Evaluation of added resistance in regular incident waves by computational fluid dynamics motion simulation using an overlapping grid system

A computational fluid dynamics simulation method called WISDAM-X was developed to evaluate the added resistance of ships in waves. The Reynolds-averaged Navier–Stokes (RANS) equation was solved by the finite-volume method and a MAC-type solution algorithm. An overlapping grid system was employed to implement rigorous wave generation, the interactions of ships with incident waves, and the resultant ship motions. The motion of the ship is simultaneously solved by combining the solution of the motion of the ship with the solution of the flow about the ship. The free surface is captured by treatment by the density-function method. The accuracy of WISDAM-X is examined by a comparison with experimental data from a container carrier hull form, and shows a fairly good agreement with respect to ship motion and added resistance. Simulations were also conducted for a bow-form series of a medium-speed tanker to examine the effectiveness of the WISDAM-X method as a design tool for a hull form with a smaller resistance in waves. It was confirmed that the WISDAM-X method can evaluate the added resistance with sufficient relative accuracy and can be used as a design tool for ships.     

利用稳定系数法估计电机的寿命

工程实践认为,电机的寿命主要取决于绕组绝缘的寿命.本文介绍一种利用电机绕组绝缘变化状况预测电机寿命的方法-稳定系数法,为电机的绝缘诊断和维护保养提供重要的依据.     

Research on the calculation method of penetration resistance of bucket foundation for offshore wind turbines

The cost of foundations for offshore wind turbines constitutes approximately 35% of the total cost of an offshore wind farm. The bucket foundations show significant potential due to their superior transportation and installation efficiencies compared to pile foundations, leading to potential cost savings for the foundation of up to 30%. For a bucket foundation to be installed successfully, the penetration resistance must be predicted. However, there is currently a lack of clarity on how to select a suitable calculation method for penetration resistance based on known geological parameters to guide construction. In order to evaluate the current methods of calculation for bucket foundation penetration resistance, this study combines theoretical calculation methods with two sets of practical measurement data from the field. The calculation methods of penetration resistance for bucket foundation are first reviewed and categorized. The applicability range of each method and the parameters needed for calculation are given. Next, according to the measured data in the process of penetration of bucket foundation on site, the evolution of compartment pressure, tilt angle, resistance and required suction in the process of penetration are analyzed. Finally, the reviewed methods are compared to the results of two practical projects in order to analyze the differences between them and make recommendations for the calculation technique. The findings can be used as a guide for calculating the bucket foundation's penetration resistance in complex geological conditions.     

基于非线性规划法的最小阻力船型优化设计

为了获得阻力性能优良船型,以兴波阻力理论为基础,利用非线性规划法并结合CAD技术研究最小阻力船型的优化设计.以总阻力为目标函数,总阻力用兴波阻力和平板摩擦阻力之和来表达,设计变量取船型修改函数的参数,在保证必要的排水量为基本约束条件下,选取Wigley船型为初始船型,分别对船体的首部和全船线型进行优化设计.通过将改良船型的阻力性能、船体线型和基于Michell积分法的优化计算结果相比较,证实了在相同的设计参数和约束条件下,采用Rankine源法进行船型优化结果更可靠.     

盾构下坡掘进对推进阻力的影响研究

以神华新街6°煤矿斜井盾构工程为背景,针对盾构下坡掘进工况,通过建立盾构上作用的水土压力载荷与坡度的数学关系模型,推导出推进阻力与坡度的数学公式。结合工程实例,计算水平掘进与6°下坡掘进各推进阻力值,并利用MATLAB软件绘制下坡掘进时推进阻力随坡度变化的曲线。结果表明:1)6°下坡掘进的总推进阻力相对于水平掘进仅减小了约8%,坡度小于13°时,可通过水平掘进时的推进阻力减去重力沿掘进轴线上的分量来近似求得,且偏差小于10%;2)总推进阻力会随坡角的不断增大而减小;3)当坡度大于50.4°后,盾构有自动向下滑移的趋势,刀盘将自动压紧开挖面,导致刀具自动嵌入开挖面,增加了启动扭矩与换刀的难度。     

断阶滑行艇喷气减阻机理研究

本文通过艇底流态显示、艇体运动姿态及阻力测量，研究了滑行艇艇底喷气对流场、阻力等的影响规律。断阶稍前处喷气引起总阻力和浸湿面积的大幅减少，喷气所减少的阻力成分为摩擦阻力，喷气对剩余阻力的影响甚微。     

人工挖孔嵌岩桩的受力机理试验研究

根据人工挖孔嵌岩桩的静载试验资料，分析了短粗的人工挖孔嵌岩桩的承载特性和荷载传递机理。     

玄武岩纤维碎石封层路用性能试验研究

碎石封层是常见的路面预防性养护技术,但是由于现代交通速度快、密度大、轴载重、渠化明显,通过跟踪实体工程,发现碎石封层养护效果不尽理想。文中将玄武岩纤维用于增强碎石封层性能,在碎石封层最佳配合比设计的基础上,对纤维沥青封层低温的抗裂性能和层间粘结性能进行了试验研究。结果表明,玄武岩纤维可增强碎石封层路用性能,更好地满足工程需求。     

GPS天线线型对AUV阻力和尾流场的影响

靠近艉部的GPS天线线型对AUV的阻力以及桨盘面处的伴流品质有直接影响。高品质的伴流场能有效地降低噪声并提高水动力性能。为了获得最优的GPS天线线型,以某自主式水下机器人(AUV)为母型,采用ICEM-CFD、Fluent等CFD软件,结合RANS方法和SSTκ-ω模型对搭载不同线型GPS天线的AUV进行数值计算。研究结果表明GPS天线设计前倾角可以有效降低天线的阻力,从而降低AUV受到的整体阻力。具有一定前倾角和尾端曲线的GPS天线有利于改善AUV尾部伴流特性,减小桨盘面伴流速度的不均匀度。     

列车基本阻力的思考

文章从分析列车气动阻力入手，结合现有试验数据，建立了我国铁路货车、客车及机车的单位基本阻力系列试用公式，经与《列车牵引诸规程》公式以及国外相关公式进行比较后，认为这种分析一试验型公式比纯试验型公式更为合理而有效。此外，作者还提出加强列车牵引理论和应用的基础性研究等建议。