International Journal of coastal and offshore engineering
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International Journal of Coastal and Offshore Engineering - Journal articles for year 2016, Volume 4, Number 0Yektaweb Collection - http://www.yektaweb.comen2016/12/11Numerical Simulation of Vortex Induced Vibration of Three Cylinders in Regular Triangle Arrangement at High Reynolds Number
http://ijcoe.org/browse.php?a_id=80&sid=1&slc_lang=en
This paper presents a three dimensional simulation of the vortex induced vibrations of three elastic cylinders in regular triangle arrangement at high Reynolds number. The motion of every single cylinder, which is free to oscillate in two degrees of freedom in a uniform flow and has the same mass and natural frequency in both X and Y directions, is modeled by a mass spring damping system. The displacement and lift forces for each cylinder are analyzed with five spacing ratios L/D changing from 2.5 to 6.5. The results indicate that the downstream cylinders are usually undergone serious fluctuating lift forces. It is found that the simultaneous resonance in the X and Y directions may occur for the downstream cylinders.<br>
The stream wise oscillation of downstream cylinders could be as large as 0.54D, and the maximum transverse amplitude of three cylinders can reach to 2.30D. It is indicated that the cross flow oscillation amplitude of three cylinders significantly increased compared with the flow induced vibration of a single elastic cylinder and the stream wise oscillation of downstream cylinders is unneglectable for vortex induced vibration of multi cylinder system.Hassan SayyaadiModeling and Control of Autonomous Underwater Vehicle (AUV) In Heading and Depth Attitude via PPD Controller with State Feedback
http://ijcoe.org/browse.php?a_id=81&sid=1&slc_lang=en
This paper focuses on design of AUV control system to control depth and pitch. Complexity and highly coupled dynamics, time-variance, and difficulty in hydrodynamic modeling and simulation, complicates the AUV modeling process and the design of proper and acceptable controller. A PD (Proportional- Derivative) controller, control the vehicle pitch and an outer P loop controller with state feedback will control the depth. The kinematic and dynamic equations will be extracted using various conditions such as the relative speed along the axis X (u), the speed along the axis Z (w), Pitch rate, forward position relative to the ground (x), depth (z), and the Pitch angle (Ɵ). Then we linearize the equations of motion of the AUV by choosing a suitable set of operating conditions. For effective control of the motion of AUVs, we need to design controllers based on the AUV’s dynamic model. Through the control of propeller and fin’s deflection, we can achieve the control system of AUVs. The simulation results indicate that developed control system is stable, competent, and efficient enough to control the AUV in tracking the two channels of heading and depth with stabilized speed.Soroush VahidOscillating Motion of Triangular Cylinder in a Viscous Fluid
http://ijcoe.org/browse.php?a_id=82&sid=1&slc_lang=en
The system consisting of two rigid bodies in a viscous fluid is considered. The main body with mass M is placed in a viscous incompressible fluid, and the body with mass m moves inside the main body. This system is known as vibrobot which can be used in arbitrary inspection fluid mechanic objects such as oil industries pipes and tanks, as well as marine industries, medicine, etc. In this paper, the interaction between the vibrobot and viscous fluid is studied to achieve the motion laws of the vibrobot with the harmonic oscillation of internal mass. Also the flow structure around vibrobot and its effects on the hydrodynamic force acting on the vibrobot are investigated. Analyses are carried out by direct numerical simulation of the vibrobot motion in a viscous fluid by OpenFOAM package. Calculations are performed for the following combinations of control parameters; The ratio of the viscous fluid mass to the vibrobot mass μ_1=0.35, the ratio of the internal mass to the vibrobot mass μ_2=0.325 and dimensionless oscillation frequency f=1/5, when Reynolds number takes values in the range of 50<Re<250. Calculations have been performed with different initial approximations, determined by different initial velocities of the incident flow.Hamid MalahWave run-up and stress imposed on a permeable coastal bed sample of the Caspian Sea
