1,720,978 research outputs found
Botulinum toxin versus lidocaine in the treatment of myofacial pain: a double blind randomized study
No full textNumerical model for fluid-particle flows
No full textIn this paper a numerical algorithm for fluid-particle flow computation is presented. The mathematical formulation is based on the averaged continuum model, in which the effects of particles are taken into account in terms of an effective viscosity. The dispersed phase equation closure is based on sedimentation and shear-induced self diffusion effects. The present model is suitable for the simulation of the interaction between waves or currents and bottom sediment. This approach allows the study of sediment transport and the evolution of the bottom shape without the need of curvilinear coordinate systems and the related step-by-step regridding. In fact, pure liquid regions, suspension regions (more or less concentrated) as well as bottom sediment are studied by a unique model with a proper effective viscosity (hindrance effect and Bingham visco-plastic model). Preliminary numerical results have been obtained for 2D Bingham flow in a driven cavity by a finite difference method
A numerical model for fluid-particle flows
No full textIn this paper a numerical algorithm for fluid-particle flow computation is presented. The mathematical formulation is based on the averaged continuum model, in which the effects of particles are taken into account in terms of an effective viscosity. The dispersed phase equation closure is based on sedimentation and shear-induced self-diffusion effects. The present work is the first step in the development of a general model for the simulation of the interaction between waves or currents and bottom sediment. Namely, the proposed approach allows the study of sediment transport and the evolution of the bottom shape without the need for curvilinear coordinate systems and related step-by-step regridding. In fact, pure liquid regions, suspension regions (more or less concentrated) as well as bottom sediment are studied by a unique model with a proper effective viscosity (hindrance effect and Bingham viscoplastic model). Preliminary numerical results have been obtained for 2D Bingham flow in a driven cavity by a finite difference method
Nonlinear diffraction effects around a surface-piercing structure
No full textIn the present paper the interaction of a wave system with a fixed body is studied. The wave diffraction in finite-depth water around a vertical cylinder and a simple shaped shoal is computed; the results are discussed in comparison with analytical solutions and experimental data. The linearized and the fully nonlinear mathematical models are studied in the frame of irrotational incompressible flow hypothesis. The numerical solution is gained by means of an integral formulation. The body surface is discretized by a classical zeroth order panel method, whereas a desingularized scheme is implemented on the free boundary. A time marching Runge-Kutta algorithm is used for the computation of the wave pattern and the velocity potential at each time step. The simulation of wave diffraction around fixed obstacles confirms and extends the theoretical results of the second order analysis (Kriebel 1990,1992): The linear model yields a very good estimation of the force amplitude acting on the body, while the wave profiles are poorly evaluated when compared with the fully nonlinear simulation and the experimental data
Nonlinear Wave Loads on Single Vertical Cylinders: Pressure and Wave Field Measurements and Theoretical Predictions
No full textThe results of a large set of experimental tests on single vertical cylinders in regular waves are presented. The aim of the research project was to investigate the local behaviour of the pressure at the wall and the wave pattern around the cylinder in the cases of inertia dominated and diffraction dominated wave loads, with a specific interest in the nonlinear features of the phenomena. To this end, the tests have been accurately designed and the used instrumentation allowed to obtain highly reliable results. The parameter ka has been varied between 0.2 and 1.4, the wave steepness H/ ranging between 1/15 and 1/50
Viscous‐inviscid coupling in free surface ship flows
No full textAn application of multidomain decomposition to the computation of the steady free surface flow past a ship hull is presented. Viscous effects are taken into account in the neighbourhood of solid walls and in the wake by the Reynolds averaged Navier‐Stokes equations, whereas the assumption of irrotationality in the external flow allows a description by a potential model. Free surface boundary conditions have been implemented in a linearized form at the undisturbed waterplane. Suitable matching conditions are enforced at the interface between the viscous and the potential regions. The numerical results obtained for two merchant ship forms (the HSVA tanker and the Series 60 hull) are compared with experimental data available in the literature. Copyright © 1995 John Wiley & Sons, Lt
Fluid–particle flow simulation by averaged continuous model
No full textIn this paper we present a numerical method for fluid–particle flow simulation. The mathematical model is based on the averaged continuum. The presence of particles is taken into account in terms of effective viscosity, which is defined by means of both Newtonian and non-Newtonian (Bingham plastic) models. The dispersed phase equation closure is based on particle buoyancy as well as on shear-induced self-diffusion effects. The proposed approach allows us to study sediment transport problems and the related evolution of bed forms, without requiring the generation of curvilinear coordinate systems and time-consuming step-by-step regridding. In fact, the present model describes the bottom shape in terms of a density contour surface, rather than a moving boundary of the fluid domain. Simple two-dimensional numerical tests have been performed: (i) Bingham flow in a driven cavity and (ii) particle settling in a pure Couette flow. Finally, preliminary results concerning (iii) two-dimensional scour below pipelines in steady flow have been presented and discussed
Applicazioni di Metodologie Sperimentali e Numeriche nella Progettazione Navale
No full textExperimental and numerical methodologies in ship design
In this paper the hydrodynamic behavior , from the wave resistance view point, of simple shake submerged bodies is studies by means of experimental techniques and numerical methods. This work is the first approach to the SWATH hydrodynamic behavior evaluation. The experimental investigation is carried out according to the longitudinal cut method, on the other hand the numerical approach is based on the integral formulation of the potential flow model. The obtained results are presented and discussed, for simple shaped as well as for coupled bodies with struts
Interaction between river mouth flow and marine structures: numerical and experimental investigation
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