JVE International
Not a member yet
1200 research outputs found
Sort by
Experimental studies of stabilization of boring cutter form – building top oscillation
Get PDFThe article deals with application of automatic control of cutting tool oscillations, which permits to control the cross-sectional form of a hole. This parameter can be controlled in mass-produced machine tools only through machine tool geometrical relationship, which is ensured during manufacturing of metal cutting machine tools. The purpose of the proposed control system is to increase technological capabilities of the equipment in order to improve boring accuracy as compared with the accuracy regulated by the standards for this type of equipment. Testing of the proposed technological equipment demonstrated high efficiency of damping in the process of boring in terms of response to mechanical and impact actions. Rational combinations of cutting modes were revealed, which provide the needed accuracy and acceptable productivity in the hole cutting process
Hopf bifurcation and stability analysis of flexible rotor-bearing system
Get PDFAnalytical model of a long bearing was used to study the self-excited vibration of a single disc flexible rotor-bearing system on sliding bearing support. A shooting method was applied to track and acquire periodic solution of flexible rotor system after the Hopf bifurcation. Stability of periodic solution was analyzed on the basis of Floquet theory. Gas film eddying, oscillation and other nonlinear features were considered. High-speed air hybrid bearing test-bed was used to verify gas film oscillation arising from coupling between natural frequency and gas film eddying frequency. The “bounded” nature of chaotic vibration and the process of rubbing caused by instability of air film were observed. Finally, a distinguishing criterion named “practical stability” was provided
Static and vibrational analysis of the GMAW and SMAW joints quality
Get PDFStructural steel S235JR is one of the main high-strength steels, while the most common welding methods are gas metal arc welding and shielded metal arc welding. Any of weld-strength-related defects can lead to weaker, less ductile welds, cracking and rupture in various steel constructions. Therefore quality of GMAW and SMAW joints were analyzed by using both the destructive tensile strength test and the non-destructive holographic interferometry method. Tensile test results of 10 arc welded specimens and holograms of harmonically excited specimens are presented in this paper. Specifications of specimens and welding parameters are also reviewed along with methodology of the experimental investigation and criteria of the analysis
Vibration condition monitoring of planetary gears based on decision level data fusion using Dempster-Shafer theory of evidence
Get PDFIn recent years, due to increasing requirement for reliability of industrial machines, fault diagnosis using data fusion methods has become widely applied. To recognize crucial faults of mechanical systems with high confidence, indubitably decision level fusion techniques are the foremost procedure among other data fusion methods. Therefore, in this paper in order to improve the fault diagnosis accuracy of planetary gearbox, we proposed a representative data fusion approach which exploits Support Vector Machine (SVM) and Artificial Neural Network (ANN) classifiers and Dempster-Shafer (D-S) evidence theory for classifier fusion. We assumed the SVM and ANN classifiers as fault diagnosis subsystems as well. Then output values of the subsystems were regarded as input values of decision fusion level module. First, vibration signals of a planetary gearbox were captured for four different conditions of gear. Obtained signals were transmitted from time domain to time-frequency domain using wavelet transform. In next step, some statistical features of time-frequency domain signals were extracted which were used as classifiers input. The gained results of every fault diagnosis subsystem were considered as basic probability assignment (BPA) of D-S evidence theory. Classification accuracy for the SVM and ANN subsystems was determined as 80.5 % and 74.6 % respectively. Then, by using the D-S theory rules for classifier fusion, ultimate fault diagnosis accuracy was gained as 94.8 %. Results show that proposed method for vibration condition monitoring of planetary gearbox based on D-S theory provided a much better accuracy. Furthermore, an increase of more than 14 % accuracy demonstrates the strength of D-S theory method in decision fusion level fault diagnosis
Simulation and analysis of blood flow in bypass grafts with a cuff
Get PDFIn the paper the hemodynamics in the blood vessel and in the bypass graft is simulated and analyzed. A new construction of a bypass graft with a cuff is applied. The goal of the research is evaluation of influence of the ratio between the length and the height of the bypass graft cuff upon the structure of the blood flow and pathogenesis of the blood vessel. The results of the analysis indicate that blood flow velocity at a junction of the bypass graft and the blood vessel depends on the parameters of the cuff. The best results are obtained when the said ratio is 1.25 and 1.5 due to uneven distribution of pressure in the cuff. Choosing such parameters of a bypass cuff ensures better hemodynamics and absence of haemostasia, thus reducing a risk of formation of thrombi in the bypass graft and the blood vessel
Characterization of mechanical properties by inverse technique for composite reinforced by knitted fabric. Part 2. Experimental evaluation of mechanical properties by frequency eigenvalues method
