Papers by Keyword: Dynamic Mesh

Abstract: This study examines numerical modeling of concentrated leak erosion in cohesive soils under turbulent flow conditions using the Hole Erosion Test (HET). Internal erosion, where soil particles detach due to subsurface flow, significantly weakens structures like dams and dikes, potentially causing floods.The study made a model to show erosion using changing meshes at the spot where water meets soil. It uses rules based on key shear force and erosion numbers. The model was tested for pipe erosion in 2D with slow water. It was then checked against the HET model. Two different soils were tested successfully using this approach, followed by a study to see how erosion factors change erosion speed and channel size. This model was proved to work when looking at experiments and Bonelli's papers. It shows leak erosion well while giving helpful flow data to better know how erosion works.

Abstract: Flow-induced vibrations occur in some of the internal components of a nuclear reactor. When specific conditions are present, these vibrations may result in excessive deformations or fatigue that can generate mechanical damage. Several boiling water reactor (BWR) of nuclear power plants (NPP) have experienced failures in the jet pump assembly due to flow-induced vibration (FIV) which could be caused by acoustic pulsations derived from recirculation pumps, vibration induced by turbulence and vibration induced by leakage at the slip joint. The purpose of this paper is to establish a viable numerical methodology to evaluate the fluid-structural interaction at the slip joint of a jet pump. In this analysis, the fluid-structural interaction was evaluated with the finite element method and finite volume method with ANSYS^® code in the case of two steel plates with a divergent gap. Results show that a critical velocity could cause fluidelastic instability, if only one flow in a two-way fluid-structural interaction was considered. This is one of the phenomena that could take place at the slip joint of a jet pump assembly.

Abstract: Research of devices for heat recovery is currently focused on increasing the temperature and heat efficiency of plate heat exchangers. The goal of optimization is not only to increase the heat transfer or even moisture but also reduce the pressure loss and possibly material costs. This study deals with a plate heat exchanger with wall shaped by intermittent ridges. We used software fluent and user defined deforming to deform computational mesh and create various heat exchange walls with different number of ridges and different number of set-offs. The intention of the set-offs is to discompose boundary layer inside channels created by ridges, mix the temperature field and thus intensify the heat transfer. We used previously formulated objective function, which is a linear combination of efficiency and pressure loss, and a simple local method to optimize the heat exchanger for required pressure loss. It was found that the objective function surface is monotone and unimodal, but is not smooth. The global optimums were identified and it was shown that the optimal wall shape has no set-off for low pressure losses. The optimal count of ridges and optimal count of set-offs rise with higher required pressure loss. It was proved that the suggested objective function is suitable for optimization of a counterflow plate heat exchanger, but use of a global optimization method would be beneficial.

Abstract: This paper illustrates an application of the mass transport model, turbulent model and dynamic mesh technique to the simulation of hydrogen leakage and dispersion in the Docking Process of exhaust pipe of rocket tank. Some numerical simulations are made to investigate on the effects of the tank pressure, docking mechanism and buoyancy. The experiment results indicate that tank pressure has significant influence in horizontal direction and vertical direction of hydrogen diffusion. Besides, the effects of buoyancy are slight. In addition, direction of hydrogen flow has been changed to vertical direction mostly at 2ms as a result of the action of docking mechanism, and there are no longer dangerous concentration areas of hydrogen inside the exhaust pipe after 2ms of leakage.

Abstract: A two-dimensional axisymmetric model was constructed to predict the ablation of the insulation layer in an end burning rocket motor by using the Computational Fluid Dynamics (CFD) software Fluent. The insulation material of graphite was used in the model. The wall surface reactions and discrete phase erosion were applied to simulate the insulation layer ablation. The influence of the burning surface movement was analyzed by using the dynamic mesh method. Numerical results show that the erosion rate increase with the increasing of burning time. The maximum erosion rate occurs at the upstream of the nozzle throat. There has a high erosion rate closing to the burning surface, and it decreases gradually away from the burning surface and becomes zero near the nozzle. It’s found that solid particle deposition appears on the inner surface of combustor closing to the nozzle, and it increases with the increasing of time.

