A Quick and Practical Approach for Concept-design of Submerged Thin-walled Stiffened Cylinders

Goal based and limit state design is nowadays a well-established approach in many engineering fields.Ship construction rules started introducing such concepts since early 2000.However,classification societies’rules do not provide hints on how to verify limit states and to determine the structural layout of submerged thin-walled stiffened cylinders,whose most prominent examples are submarines.Rather,they generally offer guidance and prescriptive formulations to assess shell plating and stiffening members.Such marine structures are studied,designed and built up to carry payloads below the sea surface.In the concept-design stage,the maximum operating depth is the governing hull scantling parameter.Main dimensions are determined based on the analysis of operational requirements.This study proposes a practical conceptdesign approach for conceptual submarine design,aimed at obtaining hull structures that maximize the payload capacity in terms of available internal volume by suitably adjusting structural layout and stiffening members’scantling,duly accounting for robustness and construction constraints as well as practical fabrication issues.The proposed scantling process highlights that there is no need of complex algorithms if sound engineering judgment is applied in setting down rationally the hull scantling problem.A systematic approach based on a computer-coded procedure developed on purpose was effectively implemented and satisfactorily applied in design practice.

Radially loading rotary extrusion for manufacturing large-size conical cylinders with inner transverse high ribs

The Large-size Conical Cylinders with Inner Transverse High Ribs(LCCWITHR) can reduce the weight of the parts while maintaining high rigidity and strength. Radially Loading Rotary Extrusion(RLRE) forming technology can achieve integral forming of LCCWITHR through the synergy of radial and rotary movements of dies. The flow law of the material during the forming process is the key to forming large-size inner ribs. At present, there is no unified understanding of the metal flow law of RLRE forming technology. An analytical expression was derived to predict the Radial Direction(RD) deformation loads. The FE simulation and process experiment were carried out to investigate the effects of the inclination angle, thickness factor and transition arc radius of the split top dies on the spacing of the metal diversion plane, the metal flow velocity of the rib area and the final radius of the inner rib. The influence of the split top dies loading distance and the bottom die rotation angle of each pass on the inner radius of the inner rib was verified. And the optimal combination of dies shape parameters and loading paths which can make the metal flow orderly was obtained: the inclination angle is 140°, the thickness factor is 3.64, the transition arc radius is 16 mm;the top dies loading distance is 15 mm, the bottom die rotation angle is 45°.The FE simulation results have been found to be in close agreement with physics experiment.The research results reveal the metal flow law of rib growth in the RLRE of LCCWITHR, which lays a theoretical foundation for subsequent thorough research and process optimization.

三角形排列波浪锥柱绕流流动特性数值分析

采用大涡模拟方法,分析了亚临界雷诺数为3 900时三角形排列波浪锥柱的横流向间距比和顺流向间距比对其升阻力特性、尾流干涉效应及三维流动结构等的影响.结果表明,上游2个波浪锥柱的升阻力特性受下游波浪锥柱影响较小,下游波浪锥柱处于上游双波浪锥柱尾流中,其升阻力特性受横流向间距比和顺流向间距比影响更为显著.3个波浪锥柱间的流动状态可分为邻近干扰、漩涡撞击和涡相互作用状态.在漩涡撞击状态下,上游波浪锥柱尾涡得以发展充分,周期性撞击在下游波浪锥柱表面,从而产生较大的脉动升力.横流向间距比、顺流向间距比分别为3和6时,下游波浪锥柱脉动升力系数较单直圆柱提升了20.93倍.

亚临界雷诺数下串列双波浪锥柱绕流数值模拟

针对风力俘能结构布局问题,基于大涡模拟(LES)方法,在亚临界雷诺数下(Re=3900)研究有限长串列双波浪锥柱的升阻力特性及其流动结构随间距比的变化规律。结果表明:由于上游波浪锥柱的影响,下游波浪锥柱的脉动升力系数大幅增大,当间距比为3时,表面时均压力系数分布形式呈反向分布;随间距比增加,上游波浪锥柱尾流充分发展,并产生大量肋状涡撞击在下游波浪锥柱表面,下游波浪锥柱产生大的脉动升力,相较于单直圆柱提升约15.3倍,阻力系数降低约0.172。所得结果可为风力俘能结构布局提供有益参考。

