Vibration and Sound Radiation of Cylindrical Shell Covered with a Skin Made of Micro Floating Raft Arrays Excited by Turbulence

To reduce the vibration and sound radiation of underwater cylindrical shells,a skin composed of micro floating raft arrays and a compliant wall is proposed in this paper.A vibroacoustic coupling model of a finite cylindrical shell covered with this skin for the case of turbulence excitation is established based on the shell theories of Donnell.The model is solved with the modal superposition method to investigate the effects of the structural parameters of micro floating raft elements on the performance of reducing vibration and sound radiation of the cylindrical shell of this skin.The results indicate that increasing the stiffness ratio,damping ratio,mass ratio,or decreasing the interval betweenmicro floating raft elements can improve the vibration and sound radiation reduction performance of this skin over the frequency range 0∼2000 Hz.Moreover,the mean quadratic velocity level and sound radiation power level of the finite cylindrical shell with this skin can be reduced by 12.00 dB and 9.65 dB respectively compared to the finite cylindrical shell with homogeneous viscoelastic coating in the frequency range from0∼2000Hz,implying a favorable performance of this skin for reducing the vibration and sound radiation of cylindrical shells.

Blockage of the Deep-Sea Mining Pump Transporting Large Particles with Different Sphericity

The present study aims to plumb blockage of the deep-sea mining pump transporting large particles with different shapes. A numerical work was performed through combining the computational fluid dynamics(CFD) technique and the discrete element method(DEM). Six particle shapes with sphericity ranging from 0.67 to 1.0 were selected. A velocity triangle is built with the absolute, relative, and circumferential velocities of particles. Velocity triangles with absolute velocity angles ranging from 90° to 180° prevail in the first-stage impeller. With declining sphericity, more particles follow the velocity triangle with absolute velocity angles ranging from 0° to 90°, which weakens the ability of particles to pass through the flow passage. Furthermore, the forces acting on the particles traveling in the impeller passage are analyzed. Large particles, especially non-spherical ones, suffer from high centrifugal force and therefore move along the suction surface of the impeller blades. Non-spherical particles undergo great drag force as a result of large surface area. The distribution of drag force angles is featured by two peaks, and one vanishes due to blockage.As particle sphericity declines, both magnitude and angle of the pressure gradient force decrease. Variation of the drag force and the pressure gradient force causes clockwise deflection of the centripetal force, resulting in deflection and elongation of particle trajectory, which increases the possibility of blockage.

Effects of Fatigue Characteristics on Static and Dynamic Performance of Eucommia Rubber Isolators

This study aimed to investigate the effect of fatigue characteristics on the static and dynamic performance of Eucommia ulmoides gum isolators, and to explore the performance changes of Eucommia ulmoides gum isolators with different formulations. For this purpose, we used five formulations of Eucommia ulmoides gum isolators and set different fatigue test methods to study the static and dynamic performance changes of Eucommia ulmoides gum isolators with different formulations by changing the amplitude. The experimental results showed that the addition of Eucommia ulmoides gum had an impact on the performance of the isolator, and the number of fatigue cycles would lead to the hardening of the Eucommia ulmoides gum isolator and changes in its static and dynamic performance. In the range of two million vibrations, the performance change of the isolator was significant in the early stage and then tended to be flat, indicating that the impact of fatigue on the performance of the isolator would not continue to persist. It is worth noting that the study found that the addition of 30% Eucommia ulmoides gum had the least impact on the performance of the isolator under fatigue. Therefore, for long-term use of Eucommia ulmoides gum isolators, attention should be paid to their fatigue characteristics to ensure their stability and reliability. Additionally, this study provides a reference for the design and application of Eucommia ulmoides gum isolators. In summary, this study provides important reference value for a deeper understanding of the fatigue characteristics of Eucommia ulmoides gum isolators and for ensuring their stable and reliable performance. .

