Low Vibration Levels Research Articles

Monitoring Vibration of A Model of Rotating Machine

Mechanical movement or motion of a rotating machine normally causes additional vibration. A vibration sensing device must be added to constantly monitor vibration level of the system having a rotating machine, since the vibration frequency and amplitude cannot be measured quantitatively by only sight or touch. If the vibration signals from the machine have a lot of noise, there are possibilities that the rotating machine has defects that can lead to failure. In this experimental research project, a vibration structure is constructed in a scaled model to simulate vibration and to monitor system performance in term of vibration level in case of rotation with balanced and unbalanced condition. In this scaled model, the output signal of the vibration sensor is processed in a microcontroller and then transferred to a computer via a serial communication medium, and plotted on the screen with data plotter software developed using C language. The signal waveform of the vibration is displayed to allow further analysis of the vibration. Vibration level monitor can be set in the microcontroller to allow shutdown of the rotating machine in case of excessive vibration to protect the rotating machine from further damage. Experiment results show the agreement with theory that unbalance condition on a rotating machine can lead to larger vibration amplitude compared to balance condition. Adding and reducing the mass for balancing can be performed to obtain lower vibration level.

Enhancing mechanical energy harvesting with dynamics escaped from potential well

The potential of utilizing the dynamics outside the potential well of a device for harvesting energy from vibrations is investigated. A pendulum-type system subjected to parametrical excitation is used to demonstrate the concept. When the dynamics of the device is outside the potential well and stays in stable orbits of period-one rotations, the harvested energy is proportional to the energy level of the orbit. It is neither dependent on the natural frequency of the device nor on the intensity of the excitation. For low-level vibrations, the effectiveness of the proposed method is limited in relatively low frequencies.

Miniature active damping stage for scanning probe applications in ultra high vacuum

Scanning probe microscope (SPM) experiments demand a low vibration level to minimize the external influence on the measured signal. We present a miniature six-degree of freedom active damping stage based on a Gough-Stewart platform (hexapod) which is positioned in ultra high vacuum as close to the SPM as possible. In this way, vibrations originating from the experimental setup can be effectively reduced providing a quiet environment for the SPM. In addition, the hexapod provides a rigid reference point, which facilitates wiring as well as sample transfer. We outline the main working principle and show that for scanning tunneling microscopy (STM) measurements of a Si(111) 7 × 7 surface, the hexapod significantly improves the stability and quality of the topographic images.

Design sensitivity analysis of dynamic responses for a BLDC motor with mechanical and electromagnetic interactions

This paper presents a design sensitivity analysis of dynamic responses of a BLDC motor with mechanical and electromagnetic interactions. Based on the equations of motion which consider mechanical and electromagnetic interactions of the motor, the sensitivity equations for the dynamic responses were derived by applying the direct differential method. From the sensitivity equation along with the equations of motion, the time responses for the sensitivity analysis were obtained by using the Newmark time integration method. The sensitivities of the motor performances such as the electromagnetic torque, rotating speed, and vibration level were analyzed for the six design parameters of rotor mass, shaft/bearing stiffness, rotor eccentricity, winding resistance, coil turn number, and residual magnetic flux density. Furthermore, to achieve a higher torque, higher speed, and lower vibration level, a new BLDC motor was designed by applying the multi-objective function method. It was found that all three performances are sensitive to the design parameters in the order of the coil turn number, magnetic flux density, rotor mass, winding resistance, rotor eccentricity, and stiffness. It was also found that the torque and vibration level are more sensitive to the parameters than the rotating speed. Finally, by applying the sensitivity analysis results, a new optimized design of the motor resulted in better performances. The newly designed motor showed an improved torque, rotating speed, and vibration level.

Cricket Bat Acceleration Profile from Sweet-Spot Impacts

The sweet spot on a cricket bat is defined as the point where the ball receives maximum acceleration. Sweet spot impacts are accompanied by minimal jarring of the hands and forearms. Using 3 axis accelerometers mounted on the bat and the wrists, ball strikes were recorded for defensive drives along the ground. There is significant evidence that sweet spot hits have low levels of vibration in the wrist sensors so that small, battery powered, accelerometers can be used to discriminate sweet spot hits during normal match play and practice.

