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G X Wu - One of the best experts on this subject based on the ideXlab platform.
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free surface gravity flow due to a Submerged Body in uniform current
Journal of Fluid Mechanics, 2020Co-Authors: Yuriy A Semenov, G X WuAbstract:The hydrodynamic problem of a Body Submerged beneath a free surface in a current is considered. The mathematical model used is based on the velocity potential theory with fully nonlinear boundary conditions. The integral hodograph method used previously in a simply connected domain is extended for the present problem to a doubly connected domain. Analytical expressions for the complex velocity and for the complex potential are derived in a rectangular region in a parameter plane, involving the theta functions. The boundary-value problem is transformed into a system of two integral equations for the velocity modulus on the free surface and for the slope of the Submerged Body surface in the parameter plane, which are solved through the successive approximation method. Case studies are undertaken both for a smooth Body and for a hydrofoil with a sharp edge. Results for the free surface shape, pressure distribution as well as resistance and lift are presented for a wide range of Froude numbers and depths of submergence. It further confirms that at each submergence below a critical value there is a range of Froude numbers within which steady solution may not exist. This range increases as the submergence decreases. This applies to both a smooth Body and a hydrofoil. At the same time it is found that at any Froude number beyond a critical value the wave amplitude and the resistance decrease as the Body approaches the free surface. In these cases nonlinear effects become more pronounced.
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simulation of complete water exit of a fully Submerged Body
Journal of Fluids and Structures, 2015Co-Authors: B Y Ni, G X Wu, Aman ZhangAbstract:Abstract The whole process of water exit of a fully-Submerged rigid Body is simulated using the boundary-element method for the velocity potential. A numerical procedure is proposed for the free-surface breakup as well as for Body detachment from water. Convergence and sensitivity studies have been conducted for the procedure and consistent results have been achieved. Detailed simulations are undertaken for a spheroid emerging and departing from water. Results are provided for pressure and force on the Body, as well as the step-by-step free surface deformation, including the development of the jet and formation of the cavity. The effect of Froude number is investigated, as well as the Body shape in terms of the ratio of its horizontal and vertical dimensions.
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water flow due to rapid part Submerged Body movement
Fluid Mechanics and its Applications 62 pp. 177-185. (2001), 2001Co-Authors: L Li, D P Papadopolous, F T Smith, G X WuAbstract:Water flow and free surface shapes induced by a rapidly plunging thin Body are studied, including effects of gravity and slippage.
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Wave radiation by a Submerged source undergoing large amplitude periodic motion
Journal of Engineering Mathematics, 1994Co-Authors: G X WuAbstract:Equations are derived to calculate the water waves radiation at infinity bya Submerged source undergoing large amplitude motion. These equations do not require the full solution of the velocity potential itself, as demonstrated by a number of two- and three-dimensional examples. The results obtained are used to derive a far field equation for calculating the steady force (the drift force) on a Submerged Body undergoing large amplitude motion. It is concluded that the equations derived are useful to cases such as a deeply Submerged Body for which the source distribution may be taken as those obtained in an unbounded fluid domain.
Allen T Chwang - One of the best experts on this subject based on the ideXlab platform.
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unsteady free surface waves due to a Submerged Body moving in a viscous fluid
Physical Review E, 2005Co-Authors: D Q Lu, Allen T ChwangAbstract:Unsteady viscous free-surface waves generated by a three-dimensional Submerged Body moving in an incompressible fluid of infinite depth are investigated analytically. It is assumed that the Body experiences a Heaviside step change in velocity at the initial instant. Two categories of the velocity change, sid from zero to a constant and siid from a constant to zero, will be analyzed. The flow is assumed to be laminar and the Submerged Body is mathematically represented by an Oseenlet. The Green functions for the unbounded unsteady Oseen flows are derived. The solutions in closed integral form for the wave profiles are given. By employing Lighthill’s two-stage scheme, the asymptotic representations of free-surface waves in the far wake for large Reynolds numbers are derived. It is shown that the effects of viscosity and submergence depth on the free-surface wave profiles are respectively expressed by the exponential decay factors. Furthermore, the unsteady wave system due to the suddenly starting Body consists of two families of steady-state waves and two families of nonstationary waves, which are confined within a finite region. As time increases, the waves move away from the Body and the finite region extends to an infinite V-shaped region. It is found that the nonstationary waves are the transient response to the suddenly started motion of the Body. The waves due to a suddenly stopping Body consist of a transient component only, which vanish as time approaches infinity.
D Q Lu - One of the best experts on this subject based on the ideXlab platform.
