Virtual Flux Method Research Articles

Comparative study of the virtual flux method and immersed boundary method coupled with regularized lattice Boltzmann method for suspension flow simulations

Suspension flows are ubiquitous in many fields, and reducing computational costs for numerical simulations of suspension flows remains a great challenge. Numerical simulations of particle-laden flows were performed here using the regularized lattice Boltzmann method (RLBM). RLBM, coupled with the virtual flux method (VFM) or the immersed boundary method (IBM) with the multi-direct forcing approach, conducted a series of three simulations for stationary and moving boundaries. The VFM and IBM results were compared for validation, and the computational efficiency was evaluated. For the two simulations using stationary and moving boundaries (i.e., a steady flow past a stationary cylinder and a plane Poiseuille flow including a single moving circular particle), the results based on the VFM and IBM were qualitatively comparable. The computational time for IBM was longer than that for VFM due to the iterations in its scheme. The pressure-driven suspension flow simulations showed that a dilute suspension's (<5%) relative viscosity was almost equivalent. The difference between the results obtained by the VFM and IBM in the semidilute regime (>10%) was discussed in terms of particle rotational motion. Even though the scalability for parallel computing was comparable between the VFM and IBM, the computational time could be effectively reduced by using the VFM instead of the IBM because of the increased suspension concentration.

Blade Dimension Optimization and Performance Analysis of the 2-D Ugrinsky Wind Turbine

With the increasing focus on renewable energy, there is a need to improve the efficiency of vertical-axis wind turbines (VAWTs). The Ugrinsky wind turbine is a type of VAWT, but there are few studies on this turbine. Previous studies have shown that the maximum power coefficient of the Ugrinsky wind turbine reaches 0.170, which is 54.5% higher than that of the Savonius type (0.110), and this turbine maintains a high power coefficient over a wide range of tip speed ratios (TSR). In this study, the dimensions of the two semicircles of the Ugrinsky wind turbine were further optimized to obtain a higher power coefficient. An analysis of the effect of the blade dimensions on the performance was conducted. The flow around the turbine was simulated using the regularized lattice Boltzmann method. The geometry of the turbine was simulated using the virtual flux method for the Cartesian grid. The optimization was conducted in terms of the output power coefficient and the average value of the power coefficient for neighboring TSR to consider the fluctuation of the TSR. This study demonstrates that a closer vortex distance favored the growth of the vortex and improved the power coefficient.

Contribution of Particle–Wall Distance and Rotational Motion of a Single Confined Elliptical Particle to the Effective Viscosity in Pressure-Driven Plane Poiseuille Flows

Rheological properties of the suspension flow, especially effective viscosity, partly depend on spatial arrangement and motion of suspended particles. It is important to consider effective viscosity from the microscopic point of view. For elliptical particles, the equilibrium position of inertial migration in confined state is unclear, and there are few studies on the relationship between dynamics of suspended particles and induced local effective viscosity distribution. Contribution of a single circular or elliptical particle flowing between parallel plates to the effective viscosity was studied, focusing on the particle–wall distance and particle rotational motion using the two-dimensional regularized lattice Boltzmann method and virtual flux method. As a result, confinement effects of the elliptical particle on the equilibrium position of inertial migration were summarized using three definitions of confinement. In addition, the effects of particle shape (aspect ratio and confinement) on the effective viscosity were assessed focusing on the particle–wall distance. The contribution of particle shape to the effective viscosity was found to be enhanced when the particle flowed near the wall. Focusing on the spatial and temporal variation of relative viscosity evaluated from wall shear stress, it was found that the spatial variation of the local relative viscosity was larger than temporal variation regardless of the aspect ratio and particle–wall distance.

Dual-Objective Control Using an SMC-Based CW Current Controller for Cascaded Brushless Doubly Fed Induction Generator

This article proposes a dual-objective control method using a sliding-mode control (SMC)-based control winding (CW) current controller for cascaded brushless doubly fed induction generator (CBDFIG), where the smooth grid synchronization and flexible grid-connected power regulation are achieved with the same CW current controller. A so-called virtual grid flux method is introduced to obtain the CW current reference value for the grid synchronization. In addition, according to the relationship between the power winding (PW) power and CW current, a novel direct power control method is proposed for CBDFIG. Furthermore, a unified form of the CW current references is investigated to achieve the dual-objective control for CBDFIG, where no mode switching operation is required and constant switching frequency can be achieved in both the control processes with space vector pulsewidth modulation. The proposed control method shows a strong robustness against the grid voltage disturbances, which is necessarily required in both the grid synchronization and grid-connected power regulation. The simulation and experiments are conducted to validate the effectiveness of the proposed control method.

