| In recent years,with the development of deep-sea resources,the demand for semi-submersible offshore platforms is increasing.Traditional semi-submersible platform are mostly symmetrical structure,platform floating body to add columns of special structure can effectively resist the wind and waves,greatly improve seakeeping,however,the structure of the platform also has some shortcomings,its heaving value often larger,therefore this article is based on an asymmetric structure of the semi-submersible lifting platform,the platform USES two floating bodies,one large and one small place two cranes on large floating body side,can more close to the target object when the lifting operation,greatly improving the work efficiency,at the same time,the platform at sea,through its ballast water adjustment,with the aid of hull and stem end special design itself,It can maintain good stability during the hoisting process.Due to the asymmetry of the structure of the target platform,when facing the incoming flow in different directions,the load and movement of the target platform are often different,and the larger environmental load and movement response will seriously threaten the safety of the platform personnel and equipment.In addition,in the complex Marine environment,due to the unique multi-column structure of the platform,when the wave meets the platform,it is often accompanied by strong hydrodynamic interference,which greatly increases the probability of the wave crashing and even the wave on the deck.Therefore,based on viscous flow theory,CFD software FINE/Marine is used in this paper to carry out numerical calculations of airflow loads of asymmetric semi-submersible lifting platforms under three working conditions,namely,operation,lifting and self-storage,and the influence of incoming flow Angle and asymmetry of the platform on it is emphatically considered.Taking the operating conditions as an example,the motion response of the platform under different wave directions and wave cycles is predicted.Meanwhile,the characteristics of the column,such as wave climbing,boom load and wave interference,are numerically studied.The main research work and analysis results are as follows:(1)Prediction of wind load of asymmetric semi-submersible lifting platform.Firstly,a semi-submersible platform model with external load model test in Shanghai Jiaotong University was selected for numerical calibration.By comparing the numerical simulation results with the test results,the flow load error was found to be less than 5.34%,indicating that the numerical method can be used for numerical simulation calculation in this paper.Then,the load at different flow angles of the platform under three working conditions is calculated respectively.The results show that the platform flow load variation rules are roughly the same under the three working conditions,and the maximum flow load appears at the flow Angle of 240° in the lifting condition.Due to the asymmetry between the bow and tail of the lifting platform and the left and right floating body,the transverse force is not 0 when the flow direction Angle is 0° and 180°.Similarly,under the direction of 90° and 270°,the hoisting platform also has some longitudinal forces.Meanwhile,the upstream column also has obvious shielding phenomenon between the downstream column and the left and right floating body,the upstream column has the most serious influence on the downstream column when the flow direction angle is 90°.(2)Research on the motion response performance of asymmetric semi-submersible lifting platform.The numerical study of the motion response of the asymmetric semi-submersible crane platform under regular wave action shows that the heave freedom of the asymmetric semi-submersible crane platform is not sensitive to the wave direction Angle,but is greatly affected by wave cycle,the difference between the maximum and minimum values of heave motion is only 0.338 m,and the pitch and roll freedom are more sensitive to the wave direction.In addition,the horizontal wave force acting on the lifting platform increases with the increase of the period.When the wave direction Angle is 180° and the period is T=12s,the horizontal wave force reaches its maximum value.(3)Study on wave climbing and internal field interference of columns of asymmetric semi-submersible hoisting platform.According to the wave climbing,slamming load and wave interference characteristics of the platform column,wave climbing on the wave approaching surface of the column,near the wall of the column and around the column with different waves are discussed respectively.The variation law of the impact load on the column facing the wave is analyzed,and the variation of the wave surface in the inner field of the column under different waves is studied.The results show that the wave climbing on the column facing the wave is the same at each wave Angle,and the wave climbing on the column face decreases and increases gradually until it reaches the column surface.In a short period,the rise of the wave near the wall of the front and rear columns is greater than that of the back columns in a long period,and the rise of the wave near the wall of the front columns is greater than that of the back columns in a long period.The slamming load of the column is mainly concentrated in a certain range above the waterline and increases gradually with the decrease of the height from the free liquid level.When facing waves and transverse waves,the wave climbs along the curve around the column in a roughly "W" shape distribution,and the back wave surface of the column usually has a second peak.Under the action of oblique waves,the interference phenomenon of the inner field wave surface is relatively serious,and the maximum rise of the wave surface occurs at a 150° wave Angle,which is roughly 1.86 times of the incident wave amplitude. |
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