Modeling Optimal Scheduling for Pumping System to Minimize Operation Cost and Enhance Operation Reliability

Traditional pump scheduling models neglect the operation reliability which directly relates with the unscheduled maintenance cost and the wear cost during the operation. Just for this, based on the assumption that the vibration directly relates with the operation reliability and the degree of wear, it could express the operation reliability as the normalization of the vibration level. The characteristic of the vibration with the operation point was studied, it could be concluded that idealized flow versus vibration plot should be a distinct bathtub shape. There is a narrow sweet spot (80 to 100 percent BEP) to obtain low vibration levels in this shape, and the vibration also follows similar law with the square of the rotation speed without resonance phenomena. Then, the operation reliability could be modeled as the function of the capacity and rotation speed of the pump and add this function to the traditional model to form the new. And contrast with the tradition method, the result shown that the new model could fix the result produced by the traditional, make the pump operate in low vibration, then the operation reliability could increase and the maintenance cost could decrease.

Block Design of Diesel Engine for Low Vibration Level Based on Topology and Shape Optimization

In order to achieve a low vibration design of engine block,verify the correctness of finite element model based on the test method,ensure the undertake of different levels of optimization model using the method of topology and shape optimization,modal frequency and vibration intensity of engine block are taken as optimization objectives,vibration analysis of engine block is made in the simulation,and the body vibration condition distribution are identified in the optimization design.The four cylinder engine block is set as the design objective,the optimal solution design variables are got through the topology optimization and shape optimization method,and then the final optimization scheme with whole layout and detailed design are obtained.The results of optimized structure show that frequencies of each mode are improved,and the vibration intensity value of engine block decreases by 34.8%,then vibration intensity of improved engine block is minimized in a safe area subject to rigidity and strength constraints.Efficiency and precision of the combination method of topology and shape optimization has an obvious enhance,and the feasibility and efficiency of the proposed methods are demonstrated by the experiment.

Piezoelectric MEMS low-level vibration energy harvester with PMN-PT single crystal cantilever

A piezoelectric MEMS vibration energy harvester with PMN-PT single material has been developed, which can convert low-level vibration energy into electrical energy. Compared with the conventional piezoelectric material, the PMN-PT single crystal has a higher coupling coefficient and electromechanical coefficient, which can improve the conversion efficiency of the power generating device. The designed device consists of a composite cantilever beam and an Ni proof mass, which is fabricated using UV-LIGA technology. Test results show that the fabricated vibration energy harvester can generate a maximum output power of 2.704 µW with a 2.08 VP-P output voltage, at a resonant frequency of 237.4 Hz and 1.0g acceleration level.

Effect of low frequency motion on the performance of a dynamic manual tracking task

The assessment of wind-induced motion plays an important role in the development and design of the majority of today's structures that push the limits of engineering knowledge. A vital part of the design is the prediction of wind-induced tall building motion and the assessment of its effects on occupant comfort. Little of the research that has led to the development of the various international standards for occupant comfort criteria have considered the effects of the low-frequency motion on task performance and interference with building occupants' daily activities. It has only recently become more widely recognized that it is no longer reasonable to assume that the level of motion that a tall building undergoes in a windstorm will fall below an occupants' level of perception and little is known about how this motion perception could also impact on task performance. Experimental research was conducted to evaluate the performance of individuals engaged in a manual tracking task while subjected to low level vibration in the frequency range of 0.125 Hz-0.50 Hz. The investigations were carried out under narrow-band random vibration with accelerations ranging from 2 milli-g to 30 milli-g (where 1 milli-g = 0.0098 <TEX>$m/s^2$</TEX>) and included a control condition. The frequencies and accelerations simulated are representative of the level of motion expected to occur in a tall building (heights in the range of 100 m -350 m) once every few months to once every few years. Performance of the test subjects with and without vibration was determined for 15 separate test conditions and evaluated in terms of time taken to complete a task and accuracy per trial. Overall, the performance under the vibration conditions did not vary significantly from that of the control condition, nor was there a statistically significant degradation or improvement trend in performance ability as a function of increasing frequency or acceleration.

