An unstructured grid-based, parallel free surface solver

An unstructured grid-based, parallel-free surface solver is presented. The overall scheme combines a finite-element, equal-order, projection-type 3-D incompressible flow solver with a finite element, 2-D advection equation solver for the free surface equation. For steady-state applications, the mesh is not moved every timestep, in order to reduce the cost of geometry recalculations and surface repositioning. A number of modifications required for efficient processing on shared-memory, cache-based parallel machines are discussed, and timings are shown that indicate scalability to a modest number of processors. The results show good quantitative comparison with experiments and the results of other techniques. The present combination of unstructured grids (enhanced geometrical flexibility) and good parallel performance (rapid turnaround) should make the present approach attractive to hydrodynamic design simulations

Modelling Fluid Structure Interaction problems using Boundary Element Method

This dissertation investigates the application of Boundary Element Methods (BEM) to Fluid Structure Interaction (FSI) problems under three main different perspectives. This work is divided in three main parts: i) the derivation of BEM for the Laplace equation and its application to analyze ship-wave interaction problems, ii) the imple- mentation of efficient and parallel BEM solvers addressing the newest challenges of High Performance Computing, iii) the developing of a BEM for the Stokes system and its application to study micro-swimmers.First we develop a BEM for the Laplace equation and we apply it to predict ship-wave interactions making use of an innovative coupling with Finite Element Method stabilization techniques. As well known, the wave pattern around a body depends on the Froude number associated to the flow. Thus, we throughly investigate the robustness and accuracy of the developed methodology assessing the solution dependence on such parameter. To improve the performance and tackle problems with higher number of unknowns, the BEM developed for the Laplace equation is parallelized using OpenSOURCE tech- nique in a hybrid distributed-shared memory environment. We perform several tests to demonstrate both the accuracy and the performance of the parallel BEM developed. In addition, we explore two different possibilities to reduce the overall computational cost from O(N2) to O(N). Firstly we couple the library with a Fast Multiple Method that allows us to reach for higher order of complexity and efficiency. Then we perform a preliminary study on the implementation of a parallel Non Uniform Fast Fourier Transform to be coupled with the newly developed algorithm Sparse Cardinal Sine De- composition (SCSD).Finally we consider the application of the BEM framework to a different kind of FSI problem represented by the Stokes flow of a liquid medium surrounding swimming micro-organisms. We maintain the parallel structure derived for the Laplace equation even in the Stokes setting. Our implementation is able to simulate both prokaryotic and eukaryotic organisms, matching literature and experimental benchmarks. We finally present a deep analysis of the importance of hydrodynamic interactions between the different parts of micro-swimmers in the prevision of optimal swimming conditions, focusing our attention on the study of flagellated \u201crobotic\u201d composite swimmers

Towards the realisation of an integratated decision support environment for organisational decision making

Traditional decision support systems are based on the paradigm of a single decision maker working at a stand‐alone computer or terminal who has a specific decision to make with a specific goal in mind. Organizational decision support systems aim to support decision makers at all levels of an organization (from executive, middle management managers to operators), who have a variety of decisions to make, with different priorities, often in a distributed and dynamic environment. Such systems need to be designed and developed with extra functionality to meet the challenges such as collaborative working. This paper proposes an Integrated Decision Support Environment (IDSE) for organizational decision making. The IDSE distinguishes itself from traditional decision support systems in that it can flexibly configure and re‐configure its functions to support various decision applications. IDSE is an open software platform which allows its users to define their own decision processes and choose their own exiting decision tools to be integrated into the platform. The IDSE is designed and developed based on distributed client/server networking, with a multi‐tier integration framework for consistent information exchange and sharing, seamless process co‐ordination and synchronisation, and quick access to packaged and legacy systems. The prototype of the IDSE demonstrates good performance in agile response to fast changing decision situations

Turning Ability Characteristics Study of a Twin Screw Vessel by CFD

The turning circle manoeuvre of a self-propelled tanker like ship model is numerically simulated through the integration of the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations coupled with the equations of the motion of a rigid body. The solution is achieved by means of the unsteady RANS solver Xnavis developed at CNR-INSEAN. The ship model is in its fully appended conguration, and it is characterized by the presence of two propellers and one rudder. Each propeller is taken into account by a model based on the actuator disk concept. It is shown that, in order to accurately predict the trajectory, the side force developed by the propeller should be taken into account; several models are tested. Comparison with experimental data from free running tests is provided. The main features of the ow eld, with particular attention to the vortical structures detached for the hull is presented as well

