A VITAL ISSUE IN MARINE STRUCTURES ENGINEERING IS HOW TO DETERMINE DYNAMICAL RESPONSE OF MARINE STRUCTURES AGAINST WAVES AND MARINE CURRENTS. THIN STRUCTURES ARE NOT ONLY EXPOSED TO WAVE FORCES, BUT ALSO THEY ARE AFFECTED BY HYDRODYNAMIC FORCES THAT ARE GENERATED AS A RESULT OF STRUCTURE MOVEMENT. WATER ELEMENTS SURROUNDING AN offshore PLATFORM, WHICH IS EXPOSED TO THE EFFECTS OF WAVES, WILL CAUSE TO FORMATION A MASS OR TO GROW AN ALREADY EXISTING MASS. HERE, WATER-STRUCTURE INTERACTION IS OF A GREAT IMPORTANCE. IN METAL FIXED platforms, IT IS POSSIBLE TO USE A GENERALIZED RELATION PROPOSED BY MORISON, ON THE BASIS OF RELATIVE SPEED METHOD THAT INDICATES THE HYDRODYNAMIC INTERACTIONS BETWEEN WATER AND PLATFORM. THIS CAN HELP US TO CALCULATE THE WAVE FORCE. MODERN platforms ARE MORE FLEXIBLE THAN OLDER ONE. THIS ARTICLE ANALYZES A FIXED PLATFORM IN ARDESHIR OIL FIELD, PERSIAN GULF, AND INVESTIGATES THE IMPACTS OF DYNAMIC AND HYDRODYNAMIC PARAMETERS.

INTRODUCTION: THE OBJECTIVE OF STRUCTURAL CODES IS TO GUIDE THE PROPER DESIGN AND CONSTRUCTION OF offshore platforms MEETING FUNCTIONALITY, SAFETY AND ECONOMICAL ASPECTS. THEY ARE CLOSELY CONNECTED TO EACH OTHER AND AN ITERATIVE PROCEDURE IS NECESSARY TO ACHIEVE AN OPTIMAL DESIGN. THE CONSEQUENCES OF FAILURE CONCERN THE SAFETY OF HUMANS, POLLUTION, AND THE COST OF STRUCTURES AND EQUIPMENT. THEREFORE, THE ASSESSMENT OF THE SAFETY OF offshore platforms INCLUDING JACK-UP PLATFORM BECOME ESSENTIAL.TIME-VARYING NATURE OF ENVIRONMENTAL LOADS SUCH AS WAVE AND WIND WILL CAUSE FLUCTUATION OF STRESSES IN STRUCTURAL COMPONENTS OF platforms. THE FATIGUE DAMAGE IS A DETERIORATION PROCESS, WHICH ARISES FROM FLUCTUATION OF STRESS, AND SHOULD BE EVALUATED BEFORE REACHING A CRITICAL LEVEL. TRADITIONALLY, FATIGUE HAS NOT BEEN CONSIDERED AS AN IMPORTANT PROBLEM IN JACK-UP platforms. THE MAIN REASON WAS THE MOST platforms WERE DESIGNED IN AREAS WITH LOW OR MODERATE ENVIRONMENT CONDITIONS. RECENTLY, BY USING JACK-UP platforms IN REGIONS WITH MORE SEVERE SEA STATES OR AS PERMANENT platforms, THE FATIGUE DAMAGE BECOMES AN IMPORTANT FACTOR IN EVALUATING THE INTEGRITY AND SAFETY OF THE STRUCTURES.

offshore platforms ARE THE MAIN WORKSTATIONS FOR OIL AND GAS EXTRACTION IN THE OCEAN. THESE STRUCTURES ARE EXPOSED TO LOW FREQUENCY VIBRATION CAUSED BY SEVERAL PHENOMENA SUCH AS WAVE AND EARTHQUAKE. THESE ENVIRONMENTAL LOADS AND MODEL UNCERTAINTIES ARE FORMED AS AN UNKNOWN DISTURBANCE. DISTURBANCE ESTIMATION IS USEFUL TO DESIGN AN APPROPRIATE CONTROLLER IN ORDER TO REDUCE THE VIBRATIONS. THEREFORE, THIS PAPER INVESTIGATES THE DESIGN OF ADAPTIVE DISTURBANCE OBSERVER FOR offshore STEEL JACKET platforms. SIMULATION RESULTS SHOW THAT THE PROPOSED METHOD IS MORE EFFECTIVE THAN OTHER METHODS INTRODUCED IN THIS PAPER.

THIS ARTICLE USES GENETIC ALGORITHM METHOD TO ENHANCE offshore STRUCTURES USING DISCRETE VARIABLES. IN THE PROCESS OF offshore STRUCTURE OPTIMIZATION, STRUCTURE ANALYSIS AND OPTIMIZATION PROCESS WILL BE TIME-CONSUMING BECAUSE OF THE DYNAMIC NATURE OF FORCES. THAT IS WHY, IN SUCH CIRCUMSTANCES, APPROXIMATE ANALYSIS IS USED. TODAY, APPLICATION OF NEURAL NETWORKS HAS BECOME WIDESPREAD FOR SUCH PURPOSES AND CAN YIELD DESIRABLE RESULTS. IN THIS RESEARCH, THE MAXIMAL VALUES OF STRESS IN MEMBERS AND THE HIGHEST NODAL DISPLACEMENTS WILL BE CALCULATED WITH A REASONABLE APPROXIMATION IN EACH DESIGN CYCLE. EMPLOYMENT OF WAVE-NET NEURAL NETWORKS WILL QUICKEN THE DURATION OF OPTIMIZATION AND ENHANCEMENT PROCESS. WAVE-NET NEURAL NETWORKS ARE COMPRISED OF BACK PROPAGATION NEURAL NETWORKS AND WAVELET THEORY. FINALLY, A NUMBER OF NUMERICAL EXAMPLES WILL BE GIVEN TO INDICATE THE EFFICIENCY OF OUR METHODOLOGY.

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1- INTRODUCTION: ADJUSTABLE PARAMETERS OF A FRICTION DAMPER DEVICE (FDD) AND A TUNED MASS DAMPER (TMD) HAVE BEEN OPTIMIZED FOR WAVE LOADING BY SPECTRAL ANALYSIS TO MITIGATE THE FATIGUE DAMAGE IN REALISTIC offshore JACKET platforms. THEIR SEISMIC PERFORMANCE IS EVALUATED IN COMPARISON WITH THAT OF FDD AND TMD DESIGNED FOR SEISMIC EXCITATION. MOREOVER, HYBRID DAMPING SYSTEMS (HDSS) ARE INTRODUCED WHICH CONSIST OF FDD AND TMD SIMULTANEOUSLY, WITH DIFFERENT COMBINATIONS. THE SEISMIC EFFECTIVENESS OF HDSS IS MEASURED AND COMPARED WITH THAT OF NON-HYBRID FDD AND TMD. IT IS INTENDED TO IMPROVE SEISMIC EFFECTIVENESS OF VIBRATION CONTROL SYSTEM WHILE MAINTAINING ITS EFFECTIVE PERFORMANCE IN FATIGUE DAMAGE MITIGATION.