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.

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.

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.

Model Tests for Safe-Return-to-Port of a Damaged Ship in Waves

2015 ◽  
Author(s):  
Jeonghwa Seo ◽  
Cristobal Santiago Bravo ◽  
Shin Hyung Rhee
Keyword(s):  
Degrees Of Freedom ◽  
Feedback System ◽  
Model Tests ◽  
Measurement Unit ◽  
Test Model ◽  
Motion Response ◽  
Six Degrees Of Freedom ◽  
Heading Angle ◽  
Wave Conditions ◽  
Damaged Ship

A series of tests using a course-keeping model ship with an autopilot system were carried out in a towing tank for research on Safe-Return-to-Port (SRTP). The autopilot system controls the rudder angle and propeller revolution rate by a feedback system. The variation of the heading angle of the test model with different control parameters was investigated first, to ensure that the test model had sufficient course-keeping maneuverability in severe wave conditions. The wave conditions and propeller revolution rate were selected based on SRTP regulations. Tests were conducted in wave conditions corresponding to sea states 4 to 6. The six-degrees-of-freedom motion response of the test model was measured by a wireless inertial measurement unit and gyro sensors to achieve fully wireless model tests. The advance speed and motion response in various wave conditions were measured and analyzed to investigate the effects of flooding behavior in a damaged condition and of waves on the propulsion and maneuvering performance of the damaged ship model.

Design of a Robust H∞ PID Control for Industrial Manipulators

1999 ◽  
Vol 122 (4) ◽  
pp. 803-812 ◽  
Author(s):  
Jonghoon Park ◽  
Wankyun Chung
Keyword(s):  
Pid Control ◽  
Degrees Of Freedom ◽  
Performance Tuning ◽  
Motion Controller ◽  
Six Degrees Of Freedom ◽  
Stability Robustness ◽  
Industrial Manipulators ◽  
And Performance ◽  
The Stability ◽  
L2 Gain

Industrial manipulators are under various limitations against high quality motion control; for example, both frictional and dynamic disturbances should be dealt with a simple PID control structure. A robust linear PID motion controller, called the reference error feedback (REF), is proposed, which solves the nonlinear L2-gain attenuation control problem for robotic manipulators. The stability, robustness, and performance tuning of the proposed controller are analyzed. Making use of the fact that the single parameter of the induced L2-gain γ controls the performance with stability attained, we propose a simple and stable method of performance tuning called “the square law.” The analytical results are verified through experiments of a six-degrees-of-freedom industrial manipulator. [S0022-0434(00)00104-0]

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.

Theory and Experiments on the Compliance Control of Redundant Robot Manipulators

1990 ◽  
Vol 112 (4) ◽  
pp. 653-660 ◽  
Author(s):  
H. Kazerooni ◽  
K. G. Bouklas ◽  
J. Guo
Keyword(s):  
Degrees Of Freedom ◽  
Control Method ◽  
Robot Manipulators ◽  
Industrial Robot ◽  
Redundant Robot ◽  
Control Approach ◽  
Six Degrees Of Freedom ◽  
The Stability ◽  
Control Methodology ◽  
Theory And Experiments

This work presents a control methodology for compliant motion in redundant robot manipulators. This control approach takes advantage of the redundancy in the robot’s degrees of freedom: while a maximum six degrees of freedom of the robot control the robot’s endpoint position, the remaining degrees of freedom impose an appropriate force on the environment. To verify the applicability of this control method, an active end-effector is mounted on an industrial robot to generate redundancy in the degrees of freedom. A set of experiments are described to demonstrate the use of this control method in constrained maneuvers. The stability of the robot and the environment is analyzed.

Numerical Simulation of Submarine Surfacing With Six Degrees of Freedom in Regular Waves

2016 ◽  
Author(s):  
Weijian Jiang ◽  
Zhilin Wang ◽  
Ran He ◽  
Xianzhou Wang ◽  
Dakui Feng
Keyword(s):  
Numerical Simulation ◽  
Wave Height ◽  
Velocity Fluctuation ◽  
Degrees Of Freedom ◽  
Wave Length ◽  
Roll Angle ◽  
Regular Waves ◽  
Rolling Moment ◽  
Six Degrees Of Freedom ◽  
Calm Water