Investigation of green water in FPSO by a particle-based numerical offshore tank

The green water is a highly non linear hydrodynamic phenomenon that occurs when the wave height exceeds the freeboard of the floating structures in harsh environments, and may compromise the operation and security of the on deck equipment. In the present study, in order to assess the effects of the green water phenomenon in FPSO and FLNG systems, the Moving Particle Semi-implicit (MPS) method, which is a fully lagrangian particle-method for incompressible flow, is adopted to model the complex fluid structure interaction problem. This article is focused on the recent developments of the MPS based simulation system of Numerical Offshore Tank (TPN-USP) and its application to the real scale offshore engineering problem. Results of large scale simulations using distributed memory architecture for models from 30 million to 100 million particles are presented

One-dimensional Advanced Beam Models for Marine Structural Applications

At preliminary design stage, the global mechanical behavior of large marine vessels such as container ships has previously been analyzed idealizing them as a classical beam. These structures are complex and a classical beam idealization significantly compromises important structural behavior associated with cross section warping or in-plane displacements. On the other hand, 3D Finite Element (FE) models have been utilized which are accurate in capturing these details but pose high computational cost. In present work, structural analyses of marine vessels with realistic boundary conditions have been presented using well-known Carrera Unified Formulation (CUF). Using CUF, higher order theories can be implemented without the need of ad-hoc formulations. The finite element arrays are written in terms of fundamental nuclei for 1D beam elements that are independent of problem characteristics and the approximation order. Thus, refined models can be developed in an automatic manner. In the present work, the beam cross sections are discretized using elements with Lagrange polynomials and the FE model is regarded as Component-Wise (CW), allowing one to model complex 3D features, such as inclined hull walls, floors and girders in the form of components. The work is mainly divided in two parts: Hull in vacuo (in absence of water) and Hull with Hydrostatic Stiffness (in presence of water). The former involves static and dynamic structural analyses of hulls with realistic geometries without the effect of water. The later involves static and dynamic analyses of realistic hull geometries that are supported by buoyancy springs. The stiffness of buoyancy springs is made part of the fundamental nuclei and the corresponding FEM matrices for hydrostatic and hydrodynamic loads are obtained. The hydrodynamic loads have been considered in the form of Radiation Wave loads which include damping and added mass effects. Utilization of Component-Wise (CW) model under hydrodynamic loads has afforded an ease in modelling the complex geometrical configurations such as realistic boat shapes and the dynamic response analyses of aircraft carrier due to moving aircraft. All the analyses have been validated with published literature and their computational efficacy is established through their comparison with the results from commercial code

Performances analysis of a semi-displacement hull by numerical simulations

The flow field generated by the towing of a semi-displacement hull, free to heave and pitch, is numerically investigated in the velocity range 18 34 Kn. The numerical code adopted is the in-house developed Xnavis, which is a general purpose unsteady RANS based solver; the solver is based on a Finite Volume approach together with a Chimera technique for overlapping grids and a Level Set approach to handle the air/water interface. The generated wave pattern shows many interesting features with an evident wave plunging near the hull bow, while the stern remains completely dry for velocities over 30 Kn. The numerical outcomes are discussed in terms of total resistance, sinkage and trim

Prediction of Manoeuvring Properties for a Tanker Model by Computational Fluid Dynamics

The turning circle manoeuvre of a self-propelled tanker like ship model is numerically simulated through the integration of the unsteady Reynolds Averaged Navier-Stokes (URANS) equations coupled with the equations of the motion of a rigid body. The solution is achieved by means of the unsteady RANS solver developed at CNR-INSEAN. The model is considered with two different stern appendages configurations (each one providing a different dynamic behaviour): twin screw with a single rudder and twin screw, twin rudder with a central skeg. Each propeller is taken into account by a model based on the actuator disk concept; anyhow, in order to correctly capture the turning manoeuvring behaviour of the model, a suitable description of the propeller performance in oblique flow operation has be considered. Comparison with experimental data from free running tests will demonstrate the feasibility of the CFD computations. The main features of the flow field, with particular attention to the vortical structures detached from the hull is presented as well

A Numerical and Experimental Study On the Hydrodynamic of a Catamara Varying the Demihull Separation

A complementary experimental and numerical study of the interference eect for a fast catamaran is presented. Resistance, sinkage and trim are collected by towing tank experiments for Froude number in the range from 0:2 to 0:8 for several separation distances and for the monohull. Resistance coefficient curves reveal the presence of two humps, the second one strongly depending on the separation length; high interference is observed in correspondence of the second hump. To gain a deeper insight into these behaviors, a complementary analysis is carried out by a numerical campaign; simulations are performed by means of an in-house unsteady RANS solver. Verication of numerical results is provided, together with validation, which is made by the comparison with both present and other experimental data. Agreement in terms of resistance coefficient is rather good, comparison error being always smaller than 2.2%