Boundaries Influence on the Flow Field Around an Oscillating Sphere

2013 ◽  
Author(s):  
Domenica Mirauda ◽  
Antonio Volpe Plantamura ◽  
Stefano Malavasi
Keyword(s):  
Free Surface ◽  
Flow Field ◽  
Boundary Conditions ◽  
Damping Ratio ◽  
Water Channel ◽  
Open Water ◽  
Free Surface Flows ◽  
The Body ◽  
Sphere Diameter ◽  
Oscillating Sphere

This work analyzes the effects of the interaction between an oscillating sphere and free surface flows through the reconstruction of the flow field around the body and the analysis of the displacements. The experiments were performed in an open water channel, where the sphere had three different boundary conditions in respect to the flow, defined as h* (the ratio between the distance of the sphere upper surface from the free surface and the sphere diameter). A quasi-symmetric condition at h* = 2, with the sphere equally distant from the free surface and the channel bottom, and two conditions of asymmetric bounded flow, one with the sphere located at a distance of 0.003m from the bottom at h* = 3.97 and the other with the sphere close to the free surface at h* = 0, were considered. The sphere was free to move in two directions, streamwise (x) and transverse to the flow (y), and was characterized by values of mass ratio, m* = 1.34 (ratio between the system mass and the displaced fluid mass), and damping ratio, ζ = 0.004. The comparison between the results of the analyzed boundary conditions has shown the strong influence of the free surface on the evolution of the vortex structures downstream the obstacle.

Hybrid SW-NS SPH models using open boundary conditions for simulation of free-surface flows

2020 ◽  
Vol 196 ◽  
pp. 106845 ◽  
Author(s):  
Xingye Ni ◽  
Weibing Feng ◽  
Shichang Huang ◽  
Xin Zhao ◽  
Xinwen Li
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Free Surface Flows ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Surface Flows

Numerical simulations of nonlinear axisymmetric flows with a free surface

1987 ◽  
Vol 178 ◽  
pp. 195-219 ◽  
Author(s):  
Douglas G. Dommermuth ◽  
Dick K. P. Yue
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Free Surface Flows ◽  
Boundary Integral ◽  
The Body ◽  
Special Treatment ◽  
Computational Domain ◽  
Vortex Sheets

A numerical method is developed for nonlinear three-dimensional but axisymmetric free-surface problems using a mixed Eulerian-Lagrangian scheme under the assumption of potential flow. Taking advantage of axisymmetry, Rankine ring sources are used in a Green's theorem boundary-integral formulation to solve the field equation; and the free surface is then updated in time following Lagrangian points. A special treatment of the free surface and body intersection points is generalized to this case which avoids the difficulties associated with the singularity there. To allow for long-time simulations, the nonlinear computational domain is matched to a transient linear wavefield outside. When the matching boundary is placed at a suitable distance (depending on wave amplitude), numerical simulations can, in principle, be continued indefinitely in time. Based on a simple stability argument, a regriding algorithm similar to that of Fink & Soh (1974) for vortex sheets is generalized to free-surface flows, which removes the instabilities experienced by earlier investigators and eliminates the need for artificial smoothing. The resulting scheme is very robust and stable.For illustration, three computational examples are presented: (i) the growth and collapse of a vapour cavity near the free surface; (ii) the heaving of a floating vertical cylinder starting from rest; and (iii) the heaving of an inverted vertical cone. For the cavity problem, there is excellent agreement with available experiments. For the wave-body interaction calculations, we are able to obtain and analyse steady-state (limit-cycle) results for the force and flow field in the vicinity of the body.

A Localized Finite-Element Method for Two-Dimensional Steady Potential Flows with a Free Surface

1978 ◽  
Vol 22 (04) ◽  
pp. 216-230
Author(s):  
Kwang June Bai
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Boundary Conditions ◽  
Complex Geometry ◽  
The Body ◽  
Finite Domain ◽  
Surface Boundary ◽  
Two Dimensional ◽  
Test Functions ◽  
Infinite Domain

A numerical method is presented for solving two-dimensional uniform flow problems with a linearized free-surface boundary condition. The boundary-value problem governed by Laplace's equation is replaced by a weak formulation (also known as Galerkin's method) with certain essential boundary conditions. The infinite domain of the fluid is reduced to a finite domain by utilizing known solution spaces in certain subdomains. The bases for the trial and test functions are chosen from the same subspace of the polynomial function space in the reduced subdomain. The essential boundary conditions are properly taken into account by an unconventional choice of the basis for the trial functions, which is different from that for the test functions in other subdomains. This method is applied to two-dimensional steady flow past a submerged elliptic section, a hydrofoil at an arbitrary angle of attack, and a bump on the bottom. In each example the body boundary condition is satisfied exactly. Both subcritical and supercritical flows are treated. We present the numerical results of wave resistance, lift force, moment, circulation strength, and flow blockage parameter. The computed pressure distributions on the hydrofoil and wave profiles are shown. The test results obtained by the present method agree very well with existing results. The main advantage of this method is that any complex geometry of the boundary can be easily accommodated.