A new numerical method for the analysis of monolithic seepage problems with complex drainage systems in a groundwater recharge area for a hydropower station in China

After construction of a dam impounding water in a reservoir, a monolithic seepage field develops in the surrounding rock mass. Here, a new finite element method is proposed for determining the shape and characteristics of the 3D monolithic seepage field including the free surface, considering complex drainage systems consisting of densely-spaced drainage holes and drainage galleries. To this end, the previously proposed virtual flux method is improved by a refined numerical integration scheme and a regularized Heaviside function for distinguishing the subregions below and above the free surface within a particular finite element. Leakage and overflow drainage holes are modeled as internal boundaries. The proposed numerical method is verified by an academic example, for which the analytical solution is available. Finally, the numerical simulation of the seepage field developing in the vicinity of a high dam and underground power house, constructed in the context of a hydropower plant project in China is used to show its application to a problem in engineering practice.

Research for high resolution analysis of the flow near blade surface on a Cartesian grid using virtual flux method

Research for high resolution analysis of the flow near blade surface on a Cartesian grid using virtual flux method

Numerical simulation on the rheology of a suspension using virtual flux method

Numerical simulation on the rheology of a suspension using virtual flux method

A Numerical Simulation of the Flow near Blade Surface on Certain Grid using Virtual Flux Method

A Numerical Simulation of the Flow near Blade Surface on Certain Grid using Virtual Flux Method

Seepage Control in a High Concrete Face-Rock Fill Dam Based on the Node Virtual Flow Method

The seepage control system of a high Concrete Face Rock-Fill Dam (CFRD) may have anti-seepage deficiencies during both construction and operation. In order to solve these, the three-dimensional Finite Element Method (FEM) model was built based on dam body filling, anti-seepage system, defect location and bedrock distribution. The seepage field simulation and computation were carried out using an improved node virtual flux method and the zero-thickness crack model theory. The water head distribution, seepage lines and dam leakage field were obtained by simulation under different conditions, and the seepage characteristics during construction and operation were analyzed systematically. Taking a high CFRD as an example, the results showed that during the flood-control construction period, the incomplete nature of the dam face slab can lead to seepage damage near the second seepage control line. Moreover, during operation period; the seepage control system was still effective when the dam face slab was incomplete.

P015 格子ボルツマン法と仮想流束法を用いた二次元羽ばたき飛行の数値解析(メカボケーション学生研究発表セッション)

P015 格子ボルツマン法と仮想流束法を用いた二次元羽ばたき飛行の数値解析(メカボケーション学生研究発表セッション)

P026 仮想流束法を用いた三次元胸部大動脈モデルにおける血液流れの数値解析(メカボケーション学生研究発表セッション)

P026 仮想流束法を用いた三次元胸部大動脈モデルにおける血液流れの数値解析(メカボケーション学生研究発表セッション)

P030 仮想流束法を用いた微粒子のろ過に関する数値シミュレーション(メカボケーション学生研究発表セッション)

P030 仮想流束法を用いた微粒子のろ過に関する数値シミュレーション(メカボケーション学生研究発表セッション)

Improved grid voltage sensorless control strategy for railway power conditioners

Rapid development of high-speed trains confronts the power grid with serious power quality problems. In this study, to compensate power quality, an improved grid voltage sensorless control method for the railway power conditioner (RPC) is proposed. The proposed control strategy utilises a moving average filter to better detect the compensating currents and a proportional-resonant controller to control the compensating currents. Moreover, a sensorless virtual flux method based on second order low-pass filters is presented to replace the AC voltage sensors. Using the proposed strategy, the dynamic and steady-state characteristic of the RPC is significantly enhanced. Through simulation tests, the effectiveness of the proposed methods is confirmed.

J1230101 デカルト格子を用いたトンネル内圧縮波の形成に関する数値解析

When a train travels through a tunnel with a high speed, a compressional wave is generated in the entrance of the tunnel. The compressional wave, which reaches the tunnel exit, causes the noise problems. The formation of this compressional wave can be predicted by using Computational Fluid Dynamics on Body-fitted grid, but this method requires high computational cost. Therefore, this study proposes a CFD on Cartesian grid using virtual flux method. In this paper, for the first stage of this study, we evaluated accuracy of the numerical simulation on the formation of compressional wave in a tunnel when a train running at Mach number of 0.2 enters the tunnel on 2-dimensional Cartesian grid, by comparing pressure variation at an inside of the tunnel with the presence of a tunnel entrance hood. As a result, we report that this method can simulate the tendency that the tunnel entrance hood can suppress a pressure rise. However the simulation overestimates the pressure rise, because of 2-dimensional simulation. To predict the compressional wave more accuracy, we need to analyze with this method on 3-dimentional simulation.

