Numerical and Experimental Tools for Offshore DP Operations

2011 ◽  
Author(s):  
Fabiano P. Rampazzo ◽  
Joa˜o Luis B. Silva ◽  
Daniel P. Vieira ◽  
Antonio L. Pacifico ◽  
Lazaro Moratelli Junior ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Experimental Tests ◽  
Coupled System ◽  
Coupled Analysis ◽  
Cfd Analysis ◽  
Maximum Condition ◽  
Commercial Code ◽  
Close Proximity ◽  
Fully Coupled ◽  
Two Bodies

DP crane vessel operation can be analyzed based on the uncoupled system or considering the fully coupled system. Parameters such as top-crane acceleration, thruster capability and vessel motions are evaluated for several environmental conditions. Numerical and experimental tools are used and the important result of this analysis is the maximum condition in such that the operation can be safely executed. Those operations are critical, since the vessel is kept in close proximity with other unit and large loads are transported in a pendulum configuration. A precise positioning of the crane-vessel is required, in order to avoid unsafe relative motions, as well as keep the load being transported on a stable position. The uncoupled analysis approach does not consider the influence of the other unit in the crane vessel. This paper presents a methodology for evaluating a DP crane vessel in the offshore operations (DP crane vessel, load being transported, mooring and assistance lines, platform) considering the fully coupled method based on integration of the in house codes with the commercial code WAMIT® system. The methodology is based on the integration of numerical and experimental tools. The dimensions of the transported modules and the proximity of the vessels change the behavior of the vessel motions and line tensions. So, a full nonlinear time domain simulator (TPN – Numerical Offshore Tank) is used to perform the coupled analysis of the system subjected to several environmental conditions, considering also the dynamics of the suspended load and the hydrodynamic interference between the bodies. In order to calibrate the numerical model, several experimental tests are performed such as wind tests with some positions of the crane, tests in towing tanks to evaluated the current effects, thrusters tests to calibrate DP algorithm and wave test with the two bodies. In some cases a complementary CFD analysis is requested in order to evaluate the current and wind shadow effect. Several alternative relative positions between the vessels can be evaluated. This methodology results a more accurate estimative of the system performance.

Reliability Analysis of Short Term Mooring Tension of a Semi-Submersible System

2018 ◽  
Author(s):  
Sheng Xu ◽  
C. Guedes Soares ◽  
Ângelo P. Teixeira
Keyword(s):  
Reliability Analysis ◽  
Line Strength ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Global Maximum ◽  
Hydrodynamic Drag ◽  
Sampling Point ◽  
Wave Condition ◽  
Drag Coefficients ◽  
Fully Coupled

A detail procedure to study mooring line strength reliability is presented. A fully coupled analysis is carried out to get the mooring tensions of a deep water semi-submersible floating systems operated in 100 year wave condition in South China Sea. The ACER method is applied to predict the 3h extreme mooring tension, and the results are validated by global maximum method. The hydrodynamic sampling points are generated by Latin Hypercube Sampling technique. The 3h extreme mooring tension is calculated by the ACER method with 10 minutes fully coupled dynamic simulation for each sampling point. The Kriging meta model method is trained to predict 3h mooring extreme tension under the effects of random hydrodynamic drag coefficients. A reliability analysis is carried out by implementing Monte Carlo simulation with the random hydrodynamic drag coefficients and mooring breaking strength considered.

Evaluating the Coupledness of the Aerodynamics and Hydrodynamics on the Estimation of Fatigue Damage Equivalent Load for a Floating Offshore Wind Platform

2018 ◽  
Author(s):  
Samuel Kanner ◽  
Bingbin Yu
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Environmental Conditions ◽  
Offshore Wind ◽  
Coupled Analysis ◽  
Offshore Wind Turbine ◽  
Wave Conditions ◽  
Equivalent Load ◽  
The Waves

