Dynamic Analysis for the Design of CALM System in Shallow and Deep Waters

1997 ◽  
Vol 119 (3) ◽  
pp. 151-157 ◽  
Author(s):  
Y.-L. Hwang
Keyword(s):  
Mathematical Model ◽  
Dynamic Analysis ◽  
Model Test ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Mooring Lines ◽  
Deep Waters ◽  
Wave Drift ◽  
The Mathematical Model ◽  
Survival Condition

This paper presents a time domain analysis approach to evaluate the dynamic behavior of the catenary anchor leg mooring (CALM) system under the maximum operational condition when a tanker is moored to the terminal, and in the survival condition when the terminal is not occupied by a tanker. An analytical model, integrating tanker, hawser, buoy, and mooring lines, is developed to dynamically predict the extreme mooring loads and buoy orbital motions, when responding to the effect of wind, current, wave frequency, and wave drift response. Numerical results describing the dynamic behaviors of the CALM system in both shallow and deepwater situations are presented and discussed. The importance of the line dynamics and hawser coupled buoy-tanker dynamics is demonstrated by comparing the present dynamic analysis with catenary calculation approach. Results of the analysis are compared with model test data to validate the mathematical model presented.

scholarly journals Time and Frequency Domain Dynamic Analysis of Offshore Mooring

2021 ◽  
Vol 9 (7) ◽  
pp. 781
Author(s):  
Shi He ◽  
Aijun Wang
Keyword(s):  
Dynamic Analysis ◽  
Frequency Domain ◽  
Time Domain ◽  
Linearization Method ◽  
Euler Method ◽  
Single Component ◽  
Hydrodynamic Drag ◽  
Lumped Mass ◽  
Mooring Lines ◽  
The Time Domain

The numerical procedures for dynamic analysis of mooring lines in the time domain and frequency domain were developed in this work. The lumped mass method was used to model the mooring lines. In the time domain dynamic analysis, the modified Euler method was used to solve the motion equation of mooring lines. The dynamic analyses of mooring lines under horizontal, vertical, and combined harmonic excitations were carried out. The cases of single-component and multicomponent mooring lines under these excitations were studied, respectively. The case considering the seabed contact was also included. The program was validated by comparing with the results from commercial software, Orcaflex. For the frequency domain dynamic analysis, an improved frame invariant stochastic linearization method was applied to the nonlinear hydrodynamic drag term. The cases of single-component and multicomponent mooring lines were studied. The comparison of results shows that frequency domain results agree well with nonlinear time domain results.

Dynamic Analysis on a Cable-Driven Interventional Active Catheter Using Kane's Method Combined with Screw Theory

2014 ◽  
Vol 527 ◽  
pp. 140-145
Author(s):  
Da Xu Zhao ◽  
Bai Chen ◽  
Guo Zhong Shou ◽  
Yu Qi Gu
Keyword(s):  
Mathematical Model ◽  
Dynamic Analysis ◽  
Motion Control ◽  
Screw Theory ◽  
Driving Forces ◽  
Structure Design ◽  
Kinematics And Dynamics ◽  
Existing Problems ◽  
Blind Area ◽  
The Mathematical Model

In view of the existing problems of traditional interventional catheters, particularly poor activity, operation difficulty and mass blind area, a novel interventional catheter with a cable-driven active head-end is proposed, and a prototype was built to verify the performance. This paper deals with the kinematics and dynamics of the cable-driven prototype, a dynamic model based on Kanes method combined with screw theory was presented in this paper. According the mathematical model and the prototypes structure, the analysis of kinematics and dynamics of active head-end-end is done in the environment of Mathematica. The needed driving forces of every joint when the system moving along planned trajectory are calculated. The results can provide a basis for the structure design and motion control of the interventional active catheter.

Time Domain Hydroelastic Analysis of a Flexible Marine Structure Using State-Space Models

2007 ◽  
Author(s):  
Reza Taghipour ◽  
Tristan Perez ◽  
Torgeir Moan
Keyword(s):  
Mathematical Model ◽  
State Space ◽  
Time Domain ◽  
State Space Model ◽  
Realization Theory ◽  
Regular Waves ◽  
Alternative State ◽  
Marine Structure ◽  
Hydroelastic Analysis ◽  
The Mathematical Model

This article deals with time-domain hydroelastic analysis of a marine structure. The convolution terms in the mathematical model are replaced by their alternative state-space representations whose parameters are obtained by using the realization theory. The mathematical model is validated by comparison to experimental results of a very flexible barge. Two types of time-domain simulations are performed: dynamic response of the initially inert structure to incident regular waves and transient response of the structure after it is released from a displaced condition in still water. The accuracy and the efficiency of the simulations based on the state-space model representations are compared to those that integrate the convolutions.

