Hydrodynamic Coefficients of a Moored Semisubmersible in Waves

1992 ◽  
Vol 114 (1) ◽  
pp. 9-15 ◽  
Author(s):  
S. K. Chakrabarti ◽  
D. C. Cotter
Keyword(s):  
Model Test ◽  
Nonlinear Damping ◽  
Added Mass ◽  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Initial Displacement ◽  
Slow Drift ◽  
Linear And Nonlinear ◽  
The Waves ◽  
Line Loads

The hydrodynamic coefficients of a semisubmersible undergoing slow-drift oscillation were determined through a model test. The semisubmersible model was moored in head seas, fore and aft, with linear springs which were pretensioned and never became slack during any test run. At the beginning of each test run, the vessel was held at an initial displacement from its equilibrium position and then released, and the resulting line loads were recorded. The semisubmersible was tested in still water and in regular waves. The amplitude of the waves at a given period was varied. The added mass and damping of the semisubmersible were determined from the decayed oscillation of the loads. The semisubmersible experienced both linear and nonlinear damping. The hydrodynamic coefficients obtained from the semisubmersible as functions of wave height and period are compared with those found previously on a tanker.

Research on Longitudinal Motion Prediction of Hybrid Monohull Considering Based on Numerical Simulation

2014 ◽  
Vol 716-717 ◽  
pp. 776-779
Author(s):  
Bo Tian ◽  
Hui Long Ren ◽  
Zhi Yuan Dong
Keyword(s):  
Numerical Simulation ◽  
Model Test ◽  
Potential Flow ◽  
Motion Prediction ◽  
Longitudinal Motion ◽  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Damping Force ◽  
Main Component ◽  
Rans Method

The shape of hybrid monohull at the bow is quite complex and the viscosity force is the main component of the damping force in the drainage area of the bow when the ship moves in waves so that the result of the motion predicition by the traditional potential flow method is very different from the result of experiments. This paper tries to use new numerical compute method considering the effect of the viscosity to improve the precision of the sea keeping predicition. Based on the Reynolds Averaged N-S Equations (RANS) method, the paper takes a hrbrid monohull to compute the hydrodynamic coefficients. According to the result of model test, the prediction of the hybrid monohull’s the longitudinal motion in regular waves at speed of 18kn also indicates that RANS method can reflect viscid influence reducing the motion of hybrid monohull in waves.

Numerical Simulation of Ship Collision and Validations With Experimental Results

2021 ◽  
Author(s):  
Xiangbiao Wang ◽  
Chun Bao Li ◽  
Ling Zhu
Keyword(s):  
Numerical Simulation ◽  
Model Test ◽  
Structural Damage ◽  
Added Mass ◽  
Ship Motion ◽  
Time Dependent ◽  
Structural Deformation ◽  
Structure Interaction ◽  
Ship Collision ◽  
Good Agreement

Abstract Ship collision accidents occur from time to time in recent years, and this would cause serious consequences such as casualties, environmental pollution, loss of cargo on board, damage to the ship and its equipment, etc. Therefore, it is of great significance to study the response of ship motion and the mechanism of structural damage during the collision. In this paper, model experiments and numerical simulation are used to study the ship-ship collision. Firstly, the Coupled Eulerian-Lagrangian (CEL) was used to simulate the fluid-structure interaction for predicting structural deformation and ship motion during the normal ship-ship collision. Meanwhile, a series of model tests were carried out to validate the numerical results. The validation presented that the CEL simulation was in good agreement with the model test. However, the CEL simulation could not present the characteristics the time-dependent added mass.

