Experimental study on the characteristics of pad fluttering in a tilting pad journal bearing

The fluttering characteristics of the upper unloaded pads in a tilting pad journal bearing were studied experimentally. In order to investigate the fluttering phenomena of the pad, the absolute vibration of the pad, the relative vibration between the bearing and the shaft, and the circumferential film thickness/film pressure were measured with the variation of the supply oil flow rate, the shaft speed, and bearing load. By analyzing the circumferential distributions of the film thickness, it was identified that the film shape of the upper pad continuously alternates between the wedge shape and the diverged shape in the rotational direction while the shaft is rotating. And it was discovered that the pads tend to a representative sub-synchronous self-excited vibration exactly like classical rotor-bearing instability, defined as the oil whirl and oil whip phenomena, with the increase of rotating speed from the cascade plot of the pad. The major finding was that the incipient fluttering velocity of the pad increased with the increase of the supply oil flow rate but decreased with the increase of the bearing load. The experimental results also showed that the fluttering amplitudes of the pad can be effectively suppressed by controlling the supply oil flow rate.     

Experimental validation of a finite element model of a composite tibia

Composite bones are synthetic models made to simulate the mechanical behaviour of human bones. Finite element (FE) models of composite bone can be used to evaluate new and modified designs of joint prostheses and fixation devices. The aim of the current study was to create an FE model of a composite tibia and to validate it against results obtained from a comprehensive set of experiments. For this, 17 strain rosettes were attached to a composite tibia (model 3101, Pacific Research Laboratories, Vashon, Washington, USA). Surface strains and displacements were measured under 13 loading conditions. Two FE models were created on the basis of computed tomography scans. The models differed from each other in the mesh and material properties assigned. The experiments were simulated on them and the results compared with experimental results. The more accurate model was selected on the basis of regression analysis. In general, experimental strain measurements were highly repeatable and compared well with published results. The more accurate model, in which the inner elements representing the foam were assigned isotropic material properties and the elements representing the epoxy layer were assigned transversely isotropic material properties, was able to simulate the mechanical behaviour of the tibia with acceptable accuracy. The regression line for all axial loads combined had a slope of 0.999, an intercept of -6.24 microstrain, and an R2 value of 0.962. The root mean square error as a percentage was 5 per cent.     

Experimental study and prediction model of the cleaning effect induced by self-resonating cavitating waterjet

Journal of Mechanical Science and Technology - Self-resonating cavitation waterjet (SRCW) has rapidly developed and been widely used in cleaning fields due to its non-thermal and environmentally...     

Experimental and computational validation of a scaled train tunnel model using modal analysis

Acoustic engineers are faced with the challenge of minimising reverberation time in their designs so as to contribute to the health and well-being of those traveling by train and those on the platforms. Although the problem is easy to identify, it is not as simple to solve. The acoustical environment of a train tunnel is complex, with a variety of noise contributing factors such as train announcements, speech of commuters, ventilation systems, electrical equipment and wheel and rail noise. As a result, there is some difficulty in modeling the complete acoustic environment with computational or acoustic first principles. In this study, an experimental rig was constructed to model the acoustic behavior within a tunnel. The modal properties for the 300 Hz to 1500 Hz range, including resonances and mode shapes were identified and were shown to successfully correspond to theoretical results and a computational model created in COMSOL using Finite Element Analysis.     

Resveratrol treatment of spinal cord injury in rat model

Spinal cord injury (SCI) is catastrophic and can culminate in disability and death. The routine therapy employed in early stages of SCI currently entails surgical procedures combined with high doses of methylprednisolone (MP). MP is highly controversial for the lack of consensus on its true therapeutic effects. Resveratrol (RES) has recently been recognized as a potential and novel therapeutic drug in SCI. Herein, we investigated the effect of RES in a SCI rat‐model and found significant improvement in Basso–Beattie–Bresnahan scores. Results obtained from histological, immunohistochemistry, and ultra‐structural examinations evidenced the tremendous treatment effect of RES. On the basis of our experimental results, we hypothesize that RES could serve as an effective SCI therapeutic with prolong treatment time following injury.     

