Applied Mechanics and Materials Vols. 110-116

Abstract: Rolling bearings are usually considered to be non-repaired items the reliability of which is characterized by mean time to failure, or so called basic rating life. Reliability describes these parameters well in case the bearings are used in operation up to the very time the failure occurs, or during the time corresponding with basic rating life. In case of railway applications the bearings are often used in large groups and are preventively replaced after much shorter operating time as compared with their basic rating life. In the article there is a model which enables us to describe the bearings reliability in this specific case and to specify a number of failures which might be expected from a group of bearings during operating time, or to determine mean operating time between failures of bearings.

Abstract: Environmental simulation has an essential contribution in attitude determination and control verification tests of satellites. Specifically, real-time modeling of space environment can provide more precise and adapted simulation of real world in order to enable satellite attitude determination system by online outputs of sensors. Design and manufacturing of a moving mechanism which simulates the motion of real Sun relative to the satellite is proposed in this paper. Indeed, an artificial Sun carried by the mechanism will sensitize Sun Sensors mounted on a 3DOF model of satellite and finally the outputs of sensors are used to determine the attitude of the model satellite. The procedure of designing and manufacturing such a mechanism is described as follows. Firstly, the motion of Sun relative to the satellite on a specific orbit was ascertained. Next, considering the constraints such as laboratory space and its equipments, an appropriate mechanism was designed conceptually to satisfy the requirements. Then, the detailed characteristics of the mechanism were determined in the preliminary design phase and approved in the detailed design phase of the project. Finally, in order to verify the designed mechanism, a scaled down prototype was fabricated. Developmental tests on the prototype proved the ability of the model to simulate the Sun motion relative to the satellite properly.

Abstract: Dynamic inversion control in conjunction with nonlinear suboptimal three dimensional (3-D) guidance law, in terminal phase, is implemented in both the pitch and yaw plane for a short range surface to surface missile with onboard active strapdown seeker. The implemented guidance and control laws intercept the target with a minimum miss distance in addition to meeting the various constraints such as line of sight, seeker field-of-view (FOV), and impact angle. This is achieved using approximate solution to Hamilton-Jacobi-Bellman (HJB) equation [1]. Dynamic inversion control is implemented in two time scales for the inner loop body rate and outer loop angles. Various nonlinearities including that due to the coupling effect between pitch and yaw channels are accounted for in the six-degree-of-freedom (6-DOF) formulation.

Abstract: Active flow control methods are used to reduce the aerodynamic drag over a car model. Method of Boundary layer suction at the top rear and air injection at the back of the car are used as the active flow control tools to suppress the aerodynamic drag. The computational results obtained using the standard model for the car model are verified first against the practical results obtained by wind tunnel experimentation so as to obtain the range of turbulence. Then a parametric study on the effect of the drag and lift coefficient of the car with respect to the parameters governing the active flow control is done. The drag coefficient is reduced by 20.25% using this strategy with 19.4% increase in the lift coefficient.

Abstract: The performance of a plate heat exchanger (PHE) is severely influenced by non-uniform distribution of flow among its channels. Not only the PHEs, but many other process equipment needs uniform flow distribution for their optimum performance. Flow maldistribution (non-uniform distribution) is a common design problem which always puzzles process equipment designers. Being important design parameters, it has been investigated by several researchers and case based solution has been proposed and documented. Present numerical work is intended to target this aspect of the problem of PHEs but starts with a general investigation with simple multichannel geometry. The numerical setup consists of two headers having multiple channels for U-and Z-turn flow configuration under multichannel geometry and a simplified PHE for plate heat exchanger simulation. The problem has been investigated from hydrodynamic and thermodynamic view point. For hydrodynamic study, flow has been varied for Reynolds number 120 to 17600. It has been found that channel flow goes on reducing along downstream side. In thermal study the effect of wall temperature on air flow mal distribution has been investigated. Numerical results have been validated with the experimental results. Investigation reveals new features of flow mal-distribution which is helpful in better understanding of associated mal-distribution physics.

