Numerical and Experimental Study of a Multi-Use Platform

2016 ◽  
Author(s):  
José A. Armesto ◽  
Javier Sarmiento ◽  
Víctor Ayllón ◽  
Arantza Iturrioz ◽  
Alfonso Jurado ◽  
...  
Keyword(s):  
Numerical Model ◽  
Time Domain ◽  
Laboratory Tests ◽  
Power Production ◽  
Ocean Basin ◽  
Mooring System ◽  
Nonlinear Friction ◽  
Friction Forces ◽  
Static Approach ◽  
Hydrodynamic Study

A complete hydrodynamic study of a Multi Use Platform designed to harvest energy from waves and wind is presented. The steps given in the study, and presented in this paper are: (i) the design of the platform, (ii) the laboratory tests performed at the Cantabria Coastal and Ocean Basin, (iii) the development of a new in-house time domain numerical model that integrates all components and (iv) the first validation cases of the numerical model. The development of time domain numerical model that coupled the behaviour of the platform and the OWCs based in Cummins equation is presented. The model includes nonlinear friction forces and a quasi-static approach to model the mooring system. The obtained system is extended to include the variation of the pressure inside each chamber. The effect of the wind turbine in the movements and power production of the platform is studied using also a quasi-static approach.

Experimental and Numerical Modelling of an Offshore Aquaculture Cage for Open Ocean Waters

2018 ◽  
Author(s):  
Alfonso Jurado ◽  
Patricia Sánchez ◽  
Jose A. Armesto ◽  
Raúl Guanche ◽  
Bárbara Ondiviela ◽  
...  
Keyword(s):  
Numerical Model ◽  
Time Domain ◽  
Environmental Conditions ◽  
Ad Hoc ◽  
Experimental Tests ◽  
Ocean Basin ◽  
Open Ocean ◽  
Offshore Aquaculture ◽  
Decay Tests ◽  
Multi Body

An innovative offshore aquaculture cage design and its hydrodynamic behavior for different environmental conditions is presented. The work involves the following blocks: (i) design of the aquaculture cage, (ii) experimental tests performed at IHCantabria facilities (Cantabria Coastal and Ocean Basin, CCOB), (iii) brief description of the ad-hoc time domain numerical model developed, and (iv) calibration of decay tests and sea states cases, in order to be able to simulate different locations of interest for aquaculture stakeholders. The offshore aquaculture cage is a floating cylindrical structure, designed according to different requirements from standards and needs of contacted aquaculture stakeholders. The cage is focused on the growing and farming of fish species in open ocean conditions. It has been specially designed to be able to withstand different environmental conditions, even waves of more than 5m height. Through numerical and physical modeling, it has been shown that it has a good seakeeping and accessibility, to reduce O&M costs. Motions and loads have been registered during the tank testing to calibrate and validate a specific coupled time domain numerical model developed for multi-body structures to simulate the behavior of the assembled structure (cage and sinker connected by tendons), including non-linear damping forces and a FEM approach to model the mooring and the tendon system.

Time-Domain Hydrodynamic Model for Mooring Analysis of a Spread Moored FPSO With Calibration of Wave Drift Forces

2020 ◽  
Author(s):  
Min Zhang ◽  
Junrong Wang ◽  
Junfeng Du ◽  
Nuno Fonseca ◽  
Galin Tahchiev ◽  
...  
Keyword(s):  
Numerical Model ◽  
Test Data ◽  
Time Domain ◽  
Transfer Functions ◽  
Low Frequency ◽  
Linear Wave ◽  
Mooring System ◽  
Wave Drift ◽  
Wave Drift Forces ◽  
Drift Forces

Abstract The paper presents calibration and validation of a time domain numerical model for mooring analysis of a spread moored FPSO in moderate seastates with and without current. The equations of motion are solved in the time domain with a fully coupled method, accounting for linear wave frequency (WF) radiation and diffraction, second order wave drift forces and nonlinear low frequency (LF) damping. The mooring system dynamics is solved by a FEM. Uncalibrated numerical models are based on input from the mooring system, vessel mass, radiation/diffraction analysis, decay tests and current coefficients. WF responses are very well predicted by standard radiation/diffraction linear analysis, therefore the focus is on the LF responses. LF motions are underpredicted by the uncalibrated numerical model. Calibration is performed by comparing simulations with model test data and adjusting hydrodynamic coefficients known to be affected by uncertainty. These include wave drift force coefficients and LF damping. Correction of the drift coefficients is based on empirical quadratic transfer functions (QTFs) identified from the test data by a nonlinear data analysis technique known as “cross-bi-spectral analysis”. The LF damping coefficients are then adjusted by matching low frequency surge and sway spectra from the model tests and from the simulations.

scholarly journals Design and Automated Optimization of an Internal Turret Mooring System in the Frequency and Time Domain

