Journal of Engineering and Thermal Sciences
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The effect of dry friction forces on the process of dielectric wafer grinding
Get PDFWe have investigated possible motions of the holder on top of the polishing pad during the process of dielectric plate grinding taking into account the forces of dry friction about its axis. A mathematical model of the mechanical device has been elaborated to describe the process of dielectric wafer grinding. The model is in the form of a non-autonomous nonlinear system with a variable structure. The structure of the phase space of the dynamical system was investigated, the qualitative studies of the possible motion modes were carried out. The values of the geometrical and dynamic parameters that qualitatively and quantitatively influence the modes of the holder motion were obtained. It was found that the inclusion of dry friction forces on the axis of the free holder result in a periodic motion of the mechanism with long stops. We present the calculations of the parameters for the type 3PD-320 machine
About formation of the stable modes of the movement of multilink mechanical systems
Get PDFThe problem of synthesis of the controlled movement of the stepping robot, the movers of that move on trajectories with the sites, which are close to rectilinear, is considered. Stabilization of movement of points on the movers of stepping robot on a rectilinear trajectory will allow synthesizing algorithm of stepping without jumps of the accelerations in points of change of phases of a support of movers. In this case, under the control object, the point of mover is understood, and the controlled coordinate is a corresponding coordinate of such point
The NAH based on complex cepstrum method in a closed space
Get PDFNAH method in non-free sound field reconstruction of the sound source will lead to considerable error. This paper proposes a method to reconstruct the sound source in a closed space. In the closed space, the total sound pressure is the sum of the source radiation pressure and the reflected sound pressure from medium interface. Reflections from medium interface is a convolution noise, rather than additive noise. In order to reconstruct a sound source in the closed space, in this paper we first adopt the complex cepstrum method to separate and radiation pressure and the reflected sound pressure, then filter them to reduction of reflected sound pressure, and then reconstruct the sound source. The simulation results show the correctness and effectiveness of the method
A rail-borne piezoelectric transducer for energy harvesting of railway vibration
Get PDFThis paper investigates design, modelling, and test issues related to piezoelectric energy transducer. The model analyzes a rail-borne “seismic” energy harvester that is designed to generate electrical energy from local variations in rail acceleration. The energy harvester analyzed in this model consists of a piezoelectric PZT film clamped at one end to the rail with a tip mass mounted on its other end. It includes two sub-models in this paper: a vehicle-track interaction model considering vehicle travelling load; and a cantilevered piezoelectric beam model for the visualization of voltage and power profile and frequency response. Four rail irregularities (American 6th grade track spectrum, Chinese track spectrum, German high and low-disturbance track spectrum) are compared and implemented into the calculation script. The calculated results indicate a rail displacement of 0.2 mm to 0.8 mm. Vibration tests of the proposed rail-borne device are conducted; a hydraulic driven system with excitation force up to 140 kN is exploited to generate the realistic wheel-rail interaction force. The proposed rail-borne energy harvester is capable of energy harvesting at low-frequency (5 Hz to 7 Hz) and small railway vibration (0.2 mm to 0.4 mm rail displacement). The output power of 4.9 mW with a load impedance of 100 kOhm is achieved. The open circuit peak-peak voltage reaches 24.4 V at 0.2 mm/7 Hz/5 g wheel-rail excitation. A DC-DC buck converter is designed, which works at the resonance frequency of 23 Hz/5 g on a lab vibration rig, providing a 3.3 VDC output
Effect of vibroacoustic therapy on pain management in adolescents with low back pain
Get PDFVibroacoustic Therapy (VT) is a very distinct form of treatment. The purpose of this study was to determine the effect of vibroacoustic therapy on low back pain management in adolescents. A total of 40 adolescents (13-18 years old) were randomly divided into two equal groups (exercise – control group, and exercise and vibroacoustic therapy – vibroacoustic group), and participated in a 3-week physiotherapy program for back pain management. The participants in both groups performed the same exercise program five times per week. The participants in the vibroacoustic group apart from exercise also received treatment on a special vibro chair set at 4-8 Hz frequency for relaxation. Music was heard through the headphones. Standard tests (Oswestry disability index and the visual analogue pain scale) to assess low back pain were used before and after the intervention to monitor changes. The intensity of low back pain significantly decreased in both groups after the intervention (P < 0.05), but there were no significant differences between the groups in low back pain management in adolescents