Numerical study of the flow-structure interactions in an air- or helium-filled simulated hard disk drive

Since its invention, the Hard Disk Drive (HDD) has been the most widely-used device for data storage. Recently, the volume of data is getting larger and the corresponding rotation speed of the HDD is increasing to allow for better data transfer. The decreasing size of the disk is increasing the density of data on the disk surface. As a result, the positioning accuracy of the Suspension Slider Unit (SSU), where the magnetic head is mounted, is the problem that has to be overcome for better performance of the HDD. Additionally, the increased rotating speed of the disk induces unsteady flow between each pair of disks. This unsteady flow becomes turbulent around the SSU and induces vibrations on the SSU which deteriorate the performance of the HDD. There have been many investigations to understand the fluid mechanics phenomena inside the HDD filled with air. Additionally, many modifications have been tried to minimize the flow-induced vibration on the SSU by placing a blockage upstream of the arm to generate a low velocity region. However, none of these investigations have explored the effect of using gases other than air. In this work, the flow physics in the HDD is investigated numerically with the drive filled with air or helium. Numerical analyses were performed using the commercial code (ANSYS/CFX) with an expanded 2 × model simulating Seagate cheetah 2.5-inch drive. Despite obvious un-addressed issues in sealing the HDD, the unsteady characteristics of the flow are dissipated sufficiently faster in helium than in air so as to warrant further studies addressing the more practical issues of working with helium. Of particular importance is the unsteady flow around the SSU. This leads to lower levels of flow-induced vibration in the case of helium flow. As such, HDD performance may be improved by using helium to improve the dynamics of the HDD at higher rotation speeds. For both air- and helium-filled drives, calculations have been performed with two different locations of the SSU and two different angular velocities, 1,000 and 3,000 rpm corresponding to 5,000 and 15,000 rpm in 3.5-inch commercial drive. Not only is it shown that the helium-filled drive suffers lower positioning errors, but also the underlying flow physics responsible for such improvement are explained.

Development and Application of High-Sensitivity Wireless Smart Sensors for Decentralized Stochastic Modal Identification

State-of-the-art smart sensor technology enables deployment of dense arrays of sensors, which is critical for structural health monitoring (SHM) of complicated and large-scale civil structures. Despite recent successful implementation of various wireless smart sensor networks (WSSNs) for full-scale SHM, the low-cost micro-electro-mechanical systems (MEMS) sensors commonly used in smart sensors cannot readily measure low-level ambient vibrations because of their relatively low resolution. Combined use of conventional wired high- sensitivity sensors with low-cost wireless smart sensors has been shown to provide improved spectral estimates of response that can lead to improved experimental modal analysis. However, such a heterogeneous network of wired and wireless sensors requires central collection of an enormous amount of raw data and off-network processing to achieveglobal time synchronization; consequently, many of the advantages of WSSNs for SHM are lost. In this paper, the development of a new high-sensitivity accelerometer board (SHM-H) for the Imote2 wireless smart sensor (WSS) platform is presented. The use of a small number of these high-sensitivity WSSs, composed of the SHM-H and Imote2, as reference sensors in the Natural Excitation Technique—based decentralized WSSN strategy is explored and is shown to provide a cost- effective means of improving modal feature extraction in the decentralized WSSN for SHM. DOI: 10.1061/(ASCE)EM.1943-7889 .0000352. © 2012 American Society of Civil Engineers. CE Database subject headings: Structural health monitoring; Probe instruments; Identification; Stochastic models. Author keywords: Structural health monitoring; Wireless smart sensor network; High-sensitivity sensor; System identification; Decentralized sensor network.

Dynamical strength and design optimization of pipe-joint system under pressure impact load

This article is focused on the dynamical strength analysis and design optimization of a pipe-joint system. A three-dimensional model of a fuel pipe-joint system is established and the strength and dynamic analysis of the system under the pressure impact load is analysed. In order to avoid dangerous forced vibrations or resonance, and to lower vibration level, the clamps’ numbers and locations are optimized. The results show that: (a) under the pressure impact load, near the T-branch pipe, clamps and elbows, the pipe system’s failure can easily occur; and (2) the numbers and locations of clamps of pipe-joint system can be optimized and the optimized pipe-joint system has better anti-vibration ability.

Damage Identification Research of Axial Vibration Modal Shape

A new method taking the second derivative of low-level axial vibration modal shape as damage index is presented on the basis of theoretical derivation axial vibration differential equation and analytical solution of three kinds of support form. The index is very sensitive to damage location and damage degree. In addition, the effect of point number is analyzed and results showed that with a few points can still calibration damage well.

