1,720,974 research outputs found
Visualization : A powerful tool for effective teaching of dynamics
No full textDynamics is an essential core engineering subject and it is considered as one of the hardest subjects in the engineering discipline. Many students acknowledged that Dynamics is very hard to understand and comprehend the\ud
abstract concepts through traditional teaching methods with normal tutorials and assignments. In this study, we\ud
conducted an investigation on the application of visualization technique to help students learning the unit with the fundamental theory displayed in the physical space. The research was conducted based on the following five basic steps of Action Learning Cycle including: Identifying problem, Planning action, Implementing, Evaluating, and Reporting. Through our studies, we have concluded that visualization technique can definitely help students in learning and comprehending the abstract theories and concepts of Dynamics
Experimental and finite element analysis to identify the source of vibration of a coach
No full textThis paper presents an investigation on the cause of severe vibration problem of a coach with four-cylinder engine running at an idle state using vibration and impact hammer\ud
modal experiments to obtain the main vibration frequency components and the natural characteristics of the coach. The vibration results indicate that the main vibration component comes from the vibration transmitted from the engine to the chassis frame, which is closely related with the engine idle speed. Based on structural simulation analysis of the coach’s chassis frame and comparison with modal testing, the coach severe vibration problem was due to coupling resonance between the engine idle frequency and the fourth natural frequency of the chassis frame. The solution to eliminate the vibration problem is provided by changing the local structure stiffness of the chassis frame. The contribution of this paper lies in providing a solution to solve similar problems
A new constraint handling method for wind farm layout optimization with lands owned by different owners
No full textFor wind farm optimizations with lands belonging to different owners, the traditional penalty method is\ud
highly dependent on the type of wind farm land division. The application of the traditional method can\ud
be cumbersome if the divisions are complex. To overcome this disadvantage, a new method is proposed\ud
in this paper for the first time. Unlike the penalty method which requires the addition of penalizing term\ud
when evaluating the fitness function, it is achieved through repairing the infeasible solutions before\ud
fitness evaluation. To assess the effectiveness of the proposed method on the optimization of wind farm,\ud
the optimizing results of different methods are compared for three different types of wind farm division.\ud
Different wind scenarios are also incorporated during optimization which includes \ud
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(i) constant wind\ud
speed and wind direction; \ud
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(ii) various wind speed and wind direction, and; \ud
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(iii) the more realisticWeibull\ud
distribution. \ud
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Results show that the performance of the new method varies for different land plots in the\ud
tested cases. Nevertheless, it is found that optimum or at least close to optimum results can be obtained\ud
with sequential land plot study using the new method for all cases. It is concluded that satisfactory\ud
results can be achieved using the proposed method. In addition, it has the advantage of flexibility in\ud
managing the wind farm design, which not only frees users to define the penalty parameter but without\ud
limitations on the wind farm division
Fracture analysis of wind turbine main shaft
No full textShaft fracture at an early stage of operation is a common problem for a certain type of wind turbine. To determine the cause of shaft failure a series of experimental tests were conducted to evaluate the chemical composition and mechanical properties. A detail analysis involving macroscopic feature and microstructure analysis of the material of the shaft was also performed to have an in depth knowledge of the cause of fracture. The experimental tests and analysis results show that there are no significant differences in the material property of the main shaft when comparing it with the Standard, EN10083-3:2006. The results show that stress concentration on the shaft surface close to the critical section of the shaft due to rubbing of the annular ring and coupled with high stress concentration caused by the change of inner diameter of the main shaft are the main reasons that result in fracture of the main shaft. In addition, inhomogeneity of the main shaft micro-structure also accelerates up the fracture process of the main shaft. In addition, the theoretical calculation of equivalent stress at the end of the shaft was performed, which demonstrate that cracks can easily occur under the action of impact loads. The contribution of this paper is to provide a reference in fracture analysis of similar main shaft of wind turbines
Optimization of wind farm layout with complex land divisions
No full textThe study of wind farm layout optimization considering the decisions of land owners has rarely been reported in literature. In this paper, the common situation of complex land divisions (e.g. unequally-spaced plots) is addressed for the first time. A new constraint handling and fitness evaluation technique is developed to address the more complex wind farm boundaries and integrated into two common wind farm optimization approaches: the grid based method and the unrestricted coordinate method. Enable by the new technique, a numerical optimization study is conducted with the goal of evaluating the impact of the participation of land owners on the economic performance of the wind farm. In particular, two scenarios are considered: 1) the varying land plot scenario, where the land plot availability is included in the decision variables of the optimization, and 2) the sequential land plot scenario, where the land plot availability is fixed prior to optimization. The study reveals that the unrestricted coordinate method under the sequential land plot scenario yields the best optimization results, with the smallest cost of energy and the largest wind farm efficiency
Comparative study on optimizing the wind farm layout using different design methods and cost models
No full textOptimizing wind farm layout is an effective tool to decrease wind power losses caused by the wake interaction between wind turbines. Current researches focus on advancing the optimization algorithms and improving the wind farm models based on two design methods (the grid based method and the unrestricted coordinate method). However, it has been rarely reported for the comparative studies of these two methods. Meanwhile, the topic of how to select a better wind farm cost model for the layout optimization has not been studied in literatures, while it is extremely important to the real wind farm design since the real wind farm cost can be highly uncertain which cannot be represented by a fixed model for different wind farms. Therefore, the wind farm layout optimization using the two design methods is conducted in this paper. Three different grid situations are considered so that the best optimization results with the grid based method can be obtained to compare with the unrestricted coordinate method more convincingly. Two widely acceptable cost models (Mosetti's model and Chen's model) are employed to unveil their influence on the optimization results. It has been found that:\ud