Abstract: In this paper, we intended to replace the fluid-structure interaction of deep water bridge piers with acceleration-dependent forces during an earthquake. The hydrodynamic pressure on bridge pier groups under seismic excitation is studied using the finite volume method. Different seismic waves with various spectrum components are selected in order to cover frequently encountered cases. The calculated forces of these cylinders are fitted into the Morison equation, and by calculation, the drag force term is negligible, thus the effect of fluid is converted into one added mass term. The paper further calculated the dynamic response of a continuous beam bridge with pier groups in water to check the validity of our proposed method.

Abstract: The numerical simulation of multipahse flow characteristics during the launch process from the tube of the submarine vehicle are investigated, obtains the variation rules of the movement characteristic of the gas inside the tube, the cavity shape of around the vehicle body, the surface pressure coefficient during the movement process. The resluts show that the launch depth and velocity have significiant impact on the shouder cavitation of the submarine vehicle, the smaller values of the depth and the velocity are, the more obvious shouber cavitation, and which led to the distribution difference of the surface pressure coefficient

Abstract: Ceiling mounted personalized ventilation (PV) aims to provide clean outdoor air into breathing zone of occupants directly without affecting indoor aesthetics. High momentum, at outlet of PV air terminal device (ATD), is utilized in order to avoid inducing more ambient air and let more personalized air come into breathing zone. In steady state, its performance depends much on the ceiling mounted ATD because supply air momentum, other than buoyancy effects and ambient air flow, is the major driving force in the micro-environment of occupied zone. In dynamic state, the movement of a person near PV ATD causes entrainment or detrainment effect, which can be regarded as another comparable factor influencing ceiling mounted PV performance. A typical office workplace consisting of either ceiling mounted PV ATD or conventional PV ATD and ambient air supply diffuser is simulated. One person is assumed to be seated and another moving person is simulated by dynamic meshes in computational fluid dynamics (CFD). Simulations at moving person velocities of 0.5, 1 and 1,5 m/s and distance between seated person and moving person of 0, 0.2, 0.4m are performed. A new index, computational personal exposure effectiveness, is utilized to assess the performance of the PV ATD in regard to inhaled air quality under the influence of moving person. According to numerical results, the stability of ceiling mounted PV, under dynamic environment with moving person, is better than that of conventional PV although the personal exposure effectiveness (PEE) is lower than that of conventional PV with the same personalized air flow rate in steady state.

Abstract: This study establishes three-dimensional numerical wave tank based on the theory of viscous flow to simulate the unsteady motion response of a Wigley advancing in regular heading waves. The governing equations, Reynolds Averaged Navier-Stokes and continuity equations are discretized by finite volume method, a Reynolds-averaged NavierStokes solver is employed to predict the motions of ship, and volume of fluid method is adopted to capture the nonlinear free surface by writing user-defined functions. The outgoing waves are dissipated inside an artificial damping zone located at the rear part (about 1-2 wave lengths) of the wave tank. The numerical simulation results are compared with theoretical and experimental data from Delft University of Technology, and show good agreement with them. This research can be used to further analyze and predict hydrodynamic performance of ship and marine floating structures in waves and help to extend the applications of numerical wave tank.

Abstract: In the oil field development process, oil wells production capacity has been severely affected by clogged wells. There are many ways to relieve clogged wells, due to easy to operate, on the lifting of the blockage formation, the pressure pulse plugging technology has good prospects, but the current theory remains to be further studied, so the pressure pulse plugging process was simulated necessarily. The task to pressure pulses pulse tube plugging device as the research object, the establishment of its three-dimensional structure model to study the internal structure of the chamber, to analyze the impact of the flow field structure size rule. Establish its simplified model two-dimensional flow field, the compiler can achieve the state of motion of the sphere device UDF, application dynamic mesh of the pulse tube through Fluent unsteady flow was simulated. By convection field pressure, velocity and import-sectional physical monitoring equipment installation depth research and analysis, work flow, pressure relief device structure and the formation process of the pressure shocks field were investigated. Reveal the pulse tube working mechanism, and promote understanding of the pressure pulse plugging the nature of technology, optimize the structure of the pulse tube design basis and direction for the pressure pulse plugging technology and its theoretical foundation dynamics simulations.