Water-Channel Analog to High-Velocity Combustion

1953 ◽  
Vol 20 (1) ◽  
pp. 115-121
Author(s):  
A. K. Oppenheim
Keyword(s):  
Flow Field ◽  
Boundary Conditions ◽  
Combustion Front ◽  
Water Channel ◽  
Combustion System ◽  
Dynamic Boundary Conditions ◽  
Proper Selection ◽  
Dynamic Boundary ◽  
Analogous System ◽  
Selection Of

Abstract This paper is a sequel to one presented in 1951, by the author (1). It was shown that during the development of detonation, the combustion zone which appears first in a unidimensional flow field as a single discontinuity, is later transformed into an unsteady, double discontinuity system, and it was demonstrated that such a transformation is necessary because of the restrictions imposed on the system by the dynamic boundary conditions. In the water channel the combustion-front discontinuity is simulated by a unidimensional source formed by admitting water from the bottom. By a proper selection of state parameters analogous relationships are derived to those between pressure and specific volume in a gaseous combustion system. Thus the consequences of restrictions imposed by dynamic boundary conditions on the propagation of combustion are illustrated in an analogous system which, being simpler in nature, is easier to understand. Moreover, the water-channel analog is utilized as an illustrative model of a system where controlled, stationary detonation could be achieved.

Effects of Waves on the Boundary Layer of a Surface-Piercing Body

1986 ◽  
Vol 30 (04) ◽  
pp. 256-274
Author(s):  
Frederick Stern
Keyword(s):  
Boundary Layer ◽  
Free Surface ◽  
Boundary Conditions ◽  
Turbulent Flow ◽  
Significant Influence ◽  
Small Amplitude ◽  
The Body ◽  
Stokes Wave ◽  
Surface Boundary ◽  
Surface Boundary Conditions

The boundary-value problem for the boundary layer of a surface-piercing body is formulated in a rigorous manner in which proper consideration is given to the viscous-fluid free-surface boundary conditions. Simplifications that are appropriate for small-amplitude waves are investigated. To this end, order-of-magnitude estimates are derived for the flow field in the neighborhood of the body-boundary-layer/free-surface juncture. It is shown that, for laminar flow, the parameter Ak/ϵ, where Ak is the wave steepness and ϵ is the nondimensional boundary-layer thickness, is important for characterizing the flow. In particular, for Ak/ϵ sufficiently large such that the free-surface boundary conditions have a significant influence a consistent formulation requires the solution of higher-order viscous-flow equations. For turbulent flow, these conclusions cannot be reached with the same degree of certainty. Numerical results are presented for the model problem of a combination Stokes-wave/flat plate. For this initial investigation, the usual thin-boundary-layer equations were solved using a three-dimensional implicit finite-difference method. The calculations are for laminar and turbulent flow and both demonstrate and quantify the influence of waves on boundary-layer development. Calculations were made using both the small-amplitude-wave and more approximate free-surface boundary conditions. Both the external-flow pressure gradients and the free-surface boundary conditions are shown to have a significant influence. The former influence penetrates to a depth of about half the wavelength and the latter is confined to a region very close to the free surface.

scholarly journals A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels

2017 ◽  
Vol 64 (1) ◽  
pp. 17-35 ◽  
Author(s):  
Yebegaeshet T. Zerihun
Keyword(s):  
Free Surface ◽  
Hydrostatic Pressure ◽  
Flow Field ◽  
Stokes Equations ◽  
Numerical Study ◽  
Free Surface Flows ◽  
Vertical Acceleration ◽  
Novel Approach ◽  
Pressure Profiles ◽  
Turbulent Characteristics

AbstractThe flow field of many practical open channel flow problems, e.g. flow over natural bed forms or hydraulic structures, is characterised by curved streamlines that result in a non-hydrostatic pressure distribution. The essential vertical details of such a flow field need to be accounted for, so as to be able to treat the complex transition between hydrostatic and non-hydrostatic flow regimes. Apparently, the shallow-water equations, which assume a mild longitudinal slope and negligible vertical acceleration, are inappropriate to analyse these types of problems. Besides, most of the current Boussinesq-type models do not consider the effects of turbulence. A novel approach, stemming from the vertical integration of the Reynolds-averaged Navier-Stokes equations, is applied herein to develop a non-hydrostatic model which includes terms accounting for the effective stresses arising from the turbulent characteristics of the flow. The feasibility of the proposed model is examined by simulating flow situations that involve non-hydrostatic pressure and/or nonuniform velocity distributions. The computational results for free-surface and bed pressure profiles exhibit good correlations with experimental data, demonstrating that the present model is capable of simulating the salient features of free-surface flows over sharply-curved overflow structures and rigid-bed dunes.

Mixing coefficient for ice-covered and free-surface flows

1985 ◽  
Vol 12 (3) ◽  
pp. 521-526 ◽  
Author(s):  
Y. L. Lau
Keyword(s):  
Free Surface ◽  
Open Water ◽  
Free Surface Flows ◽  
Flow Conditions ◽  
Surface Flows ◽  
Transverse Mixing ◽  
Mixing Coefficient ◽  
Natural Streams ◽  
River Reach ◽  
Selection Of

Dispersion experiments were conducted in four river reaches under both open-water and ice-covered flow conditions. The data were used to obtain the transverse mixing coefficient and to investigate which dimensionless mixing coefficient should be used for ice-covered flows. The results also demonstrate that the sinuosity of a river reach affects the value of the mixing coefficient and can thus be used to guide the selection of mixing coefficient for natural streams.

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