scholarly journals IDENTIFICATION OF INFLUENTIAL PARAMETERS IN A SHIP’S MOTION RESPONSES: A ROUTE TO MONITORING DYNAMIC STABILITY

2021 ◽  
Vol 154 (A1) ◽  
Author(s):  
H Enshaei ◽  
R Birmingham ◽  
E Mesbahi
Keyword(s):  
Degrees Of Freedom ◽  
Peak Frequency ◽  
Irregular Waves ◽  
Motion Response ◽  
Six Degrees Of Freedom ◽  
Beam Seas ◽  
Motion Responses ◽  
Frequency Components ◽  
Large Motion ◽  
Influential Parameters

Six degrees of freedom motion response tests of a Ro-Ro model have been carried out in irregular waves under intact conditions. A stationary model was tested in different sea states for following, astern quartering and beam seas. The investigation was limited to the effect of encountered frequency components and associated magnitude of energy of the ship’s motion responses. Analysis of heave, pitch and roll motions confirmed the vulnerability of the model to certain frequency ranges resulting in an adverse effect on the responses, and these were closely related to its natural frequencies. It was confirmed that the roll motion maintains its highest oscillation around the natural frequency in all sea conditions regardless of heading angles. However spectral analysis of the heave and pitch responses revealed the wave peak frequency. Roll is magnified when the peak frequency of wave approaches the natural roll frequency; therefore keeping them apart avoids a large motion response. It was concluded that peak frequency and associated magnitude are two important inherent characteristics of motion responses. Detection of influential parameters of encountered wave through heave and pitch responses could be utilised to limit a large ship’s motion at sea.

Identification of Influential Parameters in A Ship’s Motion Responses: A Route to Monitoring Dynamic Stability

2012 ◽  
Vol 154 (A1) ◽  
Keyword(s):  
Degrees Of Freedom ◽  
Peak Frequency ◽  
Irregular Waves ◽  
Motion Response ◽  
Six Degrees Of Freedom ◽  
Beam Seas ◽  
Motion Responses ◽  
Frequency Components ◽  
Large Motion ◽  
Influential Parameters

Six degrees of freedom motion response tests of a Ro-Ro model have been carried out in irregular waves under intact conditions. A stationary model was tested in different sea states for following, astern quartering and beam seas. The investigation was limited to the effect of encountered frequency components and associated magnitude of energy of the ship’s motion responses. Analysis of heave, pitch and roll motions confirmed the vulnerability of the model to certain frequency ranges resulting in an adverse effect on the responses, and these were closely related to its natural frequencies. It was confirmed that the roll motion maintains its highest oscillation around the natural frequency in all sea conditions regardless of heading angles. However spectral analysis of the heave and pitch responses revealed the wave peak frequency. Roll is magnified when the peak frequency of wave approaches the natural roll frequency; therefore keeping them apart avoids a large motion response. It was concluded that peak frequency and associated magnitude are two important inherent characteristics of motion responses. Detection of influential parameters of encountered wave through heave and pitch responses could be utilised to limit a large ship’s motion at sea.

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.

Experimental Study the Performance of a Compact Mooring System for a Dual Chamber Floating Oscillating Water Column Device

2020 ◽  
Author(s):  
Sheng Xu ◽  
K. Rezanejad ◽  
Shan Wang ◽  
J. F. M. Gadelho ◽  
C. Guedes Soares
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Wave Energy Converter ◽  
Air Pressure ◽  
Mooring System ◽  
Oscillating Water Column ◽  
Energy Converter ◽  
Six Degrees Of Freedom ◽  
Motion Responses

Abstract A compact mooring system concept is proposed. This novel mooring is composed of submerged buoy and three segments of nylon ropes, which is suitable for the large wave energy converters and wave energy converter array due to its high flexibility and small mooring radius. The performance of this mooring concept was studied experimentally when it was moored to an oscillating water column. The damping of the oscillating water column was modelled by an orifice on top of the chamber. Both regular and irregular head sea wave tests were conducted. In order to study the influence of wave height on system dynamics, two series of regular wave tests with same periods but different wave heights were conducted. An optical tracking system was installed to capture six degrees of freedom motion responses of oscillating water column. The air pressure in the chamber was measured by the air pressure sensor. Two load cells were installed on the top of mooring lines to measure mooring tension time series. Besides, the wave surface elevations inside the chamber were measured by the wave gauges. According to the experimental results, the six degrees of freedom motion responses of floating wave energy converter and mooring tensions are analyzed. Besides, the energy conversion efficiency is evaluated based on the measured data.