Fluid-structure Interaction Analysis and Lifetime Estimation of a Natural Gas Pipeline Centrifugal Compressor under Near-choke and Near-surge Conditions

Up to present, there have been no studies concerning the application of fluid-structure interaction（FSI） analysis to the lifetime estimation of multi-stage centrifugal compressors under dangerous unsteady aerodynamic excitations. In this paper, computational fluid dynamics（CFD） simulations of a three-stage natural gas pipeline centrifugal compressor are performed under near-choke and near-surge conditions, and the unsteady aerodynamic pressure acting on impeller blades are obtained. Then computational structural dynamics（CSD） analysis is conducted through a one-way coupling FSI model to predict alternating stresses in impeller blades. Finally, the compressor lifetime is estimated using the nominal stress approach. The FSI results show that the impellers of latter stages suffer larger fluctuation stresses but smaller mean stresses than those at preceding stages under near-choke and near-surge conditions. The most dangerous position in the compressor is found to be located near the leading edge of the last-stage impeller blade. Compressor lifetime estimation shows that the investigated compressor can run up to 102.7 h under the near-choke condition and 200.2 h under the near-surge condition. This study is expected to provide a scientific guidance for the operation safety of natural gas pipeline centrifugal compressors.

Experimental Investigation of the Resistance Performance and Heave and Pitch Motions of Ice-Going Container Ship Under Pack Ice Conditions

In order to analyze the ice-going ship’s performance under the pack ice conditions, synthetic ice was introduced into a towing tank. A barrier using floating cylinder in the towing tank was designed to carry out the resistance experiment. The test results indicated that the encountering frequency between the ship model and the pack ice shifts towards a high-velocity point as the concentration of the pack ice increases, and this encountering frequency creates an unstable region of the resistance, and the unstable region shifts to the higher speed with the increasing concentration. The results also showed that for the same speed points, the ratio of the pack ice resistance to the open water resistance increases with the increasing concentration, and for the same concentrations, this ratio decreases as the speed increases. Motion characteristics showed that the mean value of the heave motion increases as the speed increases, and the pitch motion tends to increase with the increasing speed. In addition, the total resistance of the fullscale was predicted.

Modeling and Parameter Sensitivity Analysis of Valve‑Controlled Helical Hydraulic Rotary Actuator System

As a type of hydraulic rotary actuator,a helical hydraulic rotary actuator exhibits a large angle,high torque,and compact structure;hence,it has been widely used in various fields.However,its core technology is proprietary to several companies and thus has not been disclosed.Furthermore,the relevant reports are primarily limited to the component level.The dynamic characteristics of the output when a helical rotary actuator is applied to a closed-loop system are investigated from the perspective of driving system design.Two main aspects are considered:one is to establish a reliable mathematical model and the other is to consider the effect of system parameter perturbation on the output.In this study,a detailed mechanical analysis of a helical rotary hydraulic cylinder is first performed,factors such as friction and load are considered,and an accurate dynamic model of the actuator is established.Subsequently,considering the nonlinear characteristics of pressure flow and the dynamic characteristics of the valve,a dynamic model of a valve-controlled helical rotary actuator angle closed-loop system is described based on sixth-order nonlinear state equations,which has never been reported previously.After deriving the system model,a sensitivity analysis of 23 main parameters in the model with a perturbation of 10%is performed under nine operating conditions.Finally,the system dynamics model and sensitivity analysis results are verified via a prototype experiment and co-simulation,which demonstrate the reliability of the theoretical results obtained in this study.The results provide an accurate mathematical model and analysis basis for the structural optimization or control compensation of similar systems.

Analysis and Optimization of Inside-Cushion Structure in High-Speed Hydraulic Cylinders

An inside-cushion structure with sidestep and taper-shaped plungers is studied to address the problems of high impact and vibration in high-speed hydraulic cylinders.First,the three stages of cushion processes are discussed according to the varying flow area as the piston moves.Then,to establish a precise mathematical model,the states of the flow field are estimated in terms of the Reynolds number.Accordingly,the simulation model parameterized against measured data is developed and verified by experiment.Last,the average velocity,peak cushion pressure,and terminal velocity are defined to evaluate cushion performance.According to these optimized objectives,the non-linear programming by quadratic Lagrange(NLPQL)algorithm is applied to optimize the structure parameters.The optimization results indicate that the peak cushion pressure is reduced by 28%and terminal velocity is reduced by 21%without reduction of average velocity.

