In order to preliminary investigate structural response of stiffened panel due to slamming impact, two series of fluid structure coupling analysis is carried out using a new fluid structure interaction (FSI) methodology of Incompressible Fluid Dynamics (ICFD) [1]. ICFD is the method where structure and fluid are modeled as both Lagrange methods. Firstly, slamming impact of a sphere is analyzed with ICFD and SPH methods respectively and compared with experimental and analytical results. Acceleration, slamming force and pressure are compared and discussed in detail. Secondary a fixed stiffened flat panel of offshore structure subjected to slamming impact is investigated as a part of the ISSC II.1 benchmark study. Effect of mesh size is investigated. Analysis results are compared with existing ALE method [1] as well as other results within the framework of ISSC II.1 benchmark study. In both studies, structure is modeled by elastic-plastic and by rigid respectively. By comparing these two results, effect of structural rigidity on the slamming pressure as well as slamming force is investigated.

This paper presents the assessment of the modelling error (Validation) of a Navier-Stokes solver using Volume of Fluid (VOF) and moving grid techniques in the simulation of a free falling wedge into calm water. This problem has been studied experimentally to determine the time histories of six pressure probes located on the wedge surface and the acceleration of the wedge. The simulation is restricted to the first 100ms after the impact of the wedge on the water ( t = 0 at the impact) and the mathematical model uses the following assumptions: incompressible fluid; two-dimensional, laminar flow, negligible shear-stress at the surface of the wedge and deep water. The selected quantities of interest are the peak pressures at the six sensors, time intervals between peak pressures at the sensors, sensors pressures and acceleration of the wedge at six different time instants and integrated pressure signals for 80ms after the pressure peak at the first sensor. The application of the ASME V&V 20 standard to local quantities is presented, including the estimation of experimental and numerical uncertainties. Furthermore, a multivariate metric is used to evaluate quantitatively the overall performance of the mathematical model. The results show significant comparison errors (mismatches between simulations and measurements) for the accelerations, which may be a consequence of the assumptions of a deep water boundary condition at the bottom. However, such conclusion is hampered by some doubts about the accuracy of the experimental data. On the other hand, modeling errors are significantly smaller for the pressure measurements at the six sensors for which the main challenge is to reduce the validation uncertainty U val . In many of the selected flow quantities, U val is dominated by the experimental uncertainty.

The ability of fish to maneuver in tight places, perform stable high acceleration maneuvers, and hover efficiently has inspired the development of underwater robots propelled by flexible fins mimicking those of fish. In general, fin propulsion is a challenging fluid-structure interaction (FSI) problem characterized by large structural deformation and strong added-mass effect. It was recently reported that a simplified computational model using the vortex panel method for the fluid flow is not able to accurately predict thrust generation. In this work, a high-fidelity, fluid-structure coupled computational framework is applied to predict the propulsive performance of a series of biomimetic fins of various dimensions, shapes, and stiffness. This computational framework couples a three-dimensional finite-volume Navier-Stokes computational fluid dynamics (CFD) solver and a nonlinear, finite-element computational structural dynamics (CSD) solver in a partitioned procedure. The large motion and deformation of the fluid-structure interface is handled using a validated, state-of-the-art embedded boundary method. The notorious numerical added-mass effect, that is, a numerical instability issue commonly encountered in FSI simulations involving incompressible fluid flows and light (compared to fluid) structures, is suppressed by accounting for water compressibility in the CFD model and applying a low-Mach preconditioner in the CFD solver. Both one-way and two-way coupled simulations are performed for a series of flexible fins with different thickness. Satisfactory agreement between the simulation prediction and the corresponding experimental data is achieved.

This paper is concerned with calculations of the two-dimensional nonlinear vertical and horizontal forces and overturning moment due to the unsteady flow of an inviscid, incompressible fluid over a fully-submerged horizontal, fixed box. The problem is approached on the basis of the Level I Green-Naghdi (GN) theory of shallow-water waves. The main objective of this paper is to present a comparison of the solitary and cnoidal wave loads calculated by use of the GN equations, with those computed by Euler’s equations and the recent laboratory measurements, and also with a linear solution of the problem for small-amplitude waves. The results show a remarkable similarity between the GN and Euler’s models and the laboratory measurements. In particular, the calculations predict that the thickness of the box has no effect on the vertical forces and only a slight influence on the two-dimensional horizontal positive force. The calculations also predict that viscosity of the fluid has a small effect on these loads. The results have applications to various physical problems such as wave forces on submerged coastal bridges and submerged breakwaters.

