Experimental and numerical study on bottom slamming probability of a chemical tanker subjected to irregular waves

2014 ◽  
pp. 1079-1086
Keyword(s):  
Numerical Study ◽  
Irregular Waves

Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

2016 ◽  
Author(s):  
Shaowu Ou ◽  
Shixiao Fu ◽  
Wei Wei ◽  
Tao Peng ◽  
Xuefeng Wang
Keyword(s):  
Numerical Study ◽  
Low Frequency ◽  
Optimal Operation ◽  
Hydrodynamic Interactions ◽  
Irregular Waves ◽  
Mooring System ◽  
Time Varying ◽  
Body System ◽  
The Time Domain ◽  
Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

Slowly Varying Wave Drift Forces Analyzed From Model Test Data on a Moored Ship in Shallow Water

2009 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Csaba Paˆkozdi
Keyword(s):  
Noise Reduction ◽  
Shallow Water ◽  
Model Test ◽  
Transfer Functions ◽  
Numerical Study ◽  
Wave Frequency ◽  
Irregular Waves ◽  
Spectral Peak ◽  
Frequency Range ◽  
Wave Drift

Model test estimation of quadratic transfer functions (QTFs) is investigated for slowly varying wave drift excitation on a large moored ship in shallow water. Cross-bi-spectral analysis in irregular waves is used. A numerical study is run first, with a known, synthetical QTF model characterized by a strong off-diagonal variation, combined with a very lightly damped linear slow-drift dynamical system. The purpose is to check the accuracy of the analysis. For this simple model, a good accuracy is obtained in the estimated QTF. This is because of a refined noise reduction method which works well in this case. The wave frequency range of valid estimates is where the wave spectrum S(f) is higher than 7% of the spectral peak. Without the refinement, the useful range is reduced to where S(f) is higher than 15% of the spectral peak, based on a 3-hour sea state simulation. The method is then applied on experimental surge motion records from 1:50 scaled model tests carried out in an offshore basin, simulating 15m water depth. It is found that the QTF estimation procedure works reasonably well, but the accuracy is lower than that in the numerical study because the refined noise reduction could not be used due to the particular characteristics of the QTF. Therefore a basic version without the refinement had to be used. Still, results appear to be fairly reliable in the reduced wave frequency range with S(f) > 15% of the spectral peak, i.e. from 0.07Hz to 0.10Hz in this case.

Numerical Study on the Geometric and Inertial Parameters for Oscillating Wave Surge Converters

2018 ◽  
Author(s):  
Chen-Chou Lin ◽  
Yi-Chih Chow ◽  
Shiaw-Yih Tzang ◽  
Ching-Yen Chiou ◽  
Yu-Yu Huang
Keyword(s):  
Numerical Study ◽  
Center Of Mass ◽  
Three Dimensional ◽  
Wave Climate ◽  
Absorption Efficiency ◽  
Irregular Waves ◽  
Inertial Parameters ◽  
Flap Thickness ◽  
Computational Fluid Dynamics Cfd ◽  
Peak Value

In this paper the three-dimensional numerical simulation is conducted for Oscillating Wave Surge Converters (OWSCs) using computational fluid dynamics (CFD) software FLOW-3D, based on the wave climate of the offshore sea in northeast Taiwan, that is, 1.5 meters of wave height and 7 seconds of the wave period. The results are compared with that using the wave energy converter simulation toolbox, WEC-Sim. The effects of the parameters, including the flap thickness, flap width, the position of the mass center, and flap density, are investigated, especially their influence of the energy capturing efficiency or the capture factor (CF). The simulation results show that, bigger flap thickness (d), smaller flap width (B), smaller flap density, and lower flap’s center of mass will result in a higher efficiency for power capture performance. Among the four parameters, the flap thickness is the most dominant parameter. From hydrodynamic respect, a larger drag force may occur at the sidewalls of the thick flap, and the shear force accelerate the pitch motion of the flap, in turn increasing the absorption efficiency. From a practical design aspect, the variation of the CF around the peak value is smoother for wider flap, which suggests a broad bandwidth in receiving various wave frequency in irregular waves.

Numerical study of the mooring system failure of aquaculture net cages under irregular waves and current

2020 ◽  
Vol 216 ◽  
pp. 108110
Author(s):  
Hung-Jie Tang ◽  
Po-Hung Yeh ◽  
Chai-Cheng Huang ◽  
Ray-Yeng Yang
Keyword(s):  
Numerical Study ◽  
Irregular Waves ◽  
Mooring System ◽  
System Failure ◽  
Net Cages

Springing and Ringing Response of Offshore Triceratops

2015 ◽  
Author(s):  
Srinivasan Chandrasekaran ◽  
Jamshed Nassery
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Numerical Study ◽  
Irregular Waves ◽  
Impact Loads ◽  
Beat Phenomenon ◽  
Average Wave ◽  
Gradual Decay ◽  
Asymmetric Factor ◽  
Jonswap Spectrum

This paper presents a numerical study of ringing and springing response of a relatively new Offshore Triceratops. The platform is subjected to irregular waves using JONSWAP spectrum by varying the significant wave height, average wave period, vertical asymmetric factor and the over shoot parameter. Strongly asymmetric waves, which are capable of causing impact loads on triceratops, are used to simulate ringing in offshore triceratops. Heave response shows bursts but there are no rapid built ups. Gradual decay, which is seen in the present case, resembles a beat phenomenon.

Experimental and Numerical Study of the Motions of a Turret Moored FPSO in Waves

2004 ◽  
Vol 127 (3) ◽  
pp. 197-204 ◽  
Author(s):  
C. Guedes Soares ◽  
N. Fonseca ◽  
R. Pascoal
Keyword(s):  
Degrees Of Freedom ◽  
Numerical Study ◽  
Numerical Data ◽  
Irregular Waves ◽  
Experimental Program ◽  
Six Degrees Of Freedom ◽  
Strip Theory ◽  
Wide Range ◽  
Wave Heights ◽  
Mooring Forces

This paper presents the results of an experimental program carried out with a model of a FPSO (Floating Production, Storage and Offloading) unit moored and subjected to incoming waves. In regular waves, a wide range of wavelengths were tested and the effect of the wave amplitude was also investigated. In irregular waves the model was subjected to different sea states, including very severe significant wave heights. The measured responses include the six degrees of freedom absolute motions, relative motions, and the mooring forces. The experimental data of surge, heave, and pitch is compared with calculated results from a Green’s function panel method and a strip theory program. In general, the agreement between experimental and numerical data is very good.

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