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.

Stability of offshore structures in shallow water depth

2011 ◽  
Vol 2 (2) ◽  
pp. 320-333
Author(s):  
F. Van den Abeele ◽  
J. Vande Voorde
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Fossil Fuels ◽  
Oil And Gas ◽  
Structural Response ◽  
Offshore Structures ◽  
Exploration And Production ◽  
Subsea Pipelines ◽  
Wave Induced ◽  
Shallow Water Depth

The worldwide demand for energy, and in particular fossil fuels, keeps pushing the boundaries of offshoreengineering. Oil and gas majors are conducting their exploration and production activities in remotelocations and water depths exceeding 3000 meters. Such challenging conditions call for enhancedengineering techniques to cope with the risks of collapse, fatigue and pressure containment.On the other hand, offshore structures in shallow water depth (up to 100 meter) require a different anddedicated approach. Such structures are less prone to unstable collapse, but are often subjected to higherflow velocities, induced by both tides and waves. In this paper, numerical tools and utilities to study thestability of offshore structures in shallow water depth are reviewed, and three case studies are provided.First, the Coupled Eulerian Lagrangian (CEL) approach is demonstrated to combine the effects of fluid flowon the structural response of offshore structures. This approach is used to predict fluid flow aroundsubmersible platforms and jack-up rigs.Then, a Computational Fluid Dynamics (CFD) analysis is performed to calculate the turbulent Von Karmanstreet in the wake of subsea structures. At higher Reynolds numbers, this turbulent flow can give rise tovortex shedding and hence cyclic loading. Fluid structure interaction is applied to investigate the dynamicsof submarine risers, and evaluate the susceptibility of vortex induced vibrations.As a third case study, a hydrodynamic analysis is conducted to assess the combined effects of steadycurrent and oscillatory wave-induced flow on submerged structures. At the end of this paper, such ananalysis is performed to calculate drag, lift and inertia forces on partially buried subsea pipelines.

scholarly journals Structural Assessment of the Hull Response of an FPSO Unit to Dropped Objects: A Case Study

2019 ◽  
Vol 26 (4) ◽  
pp. 39-46 ◽  
Author(s):  
Ozgur Ozguc
Keyword(s):  
Structural Damage ◽  
Local Buckling ◽  
Structural Response ◽  
Offshore Structures ◽  
Mechanical Equipment ◽  
Structural Members ◽  
Impact Area ◽  
Explicit Dynamic ◽  
The Impact

Abstract Offshore structures are exposed to the risk of damage caused by various types of extreme and accidental events, such as fire, explosion, collision, and dropped objects. These events cause structural damage in the impact area, including yielding of materials, local buckling, and in some cases local failure and penetration. The structural response of an FPSO hull subjected to events involving dropped objects is investigated in this study, and non-linear finite element analyses are carried out using an explicit dynamic code written LS-DYNA software. The scenarios involving dropped objects are based on the impact from the fall of a container and rigid mechanical equipment. Impact analyses of the dropped objects demonstrated that even though some structural members were permanently deformed by drop loads, no failure took place in accordance with the plastic strain criteria, as per NORSOK standards. The findings and insights derived from the present study may be informative in the safe design of floating offshore structures.

scholarly journals THE DYNAMIC RESPONSE OF OFFSHORE STRUCTURES TO TIME-DEPENDENT FORCES

1964 ◽  
Vol 1 (9) ◽  
pp. 29
Author(s):  
William S. Gaither ◽  
David P. Billington
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Offshore Structures ◽  
Time Dependent ◽  
Wave Forces ◽  
Ocean Bottom ◽  
Single Wave ◽  
Single Degree Of Freedom ◽  
The Many ◽  
Floating Objects

This paper is addressed to the problem of structural behavior in an offshore environment, and the application of a more rigorous analysis for time-dependent forces than is currently used. Design of pile supported structures subjected to wave forces has, in the past, been treated in two parts; (1) a static analysis based on the loading of a single wave, and (2) a dynamic analysis which sought to determine the resonant frequency by assuming that the structure could be approximated as a single-degree-of-freedom system. (Ref. 4 and 6) The behavior of these structures would be better understood if the dynamic nature of the loading and the many degrees of freedom of the system were included. A structure which is built in the open ocean is subjected to periodic forces due to wind, waves, floating objects, and due occasionally to machinery mounted on the structure. To resist motion, the structure relies on the stiffness of the elements from which it is built and the restraints of the ocean bottom into which the supporting legs are driven.

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 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.

Nonlinear Dynamic Response of a Tension Leg Platform

1999 ◽  
Vol 121 (4) ◽  
pp. 219-226 ◽  
Author(s):  
P. Bar-Avi
Keyword(s):  
Environmental Conditions ◽  
Nonlinear Dynamic ◽  
Equations Of Motion ◽  
Continuous System ◽  
Offshore Structures ◽  
Physical Parameters ◽  
Wave Forces ◽  
Tension Leg Platform ◽  
Nonlinear Dynamic Response ◽  
Nonlinear Equations Of Motion

Of the classes of offshore structures, the tension leg platform (TLP) is particularly well suited for deepwater operation. The structure investigated in this paper is assumed to consist of a flexible cable attached to a buoyant deck at the top. The cable is modeled as a beamlike continuous system subjected to wave, current, and wind forces. The derivation of the nonlinear equations of motion include nonlinearities due to geometry as well as due to wave forces. The equations of motion are solved and the TLP’s response to various environmental conditions and other physical parameters is evaluated.

