Applied Mechanics and Materials Vols. 541-542

Abstract: A numerical investigation on the space (0-46km) aero-thermodynamic characteristics of a nose cone model was performed using commercial software STAR-CCM++. Turbulence model and numerical calculation strategy was validated by the experimental phenomenon captured in a ground high-enthalpy wind tunnel and empirical formula calculation. The purpose of this paper is to discuss the distinctions between the experiment performed in ground high-enthalpy wind tunnel environment and real space flight using the validated numerical strategy, as well as the aero-thermodynamic characteristics of the nose cone model in different flight altitudes and Mach numbers, which will give a guidance to active cooling of spacecraft in real supersonic flight.

Abstract: The phenomenon of lubricant cavitation in hydrodynamic bearings and its detrimental effects have been documented in many literatures. Collapse of vapor cavitation bubbles may cause erosion wear that limits the life of the bearings. The ability to detect the occurrence of vapor cavitation using a well established condition monitoring technique is essential for the equipment operator. An experiment was conducted to investigate the vibration characteristics of vapor cavitation in steadily loaded plain journal bearings. Vibration data were collected from the bearings operating under the influence of vapor cavitation. It is shown that, vapor cavitation exhibits distinct characteristics on the vibration plots. Low amplitude, forward and reverse 0.063X frequency components, and a series of harmonics with frequencies lower than 0.5X, are observed on the full spectrum. A unique waveform with the positive peak amplitude fluctuating above and below the zero axis line is also observed.

Abstract: Gate valve is widely used for regulating flow and pressure of the pipeline in water conservation and chemical industry. High-precision, safe and efficient gate valve is a challenge for pipeline transportation. Suffered from the impact of the fluid, the gate valve is apt to be abraded and cause failure. This paper was based on the CAD/CAE (Computer Aided Design/ Computer Aided Engineering) system. Besides,this paper carried out researches on the influence of factors, including the fluid medium, the flow velocity, the wall thickness of gate valve body and the cross brace. In addition, the stress of the gate valve body was also in this paper studied. The simulation based on UG demonstrated the improvement of the gate valve stress.

Abstract: In the present work, the effects of insertion of helical screw tape on heat transfer characteristics and pressure drop in a concentric double tube heat exchanger are experimentally investigated. The heat exchanger has the outer (steel) and inner (copper) tube diameters of 50 mm and 25 mm respectively. The helical screw tape of diameter 19 mm is inserted into the inner tube to increase turbulence which helped to increase the heat transfer rate. The hot water was flowed through the inner tube and cold water was flowed in annulus. The helical screw tape was inserted in 1/3^rd length and full length of the tube. The experiments are based on Reynolds number at tube inlet, ranging from 10000 to 42855. The experimental results show that the average Nusselt numbers and friction factors are respectively, 1.41 and 2.08 times over the plain tube for 1/3^rd length insert and 1.87 and 4.31 times over the plain tube for full length insert. Furthermore, the enhancement ratio of the helical screw tape varies between 1.03 and 1.17, 1.02 and 1.26 for 1/3^rd length insert and full length insert, respectively.

Abstract: Many researchers dealt with single fault but in real life situations, combined action of two or more single faults are usually present. Multi-faults (two and three combinations) were studied by few researchers. Researchers have mostly studied the vibration behavior of a rotor with misalignment, unbalance and rub separately. This paper presents one such case, where multiple faults are considered together in a rotor system, i.e. misalignment, unbalance and rub. The objective of this paper is to experimentally investigate the vibration response of combined of three faults misalignment, unbalance and rub using Fast Fourier Transform (FFT). FFT spectrum of combination of three faults misalignment, unbalance and rub show 1 X and 2 X are predominant and many sub harmonics are generated.1X peak represent unbalance, 2X peak represents misalignment and sub harmonics shows rub fault.

Abstract: Vibration in any rotating machines is due to faults like misalignment, unbalance, crack, mechanical looseness etc. Identification of these faults in rotor systems, model and vibration signal based methods are used. Signal processing techniques such as Fast Fourier Transform (FFT), Short-Time Fourier Transform (STFT), Wigner-Ville Distribution (WVD) and Wavelet Transform (WT) are applied to vibration data for faults identification. The intent of the paper is to present a review and summarize the recent research and developments performed in condition monitoring of rotor system with the purpose of rotor faults detection. In present paper discuss the different signal processing techniques applied for fault diagnosis. Vibration response measurement has given information concerning any fault within a rotating machine and many of the methods utilizing this technique are reviewed. A detail review of the subject of fault diagnosis in rotating machinery is presented.

Abstract: Cutterhead is one of the key parts of Tunnel Boring Machine, TBM. The performance of cutterhead has a great impact on the boring capability of TBM. The impact heavy torque and thrust force bore by cutterhead during the tunneling process will cause severe vibration and lead to decline in its life even broken, which affect the boring efficiency. In this paper, a TBM mainframe model of Northwest Liaoning project has been built based on the multi-body system dynamics simulation platform ADAMS. It also has been discussed in the paper that the influence of front support on the vibration characteristics of cutterhead. The simulation results show that the front support will improve the vibration behaviors of cutterhead: The stabilization time of rotational and translational motion decreases 90% and 10% at least, the axial amplitude decreases 8%. All these conclusions have demonstrated that front support should be adopted when designing the TBM.

Abstract: In this paper, the performance of TFC slider under second-order discontinuous boundary condition was studied. A new heat transfer coefficient under this condition according to micro/nanoheat transfer theory was deduced, and the heat transfer model on the air bearing surface was established. Using the finite element method, the differences of temperature, deformation and flying-height of TFC slider under continuous and discontinuous boundary conditions were compared and analyzed. The results show that consideration of discontinuous boundary condition is critical to the simulaiton accuracy of the heat transfer at air bearing surface.

Abstract: A methodology to detect multi crack, with crack location and size due to transverse loading is presented in this paper taking the advantage of Adaptive neuro-fuzzy inference system (ANFIS) using modal analysis of cracked shaft. A simple supported shaft is subjected with axial and bending load for same angular position along with its longitudinal direction. The natural frequency of the shaft with its various crack positions and size are accurately determined analytically using strain energy release rate and stress intensity factor. The vibration parameters such as first three relative natural frequencies with their mode shapes at different locations and size are supplied to ANFIS to optimize the results. The crack location and size predicted from ANFIS model are verified with the theoretical data with acceptable error. The present method used in this paper is suitable and can be easily extended to complex structure with different orientation of multiple cracks.

Abstract: To study the velocity and pressure distribution of the oil film in a heavy hydrostatic thrust bearing, a mathematical model of the velocity is proposed and the finite volume method (FVM) has been used to simulate the flow field under different working conditions. Some pressure experiments were carried out and the results verified the correctness of the simulation. It is concluded that the pressure distribution varies small under different rotation speed when the surface load on the workbench is constant. But the velocity of the oil film is influenced greatly by the rotation speed. When the rotation speed of the workbench is as quick as enough, the velocity of the oil film on one radial side of the pad will be zero, that is to say the lubrication oil will be drained from the other three sides of the recess.