Hydrodynamic Analysis of KVLCC2 Ship Sailing near Inclined Banks

The hydrodynamic forces of KVLCC2 ship sailing near inclined banks are calculated by using CFD based on RANS equation. Corresponding CFD uncertainty analysis is conducted according to the procedure recommended by ITTC. An unstructured grid, tetrahedral grid, is employed for discretization. To control the number of grids, global element scale factor is selected as the same as refinement ratio. In numerical simulation, straightforward and oblique navigation conditions are investigated. The variation of transverse force and yaw moment with the ship-shore distance, bank angle, water depth, and drift angle are analyzed. Both hull model and hull-propeller-rudder model are considered in numerical simulation. The simulation results show the hydrodynamic characteristics of ship sailing near inclined banks.

Tetrahedral grid generation for supercomputer modeling of flow past aerospace objects

Для генерации сверхподробных тетраэдральных сеток объемом до 1 миллиарда ячеек используется открытое ПО Gmsh. Пакет позволяет строить автоматически указанные сетки на ПК в параллельном режиме OpenMP за время, не превышающее 1 часа при использовании ПК Intel i7–9700K. Описан опыт применения пакета для построения пространственных сеток для задач обтекания аэрокосмических объектов. Приведены примеры суперкомпьютерных расчетов обтекания аэрокосмических объектов. Gmsh open source software is used to generate ultra-detailed tetrahedral grids of up to 1 billion cells. The package allows one to build automatically specified grids on a PC in parallel OpenMP mode in a time not exceeding 1 hour when using an Intel i7–9700K PC. The experience of using the package to construct the spatial grids for problems of flows past aerospace objects is described. Several examples of supercomputer calculations for the flows past aerospace objects are given.

High-Order Spectral Difference Method on 3D Unstructured Grids via Mixed Elements

The high-order methods is difficultly applied in various elements. The development of a 3D solver by using the spectral difference method of unstructured grids via mixed elements is presented. A mixed tri-prism and tetrahedral grid is firstly refined using one-level h-refinement to generate a hexahedral grid while keeping the curvature of wall boundaries. The SD method designed for hexahedral elements can subsequently be applied for refining the unstructured grid. Through a series of numerical tests, the present method is high-order accurate for both inviscid and viscous flows is demonstrated; the results obtained for inviscid and viscous compressible flows compare well with other published results.

Closed-form formula of magnetic gradient tensor for a homogeneous polyhedral magnetic target: A tetrahedral grid example

A closed-form formula is developed for the full magnetic gradient tensor of a polyhedral body with a homogeneous magnetization vector. It is based on the direct derivative technique on the closed form of the magnetic field. These analytical expressions are implemented into an easy-to-use C++ package which simultaneously calculates the magnetic potential, the magnetic field, and the full magnetic gradient tensor for magnetic targets. Modern unstructured tetrahedral grids are adopted to represent the polyhedral body so that our code can deal with arbitrarily complicated magnetic targets. A prismatic body is tested to verify the accuracies of our closed-form formula. Excellent agreements are obtained between our closed-form solutions and solutions of a prismatic magnetic body with differences up to machine precision. A pipeline model is used to demonstrate its capability to deal with complicated magnetic targets. This C++ code is freely available to the magnetic exploration community.

Aerodynamic Performances of a Centrifugal Compressor With Discrete Cavities

In this study, aerodynamic performance of the centrifugal compressor was investigated by using a recirculating device called discrete cavities. A parametric study was conducted using six parameters related to the geometry of the discrete cavities, i.e., the inclined angle, the port angle and width, the length of cavity, the axial location of each cavity, and the number of cavities. Three-dimensional Reynolds-averaged Navier-Stokes equations with shear stress transport turbulence model were used for aerodynamic analysis of the centrifugal compressor with discrete cavities. The hexahedral grid was used in impeller domain and tetrahedral grid was used in volute and inclined discrete cavities. The numerical results for the adiabatic efficiency and the total pressure ratio (inlet to outlet) showed good agreements with experimental data. It was found that inclination of the discrete cavities further increased the stall margin without loss of efficiency compared to the uninclined discrete cavities.

THE INFLUENCE OF HEMODYNAMICS ON THE ULCERATION PLAQUES OF CAROTID ARTERY STENOSIS

The further rupture of atherosclerotic ulceration plaque is one of the main triggers of the carotid ischemic stroke. However, the abnormal hemodynamics is not well addressed yet. A lesion-based computational fluid dynamic (CFD) analysis is proposed to investigate the complex hemodynamic change of the ulceration plaque that prevails in patients. The 3D models including eight groups of ulcerations (six groups with single ulceration and two groups with two consecutive ulcerations), were reconstructed based on the computer tomography (CT) images, and the tetrahedral grid was taken to mesh the models with the appropriate numbers. After setting the boundary conditions, numerical simulation was carried out to analyze the pulsatile blood flow in the models. The complex flow in the vicinity of the ulcerations directly leads to a significant effect on the distribution of the wall shear stress (WSS). WSS is respectively from 3.29 to 35.41 Pa at the upstream, from 11.90 to 41.85 Pa at the downstream ulceration, and 18.60 and 30.60 Pa in the area between the two consecutive ulcerations. The rupture from these regions could cause the further rupture of ulceration plaques, particularly at the downstream ulceration and the area between the two consecutive ulcerations. The twisting and the curling of the flow at the ulcerations can lead to thrombosis which may break free later and go through the downstream stenosis by the effect of the flow. The different degrees of WSS in downstream and upstream ulcerations will damage the ulceration on the plaque because of pulling and stretching forces at the ulcerations. Furthermore, high wall shear stress gradient (WSSG) also increases the risk of the further rupture. Our study gives a better understanding in the further rupture mechanism of ulceration plaques and provides the information of the location of thrombosis after aggravated rupturing, which can be referred by surgeons to improve the surgical planning.

Numerical Research on the Change Regularity of S Series Airfoil Tip Vortex

This paper take the impeller of S series airfoil for instance, in view of the complex flow field which is in the condition for the optimum attack angle of design wind velocity with tip vortex, presents a new generating strategy of grid based on controlling gradient method which takes the non-uniform tetrahedral grid with gradient gradual change in the near blade wall flow field. The transition layer grid which is in the development from body-fitted field to the middle of the domain having relatively high density of grid contrast with the far flow field can well capture the size and location of tip vortex, and find that the decay rate of the vorticity magnitude of tip vortex of S series impeller is more quickly than the tip vortex of traditional airfoil impeller. As well as find a fraction of central vortex and tip vortex shaded into each other in the far field and Doppler effect in the downstream. Because the numerical experiment and analysis showed that through controlling gradient change of grid can get high precision of calculating results, can also get S series impeller had higher efficiency in conversion of wind energy contrast with NACA series impeller, so the generating strategy of grid is reasonable and effective.

Study on Installation Position of Sewage Treatment Mixer

According to the problem that how to choose the installation position for sewage treatment mixer was uncertain, the flow field in the sewage treatment pool was simulated by the software FLUENT 6.3, using unstructured tetrahedral grid, moving coordinate system technology, k ∼ ε turbulence model and the SIMPLE algorithm. The distribution of velocity gradient in the whole pool was analyzed, and the flow field was compared at the different installation angles of sewage treatment mixer. The results show that the fluid flows along the axial direction of sewage treatment mixer, and diffuses along the radial direction. The stirring circulation is evident when the installation deviates from the narrow side, and the flow velocity of the whole pool is relatively uniform and greater than 0.3m/s. It is consistent with their work requirements, which not only improves the efficiency, but also saves costs.