Research on the Generation Mechanism and Suppression Method of Aerodynamic Noise in Expansion Cavity Based on Hybrid Method

The expansion chamber serves as the primary silencing structure within the exhaust pipeline.However,it can also act as a sound-emitting structure when subjected to airflow.This article presents a hybrid method for numerically simulating and analyzing the unsteady flow and aerodynamic noise in an expansion chamber under the influence of airflow.A fluid simulation model is established,utilizing the Large Eddy Simulation(LES)method to calculate the unsteady flow within the expansion chamber.The simulation results effectively capture the development and changes of the unsteady flow and vorticity inside the cavity,exhibiting a high level of consistency with experimental observations.To calculate the aerodynamic noise sources within the cavity,the flow field results are integrated using the method of integral interpolation and inserted into the acoustic grid.The acoustic analogy method is then employed to determine the aerodynamic noise sources.An acoustic simulation model is established,and the flow noise source is imported into the sound field grid to calculate the sound pressure at the far-field response point.The calculated sound pressure levels and resonance frequencies show good agreement with the experimental results.To address the issue of airflow regeneration noise within the cavity,perforated tubes are selected as a means of noise suppression.An experimental platformfor airflow regeneration noise is constructed,and experimental samples are processed to analyze and verify the noise suppression effect of perforated tube expansion cavities under different airflow velocities.The research findings indicate that the perforated tube expansion cavity can effectively suppress low-frequency aerodynamic noise within the cavity by impeding the formation of strong shear layers.Moreover,the semi-perforated tube expansion cavity demonstrates the most effective suppression of aerodynamic noise.

Fabrication and characterization of highly ordered Ni_(0.5)Zn_(0.5)Fe_2O_4 nanowire/tube arrays by sol-gel template method

Highly ordered nanowire/tube arrays of Ni0.5Zn0.5Fe2O4were fabricated by the sol-gel method in the pores of anodic alumina membrane （AAM）. Whether nanowires or nanotubes were fabricated depends on immersion time. The immersion time was 15- 40 s for nanotubes and over 60 s for nanowires. The topography and crystalline structure of the nanowire arrays were characterized by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and X-ray diffraction （XRD）. It was found that the length and diameter of the Ni0.5Zn0.5Fe2O4 nanowires are related to the thickness of the AAM and the diameter of the pores. The results indicated that the Ni0.5Zn0.5Fe2O4 nanowires are uniform and parallel to each other.

A Numerical-analytic Method for Quickly Predicting Springback of Numerical Control Bending of Thin-walled Tube

Springback is one of important factors influencing the forming quality of numerical control （NC） bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process was put forward. The method is based on springback angle model derived using analytic method and simulation results from three-dimensional （3D） rigid-plastic finite element method （FEM）. The method is validated through comparison with experimental results. The features of the method are as follows： （1） The method is high in efficiency because it combines advantages of rigid-plastic FEM and analytic method. （2） The method is satisfactory in accuracy, since the field variables used in the model is resulting from 3D rigid-plastic FEM solution, and the effects both of axial force and strain neutral axis shift have been included. （3） Research on multi-factor effects can be carried out using the method due to its advantage inheriting from rigid-plastic FEM. The method described here is also of general significance to other bending processes.

SIMUUTION OF ELECTROMAGNETIC TUBE BULGING BASED ON LOOSE COUPLING METHOD

A loose coupling method is used to solve the electromagnetic tube bulging. ANSYS/ EMAG is used to model the time varying electromagnetic field with the discharge current used as excitation, in order to obtain the radial and axial magnetic pressure acting on the tube, the magnetic pressure is then used as boundary conditions to model the high velocity deformation of tube with DYNAFORM, The radial magnetic pressure on the tube decreases from the center to the tube end, axial magnetic pressure is greater near the location equal to the coil height and slight in the other region. The radial displacement of deformed workpicces is distributed uniformly near the tube center and decreases from the center to the end; Deformation from the location equal to coil height to the tube end is little. This distribution is consistent with the distribution of radial pressure; Effect of the axial magnetic pressure on deformation can be ignored, The calculated results show well agreements with the experimental results.

Numerical simulation of the preparation of semi-solid metal slurry with damper cooling tube method

In semi-solid forming process, preparing the slurry with rosette or globular microstructure is very important. A new approach named the damper cooling tube method （DCT）, to produce the semi-solid metal slurry, has been introduced. To optimize the technical parameters in designing the apparatus, the finite volume method was adopted to simulate the flow process. The temperature effects on the rheological properties of the slurries were also considered. The effects of the technical parameters on the slurry properties were studied in detail.

