1. INTRODUCTION: FATIGUE DAMAGE ACCUMULATION IS ONE OF THE MOST IMPORTANT PROBLEMS ABOUT MARINE STRUCTURE THAT ARE EXPOSED THE ALTERNATIVE LOAD. RISER IS ONE OF THESE STRUCTURES. THE SURROUND ENVIRONMENT OF RISER CAUSES THE ALTERNATIVE STRESSES AND FATIGUE IN RISER.
FOR OBTAINING THESE STRESSES THE ANALYSIS OF THE VORTEX INDUCED VIBRATION IN TWO DIRECTION, IN-LINE AND CROSS FLOW, IS NECESSARY. IN THIS ARTICLE, AT THE FIRST THE DYNAMIC BEHAVIOR IN TWO DIRECTIONS WILL BE STUDIED AND THEN THE STRESSES IN RISER ARE CALCULATED. AT THE END THE FATIGUE DAMAGE IS STUDIED BY USING MANSON THEORY AND THE EFFECT OF COMPENSATOR PARAMETERS IS INVESTIGATED.