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101.
102.
152QMI型发动机是各型号发动机中连杆最易弯曲、断裂的机型之一。经过分析检查, 引起连杆弯曲变形或断裂的原因是:1)连杆承受巨大压力及一定的弯矩,连杆受弯后,使活塞销通油孔处应力集中,强度下降;2)连杆小头孔中心与连杆小头孔毛坯外圆中心不同心,使一边孔壁变薄,强度下降。 相似文献
103.
A series of physical experiments were performed in steady current to investigate the hydrodynamic interactions between the cylinder and nets which constitute a main part of offshore aquacultural platforms. The hydrodynamic characteristics of only the cylinder, only nets and combined cylinder-net structures are measured and analyzed systematically under different current velocities, inflow angles and solidity ratios of nets. Based on experimental data, fitted formulas for hydrodynamic coefficients of a single resin net are proposed and compared to previously published empirical formulas. It is observed that the existence of the cylinder brings an increment up to 9.2% to drag coefficient of net panels whose solidity ratios are higher than 0.347, whereas this effect is negligible for nets with lower solidity ratios and perpendicular to the inflow. For nets inclined with 45°, the increment of the drag coefficient of net panels due to the existence of the cylinder is more significant (up to 22.9%) than that for perpendicularly placed nets. Furthermore, the existence of nets also leads to a noticeable increase in the drag coefficient of the cylinder, up to 40.18% for a relatively large net solidity ratio of 0.458, representative of biofouling condition. The increment increases with the rise of the solidity ratio of nets and it is larger for nets placed perpendicularly to the inflow than inclined. Effects of the cylinder and nets on lift coefficients of each other are a bit complicated, leading to an increase or reduction of lift coefficients depending on the inflow velocity, inflow angle and net solidity ratios. Finally, it is worth noting that the hydrodynamic interaction between the cylinder and nets deserves to be considered in current practice of hybrid methods by combining potential flow theory, Morison and screen models for aquacultural structures, especially for biofouling conditions. 相似文献
104.
For piggyback pipelaying operations, current-induced force and its effect on the piggyback pipe have not been thoroughly studied. In the present study, an improved method in hydrodynamic load calculation and structural modelling is proposed to simulate the pipelaying of a piggyback pipeline. In order to obtain the mean drag and lift force coefficients for the piggyback pipeline subjected to different inflow angles, two-dimensional Computational Fluid Dynamics (CFD) simulations are performed by modelling the piggyback pipeline as two cylinders attached to each other without gap. Then, the acquired force coefficients are used to calculate the hydrodynamic loads through a user-defined function in OrcaFlex based on a cross-flow principle approach. The interaction between the pipeline and the piggyback cable is modelled using two types contact elements which are ring penetrator and non-penetrating contact. The present proposed method is compared with other two widely used engineering methods based on (1) the equivalent diameter and (2) two separate cylinders without accounting for hydrodynamic interaction, in terms of the top tension, and the bending moments at Hang-off Clamps (HOC) and sagbend of the pipeline. The comparison shows that the two widely used engineering methods are not always conservative in force and response predictions. Hence, it is important to consider the hydrodynamic and structural interactions between the piggyback cable and the pipeline. With different current directions, the bending moments at the HOC predicted by the present method vary from 40% lower to 100% higher than those predicted by the two widely used engineering methods. 相似文献