Experimental study of acoustic damping induced by gas-liquid scheme injectors in a combustion chamber

In a liquid rocket engine, acoustic damping induced by gas-liquid scheme injectors is studied experimentally for combustion stability by adopting linear acoustic test. In the previous work, it has been found that gas-liquid scheme injector can play a significant role in acoustic damping or absorption when it is tuned finely. Based on this finding, acoustic-damping characteristics of multi-injectors are intensively investigated. From the experimental data, it is found that acoustic oscillations are almost damped out by multi-injectors when they have the tuning length proposed in the previous study. The length corresponds to a half wavelength of the first longitudinal overtone mode traveling inside the injector with the acoustic frequency intended for damping in the chamber. But, new injector-coupled acoustic modes show up in the chamber with the injectors of the tuning length although the target mode is nearly damped out. And, appreciable frequency shift is always observed except for the case of the worst tuned injector. Accordingly, it is proposed that the tuning length is adjusted to have the shorter length than a half wavelength when these phenomena are considered.     

Experimental validation of impact energy model for the rub-impact assessment in a rotor system

An experimental setup which can simulate the rotor-to-stator rub in a rotor system is installed. A rub screw is used to simulate the condition of local rub-impact fault. Based on the theory of elastic collision and energy conservation, an Impact Energy Model (IEM) is proposed to evaluate the probability or severity of rub-impact fault. To prove this model, the paper conducts the experiment in two steps i.e. hammer test and rub-impact fault validation. The wave signal, spectrum and axis orbit are used to analyze the severity of the rub-impact fault when it occurs. The analysis result shows that the proposed Impact Energy Model (IEM) is effective in the assessment of rub-impact fault. Furthermore, the proposed IEM can also provide a reference for the design and operation of a rotor system.     

Experimental study of simple flumes with trapezoidal contraction

There are different devices available for measuring the flow discharge. Static measuring devices such as weirs and flumes (without any moving parts) play a significant role in discharge measurement in open channels. Many researchers have focused on application of flumes in irrigation networks. This investigation set out to study the flow discharge through a trapezoidal cut-throated flume (TCTF). The flume is simply constructed by placing two triangular plates on either side of a rectangular open channel to form a trapezoidal throat. The channel cross section is rectangular while throat cross section of the flume is trapezoidal. The proposed flume is simple, low-cost, easy to install and does not require high maintenance. The present study was designed to determine the effect of different variables on the flume discharge. For this, an experimental study was carried out under free outflow conditions and under upstream subcritical flow regime to formulate the flume discharge. Three models are defined for flume discharge relation based on the Buckingham's theorem of dimensional analysis, and then calibrated using the experimental data collected during this study. The first discharge model has an average error of 1.81%, while the second and third improved models have average errors of 0.96% and 1.44% respectively. To reliably estimate the flume discharge, free-flow and submerged-flow conditions should be distinguished. For this, suitable equations with an average error less than 2.23% were presented to estimate the submergence threshold. The results of this study indicate that while the downstream wall slope influences the submergence threshold, the flume discharge is not influenced by this variable. The proposed models are simple and accurate and present appropriate estimation of discharge for flows through the TCTFs. The findings of this study will be of interest for practical hydraulic engineers.     

不同部位的功能性磁刺激对于脊髓损伤所致高反应性膀胱临床疗效研究

目的 应用不同部位功能性磁刺激(S1、S3)治疗脊髓损伤高反应性膀胱,评估治疗疗效。方法 此次研究选取2019.1.1—2021.12.31我院脊髓损伤高反应性膀胱功能障碍患者55例,按照不同部位功能性刺激为两组,S1部位治疗组及S3部位治疗组。入组时进行膀胱功能评定,在完成10次治疗后,再次进行膀胱功能评定,对比治疗前后及各组间的疗效差异。结果 两组治疗前膀胱的最大容量(ml)、最大压力(cmH_2O)、残余尿量(ml)进行分析,数据无差异。治疗前后,两组组内比较均有统计学差异(P<0.05)。两组患者治疗过程中及治疗后患者无不良反应。结论 S1、S3部位功能性磁刺激及常规康复治疗脊髓损伤高反应性膀胱功能障碍均有临床治疗效果,S3组功能性磁刺激治疗效果优于S1组,且治疗方案安全。     

Experimental study on cascaded attitude angle control of a multi-rotor unmanned aerial vehicle with the simple internal model control method

This paper proposes a cascaded control structure and a method of practical application for attitude control of a multi-rotor Unmanned aerial vehicle (UAV). The cascade control, which has tighter control capability than a single-loop control, is rarely used in attitude control of a multi-rotor UAV due to the input-output relation, which is no longer simply a set-point to Euler angle response transfer function of a single-loop PID control, but there are multiply measured signals and interactive control loops that increase the complexity of evaluation in conventional way of design. However, it is proposed in this research a method that can optimize a cascade control with a primary and secondary loops and a PID controller for each loop. An investigation of currently available PID-tuning methods lead to selection of the Simple internal model control (SIMC) method, which is based on the Internal model control (IMC) and direct-synthesis method. Through the analysis and experiments, this research proposes a systematic procedure to implement a cascaded attitude controller, which includes the flight test, system identification and SIMC-based PID-tuning. The proposed method was validated successfully from multiple applications where the application to roll axis lead to a PID-PID cascade control, but the application to yaw axis lead to that of PID-PI.

