Numerical Analysis of Flow-Induced Vibration and Noise Generation in a Variable Cross-Section Channel

Flow channels with a variable cross-section are important components of piping system and are widely used in variousfields of engineering.Using afinite element method and modal analysis theory,flow-induced noise,mode shapes,and structure-borne noise in such systems are investigated in this study.The results demonstrate that the maximum displacement and equivalent stress are located in the part with variable cross-sectional area.The aver-age excitation force on theflow channel wall increases with theflow velocity.The maximum excitation force occurs in the range of 0–20 Hz,and then it decreases gradually in the range of 20–1000 Hz.Additionally,as theflow velocity rises from 1 to 3 m/s,the overall sound pressure level associated with theflow-induced noise grows from 49.37 to 66.37 dB.Similarly,the overall sound pressure level associated with the structure-borne noise rises from 40.27 to 72.20 dB.When theflow velocity is increased,the increment of the structure-borne noise is higher than that of theflow-induced noise.

Analysis of the mass of behind-armor debris generated by RHA subjected to normal penetration of variable cross-section EFP

Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.

Equivalent bending stiffness of simply supported preflex beam bridge with variable cross-section

In order to understand mechanical characters and find out a calculating method for preflex beams used in particular bridge engineering projects, two types of simply supported preflex beams with variable crosssection, preflex beam with alterative web depth and preflex beam with aherative steel flange thickness, are dis- cussed on how to achieve the equivalent moment of inertia and Young＇ s modulus. Additionally, methods of cal- culating the equivalent bending stiffness and post-cracking deflection are proposed. Results of the experiments on 6 beams agree well with the theoretical analysis, which proves the correctness of the proposed formulas.

Modeling and analysis of piezoelectric beam with periodically variable cross-sections for vibration energy harvesting

A bimorph piezoelectric beam with periodically variable cross-sections is used for the vibration energy harvesting. The effects of two geometrical parameters on the first band gap of this periodic beam are investigated by the generalized differential quadrature rule （GDQR） method. The GDQR method is also used to calculate the forced vibration response of the beam and voltage of each piezoelectric layer when the beam is subject to a sinusoidal base excitation. Results obtained from the analytical method are compared with those obtained from the finite element simulation with ANSYS, and good agreement is found. The voltage output of this periodic beam over its first band gap is calculated and compared with the voltage output of the uniform piezoelectric beam. It is concluded that this periodic beam has three advantages over the uniform piezoelectric beam, i.e., generating more voltage outputs over a wide frequency range, absorbing vibration, and being less weight.

Study of the Bearing Capacity at the Variable Cross-Section of A Riser- Surface Casing Composite Pile

Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient N_(c) are revealed,and the calculation method of N_(c) is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section.

The development of real time data driving multi-axis linkage and synergic movement control system of 3D variable cross-section roll forming machine

The three dimensional variable cross-section roll forming is a kind of new metal forming technol- ogy which combines large forming force, multi-axis linkage movement and space synergic movement, and the sequential synergic movement of the ganged roller group is used to complete the metal sheet forming according to the shape of the complicated and variable forming part data. The control system should meet the demands of quick response to the test requirements of the product part. A new kind of real time data driving multi-axis linkage and synergic movement control strategy of 3D roll forming is put forward in the paper. In the new control strategy, the forming data are automatically generated according to the shape of the parts, and the multi-axis linkage movement together with cooperative motion among the six stands of the 3D roll forming machine is driven by the real-time information, and the control nodes are also driven by the forming data. The new control strategy is applied to a 48 axis 3D roll forming machine developed by our research center, and the control servo period is less than 10ms. A forming experiment of variable cross section part is carried out, and the forming preci- sion is better than ＋ 0.5mm by the control strategy. The result of the experiment proves that the control strategy has significant potentiality for the development of 3D roll forming production line with large scale, multi-axis ganged and svner^ic movement

CFD-Based Numerical Analysis of a Variable Cross-Section Cylinder

Using ANSYS-CFX, a general purpose fluid dynamics program, the vortex-induced vibration(VIV) of a variable cross-section cylinder is simulated under uniform current with high Reynolds numbers. Large eddy simulation(LES) is conducted for studying the fluid-structure interaction. The vortex shedding in the wake, the motion trajectories of a cylinder, the variation of drag and lift forces on the cylinder are analyzed. The results show that the vortices of variable cross-section cylinder are chaotic and are varying along the cylinder. In places where cross-sections are changing significantly, the vortices are more irregular. The motion trail of the cylinder is almost the same but irregular. The drag and lift coefficients of the cylinder are varying with the changes of diameters.