Comparison of Linear and Nonlinear Damping Effects on a Ring Vibration Isolator

2020 ◽  
pp. 13-22
Author(s):  
Ze-Qi Lu ◽  
Dong-Hao Gu ◽  
Ye-Wei Zhang ◽  
Hu Ding ◽  
Walter Lacarbonara ◽  
...  
Keyword(s):  
Nonlinear Damping ◽  
Vibration Isolator ◽  
Linear And Nonlinear ◽  
Damping Effects

The Transverse Plane Motions of Ships

1991 ◽  
Vol 28 (02) ◽  
pp. 55-72
Author(s):  
Bruce L. Hutchison
Keyword(s):  
Transverse Plane ◽  
Irregular Waves ◽  
Hydrodynamic Coefficients ◽  
Important Process ◽  
Regular Waves ◽  
Hull Form ◽  
Fishing Vessels ◽  
Transverse Stability ◽  
Roll Axis ◽  
The One

A detailed exposition of the kinematics of the transverse plane motions of ships is provided, with particular attention to the important process of total transverse acceleration in vessel coordinates. The loci of sway, sway velocity and sway acceleration are shown to follow hyperbolic distributions with respect to elevation in both regular and irregular waves. In regular waves the transverse acceleration in earth-fixed and vessel-fixed coordinates are shown to be congruent with a vertical shift in elevation of g/ω2 = λ/(2π). Expressions are given for the elevations minimizing transverse plane processes in regular and irregular waves. In long waves the elevation minimizing total transverse acceleration in vessel coordinates is shown to be g/ωn2 = g[Tn/ /(2π)]2 below the waterline. This is the roll center, which should be used in the traditional analysis of foundation loads. Its location, far below the keel for most vessels, is surprising. The elevation (OP) of the roll axis, which must be used when solving the one-degree-of-freedom equation for roll, is given and is shown to require hydrodynamic coefficients for sway as well as roll. In general, OP does not correspond to an elevation that minimizes any of the transverse plane processes. The effect of hull form, transverse stability and natural roll period on transverse plane motions are examined in an attempt to resolve the dichotomy of views between those who favor ships with low GMT and long natural roll periods and those who favor high GMT with short natural roll periods. It is demonstrated that large values of the beam-to-draft ratio (6/7) with low natural roll periods are advantageous at modest elevations above the waterline. This explains the favorable offshore experience in vessels meeting this description, such as tugs, supply vessels and fishing vessels. At higher elevations long natural periods are shown to present a clear advantage, which supports the preference for low GMT for large passenger vessels, containerships and ships with deck-loads of logs. The trends identified would seem to support the conjecture that, with regard to natural roll period, there is a "forbidden middle" that should be avoided in design.

Reynolds Number Effects on Hydrodynamic Coefficients for Pure In-Line and Pure Cross-Flow Forced Vortex Induced Vibrations

2009 ◽  
Author(s):  
Jamison L. Szwalek ◽  
Carl M. Larsen
Keyword(s):  
Reynolds Number ◽  
Prediction Models ◽  
Current Knowledge ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Added Mass ◽  
Hydrodynamic Coefficients ◽  
Vortex Induced Vibrations ◽  
Reynolds Number Effects ◽  
Sinusoidal Oscillations

In-line vibrations have been noted to have an important contribution to the fatigue of free spanning pipelines. Still, in-line contributions are not usually accounted for in current VIV prediction models. The present study seeks to broaden the current knowledge regarding in-line vibrations by expanding the work of Aronsen (2007) to include possible Reynolds number effects on pure in-line forced, sinusoidal oscillations for four Reynolds numbers ranging from 9,000 to 36,200. Similar tests were performed for pure cross-flow forced motion as well, mostly to confirm findings from previous research. When experimental uncertainties are accounted for, there appears to be little dependence on Reynolds number for all three hydrodynamic coefficients considered: the force in phase with velocity, the force in phase with acceleration, and the mean drag coefficient. However, trends can still be observed for the in-line added mass in the first instability region and for the transition between the two instability regions for in-line oscillations, and also between the low and high cross-flow added mass regimes. For Re = 9,000, the hydrodynamic coefficients do not appear to be stable and can be regarded as highly Reynolds number dependent.