Computerized design of advanced straight and skew bevel gears produced by precision forging

The computerized design of advanced straight and skew bevel gears produced by precision forging is proposed. Modifications of the tooth surfaces of one of the members of the gear set are proposed in order to localize the bearing contact and predesign a favorable function of transmission errors. The proposed modifications of the tooth surfaces will be computed by using a modified imaginary crown-gear and applied in manufacturing through the use of the proper die geometry. The geometry of the die is obtained for each member of the gear set from their theoretical geometry obtained considering its generation by the corresponding imaginary crown-gear. Two types of surface modification, whole and partial crowning, are investigated in order to get the more effective way of surface modification of skew and straight bevel gears. A favorable function of transmission errors is predesigned to allow low levels of noise and vibration of the gear drive. Numerical examples of design of both skew and straight bevel gear drives are included to illustrate the advantages of the proposed geometry.

A case report of vibration-induced hand comorbidities in a postwoman

BackgroundProlonged exposure to hand-transmitted vibration is associated with an increased occurrence of symptoms and signs of disorders in the vascular, neurological and osteoarticular systems of the upper limbs. However, the available epidemiological evidence is derived from studies on high vibration levels caused by vibratory tools, whereas little is known about possible upper limb disorders caused by chronic exposure to low vibration levels emitted by fixed sources.Case presentationWe present the case of a postwoman who delivered mail for 15 years using a low-powered motorcycle. The woman was in good health until 2002, when she was diagnosed with bilateral Raynaud's phenomenon. In March 2003 a bilateral carpal tunnel syndrome was electromyographically diagnosed; surgical treatment was ineffective. Further examinations in 2005 highlighted the presence of chronic tendonitis (right middle finger flexor).Risk assessmentFrom 1987, for 15 years, our patient rode her motorcycle for 4 h/day, carrying a load of 20-30 kg. For about a quarter of the time she drove over country roads. Using the information collected about the tasks carried out every day by the postwoman and some measurements performed on both handles of the motorcycle, as well as on both iron parts of the handlebars, we reconstructed the woman's previous exposure to hand-arm vibration. 8-hour energy-equivalent frequency weighted acceleration was about 2.4 m/s2. The lifetime dose was 1.5 × 109(m2/s4)hd.ConclusionsThe particular set of comorbidities presented by our patient suggests a common pathophysiological basis for all the diseases. Considering the level of exposure to vibrations and the lack of specific knowledge on the effects of vibration in women, we hypothesize an association between the work exposure and the onset of the diseases.

Vibratory noise to the fingertip enhances balance improvement associated with light touch

Light touch of a fingertip on an external stable surface greatly improves the postural stability of standing subjects. The hypothesis of the present work was that a vibrating surface could increase the effectiveness of fingertip signaling to the central nervous system (e.g., by a stochastic resonance mechanism) and hence improve postural stability beyond that achieved by light touch. Subjects stood quietly over a force plate while touching with their right index fingertip a surface that could be either quiescent or randomly vibrated at two low-level noise intensities. The vibratory noise of the contact surface caused a significant decrease in postural sway, as assessed by center of pressure measures in both time and frequency domains. Complementary experiments were designed to test whether postural control improvements were associated with a stochastic resonance mechanism or whether attentional mechanisms could be contributing. A full curve relating body sway parameters and different levels of vibratory noise resulted in a U-like function, suggesting that the improvement in sway relied on a stochastic resonance mechanism. Additionally, no decrease in postural sway was observed when the vibrating contact surface was attached to the subject's body, suggesting that no attentional mechanisms were involved. These results indicate that sensory cues obtained from the fingertip need not necessarily be associated with static contact surfaces to cause improvement in postural stability. A low-level noisy vibration applied to the contact surface could lead to a better performance of the postural control system.

Rat Intervertebral Disc Health During Hindlimb Unloading: Brief Ambulation With or Without Vibration

Changes in intervertebral disc (IVD) morphology and biochemistry have been characterized only incompletely in the rat hindlimb unloading (HLU) model. Here we present preliminary data on the differential effects of short periods of weight-bearing with or without low-level whole-body vibrations (WBV) on the lumbar rat IVD during HLU. Rats were subjected to HLU and exposed to daily periods (15 min x d(-1)) of either ambulatory activities (HLU+AMB) or whole body vibrations superimposed upon ambulation (HLU+WBV; WBV at 45 Hz, 0.3 g). At the end of the 4-wk experimental period and compared to age-matched control rats (AC), the lumbar IVD of HLU+AMB had a 22% smaller glycosaminoglycans/collagen ratio, 12% smaller posterior IVD height, 13% smaller cross-sectional area, 9% greater ratio of height/area, and a 24% smaller volume of the surrounding muscle tissue. Compared to HLU+AMB rats, the addition of low-level vibratory loading did not significantly alter IVD biochemistry, posterior height, area, or volume but normalized muscle volume (-8% vs. AC) and the IVD height/area ratio (-3% vs. AC) to levels similar to normal controls. Relative to AC, superposition of the vibratory stimulus onto ambulation had a greater effect on IVD area than on IVD height. IVD volume and IVD posterior height of HLU+WBV rats remained 13% and 16% smaller than in normal controls. Even though neither intervention was successful in preventing hindlimb unloading induced changes in IVD volume, compared to ambulation alone, very low-level whole-body vibrations resulted in greater total back and abdominal muscle volume and directionally altered IVD geometry.

