Ship Capsize Risk in a Seaway Using Fitted Distributions to Roll Maxima

2000 ◽  
Vol 122 (2) ◽  
pp. 141-146 ◽  
Author(s):  
Kevin A. McTaggart
Keyword(s):  
Efficient Method ◽  
Time Domain ◽  
Wave Process ◽  
Gumbel Distribution ◽  
Roll Angle ◽  
Random Wave ◽  
Seed Number ◽  
Moderate Number ◽  
Ship Capsize

This paper presents an efficient method for determining capsize risk for a given seaway and ship operational condition using time domain simulations. The risk of capsize during 1 h exposure to a given seaway is dependent on the wave process realization, which is determined by a seed number and resulting random wave phases. The dependence of maximum roll angle on wave process can be modeled by fitting a suitable distribution to maximum roll angles from a moderate number of simulations. Sample computations for a naval frigate demonstrate that a Gumbel distribution provides a very good fit to maximum roll angles from different wave realizations. [S0892-7219(00)00402-7]

Modal Control by Modal Force Technique

1991 ◽  
Author(s):  
C. D. Tsai ◽  
M. S. Ju ◽  
Y. G. Tsuei
Keyword(s):  
Feedback Control ◽  
Control Problem ◽  
Efficient Method ◽  
Time Domain ◽  
Modal Control ◽  
Global Dynamic ◽  
Recent Developments ◽  
Modal Force ◽  
Frequency Domain Approach ◽  
Direct Feedback

Abstract Modal control of structure requires the estimation of the modal states variables for feedback. One approach that does not require modal states variables estimation is the direct feedback control. Recent developments in modal control for direct feedback are mainly time domain methods. In this paper, an efficient method based on frequency domain approach named Modal Force Technique is developed. The method not only allows one to modify the global dynamic behavior of the synthesized structure but also can be utilized for modal control problem if the acceleration, velocity and displacement feedbacks are used.

Evaluation of Impact Loads on Offshore Jacket Platform During Float-Over Mating Operation

2019 ◽  
Author(s):  
Gurumurthy Kagita ◽  
Mahesh B. Addala ◽  
Gudimella G. S. Achary ◽  
Subramanyam V. R. Sripada
Keyword(s):  
Time Domain ◽  
Linear Time ◽  
Random Wave ◽  
Impact Loads ◽  
Transient Effects ◽  
Seed Selection ◽  
Mooring Lines ◽  
Contact Points ◽  
Non Linear ◽  
The Impact

Abstract In the mating phase of float-over operation, the topsides deck load from the vessel is transferred onto the jacket either by ballasting the vessel or by the combination of ballasting and hydraulic jacking system. During this phase of operation, the topsides and jacket experience impact loads through the contact points in a short duration of time. To evaluate the impact loads and to capture the transient effects precisely, a non-linear time domain hydrodynamic analysis is required. To obtain the design loads, generally the numerical jacking simulation is initiated at the time instant of maximum wave height when the jacking system is used. However, the conservative response may also depend on the relative velocity between the jacket and topsides legs. In this paper, a series of non-linear time domain as well as linear frequency domain hydrodynamic analyses are performed to evaluate the impact loads between 9000 tonne integrated topsides deck and a 4-legged jacket in a water depth of 50 m during float-over mating operation. The simulations are performed using MOSES software. The float-over hardware such as LMUs (leg mating unit), DSUs (deck support unit), Jacks, Fenders and Mooring lines are modelled as appropriate linear / nonlinear springs. The principle of the mating operation is considered through a combination of vessel ballasting and jacking operation. This paper discusses about random wave seed selection, effect of vessel response and wave headings on the impact loads of LMUs and Jacks/DSUs.

