Coupled Transient CFD and Diffraction Modeling for Installation of Subsea Equipment/Structures in Splash Zone

2013 ◽  
Author(s):  
David Jia ◽  
Madhusuden Agrawal
Keyword(s):  
Steady State ◽  
Diffraction Analysis ◽  
Time Domain ◽  
Cfd Simulation ◽  
Load Level ◽  
Body Motion ◽  
Splash Zone ◽  
Wave Loads ◽  
Added Masses ◽  
Hydrodynamics Coefficients

In development of deep water oil and gas fields, successfully and economically installing subsea equipment and structure is critically important. This paper presents a state-of-the-art methodology for predicting the motions and loads of subsea equipment/structure during such operations basing on time domain simulations of the combined installation vessel and subsea equipment/structure. The time domain diffraction simulation of the moving lifting vessel is coupled with multiphase CFD simulation of subsea equipment/structure in splash zone. Transient CFD model with rigid body motion for the equipment/structure calculates added masses, forces and moments on the equipment/structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation. This paper has many potential applications, such as, installation of pile, manifold, subsea tree, PLET/PLEM, or other subsea equipment/structure. This coupled approach has been successfully implemented on a cylindrical structure. The results show that total load level, and dynamics of the subsea equipment/structure due to waves in splash zone are predicted. Current practice of installation analysis in accordance with the recommendations from DNV-RP-H103 [1] cannot determine in detail the wave loads either during the passage through splash zone, or added mass and damping when the equipment/structure is submerged. In order to determine wave loads in detail, model tests are needed. In the absence of tests, simplified equations or empirical formulations have to be used to calculate/estimate these hydrodynamics coefficients as recommended in DNV-RP-H103. Steady-state CFD simulations on a stationary equipment/structure are usually used to predict drag and added masses on submerged structures. However the steady-state assumption in CFD ignores the resonating motion of equipment/structure in calculating hydrodynamics coefficients, which can severely affect the accuracy of these predictions. The above methods often give overly conservative results for allowable sea state which results in uneconomical vessel time or inaccurate results for installation. The methodology of this paper gives more accurate results, and provides potentially economical vessel time during installation. The intent of this paper is to demonstrate the solution and methodology.

A Parametric Study of Wave - Structure Interaction Using the Coupled Transient CFD and Diffraction Methodology

2014 ◽  
Author(s):  
David Jia ◽  
Madhusuden Agrawal ◽  
Jim Malachowski
Keyword(s):  
Steady State ◽  
Diffraction Analysis ◽  
Time Domain ◽  
Cfd Simulation ◽  
Wave Structure ◽  
Structure Interaction ◽  
Added Masses ◽  
Parametric Studies ◽  
Traditional Approaches ◽  
Wave Structure Interaction

This paper is a continuation of our previous paper [1] (OMAE2013-11569) where we demonstrated a state-of-the-art methodology for predicting the motions and loads of subsea equipment and structures during offshore operations basing on time domain simulations of subsea equipment and structures. Instead of relying on simplified equations or empirical formulations to calculate and estimate the hydrodynamics coefficients, or using steady-state CFD simulation on a stationary equipment and structure to predict drag and added masses on submerged structures in traditional approaches, this methodology couples the transient CFD with diffraction analysis. The time domain diffraction simulation is coupled with multiphase CFD simulation of subsea equipment and structures in waves. Transient CFD model with rigid body motion for the equipment and structure calculates added masses, forces and moments on the equipment and structure for diffraction analysis, while diffraction analysis calculates linear and angular velocities for CFD simulation. In this paper, parametric studies are performed to investigate effect of wavelength, wave amplitude and wave current on the motion of a hollow cylinder in waves. The results of the parametric studies in this paper show wave-structure interaction of a hollow cylinder in waves, and the effect of waves and current on the motion of the cylinder and the associated forces. The results provide better understanding of structure motion and associated forces in waves using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations [2], or by using steady-state CFD analyses in traditional decoupled approaches. The results show that the coupled physics of wave and cylinder motion is captured by using this methodology, otherwise is not captured by traditional approaches. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in wave during offshore operations.

Modelling of Wave-Structure Interaction of a Cylinder in Regular Sea Waves With Vessel Motions Using Coupled Transient CFD and Diffraction Methodology

2015 ◽  
Author(s):  
David Jia ◽  
Paul Schofield ◽  
Joanne Shen ◽  
Jim Malachowski
Keyword(s):  
Steady State ◽  
Hollow Cylinder ◽  
Cfd Simulation ◽  
Traditional Approach ◽  
Wave Structure ◽  
Sea Waves ◽  
Regular Waves ◽  
Structure Interaction ◽  
Added Masses ◽  
Wave Structure Interaction

