Journal of Engineering and Thermal Sciences
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A hybrid frequency response function formulation for MDOF nonlinear systems
Get PDFThis paper introduces a hybrid technique for formulation of frequency response functions (FRFs) for nonlinear MDOF systems, based on the Structural modification using frequency response function (SMURF) technique. The technique can produce FRFs at the desired coordinates on the structure. The term “hybrid” indicates that the underlying linear system is reduced by expressing it in FRF form, while the nonlinearities are treated in the form of describing functions based on spatial elements. The method uses several FRFs instead of the spatial model therefore it is characterized by lower computational costs. Moreover, the experimentally measured FRFs of the underlying linear structure can be applied in this technique. A system with cubic stiffness and friction damping nonlinearities is used as a numerical case study to verify the proposed technique
Seismic analysis of the condensate storage tank in a nuclear power plant
Get PDFFollowing the nuclear power plant accident in Fukushima Japan, seismic capacity evaluation has become a crucial issue in combination building safety. Condensate storage tanks are designed to supplies water to the condensate transfer pumps, the control rod drive hydraulic system pumps, and the condenser makeup. A separate connection to the condensate storage tank is used to supply water for the high pressure coolant injection system, reactor core isolation cooling system, and core spray system pumps. A condensate storage tank is defined as a seismic class I structure, playing the important role of providing flow to the operational system and the required static head for the suction of the condensate transfer pumps and the normal supply pump. According to the latest nuclear safety requirements, soil structure interaction must be considered in all seismic analyses. This study aims to rebuild the computer model of condensate storage tanks in Taiwan using the SAP 2000 program in conjunction with the lumped mass stick model and to evaluate the soil structure interaction by employing the SASSI 2000 program. The differences between the results with the soil structure interaction and spring model are compared via natural frequency and response spectrum curves. This computer model enables engineers to rapidly evaluate the safety margin of condensate storage tank following the occurrence of earthquakes or tsunamis
Entropy-based fault detection approach for motor vibration signals under accelerated aging process
Get PDFThe purpose of this study is to analyze motor vibration signals due to the bearing fault, which is artificially generated by aging process. Vibration signal data recorded by the experimental setup has been conditioned by a high-pass filter (Butterworth type) to reach the regarding frequency components of the bearing failure. Spectral analysis has been applied to realize the degradation on the bearing and the power spectral density figures revealed that the magnitudes of frequency components between 1.5-4 kHz bandwidth increased after every aging cycle. Vibration signals were investigated statistically by examining four main statistical parameters: mean value, standard deviation, skewness and kurtosis. Evaluation of these parameters indicated that significant variance occurred on standard deviation. At this point Shannon entropy became an approach to analyze the variance on the standard deviation. The probability of the aging cycles has been defined as a function of standard deviation values for each aging cycle. Entropy definition, which is a function of probability, determines the uncertainty level on the data and it has been examined to identify the effect of the aging progress on the bearing by examining the transferred entropy amount between aging cycles
Incipient defect identification in rolling bearings using adaptive lifting scheme packet
Get PDFDefects on the surface of rolling bearing elements are some of the most frequent causes of malfunctions and breakages of rotating machines. Defect detection in rolling bearings via techniques that examine changes in measured signal is a very important topic of research due to increasing demands for quality and reliability. In this paper, incipient defect identification method based on adaptive lifting scheme packet is proposed. Adaptive lifting scheme packet operators which adapt to the signal characteristic are constructed. The shock pulse value in defect sensitive frequency band is used as the defect indicator to identify the defect location and severity of rolling bearing. The proposed defect identification method is applied to analyze the experimental signal from rolling bearing with incipient inner raceway defect. The result confirms that the proposed method is accurate and robust in rolling bearing incipient defect identification
Ultrasonic systems for liquid pulverizer
Get PDFAnalyzing known liquid pulverizers which are driven by piezoelectric transducers we obtain that almost all of them are using longitudinal vibrating mode. So we decide to create a dual-effect system which will act as a pump and sprayer. Using FEM analysis the proposed model was analyzed and it is natural longitudinal frequency was found. Modeling results (frequency, displacement) were compared with real parameters of working transducer and they were nearly the same. The main study object was to find how fluid moves through a capillary under ultrasonic vibrations. The experimental results are populated below