Get PDFThis paper is the second part of the research work dedicated to evaluation of mechanical properties of polymer composites reinforced by knitted fabric. Three different approaches were applied for the task. Two of them: a) FEM analysis using Solid Works combined with structural modeling based on experimentally-determined mechanical and geometrical properties of the reinforcement and matrix, and b) direct measurement of mechanical properties (described in Part 1). Present investigation (Part 2) is based on application of vibrational analysis. Modal testing in combination with the mathematical optimization procedure were used for evaluation of elastic properties of a layered material. It is worth mentioning that the application of this approach for materials with high damping ability (laminated composites reinforced by knitted fabric) is still poorly investigated. The inverse technique exploited in this work is based on the direct orthotropic plate free vibration measurements and subsequent mathematical optimization procedure (the planning of experiments or response surface technique), which is based on minimization of error functional. Finally, elastic constants established by the inverse technique were discussed and compared with the results obtained in Part 1
Vibration analysis of geared rotor system under time varying mesh stiffness effects
Get PDFThe present work contributes to the analysis of the interactions between gears, shafts and journal bearings in a geared rotor-bearing system. Although there are analyses for both of the gear and rotor-bearing system dynamics, the coupling effect of the nonlinear variable pressure angle and geared rotor-bearing system is deficient. In contrast to the majority of the models in the literature, the variable mesh stiffness and pressure angle are introduced in this paper while they were considered as constant in previous models. The equations of motion for the geared rotor- bearing system are obtained by applying Lagrange’s equation, and the Runge-Kutta numerical method is used to solve the equations of motion. Numerical results of this study indicated that the proposed model provides realistic dynamic response of a geared rotor-bearing system
Novel attitude control devices for CubeSat satellites
Get PDFIn recent years a very modern trend of space exploration activities – constructing, launching and operating nano-satellites, became very popular. One of the main problems in implementation and control of nano-satellite is ensuring accurate yet simple and small-sized attitude control equipment. Most of the equipment implemented for that task in the past was large, bulky and could be hardly used on extremely small CubeSat standard nano-satellites. The equipment under development for attitude control of the satellites is described in this paper. The equipment relies on implementation of piezoelectric transducers for rotation of spherical body – reaction sphere, thus ensuring precise three-axis attitude control of the satellite by means of single device. Description of the device under development with some calculations and examples of implementation of such instrumentation is further described in the paper
Development of a system to obtain vertical track geometry measuring axle-box accelerations from in-service trains
Get PDFNowadays, metropolitan railway systems are in great demand, so they offer highfrequency services for the most part of the day. Therefore there are only a few hours available at night to carry out maintenance tasks. This research develops a system that records vertical accelerations undergone by the bogies of in-service railway vehicles. As accelerations are measured during regular services of trains, no additional vehicles or personnel are needed and maintenance planning is optimized. Accelerations are processed to obtain vertical track alignment in order to determine whether the track needs repair. The developed system has been validated by comparing its results to the actual state of the track provided by a track monitoring trolley. Comparison is performed by using both graphical and statistical methods. Real data was obtained from measurements taken on Line 1 of the Alicante tram network (Spain). This paper presents procedure for data collection, its mathematical processing and analysis in order to identify track condition
Frequency analysis of chatter vibrations in tandem rolling mills
Get PDFChatter in high speed tandem mills affects the quality of the product and the production rate of the rolling mill. It may also cause damage to mill components and strip rupture. To monitor chatter generation within the rolling mill, it is highly recommended to use online chatter detecting systems. This paper presents a set of guidelines to optimal control and prevention of chatter in rolling mills. Investigation is based on experimental results of the third octave chatter in a two-stand tandem rolling mill. Online vibration monitoring system that was used has provided different acceleration signals from various components of the rolling stand. Acceleration signals have been analyzed by a vibration analysis toolbox. Frequency analysis and signal processing techniques were used for examining the vibration data. From frequency spectrum analysis it is found that the prominent frequency in the vibration spectrum of the upper backup roll is the most significant one. It is demonstrated that the upper backup roll and top housing are more sensitive to chatter than the work rolls and they are suitable locations for installing the permanent acceleration sensors for chatter warning system