Current Issue : October - December Volume : 2020 Issue Number : 4 Articles : 5 Articles
Vibration signal, as an important means for diesel engine condition detection and fault diagnosis, has attracted attention for many\nyears. In traditional vibration signal analysis, most processing methods are for single-channel data. However, single-channel\nvibration signal cannot reflect the operating information of the diesel engine comprehensively because diesel engine vibration is\ncoupled by multiple source signals. This paper proposes the MVMD band energy method for fault diagnosis by four channels of\nvibration signals. First, the original multivariate signals are decomposed adaptively by MVMD, which obtains a series of\ncomponents with modal alignment. Then, the band energy values of each measuring point are calculated as the fault characteristics.\nFinally, SVM is used to realize the diagnosis and identification of diesel engine misfire. The working conditions have a\ngreat influence on the vibration signal of the cylinder. In order to obtain the best diagnostic working conditions, six working\nconditions are set for testing. The result shows that the fault identification rate is highest under the 1500 rpm and 50% load\nworking condition. The fault recognition rate of this method reaches more than 99%, which is superior to the other four\ncommon methods....
Friction stir welding (FSW) is a favorable welding technology for aluminum alloys. The FSW process involves complex heat and\nmass transfer. Explicit meshless particle methods are currently popular methods for simulating the process, but they require\nexpensive computational cost. Coupling explicit finite element method (FEM) and meshless particle methods can ease the\nproblem by making use of high efficiency of FEM and advantages of meshless particle methods. Though many efforts have been\nmade to couple FEM and meshless particle methods for transient dynamics problems, coupling them for transient heat transfer\nproblems is seldom addressed. In this work, we focus on treating this problem. We developed an explicit coupled method of FEM\nand the meshless particle method presented in a previous work and used it to simulate the thermal process during FSW. In the\nmethod, FEM using lumped heat capacity matrix and low-order numerical integration is constructed to obtain high efficiency. A\nnew coupling algorithm is proposed to link thermal calculations of the weak-form FEM and the strong-form meshless particle\nmethod. Forward Euler method is used for time integration to achieve an explicit algorithm. The coupled method is used to\ncalculate a numerical example having analytical solution. Calculated results show that it can achieve a good accuracy. The method\nis employed to simulate FSW of Al 6061-T6 plates. It predicts thermal cycles in good agreement with experimental results. It shows\nan accuracy comparable to that of the meshless particle method while having a higher efficiency than the latter....
The potential advantages of rotating detonation combustion are gradually approved, and it is becoming a stable and controllable\nenergy conversion way adopted to the propulsion devices or ground-engines. This study focuses on the rotating detonationbased\nturboshaft engine, and the architecture is presented for this form of engine with compatibility between the\nturbomachinery and rotating detonation combustor being realized. The parametric performance simulation model for the\nrotating detonation-based turboshaft engine are developed. Further, the potential performance benefits as well as their\ngeneration mechanism are revealed, based on the comprehensive performance analysis of the rotating detonation-based\nturboshaft engine. Comparisons between the rotating detonation turboshaft engine and the conventional one reveal that the\nformer holds significant improvements in specific power, thermal efficiency, and specific fuel consumption at lower compressor\npressure ratios, and these improvements decrease with the increase of compressor pressure ratio and increase as turbine inlet\ntemperature increases. The critical compressor pressure ratio corresponding to the disappearance of specific power\nimprovement is higher than that corresponding to the disappearance of thermal efficiency and specific fuel consumption. These\ncritical compressor pressure ratios are positively correlated with flight altitude and negatively correlated with flight velocity. The\nconductive research conclusion is guidable for the design and engineering application of rotating detonation-based engines....
In the present study, 1.86-mm-thick steel plates (UNS S32205) were friction-stir-welded at various rotation speeds of 300 to\n600 rpm and a constant welding speed of..................
Friction stir welding (FSW) is the most popular and efficient method for solid-state joining of similar or dissimilar metals and\nalloys. This technology is mostly applied in aerospace, rail, automotive, and marine industries. In order to reduce the weight of\nspecial auto parts, friction stir spot welding (FSSW) was proposed by some researchers for the connection of steel-aluminium\ndissimilar metals. However, the steel-aluminium joints welded by FSSW are prone to brittle fracture and have lower shear load\nalthough they have high mechanical connection strength. The friction stir spot welding brazing process integrates the brazing\neffects with the friction welding effects by the addition of solder. A study of FSSW of DP590 and 6061 with the filler metal added\nwas carried out in this paper. The orthogonal test was performed to optimize the process parameters in order to achieve the best\nshear load of the joint. The shear strength of the joint was studied by the shear test. The fracture morphology was investigated by\noptical microscopy (OM), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS). The results showed\nthat the shear load of the joint could reach 13.239 kN when the rotating speed, depth, and residence time of the mixing head were\n1000 r/min, 0.2 mm, and 90 s, respectively. The aluminium-zinc solder added could well wet the interface between aluminium and\nsteel and promote the metallurgical bonding, thereby improving the shear load of the joint. The temperature field of DP590/6061\nFSSW process was simulated by ANSYS software to verify the rationality of the optimal process parameters. The simulation results\nwere confirmed to be basically consistent with the data measured by the thermocouple....
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