In this research, the estimation of the fatigue life of a semi-submersible floating offshore wind platform is considered. In order to accurately estimate the fatigue life of a platform, coupled aerodynamic-hydrodynamic simulations are performed to obtain dynamic stress values. The simulations are performed at a multitude of representative environmental states, or “bins,” which can mimic the conditions the structure may endure at a given site, per ABS Floating Offshore Wind Turbine Installation guidelines. To accurately represent the variety of wind and wave conditions, the number of environmental states can be of the order of 103. Unlike other offshore structures, both the wind and wave conditions must be accounted for, which are generally considered independent parameters, drastically increasing the number of states. The stress timeseries from these simulations can be used to estimate the damage at a particular location on the structure by using commonly accepted methods, such as the rainflow counting algorithm. The damage due to either the winds or the waves can be estimated by using a frequency decomposition of the stress timeseries. In this paper, a similar decoupled approach is used to attempt to recover the damages induced from these coupled simulations. Although it is well-known that a coupled, aero-hydro analysis is necessary in order to accurately simulate the nonlinear rigid-body motions of the platform, it is less clear if the same statement could be made about the fatigue properties of the platform. In one approach, the fatigue damage equivalent load is calculated independently from both scatter diagrams of the waves and a rose diagram of the wind. De-coupled simulations are performed to estimate the response at an all-encompassing range of environmental conditions. A database of responses based on these environmental conditions is constructed. The likelihood of occurrence at a case-study site is used to compare the damage equivalent from the coupled simulations. The OC5 platform in the Borssele wind farm zone is used as a case-study and the damage equivalent load from the de-coupled methods are compared to those from the coupled analysis in order to assess these methodologies.

Scalability study of an implicit solver for coupled fluid-structure interaction problems on unstructured meshes in 3D

2016 ◽  
Vol 32 (2) ◽  
pp. 207-219 ◽  
Author(s):  
Fande Kong ◽  
Xiao-Chuan Cai
Keyword(s):  
Stokes Equations ◽  
Fluid Structure Interaction ◽  
Three Dimensional ◽  
Coupled System ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Krylov Method ◽  
Fine Mesh ◽  
Processor Cores ◽  
Fully Coupled

Fluid-structure interaction (FSI) problems are computationally very challenging. In this paper we consider the monolithic approach for solving the fully coupled FSI problem. Most existing techniques, such as multigrid methods, do not work well for the coupled system since the system consists of elliptic, parabolic and hyperbolic components all together. Other approaches based on direct solvers do not scale to large numbers of processors. In this paper, we introduce a multilevel unstructured mesh Schwarz preconditioned Newton–Krylov method for the implicitly discretized, fully coupled system of partial differential equations consisting of incompressible Navier–Stokes equations for the fluid flows and the linear elasticity equation for the structure. Several meshes are required to make the solution algorithm scalable. This includes a fine mesh to guarantee the solution accuracy, and a few isogeometric coarse meshes to speed up the convergence. Special attention is paid when constructing and partitioning the preconditioning meshes so that the communication cost is minimized when the number of processor cores is large. We show numerically that the proposed algorithm is highly scalable in terms of the number of iterations and the total compute time on a supercomputer with more than 10,000 processor cores for monolithically coupled three-dimensional FSI problems with hundreds of millions of unknowns.

CFD Analysis of the Active Part of the HYPER Spallation Target

2006 ◽  
Author(s):  
Nam-il Tak ◽  
Chungho Cho ◽  
Tae-Yung Song
Keyword(s):  
Turbulence Models ◽  
Active Part ◽  
Beam Power ◽  
Cfd Analysis ◽  
Spallation Target ◽  
Power Extraction ◽  
Commercial Code ◽  
Driven System ◽  
Challenging Tasks ◽  
Computational Fluid Dynamics Cfd

KAERI (Korea Atomic Energy Research Institute) is developing an accelerator driven system (ADS) named HYPER (HYbrid Power Extraction Reactor) for a transmutation of long-lived nuclear wastes. One of the challenging tasks for the HYPER system is to design a large spallation target having a beam power of 15∼25 MW. The present paper focuses on the thermal-hydraulic performance of the active part of the HYPER target. Computational fluid dynamics (CFD) analysis was performed using a commercial code CFX 5.7.1. Several advanced turbulence models with different grid structures were applied. The CFX results show the significant impact of the turbulence model on the window temperature. It is concluded that experimental verifications are very important for the design of the HYPER target.