scholarly journals Vertical Motions Damping Model Test of a Lifeboat Lowered Onto a Flat Sea Surface

2018 ◽  
Vol 25 (s1) ◽  
pp. 51-55
Author(s):  
Aleksander Kniat ◽  
Paweł Dymarski
Keyword(s):  
Mathematical Model ◽  
Model Test ◽  
Water Surface ◽  
Vertical Motion ◽  
Sea Surface ◽  
Damping Factor ◽  
Initial Speed ◽  
The Mathematical Model ◽  
Damping Model

Abstract The article presents the experiment’s results of the lifeboat model lowered with an initial speed and then released to fall onto a flat water surface. The purpose of the research is to determine the trajectory of the vertical boat motion and describe it with a mathematical model. This is closely related to determining the damping factor since the vertical motion is damped and the lifeboat gets balanced and stops moving after some time. The procedure of selecting parameters in the mathematical model to adjust to the results of the experiment was described in details. The summary describes the imperfections of the presented damping model and their probable causes.

Coupled Dynamic Analysis of a Moored Spar Platform in Time Domain

2010 ◽  
Author(s):  
M. D. Yang ◽  
B. Teng
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Dynamic Analysis ◽  
Time Domain ◽  
Surface Boundary ◽  
Spar Platform ◽  
Mooring Lines ◽  
Coupled Dynamic Analysis ◽  
Free Surface Boundary Condition ◽  
Surface Boundary Condition

A time-domain simulation method is developed for the coupled dynamic analysis of a spar platform with mooring lines. For the hydrodynamic loads, a time domain second order method is developed. In this approach, Taylor series expansions are applied to the body surface boundary condition and the free surface boundary condition, and Stokes perturbation procedure is then used to establish corresponding boundary value problems with time-independent boundaries. A higher order boundary element method is developed to calculate the velocity potential of the resulting flow field at each time step. The free-surface boundary condition is satisfied to the second order by 4th order Adams-Bashforth-Moultn method. An artificial damping layer is adopted on the free surface to avoid the wave reflection. For the mooring-line dynamics, a geometrically nonlinear finite element method using isoparametric cable element based on the total Lagrangian formulation is developed. In the coupled dynamic analysis, the motion equation for the hull and dynamic equations for mooring lines are solved simultaneously using Newmark method. Numerical results including motions and tensions in the mooring lines are presented.

Application of Peak Distribution Method for Response Based Analysis of Mooring Lines Under Tropical Storms

2020 ◽  
Author(s):  
A. Ghasemi ◽  
Y. Drobyshevski ◽  
M. Kimiaei ◽  
M. Efthymiou
Keyword(s):  
Time Domain ◽  
Nonlinear Behavior ◽  
Extreme Value Distribution ◽  
Time Domain Analysis ◽  
System Response ◽  
Response Analysis ◽  
Tropical Storms ◽  
Mooring Lines ◽  
Distribution Method ◽  
Large Variability

Abstract Response based analysis (RBA) is a comprehensive approach for the prediction of extreme responses and design metocean conditions of offshore facilities. For RBA, the structural system needs to be modelled, and its behavior analyzed when subjected to large metocean datasets, usually comprising thousands of different sea states. Due to the dynamic and nonlinear behavior of mooring systems in floating structures, application of conventional time domain analysis for RBA of these systems is a computationally demanding process. Hence, investigation of faster solvers and more efficient methods for the RBA is inevitable. Peak distribution method (PDM), which has recently been introduced and used for response analysis of mooring systems under extreme design conditions, is a possible solution to reduce the computational efforts in RBA by reducing the number of simulations. This study explores the utilization of the PDM for RBA of the mooring system of a turret-moored large FPSO subjected to tropical storms. Large variability of metocean parameters within such storms limits the applicability of intuitive judgement for the selection of governing sea states. The results are compared through both time-domain and frequency-domain simulations and a computationally efficient methodology is proposed. It provides a general robust framework of computing the extreme value distribution of the system response. The proposed methodology can be used for RBA of mooring lines tension under storm conditions comprising large number of sea states.

