Journal of Engineering and Thermal Sciences
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Vibrodiagnostics and dynamic behaviour of aggregates in small hydroelectric power plants
No full textThe presentation introduces the solution for the vibroactivity problems in small hydroelectric power plants, based on original stationary vibromonitoring and diagnostic systems as well as their application to solve various problems. Dynamic behaviour of hydromachinery and causes of increased vibrations are analysed taking into account structural, design- and construction-related issues. It is demonstrated that condition monitoring and analysis of vibrations enable identification of causes of large vibrations in hydromachiner
The new analytical method of acoustic field estimation in the room
Get PDFThe directional characteristics of sound fields in enclosures are investigation in this paper. The main object of this paper is to determine the impulse response of sound sources for calculating acoustics parameters in closed space. The new analytical method has been suggested as the result of theoretical studies. This method allows a quantitative and qualitative analysis of the interaction of dynamic processes of a sound source with air in a roo
Evaluation of cracked construction elements durability and estimation of structural strength under vibrations
Get PDFThe manuscript deals with the research of relevant problems of cracked elements under cyclic loading. In contrast to the majority of published research work that is dedicated to the case of symmetrical cyclic loading, this paper proposes a methodology for evaluation of influence of asymmetric cyclic loading. First part of the manuscript is concerned with straight crack growth dependence on loading parameters using probabilistic analysis. Speed of crack growth and stress intensity factor values are obtained from experimental studies. Assessment of these parameters can be made using method of Monte Carlo however it is not common and the current research is carried out by applying a more simple averaging method. For elements under asymmetrical loading a general-purpose equation is proposed. Symmetrical cycle and pulsing cycle parameters are used. As a result of these two parameters a general equation is obtained for computational number of loading cycles. This technique enables estimation of durability of elements under various types of loadings with the defined size of the crac
A surface micromachined comb drive with superior stability for application as an actuator
No full textThis paper presents results of ongoing research on fundamental issues related to comb drive, including mechanical and electrical properties. Attention is mostly focused on the case when comb drive is used as a power source with a cantilever beam attached to the moving plate. FEM simulations are carried out to show the resonant behaviour of balanced and unbalanced comb drive. Fringing effect, which helps to actuate the comb drive, is modeled. Different measurement approaches in frequency domain are discussed. Theoretical formulas are derived and analyzed. In this work we designed and fabricated both balanced and unbalanced comb drives using MUMPs (Multi-user MEMS Processes) technology. Balanced comb drives exhibit superior stability both in SEM observations and spectrum analysis. Formulas governing the spectrum are experimentally verified by mixing frequency measurement
Holographic interferometry methods for analysis & design of rotary converter
Get PDFA rotary converter used in mechanisms that require high precision displacement has proved that accuracy depends both on design and technological factors. An important feature of mechatronic systems containing links made of active sandwich beam is the performance of various functions by the same transducer thereby enabling the development of improved design methods. The analysis of various parameters and constructions of mechatronic systems has made it possible to introduce the mechanism containing a rotary converter which can turn any top around or turn a screw. A holographic interferometry method has been applied in the experimental work [1, 2
Mechatronic structure of modern test bench for precise angle calibration
Get PDFMany optoelectronic measuring instruments, vibro-scanning devices and deflection systems have angular sensors or circular scales as a reference measure for angle determination. Most of angle measuring devices must be tested or calibrated with a relevant precision therefore a special test rig for these purposes is needed. At current technical level the precision of measurements of vibro-displacement, amplitudes or frequency of vibrations implies not only precise manufacturing and assembly but also a necessity to incorporate modern computer technologies enabling automation of the measuring process. All these components of modern technologies can be accomplished by using mechatronic constituents. This paper presents a brief review of the angle testing/calibration equipment with the integrated mechatronic device
Failure analysis of destructive coils
Get PDFThe failure of the destructive pulsed power coils has been investigated. The destructive coil is the key element of the laboratory system which generates half-period abrupt magnetic field pulses with the amplitudes up to 45 T. The transient coupled non-linear magneto-mechanical model has been applied for finite element simulations. The mechanical behavior and operation threshold of the coil have been examined. It has been found that operation threshold of the coil with relatively thin cylindrical reinforcement could be characterized by the opening of the plastic hinge and estimated numerically. Good agreement with experimental results has been observe
Investigation of compression of packages
Get PDFThe model for the analysis of compression of a long structure with a constant thin-walled cross-section is presented. It is assumed that a structure experiences static compression and the problem of initial stability for a cross- section is solved. The analysis of compression of a shell-type structure is described assuming that a structure undergoes static compression and the problem of initial stability is solved. The results of experimental investigation of resistance to compression of paperboard packages are presented for different grammage of the materials of paperboard and for the machine and cross-machine directions of production of paperboard. The largest permissible vertical pressure load that the packages are able to resist is determine
Evaluation components of the heart rate kinetics for assessment cardiac adaptation during rehabilitation
Get PDF"The purpose of the study was assessment of the cardiovascular adaptation to the workload and physical training by analysis of the heart rate kinetics and dynamics of power spectrum components in healthy subjects and ischemic heart disease patients during rehabilitation. The contingent of study was 20 healthy subjects and 97 patients post-myocardial infarction (74 without chronic heart failure and 23 with chronic heart failure symptoms). Multistage bicycle ergometry or spiroergometry and computerized analysis of heart rate variability during active orthostatic, symptom-limited workload tests and recovery period after test were performed. The rhythmogram at 50W of the workload, and during bicycle (Kettler) training and recovery period was analyzed and the time constant (?) of the exponential function (by using Proni method), coefficients of amplification, rapidity as well as heart rate (HR) power spectral components (?VLF, ?LF, ?HF) were evaluated. Heart rate kinetics response time constant to the low-level (?50W) workload (30.3 vs. 19.3 s) and during recovery period (40 vs. 45.6 s) was delay in post-myocardial infarction patients, especially in those with CHF and low physical capacity as compared with healthy subjects. Heart rate responses (?50W) correlated with baseline HR autonomic control components (?LF, r=-0.25, ?RRB%, r=-0.24, RRB, r=0.23,) and with physical capacity (r=-0.30). In CHF patients the delay HR response to the workload and during recovery correlated with expressed ventilatory response (VE/VCO2, r=0.60) in this group. Positive dynamic of HR kinetics components (?=37.1 vs. 34.6 s) and power spectrum characteristics after low intensity bicycle training procedure and during recovery (?=42.4 vs. 39.9 s) period was observed. The faster HR reaction to the physical stressor after 3-weeks bicycle training correlated with positive dynamics of ?HF (r=-0.35). The HR power spectrum components during bicycle training changed favorably (?VLF, 15.2 vs. 16.3 ms; ?LF, 8.2 vs. 9.4 ms; ?HF, 8.8 vs. 9.4 ms) too. Conclusions. Analysis of the heart rate kinetics components and power spectrum data during exercise provides a new possibility evaluation of the cardiac adaptation to the workload and physical training procedures in ischemic heart disease patients during rehabilitation
Dynamic stability of a flexible rod under parametric excitation
Get PDFA homogeneous rod with a constant cross section, vertically mounted and cantilevered, is considered. At the unstrained state, the rod’s axis is straight. It is supposed lateral stiffness is that the rod buckles in static conditions only under gravity and its axis bends. Flexural oscillations of the rod when its base vibrates vertically are investigated. Stabilization circumstances of the rod axis rectilinearity depending on excitation parameters, internal and external damping, and rod flexibility are determined