Dynamic analyses of osteoblast vibrational responses: a finite element viscoelastic model
Get PDFMechanotransduction is an important process that influences bone remodeling and maintains viability of bone cells. To understand the effect of the vibrational mechanical stimulation on biomechanic responses of bone cells, a viscoelastic osteoblast finite element (FE) model was developed. Firstly, the mode shapes and natural frequencies of a spreading osteoblast were assessed using the FE modal analysis. The osteoblast FE model predicted the natural frequencies of osteoblasts (within the range about 19.99-34.48 Hz). Then, the effect of acceleration on the vibrational responses of in-vitro cultured osteoblasts was investigated. Three different accelerations of base excitation were selected (0.15g, 0.3g and 0.5g, where g = 9.8 m/s2) and the vibrational responses (displacement, strain and stress) of osteoblasts were simulated. It was found that values of displacement, strain and stress increase with the increase of base excitation acceleration. In addition, the response values in Z-direction are much higher than those in the other directions (X, Y-direction) for the same base excitation acceleration. These findings will provide useful information to understand how vibrational mechanical stimulus influences bone cells and provide guidance for in vitro cell culture and experimental research and ultimately clinical treatment using the external vibrating loading
Improvement of the durability of rolling bearings in high-speed drive systems
Get PDFAt present, in many high-speed machines (e.g. appliances) bearing systems based on ball bearings. These solutions are used because of the low cost of production. However, in the process of operation, it appears that the use of this type of bearings has low durability of the system associated with its underload. In these systems, the output shaft rotates at a very high speed (20 thousand RPM), so even slight imbalance causes very high inertia forces aggravating bearings with dynamic reactions. These reactions rotate with the shaft, and their rotation frequency is equal to the frequency of the shaft rotation. Clearances in the bearing lead to the situation where the shaft together with the inner ring vibrates. These vibrations cause the slip between the balls and the cage of the bearing. As a result, the cage is a subject to accelerated damage because of sliding and collisions with the balls. Another factor affecting the durability of the bearing system is work at temperatures exceeding permissible limits. The article compares two design solutions and their impact on the life of the bearings used. In the original construction very fast wear of bearings takes place, and thus the damage of the whole device. In a second experiment there was examined the durability of the system with the use of tension of the bearings with axial spring. The initial effects of changes in structure of the system have led to a change of bearing lubrication. The final result of the re-search was a proposal to change such a structure eliminating the problem of accelerated wear of the bearings
Review of advances on longitudinal vibration of submarine propulsion shafting and its vibration reduction technology
Get PDFAnalyzed the formation mechanism of longitudinal vibration of the submarine propulsion shafting system, and introduced its existing vibration control technology. The content included the improvement design of propulsion shafting system, new types of thrust bearing, composite material shaft, dynamic vibration absorber, phonon crystal band gap damping and relative active control technology. A new method for the application of metal rubber technology in thrust bearing was put forward, which provided a new idea for the research work in the future
Research on vibration and interface simulation technology of aero-engine
Get PDFExcessive vibration can cause engine fault, so the engine vibration monitoring and control is particularly important to flight safety. With the simulation platform of hardware in loop of the engine control system, the ability to handle the vibration of the engine controller can be verified. It can effectively reduce the development cost and shorten the development cycle. This paper is a result of extensive research on the vibration signal modeling and the interface simulation technology of engine, in the vibration control experiment of hardware in loop; and a universal interface simulator has been designed. The interface simulator can receive multi-channeled signal in a wide-range of values, and can also simulate different kinds of signals, simplify the signal acquisition and conditioning circuit of the electronic controller. This simulation provides a good platform for the research of engine vibration control
Numerical simulation of fluctuation pressure with liquid-filled pipes based on large eddy simulation method
Get PDFPipeline is an important part of mechanical system on ship. Fluctuation pressure produced on the pipe wall is a significant source of noise, and more and more scholars pay attention to it. In this paper, by using large eddy simulation and subgrid turbulence theory, pipeline fluctuation pressure simulation model is established, and influence of flow velocity, wall roughness and step offset of pipeline connection on pipe fluctuation pressure are studied. This provides theoretical guidance for low-noise installation and maintenance of ship piping system