Theoretical simulation of a novel birefringent photonic crystal fiber with surface plasmon resonance around 1300 nm

In this paper, a novel birefringent photonic crystal fiber （PCF） with the silver-coated and liquid-filled air-holes along the vertical plane is designed. Simulation results show that the thickness of silver layer, the sizes of holes, and the refractive index of liquid strongly strengthen the gaps between two polarized directions. The surface plasmon resonance peak along y axis can be up to 675.8 dB/cm at 1.33μB. The proposed PCF has important application in polarization devices, such as filters and beam splitters.

Block Iterative STMV Algorithm and Its Application in Multi-Targets Detection

STMV beamforming algorithm needs inversion operation of matrix, and its engineering application is limited due to its huge computational cost. This paper proposed block iterative STMV algorithm based on one-phase regressive filter, matrix inversion lemma and inversion of block matrix. The computational cost is reduced approximately as 1/4 M times as original algorithm when array number is M. The simulation results show that this algorithm maintains high azimuth resolution and good performance of detecting multi-targets. Within 1 - 2 dB directional index and higher azimuth discrimination of block iterative STMV algorithm are achieved than STMV algorithm for sea trial data processing. And its good robustness lays the foundation of its engineering application.

Effect of Liquid Temperature on Surface and Mechanical Characteristics of Al-Mg Alloy Treated with a Cavitating Waterjet

The presented study aims to reveal the effect of liquid temperature on cavitation-induced erosion of an Al-Mgalloy. An experimental work was conducted using a submerged cavitating waterjet to impact the specimen surface.For a certain cavitation number and a given standoff distance, different liquid temperatures were considered.Accordingly, a comprehensive comparison was implemented by inspecting the mass loss and surface morphologyof the tested specimens. The results show that the cumulative mass loss increases continuously with the liquidtemperature. A cavitation zone with an irregular profile becomes evident as the cavitation treatment proceeds.Increasing the temperature promotes the generation of cavitation bubbles. Large erosion pits are induced aftersevere material removal. The microhardness increases with the distance from the target surface. At a liquidtemperature of 50℃, the microhardness fluctuates apparently with increasing the depth of indentation.

Optimization of pressurization process in low-pressure casting of a 5.4-ton gigantic C95800 copper alloy casting

During the low-pressure casting of extra-large size C95800 copper alloy components,traditional linear pressurization technique leads to a rapid surge of liquid metal inlet velocity at the regions where the mold cavity cross-section enlarges.This rapid increasement of liquid metal inlet velocity causes serious entrapment of gas and oxide films,and results in various casting defects such as the bifilm defects.These defects detrimentally deteriorate mechanical properties of the castings.To address this issue,an innovative nonlinear pressurization strategy timely matching to the casting structure was proposed.The pressurization rate decreases at sections where the cross-section widens,but it gradually increases as the liquid metal level rises.By this way,the inlet velocity remains below a critical threshold to prevent the entrapment of gas and oxide films.Comparative analyses involving numerical simulations and casting verification illustrate that the nonlinear pressurization technique,compared to the linear pressurization,effectively diminishes both the size and number of bifilm defects.Furthermore,the nonlinear pressurization method enhances the casting yield strength by 10%,tensile strength by 14%,and elongation by 10%.Examination through scanning electron microscopy highlights that the bifilm defects arising from the linear pressurization process result in the reduction of the castings’mechanical properties.These observations underscore the efficacy of nonlinear pressurization in enhancing the quality and reliability of gigantic castings,as exemplified by a 5.4-ton extra-large sized C95800 copper alloy propeller hub with complex structures in the current study.

Theoretical analysis and experimental research on non-cavitation noise modulation mechanism of underwater counter-rotation propeller

The underwater counter-rotation propeller non-cavitation noise has an obvious mod- ulation characteristic which is due to the interaction of flow and blade. A modulation mecha- nism is presented in this paper. A sound pressure spectrum model is presented to describe its non-cavitation noise with application of generalized acoustic analogy method, the modulation mechanism is expressed with the improvement of sound pressure model. The power spectrum and modulation spectrum are presented by numerical simulation. Theoretical analysis and nu- merical simulation results are verified by the cavitation tunnel experiment. The modulation model of counter-rotation propeller is beneficial to the prediction modulation characteristics and identification of underwater high-speed vehicles.

