流水中重物运动过程的数学建模与分析

围绕与封堵溃口有关的重物落水后的运动问题,通过分析落水重物的受力,确定了影响其在水中运动的主要因素.建立了大实心方砖落水后竖直位移-时间、水平位移-时间的运动模型.在此基础上,通过建立包含形状因素的水流力系数模型,将各种形状试件折算为球体,建立了适应不同情况的描述重物水中运动过程的一般化模型,并对一般化模型进行合理性检验和误差分析.结合建立的模型,提出了"最有效位置触底"的猜想以及需要进行的验证试验.最后,结合相似性理论对模型进行了推广.     

物块落水后运动过程的动力学分析

采用动力学的方法,对物块在流场中的运动进行了受力分析,通过动力学微分方程和边界条件分别得到物体静止进入水中和运动进入水中的物体运动轨迹方程.对于复杂形状,通过工程中常用的体积等效和截面等效的方法获得当量直径,将物块等效为球形,并且引入了空心率的概念用于表征物块形状参数对流场中受力的影响.对于溃口封堵的真实流场,可以采用重力相似准则转化为模型适用的小型流场情况,对其进行分析.     

与封堵溃口有关的重物落水后运动过程的分析

针对2010年全国研究生数学建模竞赛B题一"与封堵溃口有关的重物落水后运动过程"中的命题背景,建立了重物在水中的运动的数学模型,并处理了小型试验获取的相关数据.     

与封堵溃口有关的重物落水后的运动过程

为了精确求解落水重物的运动轨迹,首先根据力学原理建立一个数学模型,接着利用最优化理论求解该模型,并与试验的结果进行对照.结果表明,数值模拟所得重物的下沉轨迹与试验存在一定的差距.为此,提出了一种改进模型的办法,即在原来模型的基础上加入噪声.带噪声的模型拟合所得值与试验吻合较好,从而验证了模型的可靠性和精度,可应用于实际的溃口封堵重物运动过程的数值模拟.     

重物落水后运动过程的数学模型

为了迅速有效地封堵在汛期河道堤防出现的溃口,建立了重物落水后运动过程的微分方程模型,并采用单因子分析法进行误差分析.分析了不同水流速度、不同投放高度和不同投放方式对模型的影响.然后通过小型试验验证了所建模型的合理性及正确性.结果表明,该模型能够较准确地模拟重物落水后的运动过程,有利于辅助防灾减灾工作的顺利进行.     

与封堵溃口有关的重物落水后运动过程模型

洪涝灾害经常会造成溃坝溃堤,进而引发泥石流灾害,造成国家和人民生命财产的严重损失,物体填堵方法是有效解决溃坝溃堤问题的一种手段,主要针对物体填堵时在何处投放物体最有效的问题进行了解决.在合理假设的前提下,通过对试验模型中各单件相关数据进行分析并参考相关资料,得出影响重物在水中运动的主要因素,包括流体结构、投放高度、投放方式、物体形状等.然后按照物体是否完全浸入水中把运动过程分成两个阶段,再分别从垂直和水平两个运动方向考虑,利用已知的试验数据和相关知识,建立了能够适应不同情况的、描述重物水中运动过程的数学模型.以大实心方砖为例进行分析,利用Matlab对所建的模型进行求解,对比拟合试验数据得到的和所建模型得到的运动方程,从而可以计算出离散时间点的相对误差,其值大约为8%-13%,符合容许条件,证明所建模型还是比较合理的.     

重物落水后运动过程的数学建模

分析了影响重物落水运动过程的主要因素,根据各因素权重关系及相关物理理论建立了多因素融合的大实心方砖落水过程模型,对重物在水中的运动分成部分浸入水中和重物完全浸入水体两个阶段.定性描述了两连接物体落水后耦合运动过程,并与实测数据进行拟合,根据对比的结果,实现了误差分析,根据误差原因优化模型以提高其准确度和适用性,并对未来的试验和研究工作提出了一些建议,以提高试验数据的质量.     

唐家山堰塞湖泄洪问题的研究

研究的是唐家山地震次生灾害引发的堰塞湖问题.首先对数字高程地图进行等高图像分析求解了堰塞湖不同高程水位对应的湖区面积,建立了蓄水量体积与堰塞湖水位高程的离散化模型,然后建立了神经网络模型和多元线性回归模型研究了北川降雨量与堰塞湖入库流量的关系,继而求解得到不同降雨量下每日堰塞湖水位高程.在研究泄洪过程时,首先通过对泄洪过程和溃坝过程内在机理的研究分别建立了正交多项式逼近模型和仿真模型得到溃坝时的溃口流量随时间变化的关系,继而分析求解得到溃坝时其他参数随时间变化的关系.针对淹没区的问题,综合数字高程地图和行政区域地图,利用数字地图计算了洪水到达各被淹没区域的时间,淹没范围,以便于确定撤离方案.     

指数型产品的Bayes可靠性鉴定试验

利用可靠性增长模型确定正样产品失效率的先验分布.综合考虑由弃真和存伪风险所造成的试验损失和其他试验费用,建立可靠性鉴定试验的损失评估模型.分别用两种风险准则约束两类决策风险.根据Bayes决策理论,得到失效数和总试验时间的关系,确定使得试验损失函数值最小的鉴定方案.最后通过算例体现方法的有效性,与经典方法和其他Bayes鉴定方法相比较有其优越性.     

