scholarly journals ANALYSIS OF THE RESPONSE OF OFFSHORE-MOORED SHIPS TO WAVES

1964 ◽  
Vol 1 (9) ◽  
pp. 46
Author(s):  
Jan L. Leendertse
Keyword(s):  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Longitudinal Axis ◽  
Mooring Line ◽  
Wave System ◽  
Sea Waves ◽  
Mooring Lines ◽  
Six Degrees Of Freedom ◽  
General Terms ◽  
Relationship Of

A vessel moored at sea will experience complicated series of translational and rotational oscillations due to sea waves. These motions can be considered as the summation of six components, three translational and three rotational. In the presently available analyses of motions of unmoored ships, differential equations can be written for each mode of movement. Unfortunately, motions in one of these modes are coupled to motions of other modes, and the analysis becomes rather complicated. Generally, the problem is simplified by neglecting some of the coupling effects and by specifying the position of the vessel in the wave system. This study develops and analyzes a model for a moored ship restrained by mooring lines, using the presently available mathematical models for the free ship and the force-displacement relationship of the cable-holding points on the ship. The coupled movement (three degrees of freedom) in a vertical plane through the longitudinal axis of the vessel and the generated mooring-line forces are considered in detail. The general case of six degrees of freedom in arbitrary heading is discussed briefly in general terms.

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.

scholarly journals ANALISIS NUMERIK PENGARUH KECEPATAN TERHADAP SEAKEEPING KAPAL PATROLI PADA DAERAH PELAYARAN SEASTATE 7

2021 ◽  
Vol 4 ◽  
pp. 13-17
Author(s):  
Mohammad Taufik Ar Rozi ◽  
Betty Ariani ◽  
Dedy Wahyudi
Keyword(s):  
Water Surface ◽  
Degrees Of Freedom ◽  
Body Shape ◽  
Critical Value ◽  
Vertical Movement ◽  
Sea Waves ◽  
Six Degrees Of Freedom ◽  
A Value ◽  
Wave Angle ◽  
Standard Limit

Patrol boat is designed not to be slow in its movement on the water surface. To be able to move quickly and agilely, the most important requirement for this type of ship is in its maneuverability. The ship's motion at sea (seakeeping) is influenced by several things, speed, body shape, and the direction of the ship's heading waves. In this study, we analyze the six degrees of freedom, especially on the response of the ship's vertical movement, namely rolling on the sea waves of Seastate 7, especially in extreme weather in the South China Sea. The standard limit used is NORDFORSK 1987 with Light Manual Work Criteria. By entering parameters such as variations in speed and wave angle, such as 0°, 45°, 180° and 270°, then from the graph it can be seen the critical value for each movement. The calculation is carried out with the help of computational software Maxsurf Motions Advanced 20 V8i. The results of this study are the maximum roll movement value that occurs at a speed of 14 knots with a wave angle of 45° with a roll angle value of 6.40o. Furthermore, there is a decrease in the value of the movement along with the increase in the speed of the ship. The minimum roll value occurs when the wave angle is 270° when the ship's speed is 28 knots with a value of 5.69o.

PATHS OF FREELY FALLING DISKS

2009 ◽  
Vol 23 (03) ◽  
pp. 373-376 ◽  
Author(s):  
HONGJIE ZHONG ◽  
CUNBIAO LEE
Keyword(s):  
Degrees Of Freedom ◽  
Center Of Mass ◽  
Vertical Plane ◽  
Stereoscopic Vision ◽  
Six Degrees Of Freedom ◽  
Mass Distributions ◽  
First Case ◽  
The Mean ◽  
Thin Disks ◽  
Free Falling

The free falling motion of round thin disks in quiescent water was investigated experimentally. The mean density of the disks were about 1.05 g/cm3, slightly larger than water, and thickness to diameter ratio is 0.1. In this letter, We reported two cases with different mass distributions, in one case the disk's center of mass coincided with the geometry center and in another case it was deviated. Two CCD cameras were used to photograph the falling disk simultaneously, the disk's six degrees of freedom were obtained via a stereoscopic vision method. In the first case fluttering motion was observed, the disk's oscillatory motion confined in a vertical plane, and the pitching motion occurred about an axis normal to the plane. In the second case, steady helical falling was observed, the disk moved in a helical path at constant speed, the attacking angle is constant.

Yield Surface of Deeply Buried Square Anchors Under Out-of-Plane Loading

2016 ◽  
Author(s):  
Tianyuan Zheng ◽  
Mark J. Cassidy ◽  
Yinghui Tian ◽  
Christophe Gaudin
Keyword(s):  
Yield Surface ◽  
Degrees Of Freedom ◽  
Research Work ◽  
Combined Loading ◽  
Mooring Line ◽  
Analytical Expression ◽  
Energy Devices ◽  
Six Degrees Of Freedom ◽  
Out Of Plane ◽  
Plate Anchor

Anchors are widely used offshore as foundation systems to moor floating platforms and renewable energy devices to provide uplift resistance in vertical or resistance in inclined direction. Most of the available research work has concentrated on in-plane loading. However, any failure of a single mooring line in a storm can cause out-of-plane loading on the remaining anchoring system. This research targets how this out-of-plane loading can affect the trajectory and ultimate holding capacity of the anchors. This paper presents results of a numerical investigation of the undrained bearing capacity of deeply buried square plate anchor in clay under six degrees-of-freedom loading. Finite element analyses are conducted to define the combined loading yield surface (or yield surface for the anchor in its current position) and an analytical expression of the yield surface is proposed and written directly in the six degrees-of-freedom loads. This analytical expression allows implementation of the yield surface in a plasticity approach, where the load-displacement relationship of the anchor can be described. The method to achieve this and also an illustration of how this framework on a simple plate anchor can be extended to predict the performance of more complex anchor geometries is described at the end of the paper in a description of future research.

