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Reliability analysis of an engine under uncertainty based on D-S evidence theory and Bayesian network
Get PDFThere are many methods applied including Bayesian network and D-S evidence theory to cope with uncertainty involving aleatory uncertainty and epistemic uncertainty in reliability analysis of complex systems. This paper introduces theories of these two methods briefly, and then conversion rules that convert fault tree into Bayesian network under uncertainty are put forward, including AND node, OR node, XOR node, NOT node and Two-out-of-three vote node. Comparing to probability importance, structural importance and criticality importance, epistemic importance is given to measure the influence of root event to top event. At last, a type of engine is taken for example. Bayesian network model is established by referring to the fault tree of the engine, and D-S evidence theory is used to determine the belief functions and plausibility functions of uncertain nodes by data fusion. Weak nodes in reliability design and distribution are pointed out after reliability assessment, importance analysis, and backward reasoning. And corresponding measures can be taken to improve the reliability of the whole system
Manufacturing and characterization of CNT based polymer composites
Get PDFCarbon nanotubes have been the concentration of all-encompassing research due to the excellent mechanical, thermal, electrical and magnetic properties. In the present work fifteen specimens of polymer composites is manufactured, multi walled carbon nanotubes (MWCNT’s) are considered as filler material for proposed volume based amount and for three unique direction of E glass fiber. The effect of different percent loadings of MWCNTs on the morphology and thermal behavior of the composites had been inspected. Thermal analysis investigation showed that a clear improvement of thermal stability of composites increased with increasing MWCNTs content. The experimental results are compared with statistical results and found to be in good agreement
Modeling and simulations on automated vehicles to alleviate traffic congestion
Get PDFAutomated vehicle technologies have the potential to improve traffic efficiency, stability and safety. Some models of mixed traffic are presented, which consist of automated vehicles and regular vehicles. First, a differential equation model based on automated vehicles is developed by regarding the traffic flow as a whole and using three continuous variables (traffic density, driving speed and traffic volume) to reflect the basic characteristics of traffic from the macroscopic perspective. Second, by taking into account (1) Actual Expected Speed Ratio (AESR), (2) Change Lane Count (CL), (3) Backward Distance (BD), and (4) Over Take (OT), the traffic flow evaluation model is established. Furthermore, by selecting locations randomly, we take the average value of the five cellular automata to the simulating results and validate the reliability of the model in the tolerance. Finally, optimal solutions to accommodate automated vehicles are given
Vibration-based damage detection in beams by genetic algorithm encoding locations and damage factors as decision variables
Get PDFVibration-based damage detection is based on the fact that vibration characteristics such as natural frequencies and mode shapes of structures are changed when the damage is happened. The vibration-based damage detection of a beam is formulated as a single-objective optimization problem in which genetic algorithm (GA) is used as the optimizer. This paper presents the encoding by locations and damage factor (ELD) which employs location and damage amount as the decision variables. The proposed encoding can reduce the number of decision variables that used in the previous encoding, the encoding by damage factor of each element (EDE). The search space of GA with ELD is then smaller than that of GA with EDE. The simulation results reveal that GA with ELD can identify the damage occurred in the beam more correctly than GA with EDE. Moreover, the damage predicted by GA with ELD is quite close to the actual damage for all 3 test cases
The influence of the smoothing component on the quality of algebraic forecasts
Get PDFShort term time series forecasting model with different internal smoothing techniques is presented in this paper. Computational experiments with real world time series are used to demonstrate the influence of different smoothing techniques in fitness. Algebraic forecasting results with any internal smoothing model outperformed results of the algebraic forecasting without smoothing
Transverse failure modes and control strategies of super long-span cable-stayed bridge under extreme earthquake
Get PDFThis work is focused on the failure modes and control strategies of a trial designed super long-span cable-stayed bridge (Abbr. CSB) with a main span of 1400 m under various seismic intensities, exploring the key characteristic of the failure modes of super high tower. Then several control strategies, such as the use of conventional viscous fluid dampers (Abbr. VFDs) and a new combination strategy comprising sacrificial inelastic links and conventional VFDs, are presented for the failure modes improvement and the seismic damage mitigation of the CSB under extreme earthquake (PGA = 1.0 g). It is found that the super high tower experiences an unexpected failure mode with double plastic hinges that shows a new characteristic on the tower failure in the transverse direction, which is different from that of the short- and medium-span cable-stayed bridge during earthquake excitation. Whereas the piers show a typical and expected flexural failure mode with only one plastic hinge in the transverse direction. Although conventional control strategies using the optimal VFDs can help to significantly reduce the seismic damage of the CSB, they cannot entirely make the tower satisfy seismic control targets. It is also observed that the new combination strategy can successfully improve the failure mode and seismic damage of the CSB that satisfies seismic control targets, the effects of proposed combination strategy on the CSB are superior to those of the convention control strategy with the optimal VFDs