A Preliminary Study of a Rigid Semi-Submersible Fish Farm for Open Seas

2017 ◽  
Author(s):  
Lin Li ◽  
Muk Chen Ong
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Time Domain Analysis ◽  
Fish Farm ◽  
Response Analysis ◽  
Frequency Domain Method ◽  
Mooring System ◽  
Viscous Effects ◽  
Support Structure ◽  
Mooring Lines

The development of reliable fish farm structures for open seas becomes more and more important. One of the challenges is to design a robust structure to withstand the harsh offshore environmental loads. This paper investigates a semi-submersible type offshore fish farm system for open seas. This system consists of a semi-submersible support structure with pontoons and braces, a catenary mooring system and net cages. The support structure is designed to be rigid to resist severe offshore conditions. A preliminary hydrodynamic and response analysis is carried out for this concept. The linear hydrodynamic properties using different composite models with panel and Morison elements are computed. Based on the hydrodynamic analysis, linearised frequency-domain and coupled time-domain analysis are performed to predict the extreme motions of the support structure and the extreme tensions in the mooring lines. The results indicate that the frequency-domain method underestimates the extreme responses, and the couplings between the structure and the mooring system need to be considered in the time-domain. Responses using various hydrodynamic models are also compared to evaluate the influences of the viscous effects from the pontoons and the nets of this fish farm concept.

Sea Water Pump Station Basin Mathematical Hydraulic Model Test (CFD Analysis)

2009 ◽  
Author(s):  
Sadegh Barzegar ◽  
Alireza Elhami Amiri ◽  
Pooyan Rahbar ◽  
Mehdi Assadi Niazi
Keyword(s):  
Mathematical Model ◽  
Free Surface ◽  
Model Test ◽  
Flow Rate ◽  
Sea Water ◽  
Water Pump ◽  
Pumping Station ◽  
Water Pumping ◽  
Pump Station ◽  
The Mathematical Model

Background and aim: A sea water intake, with original design of the six drum screen and twenty sea water pump intake with very different flow rate connected to header bay. The capacity of Origin Sea water intake including huge pump station and drum screen is 200,000 m3/hr. The purpose of the mathematical hydraulic model test of the sea water pumping station is to verify that the basin allows a good operating condition for each pump. To ensure a good operating condition for each pump, the design of the seawater basin has to insure: • A correct filter working; • Low transversal velocities; • A flow without vortex. Method and material: The mathematical model of the basin allows to know the flow and to verify: • The main dimensions of the pumping station; • The distance between the inlet ducts and the filters; • The distance between the filters and pump chambers. Result: in the first basin, the flow patterns no problems. Only swirl at the exit of culverts and near the free surface, and two areas where the flow has no velocity were observed. In the downstream other filters, we observe also a circulation that generates a tangential velocity. Conclusion: The mathematical model of the sea water pumping station has allowed calculating three cases (without and with filter stopped) for the low water level and nominal flow rate. In most difficult case, we observe some recirculation, mainly near the free surface, without more influence on principal flow. In the three cases, the distribution of the flow rate between the drum screens is uniform; the gap is inferior to 2%. At the entry of the pump chambers, the velocity fluctuations and the angle are low. Consequently, the secondary flows in pump chambers will be limited.

The Analysis of Motions of Semisubmersible Drilling Vessels in Waves

1970 ◽  
Vol 10 (03) ◽  
pp. 311-320 ◽  
Author(s):  
Ben G. Burke
Keyword(s):  
Mathematical Model ◽  
Test Data ◽  
Model Test ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Basic Principles ◽  
Six Degrees Of Freedom ◽  
Drilling Equipment ◽  
Wave Response ◽  
The Mathematical Model

Abstract A mathematical model was developed to compute the motions of semisubmersible drilling vessels in waves for a wide variety of semisubmersible configurations. The model was derived from a linear representation of motions, ocean waves, and forces. The semisubmersible is represented as a rigid space frame composed of a number of cylindrical members with arbitrary diameters, lengths and orientations. Forces on the semisubmersible are derived from anchorline properties, and hydrostatic hydrodynamic principles. A solution is obtained for motions in six degrees of freedom for a sinusoidal wave train of arbitrary height, period, direction and water depth. Results from the analysis of three semisubmersibles are compared with results from available model test data to verily the mathematical model. Introduction An accurate and complete representation of the response of a drilling vessel to waves is a valuable engineering tool for predicting vessel performance and designing drilling equipment. The performance and designing drilling equipment. The wave response for a floating vessel may be obtained to various degrees of accuracy from model tests or analytical means, as described by Barkley and Korvin-Kroukovsky and as applied by Bain. A review of the works cited shows that the evaluation of the wave response for a particular vessel requires considerable time and effort, either in model construction and testing or in computer programming and calculations. In order to reduce programming and calculations. In order to reduce the amount of time and effort required to evaluate a particular vessel, means were investigated to generalize and automate, on a digital computer, methods for evaluating wave response for vessels of arbitrary configuration. The mathematical model described in this paper is the result of such an investigation for semisubmersible-type drilling vessels. The paper presents a general description of the mathematical model and the basic principles and assumptions from which it was derived. The validity of the model is evaluated by comparing results of the analysis of three semisubmersibles with available model test data. MATHEMATICAL MODEL The mathematical model for calculating the motions of a semisubmersible in waves is derived from basic principles and empirical relationships in classical mechanics. All equations are derived for "small amplitude" waves and motions. The nonlinear equations that appear in the problem are replaced by "equivalent" linear equations in order to conform to the linear analysis method used in obtaining a solution. The model is implemented in a computer program that computes vessel response in all six degrees of freedom for a broad range of semisubmersible configurations and wave parameters. The basic elements in the theoretical model are outlined, with a more detailed discussion of the principles and derivations used to obtain the model principles and derivations used to obtain the model presented in the Appendix. presented in the Appendix. SEMISUBMERSIBLE DESCRIPTION AND EQUATIONS OF MOTION The semisubmersible is characterized as a space-frame of cylindrical members and is described geometrically by specifying end-coordinates and diameters for all of the members. Specification of the mass, moments of inertia, center of gravity and floating position are required to complete the description. The six equations of motion for the semisubmersible derive from Newton's second law for a rigid body. These differential equations, when written in matrix form, equate the product of the six-component acceleration vector, {x}, and the inertia matrix, I, to a six-component, force-moment vector, {FT}. SPEJ P. 311

