scholarly journals Prediction of Ship Unsteady Maneuvering in Calm Water by a Fully Nonlinear Ship Motion Model

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
Ray-Qing Lin ◽  
Tim Smith ◽  
Michael Hughes
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Ship Motion ◽  
Ship Motions ◽  
Motion Model ◽  
Forward Speed ◽  
Fully Nonlinear ◽  
Six Degrees Of Freedom ◽  
Calm Water

This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL). In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water. During the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge, sway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage, respectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions and their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering, a universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces and moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an Experimental Hull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL and experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder, which is included using a flow acceleration factor.

Numerical Simulation of Damaged Ship’s Motion in Beam Waves

2019 ◽  
Author(s):  
Qing Wang ◽  
Xuanshu Chen ◽  
Liwei Liu ◽  
Xianzhou Wang ◽  
MingJing Liu
Keyword(s):  
Degrees Of Freedom ◽  
Body Motion ◽  
Ship Motions ◽  
Rans Equations ◽  
Six Degrees Of Freedom ◽  
Calm Water ◽  
Unsteady Simulation ◽  
Ship Hydrodynamic ◽  
Physical Phenomena ◽  
Damaged Ship

Abstract The dangerous situation caused by the breakage of the ship will pose a serious threat to crew and ship safety. If the ship’s liquid cargo or fuel leaks, it will cause serious damage to the marine environment. If damage occurs accompanied by roll and other motions, it may cause more dangerous consequences. It is an important issue to study the damaged ship in time-domain. In this paper, the motions of the damaged DTMB 5512 in calm water and regular beam waves are studied numerically. The ship motions are analyzed through CFD methods, which are acknowledged as a reliable approach to simulate and analyze these complex physical phenomena. An in-house CFD (computational fluid dynamics) code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) is used for solving RANS equations coupled with six degrees of freedom (6DOF) solid body motion equations. RANS equations discretized by finite difference method and solved by PISO algorithm. Level set was used for free surface simulation. The dynamic behavior of model was observed in both intact and damaged condition. The heave, roll and pitch amplitudes of the damaged ship were studied in calm water and beam wave of three wavelengths.

Effect of Wind Loads on the Performance of Free-Fall Lifeboats

2014 ◽  
Author(s):  
Thomas Sauder ◽  
Eloise Croonenborghs ◽  
Sebastien Fouques ◽  
Nabila Berchiche ◽  
Svein-Arne Reinholdtsen
Keyword(s):  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Free Fall ◽  
Offshore Structures ◽  
Water Entry ◽  
Forward Speed ◽  
Cfd Simulations ◽  
Six Degrees Of Freedom ◽  
Complete Set ◽  
Water Exit

The paper presents a model describing the launch of free-fall lifeboats from offshore structures in strong environmental wind. Six-degrees-of-freedom numerical simulations of the lifeboat launch are performed using the free-fall lifeboat simulator VARUNA with a complete set of wind coefficients for the lifeboat. Those wind coefficients are obtained by CFD simulations validated against wind tunnel tests. The lifeboat launch simulations are then verified against time-domain CFD simulations of the whole launch in air until water entry. It is shown by means of numerical simulations that wind-induced loads on the lifeboat have a strong influence on its kinematics until water entry, and subsequently on the acceleration loads experienced by the occupants, on the structural loads on the lifeboat, and on its forward speed after water exit. It is concluded that the effect of wind-induced loads on the lifeboat performances should in general be investigated when establishing the operational limits for a given offshore installation.

Analysis of the Motion of Shipboard Missiles under the Excitation of Sea Waves

2013 ◽  
Vol 816-817 ◽  
pp. 825-830
Author(s):  
Yun Long Wang ◽  
Wei Min Lv ◽  
Jia Chen Feng ◽  
Yong Chuan Jin
Keyword(s):  
Environmental Analysis ◽  
Frequency Response Function ◽  
Degrees Of Freedom ◽  
Ship Motion ◽  
Irregular Waves ◽  
Motion Model ◽  
Sea Waves ◽  
Regular Waves ◽  
Six Degrees Of Freedom ◽  
Amplitude Frequency Response

Waves in different sea conditions are simulated by the Bretscheider double parameters spectrum using randomly chosen discrete frequencies as its parameters. Ship motion model of six degrees of freedom is established under the Ship coordinates system. As the ship system is linear, the ship motion under irregular waves can be calculated through the amplitude-frequency response function obtained by solving the model when the input is the superposition of regular waves. Finally according to the coordinate transformation between the ship coordinates system and the missile coordinates system, the motion of the shipboard missiles under excitation of sea waves can be analyzed to support the environmental analysis of its combat duty process.

scholarly journals A Fully Nonlinear, Dynamically Consistent Numerical Model for Ship Maneuvering in a Seaway

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Ray-Qing Lin ◽  
Weijia Kuang
Keyword(s):  
Experimental Data ◽  
Time Series ◽  
Adaptive Algorithm ◽  
Ship Motion ◽  
Frequency Variation ◽  
Physical Domain ◽  
Motion Model ◽  
Ship Maneuvering ◽  
Fully Nonlinear ◽  
Ship Tracks

This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL). In this paper we report our results on modeling ship maneuvering in arbitrary seaway that is one of the most challenging and important problems in seakeeping. In our modeling, we developed an adaptive algorithm to maintain dynamical balances numerically as the encounter frequencies (the wave frequencies as measured on the ship) varying with the ship maneuvering state. The key of this new algorithm is to evaluate the encounter frequency variation differently in the physical domain and in the frequency domain, thus effectively eliminating possible numerical dynamical imbalances. We have tested this algorithm with several well-documented maneuvering experiments, and our results agree very well with experimental data. In particular, the numerical time series of roll and pitch motions and the numerical ship tracks (i.e., surge, sway, and yaw) are nearly identical to those of experiments.