Abstract: Analytical solutions for vibration analysis of the rods with variable cross section are in general complex and in many cases impossible. On the other hand, approximate methods such as the weighted residual, Rayleigh-Ritz and finite difference methods also have their own shortcomings such as a limited number of natural frequencies and accuracy. Using the wave propagation method, the structure is partitioned into several continuous segments with constant cross-section, for which there exists an exact analytical solution. Waves in positive and negative directions at the entrance of each segment are obtained in terms of waves at the initial segment. Then, by satisfying the boundary conditions, the characteristic equation is obtained and all natural frequencies are calculated. By adding waves in positive and negative directions at each point, the shape modes are obtained. To verify this modified method, the frequencies and mode shapes of a rod with polynomial cross section, which has an exact analytical solution, are compared and have proven to be of highly accuracy. Therefore, this method can also be used to calculate the natural frequencies and its mode shapes of the rods with variable cross section for which no analytical solution is available.

Abstract: Efficient grinding of structural ceramics requires judicious selection of operating parameters to maximize removal rate while controlling surface integrity. Grinding of ceramics is difficult because of its low fracture toughness, making it very sensitive to cracking. In the present work, experiments were carried out to study the effect of wheel parameters such as grain size and grinding parameters like depth of cut and feed rate on the surface roughness and surface damage. The significance of the grinding parameters on the selected responses is evaluated using analysis of variance. Mathematical statistics like “Minitab” is used to analyzed the grinding conditions for maximum material removal, using a multi-objective function model, by imposing surface roughness, surface force and surface damage constraints. The choice of including manufacturer & apposes constraints on the basis of functional requirements of the component for maximizing the production rate is also embedded in the Mathematical statistics. For the verification of present work, the Mathematical statistics results are compared with experimental work.

Abstract: An Air Turbo Rocket (ATR) is a propulsion system which combines a turbo jet with a rocket engine. Currently it is being touted as a propulsion system for future missile systems, as these engines have a higher thrust density when compared to other air breathing engines. This paper explores the possibility of modifying the ATR for use in space application as well as during spacecraft re-entry. Such modified ATR’s could be used to power space vehicles up to the Low Earth Orbit (LEO) to dock with the International Space Station (ISS). In addition, thrust reversal techniques on the ATR systems could be used to improve the accuracy of Ballistic Missiles and hypersonic space planes upon Re-entry. Challenges faced would be in this type of air breathing engine would be operating at different atmospheric conditions. This paper will explore an ATR design, which will operate at different modes namely conventional mode, which will be used during below absolute ceiling, and the mission mode, which will be employed during flight in vacuum. Lastly, the reentry mode, which can be used for lessening the entry velocity of a vehicle to reduce the risks associated with reentry. The paper will try to emphasize the advantages of ATR as an affordable launch system for space shuttles and satellites with high maneuverability.

Abstract: This study compares the performance of gear fault detection using Artificial Neural Networks (ANNs) and Adaptive Neuro-Fuzzy Inference System (ANFIS). The feature vector is extracted from vibration signals by standard deviation of wavelet packet coefficients at the fourth level. An improved distance evaluation technique is proposed for feature selection, and with it, the four salient features are selected from the original feature set. These features are normalized in the range zero to one and then fed into ANN and ANFIS. The gear conditions were considered to be healthy gearbox, slightly worn, and medium worn and broken-teeth gears faults. The output layer of ANN and ANFIS consists of one node indicating the status of the gearbox by four labels. A 3-layer Multi-Layer Perceptron (MLP) neural-network and an ANFIS were designed to carry out the task. The results show that the classification accuracy of ANFIS is better than MLP. Also, the effectiveness of the proposed feature selection method is demonstrated by the test results.

Abstract: Cloud formation is a ubiquitous process and modeling it as a simplified experimental set-up may be an interesting and fruitful task. In this study different flow and thermal processes and fluid structures during cloud formation (especially Cumulus clouds) are investigated through an experimental setup. Vapor coming out of a 20cm×20cm water surface at temperature 60-800C interacts inside a square plexiglas tube of vertical height 60cm with dry, cold air passing from above the tube. An air conditioner is used to supply cold air at temperature 180C over the plexiglas tube. Various parameters like rate of evaporation, speed of cold air are regulated as per requirements. Turbulent plume structure is observed through a sheet of light. Optical visualization method is adopted for observing the condensed water droplets. Movies of vertical and horizontal views of plume structure are taken. Observation of this entrainment process reveals the turbulent nature of convection related to it and the gradual growth of cloud (aggregation of condensed water particles) with drop of temperature as clouds move up. Our present study is also important for prediction of type of Cumulus cloud formed for known environmental conditions.