玉米锥形脱粒装置仿真优化设计

我国北方地区常用的玉米籽粒直收收获机在脱粒工序中存在脱粒元件对果穗冲击强度过大的问题,为此设计一种低损高效的玉米锥形脱粒分离装置。对脱粒滚筒结构进行分析,建立果穗与脱粒凹板间的接触模型,确定滚筒最优参数的取值范围。通过EDEM软件对不同参数组合的脱粒分离装置进行仿真优化试验。结果表明,当脱粒滚筒锥角为8°,凹板选用左向圆管型结构,滚筒转速为400 r/min时,脱粒效果最佳,并与传统式脱粒滚筒相比,起脱段脱粒元件对果穗的碰撞力由284 N降低为234 N,碰撞反力由202.54 N降低为171.52 N,从而验证锥形脱粒滚筒具有降低对果穗冲击强度的特性。利用ADAMS软件对锥形脱粒装置进行运动学及动平衡仿真分析,验证研究成果的可靠性及理论可行性,且系统产生的不平衡惯性力符合农业机械设计要求。为后续玉米脱粒分离装置的创新设计和结构改进提供理论参考。

航天锥形件半自动化电磁铆枪研制及试验验证

针对航天锥形筒状结构件典型的铆接特点,文章提出了用半自动化电磁铆接技术实现其高质量、长寿命连接的方案;设计了包括轴线调整机构、缓冲机构、导向机构和刹车机构的半自动化电磁铆枪系统;完成了电磁铆接后坐力测算试验,分析了电磁铆接后坐力特征,得到1000 V电压下电磁铆接后坐力动量略小于30 N·s,可为电磁铆接缓冲机构精准设计提供支撑;完成了气动铆枪和电磁铆枪铆接强度对比试验,验证了半自动化电磁铆枪解决航天锥形件高质量、长寿命连接难题的可行性。

TRANSITION TO TAYLOR VORTEX FLOW BETWEEN ROTATING CONICAL CYLINDERS

Transition to Taylor vortex flow between two conical cylinders,with the inner one rotating and the outer one stationary,is studied by the numerical method in this article.It is found that the basic flow becomes unstable with increasing of Reynolds number（Re ） above a certain critical value Rec =117 and with the further increase of Re to about Re=300,the first stable vortex is formed near the top of the flow system.The annulus is filled with six pairs of vortices at about Re=800.These are confirmed by experimental observations.Moreover,the local extreme values of pressure and velocity are reached at the adjacent lines between neighboring vortices or at the medium lines of large vortices.The local minimum values of velocity and the local maximum values of pressure are reached at the same point,whereas the local maximum values of velocity of the flow are assumed at the point of inflection for pressure.

Chatter stability and precision during high-speed ultrasonic vibration cutting of a thin-walled titanium cylinder

Titanium alloys are widely used in the aviation and aerospace industries due to their unique mechanical and physical properties.Specifically,thin-walled titanium(Ti)cylinders have received increasing attention for their applications as rocket engine casings,aircraft landing gear,and aero-engine hollow shaft due to their observed improvement in the thrust-to-weight ratio.However,the conventional cutting(CC)process is not appropriate for thin-walled Ti cylinders due to its low thermal conductivity,high strength,and low stiffness.Instead,high-speed ultrasonic vibration cutting(HUVC)assisted processing has recently proved highly effective for Ti-alloy machining.In this study,HUVC technology is employed to perform external turning of a thinwalled Ti cylinder,which represents a new application of HUVC.First,the kinematics,tool path,and dynamic cutting thickness of HUVC are evaluated.Second,the phenomenon of mode-coupling chatter is analyzed to determine the effects and mechanism of HUVC by establishing a critical cutting thickness model.HUVC can increase the critical cutting thickness and effectively reduce the average cutting force,thus reducing the energy intake of the system.Finally,comparison experiments are conducted between HUVC and CC processes.The results indicate that the diameter error rate is 10%or less for HUVC and 51%for the CC method due to a 40%reduction in the cutting force.In addition,higher machining precision and better surface roughness are achieved during thin-walled Ti cylinder manufacturing using HUVC.

