finite dimensional optimal control problems which are solved using Newton's method. Through computational experiments we demonstrate the feasibility and applicability of the reduced basis method for control of unsteady viscous flows.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号