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.

Vortex-Induced Vibrations of A Long Flexible Cylinder in Linear and Exponential Shear Flows

A numerical study based on a wake oscillator model was conducted to determine the response performance of vortex-induced vibration(VIV) on a long flexible cylinder with pinned-pinned boundary conditions subjected to linear and exponential shear flows. The coupling equations of a structural vibration model and wake oscillator model were solved using a standard central finite difference method of the second order. The VIV response characteristics including the structural displacement, structural frequency, structural wavenumber, standing wave behavior,travelling wave behavior, structural velocity, lift force coefficient and transferred energy from the fluid to the structure with different flow profiles were compared. The numerical results show that the VIV displacement is a combination of standing waves and travelling waves. For linear shear flow, standing waves and travelling waves dominate the VIV response within the low-velocity and high-velocity zones, respectively. The negative values of the transferred energy only occur within the low-velocity zone. However, for exponential shear flow, travelling waves dominate the VIV response and the negative energy occurs along the entire length of the cylinder.

Shear flow induced vibrations of long slender cylinders with a wake oscillator model

A time domain model is presented to study the vibrations of long slender cylinders placed in shear flow. Long slender cylinders such as risers and tension legs are widely used in the field of ocean engineering. They are subjected to vortex-induced vibrations（VIV） when placed within a transverse incident flow. A three dimensional model coupled with wake oscillators is formulated to describe the response of the slender cylinder in cross-flow and in-line directions. The wake oscillators are distributed along the cylinder and the vortex-shedding frequency is derived from the local current velocity. A non-linear fiuid force model is accounted for the coupled effect between cross-flow and in-line vibrations. The comparisons with the published experimental data show that the dynamic features of VIV of long slender cylinder placed in shear flow can be obtained by the proposed model,such as the spanwise average displacement,vibration frequency,dominant mode and the combination of standing and traveling waves. The simulation in a uniform flow is also conducted and the result is compared with the case of nonuniform flow. It is concluded that the flow shear characteristic has significantly changed the cylinder vibration behavior.

Quenching Phenomena Due to a Concentrated Nonlinear Source in an Infinitely Long Cylinder

This article studies a semilinear parabolic first initial-boundary value problem with a concentrated nonlinear source in an infinitely long cylinder. We study the effects of the strength of the source on quenching. Criteria for global existence of the solution and for quenching are investigated.

基于粒子群优化的盾构推进参数预测算法

为了提高传统机器学习模型在盾构推进参数方面的预测精度,提出了基于粒子群优化(PSO)的混合模型算法。以推进油缸推力和位置预测为例,阐述了PSO优化的混合模型构建流程。以粒子群优化模型为基础,分别建立混合多层感知机(MLP)油缸推力模型、混合长短期记忆(LSTM)人工神经网络油缸推力预测模型,以及混合LSTM油缸位置预测模型。以实际工程数据为例,完成多种混合预测模型的构建,并与RF、XGBoost等传统模型对比,验证所提方法和模型的有效性和先进性。实验表明:经过PSO优化的模型准确率均有不同程度的提升,本文提出的基于粒子群优化模型对指导掘进参数调控、辅助操作人员掘进等具有一定的工程价值。

薄壁长筒壳体加工工艺和定位工装设计

分析薄壁长筒壳体加工易变形产生的原因,介绍壳体的加工工艺流程,设计两种定位装夹工装,对比两种定位工装的工作原理及使用方法,有效解决了加工过程中的变形问题,使加工精度达到设计要求,提高生产率。

亚临界雷诺数下椭圆柱绕流特性

研究了亚临界雷诺数下不同长短轴比(axial ratio,AR)下的圆柱绕流特性.通过数值模拟研究了亚临界雷诺数Re=3.9×10^(3)、5.0×10^(3)、6.0×10^(3)、8.0×10^(3)、10.0×10^(3),AR=0.1-1.6的二维椭圆柱绕流的升力系数、阻力系数以及St数的变化趋势,并结合涡量云图及压力系数分布特征分析了流动特性变化的原因.分析结果表明,在亚临界雷诺数下,不同雷诺数的最大升力系数CL.m均呈现随着AR增大而先增大后减小的趋势,并在AR=0.7时达到最大值.不同雷诺数的St数变化趋势基本一致,总体呈现上升趋势.平均阻力系数以AR=0.7的情况为临界,呈现出两种不同的变化趋势.研究结果可为基于压电构型的流致振动俘能装置的优化设计提供指导.

