Prediction of Sloshing Effects Using a Coupled Non-Linear Seakeeping and CFD Code

2013 ◽  
Author(s):  
Worakanok Thanyamanta ◽  
Don Bass ◽  
David Molyneux
Keyword(s):  
Degrees Of Freedom ◽  
Linear Time ◽  
Numerical Approach ◽  
Six Degrees Of Freedom ◽  
Non Linear ◽  
Roll Stabilization ◽  
Tank Geometry ◽  
Fully Coupled ◽  
Potential Use ◽  
Good Agreement

In this paper, a numerical approach for predicting sloshing or roll-stabilization effects is proposed. A 3D non-linear time domain seakeeping code, MOTSIM, was coupled with a commercial CFD code (Flow-3D) and used to predict roll stabilizing performance of an unconventional U-tube tank installed in an oceanographic vessel. The codes were fully coupled and thus provided coupled effects of the external flow field and the motion of the fluid with a free surface inside the anti-roll tank on the ship motion in six degrees of freedom. MOTSIM is a well validated code that has been proven to provide accurate motion prediction for various vessels. The CFD code allows for modeling of complex tank geometry as well as detailed investigation of locations in the tank where severe loads might be experienced. Comparisons of the simulation results with experimental data showed good agreement and significant effects of the anti-roll tank on decreasing the ship’s roll motion. This study also demonstrated the coupled code’s potential use for any type of sloshing problems including the design of roll-stabilization tanks and LNG carriers.

Application of non-linear H∞ control to the Tetrabot robot manipulator

1998 ◽  
Vol 212 (6) ◽  
pp. 459-465 ◽  
Author(s):  
I Postlethwaite ◽  
A Bartoszewicz
Keyword(s):  
Degrees Of Freedom ◽  
Robot Manipulator ◽  
Industrial Robot ◽  
External Disturbances ◽  
Six Degrees Of Freedom ◽  
Control Scheme ◽  
Non Linear ◽  
Modelling Uncertainties ◽  
Real Robot ◽  
Robotic Application

In this paper, an application of a non-linear H∞ control law for an industrial robot manipulator is presented. Control of the manipulator motion is formulated into a non-linear H∞ optimization problem, namely optimal tracking performance in the presence of modelling uncertainties and external disturbances. Analytical solutions for this problem are implemented on a real robot. The robot under consideration is the six-degrees-of-freedom GEC Tetrabot. Investigations are made into the selection of weights for the H∞ controller and it is shown how different selections of weights affect the Tetrabot performance. The authors believe this to be the first robotic application of nonlinear H∞ control. Comparisons of the proposed control strategy with conventional proportional-derivative and proportional-integral-derivative controllers show favourable performance of the Tetrabot under the new non-linear H∞ control scheme.

scholarly journals Geometric Non-Linear Approach to Stiffness State of Semi–Rigid Structures

2016 ◽  
Vol 6 (1) ◽  
pp. 63-70
Author(s):  
Moldovan Corina
Keyword(s):  
Degrees Of Freedom ◽  
Virtual Work ◽  
Steel Structures ◽  
Structural Level ◽  
Element Level ◽  
Present Contribution ◽  
Six Degrees Of Freedom ◽  
Non Linear ◽  
Linear Elements ◽  
Global Systems

Abstract Present contribution intends to emphasize the contribution of geometric non-linearity to the stiffness state of semi-rigid multi–storey steel structures. Though semi-rigidity of beam – column connections involves a nonlinearity at constitutive bending momentrelative rotation level, the geometric nonlinearity associated to deformed conFigure uration at element level is less referred to. The main objective of the study is to express the stiffness state of geometric non-linear elements semi-rigidly connected at its ends. Stiffness state is, in its term, expressed by element level stiffness matrix considering the six degrees of freedom of the planar element. Regarding the reference system, both local and global systems are employed allowing a simple and direct transition from element level vectorial relations to their structural level forms. The three fundamental vectorial relations (static equilibrium, kinematic compatibility, material constitutivity) emphasize that the principle of virtual work holds in the case of semi-rigidly connected skeletal structures as well.

A Six-Degree-of-Freedom Test System for the Study of Joint Mechanics and Ligament Forces

1995 ◽  
Vol 117 (4) ◽  
pp. 383-389 ◽  
Author(s):  
J. M. Hollis
Keyword(s):  
Degrees Of Freedom ◽  
Test System ◽  
Testing System ◽  
Joint Mechanics ◽  
Six Degrees Of Freedom ◽  
Position Feedback ◽  
Six Degree Of Freedom ◽  
Good Agreement

A joint testing system was designed to transmit a specified motion or force to a joint in all six degrees of freedom (d.o.f.) using a spatial linkage system for position feedback. The precise reproducibility of position provided by this method of position feedback allows determination of in situ ligament forces for external joint loadings. Load on the structure of interest is calculated from six d.o.f. load cell output after the loaded position is reproduced with all other structures removed. In a test of this system, measured loads showed good agreement with applied loads.

