Journal of Engineering and Thermal Sciences
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Static and vibrational analysis of the GMAW and SMAW joints quality
Get PDFStructural steel S235JR is one of the main high-strength steels, while the most common welding methods are gas metal arc welding and shielded metal arc welding. Any of weld-strength-related defects can lead to weaker, less ductile welds, cracking and rupture in various steel constructions. Therefore quality of GMAW and SMAW joints were analyzed by using both the destructive tensile strength test and the non-destructive holographic interferometry method. Tensile test results of 10 arc welded specimens and holograms of harmonically excited specimens are presented in this paper. Specifications of specimens and welding parameters are also reviewed along with methodology of the experimental investigation and criteria of the analysis
Propagation of weak waves in the inhomogeneous elastoviscoplastic medium with a cell structure
Get PDFNon-stationary acceleration waves in the fluid-saturated inhomogeneous elastoviscoplastic porous medium are studied using the mathematical theory of discontinuities. The equations for determining the intensity and the geometry of wave fronts of the fluidsaturated elastoviscoplastic medium were first derived. It is shown that in the medium under consideration there are two types of irrotational waves and one equivoluminal wave, that are equal to the velocities in the homogeneous elastic porous media at every point
Development of a system to obtain vertical track geometry measuring axle-box accelerations from in-service trains
Get PDFNowadays, metropolitan railway systems are in great demand, so they offer highfrequency services for the most part of the day. Therefore there are only a few hours available at night to carry out maintenance tasks. This research develops a system that records vertical accelerations undergone by the bogies of in-service railway vehicles. As accelerations are measured during regular services of trains, no additional vehicles or personnel are needed and maintenance planning is optimized. Accelerations are processed to obtain vertical track alignment in order to determine whether the track needs repair. The developed system has been validated by comparing its results to the actual state of the track provided by a track monitoring trolley. Comparison is performed by using both graphical and statistical methods. Real data was obtained from measurements taken on Line 1 of the Alicante tram network (Spain). This paper presents procedure for data collection, its mathematical processing and analysis in order to identify track condition
Nonlinear vibration of fluid-conveying double-walled carbon nanotubes under random material property
Get PDFIn this study, one performs the stochastic dynamic analysis of nonlinear vibration of the fluid-conveying double-walled carbon nanotubes (DWCNTs) by considering the effects of the geometric nonlinearity and the nonlinearity of van der Waals (vdW) force. Based on the Hamilton’s principle, the nonlinear governing equations of the fluid-conveying DWCNTs are derived. In order to truly describe the random material properties of the DWCNTs, the Young’s modulus of elasticity of the DWCNTs is assumed as stochastic with respect to the position. By adopting the perturbation technique, the nonlinear governing equations of the fluid-conveying can be decomposed into two sets of nonlinear differential equations involving the mean value of the displacement and the first variation of the displacement separately. Then one uses the harmonic balance method in conjunction with Galerkin’s method to solve the nonlinear differential equations successively. Some statistical dynamic response of the DWCNTs such as the mean values and standard deviations of the amplitude of the displacement are calculated. It is concluded that the mean value and standard deviation of the amplitude of the displacement increase nonlinearly with the increase of the frequencies for both cases of coupling between longitudinal displacement and transverse displacement and uncoupling between them. However, the coefficients of variation of the amplitude of the displacement remain almost constant and stay within certain range with respect to the frequency. The calculated stochastic dynamic response plays an important role in estimating the structural reliability of the DWCNTs
Numerical simulation research of vortex-induced vibrations of the long circular cylinders with high mass-ratio
Get PDFThe two-degrees-of-freedom vortex-induced vibrations (VIV) of the long circular cylinders with high mass-ratio are numerically simulated with the software ANSYS/CFX. The VIV characteristic of the cylinder is analyzed in the different conditions (Ur = 3, 5, 6, 8, 10). When Ur is 5, 6, 8 and 10, the conclusion is different from the vortex-induced vibrations of the cylinder with low mass-ratio. When Ur is 3, the frequency of the drag force on the cylinder is twice of that of the lift force and the in-line VIV frequency of the cylinder is twice of that of the cross-flow VIV. The in-line VIV amplitude of the cylinder is much smaller than the cross-flow VIV amplitude. The motion trace is the crescent. When Ur is 5 and 6, the frequency ratio between the drag force and lift force is still 2, but the main in-line VIV frequency of the cylinder is mainly the same as that of the cross-flow VIV and the secondary in-line VIV frequency is equal to the frequency of the drag force. The in-line VIV amplitude is still very small compared with the cross-flow VIV amplitude. When Ur is up to 8 and 10, the in-line VIV frequency of the cylinder is the same as the main frequency of the cross-flow VIV which is close to the inherent frequency of the cylinder and is different from the frequency of the drag force or lift force. But the secondary cross-flow VIV frequency of the cylinder is equal to the frequency of the lift force. The amplitude ratio between in-line VIV and cross-flow VIV is about 0.5. When Ur is 5, 6, 8 and 10, the motion trace is mainly the oval
Prognostics of vibration induced risk to operators of agricultural machinery
