scholarly journals Stochastic Response of Tension Leg Platform to Wave and Current Forces

1989 ◽  
Vol 111 (4) ◽  
pp. 221-230 ◽  
Author(s):  
A. Ertas ◽  
J.-H. Lee
Keyword(s):  
Constant Current ◽  
Response Analysis ◽  
Stochastic Dynamic ◽  
Superposition Method ◽  
Random Waves ◽  
Stochastic Response ◽  
Tension Leg Platform ◽  
Single Degree Of Freedom ◽  
Simulation Techniques ◽  
Wave Induced

The linear analysis in the frequency domain is presented for the surge motion of a tension leg platform (TLP) in the case of random waves only and random waves with constant current. A single-degree-of-freedom model of a TLP is employed for response. The superposition method, one of the simulation techniques, is applied to random sea wave, and the response analysis of TLP in time is developed with wave velocity and wave acceleration simulations. Wave-induced forces are calculated using the modified Morison equation, which takes into account relative motion. Computational methods for both analyses are developed, and the results of stochastic, dynamic response of the TLP, with and without the presence of current, are presented and compared.

Response of a Simple Tension Leg Platform Model to Wave Forces Calculated at Displaced Position

1984 ◽  
Vol 106 (4) ◽  
pp. 437-443 ◽  
Author(s):  
P. D. Spanos ◽  
V. K. Agarwal
Keyword(s):  
Structural Response ◽  
Offshore Structures ◽  
Wave Forces ◽  
Structural Members ◽  
Tension Leg Platform ◽  
Single Degree Of Freedom ◽  
Numerical Studies ◽  
Simple Tension ◽  
Stochastic Solution ◽  
Wave Induced

A simple single-degree-of-freedom model of a tension leg platform is used to assess the reliability of the common practice of calculating wave-induced forces at the undisplaced position of offshore structures. This assessment is conducted in conjunction with the Morison equation based modeling of the wave-induced forces on slender structural members. It is shown by numerically integrating the equation of motion that the calculation of wave forces on the displaced position of the structure introduces a steady offset component in the structural response. This is valid for either deterministically or stochastically described wave fields. Several parameter studies are conducted. Furthermore, reliable approximate analytical deterministic and stochastic solution techniques are developed which conform to and, in fact, predict the conclusions drawn from the results of the numerical studies.

Stochastic Response Analysis of Deepwater Structures in Short-Crested Random Seas

1999 ◽  
Vol 121 (3) ◽  
pp. 181-186 ◽  
Author(s):  
P. Teigen ◽  
A. Naess
Keyword(s):  
Time Domain ◽  
Large Volume ◽  
Time Domain Analysis ◽  
Order Theory ◽  
Offshore Structures ◽  
Response Analysis ◽  
Random Waves ◽  
Stochastic Response ◽  
Cpu Time ◽  
Random Seas

The paper discusses the problem of estimating the response statistics of moored large-volume offshore structures subjected to short-crested random waves. A general second-order theory is described that makes it possible to carry out the entire analysis in the frequency domain, which is computationally more efficient than time domain analysis, which generally requires considerably more CPU time to reach the same level of accuracy.

scholarly journals Stochastic Dynamic Response Analysis of a 10 MW Tension Leg Platform Floating Horizontal Axis Wind Turbine

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3341 ◽  
Author(s):  
Tao Luo ◽  
De Tian ◽  
Ruoyu Wang ◽  
Caicai Liao
Keyword(s):  
Dynamic Response ◽  
Horizontal Axis ◽  
Viscous Drag ◽  
Response Analysis ◽  
Stochastic Dynamic ◽  
Mooring System ◽  
Wave Load ◽  
Tension Leg Platform ◽  
Horizontal Axis Wind Turbine ◽  
Resonant Amplitude

The dynamic response of floating horizontal axis wind turbines (FHWATs) are affected by the viscous and inertia effects. In free decay motion, viscous drag reduces the amplitude of pitch and roll fluctuation, the quasi-static mooring system overestimates the resonant amplitude values of pitch and roll. In this paper, the quasi-static mooring system is modified by introducing linear damping and quadratic damping. The dynamic response characteristics of the FHAWT modified model of the DTU 10 MW tension leg platform (TLP) were studied. Dynamic response of the blade was mainly caused by wind load, while the wave increased the blade short-term damage equivalent load. The tower base bending moment was affected by inclination of the tower and the misaligned angle βwave between wind and wave. Except the yaw motion, other degrees of freedom motions of the TLP were substantially affected by βwave. Ultimate tension of the mooring system was related to the displacement caused by pitch and roll motions, and standard deviation of the tension was significantly affected by the wave frequency response. Under the action of wave load, the viscous drag would stimulate the mooring system and increase the resonance of the platform motion.

scholarly journals Complex response analysis of a non-smooth oscillator under harmonic and random excitations

2021 ◽  
Vol 42 (5) ◽  
pp. 641-648
Author(s):  
Shichao Ma ◽  
Xin Ning ◽  
Liang Wang ◽  
Wantao Jia ◽  
Wei Xu
Keyword(s):  
Excitation Frequency ◽  
System Stability ◽  
Response Analysis ◽  
External Excitation ◽  
Stochastic Response ◽  
Impact Oscillator ◽  
Nonlinear Parameters ◽  
Bifurcation Phenomena ◽  
Mc Simulation ◽  
Smooth System

AbstractIt is well-known that practical vibro-impact systems are often influenced by random perturbations and external excitation forces, making it challenging to carry out the research of this category of complex systems with non-smooth characteristics. To address this problem, by adequately utilizing the stochastic response analysis approach and performing the stochastic response for the considered non-smooth system with the external excitation force and white noise excitation, a modified conducting process has proposed. Taking the multiple nonlinear parameters, the non-smooth parameters, and the external excitation frequency into consideration, the steady-state stochastic P-bifurcation phenomena of an elastic impact oscillator are discussed. It can be found that the system parameters can make the system stability topology change. The effectiveness of the proposed method is verified and demonstrated by the Monte Carlo (MC) simulation. Consequently, the conclusions show that the process can be applied to stochastic non-autonomous and non-smooth systems.