Non-Gaussian Random Wave Simulation by Two-Dimensional Fourier Transform and Linear Oscillator Response to Morison Force

2007 ◽  
Vol 129 (4) ◽  
pp. 327-334 ◽  
Author(s):  
Xiang Yuan Zheng ◽  
Torgeir Moan ◽  
Ser Tong Quek
Keyword(s):  
Fourier Transform ◽  
Time Domain ◽  
Two Dimensions ◽  
Second Order ◽  
Linear Oscillator ◽  
Interaction Matrix ◽  
Random Wave ◽  
Two Dimensional ◽  
Near Surface ◽  
Non Gaussian

The one-dimensional fast Fourier transform (FFT) has been applied extensively to simulate Gaussian random wave elevations and water particle kinematics. The actual sea elevations/kinematics exhibit non-Gaussian characteristics that can be represented mathematically by a second-order random wave theory. The elevations/kinematics formulations contain frequency sum and difference terms that usually lead to expensive time-domain dynamic analyses of offshore structural responses. This study aims at a direct and efficient two-dimensional FFT algorithm for simulating the frequency sum terms. For the frequency-difference terms, inverse FFT and forward FFT are implemented, respectively, across the two dimensions of the wave interaction matrix. Given specified wave conditions, the statistics of simulated elevations/kinematics compare well with not only the empirical fits but also the analytical solutions based on a modified eigenvalue/eigenvector approach, while the computational effort of simulation is very economical. In addition, the stochastic analyses in both time domain and frequency domain show that, attributable to the second-order nonlinear wave effects, the near-surface Morison force and induced linear oscillator response are more non-Gaussian than those subjected to Gaussian random waves.

Time domain analysis of random wave forces on pipelines in the inertia regime

1989 ◽  
Vol 2 (1) ◽  
pp. 51-63 ◽  
Author(s):  
N. Jothi Shankar ◽  
Hin-Fatt Cheong ◽  
K. Subbiah
Keyword(s):  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Random Wave ◽  
Wave Forces

scholarly journals Time-Domain Hydro-Elastic Analysis of a SFT (Submerged Floating Tunnel) with Mooring Lines under Extreme Wave and Seismic Excitations

2018 ◽  
Vol 8 (12) ◽  
pp. 2386 ◽  
Author(s):  
Chungkuk Jin ◽  
Moo-Hyun Kim
Keyword(s):  
Time Domain ◽  
Hydrodynamic Forces ◽  
Random Wave ◽  
Element Formulation ◽  
Elastic Analysis ◽  
Seismic Excitations ◽  
Time Step ◽  
Mooring Lines ◽  
Submerged Floating Tunnel ◽  
Elastic Responses

Global dynamic analysis of a 700-m-long SFT section considered in the South Sea of Korea is carried out for survival random wave and seismic excitations. To solve the tunnel-mooring coupled hydro-elastic responses, in-house time-domain-simulation computer program is developed. The hydro-elastic equation of motion for the tunnel and mooring is based on rod-theory-based finite element formulation with Galerkin method with fully coupled full matrix. The dummy-connection-mass method is devised to conveniently connect objects and mooring lines with linear and rotational springs. Hydrodynamic forces on a submerged floating tunnel (SFT) are evaluated by the modified Morison equation for a moving object so that the hydrodynamic forces by wave or seismic excitations can be computed at its instantaneous positions at every time step. In the case of seabed earthquake, both the dynamic effect transferred through mooring lines and the seawater-fluctuation-induced seaquake effect are considered. For validation purposes, the hydro-elastic analysis results by the developed numerical simulation code is compared with those by a commercial program, OrcaFlex, which shows excellent agreement between them. For the given design condition, extreme storm waves cause higher hydro-elastic responses and mooring tensions than those of the severe seismic case.