2021 ◽  
Vol 9 (6) ◽  
pp. 581
Author(s):  
Hongrae Park ◽  
Sungjun Jung
Keyword(s):  
System Design ◽  
Time Domain ◽  
Initial Conditions ◽  
Minimum Weight ◽  
Optimization Algorithms ◽  
Local Optimization ◽  
Mooring System ◽  
Floating Offshore Wind Turbines ◽  
Global And Local Optimization ◽  
Global And Local

A cost-effective mooring system design has been emphasized for traditional offshore industry applications and in the design of floating offshore wind turbines. The industry consensus regarding mooring system design is mainly inhibited by previous project experience. The design of the mooring system also requires a significant number of design cycles. To take aim at these challenges, this paper studies the application of an optimization algorithm to the Floating Production Storage and Offloading (FPSO) mooring system design with an internal turret system at deep-water locations. The goal is to minimize mooring system costs by satisfying constraints, and an objective function is defined as the minimum weight of the mooring system. Anchor loads, a floating body offset and mooring line tensions are defined as constraints. In the process of optimization, the mooring system is analyzed in terms of the frequency domain and time domain, and global and local optimization algorithms are also deployed towards reaching the optimum solution. Three cases are studied with the same initial conditions. The global and local optimization algorithms successfully find a feasible mooring system by reducing the mooring system cost by up to 52%.

Calibration of a Time-Domain Hydrodynamic Model for A 12 MW Semi-Submersible Floating Wind Turbine

2021 ◽  
Author(s):  
Carlos Eduardo Silva de Souza ◽  
Nuno Fonseca ◽  
Petter Andreas Berthelsen ◽  
Maxime Thys
Keyword(s):  
Numerical Model ◽  
Wind Turbine ◽  
Time Domain ◽  
Quadratic Model ◽  
Wave Loads ◽  
Frequency Wave ◽  
Load Models ◽  
Wave Drift ◽  
Floating Wind Turbine ◽  
Decay Tests

Abstract Design optimization of mooring systems is an important step towards the reduction of costs for the floating wind turbine (FWT) industry. Accurate prediction of slowly-varying horizontal motions is needed, but there are still questions regarding the most adequate models for low-frequency wave excitation, and damping, for typical FWT concepts. To fill this gap, it is fundamental to compare existing load models against model tests results. This paper describes a calibration procedure for a three-columns semi-submersible FWT, based on adjustment of a time-domain numerical model to experimental results in decay tests, and tests in waves. First, the numerical model and underlying assumptions are introduced. The model is then validated against experimental data, such that the adequate load models are chosen and adjusted. In this step, Newman’s approximation is adopted for the second-order wave loads, using wave drift coefficients obtained from the experiments. Calm-water viscous damping is represented as a linear and quadratic model, and adjusted based on decay tests. Additional damping from waves is then adjusted for each sea state, consisting of a combination of a wave drift damping component, and one component with viscous nature. Finally, a parameterization procedure is proposed for generalizing the results to sea states not considered in the tests.

scholarly journals Point Load Test of Half-Cylinder Core Using the Numerical Model and Laboratory Tests: Size Suggestion and Correlation with Cylinder Core

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Fengyu Ren ◽  
Huan Liu ◽  
Rongxing He ◽  
Guanghui Li ◽  
Yang Liu
Keyword(s):  
Numerical Model ◽  
Laboratory Tests ◽  
Failure Load ◽  
Field Tests ◽  
Point Load ◽  
Diameter Ratio ◽  
Load Test ◽  
Index Test ◽  
Point Load Test ◽  
Calculation Procedures

The point load test (PLT) is intended as an index test for rock strength classification or estimations of other strength parameters because it is economical and simple to conduct in the laboratory and in field tests. In the literature, calculation procedures for cylinder cores, blocks, or irregular lumps can be found, but no study has researched such procedures for half-cylinder cores. This paper presents the numerical model and laboratory tests for half-cylinder and cylinder specimens. The results for half-cylinder and cylinder specimens are then presented, analysed, and discussed. A correlation of failure load between half-cylinder and cylinder specimens is established with a suitable size suggestion and correction factor. It is found that the failure load becomes stable when half-cylinder specimens have a length/diameter ratio higher than 0.9. In addition, the results show that the point load strength index (PLSI) of half-cylinder cores can be calculated using the calculation procedures for diametral testing on cylinder cores, and it is necessary to satisfy the conditions that the length/diameter ratio be higher than 0.9 and the failure load be multiplied by 0.8.

