| In recent years,people have paid more and more attention to the exploitation of marine resources.Under such engineering background,it is very necessary to construct the offshore platform and research it.The offshore platform is subjected to sea breeze and wave loads,so the working environment in platform is very bad.With the continuous improvement of the economic level,the large-scale platform and the high-strength steel which is used a lot in the construction of the platform,so the engineers make demand of favorable vibration performance of the offshore platform more and more.In the initial design of the offshore platform,effective vibration prediction is particularly important.As the main vibration source and noise source of the ship,the propeller's excitation load has always been the focus to the designer.Due to the rapid development of the computer performance,many high-cost full scale test is replaced with finite element analysis software gradually.In this article,the excitation force of propeller,which is installed on the semi-submersible offshore platform,is calculated firstly.And then the APDL and UIDL methods are used to model the semi-submersible platform efficiently.Finally,the propeller excitation force is applied to the semi-submersible platform to obtain its vibration characteristics.The details of this article are as follows:Firstly,this paper chooses a semi-submersible offshore platform and its full rotation propeller as the calculation object,and uses software ICEM to model and mesh.The hydronamic performance of the propeller and the resistance of the platform are calculated respectively to verify the accuracy of the excitation load of the model and the calculation method.Then,the propeller's axial force and pulsating pressure are analyzed in a chosen working condition,and the spectral characteristics of the propeller are analyzed by fast Fourier transform.At the same time,considering the influence of velocity of flow and rotating speed,the propeller pulsating pressure and axial force are analyzed in such condition.At the same time,in order to greatly shorten the design period of the offshore platform and obtain the accurate vibration characteristic forecast quickly,the marine engineering designer urgently needs a fast modeling method to improve the design efficiency and improve the forecast speed.In this paper,a rapid modeling method is developed in the finite element analysis software ANSYS environment by using APDL(ANSYS Parametric Design Language)and UIDL(User Interface Design Language)method for the structural characteristics of semi-submersible offshore platform.Parameters are defined by operator,and the software automatically build semi-submersible offshore platform model.Except this a dedicated ANSYS interface which is created in order to achieve rapid modeling goals.And the wet and dry mode analysis of the offshore platform model established by rapid establishment method aiming to show the feasibility and the practicality of the rapid modeling method from two perspectives.Finally,the vibration characteristics of the semi-submersible platform under the action of the propeller excitation force are calculated,that is,the pulsating pressure and axial force of the propeller are applied to the finite element model in the corresponding position of semi-submersible platform using APDL rapid modeling method.At last,the vibration characteristics of the different compartments of semi-submersible paltform under the excitation loads are compared with the experimental data to analyze the performance. |
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