1,721,106 research outputs found
Internal waves produced by a submerged slender body moving in a stratified fluid
No full textSolutions are obtained for the velocity components generated by a singularity moving horizontally in a fluid of constant Brunt-Väisälä frequency. A radiation condition is enforced using an artificial damping mechanism. Two solutions are combined to produce a Rankine ovoid and a continuous line distribution is used to model a prolate spheroid. The distribution velocity field generated by the body displays the characteristics associated with the propagation of internal waves. The disturbance velocities calculated on the fluid’s surface are compared with those obtained from a three layer model. The patterns produced display significant differences
Numerical simulations of the hydrodynamic responses of a body interacting with wave and current over a sloping seabed
No full textThe interaction influences of a two dimensional incident wave and current on the hydrodynamic responses of a floating or fixed body in the presence of a flat or sloping seabed are examined. A solution of this wave-current-seabed scenario is determined by considering steady, diffraction, and reflection potential problems individually and through their combinations. All these components are formulated using a boundary element model involving a continuous Rankine source method subject to appropriate boundary conditions. The validity of the mathematical model and accompanying numerical scheme of study are assessed by comparisons with available published data. Numerical results show that either an incoming waves, current or seabed plays a significant role affecting the body hydrodynamic responses for both fixed and freely floating bodies.</p
General theorems and generalized variational principles for nonlinear elastodynamics
No full textGeneralized variational principles with 11 - arguments, 9 - arguments, 5 - arguments, 3 - arguments and the variational principles of action of potential/complementary energy are developed to solve initial-value, final-value and two time boundary-value problems in nonlinear elastodynamic systems. The displacement gradient is decomposed into a symmentric part D subscript ij and a rotation part W subscript ij = -e subscript ijk W subscript k which are variables in functionals.The theoretical approach is illustrated by examining one-dimensional elastostatic and elastodynamic problems. In the former, it is shown that by solving for the displacement gradient u subscript ij as a function of the stress tensor ? subscript ij from the constraint equations of the variational principle of complementary energy, the functional of the variational principle of complementary energy can be expressed in a form involving the single argument ? subscript ij only.An application of the variational principles is illustrated in an elastodynamic final-value problem. Complementing these examples is a discussion indicating how other generalized variational principles may be deduced and how numerical schemes of study may be enhanced through a matrix decomposition of the displacement gradient u subscript ij
A mixed finite element - finite difference method for nonlinear fluid - solid interaction dynamics
No full textA 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
Variational principles of nonlinear fluid-solid interaction dynamics in the Arbitrary-Lagarange-Eulerian description
No full textTrapped internal waves produced by a submerged slender body moving in a stratified fluid
No full textAnalytical solutions are obtained for the disturbance generated by a singularity moving horizontally in a layer of a three layer fluid, each layer possessing a constant Brunt-Väisälä frequency. A radiation condition is enforced using an artificial damping mechanism. The singularity solution is developed into a continuous source/sink line distribution which is used to model a prolate spheroid. The disturbance velocity field generated by the body displays the characteristics associated with the propagation of trapped internal waves. The disturbance calculated on the fluid's surface is compared with those obtained using a constant density three layer fluid model and a constant Brunt-Väisälä frequency model. The patterns produced by the current model described herein display significant departures from previous patterns
Interfacial waves produced by a submerged body moving in a layered fluid
No full textVelocity potential solutions are derived for an arbitrary shaped body moving horizontally in a fluid system consisting of three layers, the lower layer of infinite depth. The body may be located in any one of the three layers. The boundary conditions on the free surface and interface are linearised and a radiation condition imposed. Expressions for the far field free surface and interface elevations are derived. A three dimensional extension of Lagally's theory provides a method which allows the wave resistance of the body to be determined. The application of a slender body approximation permits the derivation of analytical expressions for the elevations and wave resistance. Plots of the far field free surface and interface wave systems are presented when the body is located in each layer. The wave resistance of a prolate spheroid length L to diameter d for a series of L/d ratios is calculated over a Froude number range. The "dead water" effect being apparent in every case. The results of other parametric studies are also included
An updated Arbitrary-Lagrangian-Eulerian description in continuum mechanics and its application to nonlinear fluid-structure interaction dynamics
No full textAn updated Arbitrary-Lagrangian-Eulerian (UALE) coordinate system is proposed to solve problems in continuum mechanics. It is compared to and distinguished from an ALE system. The governing equations in differential and integral forms in an UALE system are derived. A key feature of the UALE system is that the current position coordinates defined in a Cartesian Eulerian Spatial System (CESS) are chosen as the reference coordinates to investigate the motion of the continuum. When the reference point moves to a new position, the reference coordinates are updated to the new position coordinates in CESS. This UALE system and the updated Lagrangian (UL) system have the same base vectors as the CESS at each point in space, which provides a convenient way to overcome fundamental difficulties occurring in a nonlinear fluid-structure analysis. In the fluid's UALE system and the solid's UL system in solids, variational principles and a mixed finite element finite volume approach for nonlinear fluid-structure interaction dynamics are developed and formulated
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