A New Technique for Testing a Sailing Yacht in Waves

1991 ◽  
Author(s):  
G. K. Kapsenberg
Keyword(s):  
Degrees Of Freedom ◽  
Water Resistance ◽  
Ship Motions ◽  
Added Resistance ◽  
Regular Waves ◽  
Six Degrees Of Freedom ◽  
Resistance Increase ◽  
Calm Water ◽  
Sailing Yacht ◽  
A New Technique

A new experimental technique is presented to test sailing yachts in waves. The method is suitable for the investigation of ship motions in all six degrees of freedom and added resistance for the close hauled condition. Measurements can be made both in regular waves and in irregular seas. The technique has been tried out on a model of a 12-Meter class yacht and showed a resistance increase for the yacht sailing to windward in a wind generated sea of 90% of the calm water resistance.

SHIP MOTIONS DURING REPLENISHMENT AT SEA OPERATIONS IN HEAD SEAS

2021 ◽  
Vol 152 (A4) ◽  
Author(s):  
G Thomas ◽  
T Turner ◽  
T Andrewartha ◽  
B Morris
Keyword(s):  
Experimental Study ◽  
Green Function ◽  
Prediction Method ◽  
Ship Motion ◽  
Motion Prediction ◽  
Ship Motions ◽  
Forward Speed ◽  
Theoretical Predictions ◽  
Relative Separation ◽  
Replenishment At Sea

During replenishment at sea operations the interaction between the two vessels travelling side by side can cause significant motions in the smaller vessel and affect the relative separation between their replenishment points. A study into these motions has been conducted including theoretical predictions and model experiments. The model tests investigated the influence of supply ship displacement and longitudinal separation on the ships’ motions. The data obtained from the experimental study has been used to validate a theoretical ship motion prediction method based on a 3-D zero-speed Green function with a forward speed correction in the frequency domain. The results were also used to estimate the expected extreme roll angle of the receiving vessel, and the relative motion between the vessels, during replenishment at sea operations in a typical irregular seaway. A significant increase in the frigate’s roll response was found to occur with an increase of the supply ship displacement, whilst a reduction in motion for the receiving vessel resulted from an increase in longitudinal separation between the vessels. It is proposed that to determine the optimal vessel separation it is vital that the motions of the vessels are not considered in isolation and all motions need to be considered for both vessels simultaneously.

A Nonlinear Mathematical Model for Ship Turning Circle Simulation in Waves

2005 ◽  
Vol 49 (02) ◽  
pp. 69-79 ◽  
Author(s):  
Ming-Chung Fang ◽  
Jhih-Hong Luo ◽  
Ming-Ling Lee
Keyword(s):  
Mathematical Model ◽  
Degrees Of Freedom ◽  
Regular Waves ◽  
Nonlinear Mathematical Model ◽  
Ship Maneuvering ◽  
Sea Trial ◽  
Six Degrees Of Freedom ◽  
Strip Theory ◽  
Calm Water ◽  
Maneuvering Motion

In the paper, a simplified six degrees of freedom mathematical model encompassing calm water maneuvering and traditional seakeeping theories is developed to simulate the ship turning circle test in regular waves. A coordinate system called the horizontal body axes system is used to present equations of maneuvering motion in waves. All corresponding hydrodynamic forces and coefficients for seakeeping are time varying and calculated by strip theory. For simplification, the added mass and damping coefficients are calculated using the constant draft but vary with encounter frequency. The nonlinear mathematical model developed here is successful in simulating the turning circle of a containership in sea trial conditions and can be extended to make the further simulation for the ship maneuvering under control in waves. Manuscript received at SNAME headquarters February 19, 2003; revised manuscript received January 27, 2004.

Ship Motions in Shallow Water

1970 ◽  
Vol 14 (04) ◽  
pp. 317-328 ◽  
Author(s):  
E. O. Tuck
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Incident Wave ◽  
Degrees Of Freedom ◽  
Added Mass ◽  
Exciting Force ◽  
Ship Motions ◽  
Wave System ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients

The problem discussed concerns small motions of a ship, in all six degrees of freedom, but at zero speed of advance, due to an incident wave system in shallow water of depth comparable with the ship's draft. The problem is completely formulated for an arbitrary ship, and is partially solved for the case when the ship is slender and the wavelength much greater than the water depth. Sample numerical computations of heave, pitch, and sway added mass and damping coefficients and the sway exciting force are presented.

Model Tests of a Caisson in Wet Towing for Assessing Resistance and Stability in Calm Water and Waves

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Chang-Wook Park ◽  
Jeonghwa Seo ◽  
Shin Hyung Rhee
Keyword(s):  
Degrees Of Freedom ◽  
Model Tests ◽  
Added Resistance ◽  
Power Requirement ◽  
Effective Power ◽  
Six Degrees Of Freedom ◽  
Calm Water ◽  
Improved Stability ◽  
Scale Ratio ◽  
The Stability

A series of model tests of a caisson in wet towing were conducted in a towing tank to assess the stability and effective power requirement in calm water and head sea conditions. The scale ratio of the model was 1/30, and the model-length-based Froude number in the tests ranged from 0.061 to 0.122, which is equivalent to 2 and 4 knots in the full scale, respectively. During the towing of the model, tension on the towline and six-degrees-of-freedom (6DOF) motion of the model were measured. Under the calm water condition, the effects of towing speed, draft, and initial trim variation on the towing stability and effective power were investigated. Initial trim improved stability and reduced required towing power. In head seas, effective power and towing stability were changed with the wavelength. It increased as the wavelength became longer, but the added resistance in long waves also stabilized the model with reduced yaw motion.

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