A numerical investigation of the flow between rotating conical cylinders of two different configurations

The flow between two coaxial conical cylinders is numerically studied for two different configurations, with the inner cone rotating and the outer one at rest. It is found that, in one configuration,at least at a small Reynolds number（Re）, the pressure is a decreasing function of z while in the other configuration, it is an increasing function of z. In the first configuration, the pressure curves for different Re have intersections, while in the second configuration they do not. The gap between two conical cylinders is filled with six pairs of Taylor vortices at about the same Reynolds number and in each pair of vortices in the first configuration, the upper vortex is larger than the bottom one while in the second configuration, the bottom vortex is larger than the upper one.

面向航空航天的薄壁锥形筒件轧制成形过程几何状态综合控制方法

针对航空航天薄壁锥形筒件轧制过程几何变形状态难以控制的问题,研究了薄壁锥形筒件轴线偏移、轴线倾斜、小端拉缩三种典型异常变形状态及形成机理,提出了基于筒件线速度反馈的锥辊运动协调控制方法,建立了锥形筒件轧制过程锥辊运动控制模型;提出了薄壁锥形筒件坯料优化设计方法,并建立了相应的芯辊倾斜进给控制策略,保证了锥形筒件直径长大速度的一致性,消除了因金属轴向和周向流动不匹配导致的小端拉缩现象;基于ABAQUS软件和VUAMP子程序开发,建立了集成所提控制方法和策略的薄壁锥形筒件轧制有限元模型。对比分析了常规规划控制、上述方法独立控制和综合控制下的筒件轧制成形效果,结果表明,综合控制方法下的轴线偏移量、圆度误差、同心度误差和倾斜角误差等指标相比于常规规划控制在整圆阶段内分别降低了93.6%、75.3%、95.1%、97.2%。

半圆柱阻流体锥形腔无阀压电泵

为了提高半圆柱阻流体无阀压电泵的流量,结合锥形腔的流阻不等特性,该文设计了一种半圆柱阻流体锥形腔无阀压电泵,并建立了其流量的理论公式。数值模拟了该泵的泵腔流速分布,对比分析了其与半圆柱阻流体无阀压电泵的阻力特性。模拟结果表明,半圆柱阻流体锥形腔无阀压电泵能实现流体的单向输送,且其输送能力优于半圆柱阻流体无阀压电泵。制作了两种泵的样机并进行了流量和压力差试验。试验结果表明,在驱动电压220 V下,半圆柱阻流体锥形腔无阀压电泵的最高流量和压力差分别为30.96 g/min和394 Pa,与半圆柱阻流体无阀压电泵相比,其流量和压力差均得到提高。

横向过载下锥孔三维药柱的内弹道特性

高空中作机动飞行的导弹易出现内弹道异常,严重时可能导致飞行任务失败。为了分析内弹道异常机理,对横向过载下发动机内弹道特性展开研究,进行过载下丁羟三组元推进剂燃速测量试验,建立过载下该推进剂燃速模型;基于此模型,模拟锥孔三维药柱非均匀燃面退移,进行全程横向过载、短时恒定横向过载、短时振荡横向过载三种过载方式下发动机的内弹道特性研究。研究结果表明:横向过载会使燃烧室压强增加,绝热层暴露时间提前;振荡式过载产生的压强振荡频率与过载振荡频率一致;瞬间横向过载会使燃烧室压强发生跃迁,在100 g过载下,压强增加8%左右,过载消失,压强骤降;若受横向过载时间间隔一定,则导弹在压强稳定时做机动飞行更有利。

气瓶圆锥螺纹量规中径的检测方法

气瓶圆锥螺纹用于气瓶的瓶口与瓶阀连接,螺纹的强度及密封性是保证气瓶质量的关键环节之一,也是密封相对薄弱的环节。气瓶螺纹的质量与企业安全生产和人民生活安全密切相关。因此,详细了解、正确使用、准确检测气瓶锥螺纹量规是非常必要的。本文主要介绍了用中图测长机检测气瓶圆锥螺纹塞规、环规中径的方法和步骤,并对其基本牙型参数作了简单介绍。

