1.1. Background of Study
Vortex induced motion (VIM) or vortex induced vibration (VIV) is an object vibration influenced by the vortex shedding. When fluid flow across the blunt body, wake formed behind the bluff object and resulting in vortex shedding. Due to the long periods of motions, the vortex induced vibration will commonly refer as vortex induced motion.
Vortex-induced motion is an important source of fatigue damage for blunt cylindrical body underwater especially for production risers. When the shedding frequency matches the body Eigen frequency, the body will begin to resonate and the body’s movement becomes self-sustaining. Continuing resonating will lead to material tiredness and the materials tend to fracture or fatigue.
Vortex shedding was one of the causes proposed for the failure of the Tacoma Narrows Bridge in 1940. During the winter of 2001, a thrill ride “Vertigo” in Ohio suffered the vortex shedding result one of the three towers collapsed. On 1968, vortex shedding due to high winds caused the collapse of three towers at Ferrybridge power station.
Through countless of studies and researches, several vortex suppression methods developed designed to reduce the effects of vortex induced motion on blunt body. Commonly the fairing is used in reducing vortex shedding effect for cylindrical body. Fairing will effectively reduce the drag force and wake generated by fluid flow.
This research begins with the understanding on principles, parameters and consequence of vortex induced motion (VIM) or vortex induced vibration (VIV) then follow by conducting simulation. The analysis is simulated by CFD software which is ANSYS Fluent. The results obtained will be compared with the experimental results conducted by other researchers.
1.2. Problem Statement
In carrying out the research, several issues need to be clarified: i. The effects of waves and current on VIM
ii. The effects of cylinder dimension on VIM
iii. The effects fairing on vortex suppression
iv. Any suppression method is more effective than fairing
1.3. Objective of Study
The objective of study as follow:
i. To investigate the influences of waves and current on VIM ii. To investigate the influences of cylinder dimension on VIM iii. To identify the effects of fairing on vortex suppression iv. To develop an effective method in vortex suppression
1.4. Significant of Study
The important of this research is to develop an effective method for vortex suppression. The method will be able to suppress the vortex shedding more effectively compare to the other methods. Besides, this method will reduce the drag force and lift force generated by the vortex shedding. The forces are the main contribution to the material fracture. 1.5. Scope of Study
The scopes of study of this research are listed as follows:
i. Investigate and understand the basic principles of VIM and VIV on circular cylinder ii. Analyses VIM using CFD simulation
iii. Develop an effective vortex suppression method
1.6. Research Flow Chart
1.7. Research Gantt Chart
LITERATURE REVIEW (1st Draft)
Vortex-induced motion (VIM) or vortex-induced vibration (VIV) is a phenomenon happens when fluid flow across a cylindrical body. When a fluid flow across a cylindrical body, an unsteady flow with oscillating motion formed behind the body is called shedding frequency. This shedding frequency will associated with formation of vortices. When the vortices are not formed symmetrically around the body, a time varying non-uniform pressure distribution will generate, resulting lift force acting on each side of body. As the time varying lift force continues acting on the body, the body will vibrate in inline and transverse to the flow. When the shedding frequency is close or equal to the Eigen frequency of the body, resonance occur and the vibration amplitude of the...
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