基于贝塞尔曲线的数控加工刀具路径平滑方法

应用常规方法平滑数控加工刀具路径后,路径平滑指数和产品合格率均较低。因此,提出基于贝塞尔曲线的数控加工刀具路径平滑方法。根据双弓高误差判断条件识别连续微小线段加工区域,利用分段有理多项式函数表示加工区域的贝塞尔曲线,选择控制点后,通过约束贝塞尔曲线,实现对数控加工刀具路径的自动化平滑处理。结果表明,应用该方法后,路径平滑指数始终在0.96以上,且数控加工产品的合格率最高可达98.16%,说明此方法在数控加工刀具路径平滑方面具有良好的应用前景。

单船港内首尾双锚锚泊允许波高的试验研究

目前我国渔港港内锚地允许波高的规定是参照国外规定按经验确定,缺乏有效的试验支撑。为了验证现行规定的港内锚地允许波高的合理性,以275HP拖网渔船为代表船型进行了单船首尾双锚锚泊的物理模型试验,研究了渔船首尾双锚锚泊系统在不规则波作用下的锚泊力及运动量的情况,分析了波浪入射角度、渔船载况、波高及周期对锚泊力和运动量的影响。实验结果表明,锚泊力在90°横浪作用时最大,随着载重和波高的增大而增大,随着周期的增大而减小。横摇角度同样在90°横浪作用时最大,随着载重的增大而减小,随着波高的增大而增大;当波浪周期接近渔船横摇周期时,横摇角度达到最大,随后随着周期的增大而减小。试验结果得出,在本次试验范围内,此渔船单船首尾双锚锚泊时的允许有效波高建议取为0.7m。研究结果为港内锚泊允许波高的确定以及渔船缆绳的设计提供了有效的支持。

倒拖调迁船和双向推进船规范要求适用性分析

船首的含义一般非常明确,与船舶相关的国际公约、船旗国主管机关的法定要求和船级社规范中的很多条文均与船首的定义密切相关,但对于双向推进船和倒拖调迁非自航船而言,其船首的含义有其特殊性。对此,探讨双向推进船和倒拖调迁船船首的定义,分析相关条文,重点分析防撞舱壁、船端加强、号灯布置、最小船首高度和艏锚布置的相关要求,并提出规范对这些船的适用性建议。分析所得结果有助于明确国际公约、船旗国主管机关的法定要求和船级社规范对船首的定义,为船舶的设计、审图和建造提供参考。

三船并排首尾锚泊时港内允许波高的试验研究

目前我国渔港港内锚地允许波高是参照国外规定根据经验确定的,国内缺乏相应研究。以212 k W(275 HP)拖网渔船为代表船型进行三船并排首尾锚泊的物理模型试验,研究不规则波作用下并排渔船的锚泊力及运动量的情况,同时与单船锚泊时的结果进行对比。结果表明:三船并排锚泊时内侧非直接受浪作用的渔船,其拉力和横摇角度均大于最外侧直接受浪作用的渔船;当港内波高较大且周期也较大时,三船并排锚泊比单船锚泊安全性更高些;在本次试验范围内,三船并排首尾双锚锚泊时的允许有效波高比单船允许的波高要偏大,建议取为0.9 m。

一种自由曲面抛光机器人轨迹规划方法

针对机器人抛光自由曲面轨迹规划困难,抛光精度不高等问题,提出了一种机器人抛光轨迹规划方法。该方法在UG软件环境下完成对自由曲面的建模,借鉴铣削加工中刀轨生成方法并结合抛光工艺特点,利用等残余高度算法生成抛光轨迹,在此基础上,提出了改进的Douglas-Peucker算法,该算法用于对抛光刀触点的提取,能够将弓高误差控制在给定的范围内,提高抛光精度,最后根据连续抛光刀位点数据求解出机器人各关节转角。实例表明,该抛光轨迹规划方法精度高,可解决自由曲面抛光轨迹规划问题。

