Key Engineering Materials Vols. 656-657

Abstract: It is absolutely important for ultra-compact rotational machineries to achieve sable shaft rotation at ultra-high-speed. This paper discussed herringbone-grooved aerodynamic journal bearing systems developed for the purpose. In this system, the bearings are supported by rubber-O-rings for accurate and stable operations. To grasp the possibility for stabilization, two types of O-rings with different stiffness and damping properties under bearing supporting were tested in the experiment. As the results, the bearing system demonstrated the maximum rotational speed over 460,000 rpm without unstable phenomenon called whirl. However, the difference in rubber O-rings definitely affected the stability of the bearing system.

Abstract: This study propose a new nonlinear model for offset printing press gear-cylinder-bearing system by the lumped parameter approach. The multi-DOF model consists of helical gear pairs and spur gear pairs with time-varying meshing stiffness. Bearing and shaft flexibilities are include in the model as well. The equations of motion are obtained by Darren Bell principle and Runge-Kutta numerical method is used to slove the equations of motion. The results show that meshing stiffness and bearing stiffness significantly affect critical speed, vibration acceleration and meshing force. Multi-body dynamics software are applied to compare with lumped parameter model. The results show that there are many similarities in different aspects. Results of experimental study on offset printing press are also presented for validation of different models. After Discrete Fourier Transform, the graphics display that acceleration peaks frequencies are an integer multiple of the gear mesh frequency. It demonstrate that mechanical vibration is mainly from gear transmission system at high printing speed and gear transmission system lead to nonlinear vibration. This work provide a foundation for further improvement of the dynamics of gear system.

Abstract: In this paper, a new fault diagnosis method is proposed based on CFD technology in order to research the fault mechanism of mine axial fan. The method combined RANS equation and Realizable k-turbulence model realizes the three dimensional aerodynamic performance analysis of the fan impeller. Three-dimensional impeller model of axial fan was set up in three conditions which including normal, crack and blade loose, and comparing the turbulence characteristic of the three models. The research provides the theoretical basis for the fault mechanism of blade failure, and it has important reference value for fault diagnosis method based on CFD of mine axial fan.

Abstract: J. C. Maxwell applied the quaternion analysis and vector terminology to study the physics properties of electromagnetic field. Nowadays the spaces of electromagnetic and gravitational fields can be chosen as the quaternion spaces, while their coordinates are able to be the complex numbers. The complex quaternion space can be used to describe the physics feature of forces in the electromagnetic and gravitational fields. The paper is capable of writing the terms of force into a single definition, including the inertial force, gravity, electromagnetic force, energy gradient and so on. Further the definition of force can deduce some new but weak terms of force. One of them is the ‘strength gradient force’. The strength gradient force relates only with the gradient and distribution of field strength, and is independent to the electric charge and mass. And this force is able to exert the interaction on neutral and charged particles. As the driving force, the strength gradient force can be used to drive precisely the motion of small mass, and applied to operate the precision machine. By analogy with the optical tweezers and magnetic mirror, the strength gradient force is possible to be applied to devices in the future, including in the precision machine for the focusing, the collimating of the polarization maintaining optical fibers and so forth.

Abstract: The open source code software, OpenFOAM, based on the computational fluid dynamics (CFD) was implemented to simulate the methane jet flame. The large eddy simulation (LES) of turbulence model was written using C++ language. The mixture fraction approach and infinitely-fast chemistry assumption was combined with this LES turbulence model. The results of jet flame simulation were validated with Yi Zeng et al., (2011) experiments based on flame lengths under flow rate and pressure conditions of 5.95-23.81 mg/s and 50-100 kPa, respectively. It was found that an average error of flame lengths obtained from the developed CFD model was 8.57% when referred the 1% O₂ remaining was a flame shape.

Abstract: The product quality of an ultra-precision spindle of milling machine is affected by many factors such as assembly tolerance, assembly process, and working circumstances. The purpose of this study is to find optimal assembly tolerance in order to enhance product quality. This study collects assembly parameters and testing results. In addition, those collecting data are used to train and test by the back-propagation neural network (BPNN) to obtain a quality index predictor so as to predict vibration level and temperature rise level. A variable control chart of SPC is employed to analyze the assembly tolerance data that impact on temperature rise level and vibration level. The results of the propose study not only increase the rotation accuracy and machining efficiency, but also decrease the vibration and temperature rise for ultra-precision spindle during operating.

Abstract: Hydrodynamic journal bearings induced serious shaft vibrations called oil whirl. Since they often give severe damages to the mechanical systems, it is important to fully understand the phenomenon to avoid the occurrence by the proper bearing design. This study theoretically and experimentally investigated both cylindrical and conical whirl instabilities, which can be appeared in journal bearings, and their relation was discussed. As the result, the span length of the bearings had a significant effect on the vibration mode. The transitional state in which the cylindrical and conical whirl instabilities alternately appeared was observed.

Abstract: In this study, a non-linear finite element model for a simplified single-bolted joint structure model is built. Static analysis on the structure under different shear force and pretension effect is done, and the non-linear contact behavior is analyzed. Through comparing datum, it is found that interface area of each bolted joint region can be described an annular region around bolt hole, whose outer radius has increased by 85% compared with radius of bolt hole. Also, the frequency responses of the multi-bolted joint structure under sinusoidal excitation are investigated. Simulation results show that the resonance regions basically remain unchanged in different pretension effect and the largest amplitude will increase with the increasing preloads. Finally, the vibration experiments are conducted. Interface nonlinear affect dynamic stiffness considerably. The test results illustrate that dynamic behaviors of bolted joint agree with the simulation results and the proposed non-linear contact model was reasonable.

Abstract: The blower is a kind of garden machinery, which blows strong wind to clean up leaves by a centrifugal fan, but it causes a loud aerodynamic noise. To compromise the contradiction between large air flow rate and low fan noise, some optimizations are proposed to reduce fan noise without lowering its air volume. In this paper, a CFD numerical model to compute airflow field of blower is established, where the centrifugal fan is simulated by the MRF model, and theturbulent model is selected. By smoothing the transition section, improving the volute tongue and optimizing the shape and optimizing number of fan blade, the blower work performance is increased obviously. In order to find out the actual working point, both the fan and motor load characteristic curves are drawn out. The simulation results show that, at the actual working point, the speed of the centrifugal fan is reduced, while the flow rate of blower is raised up. The optimizations are applied to the blower, and the experiment of the improved blower shows the flow rate is increased 5%, and the noise is reduced 2dB.

Abstract: An advanced method named hybrid FE-SEA method was introduced to study the acoustic radiation characteristic for cylindrical structure with elastic plate cap in medium-frequency region. This method consists of the finite element method (FEM) for low-frequency region and the statistical energy analysis (SEA) for high-frequency region, which can be employed to deal with the problem of acoustic radiation result from model coupling of elastic connection effectively. According to the FE-SEA theory, a hybrid model of cylindrical structure with elastic plate cap was built to validated whether the hybrid method was feasible to calculate the acoustic radiation in the medium-frequency region. Moreover, the acoustic radiation characteristic of such model under the single point force excitation was studied. The result of numerical calculation agreed well with that of experiment, which validated the accuracy and validity of the hybrid FE-SEA method in solving the medium-frequency acoustic radiation of the cylindrical structure with elastic plate cap.