Nonlinear Time Domain Seismic Analysis for a Coupled Mooring Jacket-Yoke-FSO System

2009 ◽  
Author(s):  
Partha Chakrabarti
Keyword(s):  
Dynamic Analysis ◽  
Time Domain ◽  
Vibration Isolation ◽  
Wind Wave ◽  
Time History ◽  
Coupled System ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Isolation Device ◽  
Nonlinear Time Domain

A mooring facility for a Floating Storage and Offloading (FSO) system, due to site conditions such as shallow water, often uses a fixed mooring tower for mooring of the FSO. When a fixed mooring tower in the form of a jacket structure is used, the turntable is mounted on the top of the jacket so that the FSO can weathervane due to actions of wind, wave and current forces. Product swivels are also located on this structure for uninterrupted flow of the product to the FSO when it rotates. The connection of the FSO to the turntable is through a rigid yoke. The yoke consists of two yoke arms meeting at a point hinged at the turntable, one large diameter cylinder for providing the stabilizing ballast load and two pendants supporting the ballast. The jacket has to be designed for the mooring loads in addition to the wind, wave and current loads on itself. The rigid yoke system is designed so that the varying draft conditions of the FSO as well as its motions can be suitably handled and absorbed. Complications may arise when the jacket is located in a seismically active site. When a site is prone to very strong ground motions, seismic response of the jacket in conjunction with the moored FSO has to be studied. The additional requirement is that any vibration of the jacket is suitably absorbed by the yoke system or a suitable isolation device is designed between the link or the yoke structure and the FSO. The weight of the suspended mass is a key design variable which affects this behavior. A structural dynamic model of the coupled jacket-yoke-frame-FSO system is analyzed using nonlinear time domain analysis technique. The calibrated El Centro ground accelerations are used for this analysis as a representative seismic excitation. A comparison of the results for jacket alone and the coupled system enables us to determine the effect of the yoke-frame-FSO on the dynamic response. The requirement, if any, of vibration isolation device for the nonlinear link (yoke) structure is decided from the dynamic analysis results. The dynamic analysis of the coupled system is complex. The complexities in the model arise due to: • The nonlinearity of the soil-pile system; • Nonlinearity of the yoke mechanism; • The fact that the FSO is a floating structure and it is free from the base excitation; • The FSO involves a large mass and is essentially free floating in water. The dynamic analyses are performed in several stages in view of the above complexities. Initially, the mode shapes and frequencies of the jacket alone are evaluated. Then the jacket is analyzed using the response spectrum approach with the design seismic spectrum. Subsequently time domain analysis of the jacket alone is performed using the calibrated El Centro seismic time history. Finally, the coupled system is analyzed for the time history of ground motion. Since the seismic event represents the design Strength Level Earthquake (SLE) condition, which is a rare event, only the FSO is coupled to the jacket, the offtake tanker is not assumed to be present during this extreme event. The nonlinear time domain analysis includes the nonlinear link (yoke) which is a mechanism by virtue of the hinges present. Therefore, the analysis requires geometric nonlinearity of the link to be considered to simulate the large displacements and the large rotations of the link, in addition to the nonlinearities of the pile-soil system. From the results of the analyses conclusions are drawn about effectiveness of vibration isolation by comparing the results of the jacket-yoke-FSO system to those of the jacket alone.

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