Get PDFFrequent use of vibrating hand-held tools and operation of machinery can result in various chronic diseases. Operators of machinery are often afflicted with peripheral and systematic disorders. The statistical data collected over several decades clearly indicate the lack of operator’s safety from exposure to vibrations. The causes and impacts of vibration effects on humans are reviewed in annual reports by health and safety experts in many countries. One of the most common occupational diseases that has been frequently reported is the musculoskeletal disorder due to extended exposure to mechanical vibrations. The influence of vibrations during time period τ can be described by vibro-energy load aτ2·τ. If this load value over a specified time period does not exceed the permissible level a2·T0, it will not induce negative effects on human health. This approach was used in the present study for the prediction of hands and whole body vibration effects on operators of various vibration inducing machinery. Agricultural operators were selected as test subjects, since agricultural tractors and other mobile machinery emit high levels of vibration. Vibration data were obtained from statistical reports developed in the time period from 1988 to 2008. It was found that majority of agricultural machinery does not guarantee proper vibration safety. Thus organizational prevention methods should be developed and implemented. Reduction of vibrations by various technical methods and/or reduction of vibration exposure could be costly, but they are needed in order to provide effective solutions in reducing vibration risk to operators
On the approximate analytical solution for parametrically excited nonlinear oscillators
Get PDFIn this study we have analytically analyzed the vibration of parametrically excited oscillators based on Mathieu-Duffing equation. He’s Variational iteration method (VIM) is applied to obtain analytical solution, while Runge-Kutta method is used to obtain the numerical solution. It is demonstrated that VIM is very effective and convenient therefore may find wide applicability in engineering and other sciences. Finally, to confirm the validity of the applied method, the results of VIM are compared with those obtained by Runge-Kutta method. The results from VIM indicate an excellent agreement with the numerical solutions
Correlation between shape errors in flat grinding
Get PDFCorrelation between shape errors of the tool and ceramic work-pieces are presented in the paper. A new tool, on which different shape errors of convexity or concavity can be set, was used during experiments. Results from flat grinding, such as the shape errors, are presented and analyzed. Computational calculations concerning the local shape errors of the tool and the technological effects such as surface roughness and waviness parameters as well as the workpiece plane-parallelism are also presented
Combustion variability and uniqueness in cylinders of a large power radial engine
Get PDFThis paper analyzes variability and uniqueness of a combustion process in the spark ignition radial engine having nine cylinders. In the case of single cylinder disturbances, multifractal approach is proposed to identify faults in the measured cylinder pressure. For better clarity, the pressure cyclic response is illustrated by means of wavelet results. The examined engine was powered by an electronic fuel injection, giving the possibility of varying doses supplied to the individual cylinders
Establishment and safety evaluation of a flexible test platform for the vertical-axis wind turbine
Get PDFThis work intends to construct and execute the safety evaluation of an test platform for the small vertical-axis wind turbine (VAWT), which is mounted on the rooftop of a 60 mheight building. The experiment platform designed here is flexible and suitable for carrying out the systematic performance evaluation on different types of VAWT. The wind turbine performance measurement is conducted by utilizing the data acquisition system. All environmental information and power data from sensors and generator on this platform are recorded and transferred to the computer automatically. Later, these analogy signals are transformed to digital format for transmitting into computer. Also, with the aids of a visual software programming within the framework of LabVIEW, the real-time monitoring on the input/output parameters of generator and the wind condition can be accomplished simultaneously. Afterwards the data processing and in-depth analysis on the experimental outcomes are carried out via the established computer program. Consequently, the on-site performance of the wind turbine generator system is attained in an automatic and systematic manner. Moreover, to ensure for providing sufficient data and its accuracy, statistic concept is enforced to judge whether the test data are qualified or not in the data-processing procedure. Regarding the safety evaluation of wind turbine on this test platform, the numerical models of wind turbine and platform are analyzed via ANSYS Workbench to obtain the forces exerting on the main shaft and blades. This force distribution can be analyzed for checking if they can stand and meet the safety criterion under various wind speeds. Furthermore, a 2 m-diameter, multiblade vertical-axis wind turbine (MVAWT) is installed as a demonstrating case of the entire procedural test. Firstly atmospheric parameter, such as wind velocity, wind direction, air temperature, and air pressure is measured based on IEC 61400-12 standard on the rooftop of building for one year range measurement time. By collecting and observing the wind parameter data, such as mean wind velocity and wind direction distribution, the wind energy estimation of this MVAWT can be analyzed quantitatively. In summary, together with the data-acquisition software programmed under the framework of LabVIEW, this experimental system can provide the capability for monitoring, recording, and filtering these test data in an rigor manner, and is appropriate for executing the R&D and performance evaluation on different VAWTs