A joint stiffness identification method based on finite element modeling and frequency response functions
Get PDFAccurate finite element (FE) modeling of mechanical structures is extremely difficult with unknown joints or boundary conditions. An alternative joint stiffness identification method that involves a hybrid of FE model and frequency response functions (FRFs) is presented. Firstly, the joint stiffness is assumed by experience and the mechanical structure is modeled with the FE method. Secondly, the FRFs at the concerned nodes of the structure are simulated and measured, respectively. Then the norm of residual FRFs between the simulations and measurements is calculated. Finally, a sensitivity-based iterative algorithm is derived for minimizing the norm of residual FRFs and the least square method is used to solve over-determined iterative equation. The joints stiffness parameters are identified through the iteration process, while the FE model is updated simultaneously. The proposed joint stiffness identification method is applied on a clamped beam assembly. The first three natural frequencies calculated by the FE model are compared with the measured values. The largest relative error of the simulation deceases from 16.7 % to 2.5 % after the joint stiffness parameters are identified, which demonstrates the effectiveness of the presented method
Impact of anti-intrusion beam effectiveness on reducing fatalities and injuries of vehicle occupants
Get PDFSide impact of vehicles is the second leading cause of fatalities and serious injuries in the traffic accidents after frontal collisions. The paper deals with the evaluation of effectiveness of anti-intrusion beam in vehicle side door. The presented analysis aims to determine the influence of the considered passive safety device on reduction of occupant fatalities and injuries. Results of dynamic numerical investigation are presented. The analysis of estimated deflection indicates the potential for reduction of the depth and velocity of door intrusion
Modifying the brake drum geometry to avoid self-excited vibrations and noise
Get PDFA squealing noise of 50 dB was measured on a vehicle homologation test at around 900 Hz on the existing brake drum design, mounted on the rear axle of the mid-sized passenger automobile. Therefore, analysis of eigenfrequencies of the original drum design was performed using the impact hammer test and numerical analysis. It was established that a critical mode shape 0/2 exists at around 900 Hz, exactly where the squeal noise was recorded at the brake road noise evaluation vehicle test. The analysis was carried out with the intention to eliminate the possibility of the squealing noise by increasing the critical mode above 900 Hz. The relation between different brake drum modifications parameters and the eigenfrequencies was determined and the best solution was obtained. The first eigenfrequency of the proposed drum design was increased by 58 Hz and the difference between the in-plane and out-of plane mode shape was sufficient. We can conclude that the modified drum design will not have squeal issues at 900 Hz as there are no eigenfrequencies of the brake drum in that range and therefore the problem of the loud brake is solved
ANN prediction and RSM optimization of cutting process parameters in boring operations using impact dampers
Get PDFThe cantilever shape of the boring bar induces chatter vibrations in boring operations. Chatter vibrations consequently lead to increase in tool wear. Present work focuses on the prediction and optimization of cutting process parameters using ANN and RSM methods for phosphor bronze damping material attached to the boring tool. All-geared head lathe with temperature measurement setup was used to conduct experiments for various levels of cutting speed, depth of cut and position of damper from the cutting edge. Tool wear was measured using profilometer, while the temperature and tool wear were accurately predicted using the developed ANN model. The minimum value of temperature of 2800 C and tool wear of 0.13 mm were obtained by using Response Surface Methodology for the following input conditions: cutting speed of 300 rpm, depth of cut of 0.25 mm and damper position of 65 mm from the cutting edge
Feasibility and principle analyses of morphing airfoil used to control flight attitude
Get PDFMorphing airfoil technology can enable an aircraft to adapt its shape to enhance mission performance and replace the traditional flap, ailerons, elevator and rudders to optimize flight attitude control efficiency. A set of optimal airfoil shapes are obtained aimed to minimize the aerodynamic drag character by optimizing morphing configurations at different under the two-dimensional steady-flow simulation. The traditional airfoil and morphing airfoil at different are compared. It is proved that morphing wing can be used instead of a traditional wing. Couples of traditional control surface and morphing airfoil are chosen to simulate and analyze the aerodynamic difference. The flow mechanism is described on the basis of aerodynamic simulations performed by CFX. It is demonstrated why the morphing wing can provide the same with a small