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Study on the Behavior of Ship’s Bottom Structure under Grounding Phenomenon

Omidi, Yaser | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44602 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Abbaspour, Majid; Omidvar, Mohammad Taghi
  7. Abstract:
  8. Whenever and wherever there is shipping, there exist risks of marine accidents. Subsequently, such accidents at sea may result in potential economic loss,environmental pollution and fatalities. In fact, ship grounding accident is a type of marine accident that involves the impact of a ship on seabed or waterway side. It may result in the damage of the submerged part of the ship’s hull and in particularly the bottom structure; potentially leading to water ingress, which may at the end compromise the ship's structural integrity, stability, and finally safety. An overall view on groundings categorizes the accidents in two major groups: Soft Grounding and Hard Grounding. A soft grounding does not lead to adverse effects on a ship, but in hard grounding, ship grounded on hard bottoms. The primary concern here is the local crushing and tearing of the ship bottom due to a cutting rock. Therefore the focus of this thesis is on simulation of the response of ship’s bottom under grounding actions using finite elements. The present analysis was divided into three parts. Firstly the numerical model was validated by comparison with experimental data of the resistance of stiffened panels to penetration damage. In this numerical model the forming limit diagram method was used as a model of material failure for prediction and evolution damage. Secondly the analysis was extended to compare the resistance with damage (crashworthiness) of various types of double bottom structures in a stranding event. The ship bottom is loaded with a conical indenter with a rounded tip, which is forced laterally into the structures in different positions. This comparative analyses show that the use of sandwich panels in bottom structure can offer up to five and eleven percent weight saving and crashworthiness, respectively. Thirth part deals with raking of an oil tanker in large scale. For simplicity, this vessel is modeled as a hold (Tank) plus an equivalent beam (hull girder). This numerical model considers sectional properties, ship mass, added mass and the hydrodynamic restoring and damping force. The hydrodynamic forces was simulated by a group of springs.
  9. Keywords:
  10. Refraction ; Ship Grounding ; Bottom Structure ; Forming Limit Diagram (FLD) ; Crashworthiness ; Finite Element Method ; Sandwich Panel

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