1,595 research outputs found
A simulation of free surface waves for incompressible two-phase flows using a curvilinear level set formulation
No full textA level set formulation in a generalized curvilinear coordinate is developed to simulate the free surface waves generated by moving bodies or the sloshing of fluid in a container. The Reynolds-averaged Navier-Stokes (RANS) equations are modified to account for variable density and viscosity in two-phase (i.e. water-air) fluid flow systems. A local level set method is used to update the level set function and a least square technique adopted to re-initialize it at each time step. To assess the developed algorithm and its versatility, a selection of different fluid-structure interaction problems are examined, i.e. an oscillating flow in a two-dimensional square tank, a breaking dam involving different density fluids, sloshing in a two-dimensional rectangular tank and a Wigley ship hull travelling in calm water
Numerical simulation of liquid sloshing in LNG tanks using a compressible two-fluid flow model
No full textIn this investigation the Reynolds-Averaged Navier-Stokes (RANS)
equations are modified to account for variable density and viscosity of
the two-fluids flow (i.e. water-air), assuming both fluids compressible.
By introducing a preconditioner, the governing equations in terms of
primitive variables are solved for both fluids in a unified manner. The
non-conservative implicit Split Coefficient Matrix Method (SCMM) is
modified to approximate convective flux vectors in the dual time
formulation. The free surface waves inside the tank, due to sloshing, are
implicitly captured by using a level set approach.
The method is illustrated through applications to rectangular and
chamfered tanks subject to sway or roll motions at different filling
levels and excitation conditions (i.e. amplitude and frequency of
oscillation). Comparisons are made between calculated and
experimental pressures, where available
Numerical simulation of liquid sloshing in a partially filled container with inclusion of compressibility effects
Get PDFA numerical scheme of study is developed to model compressible two-fluid flows simulating liquid sloshing in a partially filled tank. For a two-fluid system separated by an interface as in the case of sloshing, not only a Mach-uniform scheme is required, but also an effective way to eliminate unphysical numerical oscillations near the interface. By introducing a preconditioner, the governing equations expressed in terms of primitive variables are solved for both fluids (i.e. water, air, gas etc.) in a unified manner. In order to keep the interface sharp and to eliminate unphysical numerical oscillations in unsteady fluid flows, the non-conservative implicit Split Coefficient Matrix Method (SCMM) is modified to construct a flux difference splitting scheme in the dual time formulation. The proposed numerical model is evaluated by comparisons between numerical results and measured data for sloshing in an 80% filled rectangular tank excited at resonance frequency. Through similar comparisons, the investigation is further extended by examining sloshing flows excited by forced sway motions in two different rectangular tanks with 20% and 83% filling ratios. These examples demonstrate that the proposed method is suitable to capture induced free surface waves and to evaluate sloshing pressure loads acting on the tank walls and ceiling
Empirical likelihood confidence intervals for complex sampling designs
No full textWe define an empirical likelihood approach which gives consistent design-based confidence intervals which can be calculated without the need of variance estimates, design effects, resampling, joint inclusion probabilities and linearization, even when the point estimator is not linear. It can be used to construct confidence intervals for a large class of sampling designs and estimators which are solutions of estimating equations. It can be used for means, regressions coefficients, quantiles, totals or counts even when the population size is unknown. It can be used with large sampling fractions and naturally includes calibration constraints. It can be viewed as an extension of the empirical likelihood approach to complex survey data. This approach is computationally simpler than the pseudoempirical likelihood and the bootstrap approaches. The simulation study shows that the confidence interval proposed may give better coverages than the confidence intervals based on linearization, bootstrap and pseudoempirical likelihood. Our simulation study shows that, under complex sampling designs, standard confidence intervals based on normality may have poor coverages, because point estimators may not follow a normal sampling distribution and their variance estimators may be biased.<br/
An anti-diffusive method for computational modelling of sloshing in an LNG tank
No full textA new VOF method is presented comprising of a combination of the first order limited downwind scheme with other high order accurate schemes. The method developed is characterized by keeping a sharp interface but avoids complicated geometrical reconstruction as occurs in most volume tracing algorithms. To demonstrate the accuracy and robustness of the method, a selection of numerical experiments are presented involving a pure advection problem, a water wave impact caused by a dam breaking and liquid sloshing in a partially filled tank
Soil morphological variations on the Taoyuan terrace, Northwestern Taiwan: Role of topography and groundwater.
No full text
A mixed finite-element finite-difference method for nonlinear fluid-structure interaction dynamics. I. Fluid-rigid structure interaction
No full textA mixed finite-element finite-difference numerical method is developed to calculate nonlinear fluid-solid interaction problems. In this study, the structure is assumed to be rigid with large motion and the fluid flow is governed by nonlinear, viscous or non-viscous, field equations with nonlinear boundary conditions applied to the free surface and fluid-solid interaction interfaces. A moving coordinate system fixed at a point in the structure is used to describe the fluid flow, and for numerical analysis purposes, an arbitrary Lagrangian-Eulerian mesh system is constructed relative to this moving system. This provides a convenient method of overcoming the difficulties of matching fluid meshes with large solid motion. Nonlinear numerical equations describing nonlinear fluid-solid interaction dynamics are derived through a numerical discretization scheme of study. A coupling iteration process is used to solve these numerical equations. A selection of numerical examples illustrates the developed mathematical model and through numerical simulations it is shown that the proposed approach is practical and useful
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