Journal of Vibroengineering
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Research on torsional vibration reduction of crankshaft in off-road diesel engine by simulation and experiment
Get PDFFormerly, torsional vibration of crankshaft in off-highway diesel engine (agricultural machinery) were given little attention at their developmental stages, however with increasing agricultural activities, numerous torsional vibration problems have been noted to occur in agricultural machinery, especially in their diesel engines. This results in engine vibration, crankshaft failure and undesirable engine noise. In this paper, a six-cylinder four-stroke inline diesel engine’s crankshaft model was developed using AVL Excite Designer. After experimentally validating the model, it was used to numerically determine the torsional vibrations of a crankshaft. For the reduction of torsional vibration, two methods of crankshaft improvements were proposed based on simulation results. The first method, is to decrease the inertia of the crank pulley while the second, involves the replacement of the crank pulley with a torsional vibration damper. To ensure minimal engine alterations and cost effectiveness, the second improvement method was adopted for improving torsional vibration. Afterwards, engine radiating noise and surface vibration measurements were conducted to ensure that the required limits were achieved by the improved engine. The simulation, experiment and the improvement process of the crankshaft torsional vibration are documented further in this research. These improvements have applicable values in the developmental or quality enhancement stage of diesel engines used in agricultural machinery
Vibration of a segment tunnel lining under internal blast loading
Get PDFSegmental tunnel is common in subway tunnel engineering, which is at risk of being attacked by terrorists’ bombing and accidental explosions. Due to the discreteness of segmental tunnel lining, it’s difficult to model its dynamic response to internal blast loading. In this paper, a simplified equivalent model was proposed to model the segmental tunnel lining’s vibration response to axisymmetric internal blast loading. This model can account for joints’ reduction of lining’s sectional rigidity, and concentrations of stress and strain on joints can be calculated. This research may aid in protective design and hardening measures for critical part of subway tunnels of segmental lining structure
Experimental study of the vortex-induced vibration of marine risers under middle flow
Get PDFA considerable number of studies for vortex induced vibration (VIV) under uniform flow have been performed. However, investigation of VIV under middle flow is scarce. An experiment for VIV under middle flow was conducted in a deep-water offshore basin. Various measurements were obtained by the fiber Bragg grating strain sensors placed on the riser, and VIV under the effect of middle flow with was investigated. Results show that the riser vibrates at different order natural frequencies along the water depth in the CF and IL directions appearing as the multi-frequencies under middle flow. The variation vortex shedding frequencies along the riser under middle flow may generate different wake modes and vibration modals as the corresponding vortex shedding frequencies approach the riser natural frequencies. The dominant vibration frequency of the entire riser is consistent, and determined by high order natural frequency and the corresponding closing vortex shedding frequencies under the middle flow. Meanwhile, the vibration modal under middle flow appears multi-modals and other lower modal have effect on riser vibration. The VIV mechanism under middle flow possesses some aspects similar to those of uniform flow and several unique features
Simulation and feature analysis of modal acoustic emission wave in planar C/SiC composite
Get PDFA catastrophic accident may be caused for nearby spacecraft due to the damage occurred in C/SiC thermal protection structure. Therefore, it is significant to analyze the damage feature of the ceramic composite structure. Acoustic emission (AE) is an effective non-destructive testing method which is widely used in aerospace industry. However, some key problems should be solved when the AE technology applied to the engineering field. In this paper some propagation characteristics of AE waves in C/SiC plate were investigated based on the finite element method. Firstly, two kinds of AE sources were established by combining plate wave theory and finite element method. Secondly, a novel simulation model was established which included the mechanical characters of C/SiC composite. Then to simulate the AE source, a stepped load and a dipole force is applied to generate the release of power loss. Additionally, the results of simulation are validated through the AE experiment with the analysis method of Choi-Williams transformation. Finally, the attenuation of AE signals propagation in C/SiC plate is discussed. The results of this research work demonstrated that the simulation method of AE waves in C/SiC structure proposed in this paper can be effectively used to study the wave propagation phenomeno
Artifacts in magnetic resonance imaging: how it can really affect diagnostic image quality and confuse clinical diagnosis?