HEAT TRANSFER STUDIES OF HIGHLY VISCOUS NON-NEWTONIAN FLUIDS IN VERTICAL TUBES BY FINITE ELEMENT METHOD

A numerical method capable is developed for handling steady laminar flow and heat trans-fer of a highly viscous power-law fluid whose density,viscosity,specific heat and thermalconductivity,vary with temperature.The governing equations are found to be continuity,monmentumand energy expressions.Important effects such as varying viscosity,natural convection and viscousdissipation are incorporated in the theoretical model.These equations are being attracted by employing a decoupled finite element method.Galerkin’sprinciple is used to handle the momentum and continuity equations.Consistent(SU/PG)andnon-consistent(SU)streamline upwind methods are employed for the energy equation.Comparisonof calculated results and experimental data shows good agreement.Similar results are obtained withSU and SU/PG methods.Velocity and temperature profiles which provide insights into the processare also given.

A CALCULATION METHOD FOR FULLY DEVELOPED FLOWS IN CURVED RECTANGULAR TUBES

In this paper, A method, consisted of perturbation method, Garlerkin method and finite-difference method, is designed to calculate fully developed flows in curved tubes of rectangular cross-section. It costs less computation than that of direct solving N-S equations, and prevents from building high-order difference equations and extra dealing with the boundary conditions. Numerical results in the situation of small curvature and low Dean number is in accordance with former's numerical and experimental results in quality, and it shows the feasibility of this paper's method.

Application of Compactness Detection to Complicated Concrete-Filled Steel Tube by Ultrasonic Method

An example of using ultrasonic method to detect the compactness of complicated concrete-filled steel tube in certain high-rise building was discussed in this study.Because of the particularity of the complicated concrete-filled steel tubular column,the plane detection method and embedded sounding pipe method were adopted in the process of effectively detecting the column.According to the results of the plane detection method and embedded sounding pipe method,the cementing status of steel tube and concrete can be concluded,which cannot be judged by the hammering method in the rectangular steel tube-reinforced concrete.

The pressure field in the liquid column in the tube-arrest method

We have been using the method of tube-arrest as a means of producing transient single cavitation bubble. In the present paper we seek to comprehend the mechanism of production and inquire into the structure of the ab initio pressure field in the arrested liquid column. The generated pressure wave is shown by combining the theoretical analysis with the experimental observation to be a slightly varied version of water hammer. With relatively clean liquid, the magnitude of the tension peak generating the TSB is likely to reach of several millions Pa. It is also shown that the so generated cavitation bubble originating from the gas-containing bulk liquid is in ‘violent’ motion.

Axial Compression Behavior and Analytical Method of L-Shaped Column Composed of Concrete-Filled Square Steel Tubes

Based on the characteristics of an L-shaped column composed of concrete-filled square steel tubes, the axial compression experiment and nonlinear finite element analysis were carried out to study the mechanical property of the L-shaped column. The load-displacement curve for the L-shaped column, the deflection and load-strain curves for the mono columns were obtained by the axial compression experiment. The results show that the L-shaped column exhibits a flexural-torsional buckling failure mode. The numerical simulation by the finite element analysis shows that the bearing capacity and failure mode are in accordance with those of the axial compression experiment and the feasi- bility of the finite element analysis is proved. For the calculation of the bearing capacity of the L-shaped column com- posed of concrete-filled square steel tubes, an analytical method is proposed based on the theory of the elastic stability and spatial truss model. The results of the analytical method are in good agreement with those of the axial compression experiment and the finite element analysis.

THE APPLICATION OF BOUNDARY ELEMENT METHOD IN STRESS ANALYSIS OF AUTOFRETTED TUBE WITH NOTCH

In this paper, the boundary element method is applied to investigate the internal state of stress of autofretted tube with notch and the calculated results are important in the practical design.

Magneto-Hydrodynamic Flow of an Incompressible Fluid in a Collapsible Elastic Tube with Mass and Heat Transfer

The aim of this study is to examine unsteady incompressible Magnetohydrodynamic fluid flow together with soret and dufour effects on mass and heat transfer through a collapsible elastic tube. The governing equations are continuity equation, momentum equation, energy equation and concentration equation. The velocity, temperature and concentration profiles together with heat and mass transfer rate were determined. The system of nonlinear partial differential equations governing the flow solved numerically by applying collocation method and implemented in MATLAB. The numerical solution of the profiles displayed both by graphically and numerically for different values of the physical parameters entering into the problem. The effects of varying various parameters such as Reynolds number, Hartmann number, Soret number, Dufour number and Prandtl number on velocity, temperature and concentration profiles also the rate of heat and mass transfer are discussed. The study is significant because heat and mass transfer mechanisms with the soret and dufour effects considerations play an important role due to its wide range of application including but not limited to medical fields, biological sciences and other physical sciences where collapsible tubes are applied.