Incremental dynamic analysis of SDOF by using nonlinear earthquake accelerograms based on modified inverse Fourier transform
Get PDFIn evaluation of structures, performing nonlinear response of model over a time analysis or incremental dynamic analysis needs more time. Hence, it can be beneficial if the event history report is carried out with long time steps without loss of accuracy. This study includes a method to simplify of accelerograms meant on the change of their Fourier reports. So, the Fourier Spectrum of the accelerogram is initially determined. Next applying a PC code generation, the similar Inverse Fourier Convert is computed utilizing a comparatively large time stage, depending on the structure’s times; that is ordinarily five to ten times bigger than primary accelerogram’s duration stage to generate the visible accelerogram. This application from the simplified accelerogram apparently takes much less time. Results indicates that the analysis time can be reduced up to 80 % by using the proposed method. While the maximum response shows an error of merely five to ten percent, about the sort of structure and the characteristics of the records used
Numerical computation for the impact of flow rate and rotational speed on the flow-induced noise of the centrifugal pump
Get PDFThis paper adopted an indirect mixed method (computational fluid dynamics + boundary element method) based on computational fluid dynamics + Lighthill acoustic analogy theories to compute the flow field and flow-induced noise of the centrifugal pump, and experimentally verified the correctness of computational results. The pressure distribution of the centrifugal pump through an unsteady computation showed that there were obvious separation vortexes at the outlet of the centrifugal pump and pressure at the edge of impellers was obviously more than that of other parts. There were many peak noises on the sound pressure level curve at the outlet of the centrifugal pump. The sound pressure level gradually decreased with the increased frequency. However, sound pressure levels will be a stable value when the analyzed frequency was more than 3000 Hz. Sound pressures at the inlet and outlet of the centrifugal pump were relatively large. Sound pressures at the inlet pipeline gradually decreased from outside to inside and sound pressures of outlet pipeline gradually decreased from inside to outside. The structure of the centrifugal pump was not completely symmetrical, and the sound field was not symmetrical. In addition, the radiation noises in the external field at the inlet and outlet of the centrifugal pump were similar to the radiation of many point sound sources. Peak values of flow-induced noises at the outlet of the centrifugal pump were more than those at the inlet of the centrifugal pump under the working condition of different rotational speeds and flow rates. In the meanwhile, sound pressure levels at the inlet and outlet of the centrifugal pump did not show many differences in amplitudes when the rotational speed was small. When the rotational speed reached up to 3000 r/min, the sound pressure at inlet was more than that at outlet within 1500 Hz-4500 Hz. At many peak frequency points, peak noises at outlet were obviously more than those at inlet, which thus proved that fluid caused large pressure fluctuations due to the interaction between impellers and volutes after flowing through the centrifugal pump and flow-induced noises caused by pressure fluctuations were mainly reflected in blade frequency. The change of the rotational speed and flow rate would not only increase the flow-induced noise in the centrifugal pump, but also seriously affect the external radiation sound field of the centrifugal pump
Energy absorption characteristics of cement-soil under confining pressure based on SHPB test
Get PDFCement-soil has been widely used for engineering application. However, no attention has been paid to the energy absorption characteristics of cement-soil under impact loading. In this paper, a series of split Hopkinson pressure bar (SHPB) tests have been conducted to explore the energy absorption characteristics of cement-soil, and the effects of confining pressure (from 0 to 2.0 MPa) and strain rate (from 130 to 172 s-1) on the absorbed energy and the energy absorbency rate are investigated. The results show that the energy evolution of cement-soil under confining pressure is found to be similar at different strain rate. Both the absorbed energy and the energy absorbency rate are influenced by the confining pressure. Moreover, both the absorbed energy and the energy absorbency rate increase at first and then remain stable at a certain value with the increase of confining pressure. In addition, the absorbed energy linearly increases with the incident energy increasing, and a similar tendency is found between the absorbed energy and the strain rate, yet no obvious effect on the energy absorbency rate by the strain rate. Moreover, the energy mechanism of cement-soil is explained from the perspective of failure modes of cement-soil specimen
Discrete phase numerical analysis of servo valve nozzle
Get PDFIn order to study the polishing quality of abrasive flow, The FLUENT15.0 software is used as the platform, taking the way that LES (Large-eddy simulation) model is combined with the Mixture model, the numerical simulation of Grain Flow Processing was carried out by regarding the servo valve nozzle as the research object. The results turn out that with the increase of the inlet speed, the flow state of the abrasive flow is more disorderly, and there is a dramatically improvement in dynamic pressure, which indicates that the collision and friction between the abrasive grains and the wall is more intense. In addition, the vortices and turbulence are more apparent, which are conducive to improving the polishing efficiency of abrasive flow so that achieve precision machining