筒体悬挂结构若干问题分析

以菏泽博物馆新馆项目为背景,从计算方法、构件受力和设计、整体屈服机制等八个方面对筒体悬挂结构体系做了较全面的研究。结果表明:1)计算筒体悬挂结构水平地震作用时无需调整层质量;2)规范底部轴力法、振型分解反应谱法并不适用筒体悬挂结构竖向地震作用计算,考虑最小限值调整后的吊柱设计仍可能偏不安全;3)采用长孔螺栓节点设计能让筒体悬挂结构吊柱在各工况下处于理想轴向拉压受力状态;4)中高烈度区吊柱在大震组合作用下可能受压,有必要复核其受压稳定和承载力;5)吊柱受力在小震阶段为恒、活载控制,大震阶段其恒、活载占比降低,地震逐渐起控制作用;6)合理的吊柱布置除满足建筑条件外,还需兼顾核心筒顶受力,减小筒顶不平衡弯矩;7)核心筒顶上包与否均能实现与屋面悬挂桁架的有效刚性连接;8)合理的筒体悬挂结构屈服机制就是落地核心筒的延性破坏过程,即始于连梁开裂破损,终于筒底墙肢钢筋拉屈、混凝土压溃。

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.

精梳落棉生产集聚纺普梳纱实践

为了实现用低配棉纺高质量纱,以细绒棉和长绒棉精梳落棉为原料纺集聚普梳纱,根据原料物理指标制定纺纱工艺流程,详述清花、梳棉、并条、粗纱、细纱工序的主要工艺参数及技术措施。通过试纺对比发现,使用25%和35%长绒棉精梳落棉与含8%再用棉的细绒棉纺集聚纺18.2 tex普梳纱,以及使用10%长绒棉精梳落棉与含8%再用棉的细绒棉纺集聚纺14.6 tex普梳纱,其成纱质量指标均在GB/T 398—2018二等纱指标范围内。指出:使用长绒棉精梳落棉纺纱,选择合适的工艺路线非常重要;高比例使用精梳落棉的关键在于清梳工序减少纤维损伤、并粗工序控制短纤维运动,以及在清梳工序提高细绒棉纤维的开松和除杂效果,在并条工序改善条子的混合效果、减少意外牵伸,在细纱工序采用集聚纺技术,提高纤维集聚程度,同时要充分发挥器材专件功效。

Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators

The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage.

An experimental investigation of dual-resonant and non-resonant responses for vortex-induced vibration of a long slender cylinder

Experimental results of the dual-resonant and non-resonant responses are presented for vortex-induced vibrations(VIV)of a long slender cylinder.The cylinder has a diameter of 10mm and a length of 3.31 m,giving an aspect ratio of 331.The cylinder was towed by a carriage with the velocity up to 1.5 m/s,with the Reynolds number varying from 2500 to 38000.Three different weights were used to provide the initial tension.Dual resonance means that resonance occurs simultaneously in both the cross-flow(CF)and in-line(IL)directions.The experiments were conducted in two stages.At the first stage,dual-resonant dynamic features of the cylinder subjected to vortex-induced excitation were investigated.The features of CF and IL vibration amplitude,motion orbits,phase angle differences,dominant frequencies and mode order numbers are presented.At the second stage of the experiments,particular emphasis was placed on non-resonant dynamic features.The variation of multi-mode modal displacement amplitudes was investigated in detail.

驮英灌区东干渠输水工程PCCP水压试验的方法

在长距离倒虹吸工程预应力钢筒混凝土管安装施工完成后,需对管道进行水压试验,以检验施工安装质量,确保满足管道在后续运行中的使用功能。笔者以广西驮英灌区东干渠输水工程东门倒虹吸为例,对长距离大口径预应力钢筒混凝土管水压试验段划分、分段处堵板和后背设计以及试验压力确定进行论述,详细阐述分段水压试验方法和步骤。试验结果满足规范及设计要求,并有效地检验管道安装质量,为以后类似工程积累经验,具有一定的参考价值。

大口径超长薄壁筒类开槽零件防变形加工技术

公司承担的某产品大口径超长薄壁筒加工任务,采用常规车削、铣削的方法无法满足图纸要求。基于公司现有的设备条件,开展大口径超长薄壁筒数控车削加工、大口径深孔镗削加工、数控刨台开槽加工研究,解决了大口径超长薄壁筒尺寸精度及形位公差达不到技术要求的问题。