A Numerical Study on Motion Responses of a Mat-Support Jack-Up During Positioning

2015 ◽  
Author(s):  
Zhaode Zhang ◽  
Yuhong Wang
Keyword(s):  
Numerical Analysis ◽  
Environmental Conditions ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Analysis Software ◽  
Floating Structure ◽  
Six Degrees Of Freedom ◽  
Motion Responses ◽  
Different Depths ◽  
Jack Up

The motion response of a mat-support jack-up during positioning is studied in this paper using numerical analysis software SESAM. In the process of jack-up positioning, the square bottom mat is gradually lowered and the floating jack-up, secured by anchor chains, moves in six degrees of freedom in response to the dynamic loading of wave, current and wind combined. Numerical simulations are carried out to solve motion responses of the floating structure with mat at different depths. The sensitivity of motion responses to wave periods and directions are analyzed. The maximum motion amplitudes under the design environmental conditions and the risk of the mat crashing with the seafloor are evaluated.

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.

Numerical and Experimental Study of 3-D Sloshing in Tanks of LNG Carriers

2006 ◽  
Author(s):  
Makoto Arai ◽  
Humberto S. Makiyama ◽  
Liang-Yee Cheng ◽  
Atsushi Kumano ◽  
Takahiro Ando ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Wave Spectrum ◽  
Irregular Waves ◽  
3D Analysis ◽  
Six Degrees Of Freedom ◽  
Strong Relation ◽  
3D Effects ◽  
Membrane Type ◽  
Tank Geometry ◽  
The Given

This paper describes a numerical analysis of sloshing in liquid cargo tanks of membrane-type liquefied natural gas (LNG) carriers in a rough sea. The numerical method used in this study is based on a finite-difference method, in which impact pressure on the tank ceiling is treated accurately by a numerical boundary condition proposed by the authors. Tank motion with six degrees of freedom was given by the response amplitude operator of a ship, and sloshing that occurs in regular and irregular waves is examined. An ISSC wave spectrum is used to generate the irregular waves. We describe the influence of 3D effects due to tank motion and tank geometry on the sloshing flow, and show the strong relation of the sloshing to the frequency of the given ship motion. Comparison of the numerical results with the measured data shows the effectiveness of the presented 3D analysis method.

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 Dynamic Response of Coupled Mooring Lines and Floating Wave Energy Devices in Waves / Currents

2019 ◽  
Vol 8 (12) ◽  
pp. 5539-5545
Keyword(s):  
Renewable Energy ◽  
Dynamic Response ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Ocean Waves ◽  
Irregular Waves ◽  
Mooring Lines ◽  
Energy Devices ◽  
Six Degrees Of Freedom ◽  
The Government

Various global studies have shown that ocean waves energy have large potential in renewable energy sector. Their role within renewable energy gets high priority in the future by the government of United Kingdom. The principle concept of wave energy is when wave energy is converted into potential energy by the wave energy devices to generate electricity. An understanding of the dynamic response of the devices and mooring lines is important for this paper. This paper deals with the analysis of the various effects that influence the different design of wave energy converter devices. The mooring design idea is also analyzed to show which mooring layout is suitable to fulfill the requirement. The design of mooring configuration also influence how wave power is extracted and how such system are operated and maintained. The effects investigated in this paper are regular and irregular waves, motion @ six degrees of freedom, maximum and minimum mooring tension, different waves direction, wave current, energy and power take off.

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