An Analytical Scheme for Stochastic Dynamic Systems Containing Fractional Derivatives

1999 ◽  
Author(s):  
Om P. Agrawal
Keyword(s):  
White Noise ◽  
Expansion Method ◽  
Stochastic Dynamic ◽  
Stochastic Response ◽  
Analytical Technique ◽  
Analytical Scheme ◽  
Damped System ◽  
Duhamel Integral ◽  
General Response ◽  
Stochastic Dynamic Systems

Abstract This paper presents an analytical technique for the analysis of a stochastic dynamic system whose damping behavior is described by a fractional derivative of order 1/2. In this approach, an eigenvector expansion method proposed by Suarez and Shokooh is used to obtain the response of the system. The properties of Laplace transforms of convolution integrals are used to write a set of general Duhamel integral type expressions. The general response contains two parts, namely zero state and zero input. For a stochastic analysis the input force is treated as a random process with specified mean and correlation functions. An expectation operator is applied on a set of expressions to obtain the stochastic characteristics of the system. Closed form stochastic response expressions are obtained for white noise. Numerical results are presented to show the stochastic response of a fractionally damped system subjected to white noise.

Analytical investigation of nonlinear heave-coupled response of tension leg platform

2018 ◽  
Vol 233 (3) ◽  
pp. 699-713
Author(s):  
Mohammad Reza Tabeshpour ◽  
Reza Hedayatpour
Keyword(s):  
Degrees Of Freedom ◽  
Structural Response ◽  
Wave Theory ◽  
Equation Of Motion ◽  
Analytical Investigation ◽  
Response Analysis ◽  
Wave Forces ◽  
Tension Leg Platform ◽  
Heave Motion ◽  
Diffraction Effects

Having deep view in structural response of tension leg platform is important issue not only for response analysis but also for engineering design. Coupling between surge and heave motions of tension leg platform is such a problem. Here, tension leg platform motions are considered only in surge and heave degrees of freedom without pitch effect. The coupled term of heave is a nonlinear differential equation. Because the focus of this article is on this term, therefore, Duffing equation of motion in the surge direction is linearized. The wave forces are calculated using Airy’s wave theory and Morison’s equation, ignoring the diffraction effects. Current force also can be very important in dynamic analysis of tension leg platform. Because it affects the term of heave that is coupled with surge. It is shown that the effect of surge motion coupling on heave motion is very important in large displacement of surge motion in many sea states. The main result is that the coupling effects appeared in some frequencies such as heave and surge frequency, twice the frequency of wave, twice the natural surge frequency, and summation and difference of frequency of wave and surge frequency.

scholarly journals Wave-Induced Seabed Response around a Dumbbell Cofferdam in Non-Homogeneous Anisotropic Seabed

2019 ◽  
Vol 7 (6) ◽  
pp. 189 ◽  
Author(s):  
Linya Chen ◽  
Dong-Sheng Jeng ◽  
Chencong Liao ◽  
Dagui Tong
Keyword(s):  
Shear Modulus ◽  
Vertical Distribution ◽  
Pore Pressure ◽  
Wave Structure ◽  
Offshore Structures ◽  
Hydrodynamic Process ◽  
Response Analysis ◽  
Depth Function ◽  
Wave Induced ◽  
The Vertical Distribution

Cofferdams are frequently used to assist in the construction of offshore structures that are built on a natural non-homogeneous anisotropic seabed. In this study, a three-dimensional (3D) integrated numerical model consisting of a wave submodel and seabed submodel was adopted to investigate the wave–structure–seabed interaction. Reynolds-Averaged Navier–Stokes (RANS) equations were employed to simulate the wave-induced fluid motion and Biot’s poroelastic theory was adopted to control the wave-induced seabed response. The present model was validated with available laboratory experimental data and previous analytical results. The hydrodynamic process and seabed response around the dumbbell cofferdam are discussed in detail, with particular attention paid to the influence of the depth functions of the permeability K i and shear modulus G j . Numerical results indicate that to avoid the misestimation of the liquefaction depth, a steady-state analysis should be carried out prior to the transient seabed response analysis to first determine the equilibrium state caused by seabed consolidation. The depth function G j markedly affects the vertical distribution of the pore pressure and the seabed liquefaction around the dumbbell cofferdam. The depth function K i has a mild effect on the vertical distribution of the pore pressure within a coarse sand seabed, with the influence concentrated in the range defined by 0.1 times the seabed thickness above and below the embedded depth. The depth function K i has little effect on seabed liquefaction. In addition, the traditional assumption that treats the seabed parameters as constants may result in the overestimation of the seabed liquefaction depth and the liquefaction area around the cofferdam will be miscalculated if consolidation is not considered. Moreover, parametric studies reveal that the shear modulus at the seabed surface G z 0 has a significant influence on the vertical distribution of the pore pressure. However, the effect of the permeability at the seabed surface K z 0 on the vertical distribution of the pore pressure is mainly concentrated on the seabed above the embedded depth in front and to the side of the cofferdam. Furthermore, the amplitude of pore pressure decreases as Poisson’s ratio μ s increases.

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