基于桥梁经验数据的理论易损性曲线校准

基于理论计算或试验研究定义桥梁损伤状态建立的理论易损性曲线,通常不能将桥梁构造(包括几何性质、材料性质等)、地面运动和场地条件等因素均考虑在内.鉴于此,为更加精确地以易损性曲线的形式评估桥梁抗震性能,首先利用1994年北岭地震桥梁损伤数据建立双参数对数正态分布的经验易损性曲线;其次,给出一种多跨桥梁力学模型,定义桥墩柱转动延性值量化桥梁损伤状态,获得4种损伤状态下的理论易损性曲线;最后,以90%置信区间的经验易损性曲线对理论易损性曲线进行校准.计算结果表明:利用桥梁力学模型建立的理论易损性曲线校准后能近似吻合经验易损性曲线,且3种损伤状态阈值由SRSS优化公式得到校准.随着结构损伤知识的进展,未来可利用更详细的结构损伤过程对校准后的理论易损性曲线做二次更新,进一步提高桥梁系统风险评估的精确性,尤其是遭受强震灾害下由多座桥梁组成的高速公路网络.     

Theoretical model of laminar flow in tubes in rolling motion

The theoretical model of laminar flow in tubes in rolling motion is established. The velocity and temperature correlations are derived, and the frictional resistance coefficient and Nusselt number are also obtained. The oscillation of parameters is induced by the tangential force due to rolling motion. The effect of centrifugal and Coriolis forces on the flow is negligible. The tangential force does not effect on the average parameters. The oscillating amplitude of Nusselt number increase with the Prandtl number increasing. Both the oscillating amplitudes of frictional resistance coefficient and Nusselt number increase with the rolling frequency increasing.     

System of sticking diffusion particles of variable mass

We construct a mathematical model of an infinite system of diffusion particles with interaction whose masses affect the diffusion coefficient. The particles begin to move from a certain stationary distribution of masses. Their motion is independent up to their meeting. Then the particles become stuck and their masses are added. As a result, the diffusion coefficient varies as a function inversely proportional to the square root of the mass. It is shown that the mass transported by particles is also characterized by a stationary distribution.     

The optimal quasi-stationary motion of a vibration-driven robot in a viscous medium

We consider a rectilinear quasi-stationary motion of a two-mass system in a viscous medium. The motion of the system as a whole occurs due to periodic movements of the internal mass relatively to the shell. The problem is to describe the law of motion of the internal mass that provides the minimum energy consumption with a specified average velocity of the shell. We propose an algorithm for solving the problem with any law of the resistance of the medium. We obtain the energy-optimal law of motion of a spherical shell in a viscous liquid.     

Small mass asymptotic for the motion with vanishing friction

We consider the small mass asymptotic (Smoluchowski–Kramers approximation) for the Langevin equation with a variable friction coefficient. The friction coefficient is assumed to be vanishing within certain region. We introduce a regularization for this problem and study the limiting motion for the 1-dimensional case and a multidimensional model problem. The limiting motion is a Markov process on a projected space. We specify the generator and the boundary condition of this limiting Markov process and prove the convergence.     

The periodic risk model with investment

We consider a periodic risk model with the possibility of investing into a risky asset, given by a geometrical Brownian motion. The aim is to maximize the adjustment coefficient of the risk process. It is shown that the optimal investment strategy only depends on the averaged data of the model and is constant over time. Thus maximizing the adjustment coefficient is a very weak optimization criterion.     

The optimal periodic motions of a two-mass system in a resistant medium

The rectilinear motions of a two-mass system, consisting of a container and an internal mass, in a medium with resistance, are considered. The displacement of the system as a whole occurs due to periodic motion of the internal mass with respect to the container. The optimal periodic motions of the system, corresponding to the greatest velocity of displacement of the system as a whole, averaged over a period, are constructed and investigated using a simple mechanical model. Different laws of resistance of the medium, including linear and quadratic resistance, isotropic and anisotropic, and also a resistance in the form of dry-friction forces obeying Coulomb's law, are considered.     

Energy decay and global solutions for a damped free boundary fluid–elastic structure interface model with variable coefficients in elasticity

ABSTRACT

We study a free boundary fluid-structure interaction model. In the model, a viscous incompressible fluid interacts with an elastic body via the common boundary. The motion of the fluid is governed by Navier–Stokes equations while the displacement of the elastic structure is described by variable coefficient wave equations. The dissipation is placed on the common boundary between the fluid and the elastic body. Given small initial data, the global existence of the solutions of this system is proved and the exponential decay of solutions is obtained.     

Martingale Solution to Equations for Differential Type Fluids of Grade Two Driven by Random Force of Lévy Type

In this article we study a system of nonlinear non-parabolic stochastic evolution equations driven by Lévy noise type. This system describes the motion of second grade fluids driven by random force. Global existence of a martingale solution is proved under general conditions on the noise. Since the coefficient of the noise does not satisfy a Lipschitz property, we could not prove any pathwise uniqueness result. We note that this is the first work dealing with a stochastic model for non-Newtonian fluids excited by external forces of Lévy noise type.     

Chaos in vibroimpact systems with one degree of freedom in a neighborhood of chatter generation: II

We study the rectilinear motion of a mass point with impacts against a stopper. The motion between the impacts is described by a second-order ordinary differential equation with a parameter. The impact recovery coefficient also depends on the parameter of the vibroimpact system. We describe a bifurcation that leads to the generation of a Smale horseshoe in a parametric neighborhood of the chatter phenomenon. We prove the existence of an invariant set described by symbolic dynamics.     

Chaos in vibroimpact systems with one degree of freedom in a neighborhood of chatter generation: I

We study the rectilinear motion of a mass point with impacts against a delimiter. The motion between the impacts is described by a second-order ordinary differential equation with a parameter. The impact recovery coefficient also depends on the parameter of the vibroimpact system. We describe a bifurcation that leads to the generation of a Smale horseshoe in a parametric neighborhood of the chatter phenomenon. We prove the existence of an invariant set described by symbolic dynamics.