A Non-Linear Numerical Method for the Simulation of Parametric Roll Resonance in Regular Waves

2008 ◽  
Author(s):  
T. M. Ahmed ◽  
E. J. Ballard ◽  
D. A. Hudson ◽  
P. Temarel
Keyword(s):  
Numerical Method ◽  
Potential Flow ◽  
Degrees Of Freedom ◽  
Linear Time ◽  
Three Dimensional ◽  
Regular Waves ◽  
Time Step ◽  
Parametric Roll ◽  
Non Linear ◽  
Parametric Roll Resonance

In this paper, a non-linear time-domain method is used for the prediction of parametric roll resonance in regular waves, assuming the ship to be a system with three degrees of freedom in heave, pitch and roll. Coupled heave and pitch motions are obtained using a three-dimensional frequency-domain potential flow method which also provides the requisite hydrodynamic data of the ship in roll i.e. the potential flow based added inertia and damping. Periodic changes in the underwater hull geometry due to heave, pitch and the wave profile are calculated as a function of the instantaneous breadth. This is carried out using a two-dimensional approach i.e. for sections along the ship and at each time step. This formulation leads to a mathematical model that represents the roll equation of motion with third order non-linearities in the parametric excitation terms. Non-linearities in the roll damping and restoring terms are also accounted for. This method has been applied to two different hull forms, a post-Panamax C11 class containership and a transom stern Trawler, both travelling in regular waves. Special attention is focused on the influence of different operational aspects on parametric roll. Obtained results demonstrate that this numerical method succeeds in producing results similar to those available in the literature, both numerical and experimental.

Development of Six Degrees of Freedom Vibration Isolation System for Microgravity Environment

1995 ◽  
Author(s):  
Toshiyuki Suzuki ◽  
Koji Tanida ◽  
Akira Tanji ◽  
Koichi Okubo
Keyword(s):  
Degrees Of Freedom ◽  
Vibration Isolation ◽  
Parabolic Flight ◽  
Microgravity Environment ◽  
External Disturbances ◽  
Isolation System ◽  
Vibration Isolation System ◽  
Six Degrees Of Freedom ◽  
Active Vibration ◽  
Good Agreement

Abstract An active vibration isolation system, under development for use in microgravity environment, provides electromagnetic suspension by means of voice coils arranged in pairs to control the translational and rotational movements of the payload, three pairs of which cover the three axes to ensure control of payload movement in all six degrees of freedom. A series of tests performed on this system in microgravity environment created by parabolic flight proved that external disturbances in frequencies above 0.1 Hz were effectively reduced by applying the system. Also, good agreement was obtained between the measured performance and results of numerical simulation.

Marine Vessel Dynamics Using 6-DOF Simulations

2008 ◽  
Author(s):  
Craig J. Pregnalato ◽  
Kyong-Huhn Lee
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
High Amplitude ◽  
Cfd Simulations ◽  
Six Degrees Of Freedom ◽  
Interface Capturing ◽  
Surface Ship ◽  
Vessel Motion ◽  
Marine Vessels ◽  
Fully Coupled

The response of marine vessels to steady currents and unsteady wave motions is presented using six degrees-of-freedom CFD simulations. The equations governing the fluid flow are coupled with the rigid-body equations of motion to predict the response of surface ships when driven by high-amplitude waves. In addition, the maneuvering performance of a submarine is analysed for a constant heading and depth. Such fully coupled simulations allow the accurate prediction of the hydrodynamic forces acting on the vessel as well as the corresponding vessel motion and are becoming increasingly important from a design standpoint. In these simulations, a high-resolution interface-capturing scheme is used to efficiently capture the dynamics of breaking and overturning waves and to examine their impact on a surface ship. The dynamics of the vessel are investigated in detail with particular emphasis on its angular response (i.e. pitch, roll and yaw).

scholarly journals Novel Numerical Approach Based on Modified Extended Cubic B-Spline Functions for Solving Non-Linear Time-Fractional Telegraph Equation

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1154 ◽  
Author(s):  
Tayyaba Akram ◽  
Muhammad Abbas ◽  
Azhar Iqbal ◽  
Dumitru Baleanu ◽  
Jihad H. Asad
Keyword(s):  
Linear Time ◽  
Numerical Study ◽  
Numerical Approach ◽  
Telegraph Equation ◽  
High Order Accuracy ◽  
Spline Functions ◽  
B Spline ◽  
Fractional Telegraph Equation ◽  
Non Linear ◽  
Taylor’S Series

