Evaluation Of Hydrodynamic Forces Research Articles

Evaluation of hydrodynamic forces on the impeller of an axial blood pump using computational fluid dynamics

The work is aimed at determining the hydrodynamic forces and moments acting on the impeller of the axial blood pump using computational fluid dynamics (CFD). ANSYS CFX software was used for this purpose. The problem solved as steady state with k-ε turbulence. Blood is considered as a Newtonian fluid with constant dynamic viscosity value of 0.00345 Pas for ranges of angular impeller velocities (6000 – 15000 rpm) and volume flow rates (1 - 6 lmin−1). Radial force and torque diagrams were plotted as the result of the numerical experiment.

Immersed boundary–simplified thermal lattice Boltzmann method for incompressible thermal flows

An immersed boundary–simplified lattice Boltzmann method (IB-STLBM) is proposed in this paper for the simulation of incompressible thermal flows with immersed objects. The fractional step technique is adopted to resolve the problem in two successive steps. In the predictor step, the simplified thermal lattice Boltzmann method (STLBM) is utilized to resolve the intermediate flow variables without considering the immersed objects. The STLBM is advantageous over the conventional thermal lattice Boltzmann method (TLBM) in memory cost, boundary treatment, and numerical stability. In the corrector step, the boundary condition-enforced immersed boundary method (IBM) is used to give correction values of velocity and temperature for accurate interpretation of the Dirichlet boundary conditions on the surface of the immersed objects. Based on the present IBM, some novel strategies can be applied in the evaluation of hydrodynamic forces or thermal parameters of the immersed objects. Five numerical examples are presented for comprehensive validation of the accuracy and robustness of IB-STLBM in various two- and three-dimensional thermal flow problems.

A CFD approach to rubble mound breakwater design

The paper provides some developments of a numerical approach (“Numerical Calculation of Flow Within Armour Units”, FWAU) to the design of rubble mound breakwaters. The hydrodynamics of wave induced flow within the interstices of concrete blocks is simulated by making use of advanced, but well tested, CFD techniques to integrate RANS equations.While computationally very heavy, FWAU is gaining ground, due to its obvious advantages over the “porous media”, i.e. the possibility of accounting for the highly non stationary effects, the reduced need of ad hoc calibration of filtration parameters and also – in perspective – the evaluation of hydrodynamic forces on single blocks. FWAU however is a complex technique, and in order to turn it into a practical design tool, a number of difficulties have to be overcome.The paper presents recent results about this validation, as well as insight into fluid dynamical aspects.

Evaluation of hydrodynamic forces on turbine ring gate during emergency shutdown process

This work uses numerical methods to investigate the hydrodynamic forces that act on a turbine ring gate during emergency shutdown. Accurately predicting the hydrodynamic forces on such gates is important because the forces constitute a design criterion of ring gates, especially in the case of the downward-pulling hydrodynamic force, which directly affects the opening or closing of the gate. In this article, we use Fluent, which is a computational fluid dynamics code, to simulate the flow patterns around the ring gate and to calculate the hydrodynamic forces on the gate. We numerically simulate the three-dimensional unsteady turbulence over the entire flow passage of the turbine. The numerical results show that the hydrodynamic forces are induced mainly by flow acceleration under the bottom surface of the ring gate. When the ring gate is at 90% closing position, the downward-pulling hydrodynamic force is maximal; near the completely closed position, the hydrodynamic force is more sensitive to the position of the ring gate. This investigation of the hydrodynamic forces that act on the ring gates provides the theoretical basis for determining the operational capacity and the optimal design of ring gates.

LATTICE BOLTZMANN SIMULATION OF THE MOTION OF SPHERICAL PARTICLES IN STEADY POISEUILLE FLOW

A technique, based on the stress-integration method, for the evaluation of hydrodynamic forces on solid boundaries is proposed to simulate the solid-fluid flow systems in three dimensions in lattice Boltzmann simulations. The accuracy of the scheme is demonstrated by simulating the sphere migrating in a pressure-driven Newtonian fluid flow in a cylindrical tube. The numerical simulation results recover the Segré–Silberberg effect. Using this scheme, we investigate the behavior of a pair of spheres in a tube Poiseuille flow. Oscillatory states are observed for two spheres with different radii placed on opposite sides. The simulation results show that the present model is an effective and efficient direct numerical simulation method for simulating particle motions in fluid flows at finite Reynolds numbers in three dimensions.

Triangular Configuration Tension Leg Platform behaviour under random sea wave loads

This study investigates the dynamic response of a Triangular Configuration Tension Leg Platform (TLP) under random sea wave loads. The random wave has been generated synthetically using the Monte-Carlo simulation with the Peirson–Moskowitz (P–M) spectrum. Diffraction effects and second-order wave forces have not been considered. The evaluation of hydrodynamic forces is carried out using the modified Morison equation with water particle kinematics evaluated using Airy's linear wave theory. Wave forces are taken to be acting in the surge degree-of-freedom. The effect of coupling of various structural degrees-of-freedom (surge, sway, heave, roll, pitch and yaw) on the dynamic response of the TLP under random wave loads is studied. Parametric studies for random waves with different H s and T z under the presence of current have also been carried out. For the orientation of the TLP, surge, heave and pitch degrees-of-freedom responses are influenced significantly. The surge power spectral density function (PSDF) indicates that the mean square response is affected by the amplification at the natural frequency of the surge degree-of-freedom and also at the peak frequency of the wave loading. The PSDF of the heave response shows higher peak values near the surge frequency and near the peak frequency of the wave loading. Surge response, therefore, influences heave response to the maximum. Variable submergence seems to be a major source of nonlinearity and significantly enhances the responses in surge, heave and pitch degrees-of-freedom. In the presence of current, the response behaviour of the TLP is altered significantly introducing a non-zero mean response in all degrees-of-freedom.

A numerical method for the evaluation of hydrodynamic forces of translating bodies under a free surface

A numerical method for the evaluation of hydrodynamic forces of translating bodies under a free surface

On the Prediction of Hydroelastic Behaviours of a Huge Floating Structure in Waves

A prediction method of the hydroelastic behaviors of a very large floating structure (VLFS) that may be used for such purposes as an international airport or an offshore city is prensented. In the present analysis the structure is divided into a number of small structures and the continuous deformation of the structure is represented by the succession of the discrete displacement of each small structure. Each structure is treated as if it were an independent floating body while the structural constraints are taken into account as additional restoring forces on its motions. The hydrodynamic interactions among the divided structures are accounted for in the evaluation of hydrodynamic forces by the method of Kagemoto & Yue (1986) once their complex motion amplitudes are known. The motion amplitudes are, in turn, determined from the equation of motions which are excited by the hydrodynamic forces. Therefore by solving the equations of hydrodynamic interactions and those of motions simultaneously, the hydroelastic interactions are properly accounted for and the motions of each small structure, which represent the local behaviours of the total VLFS, are determined in one computation.The effect of the present method is discussed by comparing predicted dynamic behaviors of elastic floating structures with their experimental results, and the method can be used to carry out the hydroelastic analysis of a VLFS through several example calculations.

A dynamic two-phase flow model for a purification plant

A mathematical model for the flow through the siphon of a sewage purification machine is presented. The model is based on the average unidirectional flow velocities of the two phases (water and bubbles of air), the evaluation of hydrodynamic forces corresponding to the plant's geometry, and on estimates of the mechanical interaction of the two phases. Data from experiments with an industrial machine are used to identify the model parameters and a comparison of the model's trajectories with the experimental records is given.