Submarine surfacing in waves is three dimensional unsteady motion and includes complex coupling between force and motion. This paper uses computational fluid dynamics (CFD) to solve RANS equation with coupled six degrees of freedom solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface. Computations were performed for the standard DARPA SUBOFF model. The structured dynamic overset grid is applied to the numerical simulation of submarine surfacing (no forward speed) in regular waves and computation cases include surfacing in the calm water, transverse regular waves with different ratio of wave height and submarine length (h/L = 0.01, 0.02, 0.03, 0.04) and transverse regular waves with different ratio of wave length and submarine length (λ/L = 0.5, 1, 1.5). The asymmetric vortices in the process of submarine surfacing can be captured. It proves that roll instability is caused by the destabilizing hydrodynamic rolling moment overcoming the static righting moment both under the water and in regular waves. Relations among maximum roll angle, surfacing velocity fluctuation and wave parameters are concluded by comparison with variation trend of submarine motion attitude and velocity of surfacing in different wave conditions. Simulation results confirm that wave height h/L = 0.04 and wave length λ/L = 1.5 lead to surfacing velocity fluctuation significantly. Maximum roll angle increases with the increase of wave height and wave length. Especially the law presents approximate linear relationship. Maximum roll angle with wave height (h/L = 0.04) can reach to 7.29° while maximum roll angle with wave length (λ/L = 1.5) can reach to 5.79° by contrast with 0.85° in calm water. According to the above conclusions, maneuverability can be guided in the process of submarine surfacing in waves in order to avoid potential safety hazard.

Model Tests of the PACT Base America's Cup Hull in Following Seas

1997 ◽  
Author(s):  
Jesse Falsone
Keyword(s):  
Degrees Of Freedom ◽  
Model Tests ◽  
Response Amplitude ◽  
Scale Model ◽  
Radius Of Gyration ◽  
Added Resistance ◽  
Following Seas ◽  
America’S Cup ◽  
Wave Slope ◽  
Response Amplitude Operators

Model tests were conducted at the Davidson Laboratory to investigate the effect of following seas on the added resistance of the PACT (Partnership for America's Cup Technology) base America's Cup hull. A 1 :8 scale model of an International America's Cup Class yacht was provided by Team Dennis Conner and was refinished with funding from US Sailing to its original lines as the PACT base hull. Using this hull (canoe body with no appendages), model tests were conducted in the following seas condition. Upright, resistance tests were carried out at constant speed in both smooth water and regular waves of varying length and slope. The model was free to heave and pitch while restraining all other degrees of freedom. The data analysis revealed that at wavelengths approximately greater than two model lengths, the added resistance of the model is negative. A negative added resistance implies that the average drag force of the model in a particular following sea is less than the still-water drag of the model at the same speed. At wavelengths below this point, the added resistance of the model is greater than the still-water resistance. Furthermore, the form of the data suggests that at waves longer than were tested in this experiment (wavelengths greater than five model lengths), the added resistance of the model converges to the still­water resistance. The experiment also verifies that the added resistance is proportional to the square of the wave height. The pitch and heave characteristics of the model as expressed in the form of response amplitude operators are independent of wave slope. This is to say that for a particular motion, the response amplitude operators for each wave slope overlap one another. The results of these model tests were to be used as a database for the IMS Pitching Moment Project established in an attempt to quantify the sensitivity of radius of gyration on yacht performance. Also, these results were to be used to validate CFD estimates of added resistance.

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.

Simulating the Acceleration to Take-Off Phase of a WIG-Craft Using Results of a Constrained Experiment

2020 ◽  
Author(s):  
Ombor Pereowei Garrick ◽  
Zhiqiang Hu ◽  
Lei Song
Keyword(s):  
Simulation Model ◽  
High Speed ◽  
Model Tests ◽  
Constant Speed ◽  
Develop Model ◽  
State Variables ◽  
Acceleration Phase ◽  
Power Requirement ◽  
Captive Model Tests ◽  
Calm Water

Abstract The acceleration to take-off (in calm water and rough seas) is a short duration but very important motion regime of a WIG-craft. It determines the transport efficiency of a WIG-craft as a viable alternative to high speed marine vehicles or low speed aircrafts used in conveying workers to and offshore oil and gas fields. The development of a simulation model based on results from constant speed captive model tests for a WIG boat is imperative, when in the absence of appropriate experimental test rig, there is the need to investigate the attitude of the WIG-craft during its acceleration phase. Theoretical tools for investigating the characteristics of the acceleration phase of a WIG boat are uncommon and where they exist, they are almost unreliable, not been experimentally validated. Moreover, the cost associated with conducting acceleration tests is huge. The test facilities are not readily available in most maritime engineering research institutions. This study is concerned with the development of a simulation model with input from results of captive model tests to investigate the running attitude, forces and moments acting on a WIG-boat accelerating to take-off in calm water. A constrained model tests at constant speed levels were conducted for a range of model draughts and trim angles. Multivariate multiple regression method was used to develop model equations that fits the measured aero-hydro dynamic lift, drag and moment data as a function of draught, speed and trim angle. The hydrostatic and aero-hydrodynamic steady state forces and moments where combined into a state-space form which are solved in MATLAB. The state variables and the first and second derivatives of the states of the boat as well as the forces and moments acting on it are generated as output from the simulation model. Though the simulation model proved successful in predicting the attitude of the WIG-boat including crashing and excessive acceleration and power requirement during take-off, the results from the model still need to be verified with CFD analysis, a full WIG-boat trial tests or with the expensive high speed towing tank capable of carrying out acceleration runs. The method has the potential to be improved to account for the unsteady forces and moments that exists when the WIG-boat accelerates from offshore environment.

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