In-Plane Impact Dynamics Analysis of Re-Entrant Honeycomb with Variable Cross-Section

Due to the unique deformation characteristics of auxetic materials(Poisson’s ratioμ<0),they have better shock resistance and energy absorption properties than traditional materials.Inspired by the concept of variable crosssection design,a new auxetic re-entrant honeycomb structure is designed in this study.The detailed design method of re-entrant honeycomb with variable cross-section(VCRH)is provided,and five VCRH structures with the same relative density and different cross-section change rates are proposed.The in-plane impact resistance and energy absorption abilities of VCRH under constant velocity are investigated by ABAQUS/EXPLICIT.The results show that the introduction of variable cross-section design can effectively improve the impact resistance and energy absorption abilities of auxetic re-entrant honeycombs.The VCRH structure has better Young’s modulus,plateau stress,and specific energy absorption(SEA)than traditional re-entrant honeycomb(RH).The influence of microstructure parameters(such as cross-section change rateα)on the dynamic impact performance of VCRH is also studied.Results show that,with the increase in impact velocity andα,the plateau stress and SEA of VCRH increase.A positive correlation is also found between the energy absorption efficiency,impact load uniformity andαunder both medium and high impact speeds.These results can provide a reference for designing improved auxetic re-entrant honeycomb structures.

Dynamic symmetry breaking and structure-preserving analysis on thelongitudinal wave in an elastic rod with a variable cross-section

The longitudinal wave propagating in an elastic rod with a variable cross-section owns wide engineering background,in which the longitudinal wave dissipation determines some important performances of the slender structure.To reproduce the longitudinal wave dissipation effects on an elastic rod with a variable cross-section,a structure-preserving approach is developed based on the dynamic symmetry breaking theory.For the dynamic model controlling the longitudinal wave propagating in the elastic rod with the variable cross-section,the approximate multi-symplectic form is deduced based on the multi-symplectic method,and the expression of the local energy dissipation for the longitudinal wave propagating in the rod is presented,referring to the dynamic symmetry breaking theory.A structure-preserving method focusing on the residual of the multi-symplectic structure and the local energy dissipation of the dynamic model is constructed by using the midpoint difference discrete method.The longitudinal wave propagating in an elastic rod fixed at one end is simulated,and the local/total energy dissipations of the longitudinal wave are investigated by the constructed structure-preserving scheme in two typical cases in detail.

THE APPROXIMATE ANALYTICAL SOLUTION FOR THE BUCKLING LOADS OF A THIN-WALLED BOX COLUMN WITH VARIABLE CROSS-SECTION

For a thin-walled box column with variable cross-section, the three governing equations for torsional-flexural buckling are ordinary differential equations of the second or fourth order with variable coefficients, so it is very difficult to solve them by means of an analytic method. In this paper, polynomials are used to approximate the geometric properties of cross-section and certain coefficients of the differential equations. Based on the energy principle and the Galerkin's method, the approximate formulas for calculating the flexural and torsional buckling loads of this kind of columns are developed respectively, and numerical examples are used to verify the correctness of the solutions obtained. The results calculated in this paper provide the basis for demonstrating the stability of thin-walled box columns with variable cross-section. This paper is of practical value.