The telegraph model describes that the current and voltage waves can be reflected on a wire, that symmetrical wave patterns can form along a line. A numerical study of these voltage and current waves on a transferral line has been proposed via a modified extended cubic B-spline (MECBS) method. The B-spline functions have the flexibility and high order accuracy to approximate the solutions. These functions also preserve the symmetrical property. The MECBS and Crank Nicolson technique are employed to find out the solution of the non-linear time fractional telegraph equation. The time direction is discretized in the Caputo sense while the space dimension is discretized by the modified extended cubic B-spline. The non-linearity in the equation is linearized by Taylor’s series. The proposed algorithm is unconditionally stable and convergent. The numerical examples are displayed to verify the authenticity and implementation of the method.

Numerical and Experimental Study of 3-D Sloshing in Tanks of LNG Carriers

2006 ◽  
Author(s):  
Makoto Arai ◽  
Humberto S. Makiyama ◽  
Liang-Yee Cheng ◽  
Atsushi Kumano ◽  
Takahiro Ando ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Wave Spectrum ◽  
Irregular Waves ◽  
3D Analysis ◽  
Six Degrees Of Freedom ◽  
Strong Relation ◽  
3D Effects ◽  
Membrane Type ◽  
Tank Geometry ◽  
The Given

This paper describes a numerical analysis of sloshing in liquid cargo tanks of membrane-type liquefied natural gas (LNG) carriers in a rough sea. The numerical method used in this study is based on a finite-difference method, in which impact pressure on the tank ceiling is treated accurately by a numerical boundary condition proposed by the authors. Tank motion with six degrees of freedom was given by the response amplitude operator of a ship, and sloshing that occurs in regular and irregular waves is examined. An ISSC wave spectrum is used to generate the irregular waves. We describe the influence of 3D effects due to tank motion and tank geometry on the sloshing flow, and show the strong relation of the sloshing to the frequency of the given ship motion. Comparison of the numerical results with the measured data shows the effectiveness of the presented 3D analysis method.

scholarly journals Comparison of Wave Energy Park Layouts by Experimental and Numerical Methods

2020 ◽  
Vol 8 (10) ◽  
pp. 750
Author(s):  
Marianna Giassi ◽  
Jens Engström ◽  
Jan Isberg ◽  
Malin Göteman
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Domain Model ◽  
Algorithm Optimization ◽  
Six Degrees Of Freedom ◽  
Wave Energy Converters ◽  
Numerical Predictions ◽  
Optimization Routine ◽  
Sway Motion ◽  
Good Agreement

An experimental campaign of arrays with direct-driven wave energy converters of point-absorbing type is presented. The arrays consist of six identical floats, moving in six degrees of freedom, and six rotating power take-off systems, based on the design developed at Uppsala University. The goals of the work were to study and compare the performances of three different array layouts under several regular and irregular long-crested waves, and in addition, to determine whether the numerical predictions of the best performing array layouts were confirmed by experimental data. The simulations were executed with a frequency domain model restricted to heave, which is a computationally fast approach that was merged into a genetic algorithm optimization routine and used to find optimal array configurations. The results show that good agreement between experiments and simulations is achieved when the test conditions do not induce phenomena of parametric resonance, slack line and wave breaking. Specific non-linear dynamics or extensive sway motion are not captured by the used model, and in such cases the simulation predictions are not accurate, but can nevertheless be used to get an estimate of the power output.

Non-Linear Time Domain Simulation of Dynamic Instabilities in Longitudinal Waves

2008 ◽  
Author(s):  
S. Ribeiro e Silva ◽  
C. Guedes Soares
Keyword(s):  
Time Domain ◽  
Degrees Of Freedom ◽  
Linear Time ◽  
Simulation Method ◽  
Ship Motions ◽  
Computational Technique ◽  
Parametric Rolling ◽  
Longitudinal Waves ◽  
Six Degrees Of Freedom ◽  
Strip Theory

A time domain numerical simulation method is developed to determine ship motions in six degrees-of-freedom and to detect dynamic instabilities in both regular and irregular longitudinal waves. The basic approach of the simulation program involves computation of hydrodynamic coefficients of added mass and damping, restoring coefficients and diffraction and Froude-Krylov excitation forces at each step in time according to the instantaneous waterline and vessel position, using a strip theory method and a pressure integration technique along the segments. This paper briefly describes the computational technique utilized and makes comparisons between numerical and experimental roll damping data to infer about its influence on roll amplitude under parametric rolling conditions. An investigation into the dynamic stability in waves of a container vessel example.

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