水声材料声振特性的驻波管测量方法

提出了一种基于驻波管的测量方法,以获得水声材料在静水压条件下的声学和振动特性参数。设计了带有气压补偿功能的低频发射换能器,作为驻波管的声源,通过水柱将换能器的平面活塞振动耦合到水面下的被测样品。在被测样品背衬上安装加速度计,测量样品背面振速;同时在管壁中嵌入一对水听器,测量水柱声压。导出样品声波入射面的振速和声压,进而计算出样品前表面和背衬面之间的振速传递系数(去耦系数)、样品的输入阻抗和声压反射系数。建立低频驻波管测试系统,声管尺寸为内径300 mm、外径600 mm、高3 m,工作频率范围100~1000 Hz,利用水层样品和多层穿孔橡胶样品开展了实验研究。实验结果显示,测量数据与仿真计算数据吻合较好,验证了测量方法的有效性。

基于内压法的锆合金薄壁管泊松比试验研究

锆合金包壳管在核电应用中存在变形及破裂等问题,严重影响核电运行安全。为了更好地评价锆合金包壳管等薄壁管材受内压时的变形性能,给燃料组件的设计、计算、验证提供参考,设计基于内压法的泊松比测试方法。根据薄壁圆筒受均匀内压时的应力解,推导出基于内压加载的薄壁管泊松比理论公式。按照该理论公式设计合理的内压试验方法,采用该方法对N36锆合金薄壁管开展20~400℃下的泊松比试验,同时通过拉伸法进行相应温度下的对比试验。结果表明,内压试验方法可以有效获得不同温度下锆合金薄壁管的泊松比,且内压试验方法得到的锆合金薄壁管泊松比与拉伸法结果较为一致,相对误差均在2%以内。试验结果同时表明:N36锆合金薄壁管的泊松比随试验温度的增加呈增大趋势。

多感官刺激联合间歇经口至食管管饲法在老年脑卒中吞咽障碍的应用

目的观察多感官刺激联合间歇经口至食管管饲法在老年脑卒中吞咽障碍的应用效果。方法选择2021年2月至2022年10月收治的脑卒中吞咽障碍患者为研究对象,随机分为对照组、观察A组、观察B组,对照组在常规治疗基础上,采用鼻留置胃管管饲;观察A组在常规治疗基础上,采用间歇经口至食管管饲法;观察B组在观察A组基础上,加用多感官刺激方案。3组均干预8周,在干预前和干预8周后观察洼田饮水试验、标准吞咽功能评价量表(SSA)、吞咽困难生活质量量表(SWAL-QOL)、体质指数(BMI)、营养风险筛查表2002(NRS2002)以及舌骨喉复合体动度检查(舌骨上移距离、甲状软骨上移距离、舌骨前移距离、甲状软骨前移距离)。结果干预8周后,除对照组SWAL-QOL评分以外,其余3组洼田饮水试验、SSA评分和SWAL-QOL评分优于干预前(P<0.05)。而观察B组在洼田饮水试验与其余2组差异有统计学意义(P<0.05),SSA评分低于其余2组,SWAL-QOL评分高于对照组(P<0.05),与观察A组差异无统计学意义(P>0.05)。在营养情况方面,干预8周后3组BMI均高于干预前,NRS2002均低于干预前(P<0.05)。组间比较,3组BMI差异无统计学意义(P>0.05);在NRS2002方面,观察A组和观察B组均低于对照组(P<0.05),而观察A组和观察B组之间差异无统计学意义(P>0.05)。在喉复合体动度检查方面,干预8周后,除对照组舌骨上移距离,其余3组各项距离高于干预前(P<0.05)。观察B组舌骨上移距离、舌骨前移距离高于其余2组(P<0.05),甲状软骨前移距离、甲状软骨上移距离仅高于对照组,与观察A组差异无统计学意义(P>0.05)。结论多感官刺激联合间歇经口至食管管饲法作用于脑卒中吞咽障碍患者,能够改善患者的吞咽功能,提高生活质量,值得进一步研究。

基于高压气体驱动的爆炸波模拟激波管冲击波衰减历程控制方法

基于高压气体驱动的爆炸波模拟激波管,一般采用驱动段、喉部、膨胀段的结构形式,可产生特征与爆炸波接近的模拟冲击波,是实验室中开展长正压作用时间爆炸毁伤效应研究的理想平台。通过调整激波管的变截面结构和驱动段形状,实现冲击波超压衰减历程的控制,是此类爆炸波模拟激波管设计面临的核心问题之一。基于实验室现有的爆炸波模拟激波管结构,建立了激波管内一维流动数值计算模型;参考统计学理论,提出了基于决定系数的激波管模拟冲击波与标准爆炸波相似度评价方法;进而以变截面激波管的流动特性为基础,研究了驱动段形状对冲击波衰减历程的影响机理。研究结果表明:采用距离喉部越远、截面直径越小的驱动段形状,以决定系数为量化标准、优化驱动段形状,控制稀疏波、压缩波在激波管内的运动过程,可以获得接近于爆炸波指数衰减特征的模拟冲击波。