Higher Order Wave-Current Elevations in Deep Water

2011 ◽  
Author(s):  
Anne Katrine Bratland ◽  
Ragnvald Bo̸rresen ◽  
Per Ivar Barth Berntsen
Keyword(s):  
Deep Water ◽  
Higher Order ◽  
Irregular Waves ◽  
Ocean Current ◽  
Regular Waves ◽  
Third Order ◽  
Uniform Current ◽  
Current Interaction ◽  
The Waves ◽  
Wave Elevations

Wave-current interaction refers to the interaction between surface gravity waves and ocean current flow. This interaction implies an exchange of energy, i.e. both the waves and the current are affected. The present paper describes the calculation of wave elevations in higher order unidirectional, irregular waves with a uniform current in deep water. Results for regular waves are compared with those obtained for Stokes second and third order waves with uniform current according to the method described by Fenton [1]. The results for higher order wave elevations in irregular waves have been compared with waves and current generated in a model test basin and reasonable agreement has been found.

Experimental Study on Hydrodynamics of Hybrid Deep-V Monohull With Different Built-Up Appendages

2018 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Li ◽  
Muk Chen Ong
Keyword(s):  
Model Test ◽  
Performance Model ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Vertical Acceleration ◽  
Test Results ◽  
Regular Waves ◽  
Sea State ◽  
Seakeeping Performance

The hydrodynamic characteristics of a hybrid deep-V monohull with different built-up appendages are investigated experimentally in order to improve the resistance and seakeeping performance. Model tests have been carried out to study the hydrodynamic performance between a bare deep-V vessel and a deep-V monohull with different built-up appendage configurations (i.e. a hybrid deep-V monohull). From the model test results, it is found that the existence of the appendages will reduce the amplitude of pitching angle and bow vertical acceleration compared to that of the bare deep-V vessel in heading regular waves. However, the resistances for the hybrid deep-V monohull with built-up appendages are increased 15.6% for Fn = 0.264, and 0.1% for Fn = 0.441 compared to the resistance of the bare deep-V vessel. The model test results of seakeeping performance in irregular waves show that the hybrid deep-V monohull gives a better seakeeping performance than the deep-V vessel. The pitching angle and bow vertical acceleration of the hybrid deep-V monohull containing a built-up appendage are reduced 15.3% and 20.6% compared to the deep-V monohull in irregular waves at Fn = 0.441 in 6th class sea state (H1/3 = 6m).

scholarly journals Determination of coupled sway, roll, and yaw motions of a floating body in regular waves

2004 ◽  
Vol 2004 (41) ◽  
pp. 2181-2197 ◽  
Author(s):  
S. N. Das ◽  
S. K. Das
Keyword(s):  
Dynamic Equilibrium ◽  
Numerical Models ◽  
Equations Of Motion ◽  
System Stability ◽  
Floating Body ◽  
Regular Waves ◽  
Laplace Transform Technique ◽  
Restoring Forces ◽  
The Waves

This paper investigates the motion response of a floating body in time domain under the influence of small amplitude regular waves. The governing equations of motion describing the balance of wave-exciting force with the inertial, damping, and restoring forces are transformed into frequency domain by applying Laplace transform technique. Assuming the floating body is initially at rest and the waves act perpendicular to the vessel of lateral symmetry, hydrodynamic coefficients were obtained in terms of integrated sectional added-mass, damping, and restoring coefficients, derived from Frank's close-fit curve. A numerical experiment on a vessel of19190ton displaced mass was carried out for three different wave frequencies, namely,0.56rad/s,0.74rad/s, and1.24rad/s. The damping parameters (ςi) reveal the system stability criteria, derived from the quartic analysis, corresponding to the undamped frequencies (βi). It is observed that the sway and yaw motions become maximum for frequency0.56rad/s, whereas roll motion is maximum for frequency0.74rad/s. All three motions show harmonic behavior and attain dynamic equilibrium for timet>100seconds. The mathematical approach presented here will be useful to determine seaworthiness characteristics of any vessel when wave amplitudes are small and also to validate complex numerical models.

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