钛合金锥形筒体复合铸型成形工艺研究

针对某型复杂薄壁钛合金锥形筒体铸件,设计了陶瓷型芯、机加工石墨型相结合的复合铸型成形方法。采用陶瓷型芯成形复杂内腔,以提高铸件的尺寸精度和表面质量;采用机加工石墨制得石墨外模,便于浇冒系统设置。采用该复合铸型成功制得具有较高的内部质量、表面质量的钛合金锥形筒体铸件。

纵轴流锥型滚筒脱粒装置设计与试验

为了降低功耗,加快脱粒滚筒轴向物料输送速度,提高小区育种小麦种子收获机清机效率,设计了一种纵轴流锥型滚筒脱粒装置,滚筒采用锥型短纹杆-板齿结构。试验结果表明,该纵轴流锥型滚筒脱粒装置在作业时小麦脱粒混合物料轴向输送速度快、功耗低,罩壳内部种子残留量小,无需人工清机,适用于以旋风分离器为气流清选装置的半喂入式小区育种小麦种子收获机。

小区小麦育种收获机锥型脱粒滚筒性能试验

小区小麦育种收获机锥型脱粒滚筒体积小、功耗低,可加快脱粒滚筒轴向物料输送,提高清机效率。为了进一步研究锥型脱粒滚筒作业性能,结合自行研制的纵轴流锥型滚筒脱粒装置,通过改变锥型滚筒主要结构参数进行对比试验,得出滚筒锥角及滚筒脱粒元件是影响滚筒作业性能的主要结构参数。在选取最优参数后研制出一种集钉齿、短纹杆-板齿于一体,锥角为13°的组合齿锥型滚筒,并进行试验。试验结果表明,该滚筒作业时种子破碎率为0.52%,滚筒脱粒损失率及籽粒含杂率分别为0.43%及6.23%,装置内部种子残留率为0,功耗为2.48kW,符合小区小麦育种收获要求。

六圆柱-圆锥轮式月球车的设计

针对月球表面的非结构化环境,设计了一种新型六圆柱-圆锥轮式月球车.整车由三节串联而成,每节具有一对独立驱动的圆柱-圆锥轮,由两个三自由度的悬架结构连接,三节之间能够被动实现俯仰和扭转相对运动;悬架关节中设计有离合器或制动器,能够根据需要锁住关节或在电机驱动下实现主动俯仰或前摆运动,从而能够使月球车根据路况以轮式或轮步方式移动.为了降低刚性车轮产生的振动,在车轮和支承轴之间设计了由金属橡胶构成的减振器.对月球车的结构参数优化和移动性能的分析,结果表明,该车具有很强的地形适应能力和越障能力.

换热器进口管箱流场的数值分析与应用

采用计算流体力学方法 ,对管壳式换热器进口管箱内流场进行数值分析 ,模拟结果清晰地显示出管箱内流体流动状况 ,可用于分析管子与管板连接接头发生冲蚀和泄漏 ,以及不同区域的管子换热强度不同的原因。应用数值分析方法提出了锥形导流筒结构 ,明显地改善了管箱内流体流动和压力分布的均匀性 。

圆锥壳的精确解与等效圆柱壳的解的比较

在目前的潜艇结构设计中 ,通常对不同锥度壳体结合处的应力采用等效圆柱壳的解来进行设计计算。等效圆柱壳的解的精度是 h/R。对于圆锥壳体的应力计算 ,文献中曾给出过精确解 ,但给的并不很全 ,同时在提供的解中还含有一些错误。本文从旋转壳体的基本微分方程出发 ,重新推导了圆锥壳体应力计算的精确解 ,给出了全部的计算公式及计算程序。并以此为基础 ,讨论了采用等效圆柱壳的解的精度问题。本文的讨论对正确使用现有的潜艇结构设计计算规则有一定的参考价值。

一种双频段圆锥喇叭天线的设计

介绍了一种双频段圆锥喇叭天线的设计。作为星载阵列天线单元的圆锥喇叭天线需要满足20/30GHz双频段工作的需要。此处采用在光壁圆锥喇叭内加载一个外形渐变的金属柱体来改变天线的输入阻抗,调节金属柱体的尺寸,包括两端的口径和长度,可以在要求的频段得到理想的输入阻抗。仿真分析和实验测试结果说明该天线具有满意的频带特性和方向图特性。