Journal of Engineering and Thermal Sciences
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Application of incremental polymeric scales for high precision piezoelectric angular positioning system
Get PDFA high precision piezoelectric rotational stage with low-cost incremental polymeric scales is proposed and investigated in this work. For avoiding datum plane surface errors caused by application of additional bearings to support the rotational part, the latter one contacts with a stationary piezoelectric disc, which oscillates in travelling wave mode, at three specific points via contacting ring. The resolution of rotation is determined only by geometrical errors of external surface of the piezoelectric disc and can be easily achieved to be in the range of 1 µm. Low-cost polymeric scales are applied to measure angular displacement by means of moiré fringes. Peculiarities of scales fabrication are defined taking into consideration the final accuracy of the device
Design and numerical analysis of a novel coaxial rotorcraft UAV
Get PDFThis paper reports the design of a novel coaxial rotorcraft UAV with canard wing, main wing and tail rotor, which is capable of converting status between contra-rotating case model and fixed wing model. Computational fluid dynamics approach involving momentum source method is adopted to study its aerodynamic characteristics in various states. A validation case is introduced in this paper to verify the reliability and precision of this method. The result proves that the designed coaxial rotorcraft UAV is able to hover, take off and land vertically as well as change between the contra-rotating case model and the fixed wing model. Accordingly, it is able to accomplish various operating statuses and demonstrate good aerodynamic characteristics during the whole fight envelope
Study of characteristic variations of high-speed spindles induced by centrifugal expansion deformations
Get PDFHigh-speed machining has continuously pushed the demand of spindles with higher speed and higher reliability. In order to design, analyze, and test spindles in a virtual environment, accurate modeling of the spindle dynamics during the running state is essential. This paper investigates the variations of interference fit and bearing preload condition induced by centrifugal expansion deformations at high speed. Firstly, the elastic expansion deformations of the rotating parts due to centrifugal force are calculated based on mechanics of elasticity. It is found that the centrifugal expansion deformation of the bearing inner ring is much larger than the deformation of the shaft when the rotational speed increases, and therefore the amount of the interference between the shaft and the bearing decreases with the speed. Then, with consideration of the centrifugal expansion deformation, a dynamic model of high-speed rolling ball bearings is presented with experimental validation. With the proposed bearing model, centrifugal effects on the bearing preload condition are studied in detail. It is shown that the bearing contact angle decreases, while the contact load increases with the centrifugal expansion deformation of the bearing inner ring. The radial bearing stiffness increases, whereas the axial bearing stiffness decreases a little, due to the resultant effects of the decreased contact angle and the increased contact load. The preload condition of the spindle bearing is strengthened by the centrifugal expansion effect of the bearing inner ring
Geometry optimization of double wishbone suspension system via genetic algorithm for handling improvement
Get PDFMotion control, stability maintenance and ride comfort improvement are fundamental issues in design of suspension systems in off-road vehicles. In this paper, a double wishbone (DW) suspension system, mostly used in off-road vehicles, is modeled using ADAMS software. Geometric parameters of suspension system are optimized using genetic algorithm (GA) in a way that ride comfort, handling and stability of vehicle are improved. Simulation results of suspension system and variations of geometric parameters due to road roughness and different steering angles are presented in ADAMS and effects of optimization of suspension system during various driving maneuvers in both optimized and non-optimized conditions are compared. Simulation results indicate that the type of suspension system and geometric parameters have significant effect on vehicle performance
The concept of transducer for detection of trackway surface condition basing on frictional coupling of wheel with a rail and its experimental verification
Get PDFDescription of design and rules of operation of transducer for detection of trackway surface condition in mine underground workings is the project objective. Information about the surface condition collected with use of the transducer will enable adaptive (depending on track surface conditions) control of breaking torque of wheels of rail locomotives and, in a result, shortening of braking distance by minimization of slippage. At first the requirements for braking systems of mining locomotives, with reference to real conditions of their operation, will be presented. Then selected braking systems, which are applied in the locomotives used in the coal mine industry, will be described with a special attention paid to the solutions, which potentially shorten the braking distance, including also the solutions based on ABS system used in the automotive industry. A concept of dedicated transducer, task of which is a continuous detection of surface condition of trackway, on which the locomotive moves, will be described with reference to the presented solutions. Transducer for detection is based on frictional coupling between its active component (so-called “tracking wheel”) and a rail. Presented concept will be proved by a series of verification experimental tests. Presentation of tests results and determination of further directions of R&D work as regards discussed problems will be the summary of the project
