KR Webzine Vol.152

1. Introduction

2. Motion Analysis and Load Generation

In this project, the ship's motion analysis and statistical analysis were performed using Lomos3D of KR SeaTrust-ISTAS. In addition, design wave considering the Dominant Load Parameter(hereafter DLP) was mapped to the global structural model using LoadGen3D of KR SeaTrust-ISTAS.

 Ship motion and wave load was calculated according to the "Guidance Relating to the Rules for the Classification of Steel Ship, Pt.3, Annex 3-2 Guidance for the Direct Strength Assessment"(hereafter KR Annex 3-2). Design loads was numerically defined through long-term analysis using IACS North Atlantic wave scatter data.

 The direct structural analysis was performed based on the largest design load that a ship can encounter during its design life. It was performed in consideration of the DLP according to "KR Annex 3-2". Through this process, KR has achieved competence to provide technical services for motion analysis and statistical analysis of Ultra Large Container Ships to Owners and Shipyards.

3. Yield, Buckling and Fatigue Strength Evaluation

Through the direct global structural analysis based on design load technique for Ultra Large Container Ships, the structural safety was evaluated by performing the yield and buckling strength evaluation of the global structure. In addition, the evaluation target member for the spectral fatigue analysis was determined by screening the stress concentration due to the geometric discontinuity through the global structure. The long-term fatigue damage was calculated considering each sea condition in the wave scatter data. Through the whole systematic analysis processes, KR has achieved competence to provide structural safety evaluation technical services for Ultra Large Container Ships to Owner and Shipyard.

4. Whipping Analysis

The whipping phenomenon is a dynamic response induced by an impact load such as slamming on the ship, which can be superimposed on the load response component caused by the motion of the ship to increase the overall response. Therefore, it is necessary to evaluate the whipping phenomenon in ships having characteristics such as high speed and bow & aft shape that can cause large slamming load.

 The whipping analysis was reviewed in accordance with "Guidance on Strength Assessment of Container ships Considering the Whipping Effect".

 Therefore, in order to evaluate the whipping effect due to slamming of Ultra Large Container Ships, the short-term sea state that the greatest contribution to the extremes that can cause slamming are calculated. Irregular wave was simulated from the wave spectrum and a fluid-structure coupling analysis was performed in the time domain, and time series data of the longitudinal vertical bending moment including the whipping response due to slamming was calculated. KR has achieved competence to provide technical service to Owner and Shipyard in order to evaluate the whipping response of Ultra Large Container Ship using this design sea state method.

    
5. Springing Analysis

Hull structural vibrations, such as springing due to resonance with waves, are more likely to occur in frequency bands corresponding to the large energies of ocean waves. Accordingly, springing analysis of the hull is becoming increasingly important for hull structural safety.

 The springing analysis was performed in addition to the spectral fatigue analysis, and was reviewed in accordance with "Guidance for Fatigue Strength Assessment Including Springing".

 "Guidance for Fatigue Strength Assessment Including Springing" is a guideline that can consider the hydro-elastic effect of high-speed slender ship and low-speed blunt ships as shown in the figure below.
 In case of Ultra Large Container Ship, a springing analysis was performed according to the procedure for high-speed slender ship. KR has achieved competence to provide a technical service that fatigue analysis considering springing effect was additionally performed on the structural members for which the spectral fatigue analysis was performed.