Research and application of fast-convergent minimum variance distortionless response algorithm

The conventional MVDR adaptive beamformer is a high-resolution narrowband beamformer which estimates the optimal beamforming weights using narrowband CSDM of real acoustic field. In practical applications, MVDR algorithm needs long observation time to estimate the covariance matrix. This inherent property makes it difficult to localize fast-moving targets. For wideband signals, MVDR algorithm needs inverting every CSDM which increases the computational demands. For correlated sources, the performance of MVDR will degrade dramatically because the signals will cancel each other. A fast-convergent MVDR algorithm based on subband subarray processing is proposed. The full frequency band is divided into sets of subbands and the line array is divided into sets of subarrays. For every subband the STCM of reduced dimensions is calculated. Then adaptive beamforming weight of fast-convergent MVDR algorithm and spatial spectrum estimation are obtained. At the same time, spatial spectrum estimation can be made for correlated sources using the two-sided spatial smoothing method. Results of simulation and trial data show that the proposed method has high-resolution and near-instantaneous convergence property, two-sided spatial smoothing has satisfactory validity of decorrelation.

使用带孔阻尼套的座阀液动力试验和数值研究（英文）

目的:液压自由活塞发动机性能受燃油喷射系统开关阀性能限制。本文旨在对开关阀内部结构进行优化,降低液动力,从而提高阀的开启速度。创新点:1.提出一种易于安装的带孔阻尼套结构,可以用于改变阀芯表面压力分布和油液射流角,从而降低液动力;2.建立数值仿真模型,分析阻尼套不同结构和安装参数对液动力和空化的影响。方法:1.进行数值模拟,分析阀芯表面压力分布和内部流场分布,并通过实验验证方法有效性和模型准确性;2.对不同阻尼孔宽度、深度和相对位置下的阀芯液动力和流量损失情况进行对比和分析;3.对上述不同阻尼孔结构下阀内空化情况进行仿真和对比;4.建立燃油喷射系统试验台,验证阻尼套对提高阀开启速度的作用。结论:1.提出的带孔阻尼套结构可以有效降低阀芯液动力。2.随阻尼孔的减小,其对液动力的改变作用和节流作用逐渐增强;阻尼孔足够小时液动力反向并逐渐加强。3.阻尼套对油液的阻碍作用也会改变流场内的空化情况,但空化强度不一定随节流孔的变大而单调变强,其还受相对安装位置影响。4.带孔阻尼套可以有效降低阀的开启时间。

Effects of quenching and partitioning process on mechanical properties of TRIP780 steel

A transformation-induced plasticity (TRIP) steel was applied to test its mechanical properties in quenching and partitioning (Q&P) process. A series of Q&P experiments followed by tensile tests, Charpy impact tests, fracture morphology analyses and microstructure observations were conducted. The experimental results showed that the Q&P treatment could increase the mechanical properties of TRIP steel evidently. The strength of tested TRIP780 after Q&P process reaches more than 1500 MPa with elongation of 17.8%, which is obviously greater than that of 22MnB5 after hot stamping. The microstructure observations indicate that the good combination of high strength and plasticity of TRIP steel after Q&P process is attributed to the multi-phase microstructure of hard martensite matrix and soft retained austenite.

Application of the hybrid RANS/LES method on the hydraulic dynamic performance of centrifugal pumps

The nonlinear hybrid RANS/LES method has been developed considering the simulation efficiency and accuracy to simulate the hydraulic dynamic characteristics of the centrifugal pump. It has been proved that the nonlinear hybrid RANS/LES method could effectively capture the unsteady flow structure and pressure pulsation in 2?D centrifugal pumps. To further investigate the hydraulic dynamic performance of a redesigned 3-D-gap drainage centrifugal pump, the nonlinear hybrid RANS/LES method is employed. Both numerical simulation and experimental results show that the hydraulic performance and pressure pulsation characteristics of the 3-D-gap drainage impeller centrifugal pump are significantly enhanced.