Evaluation of a Pulse Width Modulated Bypass Nozzle for the Development of a Variable Load Residential Oil Burner

Due to the need for energy conservation in buildings and the simultaneous benefit of cost savings, the development of a low firing rate load modulating residential oil burner is very desirable. One of the two main requirements of such a burner is the development of a burner nozzle that is able to maintain the particle size distribution of the fuel spray in the desirable (small) size range for efficient and stable combustion. The other being the ability to vary the air flow rate and air distribution around the fuel nozzle in the burner for optimal combustion at the current fuel firing rate. In this paper, which deals with the first requirement, we show that by using pulse width modulation in the bypass channel of a commercial off-the-shelf bypass nozzle, this objective can be met. Here we present results of spray patterns and particle size distribution for a range of fuel firing rates. The results show that a desirable fuel spray pattern can be maintained over a fuel firing rate turndown ratio (Maximum Fuel Flow Rate/Minimum Fuel Flow Rate) of 3.7. Thus here we successfully demonstrate the ability to electronically vary the fuel firing rate by more than a factor of 3 while simultaneously maintaining good atomization.

Failure analysis and control technology of intersections of large‑scale variable cross‑section roadways in deep soft rock

In deep underground mining,achieving stable support for roadways along with long service life is critical and the complex geological environment at such depths frequently presents a major challenge.Owing to the coupling action of multiple factors such as deep high stress,adjacent faults,cross-layer design,weak lithology,broken surrounding rock,variable cross-sections,wide sections up to 9.9 m,and clusters of nearby chambers,there was severe deformation and breakdown in the No.10 intersection of the roadway of large-scale variable cross-section at the−760 m level in a coal mine.As there are insufcient examples in engineering methods pertaining to the geological environment described above,the numerical calculation model was oversimplifed and support theory underdeveloped;therefore,it is imperative to develop an efective support system for the stability and sustenance of deep roadways.In this study,a quantitative analysis of the geological environment of the roadway through feld observations,borehole-scoping,and ground stress testing is carried out to establish the FLAC 3D variable cross-section crossing roadway model.This model is combined with the strain softening constitutive(surrounding rock)and Mohr–Coulomb constitutive(other deep rock formations)models to construct a compression arch mechanical model for deep soft rock,based on the quadratic parabolic Mohr criterion.An integrated control technology of bolting and grouting that is mainly composed of a high-strength hollow grouting cable bolt equipped with modifed cement grouting materials and a high-elongation cable bolt is developed by analyzing the strengthening properties of the surrounding rock before and after bolting,based on the Heok-Brown criterion.As a result of on-site practice,the following conclusions are drawn:(1)The plastic zone of the roof of the cross roadway is approximately 6 m deep in this environment,the tectonic stress is nearly 30 MPa,and the surrounding rock is severely fractured.(2)The deformation of the roadway progressively increases from small to large cross-sections,almost doubling at the largest cross-section.The plastic zone is concentrated at the top plate and shoulder and decreases progressively from the two sides to the bottom corner.The range of stress concentration at the sides of the intersection roadway close to the passageway is wider and higher.(3)The 7 m-thick reinforced compression arch constructed under the strengthening support scheme has a bearing capacity enhanced by 1.8 to 2.3 times and increase in thickness of the bearing structure by 1.76 times as compared to the original scheme.(4)The increase in the mechanical parameters c andφof the surrounding rock after anchoring causes a signifcant increase inσt;the pulling force of the cable bolt beneath the new grouting material is more than twice that of ordinary cement grout,and according to the test,the supporting stress feld shows that the 7.24 m surrounding rock is compacted and strengthened in addition to providing a strong foundation for the bolt(cable).On-site monitoring shows that the 60-days convergence is less than 30 mm,indicating that the stability control of the roadway is successful.

Radial Growth Responses of Four Deciduous Species to Climate Variables in Central Ontario, Canada

To address the central question of how climate change influences tree growth within the context of climate will become warmer and drier in central Ontario, we used dendroclimatological analysis to understand the radial growth responses of four co-occurring hardwood species: sugar maple (Acer saccharum Marsh.), yellow birch (Betula alleghaniensis Britton), American beech (Fagus grandifolia Ehrh.), and red oak (Quercus rubra L.) to climatic variables in central Ontario, Canada. Ring width chronologies were developed for the target species within three regions (Algonquin Park, Haliburton, and North Bay) of the study area. Seven of the eleven chronologies exceeded the 0.85 expressed population signal (EPS) and were used for further analysis. Mean sensitivity and standard deviation values of the Ontario chronologies indicated lower sensitivity to climate fluctuations than in southern North America. Positive correlations with precipitation variables from the current and prior growing season supported previous studies in sugar maple, while a positive response to growing degree days suggested the importance of warmer temperatures and a longer growing season at the northern limit of the distribution range of sugar maple. Yellow birch ring width was correlated with precipitation from the previous growing season and from the end of the current growing season also suggesting that mature trees with deep root systems might utilize moisture from deep soil. Radial growth of American beech positively correlated to precipitation of the previous season, suggesting that the amount of moisture reserves stored in the previous year might affect growth in the following year. Drought stress at the start of the growing season for red oak had negative correlations with precipitation in August indicating possible cessation of cambial activity. This decline in growth process would also affect ring width of red oak the following year as expressed by negative correlations with mean annual temperature from the previous year. Abnormally, warm seasonal temperatures may be indicative of drought stress in red oak.

