Stochastic Analysis of Vertical Wave Loads on Deck

2008 ◽  
Author(s):  
Ravikiran S. Kota ◽  
Torgeir Moan
Keyword(s):  
Impact Load ◽  
Added Mass ◽  
Two Dimensional ◽  
Wave Loads ◽  
Random Waves ◽  
Statistical Measures ◽  
Model Following ◽  
Wave Slamming ◽  
Stationary Gaussian Processes ◽  
Maximum Minimum

Vertical loads on a platform deck due to incident random waves — long-crested and Gaussian, are studied. Loads on the deck are due to wave-slamming, added-mass over the wetted length and nonlinear Froude-Krylov components. Reliable estimation of these loads and their duration is important in evaluating their effects on platform response (global or local). Emphasis of the present work is to study statistical measures such as expected maximum/minimum impact load and its duration. Gaussian waves are numerically simulated over several points of a two-dimensional deck in time-domain and each deck-wetting event identified and tracked from its inception to expiry. Forces are modeled using a simplified two-dimensional slamming model following Kaplan’s (1987) approach. Use of von Ka´rma´n method, and hence instantaneous wave profile, enables multiple slamming regions to be considered. Simulated results for expected deck-wetting duration and expected maximum wetted length are then compared against analytical results for one- and two-dimensional stationary Gaussian processes.

Statistical measures of two dimensional point set uniformity

2012 ◽  
Vol 56 (6) ◽  
pp. 2159-2181 ◽  
Author(s):  
Meng Sang Ong ◽  
Ye Chow Kuang ◽  
Melanie Po-Leen Ooi
Keyword(s):  
Two Dimensional ◽  
Statistical Measures ◽  
Point Set

Wave Loads on Floaters of Aquaculture Plants

2008 ◽  
Author(s):  
David Kristiansen ◽  
Odd M. Faltinsen
Keyword(s):  
Stokes Equations ◽  
Model Tests ◽  
Staggered Grid ◽  
Physical Parameters ◽  
Surface Zone ◽  
Two Dimensional ◽  
Wave Loads ◽  
Wave Load ◽  
Constrained Interpolation ◽  
Advection Term

This paper addresses wave loads on horizontal cylinders in the free surface zone by means of model tests and numerical simulations. This has relevance for the design of floating fish farms at exposed locations. Two model geometries were tested, where two-dimensional flow conditions were sought. The cylinders were fixed and exposed to regular wave trains. Wave overtopping the models were observed. A two-dimensional Numerical Wave Tank (NWT) for wave load computations is described. The NWT is based on the finite difference method and solves the incompressible Navier-Stokes equations on a non-uniform Cartesian staggered grid. The advection term is treated separately by the CIP (Constrained Interpolation Profile) method. A fractional and validation of the NWT is emphasized. Numerical results from simulations with the same physical parameters as in the model tests are performed for comparison. Deviations are discussed.

Prediction of Extreme Wave Slamming Loads on a Fixed Platform

2018 ◽  
Author(s):  
Grzegorz P. Filip ◽  
Wenzhe Xu ◽  
Kevin J. Maki
Keyword(s):  
Wave Structure ◽  
Nonlinear Process ◽  
Extreme Value ◽  
Wave Loads ◽  
Oil Platforms ◽  
Offshore Oil Platforms ◽  
Highly Nonlinear ◽  
Extreme Load ◽  
Wave Slamming ◽  
Extreme Responses

Design of offshore oil platforms requires accurate prediction of the maximum wave loads due to slamming on horizontal decks. The physical processes that influence the load are the propagation of irregular short-crested wind-driven storm seas, wave breaking, and wave-structure interaction. Furthermore, the ocean is a stochastic environment, so the load and its maximum can be considered as random variables. Ideally, the designer would like to know not only the most probable extreme load, but also the extreme load distribution. In this paper we will use a novel technique to prescribe wave environments that lead to extreme responses so that high-fidelity simulations of the highly-nonlinear process can be investigated in detail. Specifically, the dynamics of the relative motion of the sea surface and the platform will be assumed via the selection of a sea spectrum, and the extreme-value probability distribution function (PDF) will be calculated for a given exposure window. The novel aspect of the work is in the way that a set of deterministic sea environments will be generated that are amenable for simulation with a state-of-the-art computational-fluid dynamics (CFD) software. The resulting wave environments will be simulated to estimate the extreme-value PDF.