Comparison investigations of numerical simulations of incompressible viscous flows by the SPH (smoothed particle hydrodynamics) and the MPS (moving particle semi-implicit) are presented. A dam-break problem is chosen as the test case. In the calculation with the SPH method, weakly compressible model is used, i.e. WCSPH, which describes water as a nearly incompressible fluid, while in MPS method, the pressure Poisson equation is introduced to keep the density of fluid to be constant. The numerical results show that the two particle methods are robust and flexible, numerical results qualitatively agree with the experimental data. It can be seen that both the SPH method and the MPS method can be easily applied to the complex free surface flow problems.

The oscillatory motions induced by a propagating wave of small amplitude through a viscous incompressible fluid contained in a prestressed and thick-walled viscoelastic tube are studied by a perturbation analysis based on equations of motion in the Lagrangian system. While the finite-amplitude initial displacements of the wall are found at the zeroth order, the wave kinematics and dynamics are determined at the first order as analytical functions of the wall and fluid properties, prestress, and the Womersley number for the cases of a free or tethered tube.

The sloshing waves in rectangular tanks are studied experimentally and numerically based on the fully nonlinear wave theory. A moving-particle semi-implicit (MPS) method belonging to the category of the particle method is utilized to solve the Navier-Stokes equation that is the governing equation of the incompressible fluids. The motion of each particle is calculated through interactions with neighboring particles covered with the kernel function. The governing equations are solved by Lagrangian approach and no grid is needed in the computation. The incompressibility is satisfied by keeping the particle number density constant. When the tank undergoes two-dimensional motion, the numerical results obtained are found to be in good agreement with other published data as well as our experimental results obtained by shake-table tests. Experiments with rectangular tanks have been conducted to validate the numerical results, for which favorable agreement is shown. Results will also be presented for the study which is currently extended to three dimensional sloshing by exciting the tank at an inclined angle.

This development is a description of the transport of mass, energy and momentum in flowing viscous fluids at the molecular level; and results in: • A thermostatistical link between Reynolds’ number and momentum and free energy, • A wave characterization of the behavior of flowing fluids using the forces of attraction between molecules as a basis, • Calculation of the velocity components in flowing fluids for all Reynolds’ numbers greater than 535; thus defining a mathematical theory of turbulence, • An analytic solution of the Navier-Stokes equations for incompressible fluids in 3-dimensions. The following steps lead to the solution: • Definition of the fluid Model, • A re-characterization of Reynolds’ number in terms of momentum and free energy, • Calculation of the shear and circulatory components of velocity, • Transformation of the Navier-Stokes equations into the curvilinear coordinates of the intermolecular force waves, • Using the transformed equations to calculate the velocity components and Pressure-wave front resulting from the current, • Corroboration of the theoretical results with: a) wave fronts as manifest in the behavior of sails in uniform flow, b) boundary layer definition/behavior compared to theoretical and empirical developments of Schlichting and others, and c) empirical results for forces measured in the OCEANIC/DeepStar high R e beam-tow tests.

Synthetic Aperture Radar (SAR) imaging of ocean waves involves both the geometry and the kinematics of the sea surface. However, the traditional linear wave theory fails to describe steep waves, which are likely to bring about specular reflection of the radar beam, and it may overestimate the surface fluid velocity that causes the so-called velocity bunching effect. Recently, the interest for a Lagrangian description of ocean gravity waves has increased. Such an approach considers the motion of individual labeled fluid particles and the free surface elevation is derived from the surface particles positions. The first order regular solution to the Lagrangian equations of motion for an inviscid and incompressible fluid is the so-called Gerstner wave. It shows realistic features such as sharper crests and broader troughs as the wave steepness increases. This paper proposes a second order irregular solution to these equations. The general features of the first and second order waves are described, and some statistical properties of various surface parameters such as the orbital velocity, the slope and the mean curvature are studied.

A parallel finite element fluid-structure interaction free-surface solver is developed for numerical simulation of water waves interacting with floating objects. In our approach, the governing equations are the Navier-Stokes equations written for two incompressible fluids. An interface function with two distinct values serves as a marker identifying the location of the interface. The numerical method is based on writing stabilized finite element formulations in an arbitrary Lagrangian-Eulerian frame. This allows us to handle the motion of the floating objects by moving the computational nodes. In the mesh-moving schemes, we assume that the computational domain is made of elastic materials. The linear elasticity equations are solved to obtain the displacements. In order to update the position of the floating object, the nonlinear rigid body dynamics equations are coupled with the governing equations of fluids and are solved simultaneously. The mooring forces are modeled using nonlinear cables and linear spring models. The finite element formulation is implemented on Cray X1.