Current Issue : January - March Volume : 2019 Issue Number : 1 Articles : 5 Articles
Prediction of minimum film thickness is often used in practice for calculation of film\nparameter to design machine operation in full film regime. It was reported several times that majority\nof prediction formulas cannot match experimental data in terms of minimum film thickness. These\nstandard prediction formulas give almost constant ratio between central and minimum film thickness\nwhile numerical calculations show ratio which spans from 1 to more than 3 depending on M and L\nparameters. In this paper, an analytical formula of this ratio is presented for lubricants with various\npressureâ??viscosity coefficients. The analytical formula is compared with optical interferometry\nmeasurements and differences are discussed. It allows better prediction, compared to standard\nformulas, of minimum film thickness for wide range of M and L parameters....
In this paper, a control method for a hydraulic loading system of an electromechanical platform\nbased on a fractional-order PID (Proportion-Integration-Differentiation) controller is proposed, which\nis used to drive the loading system of a mechatronic journal test rig. The mathematical model of the\ncontrol system is established according to the principle of the electro-hydraulic system. Considering the\nindetermination of model parameters, the method of parameter identification was used to verify the\nrationality of the theoretical model. In order to improve the control precision of the hydraulic loading\nsystem, the traditional PID controller and fractional-order PID controller are designed by selecting\nappropriate tuning parameters. Their control performances are analyzed in frequency domain and\ntime domain, respectively. The results show that the fractional-order PID controller has better control\neffect. By observing the actual control effect of the fractional-order PID controller on the journal test\nrig, the effectiveness of this control algorithm is verified....
Welding is a thermal process which results in high strain and stress values in the\nmaterial and leads to its change of phase. This might cause significant distortions in the welded\nstructure, which often becomes a relevant design and manufacturing issue. This study deals with\na line-heating-based forming process that is applied at the moment of the welding operation,\nwith the final objective of minimizing distortion. A FEM (finite element method) based on\na thermo-elastoplastic approach is used here. The computational method is first calibrated in three\nstages: heatline forming calibration, flame heat source calibration, and the weld process. The final\nmodel presented in this work simulates a hybrid process called htTTT (high-temperature thermal\ntransient tensioning) which was optimized over large T welds to minimize the final distortion of\nthe components...
Heat dissipation has become an important issue due to the miniaturization of various\nelectronic devices. Various methods such as spray and nozzle coolers, heat sinks and so on are\nused for heat dissipation. However, the emergence of ferrofluids drastically improves the operating\ncharacteristics of electromagnetic systems and devices. A ferrofluid is a suspension containing\n10-nm magnetic particles in a colloidal solution. This material exhibits paramagnetic behavior and is\nsensitive to magnetic field and temperature. In this study, heat transfer characteristics of ferrofluids\nin a rotating eccentric cylinder were investigated using the commercial code, COMSOL Multiphysics.\nNumerical results of the local Nusselt number, magnetophoretic force and velocity distributions were\nobtained from various eccentricities of the cylinder, and the results were graphically depicted with\nvarious flow conditions....
This research aims to analyze the vibration response of damaged rolling element bearings\nexperimentally and to assess their degree of degradation by examining parameters extracted from\nthe time domain. This task was accomplished in three phases. In the first phase, a test rig was\ncarefully designed and precisely manufactured. In particular, an innovative solution for rapidly\nmounting and dismounting bearings on the supporting shaft was tested and used successfully. In the\nsecond phase, a specific technique of seeding defects inside the ball bearings was developed. In the\nlast phase, damaged bearings (and healthy ones serving as a reference) were installed on the test\nrig, and different vibration measurements were taken. The results obtained from this work show\nthat different parameters could be extracted from the time domain. In addition to the six common\nindicators (peak, root mean square, crest factor, kurtosis value, impulse factor, and shape factor),\nfour hybrid new ones have been proposed (Talaf, Thikat, Siana and, Inthar). The experimental results\nconfirm the well-known efficiency of kurtosis in the detection of bearing defects. However, the newly\nproposed parameters were found to be more responsive to defect growth....
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