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unsteady free surface waves due to a Submerged Body moving in a viscous fluid
Physical Review E, 2005Co-Authors: D Q Lu, Allen T ChwangAbstract:Unsteady viscous free-surface waves generated by a three-dimensional Submerged Body moving in an incompressible fluid of infinite depth are investigated analytically. It is assumed that the Body experiences a Heaviside step change in velocity at the initial instant. Two categories of the velocity change, sid from zero to a constant and siid from a constant to zero, will be analyzed. The flow is assumed to be laminar and the Submerged Body is mathematically represented by an Oseenlet. The Green functions for the unbounded unsteady Oseen flows are derived. The solutions in closed integral form for the wave profiles are given. By employing Lighthill’s two-stage scheme, the asymptotic representations of free-surface waves in the far wake for large Reynolds numbers are derived. It is shown that the effects of viscosity and submergence depth on the free-surface wave profiles are respectively expressed by the exponential decay factors. Furthermore, the unsteady wave system due to the suddenly starting Body consists of two families of steady-state waves and two families of nonstationary waves, which are confined within a finite region. As time increases, the waves move away from the Body and the finite region extends to an infinite V-shaped region. It is found that the nonstationary waves are the transient response to the suddenly started motion of the Body. The waves due to a suddenly stopping Body consist of a transient component only, which vanish as time approaches infinity.
Yuriy A Semenov - One of the best experts on this subject based on the ideXlab platform.
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free surface gravity flow due to a Submerged Body in uniform current
Journal of Fluid Mechanics, 2020Co-Authors: Yuriy A Semenov, G X WuAbstract:The hydrodynamic problem of a Body Submerged beneath a free surface in a current is considered. The mathematical model used is based on the velocity potential theory with fully nonlinear boundary conditions. The integral hodograph method used previously in a simply connected domain is extended for the present problem to a doubly connected domain. Analytical expressions for the complex velocity and for the complex potential are derived in a rectangular region in a parameter plane, involving the theta functions. The boundary-value problem is transformed into a system of two integral equations for the velocity modulus on the free surface and for the slope of the Submerged Body surface in the parameter plane, which are solved through the successive approximation method. Case studies are undertaken both for a smooth Body and for a hydrofoil with a sharp edge. Results for the free surface shape, pressure distribution as well as resistance and lift are presented for a wide range of Froude numbers and depths of submergence. It further confirms that at each submergence below a critical value there is a range of Froude numbers within which steady solution may not exist. This range increases as the submergence decreases. This applies to both a smooth Body and a hydrofoil. At the same time it is found that at any Froude number beyond a critical value the wave amplitude and the resistance decrease as the Body approaches the free surface. In these cases nonlinear effects become more pronounced.
Johan F. Malmliden - One of the best experts on this subject based on the ideXlab platform.
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A fast iterative method to compute the flow around a Submerged Body
Mathematics of Computation, 1996Co-Authors: Johan F. Malmliden, N. Anders PeterssonAbstract:The authors develop an efficient iterative method for computing steady linearized potential flow around a Submerged Body moving in a liquid of finite constant depth. In this paper they restrict the presentation to the two-dimensional problem, but the method is readily generalizable to the three-dimensional case, i.e., the flow in a canal. The problem is indefinite, which makes the convergence of most iterative methods unstable. To circumvent this difficulty, the authors decompose the problem into two more easily solvable subproblems and form a Schwarz-type iteration to solve the original problem. The first subproblem is definite and can therefore be solved by standard iterative methods. The second subproblem is indefinite but has no Body. It is therefore easily and efficiently solvable by separation of variables. The authors prove that the iteration converges for sufficiently small Froude numbers. In addition, they present numerical results for a second-order accurate discretization of the problem. They demonstrate that the iterative method converges rapidly, and that the convergences rate improves when the Froude number decreases. They also verify numerically that the convergence rate is essentially independent of the grid size. 20 refs., 6 figs., 10 tabs.
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computing the flow around a Submerged Body using composite grids
Journal of Computational Physics, 1993Co-Authors: Anders N Petersson, Johan F. MalmlidenAbstract:The subject of this paper is an accurate numerical method for solving the linear two-dimensional steady potential flow around a Body which moves in a liquid of finite constant depth at constant speed and distance below the free surface. The differential equation is discretized by a second-order accurate finite difference scheme on a composite grid. The composite grid consists of two overlapping component grids; one curvilinear grid close to the Body and one Cartesian grid which covers the surrounding liquid. To solve the problem numerically, the infinite domain is truncated to finite length. The inflow and outflow boundary conditions are formed by making an eigenfunction expansion of the solution ahead of and behind the Body. Each eigenfunction is required to be bounded and satisfy the upstream condition at infinity. This is imposed by functional relations between the solution and its normal derivative at the inflow and outflow boundaries. The method is carefully validated and the computed solutions are found to be in very good agreement with existing results.