Comparison of virtual flux method on LBM and on other methods on a GPU

The authors implemented artificial compressibility method (ACM) with virtual flux method (VFM) on a GPU to simulate incompressible unsteady state flow fields around a cylinder, and lattice Boltzmann method (LBM) on a GPU to simulate incompressible turbulent flows. In this study, unsteady flow fields around a circular cylinder were calculated by LBM with VFM. The history of the length of twin vortex behind a circular cylinder and the Strouhal number were compared with that of the other researchers; also, the speedup obtained by a GPU is shown.

Influence of Vortices in the Sinus of Valsalva on Local Wall Shear Stress Distribution

Transposition of the great arteries (TGA) is one of the most severe congenital heart diseases. The arterial switch operation (ASO) is the procedure of preference for treatment of TGA. After ASO, some patients suffer from circulatory system problems such as neo-aortic root dilatation and neo-aortic valve regurgitation, and supravalvar pulmonary stenosis. The neo-aortic root dilatation is often explained by the structural vascular difference between normal great arteries and the neo-aorta after ASO. Since the aortic and pulmonary roots generally remain in situ after ASO, i.e., the original pulmonary artery is connected to the left ventricle (LV), whereas the original aorta is connected to the right ventricle, the neo-aorta has no sinus of Valsalva after ASO. The influence of these morphological changes on the blood flow field at the aortic root should be investigated in detail as well as the structural vascular difference to consider the circular system problems. In this study, we apply the virtual flux method (VFM), which is a tool to describe stationary or moving body shapes in a Cartesian grid, to the 2D aortic valves and reproduce the blood flow fields around the aortic valves and the sinus of Valsalva by regularized lattice Boltzmann method (RLBM), and consider the influence of longitudinal length of sinus of Valsalva on blood flow fields around the aortic valves. As a result, we found that the longitudinal length of the sinus affects development of vortices around the aortic valves strongly. We also assessed the wall shear stress (WSS) distribution on the aortic valves and sinus wall and showed the effect of vortices in the sinus of Valsalva on local WSS distribution.

G011052 直交座標系格子を用いた任意形状に対する非定常熱伝導解析([G011-05]計算力学部門,一般セッション(5) : 熱・燃焼・油膜)

CAE is an important tool for designing the mold in injection molding and has been used extensively. The filling, packing and cooling stages in injection molding, as well as the warpage after ejection can be simulated. The purpose of this study is to develop a numerical method for solving the incompressible Navier-Stokes equations and the heat conduction equation simultaneously on a Cartesian grid. For computing unsteady incompressible viscous flows, we confirmed that kinetically reduced local Navier-Stokes (KRLNS) equations is a promising method in terms of accuracy, efficiency and the capability to capture the correct transient behavior without sub-iterations. In this paper, the numerical simulations of unsteady heat conduction were carried out by using virtual flux method (VFM), which can treat arbitrary geometries on a Cartesian grid. The two types of boundary conditions were specified. The numerical solutions were compared with those obtained theoretically. The good agreement was obtained.

201 仮想流束法の高速数値シミュレーションに関する研究(GS-5 数値解析(1))

201 仮想流束法の高速数値シミュレーションに関する研究(GS-5 数値解析(1))

An Eulerian approach for fluid–structure interaction problems

This paper describes a numerical method for simulating fluid–structure interaction problems on a fixed Cartesian grid. The fluid–structure interfaces are sharply represented by the aid of the level-set function and virtual flux method. The virtual flux method is one of the sharp interface Cartesian grid methods. The numerical flux across the interface is replaced with the virtual flux so that proper interface conditions must be satisfied there. For fluid and elastic structure interaction problems, the Navier–Stokes equations and unsteady evolution equations for the Eulerian strain tensor of elastic solid are simultaneously solved, so that the strain and stress tensors as well as velocities and pressures in both fluid and solid mediums can be analyzed on the fixed grid. Validity of the numerical method is demonstrated for numerical simulations about reciprocating engines, reciprocating compressors, and deformations of elastic particles in fluid flows. It is confirmed that the Eulerian approach is easily applicable to the simulation of fluid–structure interaction problems.

G010021 非圧縮性局所ナビエ・ストークス方程式と仮想流束法を用いた流路内流れの数値計算

G010021 非圧縮性局所ナビエ・ストークス方程式と仮想流束法を用いた流路内流れの数値計算