Numerical and Experimental Study of Wave-Induced Load Effects on a Submerged Body Near the Surface

2018 ◽  
Author(s):  
L. M. Jones ◽  
J. T. Klamo ◽  
Y. W. Kwon ◽  
J. M. Didoszak
Keyword(s):  
Numerical Study ◽  
Experimental Studies ◽  
Wave Forces ◽  
Dynamics Model ◽  
Marine Structures ◽  
Numerical Studies ◽  
Submerged Body ◽  
Load Effects ◽  
Wave Maker ◽  
Wave Induced

Marine structures are subjected to wave forces whether they are stationary or moving. Such wave forces play a significant role in the design and operation of marine structures. The aim of this study is to understand and predict the unsteady hydrodynamic loads experienced by a submerged body near the surface. Both numerical and experimental studies were conducted. For the experimental work, a newly constructed wave maker inside a tow tank was utilized while a computational fluid dynamics model was developed for the numerical study. Both experimental and numerical studies can complement each other. First, the computational model was validated against experimental wave data so as to understand what parameters in numerical modeling influence the reliability of the numerical results. The second aim was to understand the force and moment that a submerged body would experience for different wave lengths.

Closed-Form Expressions Of Wave Induced Forces On Members Of Offshore Structures In Deep Water

1997 ◽  
pp. 41-56
Author(s):  
Mohd. Ramzan Mainal ◽  
Pratul C. Chatterjeel
Keyword(s):  
Closed Form ◽  
Offshore Structures ◽  
Beam Element ◽  
Reference Plane ◽  
Wave Forces ◽  
Fe Model ◽  
Standard Pattern ◽  
Drag Forces ◽  
Vertical Beam ◽  
Wave Induced

The paper deals with the estimation of equivalent nodal forces and moments which can be useful in the analysis of beam element based Finite Element (FE) models of offshore structures. Ocean wave forces do not follow any standard pattern, thus, if the global X-Y reference plane is horizontal, the X and Y co-ordinates will not vary along the length of a vertical beam element. Taking advantage of such a situation, a number of closed form expressions for equivalent nodal loads can be derived. The analytical diffraction force from the MacCamy and Fuchs' theory as well as the Morison equation based inertia and drag forces are considered here as wave loading. A step-by-step calculation procedure is also proposed which transfers complex member loads to the nodes of a FE model with beam elements, arbitrarily oriented in space.

Quantification of Predicted Wave Forces From Distant Elevation Measurements

2019 ◽  
Author(s):  
Spencer T. Hallowell ◽  
Sanjay R. Arwade ◽  
Hannah Johlas ◽  
Pedro Lomonaco ◽  
Andrew Myers
Keyword(s):  
Breaking Waves ◽  
Offshore Structures ◽  
Irregular Waves ◽  
Wave Forces ◽  
Structural Members ◽  
Prediction Equations ◽  
Linear Dispersion ◽  
Force Prediction ◽  
Wave Kinematics ◽  
Wave Measurements

Abstract The vast spatial scale of offshore structures causes wave loading to be correlated amongst nearby structural members. Certain engineering activities including health monitoring, maintenance, and preliminary design of offshore structures requires the prediction of wave forces on said structural members. The high cost and low availability of environmental wave measurements requires the reconstruction of wave kinematics and force profiles to accurately capture the forcing history on offshore structures. A method for predicting wave forces on a cylinder from nearby wave elevation measurements is proposed. The formulation utilizes the Fast Fourier Transform to calculate wave kinematics propagation in the frequency domain and applies the kinematics to the Morison equation for calculation of cylinder forces. The prediction equations are applied to three types of waves: regular periodic waves, random irregular waves, and solitary breaking waves, and the error in both elevation prediction and force prediction when compared to measured values is calculated. The force prediction equations were shown to perform best for small wave heights, with errors as low as 5% in the force predictions for small regular and irregular waves. The error in force prediction increases nonlinearly with the increase in wave height due to the deficiencies of the linear dispersion relationship used in the formulation.

scholarly journals Structural Response of Offshore Blast Walls under Accidental Explosion

2014 ◽  
Vol 1043 ◽  
pp. 278-282 ◽  
Author(s):  
Shaikh Atikur Rahman ◽  
Zubair Imam Syed ◽  
John V. Kurian ◽  
M.S. Liew
Keyword(s):  
Structural Response ◽  
Offshore Structures ◽  
Extensive Study ◽  
Design Guidelines ◽  
Critical Systems ◽  
Structural Behaviour ◽  
Single Degree Of Freedom ◽  
Structural Responses ◽  
Simplified Calculation ◽  
Explosion Load

Adequate blast resistant barriers are requisite to protect personnel and critical systems from the consequences of an accidental explosion and subsequent fire. Many of the blast walls currently installed in offshore structures were designed using simplified calculation approaches like Single Degree of Freedom models (SDOF) as recommended in many design guidelines. Over simplified and idealised explosion load used for response calculation and design of blast wall can lead to inadequate or overdesign of offshore blast walls. Due to lack of presence of a well-accepted design guidelines supported by extensive study, the protection provided by the conventional blast walls for offshore structures can be inadequate. In-depth understanding of structural response of blast walls under different blast loading can provide better design practice of blast walls for adequate protection. In this study, structural responses of conventional offshore blast walls were investigated. A computation fluid dynamics (CFD) approach was used to predict effect of different explosions on the barrier walls and non-linear finite elements analyses were performed to study the behaviour of the blast-loaded walls under different explosions. Effect of different parameters related to blast wall and accidental explosions were investigated to gain detail understanding of structural behaviour of typical steel blast wall.

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