This paper is a continuation of our previous paper [1] (OMAE2014-23225) where we did a parametric study for wave-structure interaction of a hollow cylinder in regular sea waves without vessel motions. The effect of waves and current on the motion of the cylinder and the associated forces were evaluated using a state-of-the-art methodology [2] (OMAE2013-11569) for predicting the motions and loads of subsea equipment and structures during offshore operations. In this paper, we extend the solution to include wave – structure interaction in regular sea waves and vessel motions. The 5th order Stokes regular waves in CFD and vessel motions are included in the modeling. This methodology couples the transient CFD with a hydrodynamic motion analysis after diffraction analyses, instead of relying on the traditional approach which uses simplified equations or empirical formulae to estimate hydrodynamic coefficients [3], or using steady-state CFD simulation on stationary equipment and structures to predict drag and added masses on submerged structures. The time domain diffraction simulation is coupled with a multiphase CFD simulation of subsea equipment and structures in waves. A transient CFD model with rigid body motions for the equipment and structures calculates added masses, forces and moments on the equipment and structures for the diffraction analysis, while the diffraction analysis calculates linear and angular velocities for the CFD simulation. In this paper, simulations are performed to investigate effect of the vessel motions on the motion of a hollow cylinder in regular sea waves. The results are compared with that from the traditional approach. This coupled methodology has potential applications in analyses of the motions of subsea equipment and structures in waves during offshore operations. The results in this paper show wave-structure interaction of a hollow cylinder in regular sea waves, and the effect of vessel motions on the motion of the cylinder. The results provide better understanding of structure motion in regular waves with vessel motions using this coupled methodology. The coupled methodology eliminates the inaccuracy inherited from assumed or calculated hydrodynamic properties that are obtained by using simplified equations or empirical formulations, or by using steady-state CFD analyses in traditional decoupled approaches. The results show that the coupled physics of regular sea waves, vessel motions and cylinder motion is captured by using this methodology. The coupled physics is not captured by the traditional approach.

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.

Robust Stabilizing Controller Design for Inverted Pendulum System

2014 ◽  
Vol 71 (1) ◽  
Author(s):  
Hazem I. Ali
Keyword(s):  
Steady State ◽  
Time Domain ◽  
State Feedback ◽  
Inverted Pendulum ◽  
Controller Design ◽  
H Infinity ◽  
Pendulum System ◽  
Stabilizing Controller ◽  
Inverted Pendulum System ◽  
System Uncertainties

In this paper the design of robust stabilizing state feedback controller for inverted pendulum system is presented. The Ant Colony Optimization (ACO) method is used to tune the state feedback gains subject to different proposed cost functions comprise of H-infinity constraints and time domain specifications. The steady state and dynamic characteristics of the proposed controller are investigated by simulations and experiments. The results show the effectiveness of the proposed controller which offers a satisfactory robustness and a desirable time response specifications. Finally, the robustness of the controller is tested in the presence of system uncertainties and disturbance.

scholarly journals CFD Simulation and Experimental Study on Coupled Motion Response of Ship with Tank in Beam Waves

2022 ◽  
Vol 10 (1) ◽  
pp. 113
Author(s):  
Tao He ◽  
Dakui Feng ◽  
Liwei Liu ◽  
Xianzhou Wang ◽  
Hua Jiang
Keyword(s):  
Working Conditions ◽  
Large Scale ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Body Motion ◽  
Time Step ◽  
Coupled Motion ◽  
Motion Response ◽  
Time Step Size ◽  
Tank Sloshing

Tank sloshing is widely present in many engineering fields, especially in the field of marine. Due to the trend of large-scale liquid cargo ships, it is of great significance to study the coupled motion response of ships with tanks in beam waves. In this study, the CFD (Computational Fluid Dynamics) method and experiments are used to study the response of a ship with/without a tank in beam waves. All the computations are performed by an in-house CFD solver, which is used to solve RANS (Reynold Average Navier-Stokes) equations coupled with six degrees-of-freedom solid-body motion equations. The Level Set Method is used to solve the free surface. Verification work on the grid number and time step size has been conducted. The simulation results agree with the experimental results well, which shows that the numerical method is accurate enough. In this paper, several different working conditions are set up, and the effects of the liquid height in the tank, the size of the tank and the wavelength ratio of the incident wave on the ship’s motion are studied. The results show the effect of tank sloshing on the ship’s motion in different working conditions.

Time Domain Computation of the Wave-Making Resistance of Ships

2005 ◽  
Vol 49 (02) ◽  
pp. 144-158 ◽  
Author(s):  
F. Kara ◽  
D. Vassalos
Keyword(s):  
Steady State ◽  
Time Domain ◽  
Three Dimensional ◽  
Impulse Response Function ◽  
The Body ◽  
Source Distribution ◽  
Research Centre ◽  
Surface Source ◽  
Calm Water ◽  
Marine Engineering

The Ship Stability Research Centre, Department of Naval Architecture and Marine Engineering, The Universities of Glasgow and Strathclyde, Scotland, UKA linearized three-dimensional potential flow formulation in time domain is applied to calculate wave-making resistance of ships in calm water. Steady-state perturbation potentials for resistance are obtained as the steady-state limit of the surge radiation impulse response function using the transient free surface source distribution over the body surface. Five different vessels are used to validate the present numerical approximation. The results, including steady-state wave-making resistance, sinkage force, trim moment, and wave profile along the waterline, are compared with other published numerical and experimental results.