Research of Elastic and Elastic-Plastic Deformation on Bending Problems of Variable Stiffness Beams

A novel variable stiffness model was proposed for analyzing elastic-plastic bending problems with arbitrary variable stiffness in detail.First,it was assumed that the material of a rectangular beam is an ideal isotropic elastic-plastic material,whose elastic modulus,yield strength,and section height are functions of the axial coordinates of the beam respectively.Considering the effect of shear on the deformation of the beam,the elastic and elastic-plastic bending problems of the axially variable stiffness beam were studied.Then,the analytical solutions of the elastic and elastic-plastic deformation of the beam were derived when the cross-section height and the elastic modulus of the material were varied by special function along the length of the beam respectively.The elastic and elastic-plastic analysis of the variable stiffness beam was carried out using Differential Quadrature Method(DQM)when the bending stiffness varied arbitrarily.The influence of the axial variation of the bending stiffness on the elastic and elastic-plastic deformation of the beam was analyzed by numerical simulation,DQM,and finite element method(FEM).Simulation results verified the practicability of the proposed mechanical model,and the comparison between the results of the solutions of DQM and FEM showed that DQM is accurate and effective in elastic and elastic-plastic analysis of variable stiffness beams.

Asymmetric Three-Phase Cascading Trinary-DC Source Multilevel Inverter Topologies for Variable Frequency PWM

Asymmetric three-phase cascading Trinary-DC source Multilevel Inverter which can achieve reduced harmonics and superior root mean square (RMS) values of the output voltage is proposed. This topology can achieve cascaded full bridge inverter operation with dissimilar (unequal) DC Source and it is fired by using variable frequency pulse with modulation technique as a switching strategy. This pulse width modulation switching strategy has a newly adopted multicarrier single reference technique. The performance parameter factors like Form Factor (FF), Crest Factor (CF), Total Harmonic Distortion (THD) and fundamental RMS output voltage (VRMS) are estimated by using proposed asymmetrical three-phase cascading multilevel inverter for several modulation indices (0.8 - 1). The research study carries with MATLAB/SIMULINK based simulation and experimental results obtained using appropriate prototype (test board) to prove the viability of the proposed concept.

电磁阀异步启闭的PWM喷雾系统设计与试验

PWM变量喷雾是国内外精准农业领域的研究热点,但PWM变量喷雾过程中电磁阀的快速启闭在管路内易形成压力脉冲,致使喷头喷雾压力发生变化,导致喷雾质量下降。为了降低压力脉冲,设计了一种相邻电磁阀异步启闭的PWM喷雾系统,由移动底盘、药箱、隔膜泵、稳压罐、PWM控制器、电磁阀及压力表等组成,通过延时控制,实现电磁阀异步启闭。在室内无风环境条件下,探究了喷雾系统电磁阀前管路内压力波动特性和沉积量分布均匀性。试验表明:与电磁阀同步启闭的PWM喷雾系统相比,电磁阀异步启闭可有效降低管路内压力峰值,不同PWM频率工况条件下,50%占空比时降幅最大,降幅最高为14%;20Hz频率条件下,异步启闭PWM喷雾的沉积量分布均匀性变异系数略高于常规连续喷雾,但均小于15%。上述结果符合喷杆喷雾机技术性能国家标准。

