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Optimization on the jet characteristics of the main nozzle of hot-blowing snow removal device
Get PDFThe exhaust devices used by snow removal vehicles are mainly based on hot-blowing snow removal. Due to the inherent characteristics of the turbojet engine such as low flow rate and high exhaust temperature, the modified hot-blowing snow removal device has problems of low snow removal efficiency and the possibility of ablation and damage to the road surface. In order to solve the problem, transforming the turbofan engine with a high flow rate and a low exhaust temperature into a hot-blowing snow removal device is an important improvement to achieve efficient and safe snow removal operations. In order to convert a medium bypass ratio turbofan engine into a hot-blowing snow removal device, the computational fluid dynamics (CFD) software CFX was used to analyze the internal and external flow field characteristics of the main nozzle of an exhaust device under the 60 % rated condition of the engine. The effective area sizes of the jet velocity and temperature predicted by the external flow field were used to optimize the layout of the main nozzle
Repetitive impacts recovering using variational mode extraction with constructed reference enhanced by improved blind deconvolution
Get PDFThe impulse and modulation characteristic of rolling bearing’ faulty signal is often very weak when early fault arises in rolling bearing or gears, and the main reasons are due to the signal attenuation caused by too long signal acquisition path and the interference of other multi-source vibration. In order to extract the weak feature accurately, a method named as variational mode extraction (VME) based on constructed reference enhanced by improved minimum entropy de-convolution (IMED) is proposed, which combines both the advantages of IMED in solving the influence of the long signal acquisition path and VME based on constructed reference in extracting the impulse and modulation characteristic of vibration signal. Firstly, IMED is used as signal preprocessing method to analyze the vibration signal of rotating machinery to eliminate the influence of long signal acquisition path and enhance the repetitive impulse characteristics. Then, reference signal is constructed according to the prior knowledge of the rotating machinery and input it with the output signal of IMED into the VME model together, and the output result of VME not only could further enhance the impulse characteristic of vibration signal, but also obtain the modulation characteristic simultaneously. Finally, envelope spectral or enhanced envelope spectral is performed on the output signal of VME and satisfactory fault features are extracted. In order to solve the shortcomings of traditional MED, an IMED based on D-norm is proposed which has higher computational efficiency and could extract multi-harmonic impulse features. In addition, VME based on constructed reference is proposed to improve the accuracy of VME in extracting the target signal. Feasibility and superiority of the proposed method are verified by one experimental case and one engineering case
Failure mechanism on sulfate attack and dissolved corrosion of diseased tunnel lining structure
Get PDFTo study the corrosion failure mechanism of tunnel lining structure subjected to sulfate attack and dissolved corrosion, site investigation was carried out on a diseased tunnel in Chongqing. The corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the tunnel lining structure had been exposed to groundwater containing substantial concentrations of salts (SO42-, HCO3-, et al.) for many years, resulted that the concrete strength was lower than its design value. The formation of thaumasite made concrete lose its strength completely. Concrete structure would be destroyed when crystallization pressure exceeded the tensile strength of concrete. The tunnel also appeared dissolved corrosion which made the cement stone density and concrete strength reduce
A position optimization strategy of the dynamic vibration absorber for the noise control of the power equipment
Get PDFPower equipment shows obvious low frequency line spectrum noise characteristics due to the power frequency. The effective noise control of the power equipment can be achieved by installing dynamic vibration absorbers (DVAs) on the structure surface of electrical equipment. However, if DVAs are not installed properly, considering the cases that they are installed at the vibration mode node position, the low radiation vibration mode and the redistribution of the integrate vibration power, the vibration and noise absorbing performances of DVAs may degrade. In order to achieve efficient vibration absorption and noise reduction on the power equipment, this paper proposes a low-frequency noise reduction technology for power equipment based on DVAs. The position optimization of the DAVs using in the power equipment is studied for the first time. Aimed at the single frequency radiated sound power of equipment, the integrate radiated sound power of the equipment is minimized through adjusting the position parameters of DVAs. A numerical case is studied to verify the effectiveness of the proposed DVAs position optimization. The results show that the noise control effect of the power equipment with the optimized DVAs is significantly improved. The method proposed in this paper solves the noise problem of the power equipment, which provides reference for power noise control
Bearing fault feature selection method based on dynamic time warped related searches
Get PDFTraditional feature selection algorithms rarely consider the dynamic misalignment between different time series, and have poor fault tolerance and robustness. In this paper, a fault feature selection method for rolling bearings based on Dynamic Time Warped Related Searches (DTWRS) is proposed. Firstly, the bearing fault feature set is constructed, and the dynamic time warping algorithm is used to calculate the shortest cumulative distance between feature of different faults, and this distance is used as the correlation evaluation standard. Then, two new search rules, dynamic time warping difference and dynamic time warping entropy, are proposed based on the minimum redundancy between bearing fault features and the maximum correlation between fault features and feature categories, use these two search rules to judge the ability of the feature to express the fault, define the quality of the fault feature and sort from good to bad according to the level of ability. Finally, in this order, the number of features is gradually increased and input to the fault classifier, and the sensitive fault feature set is obtained based on the principle of the highest recognition rate and the least number of features. The experimental results show that the fault feature selection method of rolling bearing based on DTWRS can increase the accuracy of fault diagnosis while minimizing the number of features, and improve the efficiency and effect of fault diagnosis