Nonlinear Wave Loads Acting on Cylinder Array Slowly Oscillating in Diffraction and Radiation Wave Fields

2005 ◽  
Author(s):  
Weiguang Bao ◽  
Takeshi Kinoshita ◽  
Motoki Yoshida
Keyword(s):  
Nonlinear Wave ◽  
Perturbation Expansion ◽  
Low Frequency ◽  
Added Mass ◽  
Wave Loads ◽  
Wave Fields ◽  
Wave Drift ◽  
Cylinder Array ◽  
Radiation Wave ◽  
Low Frequency Motion

The problem of a circular cylinder array slowly oscillating in both diffraction and radiation wave fields is considered in the present work. As a result of the interaction between the wave fields and the low-frequency motion, nonlinear wave loads may be separated into the so-called wave-drift added mass and damping. They are force components proportional to the square of the wave amplitude but in phase of the acceleration and velocity of the low-frequency motion respectively. The frequency of the slow oscillation is assumed to be much smaller than the wave frequency. Perturbation expansion based on two time scales and two small parameters is performed to the order to include the effects of the acceleration of the low-frequency motion. Solutions to these higher order potentials are suggested in the present work. Wave loads including the wave drift added mass and damping are evaluated by the integration of the hydrodynamic pressure over the instantaneous wetted body surface.

scholarly journals Dynamic response of a wedge through asymmetric free fall in 2 degrees of freedom

2017 ◽  
Vol 233 (1) ◽  
pp. 229-250 ◽  
Author(s):  
Parviz Ghadimi ◽  
Sasan Tavakoli ◽  
Abbas Dashtimanesh ◽  
Pouria Taghikhani
Keyword(s):  
Experimental Data ◽  
Dynamic Response ◽  
Degrees Of Freedom ◽  
Time Derivative ◽  
Free Fall ◽  
Added Mass ◽  
Roll Motion ◽  
Physical Parameters ◽  
Two Dimensional ◽  
Roll Speed

In this article, a mathematical model is presented for simulation of the coupled roll and heave motions of the asymmetric impact of a two-dimensional wedge body. This model is developed based on the added mass theory and momentum variation. To this end, new formulations are introduced which are related to the added mass caused by heave and roll motions of the wedge. These relations are developed by including the asymmetrical effects and roll speed. In addition, by considering the roll speed, a particular method is presented for the time derivative of half-wetted beam of an asymmetric wedge. Furthermore, two equations are derived for the roll and heave motions in which damping terms appear. Validity of the proposed method is verified by comparing the predicted results against available experimental data in two conditions of roll motion and no roll motion. Favorable agreement is observed between the predicted results and experimental data. The pressure and hydrodynamic load are computed, and the differences between the results associated with the considered conditions are explored. Subsequently, the effects of different physical parameters including deadrise angle, initial roll angle, and initial velocity on the dynamic response of a two-dimensional wedge section are investigated. Ultimately, time histories of hydrodynamic coefficients are determined in order to provide a better understanding of the derived equations.

Simulation of Wave Slamming on Open-Piled Structures Based on FLUENT

2012 ◽  
Vol 256-259 ◽  
pp. 1960-1964
Author(s):  
Feng Jin
Keyword(s):  
Experimental Data ◽  
Wave Height ◽  
Impact Pressure ◽  
Two Dimensional ◽  
Numerical Wave Tank ◽  
Regular Wave ◽  
Wave Impact ◽  
Wave Tank ◽  
Wave Slamming ◽  
Numerical Wave

In order to study the specialties of wave slamming on open-piled structures, a two-dimensional regular wave tank was established based on commercial CFD software FLUENT. Three typical cases of regular wave slamming on the open-piled structures were reproduced by using the numerical wave tank and compared with the experimental data available. Good agreements were obtained between the numerical and experimental results and the average of peak impact pressure was chosen as the characteristic impact pressure. Then regular wave impact pressure on the open-piled structures under various wave height, period and over height were simulated. The influences of the three parameters on the distribution of impact pressure were analyzed.

Wave Slamming on External Turrets of FPSOs

2009 ◽  
Author(s):  
Bas Buchner ◽  
Arjan Voogt
Keyword(s):  
Model Test ◽  
Impact Load ◽  
Complex Loading ◽  
Rate Of Change ◽  
Maximum Pressure ◽  
Test Results ◽  
Air Entrapment ◽  
Empirical Relations ◽  
Wave Slamming ◽  
Reduced Rate

The paper discussed the possible slamming loads on the underside of the (chaintable of) external turret moored F(P)SOs. For this problem of turret slamming, a combined exceedance of the airgap between the underside of the chaintable and the relative wave is needed, as well as a certain relative wave velocity. A model test series was carried out to determine these loads on a typical external turret. The model test results provide insight into the complex loading process of external turret type structures. A clear quadratic relation between submergence velocity and impact load, as typically observed for slamming problems, has not been identified. This is probably a result of local effects, such as the strong disturbance of the free surface (giving a locally different deadrise angle) and air entrapment effects. The maximum pressure on the conical turret (chain table) is significantly reduced compared to the flat turret, which was expected based on the reduced rate of change of momentum with the conical turret. Based on linear 3D diffraction analysis and the empirical relations derived from the model tests, a method is presented to determine first design estimates of the pressures.

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