Research On The Key Structural Strength And Vibration Characteristics Of Offshore Lightering Platform

Compared with the construction of fixed port bulk terminal,offshore lightering platform as a "maritime mobile terminal", has the characteristics of high adaptability, flexible operation, wide service radius, high investment yield, and so on. The barge platform in port provides an economical and convenient bulk transport solution when navigable water level, wharf berthing capacity and construction conditions are limited,. Overside flat work at sea is susceptible to the complex environment such as wind, wave, flow load, with the joint action of multiple components above including crane machine, belt conveyor system, shipment, etc. Thus the force on the overside platform will present excessively,concentratively and unevely. As a new type of marine engineering operations, in order to ensure the lightering platform can work normally, it is necessary to research on the key structural strength and vibration characteristics, so that a comprehensive understanding of the type of ship in the working process of the mechanical characteristics and vibration characteristic, providing technical support for this type of ship design.In this paper, the key structure strength and vibration characteristics of offshore over barge platform have been studied. First, it focuses on the calculation of the whole ship wave load, which lays the foundation for the finite element analysis of the whole vessel and partial part later. Second, taking a typical offshore overside platform as the research object, it builds a finite element modelof the whole ship, directly calculates structure strength and gets the hull structure deformation and stress distribution to find out the high stress area. Then the local strength of crane base structure is calculated and analyzed, and 3 kinds of strengthening schemes are put forward. According to the stress results, the best local reinforcement scheme is determined. Finally, targeted on the arm frame structure of the ship loader, its inherent frequency and vibration model in first eight phases have been gotten by modal analysis. Vibration response of arm frame structure is gained by frequency response method.The main research work of this paper is as follows:(1) Calculation of wave load on the whole offshore platform. Using NAPA software to establish the wet surface model of the hull, load the modal compartment one by one and define lightweight. Gravity and buoyancy distribution of the ship are calculated. What's more, based on trochoidal wave theory, wave elements are applied to different working conditions. Calculate ship's equilibrium point in static wave by changing the relative position between the ship and the peak or trough. And then draw the wave curve of the ship in the middle of the arch and the middle, which lays the foundation for the finite element analysis of the whole ship and partial strength later.(2) Finite element analysis of the structure strength of the offshore platform. Based on the finite element theory, taking a typical offshore platform as an object, use MSC.Patran/Nastran software to establish the three-dimensional finite element model of the whole ship structure. Boundary conditions are taken by the inertia release method. Chosen 6 typical working conditions in the actual operation, the overall process of finite element analysis of the whole ship is fully presented by direct calculation of structure strength. The total strength stress distribution of the ship and the high stress area are obtained, and the relative deformation of the hull is predicted, which can be the key to estimate the total longitudinal strength and local strength.(3) Slewing crane pedestal structure local strength and strengthening scheme research. Use MSC.Patran/Nastran to carry out finite element local strength analysis of offshore overside platform base structure. First of all, determining the scope of the model and calculating working condition. Then to directly calculate and analysis the result of the structural stress and deformation, under the selected load and boundary conditions to find out the main destructive load, poor strength parts and its reasons. Choose three meet base structure strength strengthening scheme, and carries on the direct calculation, from two aspects of mechanical properties and structure of three kinds of strengthening schemes compares the calculation results of analysis, determine the three solutions to meet the requirements of the strength of the optimal strengthening scheme. Then the thickness of the crossbeam III program manually optimized results when the thickness is 8mm for Optimal.(4) Vibration characteristics of the boom structure of the ship loader. Based on the theory of vibration and modal analysis,using the finite element analysis software to model and analyze the structure of the outer boom of the ship loader. The first eight natural frequencies and mode shapes are obtained by modal analysis. Then the vibration transfer characteristics of the outer boom are studied with the transfer rate as the parameters, and the vibration response of the structure under the impact of single-point force and single-point moment is obtained based on the frequency response method.