Numerical Analysis of a Floating Fish Cage With Feeding Systems

2020 ◽  
Author(s):  
Lin Li ◽  
Mathias Bruset ◽  
Muk Chen Ong ◽  
Xiaopeng Wu
Keyword(s):  
Environmental Conditions ◽  
Numerical Study ◽  
Coupled System ◽  
Feeding Tube ◽  
Fish Farm ◽  
Dynamic Responses ◽  
Feeding System ◽  
Solidity Ratio ◽  
Sensitivity Studies ◽  
Fish Cages

Abstract A modern marine-based fish farm normally consists of a feeding barge, several fish cages, and feeding tubes. Although many studies, both experimental and numerical, are available in the literature to investigate the global responses of the fish cages under wave and current conditions, research on the coupled system including both the fish cage and the feeding system is very limited. This paper presents a numerical study on the coupled system with a floating fish cage and the feeding system. The purpose is to study the dynamic responses of the coupled system under different environmental conditions and configurations of the fish farm. A numerical model is firstly established in the numerical program OrcaFlex, comprising of a feeding barge, a gravity-based floating fish cage with mooring systems, and a feeding tube between the barge and the cage. Time-domain simulations of this coupled system are then performed under environmental conditions corresponding to 1-year and 50-year return periods for a reference site. The deformation of the fish cage, the tensions in the anchor lines and in the feeding tube are compared under various conditions. Sensitivity studies on the solidity ratio of the fish net as well as the lengths of the feeding tube are addressed, and their influences on the responses of the coupled system are also discussed.

Fretting Fatigue on Thin Sheets

2015 ◽  
Vol 651-653 ◽  
pp. 504-509
Author(s):  
Eduardo Luis Gaertner ◽  
José Divo Bressan ◽  
Anne Karollyne Petry
Keyword(s):  
Sheet Thickness ◽  
Experimental Tests ◽  
Fretting Fatigue ◽  
Relative Displacement ◽  
Thin Sheets ◽  
Stainless Steel Sheet ◽  
Small Reduction ◽  
Dedicated Machines ◽  
Number Of Cycles ◽  
Two Bodies

The fretting is responsible for many failures of components in the industry. It is present in assemblies like rivet and screw fixture, dovetailjoint, shaft and hub with key, and all connections of two bodies with a contact force and a small induced relative displacement. Topic of studies for decades, the researchers perform experimental tests with some simplification in order to accelerate the phenomenon, some times using standard devices or creating dedicated machines for better representing the behavior of the desired components. There are a few studies with thin sheets, in which the fretting fatigue has more impact because a small reduction of the cross section due to the wear of crack results in a significant increase of stress and rate of crack propatation, decresing the number of cycles until failure. In this work, it wasbuild a device to generate the fretting fatigue with two different shape of contact pad. The specimen is a stainless steel sheet thickness 0.152mm, which fractures and surfaces were analyzed using the SEM and white light interferometer to understand the fractures.

Sea-state dependency of air-sea fluxes for high winds in ECMWF Earth System Model

2020 ◽  
Author(s):  
Jean Bidlot
Keyword(s):  
Drag Coefficient ◽  
Tropical Cyclones ◽  
Coupled System ◽  
Wave Model ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Sea State ◽  
Medium Range ◽  
Fully Coupled