     

Identification of flexion withdrawal reflex using linear model in spinal cord injury

The aim of this study was to identify the characteristics of the flexion withdrawal reflex modulated by the hip angle and hip movement in spinal cord injury (SCI). The influence of the hip position and passive movement were tested in 6 subjects with chronic SCI. Each subject placed in a supine position and lower leg was fixed with the knee at 5–45 degree flexion and the ankle at 25–40 degree plantar flexion. A train of 10 stimulus pulses were applied at 200 Hz to the skin of the medial arch to trigger flexion reflexes. From results of the regression analysis, static properties of normalized muscle activation of flexor muscles have the linear relationship with respect to hip angle (P<0.05). In order to verify the neural contribution of flexion reflex, we compared the static and dynamic gains of estimated muscle activations with measured EMG of ankle flexor muscle. Form this study, we postulate that the torque and muscle response of flexion withdrawal reflex have linear relationship with hip angle and angular velocity.     

Experimental validation of numerical model for turbulent flow in a tangentially fired boiler with platen reheaters

A 1 : 20 laboratory scale test rig of a 200 MW tangentially fired boiler is built up with completely simulated structures such as platen heaters and burners. Iso-thermal turbulent flow in the boiler is mapped by 3-D PDA (Particle Dynamic Analyzer). The 3-D numerical models for the same case are proposed based on the solution ofk-ε model closed RANS (Reynolds time-Averaged Navier-Stokes) equations, which are written in the framework of general coordinates and discretized in the corresponding body-fitted meshes. Not only are the grid lines arranged to fit the inner/outer boundaries, but also to align with the streamlines to the best possibility in order to reduce the NDE (numerical diffusion errors). Extensive comparisons of profiles of mean velocities are carried out between experiment and calculation. Predicted velocities in burner region were quantitatively similar with measured ones, while those in other area have same tendency with experimental counterpart.     

Experimental study of cavitation phenomenon in a centrifugal blood pump induced by the failure of inlet cannula

Cavitation of centrifugal blood pump is a serious problem accompany with the blocking failure of short inlet cannula. However, hardly any work has been seen in published literature on this complex cavitation phenomenon caused by the coupling effect of inlet cannula blocking and pumps suction. Even for cavitation studies on ordinary centrifugal pumps, similar researches on this issue are rare. In this paper, the roles of throttling, rotation speed and fluid viscosity on bubble inception and intensity in a centrifugal blood pump are studied, on the basis of experimental observations. An adjustable throttle valve installed just upstream blood pump inlet is used to simulate the throttling effect of the narrowed inlet cannula. The rotation speed is adjusted from 2 600 r/rain to 3 200 r/min. Glycerin water solutions are used to investigate the influences of kinetic viscosity. Bubbles are recorded with a high-speed video camera. Direct observation shows that different from cavitation in industrial centrifugal pumps, gas nuclei appears at the nearby of vane leading edges while throttling is light, then moves upstream to the joint position of inlet pipe and pump with the closing of the valve. It＇s found that the critical inlet pressure, obtained when bubbles are first observed, decreases linearly with viscosity and the slope is independent with rotation speeds; the critical inlet pressure and the inlet extreme pressure which is obtained when the throttle valve is nearly closed, fall linearly with rotation speed respectively and the relative pressure between them is independent with rotation speed and fluid viscosity. This paper studies experimentally on cavitation in centrifugal blood pump that caused by the failure of assembled short inlet cannula, which mav beneficial the desima of centrifugal blood Dumo with inlet cannula.     