Experimentally calibrated simplified time-domain numerical model for a multi-chamber OWC device

2015 ◽  
pp. 463-469
Author(s):  
A Iturrioz ◽  
J Sarmiento ◽  
J Armesto ◽  
R Guanche ◽  
C Vidal ◽  
...  
Keyword(s):  
Numerical Model ◽  
Time Domain

The Stick Motion of a Harmonically Excited, Friction-Induced Oscillator on a Sinusoidally Traveling Surface

2006 ◽  
Author(s):  
Albert C. J. Luo ◽  
Brandon C. Gegg ◽  
Steve S. Suh
Keyword(s):  
Dynamical Systems ◽  
Numerical Simulations ◽  
Dry Friction ◽  
The Other ◽  
Linear Oscillator ◽  
Analytical Prediction ◽  
Nonlinear Friction ◽  
Friction Forces

In this paper, the methodology is presented through investigation of a periodically, forced linear oscillator with dry friction, resting on a traveling surface varying with time. The switching conditions for stick motions in non-smooth dynamical systems are obtained. From defined generic mappings, the corresponding criteria for the stick motions are presented through the force product conditions. The analytical prediction of the onset and vanishing of the stick motions is illustrated. Finally, numerical simulations of stick motions are carried out to verify the analytical prediction. The achieved force criteria can be applied to the other dynamical systems with nonlinear friction forces possessing a CO - discontinuity.

Numerical Model of Towing Line in Sea Transport

2014 ◽  
Author(s):  
Ivan Ćatipović ◽  
Nastia Degiuli ◽  
Andreja Werner ◽  
Većeslav Čorić ◽  
Jadranka Radanović
Keyword(s):  
Numerical Model ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Cost Effective ◽  
Offshore Wind ◽  
Offshore Wind Turbine ◽  
Sea Transport ◽  
Nonlinear Properties ◽  
Wave Induced

Towing as a specific type of sea transport is often used for installing objects for drilling and exploitation of underwater gas and oil wells. Also, towing proved to be a cost-effective solution for the installation of the offshore wind turbine electric generators at sea locations. Because of the mass of these objects the need for towing increases progressively. Time domain numerical model for the wave-induced motions of a towed ship and the towline tension in regular head seas is presented in this paper. For the sake of simplicity, one end of the towing line is attached to ship’s bow and another end has prescribed straight line motion. All considerations are done in the vertical plane so the ship is modeled as a rigid body with three degrees of freedom. Hydrodynamic loadings due to waves are taken into account along with added mass and damping. Dynamics of the towing line is described by finite elements. Due to the nonlinear properties of the problem calculations are done in time domain. Comparison of the obtained numerical results is made with previously published results.

Calibration of Hydrodynamic Coefficients for a Semi-Submersible 10 MW Wind Turbine

2018 ◽  
Author(s):  
Marit I. Kvittem ◽  
Petter Andreas Berthelsen ◽  
Lene Eliassen ◽  
Maxime Thys
Keyword(s):  
Numerical Model ◽  
Line Tension ◽  
Offshore Wind ◽  
Scale Model ◽  
Viscous Drag ◽  
Mooring System ◽  
Drag Coefficients ◽  
Damping Coefficients ◽  
Decay Tests ◽  
Drift Forces

Hydrodynamic model tests and numerical simulations may be combined in a complementary manner during the design and qualification of new offshore structures. In the EU H2020 project LIFES50+ (lifes50plus.eu), a model test campaign of floating offshore wind turbines using Real-Time Hybrid Model (ReaTHM) testing techniques was carried out at SINTEF Ocean in fall 2017. The present paper focuses on the process of calibrating a numerical model to the experimental results. The concepts tested in the experimental campaign was a 1:36 scale model of the public version of the 10MW OO-Star Wind Floater semi-submersible offshore wind turbine. A time-domain numerical model was developed based on the as-built scale model. The hull was considered as rigid, while bar elements were used to model the mooring system and tower in a coupled finite element approach. First-order frequency-dependent added mass, potential damping, and excitation forces/moments were evaluated across a range of frequencies using a panel method. Distributed viscous forces on the hull and mooring lines were added to the numerical model according to Morison’s equation. Potential difference-frequency excitation forces were also included by applying Newman’s approximation. The quasi static properties of the mooring system were assessed by comparing the restoring force and maximum line tension with the pull-out test. Drag coefficients for the line segments were estimated by imposing the measured fairlead motion from model tests as forced displacement and comparing the calculated and measured dynamic line tension. The linear and viscous damping coefficients were first estimated based on the decay tests, and the tuned damping coefficients were compared to initial guesses based on the Reynolds and Keulegan-Carpenter number at model scale. The results were then applied in the numerical model, and simulations in extreme irregular waves were compared to the experiments. It was found that second order drift forces proved to be significant, particularly for the severe irregular seastate. These could not be modelled correctly applying the potential drift forces together with quadratic damping matrix tuned to the free decay test. And the model with viscous drag coefficients tuned to decay tests also underestimated the slow drift motions. Thus, new viscous drag coefficients were determined to match the low frequency platform response. To inverstigate the performance of the tuned model, comparisons were made for a moderate seastate and for a simulation with both waves and wind on an operating turbine. In the end, possible further improvements to the modelling were suggested.

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