Multi-objective optimization of surface texture for the slipper/swash plate interface in EHA pumps

Well-designed surface textures can improve the tribological properties and the efficiency of the electro-hydrostatic actuator(EHA)pump under high-speed and high-pressure conditions.This study proposes a multi-objective optimization model to obtain the arbitrarily surface textures design of the slipper/swash plate interface for improving the mechanical and volumetric efficiency of the EHA pump.The model is composed of the lubrication film model,the component dynamic model considering the spinning motion,and the multi-objective optimization model.In this way,the arbitrary-shaped surface texture with the best comprehensive effect in the EHA pump is achieved and its positive effects in the EHA pump prototype are verified.Experimental results show a reduction in wear and an improvement in mechanical and volumetric efficiency by 1.4%and 0.8%,respectively,with the textured swash plate compared with the untextured one.

Iterative Algorithm of Steered Minimum Variance and Its Application in Weak Targets Detection

The steered covariance matrix(STCM) and its inverse matrix should be calculated in each beam for steered minimum variance(STMV) . The inverse matrix needs complex computation and restricts its application in engineering. Combining the integration character of one-phase regressive filter with the iterative formula of inverse matrix,an STMV iterative algorithm is proposed. The computational cost of the iterative algorithm is reduced approximately to be 2/M times of the original one when there are M sensors,and is more advantaged for the realization of the algorithm in real time. Simulation results show that the STMV iterative algorithm can preserve the characters of STMV on high azimuth resolution and weak target detection while the computational cost reduced sharply. The analysis on sea trial data proves that the proposed algorithm can estimate each target's azimuth even when the source powers differ in large scales or their bearings are very approximate.

Influence of the prestressed layer on spherical transducer in sound radiation performance

To improve the acoustic radiation performance of the spherical transducer,a prestressed layer is formed in the transducer through fiber winding.The influence of the prestressed layer on the transducer is studied from the effects of the radial prestress(Tr)and acoustic impedance,respectively.First,a theoretical estimation of Tr is established with a thin shell approximation of the prestressed layer.Then,the acoustic impedance is measured to evaluate the efficiency of sound energy transmission within the prestressed layer.Further,the ideal effects of Tr on the sound radiation performances of the transducer are analyzed through finite element analysis(FEA).Finally,four spherical transducers are fabricated and tested to investigate their dependence of actual properties on the prestressed layer.The results show that with the growth of Tr,the acoustic impedance of the prestressed layer grows,mitigating the enormous impedance mismatch between the piezoelectric ceramic and water,while increasing attenuation of the acoustic energy,resulting in a peak value of the maximum transmitting voltage response(TVRmax)at 1.18 MPa.The maximum drive voltage increases with Tr,leading to a steady growth of the maximum transmitting sound level(SLmax),with a noticeable ascend of 3.9 dB at a 3.44 MPa Tr.This is a strong credibility that the prestressed layer could improve the sound radiation perfor­mance of the spherical transducer.

Structural Design Optimization Based on the Moving Baseline Strategy

Structural design optimization has always been a topic of concern in industry because good design can improve the safety and economic efficiency of structures during their service periods.Selecting the appropriate optimization algorithm is the key to solving structural optimal design problems.In this study,a new global optimization idea is proposed and named the moving baseline strategy.A baseline is initially set and will be repeatedly moving upward or downward to approach the optimal value.The proposed strategy is a simple but effective,general,and stable algorithm that can be used to solve constrained and unconstrained structural optimization problems.Different from traditional gradient-based,stochastic and heuristic algorithms,the developed algorithm provides a completely new idea to solve global or local optimization problems.Some unconstrained and constrained numerical benchmark examples are used to test the proposed methodology.In addition,structural optimal design problems of a ten-bar planar truss structure and a hypersonic wing structure(X-37B)are utilized to verify the effectiveness of the developed strategy in addressing structural design optimization problems in engineering.