Design and performance of an advanced metrology building for MIKES

Fundamental metrology is closely linked to the development of science and needs good facilities to achieve low measurement uncertainty in demanding experiments. The laboratories must have good temperature stability, low vibration level, good electromagnetic shielding, clean room air, and humidity control. This paper outlines specification and design principles of a compact laboratory building that brings most of the activities of MIKES under one roof, thus attaining the performance of the most demanding laboratories. The most demanding specifications of temperature and vibration were set for the length and mass laboratories. The tightest room temperature specification was (20 ± 0.05) °C. The vibration level was specified at the tightest level to 1 μm/s at frequencies of 0.1–5 Hz. Electromagnetic shielding was specified at best to 100 dB for plane waves up to 20 GHz. Relative humidity was specified (48 ± 2)% at 20 °C. The specifications were clearly achieved and state of the art metrology laboratories implemented.

Low-Level Vibrations Retain Bone Marrow's Osteogenic Potential and Augment Recovery of Trabecular Bone during Reambulation

Mechanical disuse will bias bone marrow stromal cells towards adipogenesis, ultimately compromising the regenerative capacity of the stem cell pool and impeding the rapid and full recovery of bone morphology. Here, it was tested whether brief daily exposure to high-frequency, low-magnitude vibrations can preserve the marrow environment during disuse and enhance the initiation of tissue recovery upon reambulation. Male C57BL/6J mice were subjected to hindlimb unloading (HU, n = 24), HU interrupted by weight-bearing for 15 min/d (HU+SHAM, n = 24), HU interrupted by low-level whole body vibrations (0.2 g, 90 Hz) for 15 min/d (HU+VIB, n = 24), or served as age-matched controls (AC, n = 24). Following 3 w of disuse, half of the mice in each group were released for 3 w of reambulation (RA), while the others were sacrificed. RA+VIB mice continued to receive vibrations for 15 min/d while RA+SHAM continued to receive sham loading. After disuse, HU+VIB mice had a 30% greater osteogenic marrow stromal cell population, 30% smaller osteoclast surface, 76% greater osteoblast surface but similar trabecular bone volume fraction compared to HU. After 3 w of reambulation, trabecular bone of RA+VIB mice had a 30% greater bone volume fraction, 51% greater marrow osteoprogenitor population, 83% greater osteoblast surfaces, 59% greater bone formation rates, and a 235% greater ratio of bone lining osteoblasts to marrow adipocytes than RA mice. A subsequent experiment indicated that receiving the mechanical intervention only during disuse, rather than only during reambulation, was more effective in altering trabecular morphology. These data indicate that the osteogenic potential of bone marrow cells is retained by low-magnitude vibrations during disuse, an attribute which may have contributed to an enhanced recovery of bone morphology during reambulation.

Optimization of an electret-based energy harvester

Thanks to miniaturization, it is now possible to imagine self-powered systems that usevibrations to produce their own electrical energy. Many energy harvesting systems alreadyexist. Some of them are based on the use of electrets: electrically charged dielectrics thatcan retain charge for years. This paper presents an optimization of an existing system andproves that electret-based electrostatic energy scavengers can be excellent solutions to powermicrosystems even with low-level ambient vibrations. Thereby, it is possible to harvest up to200 µW with vibrations of acceleration lower than1g (typically 50 µmpp at 50 Hz) using thinSiO2 electrets with anactive surface of 1 cm2 and a mobile mass of 1 g. This paper optimizes such a system (geometric, electrostatic andmechanical parameters), using FEM (finite element method) software (ComsolMultiphysics) and Matlab to compute the parameters, and proves the importance of suchan optimization to build efficient systems. Finally, it is shown that the use of electrets withhigh surface potential is not always the best way to maximize output power.