<p>The global analyses and medium range forecasts from the European Centre for Medium range Weather Forecasts rely on a state-of-the-art Numerical Weather Prediction (NWP) system. To best represent the air-sea exchanges, it is tightly coupled to an ocean wave model.  As part of ECMWF approach to Earth System Model, it is also coupled to a global ocean model for all its forecasting systems from the medium range up to the seasonal time scale.</p><p>Because the feedback from and to the ocean can be significant, it is only in the fully coupled system that parameterisation for air-sea processes should be revisited. For instance, it is now accepted that the drag coefficient should generally attained maximum values for storm winds but should level or even decrease for very strong winds, namely in tropical cyclones or intense mid-latitude wind storms.</p><p>A modification of the wind input source was tested, whereby the Charnock coefficient estimated by the wave model and therefore the drag coefficient sharply reduce for large winds (> 30 m/s). As a consequence, ECMWF tendency to under predict strong tropical cyclones was sharply alleviated, in better agreement with observational evidence. This change is now planned for operational implementation with the next model cycle (CY47R1, June 2020).</p><p>Experimental evidences also point to a sea state/wind dependency of the heat and moisture fluxes.  Following an extension of the wind wave generation theory, a sea state dependent parameterisation for the roughness length scales for heat and humidity has been tested. Again, a proper assessment of the different parameterisations warrants the fully coupled system. Experimentations so far indicate the benefit of such change. Ongoing work aims at future operational implementation.</p>

scholarly journals A COMPARISON OF ONE- AND TWO-SIDED KRYLOV–ARNOLDI PROJECTION METHODS FOR FULLY COUPLED, DAMPED STRUCTURAL-ACOUSTIC ANALYSIS

2013 ◽  
Vol 21 (02) ◽  
pp. 1350004 ◽  
Author(s):  
R. SRINIVASAN PURI ◽  
DENISE MORREY
Keyword(s):  
Coupled System ◽  
Dimensional Subspace ◽  
Second Order ◽  
Reduced Order Model ◽  
Order Model ◽  
Reduced Order ◽  
Frequency Moments ◽  
Arnoldi Algorithm ◽  
Higher Dimensional ◽  
Fully Coupled

The two-sided second-order Arnoldi algorithm is used to generate a reduced order model of two test cases of fully coupled, acoustic interior cavities, backed by flexible structural systems with damping. The reduced order model is obtained by applying a Galerkin–Petrov projection of the coupled system matrices, from a higher dimensional subspace to a lower dimensional subspace, whilst preserving the low frequency moments of the coupled system. The basis vectors for projection are computed efficiently using a two-sided second-order Arnoldi algorithm, which generates an orthogonal basis for the second-order Krylov subspace containing moments of the original higher dimensional system. The first model is an ABAQUS benchmark problem: a 2D, point loaded, water filled cavity. The second model is a cylindrical air-filled cavity, with clamped ends and a load normal to its curved surface. The computational efficiency, error and convergence are analyzed, and the two-sided second-order Arnoldi method shows better efficiency and performance than the one-sided Arnoldi technique, whilst also preserving the second-order structure of the original problem.

Towards the Integration of Analysis and Design of Mooring Systems and Risers: Part I — Studies on a Semisubmersible Platform

2002 ◽  
Author(s):  
Stael Ferreira Senra ◽  
Fabricio Nogueira Correa ◽  
Breno Pinheiro Jacob ◽  
Ma´rcio Martins Mourelle ◽  
Isai´as Quaresma Masetti
Keyword(s):  
Motion Analysis ◽  
Production Systems ◽  
Companion Paper ◽  
Coupled Analysis ◽  
Mooring Line ◽  
Mooring System ◽  
Analysis And Design ◽  
Design Methodologies ◽  
Campos Basin ◽  
Fully Coupled

The objective of this paper is to study different analysis methodologies for the design of floating production systems. The main issues are the use of uncoupled and coupled analysis methods, and the integration in the analysis and design of the mooring system and the risers. This paper is a companion to another paper also presented in the OMAE2002 Conference [1] The present paper begins describing a “basic” classic, uncoupled methodology, and proceeds with comments on some refinements in the representation of the behavior of the lines in the motion analysis of the vessel. Comments regarding the introduction of some level of integration between mooring line and riser behavior are also presented. These issues are illustrated with studies applying some of the considered design methodologies to the P-18 semi-submersible platform in Campos basin. The companion paper [1] proceeds describing a fully coupled methodology, and some hybrid methodologies that combine coupled and uncoupled analysis tools, and illustrates their application to a DICAS system for deepwater applications in Campos basin.

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