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.

Numerical Simulations of OC3 Spar and OC4 Semi-Submersible Type Platforms Under Extreme Conditions in the East Sea, Korea

2019 ◽  
Author(s):  
Hyunkyoung Shin ◽  
Youngjae Yu ◽  
Thanh Dam Pham ◽  
Junbae Kim ◽  
Rupesh Kumar
Keyword(s):  
Renewable Energy ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Reanalysis Data ◽  
Environmental Data ◽  
Offshore Wind ◽  
East Sea ◽  
Mooring Line ◽  
Six Degrees Of Freedom ◽  
Floating Offshore Wind Turbines

Abstract Since the Paris Conference of the parties in 2015, interest in renewable energy around the world is higher than ever. Korea also has plans to increase the proportion of renewable energy to 20% by 2030 through the renewable energy 3020 policy. Of these, 16.5GW is filled with wind power, the installation area is expanding from land to sea. Among them, some of big plans are using floating offshore wind turbines based on the marine environments in Korea. In this study, numerical simulations of the NREL 5MW wind turbine were performed using NREL FAST V.8. A comparison was made between two types of floaters, spar and semi-submersible, installed 58km off the Ulsan Coast with 150m water depth in the East Sea, Korea. The environmental data were obtained from the Meteorological Administration’s measured data and NASA’s reanalysis data, MERRA-2. Design Load Cases were selected by referring to IEC 61400-3. Maximum moments at both blade root and tower base, six-degrees of freedom motions and three mooring line tensions were compared.

FPSO Mooring Line Integrity Supervising System Based on Motion Data and Natural Frequency Estimation

2021 ◽  
Author(s):  
José Lucas De Melo Costa ◽  
Asdrubal N. Queiroz Filho ◽  
Ismael H. F. Santos ◽  
Rodrigo Augusto Barreira ◽  
Anna Helena Reali Costa ◽  
...  
Keyword(s):  
Frequency Estimation ◽  
Longitudinal Axis ◽  
Mooring Line ◽  
Mooring System ◽  
Mooring Lines ◽  
Natural Period ◽  
Motion Data ◽  
Initial Hypothesis ◽  
The Difference ◽  
Property Losses

Abstract Offshore production facilities play a central role in the oil industry given the growing demand for energy resources. The mooring system of these floating structures is a critical component for safety maintenance. The timely identification of mooring lines failures can prevent environmental pollution, property losses and further system failures. In this paper we propose a system to detect and classify failures of the mooring lines based on the natural period in the longitudinal axis and in the lateral axis of the long drift oscillatory motion of the platform. The proposal starts from the hypothesis that when a line break occurs, the natural period of oscillation of the platform is increased, and this difference may indicate the malfunction of the mooring system. The proof of concept developed for the proposed system demonstrates the potential of using the natural period to detect failures in mooring lines for floating vessels, validating the initial hypothesis that the difference in a natural period appears when a line breaks and that this difference may detect line break.

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.

Experimental Study for the Effect of Appendages on Vortex-Induced Motions of Tension Leg Platform

2018 ◽  
Author(s):  
Chenling Tian ◽  
Mingyue Liu ◽  
Shisheng Wang ◽  
Xinru Wang ◽  
Haobo Li
Keyword(s):  
Degrees Of Freedom ◽  
Experimental Studies ◽  
Vertical Plane ◽  
Mass Ratio ◽  
Mooring Lines ◽  
Academic Fields ◽  
Load Cells ◽  
Maximum Decrease ◽  
Restoring Forces ◽  
6 Degrees Of Freedom

Vortex-induced motions (VIM) of large marine structures have been emerged as hot issues both in engineering and academic fields. Aiming to investigate the effect of the appendages on the VIM phenomenon of the tension leg platforms (TLP), experimental studies were carried out in a towing tank., The tendon pretensions and mass ratio were modeled exactly by using an air-bearing system. Additionally, the motions in vertical plane were almost restricted and the TLP model was allowed to move freely in horizontal plane. The 6-degrees of freedom (6-DOF) motions of the model were recorded by the motion acquisition system, consistent with an acceleration sensor installed at the deck as well as four load cells employed to acquire the restoring forces of the four mooring lines respectively. This paper presents the VIM responses of the TLP model with bare hull and the model with appendages located at the surface of columns with different relative positions to the current (i.e., 0°, 45°, 90° and 135°, respectively). In addition, the dynamic behaviors are also processed. The results show that the amplitudes of VIM response in the transverse direction are mitigated significantly for the configuration of 45°-appendages, lower than that of the bare hull model about 65 percent but slightly subsided at other locations. Moreover, the appendages at all locations can obviously reduce the amplitudes of the yaw motions, with the maximum decrease of 52 percent of the yaw responses for the configuration of 0°-appendages and 45°-appendages, compared with that of the bare hull model.

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