Analysis on the seismic wave caused by low frequency sound source in shallow sea based on multi-transmitting formula artificial boundary
Get PDFThe elastic waves propagating in seabed caused by sailing ships are called ship seismic waves, which can be used to identify ship targets. The wave components and the influences of source frequency, source depth and depth of seawater to the seismic waves are important to the application of seismic wave to detect ship targets. Thus, a forward numerical simulation of seismic waves in shallow sea excited by low frequency sources in time domain was carried out with finite element method based on the Multi-Transmitting Formula artificial boundary. The numerical results show that the body waves and conical waves decay faster in space, but the interface wave decays relatively slow. Multi-transmitting Formula (MTF) artificial boundary has achieved good transmitting effect for longitudinal wave, upstream and downstream acoustic wave and transverse wave. When the source frequency is very low and the seawater layer is shallow, due to the effect of low-frequency cutoff, there is no normal mode wave which can propagate without attenuation in the seawater waveguide, and only the interface wave is propagating near the sea bottom surface. When the frequency of the source or the depth of the seawater layer increases, the effect of low frequency cutoff in the shallow water waveguide is weakened, and the normal mode waves propagating in seawater layer are gradually excited. The intensity of the interface wave caused by low-frequency point sound source mainly depends on the distance between the source and the seafloor
Vehicle state and parameter estimation based on double cubature Kalman filter algorithm
Get PDFObtaining vehicle status in real-time and accurately during the driving process is of great significance for active safety control of the vehicle. In response to this problem, combining a 7-DOF vehicle dynamic model and the magic formula tire model, the research designed a time-sensitive and robust double cubature Kalman filter (DCKF) observation algorithm. The DCKF algorithm addressed singular value decomposition to optimize the error covariance matrix, and connected driving state observer information of the vehicle to update the observation signal realizing the real-time estimation of the vehicle state. The DCKF algorithm is verified on the simulation platform, and compared and analyzed with the virtual test with CarSim data. The results show that the DCKF algorithm has faster response speed, higher precision of the estimation of the vehicle state, and stronger real-time performance
Investigation and optimization of the cable force of a combined highway and railway steel truss cable-stayed bridge in completion state
Get PDFIn order to study the reasonable cable force of a highway and rail dual-purpose steel truss cable-stayed bridge in the completion state, this paper employs four methods, i.e. the rigid supported continuous beam method, bending minimum energy method, influence matrix method and BP neural network method combined with a genetic algorithm. The Baijusi Yangtze river bridge, with a main span of 660 m in the completion state, is chosen as the object of study. Through comparative analysis, it is found that the rigid supported continuous beam combined with the influence matrix method can determine the reasonable cable force of the highway and rail dual-purpose steel truss cable-stayed bridge more quickly and effectively
Vibration analysis of reconditioned high-speed electric motors
Get PDFThis paper discusses the issue of assessing the condition of three-phase induction motors (which are used as power units for tools on manufacturing lines in the furniture industry) following major repairs. These high-speed motors differ from standard motors in higher frequency power input, more durable bearings and reinforced structure of the terminal part of the rotor shaft. The rotational speed of the rotor is 10,000-18,000 rpm. Such high values of rotational speed trigger a situation in which exceeding the allowable limit of residual unbalance for the rotor unit damages the motor. The damage might necessitate a comprehensive repair. Such cases are frequent. The conducted studies resulted in designing a vibration analysis for assessing the condition of reconditioned high-speed motors (a method for controlling the quality of repairs). Both high- and low-frequency analyses with a signal selection module and the basic general measurements were applied. The analysis provides the possibility of verifying the efficacy of reconditioning in relation to the mechanical validity of the repaired motors
Natural frequency analysis of a functionally graded rotor system using three-dimensional finite element method
Get PDFThree-dimensional Finite Element (FE) analysis has been carried out using ANSYS software to study the natural frequencies of functionally graded (FG) rotor system. Temperature and position-dependent material properties of the FG shaft system are considered to be graded in the radial direction. Power-law with the nonlinear temperature distribution (NLTD) and exponential law with exponential temperature distribution (ETD) have been used to model the material gradation and temperature distribution. Rotor systems of two different FG materials, namely Stainless Steel-ZrO2 and Stainless Steel-Al2O3 have been studied. Python codes have been developed to generate ANSYS macros that apply the material properties. Simply supported FG shaft and FG rotor system supported on bearings have been analyzed in the current work. The results show the influence of different power-law coefficients, different material and material laws on the natural frequencies of the rotor system. The effect of these parameters on whirl frequencies has also been studied for FG rotor systems