A random wave process

1984 ◽  
Vol 12 (1) ◽  
pp. 97-114 ◽  
Author(s):  
D. A. Dawson ◽  
G. C. Papanicolaou
Keyword(s):  
Wave Process ◽  
Random Wave

Full Stochastic Fatigue Analysis of Stiffened Panels Subjected to Wave Slamming

2008 ◽  
Author(s):  
Dilnei Schmidt ◽  
Carlos A. Bardanachvili ◽  
Paulo M. Videiro
Keyword(s):  
Structural Analysis ◽  
Time Domain ◽  
Ocean Basin ◽  
Sea Surface ◽  
Stiffened Panel ◽  
Random Wave ◽  
Offshore Structure ◽  
Stiffened Panels ◽  
Wave Slamming ◽  
Supporting Structures

The aim of the present work is the evaluation of the fatigue lifespan of a horizontal stiffened panel of an offshore structure subjected to random wave slamming. In order to achieve this objective, a methodology for time-domain slamming prediction was developed. Time series for the relative distance and velocity between the bottom panel and sea surface and the angle between the panel and the sea surface are simulated to provide a way to evaluate when the slamming occurs and the loads associated with slamming, using factor calibrated after a model test on ocean basin. With the loads obtained from these simulations, the structural analysis is then performed, considering all the shell plating, main stiffeners as well as other main supporting structures, by using a finite element structural analysis. The fatigue lifespan is estimated in a complete stochastic analysis, considering all possible sea states during the lifetime of the offshore structure as well as each probability of occurrence associated. All phases of the methodology used for the evaluation of the slamming loads and the fatigue analyses are presented.

Nonlinear Random Wave Time Domain Analysis of Jack-Up Rigs Including Foundation

2017 ◽  
Author(s):  
Partha Chakrabarti ◽  
Deepak Sankar Somasundaram ◽  
Abhijeet Chawan
Keyword(s):  
Time Domain ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Analysis Procedure ◽  
Random Wave ◽  
Two Stage ◽  
Deterministic Analysis ◽  
One Stage ◽  
Stage Analysis ◽  
Jack Up

A jack-up rig has to be designed for extreme storm conditions in its elevated mode during operations. Guidelines of ISO 19905-1 [1] and SNAME TR-5-5A [2] for site specific assessment of jack-up rigs explain in detail such analysis and assessment requirements. It is well known that for higher water depths and extreme environment, structural dynamics and spudcan-soil interaction plays a very significant role. The extreme storm response can be determined either by a two-stage deterministic storm analysis procedure using a quasi-static analysis that includes an inertial load set or by a more detailed fully integrated (random wave) dynamic analysis procedure that uses a stochastic analysis. More commonly, however, jack-up rigs are assessed using a two-stage deterministic wave model along with steady wind loads, since this is much simpler. In two-stage deterministic analysis, the first step is the determination of the inertial load set and structural analysis for all the environmental and gravity loads. To include the effects of the spudcan and soil foundation, an initial rotational stiffness or fixity is assumed that depends on the soil type and the preload. Assessment of the foundation is performed thereafter using the yield interaction approach. This is normally an iterative approach to arrive at the right fixity that satisfies the assessment. The two-stage approach, although simpler could be conservative leading to adverse conclusions for the suitability of a jack-up at a site. As indicated, the other approach is the one-stage approach involving random time domain analysis which is normally not used and reported in the literature probably due to its complexity and difficulty. The present paper describes random wave time domain analysis of a specific jack-up using a 3D model in 400 ft water depth using USFOS software [3]. This software has the spudcan-soil interaction integrated, to simulate the foundation behavior. In this one-stage analysis, the assessment for the foundation is performed through an iterative approach inside the software using yield and bounding surfaces. Extreme values of some of key responses are compared with traditional deterministic analysis. Benefits and limitations of random wave time domain analysis are explained and quantified. These benefits are sometimes so significant that one-stage analysis may lead to favorable conclusions where the conservative two-stage analysis approach had failed to show the adequacy of the rig. These observations and the overall methodology of analysis used here could be beneficial to any rig’s applicability at a specific site.

scholarly journals An efficient method for quantum transport simulations in the time domain

2011 ◽  
Vol 391 (1) ◽  
pp. 69-77 ◽  
Author(s):  
Y. Wang ◽  
C.-Y. Yam ◽  
Th. Frauenheim ◽  
G.H. Chen ◽  
T.A. Niehaus
Keyword(s):  
Quantum Transport ◽  
Efficient Method ◽  
Time Domain ◽  
The Time Domain
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