scholarly journals Two-dimensional CFD simulation and pilot-scale experimental verification of a downdraft gasifier: effect of reactor aspect ratios on temperature and syngas composition during gasification

2020 ◽  
Vol 7 (3) ◽  
pp. 536-550
Author(s):  
Chootrakul Siripaiboon ◽  
Prysathyrd Sarabhorn ◽  
Chinnathan Areeprasert
Keyword(s):  
Steady State ◽  
Temperature Profile ◽  
Fuel Consumption ◽  
Cfd Simulation ◽  
Pilot Scale ◽  
Reactor Wall ◽  
Two Dimensional ◽  
High Concentration ◽  
Downdraft Gasifier ◽  
Aspect Ratios

Abstract This paper focuses on a two-dimensional CFD simulation of a downdraft gasifier and a pilot-scale experiment for verification using wood pellet fuel. The simulation work was carried out via the ANSYS-Fluent CFD software package with in-house coding via User Defined Function. Three gasification parameters were taken into account in the simulation and validation to achieve highly accurate results; namely, fuel consumption, temperature profile, and syngas composition. After verification of the developed model, the effects of aspect ratios on temperature and syngas composition were investigated. Results from simulation and experimental work indicated that the fuel consumption rate during the steady state gasification experiment was 1.750 ± 0.048 g/s. The average steady state temperature of the experiment was 1240.32 ± 14.20 K. In sum, the fuel consumption and temperature profile during gasification from modeling and experimentation show an error lower than 1.3%. Concentrations of CO, CO2, H2, and CH4 were 20.42 vol%, 15.09 vol%, 8.02 vol%, and 2.6 vol%, respectively, which are comparable to those of the experiment: 20.00 vol%, 15.48 vol%, 8.00 vol%, and 2.65 vol%. A high concentration of syngas is observed in the outer radial part of the reactor because of the resistive flow of the air inlet and the synthesis gas produced. The average temperatures during the steady state of the gasifier with aspect ratios (H/D) of 1.00, 1.38 (experiment), and 1.82 were 978.77 ± 11.60, 1256.46 ± 9.90, and 1368.94 ± 9.20 K, respectively. The 1.82 aspect ratio reactor has the smallest diameter, therefore the radiative heat transferred from the reactor wall affects the temperature in the reactor. Syngas compositions are comparable. Inverse relationships between the aspect ratios and the syngas LHV, (4.29–4.49 MJ/N m3), cold gas efficiency (29.66% to 31.00%), and carbon conversion (79.59% to 80.87%) are observed.

scholarly journals STEADY-STATE ANALYSIS OF NONLINEARLY COUPLED CHUA'S CIRCUITS WITH PERIODIC INPUT

2003 ◽  
Vol 13 (11) ◽  
pp. 3395-3407 ◽  
Author(s):  
F. A. SAVACI ◽  
M. E. YALÇIN ◽  
C. GÜZELIŞ
Keyword(s):  
Steady State ◽  
Time Domain ◽  
Transfer Functions ◽  
Piecewise Linear ◽  
Time Domain Analysis ◽  
Steady State Analysis ◽  
Linear Dynamic Systems ◽  
Periodic Input ◽  
The Time Domain ◽  
State Analysis

In this paper, nonlinearly coupled identical Chua's circuits, when driven by sinusoidal signal have been analyzed in the time-domain by using the steady-state analysis techniques of piecewise-linear dynamic systems. With such techniques, it has become possible to obtain analytical expressions for the transfer functions in terms of the circuit parameters. The proposed system under consideration has also been studied by analog simulations of the overall system on a hardware realization using off-the-shelf components as well as by a time-domain analysis of the synchronization error.

Dynamics and Stability of Turn-Milling Operations With Varying Time Delay in Discrete Time Domain

2018 ◽  
Vol 140 (10) ◽  
Author(s):  
Alptunc Comak ◽  
Yusuf Altintas
Keyword(s):  
Time Domain ◽  
Chip Thickness ◽  
Body Motion ◽  
Depth Of Cut ◽  
Time Varying Delay ◽  
Milling Operations ◽  
Varying Time Delay ◽  
The Stability ◽  
Five Axis ◽  
Turn Milling

Turn-milling machines are widely used in industry because of their multifunctional capabilities in producing complex parts in one setup. Both milling cutter and workpiece rotate simultaneously while the machine travels in three Cartesian directions leading to five axis kinematics with complex chip generation mechanism. This paper presents a general mathematical model to predict the chip thickness, cutting force, and chatter stability of turn milling operations. The dynamic chip thickness is modeled by considering the rigid body motion, relative vibrations between the tool and workpiece, and cutter-workpiece engagement geometry. The dynamics of the process are governed by delayed differential equations by time periodic coefficients with a time varying delay contributed by two simultaneously rotating spindles and kinematics of the machine. The stability of the system has been solved in semidiscrete time domain as a function of depth of cut, feed, tool spindle speed, and workpiece speed. The stability model has been experimentally verified in turn milling of Aluminum alloy cut with a helical cylindrical end mill.

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