Papers by Keyword: Random Load

Abstract: This study presents random load forecasts for the Nigerian 330 kV 38-bus transmission grid using a complex trend analysis technique. By considering randomness of monthly load peaks and normal distribution function, yearly load mean and confidence intervals were predicted for the transmission buses from an obtained 10-year historical load population. Also using the proposed algorithm of the mentioned technique, long-term random load forecasts for the transmission system were obtained. The obtained forecasts were compared with results from an earlier prediction model created for the same grid, which comprises a Monte Carlo technique that considers the location’s predominant control variables as population and GDP growth; the maximum obtainable error was 24%. The obtained results of forecasts and comparison are applicable for determining effective transmission system planning policy in Nigeria for the forecast period.

Abstract: To study the fatigue damage of a cutter used for cutting cashew nut, the integrated
simulation platform is established with Hypermesh, LS-Dyna, LS-PrePost, and nCode GlyphWorks.
The simulation model is established by Hypermesh. LS-Dyna is used to calculate the k file.
LS-PrePost is used as the post-processing software. The rain-flow counting, load superposition and
extrapolation are executed using Rainflow module in nCode GlyphWorks. The analysis of the
fatigue damage of the cutter is executed using Stress Life module in nCode GlyphWorks. The
equivalent stress time history of different elements in the upper and lower cutters, rain-flow
counting histogram after load spectrum superposition, rain-flow counting histograms after load
spectrum extrapolation, and damage histogram of the cutter are obtained. The results show that the
cutter has excellent mechanical properties, and the minimum fatigue life of the cutter is about 495
days, which is a conservative solution.

Abstract: A fatigue life prediction tool was developed for caliper guide pins under random vibrational loading. The Pie-Slice model was designed to provide detailed information about the failure location, orientation, and damage magnitude. A component test fixture was developed to determine the strain-life curve for a given guide pin design. Statistical analysis was conducted to insure the repeatability of the failure mode and the robustness of the setup. Weibull analysis was performed to the measured guide pin strain-life in order to insure that the developed strain-life data to insure that developed strain-life curve will account for all the manufacturing process variations, from a component, assembly, and a system level to a certain level of reliability and confidence. Rainflow cycle count was used to bin the damaging and non-damaging cycles based on their stain level. Fatigue life calculation was performed using the Smith-Watson-Topper strain-life approach. The predictive tool was able to accurately estimate the cumulative fatigue damage for guide pins under random loading conditions. The Pie-Slice model was also able to predict the failure location and orientation of a crack, as well as the damage magnitude. Both tools were validated using a pre-designed random block-load sequence at constant amplitude..

Abstract: Aim at the dynamic reliability of stochastic truss structures under stationary random excitation. In consideration of the randomness of structural physical parameters and the geometric parameters and the random excitations were first transformed into sinusoidal ones in terms of the pseudo excitation method ( PEM) , that turned the joint-random problem into a single random problem for which only structural parameters remain random, and thus the analysis is greatly simplified. The mean value and the variance of the mean square value of the structural displacement and velocity were computed by using the theory of spectral analysis. And then the expressions of stochastic truss structural dynamic reliability were educed from the Poisson formula. Finally, the influence of the randomness of structural parameters on the structural dynamic reliability was analyzed by an example; the method of this paper was proved feasible and available comparing with the Monte Carlo method.

Abstract: Gear box in caterpillar is designed with the static strength theory. While the dynamic characteristics of planetary parts in different working condition is difficult to obtain with the limit of traditional method, so research on reliability and fatigue life prediction of gear box is very difficulty which result that designed life is much longer than practical life. The reliability of caterpillar is affected deeply. The dynamic loads suffered by gear box in different working condition is obtained based on running simulation with MSC.ATV, and then the fatigue life of planetary frame is calculated with fatigue life prediction system of gear box. The study case prove the new method is feasible.

Abstract: Nonlinear dynamics model of the C₆₂ freight car was established firstly and the random load spectrum acted on the wheelset was obtained by the simulation of the freight car running on a typical line. Taking the cyclic constructive relation of LZ50 axle steel into account in the finite element analysis of the wheelset, the stress time histories of the key parts of the axle in some typical conditions were got. Furthermore, based on the stress spectrum analysis of the hazard sections of the axle, the probabilistic fatigue stress spectrums with given probability and confidence were obtained. Finally, combining with the linear cumulative damage rules, the stress distribution of RD₂ axle was investigated, which is fundamental for the further prediction of the fatigue life of axle.

Abstract: In order to study characteristics of loads on a cutting drum of a continuous miner, a mathematic model of random loads on the drum is set up in the paper by means of defining probability distributions of three-direction loads, loads and their variations on a cutting drum are given by building a computer simulation program when it cuts pure coal, rock and hard parcel. Results show that swing resistance is the greatest, forward resistance is the second, axial resistance is the least; a cutting resistance torque increases with the increase of broken media strength; loads cut stone layer are much larger than pure coal; range of load change and load fluctuations are big as cutting hard parcel, these conclusions are correspond with the actual situation.

Abstract: For the bending fatigue under the random load condition, the Miner cumulative fatigue theory was analyzed qualitatively. Random amplitude fatigue load spectrum for experiments was compiled according to that gears work under the load with Gaussian distribution load spectrum. Gear bending fatigue was carried out by the method of group test under the conditions of random load on the electro-hydraulic servo testing machine. Then the P-S-N curve of bend fatigue was got under Gaussian distribution load spectrum with particular coefficient of variation. Experiments prove that fatigue life from the result of random luffing amplitude fatigue experiments is lower than that from constant amplitude fatigue experiments, in which the upper limit of fatigue loads is the mean of load spectrum. It will be not reliable to estimate the bending fatigue life of gears that in the actual service.

Abstract: The first excursion failure criterion was introduced to calculate the dynamic reliability of drill string elements. Considering the random of geometry size and mechanical property parameters of drill string in deep & ultra-deep wells, the drill string system was dispersed into several basic elements according to the structure, strength and differences in the nature of formation rock in the well depth direction. And the overall dynamic reliability was quantitatively calculated through the serial theory. Through an example, the results show that the dynamic reliability of the drill string elements appeared fluctuation near the depth of 4500 meters for the inside worn of the drill string and casing, and uneven loading of drill string. The dynamic reliability of drill string in deep and complicated formation was less than any other drill strings. The drilling pressure, rotation speed and drilling depth were the main influencing factors on the dynamic reliability of drill string.

Abstract: Structures often enduring random amplitude load or multilevel amplitude load. However, the test researches on fatigue often using equivalent amplitude load. It is very important for fatigue research that how to accurately evaluate structure’s fatigue properties of random amplitude load or multilevel amplitude load when only using equivalent amplitude load fatigue test results. According to damaging degree equivalent principle of multilevel amplitude load or random amplitude load, deduced equivalent stress amplitude calculation formula using linearity Miner accumulative damage rule and Corten-Dolan accumulative damage rule. Introduced the formula’s using method on fatigue detail or fatigue life evaluation. Utilizing the S-N curve and S-N equation from RC beams fatigue experiment, verified the formula aiming at 3 RC beams’ random amplitude fatigue experiment results, and it is indicated that the formula’s results had quite high precision and approached the experimentation result though it is partial security. The formula operated convenience and it had higher precision compared to similar formula, so the formula suit for engineering application.