http://ijcoe.org/browse.php?a_id=54&sid=1&slc_lang=en
This research aims to reconsider the wave run-up and eulerian schematic of flow contours and the fluid movement path in the sediment sample gathered from southern Caspian Seashore bed, using experimental method in wave flume.The general characteristics of flow depend on the kind of bed structure, the bed shear tension, vertical velocity profile and the permeation velocity, could be changeable. While, because the increasing of water surface height, the fluid penetrates bed, and consequently the suction phase happens within the bed. Through this condition the flow contours approach the bed and the mean velocity accelerates near the bed, and then the tension rises about 3 times.<br>
Because the decreasing of water surface height, the fluid permeates out from the bed and the injection phase happens, so that the flow contours get away from the bed and the mean velocity falls down near the bed , so the tension slakes about 80%. This studyuses 3 waves with a sharpness ranges from 0.01 to 0.06.The wave run-up has been measured using the wave height recorders which have been installed on a ramped shore with a constant slop of 1:5.<br>
By using a camera under water and also color injection into the bed, the flow contours and movement path of fluid in the sample of Caspian Sea, the permeability ranges have been drawn.Meantime, the flow velocity is estimated in two positions including near the bed surface and the bed deep. Through the relative non-dimensional permeation velocity (Ũ=Vz/Vx), it is shown that in a given wave frequency, by increasing velocityin the suction phase, the tension imposed on the bed is risen up, whiles by increasing the relative velocity in injection phase the tension imposed on the bed is fallen down.<br>
mojtaba zoljoodiThe Ability LNG, LPG and General Port Vessels Maneuvering in Berthing Zone of IRAN LNG Project Jetties in Persian Gulf
http://ijcoe.org/browse.php?a_id=83&sid=1&slc_lang=en
For the purpose of having a safety navigation, the transportation path, deployment of carrier, physical specifications, locations and … have high level of importance. In this research, along with the above mentioned factors, we have compared the result with technical standard and commentaries for port and harbor facilities in Japan, and to analysis both advantage and disadvantages of them. The IRAN LNG project (ILC), will product the overall amount of 10/80 million tons of LNG per annum. Based on the type and capacity of LNG ship (Membrane Type,150000 m3 ), 13 vessels and 6 tug boat are estimated, mostly considered as high capacity LNG carriers. Since the IRAN LNG ships enter to terminal on ballast and after loading departure and also with considering number and marine traffic on South pars, one way channel with 0.5 L (L is length of ship) considered. On this base, we need Maximum width of 157.5 m and minimum 122m (for LNG Ships), and Maximum width 120m and minimum 89m (for LPG Ships). Area, circumference and diameter of basin with anchorage & buoys on general jetty that in collusive general Cargo, Sulphar & Ro-Ro berth respectively are 154610 m2, 1830m and 320m that covered Japanese’s standard completely but about turning circle, we have area, circumference and diameter respectively 5896 m2, 250m and 708m which doesn’t coordinate with Japan’s standard except only one subject (Sulphar berth with aids tug boat). Ali SheikhbahaeiNumerical Analysis of Dynamics of Ship-OWT (Offshore Wind Turbine) Collision
http://ijcoe.org/browse.php?a_id=84&sid=1&slc_lang=en
Offshore Structures supply vessels during operation are at risk of collision. The ship has random load, including offshore structures resistance is raised. In this paper, under the impact of a wind turbine offshore supply vessel with 5 different mass displacements are analyzed. Structural study examined the environmental conditions intermediate depth ocean water using ABAQUS finite element model of the software. The effects of static preload weight of turbine blades and environmental loads (wind, wave, sea current and the water pressure on the turbines) before hitting the ship dynamics, in terms of the structural behavior. Parameters such as power and momentum of support, around the turbine horizontal displacement, stress and strain Von-Mises different parts of turbines in different loading conditions (change in mass displacement of picky float) compared together and the results are discussed.Hossein Nemati