转头前倾法在脑卒中吞咽功能障碍患者留置胃管中的效果观察

目的研究转头前倾法在脑卒中吞咽功能障碍患者留置胃管中的作用。方法临床纳入2022年1月至2023年2月期间我院收治的84例脑卒中吞咽功能障碍患者作为研究对象,将患者分为两组各42例(随机数字表法),所有患者均需留置胃管。其中42例患者采用常规方法进行留置胃管作为对照组;另42例患者采用转头前倾法进行留置胃管作为观察组。观察两组患者置管成功率、不良反应发生率、生活质量以及护理人员对吞咽功能障碍摄食训练相关知识的知晓率情况。结果观察组一次置管成功率和再次置管成功率分别为92.86%、100.00%,均高于对照组的76.19%、30.00%,均有差异(P<0.05)。观察组不良反应发生率明显低于对照组的不良反应发生率(4.76%vs 19.05%),有差异(P<0.05)。干预前两组患者生活质量各评分对比无差异(P>0.05);干预后观察组生活质量各评分均优于对照组,均有差异(P<0.05)。培训后护理人员对吞咽功能障碍摄食训练相关知识的知晓率为96.67%,明显高于培训前的53.33%,有差异(P<0.05)。结论转头前倾法能使护理人员更好掌握吞咽功能障碍摄食训练的相关知识,有效提高脑卒中吞咽功能障碍患者留置胃管的成功率,降低不良反应发生率,进一步提高患者生活质量,值得临床应用及推广。

局部环向变厚度方钢管混凝土柱偏压力学性能研究

针对海洋环境中飞溅区造成的钢管混凝土柱局部环向腐蚀现象,采用机械削减方式模拟钢管壁厚局部环向腐蚀,进行了7个方钢管混凝土柱偏压试验,揭示了削弱率和偏心率对其偏压承载力的影响,并通过数值模拟对削弱率进行拓展分析.提出了基于削弱率的偏压承载力降低系数,代入中、美规范进行偏压承载力计算.结果表明:钢管的局部环向变厚度严重削弱了方钢管混凝土柱的偏压承载力和侧向挠曲能力;较大的加载偏心率也降低了其偏压承载力,但增大了其侧向挠曲能力.引入偏压承载力降低系数后,根据中、美规范计算得到的偏压承载力与试验值均吻合较好;相比于我国规范,美国规范在计算偏压承载力时相对更加保守.

便捷填充U型管盐桥的制备与探索

Cu-Zn原电池实验是基础化学实验的重要组成部分,盐桥批量制备的品质是实验的关键,常规操作的温度高、消耗大、效率低。本文分别从U型管盐桥的填充材料和灌装方式两方面进行研究。针对盐桥的制作难度及功能特点进行探索,对琼脂和可溶性淀粉载体盐桥的导电能力、凝结时间进行分析。改进灌装方式,针对大批量盐桥制作需求,设计半自动式灌装机代替传统人力操作,提高盐桥的制作效率。为化学实验中盐桥的制备提供便捷高效的解决方案,提高相关实验数据的准确性和稳定性。

钢管预置集料混凝土中长柱受压性能试验

为了探究钢管预置集料混凝土中长柱受压性能,首先,考虑混凝土类型、混凝土强度、径厚比、长径比和偏心率等参数影响,设计了11根钢管预置集料混凝土中长柱和3根普通钢管混凝土中长柱;其次,通过轴压和偏压试验,并结合有限元分析法,研究了试件破坏形态、承载力、变形特征等变化规律;最后,基于极限平衡理论,提出了适用于钢管预置集料混凝土中长柱轴压与偏压承载力计算公式。研究结果表明:钢管预置集料混凝土中长柱破坏形态与普通钢管混凝土中长柱的破坏形态相似,均为弯曲失稳破坏;钢管预置集料混凝土中长柱承载能力与普通钢管混凝土中长柱承载能力相当,但钢管预置集料混凝土试件轴向刚度是普通钢管混凝土试件轴向刚度的1.2倍左右,表现出良好的抗变形能力;钢管预置集料混凝土中长柱径厚比由39.75降低至19.88,承载能力提高33.8%;长径比由6增大至15时,承载能力降低20.5%;偏心率由0.25增大至1.0时,承载力降低49.5%;钢管预置集料混凝土中长柱稳定系数受混凝土强度和径厚比影响较小,但随着长径比和偏心率增大而近乎呈线性降低趋势。本文提出的承载力计算公式可为钢管预置集料混凝土中长柱设计提供参考。