Energetic walking gaits studied by a simple actuated inverted pendulum model

The mechanical structure and the joint torques configuration are the important parts in the biped robot design. Meanwhile, different walking speed and step length should be chosen to achieve efficient gait according to different need of walking environment. Therefore, this paper investigates the energetic walking gaits using a simple actuated inverted pendulum model. Joint torques and push-off impulse are both added in the model. The walking gaits with different joint torques configuration and with different combination of walking speeds and step lengths are analyzed. The results show that hip velocity direction is changed by the push-off impulse just before the heelstrike, which reduces the energy consumption of each step. The walking gait with minimal energy consumption is the walking pattern only with push-off, the energy cost of which is 1/4 of the walking pattern only with joint torque during the swing phase. The cost of transport (COT) and the push-off impulse of the walking gait is increasing with the increase of walking speed and step length. Using same value of push-off impulse, the walking with long step length and slow speed is more efficient. The paper can provide suggestions for designing advanced legged robot systems with high energy efficiency and various gaits. For example, the consideration of push-off mechanism can be used in the biped robots design.

     

Development and validation of a pedestrian deformable finite element model

Pedestrian protection has become an increasingly important consideration in vehicle crash safety. Pedestrian-vehicle crashes cause a significant number of pedestrian fatalities and injuries globally. Computer models are powerful tools for understanding how to reduce the severity of injuries in such crashes. Real-world studies of pedestrians provide an important source of information for evaluating pedestrian model dynamic performance and ability to reconstruct injury-causing events. This study describes the validation process of deformable pedestrian model using published postmortem human subject (PMHS) trajectory and head resultant velocity corridors, and demonstrates its applicability to pedestrian — vehicle impact research. We implemented the deformable pedestrian model using LS-DYNA finite element code. Based on PMHS data, the pedestrian model is used to validate the displacement trajectories of the head, pelvis, knee and foot. The finite element pedestrian model thus obtained can help assess the friendliness of vehicles with pedestrians in traffic crashes and assist in the future development of pedestrian safety technologies. This paper was recommended for publication in revised form by Associate Editor Young Eun Kim Tso-Liang Teng is a Professo r in the Department of mechanical and automation engi-neer ing and the Dean of engineeri ng college at the Da-Yeh Uni versity, Taiwan. He received a BS (1981), MS (1986) and PhD (1994) from the Chung Cheng Institute of Technology. His research intere sts include design of passive safety systems in ve hicles, crash tests simulation, passenger and pedest rian injuries analysis, design of pedestrian protecti on systems.     

磨损预测模型的试验研究

分析了影响材料摩擦磨损性能的主要因素,将环境因素中的润滑介质、工作参数中的载荷和滑动速度以及材料的表面硬度作为建立磨损预测模型的影响因素.根据均匀设计试验原理进行试验方案的制定,应用逐步回归方法建立磨损预测模型,经检验,模型具有较高的显著性,并有较好的预测效果.     

电站汽轮机调节阀振动试验研究

针对电站汽轮机常用调节阀的不稳定和振动工况进行试验研究，利用微小型高频动态压力传感器等先进测试仪器，测量阀门内部流场，尤其是阀座喉部、阀瓣头部等关键部位，获得阀门流体诱发振动结论。在大压比、大升程条件下，喉部各测点的脉动压力不大，流动稳定。中小压比、中小升程时，压力脉动达到相对的最大值或变化最大，此时气流对阀瓣的作用力也达到最大。气流脉动一般含有小于几百Hz的主频，所以这种条件下气流与结构相对容易发生共振。     

Experimental study and finite element analysis of simple X- and T-branch tube hydroforming processes

The tube hydroforming process is a relatively complex manufacturing process; the performance of this process depends on various factors and requires proper combination of part design, material selection and boundary conditions. Due to the complex nature of the process, the best method to study the behaviour of the process is by using numerical techniques and advanced explicit finite element (FE) codes. In this work, X- and T-branch components were formed using a tube hydroforming machine and experimental load paths (forming pressure and axial feed) were obtained for the processes via a data acquisition system integrated with the machine. Subsequently, the processes were simulated using LS-DYNA3D explicit FE code using the same experimental boundary, loading conditions and the simulation results were compared with the experimental results. It was found that the developed branch height and the wall thickness distribution along different planes were in good agreement with the experimental results.     

Development and validation of a new friction model for cutting processes

The International Journal of Advanced Manufacturing Technology - The friction model in the tool-chip interface has significant influences on predicting chip forms, cutting forces, and cutting tool...     

Development and validation of a nonlinear dynamic impact model for a notch impact

The International Journal of Advanced Manufacturing Technology - Finite element simulations are being more and more applied when studying the crash-worthiness of vehicles during impact. This paper...