A new density estimation neural network to detect abnormal condition in streaming data
Get PDFAlong with the development of monitoring technologies, numerous measured data pour into monitoring system and form the high-volume and open-ended data stream. Usually, abnormal condition of monitored system can be characterized by the density variation of measured data stream. However, traditional density estimation methods can not dynamically track density variation of data stream due to the limitation of processing time and computation memory. In this paper, we propose a new density estimation neural network to continuously estimate the density of streaming data in a time-based sliding window. The network has a feedforward structure composed of discretization, input and summation layer. In the discretization layer, value range of data stream is discretized to network nodes with equal intervals. Measured data in the predefined time window are pushed into input layer and updated with the window sliding. In summation layer, the activation results between input neurons and discretization neurons are summed up and multiplied by a weight factor. The network outputs the kernel density estimators of sliding segment in data stream and achieves a one-pass estimation algorithm consuming constant computation memory. By subnet separation and local activation, computation load of the network is significantly reduced to catch up the pace of data stream. The nonlinear statistics, quantile and entropy, which can be consecutively figured out with the density estimators output by the density estimation neural network, are calculated as condition indictors to track the density variation of data stream. The proposed method is evaluated by a simulated data stream consisting of two mixing distribution data sets and a pressure data stream measured from a centrifugal compressor respectively. Results show that the underlying anomalies are successfully detected
Evaluation of the natural draught cooling tower shell using linearly and non-linearly numerical analysis
Get PDFThe shell shape of the natural cooling tower determines the sensitivity of the whole structure against wind excitation. This study analyses influence of the tower shell geometric parameters on the structural behavior, evaluated by linearly and nonlinearly numerical analyses. The goal of the study is to give an informative statement for the form-finding process of the cooling tower shell in the engineering practice. The generated 32 towers from an existing cooling tower are linearly analyzed base on the natural frequency. Further three representative models were selected, they were analyzed based on the buckling factor and the reinforced amount required according to a design guideline. The hyperbolic shell with overall radii as small as possible yielded not only a higher first natural frequency, thus less wind-insensitivity, but also a safer buckling behavior and a economical design due to less requirement of concrete and reinforcement. This advantageous structural behavior could be consistently verified in the nonlinear analysis, evaluated by load-deformation curves and damage indices based on the natural frequencies and modal contribution factors
Experimental and numerical investigation on the structural performance of the tensioning air beam system
Get PDFAn experimental and numerical study on the structural performance of the tensioning air beam system (TABS) is presented. TABS is a hybrid structural system consisting of a membrane air beam, steel frames and cable struts. This system has the advantage of reduced self-weight and is easy to construct while it can improve the load bearing capacity of membrane structures. It maximizes the structural capacities of individual elements, thus can be considered as a very effective system in terms of both structural and economical aspects. In this paper, a test was carried out to examine the structural performance of TABS under different membrane pressure conditions. The material properties of the air beam were obtained from the results of two membrane tensile strength tests, which were performed prior to the main test. A simple numerical model was proposed to predict the structural behavior of TABS and its validity was evaluated by comparing its results with the test values
Free vibration of transversely isotropic magneto-electro-elastic plates in contact with fluid
Get PDFIn this study, one investigates the free vibration behaviors of transversely isotropic Magneto-electro-elastic (MEE) rectangular plates in contact with fluid. In particular, one derives the mathematical formulation on the determination of added virtual mass for MEE rectangular plates with uniform thickness, which is in contact with fluid. A fluid-structure interaction model is constructed and analyzed on the basis of the recently derived differential equation governing the dynamical responses of the MEE rectangular plates. The added virtual mass incremental (AVMI) factor of the system is computed by adopting the proposed method and the added virtual mass can then be estimated. The natural frequencies based on the proposed approach play an important role in the vibration analysis and design of the fluidcontacting MEE plate
Approach to modeling of thermal airflow dynamics
Get PDFThis work considers the modeling of thermal airflow. The dynamic airflow is spit on flat circular elements. The extrapolation method, which is referred to as adaptive extrapolation, is proposed. The extrapolation which is influenced by stochastically changing settings is the key for adaptive extrapolation. The change of these parameters is determined experimentally during real flight or using prediction techniques. This paper presents modeling with preset parameters. The thermal airflow is modeled by taking into account its inclination towards wind and the change of diameter in accordance with linear and nonlinear laws