大缸径机体狭长砂芯制芯组芯工艺探究

本文以大缸径机体几种典型的狭长砂芯为例,从砂芯分芯设计、制芯工艺设计、工艺工装开发以及整体组芯等方面,探讨了长条状砂芯的分芯、制芯、组芯工艺设计关注点,以及对生产操作和铸件精度的影响。

棒-板长间隙正极性放电仿真模型

长间隙放电模型常被用于仿真放电过程、分析机理及预测放电参数,对于绝缘设计具有重要的指导意义。针对棒-板长间隙正极性放电过程,提出了一种仿真模型。在假设流注区轴向电位梯度恒定的前提下,通过比较背景场与实际场求取流注区位置,提出双圆柱模型以计算长间隙放电过程中的空间电荷变化,在此基础上计算了先导发展速度并根据气体热力学理论分析了不同时刻产生的先导在放电过程中的变化,从而建立了正极性长间隙放电仿真模型。利用该模型对10m棒-板间隙正极性放电过程仿真,仿真结果在先导长度、空间电荷量、击穿时间及击穿电压等主要参数上与实验数据均较为符合,证明了模型的有效性。

钢制薄壁内压长圆筒屈服强度分布规律与参数

基于钢制薄壁内压长圆筒爆破强度统计分析数据和可靠性数学理论,建立了分析钢制薄壁内压长圆筒屈服强度的分布规律与参数的新方法。研究表明:在显著度为5%时,钢制薄壁内压长圆筒屈服强度实测值与均值之比是基本符合正态分布的随机变量;在置信度为98%时,该随机变量的均值不小于0.988 3但不大于1.013 1,标准差不小于0.111 79但不大于0.121 56;在可靠度为99.75%时,钢制薄壁内压长圆筒屈服强度实测值与均值之比不小于0.624但不大于1.378;17组试验数据验证表明,用文中新方法得到的分布参数具有波动范围小和精度高的特点。

摩擦与配合间隙对超长大型液压缸承载能力影响规律研究

以水利工程中启闭机油缸为例,对超长大型液压缸最大轴向载荷进行计算分析.研究了两端耳环与支座轴销之间的摩擦、缸筒与活塞杆的配合间隙对轴向承载能力的影响规律,利用有限元软件ANSYS对液压缸进行非线性屈曲分析.样机试验得出最大轴向载荷为580kN,与理论计算值相差约6%,验证了理论模型的合理性.分析结果表明,由强度条件确定的极限载荷小于由稳定性条件确定的临界载荷,液压缸允许的最大轴向载荷由极限载荷衡量.随着配合间隙的减小或摩擦因数的增大,液压缸轴向承载能力增加,如当摩擦因数从0增加到0.3,允许的最大轴向载荷增加约5.5%.

大缸径长行程液压缸试验台设计及工程实践

依据液压缸试验标准及现有液压缸试验台存在的不足,设计出能够对最大缸径为320 mm、最长行程为1 500mm、最大额定压力为16 MPa的液压缸进行型式试验的试验台。为了减小装机功率、满足被测试缸对加载力的需求以及提高测试效率,试验台液压系统采用了高低压泵组合、比例加载系统和同步定位系统;针对不同缸径、不同行程规格的被测试缸的试验要求,设计出一种新型的液压变行程可微调定位锁紧式液压缸试验台架,并结合ANSYS软件完成了强度校验。对安装调试中出现的故障问题进行处理,并对Ф200 mm的液压缸进行测试,结果表明:该试验台设计是合理的、达到了设计要求。

考虑大变形的大柔性立管涡激振动模型

在总结深海大柔性立管涡激振动研究基础上,提出考虑大变形的大柔性立管涡激振动数学模型,开发出相应的计算程序。在验证新模型计算程序可靠的基础上,分别在雷诺数Re=6300、Re=1.2×105情况下研究深水顶张式立管涡激振动特征。结果表明,低雷诺数时立管涡激振动以低阶单模态振动为主;随雷诺数的增大,立管涡激振动出现多模态参与振动及涡激振动非完全对称大变形现象。考虑大变形的大柔性立管涡激振动数学模型可用于深水、极深水立管系统涡激振动响应分析预测。