水动力学研究与进展:英文版最新文献

A numerical study on violent liquid sloshing phenomenon in a partially filled rectangular container is carried out by using moving particle semi-implicit (MPS) method. The present study deals with the implementation of five modifications all together over the original MPS method. The modifications include improved source terms for pressure Poisson equation, special approximation technique for the representation of gradient differential operator, collective action of mixed free surface particle identification boundary conditions, effecting Neumann boundary condition on solving the PPE and fixing judiciously the parting distance among particles to prevent collision. The suitability of the kernel function used in the original MPS method along with these five modifications is investigated for violent sloshing problems. The present model ensures a good agreement between numerical results with the existing experimental observations. The model is successfully applied to a partially filled tank undergoing horizontal sinusoidal excitation to compute the sloshing wave amplitudes and pressure on tank walls. The assessment of dynamic behaviour manifested in terms of base shear, overturning moment and impact pressure load exerted on tank ceiling induced by violent sloshing motion using MPS method is not reported in the open literature and has been efficiently carried out in the present study.

The polymer solution for polymer flooding is a viscoelastic fluid. There exist both shear flow and elongational flow when the polymer solution flows in a porous medium, where an additional dissipation is involved. The additional dissipation caused by elongational deformation is often ignored while studying the flow of the fluid in a porous medium. For a complex polymer solution, the generated elongational pressure drop cannot be ignored. In a capillary of fixed diameter, the polymer solution is only impacted by the shear force, and its rheological property is pseudoplastic. Therefore the variable diameter capillary and the converging-diverging flow model with different cross sections are required to describe the flow characteristics of the polymer solution in porous media more accurately. When the polymer solution flows through the port, we have the elongational flow and the polymer molecules undergo elongational deformation elastically. By using the mechanical energy balance principle and the minimum energy principle, a mathematical model of non-Newtonian fluid inlet flow was established by Binding. On the basis of the Binding theory, with the application of the theory of viscoelastic fluid flow in the circular capillary and the contraction – expansion tube, the relations between the viscoelastic fluid flow rate and the pressure drop are obtained.

Recent studies have shown that the collapse of cavitation bubbles in a jet pump can generate an extremely high pressure with many potential applications. The dynamics of the bubble is governed by the Rayleigh-Plesset equation. With the bubble dynamics equation and the heat and mass transfer model solved with the Runge-Kutta fourth order adaptive step size method, the oscillations of the bubble in the diffuser of the jet pump are assessed under varied conditions. To obtain the pressure variation along the diffuser, the Bernoulli equation and the pressure measured in experiment are coupled. The results of simulation show that a transient motion of the bubbles can be obtained in the diffuser quantitatively, to obtain the pressure and temperature shock in the bubble. Moreover, increasing the outlet pressure coefficient would result in a more intense bubble collapsing process, which can be used in the subsequent studies of the cavitation applications. The predictions are compared with experiments with good agreement.

In this work the feasibility of a numerical wave tank using a hybrid particle-mesh method is investigated. Based on the fluid implicit particle method (FLIP) a formulation for the hybrid method is presented for incompressible multiphase flows involving large density jumps and wave generating boundaries. The performance of the method is assessed for a standing wave and for the generation and propagation of a solitary wave over a flat and a sloping bed. A comparison is made with results obtained with a well-established SPH package. The tests demonstrate that the method is a promising and attractive tool for simulating the nearshore propagation of waves.

This paper proposes the critical conditions for a submerged ice block beneath an intact ice cover to become unstable, as a fundamental component of any numerical model to successfully predict the ice jam formation or the ice jam release events. The flume model experimental and numerical simulation methods are both applied to analyze the stability of submerged ice blocks. The flume model experiment is first conducted, and the experimental results indicate that the influencing factors of the stability of a submerged ice block include the relative length, the relative water depth and the relative width. It was shown that the effect of the relative width on the stability of submerged ice blocks was not well studied. Based on the experimental results, k – ɛ the turbulence model is applied to establish a 3-D numerical model for studying the pressure distribution beneath submerged ice blocks. The effects of the relative width on the Venturi pressure and the leading edge pressure are evaluated. Finally, according to the force balance equation and the moment balance equation, this paper proposes a computational formula for the sliding and underturning critical conditions of submerged ice blocks, and the results are in good agreement with the experimental results.

The 1st International Conference on the Material Point Method for “Modelling Large Deformation and Soil–Water– Structure Interaction” (MPM2017) was held in Delft, The Netherlands on 10–13 January 2017. This is the first conference organised by the Anura3D MPM Research Community, following a series of international workshops and symposia previously held in The Netherlands, UK, Spain and Italy, as part of the European Commission FP7 Marie-Curie project MPM-DREDGE. We are delighted to present seven contributions in this Special Column of the Journal of Hydrodynamics, and take this opportunity to announce that the 2nd conference, MPM2019, will be held in Cambridge, UK in January 2019.

The main aim of this paper is to describe and analyse the modelling of vertical column tests that undergo fluidisation by the application of a hydraulic gradient. A recent advancement of the material point method (MPM), allows studying both stationary and non-stationary fluid flow while interacting with the solid phase. The fluidisation initiation and post-fluidisation processes of the soil will be investigated with an advanced MPM formulation (Double Point) in which the behavior of the solid and the liquid phase is evaluated separately, assigning to each of them a set of material points (MPs). The result of these simulations are compared to analytic solutions and measurements from laboratory experiments. This work is used as a benchmark test for the MPM double point formulation in the Anura3D software and to verify the feasibility of the software for possible future engineering applications.

The simulation of slope failures, including both failure initiation and development, has been modelled using the material point method (MPM). Numerical case studies involving various slope angles, heterogeneity and rainfall infiltration are presented. It is demonstrated that, by utilising a constitutive model which encompasses, in a simplified manner, both pre- and post-failure behaviour, the material point method is able to simulate commonly observed failure modes. This is a step towards being able to better quantify slope failure consequence and risk.

The orientation of suspended fibers in the turbulent contraction is strongly related to the contraction ratio, which in some cases may be detrimental to the actual production. Here for a certain contraction ratio, the contraction geometry shape is optimized to obtain the desired fiber orientation. In view of the nonlinearity and the complexity of the turbulent flow equations, the parameterized shape curve, the dynamic mesh and a quasi-static assumption are used to model the contraction with the variable boundary and to search the optimal solution. Furthermore the Reynolds stress model and the fiber orientation distribution function are solved for various wall shapes. The fiber orientation alignment at the outlet is taken as the optimization objective. Finally the effect of the wall shape on the flow mechanism is discussed in detail.

Material point method (MPM) was originally introduced for large deformation problems in solid mechanics applications. Later, it has been successfully applied to solve a wide range of material behaviors. However, previous research has indicated that MPM exhibits numerical instabilities when resolving incompressible flow problems. We study Chorin's projection method in MPM algorithm to simulate material incompressibility. Two projection-type schemes, non-incremental projection and incremental projection, are investigated for their accuracy and stability within MPM. Numerical examples show that the non-incremental projection scheme provides stable results in single phase MPM framework. Further, it avoids artificial pressure oscillations and small time steps that are present in the explicit MPM approach.