地铁车辆低落弓位受电弓线导板算法研究

在建立地铁车辆低落弓位受电弓结构数学模型的基础上,以受电弓在工作高度范围内的静态接触压力保持恒定为目标,基于恒定静态接触力下受电弓的平衡方程,采用矩阵法建立了升弓转矩计算函数,计算受电弓的升弓转矩。通过对升弓装置工作机理的深入研究,对其进行简化,建立了相应的计算模型,提出了适用于地铁低落弓位受电弓线导板廓形的计算方法。利用MATLAB软件编写了计算程序。通过试验,验证了算法的有效性。

Numerical Investigation of Heave and Pitch Motion Effects on Green Water Loading for a Floating Body

In this paper,the influence of heave and pitch motions on green water impact on the deck is numerically investigated.The vessel motions are determined using a potential theory based method and provided as input to finite volume based CFD computations of green water phenomenon.A dynamic mesh approach is adopted to determine instantaneous body positioning in the fluid domain.Detailed validation studies with published experimental results for 2D and 3D fixed vessel cases are initially performed to validate the present numerical approach before studying the moving vessel problem.The results show that inclusion of heave and pitch motion changes the disturbed wave field near the bow which influences the free surface as well as the impact loading due to green water.The effect of wave steepness on green water impact is also investigated and it is seen that the present numerical method is capable of capturing green water load.It is observed that the effects of vessel motions on green water load are not negligible and one should consider this effect too.The incorporation of vessel motions in the vertical plane affects the green water loading on the deck.

半潜船艏部砰击分析

分析某半潜船试航过程中船艏砰击振动原因，发现主要因为船艏浮箱处线型欠佳，造成船艏浮箱处波高增大，波浪在船艏浮箱处爬升，兴波阻力增大。同时，浮箱与船体相交的横剖面形状为钝形，浮箱底部形成较大的漩涡，造成低压，船艏易于埋艏，当船舶在高速航行时，来流撞击到浮箱表面，船体砰击振动较大。通过对浮箱改型前后CFD数值分析，比较船艏浮箱处波浪高度和升沉变化，实船试航表明，改型后船艏砰击振动现象消除，说明改型方案合理可行。

Static magnetic field analysis of hollow-cup motor model and bow-shaped permanent magnet design

The hollow-cup Permanent Magnet(PM) motors have the characteristics of low power consumption, and are widely used in the aerospace field. At present, the tile-shaped PMs used by hollow-cup PM motors have poor sinusoidal characteristics of the air gap magnetic flux density waveform, which will cause torque ripple. The existing method for improving the air gap magnetic flux density waveform is not very effective when applied to hollow cup, a special motor with no stator core and large air gap. A bow-shaped PMs structure is designed for the hollow-cup motor in this paper. First, the equivalent surface current method is used to calculate the analytical formula of the static magnetic field of the model. Then, the Finite Element(FE) method is used to calculate the static air gap flux density waveform of conventional tile-shaped PMs and bow-shaped PMs with different bow heights, and the corresponding harmonics and sine distortion are obtained by Fourier decomposition. The simulation results show that the bow-shaped PMs can effectively improve the sinusoidal characteristics of the static air gap flux density waveform. And the suitable bow height is determined. Finally, a prototype is made based on the suitable bow height for experiments, and compared with the analytical result and the FE result, and the accuracy and effectiveness of the bow-shaped PMs with the suitable bow height are verified.

Ship bow waves

The bow wave generated by a ship hull that advances at constant speed in calm water is considered. The bow wave only depends on the shape of the ship bow （not on the hull geometry aft of the bow wave）. This basic property makes it possible to de- termine the bow waves generated by a canonical family of ship bows defined in terms of relatively few parameters. Fast ships with fine bows generate overturning bow waves that consist of detached thin sheets of water, which are mostly steady until they hit the main free surface and undergo turbulent breaking up and diffusion. However, slow ships with blunt bows create highly unsteady and turbulent breaking bow waves. These two alternative flow regimes are due to a nonlinear constraint related to the Bernoulli relation at the free surface. Recent results about the ove^urning and breaking bow wave regimes, and the boundary that divides these two basic flow regimes, are reviewed. Questions and conjectures about the energy of breaking ship bow waves, and free-surface effects on flow circulation, are also noted.

试议从设计的源头把握船舶设计

本文介绍如何从船舶设计的源头把握船舶设计，使船舶设计从设计的一开始便走上正确的道路，从而为有条不紊、循序渐进地开展设计打下坚实的基础。