Get PDFDifferent kinds of artifacts can occur during a magnetic resonance imaging (MRI) scans due to hardware or software related problems, human physiologic phenomenon or physical restrictions. Some of them can seriously affecting diagnostic image quality, while others may simulate or be confused with different pathology. On another word artifact as an artificial feature appearing in an image that is not present in the original investigative object. It is important to recognize these artifacts according to a basic understanding of their origin, especially those mimicking pathology, as they can lead to incorrect diagnosis and cause serious after-effects on patient’s health and outcomes. We presented an overview of the most common MRI artifacts and methods to fix or rectify them. We also provide the original artifacts images and statistics from the Lithuanian University of Health Sciences Kaunas Clinical Hospital, Dept of Radiology, mainly obtained from image databases and some images from data base of other Lithuanian hospitals
Novel gear fault diagnosis approach using native Bayes uncertain classification based on PSO algorithm
Get PDFTraditionally, gear faults can be classified with the ignorance of the sample uncertainty. In this paper, a novel approach is proposed for the problem diagnosis of uncertain gear interval faults. First, a statistical property interval feature vector composed of mean, standard deviation, skewness, kurtosis, etc. is proposed. Then, the native Bayes uncertain classification (NBU) is used for the diagnostics of these uncertain gear interval faults. Conventionally, the NBU utilizes all the attributes to distinguish fault types. However, each fault type has its own distinct classification accuracy for different feature vector attributes. Thus, the particle swarm optimization (PSO) is used to select the optimal feature vector attributes for each fault type in the NBU (NBU_PSO_EACH). The experimental results show: (1) the accuracy of the proposed method is better than that of NBU1, NBU2 or FBC; (2) in terms of accuracy, the proposed method is also more advanced than the method which selects the same optimal attributes for all fault types based on the PSO (NBU_PSO); (3) the proposed method can reduce the physical size of feature vectors
Incipient fault diagnosis of rolling bearing using accumulative component kurtosis in SVD process
Get PDFRolling element bearing faults account for main causes of rotating machine failures. It is crucial to identify the incipient fault before the bearing steps into serious fault condition. The Hilbert envelope spectrum has been proved powerful and with high practical value to detect transient components in vibration signal but sensitive to noise. Based on the conventional singular value decomposition (SVD) theory, accumulative component kurtosis (ACK) is introduced to de-noising of vibration signal processing. The proposed ACK-SVD emphasizes the accumulative components (ACs) rather than the single singular component (SC) to select the effective SCs to recover signal. The superiority of the ACK-SVD over traditional SVD de-noising is verified by both simulated signals and actual vibration data from two rolling element bearing rigs. The results demonstrate the proposed method can efficiently identify the rolling element bearing faults, especially the early ones with strong background noise
Seismic performance of box-plate, box-plate with UNP, box-plate with L-plate and ordinary rigid beam-to-column moment connections
Get PDFNowadays, using high-ductility structures in construction and significant buildings is highly appreciated. To use better ductile structures, effort has been made in this research to introduce box-plate, box-plate with UNP, box-plate with L-plate and ordinary beam-to-column connections. Eleven models with different shapes and thickness were analyzed and compared in this research, and they underwent hysteretic loading. Parameters such as restraint percentage, stiffness, strength, plastic hinge location, and ductility under cyclic loads were calculated for each model. It was found, from their moment-rotation curves that the bending capacity and ductility of the box-plate with UNP connection was greater than any other rigid connections, and those of the latter were greater than those of the normal, typical ones. It was also shown that stress concentration in box-plate with UNP connections disappear over the top and bottom flange plates
Dynamic analysis of offshore wind turbine blades under the action of wind shear and fluctuating wind
Get PDFAiming at large-scale offshore wind turbine blades, governing equations in fluid domain and motion equations in structural domain with geometric nonlinearity were built by the aid of ALE method. A three dimensional model under fluid-structure interaction (FSI) was established by using UG software and Geometry module, and numerical calculation for FSI vibration characteristics of wind turbine blades under the effects of wind shear and fluctuating wind was carried out based on ANSYS Workbench. The results indicate that the contribution of the combined action to displacement and Mises stress chiefly derives from the wind shear effect, which not only causes a comparatively larger increase for the maximum displacement and Mises stress, but also becomes bigger and bigger with the increase of average wind speed, and the fluctuating wind effect is insignificant. The maximum value of Mises stress in the blade section appears at the relative wingspan of 0.55, the maximum Mises stress varying with relative span length decreases progressively from the middle to both sides of the blade, and the contribution of wind shear effect alone, the combined action or wind speed increment to stress also shows the same change rule. Furthermore, in the maximum stress section along wingspan, Mises stress along the direction of blade thickness or chord length respectively presents two distribution laws, and reaches the maximum on the blade surface
Loss factor estimation of the layered panels
Get PDFThe loss factor identification is the effective way to get the proper acoustic analysis in the virtual environment. Using the predictive model is a necessary part of the virtual development. The detection of the inappropriate materials or malfunction designs in the early phase of product development and can dramatically save the cost and development time. The loss factor is the nonlinear parameter for the material modeling of the noise suppression during acoustic analysis. The identification of the loss factor is necessary to perform on the real specimen. The Decay Rate Method is the effective methodology to get accurate results by using standard measuring equipment and is ideal to use in-situ environment. The article describes loss factor identification for plywood material and applications for the automotive industry for glass materials. The complete results analysis is confidential, but the overall procedure of the method is described in specimen analysis