变量施药系统压力波动特性及其消除方法研究进展

变量施药系统具有提高农药利用率、降低农药残留、减轻环境污染等优点,根据控制方式可分为药液浓度调节式、压力调节式和流量调节式。基于脉宽调制技术的变流量式施药系统因流量调节范围广、雾滴特性稳定等优点成为国内外研究热点,但在变量施药过程中因部分喷头启闭、泵源脉动、阀体开关动作等会造成管路压力波动,导致雾化质量差,药量不精准等亟待解决的问题。从变量施药系统类型、系统压力波动特性研究、系统压力波动抑制方法与装备方面综述国内外研究现状,分析总结药液浓度调节式、压力调节式、流量调节式变量施药系统的构成、优势和缺陷,重点阐述和归纳国内外施药系统中管路和喷头附近压力波动特性,主要介绍回流稳压、空气阀、稳压喷嘴等压力冲击抑制方法和装备,指出我国在变量施药系统精确性、变量施药系统压力稳定产品开发等方面的不足并提出展望,为实现变量施药系统的进一步精准化、智能化提供思路。

多向振动俘能器设计及能量收集实验研究

针对线性、单一的振动能量俘能器存在工作频带狭窄、只能采集单向振动等问题,该文提出了一种适应货运列车等多向振动应用场景的新型多向振动俘能装置,以增强对环境中振动能量的俘获。该装置结合压电和电磁俘能器,通过螺旋圆柱弹簧和顶端质量有效捕获多向振动,并通过磁力传递振动能量至压电梁。合理设计了弹簧-质量结构,使其在较低的频率范围内可实现多种振动模态,拓宽了俘能器的谐振频带。为了充分利用压电材料,采用了变宽度压电悬臂梁,使应力均匀分布。压电梁自由端的永磁体随着压电梁的振动而产生变化的磁场,在线圈中产生感应电压。通过有限元分析和实验测试,验证了复合式俘能器可以采集多向振动能量,并测试了在z向振动激励下压电、电磁及复合式俘能器的最大输出功率。在频率9.5 Hz、z向振幅2 mm的正弦波激励下,复合式俘能器输出最大功率为3.276 mW。该系统在理论上可为低功耗传感器提供持续电力,为机械能收集与能量转换领域提供技术支持。

基于滞环控制的航空发动机快速电磁阀控制仪设计

使用滞环控制方法实现快速电磁阀两端电压的脉宽调制,精确控制流过快速电磁阀的强激电流和维持电流的幅值,使用变频变占空比的方法控制流过快速电磁阀电流脉冲的占空比,具备输入过压、输入欠压和输出短路保护功能,设计了一款基于滞环控制的快速电磁阀控制仪。该快速电磁阀控制仪已经在航空发动机快速电磁阀及其主燃油控制附件的维修过程批量使用,杜绝了因控制器输入信号不稳定导致的航空发动机主燃油系统故障,且抗干扰能力强,能够预防维修过程人为差错,起到了提高航空快速电磁阀维修质量的作用。

变宽度孤岛工作面回采期间冲击危险性数值评估研究

对采掘工作面进行冲击危险性评价是开展冲击地压防治的首要步骤。针对综合指数法对大量特殊地质和开采条件工作面难以适用的困境,本文以山西省杜儿坪煤矿变宽度孤岛工作面为对象,开展了基于有限差分数值计算方法的特殊开采条件工作面回采期间的冲击危险性评价研究。研究根据矿井实际煤岩赋存条件建立了工作面大尺度三维模型,先后计算了工作面准备阶段、两侧采空阶段、孤岛工作面回采阶段等三个阶段工作面围岩冲击危险区分布范围和危险程度,进而确定了变宽度孤岛工作面回采期间的冲击危险区段。研究结果表明,杜儿坪煤矿变宽度孤岛工作面回采过程中主要冲击危险性影响因素为冲击地压为工作面几何尺寸的突变和孤岛工作面临空条件的突变,该因素导致了回采过程中的两个主要冲击危险区段,分别为工作面变宽度区段和末采区段,对工作面在该区段的回采作业发出了冲击危险性预测和防冲措施建议,最终保证了工作面的安全回采。研究证明了有限差分数值计算方法对于特殊开采条件工作面冲击危险性评价的可行性,可作为综合指数法的互补方法。