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- (i) 20×20 grids should be preferred for the grid based method instead of the previously widely applied 10×10 grids; \ud
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- (ii) compared to using the grid based method, there is a small improvement for the optimization result using the unrestricted coordinate method. Nevertheless, more computation cost is needed for the method when a large number of turbines are optimized, and; \ud
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- (iii) there is a big discrepancy between the optimization with different cost models. Mosetti's cost model is more accurate than Chen's cost model when the optimized number of turbines is large and vise versa
Residential balconies with road traffic noise : a combined source image and radiosity model
No full textSeveral significant studies have been made in recent decades toward understanding road traffic noise and its effects on residential balconies. These previous studies have used a variety of techniques such as theoretical models, scale models and measurements on real balconies. The\ud
studies have considered either road traffic noise levels within the balcony space or inside an adjacent habitable room or both. Previous theoretical models have used, for example, simplified specular reflection calculations, boundary element methods (BEM), adaptations of CoRTN or the use of Sabine Theory. This paper presents an alternative theoretical model to predict the effects of road traffic noise spatially within the balcony space. The model includes a specular reflection component by calculating up to 10 orders of source images. To account for diffusion effects, a two compartment radiosity component is utilised. The first radiosity compartment is the urban street, represented as a street with building facades on either side. The second radiosity compartment is the balcony space. The model is designed to calculate the predicted road traffic noise levels within the balcony space and is capable of establishing the effect of changing street and balcony geometries. Screening attenuation algorithms are\ud
included to determine the effects of solid balcony parapets and balcony ceiling shields
Fault detection of slow speed rolling element bearing with noise removal techniques
No full textRolling Element Bearings (REBs) are vital components in rotating machineries for providing rotating motion. In slow speed rotating machines, bearings are normally subjected to heavy static loads and a catastrophic failure can cause enormous disruption to production and human safety. Due to its low operating speed the impact energy generated by the rotating elements on the defective components is not sufficient to produce a detectable vibration response. This is further aggravated by the inability of general measuring instruments to detect and process the weak signals at the initiation of the defect accurately. Furthermore, the weak signals are often corrupted by background noise. This is a serious problem faced by maintenance engineers today and the inability to detect an incipient failure of the machine can significantly increases the risk of functional failure and costly downtime. This paper presents the application of noise removal techniques for enhancing the detection capability for slow speed REB condition monitoring. Blind deconvolution (BD) and adaptive line enhancer (ALE) are compared to evaluate their performance in enhancing the source signal with consequential removal of background noise. In the experimental study, incipient defects were seeded on a number of roller bearings and the signals were acquired using acoustic emission (AE) sensor. Kurtosis and\ud
modified peak ratio (mPR) were used to determine the detectability of signal corrupted by noise
Estimating health related costs and savings from balcony acoustic design for road traffic noise
No full textA multi-faceted study is conducted with the objective of estimating the potential fiscal savings in annoyance and sleep disturbance related health costs due to providing improved building acoustic design standards. This study uses balcony acoustic treatments in response to road traffic noise as an example. The study area is the State of Queensland in Australia, where regional road traffic noise mapping data is used in conjunction with standard dose–response curves to estimate the population exposure levels. The background and the importance of using the selected road traffic noise indicators are discussed. \ud
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In order to achieve the objective, correlations between the mapping indicator (LA10 (18 hour)) and the dose response curve indicators (Lden and Lnight) are established via analysis on a large database of road traffic noise measurement data. The existing noise exposure of the study area is used to estimate the fiscal reductions in health related costs through the application of simple estimations of costs per person per year per degree of annoyance or sleep disturbance. The results demonstrate that balcony acoustic treatments may provide a significant benefit towards reducing the health related costs of road traffic noise in a community
A practical signal processing approach for condition monitoring of low speed machinery using Peak-Hold-Down-Sample algorithm
No full textA simple and effective down-sample algorithm, Peak-Hold-Down-Sample (PHDS) algorithm is developed in this paper to enable a rapid and efficient data transfer in remote condition monitoring applications. The algorithm is particularly useful for high frequency Condition Monitoring (CM) techniques, and for low speed machine applications since the combination of the high sampling frequency and low rotating speed will generally lead to large unwieldy data size. The effectiveness of the algorithm was evaluated and tested on four sets of data in the study. One set of the data was extracted from the condition monitoring signal of a practical industry application. Another set of data was acquired from a low speed machine test rig in the laboratory. The other two sets of data were computer simulated bearing defect signals having either a single or multiple bearing defects. The results disclose that the PHDS algorithm can substantially reduce the size of data while preserving the critical bearing defect information for all the data sets used in this work even when a large down-sample ratio was used (i.e., 500 times down-sampled). In contrast, the down-sample process using existing normal down-sample technique in signal processing eliminates the useful and critical information such as bearing defect frequencies in a signal when the same down-sample ratio was employed. Noise and artificial frequency components were also induced by the normal down-sample technique, thus limits its usefulness for machine condition monitoring applications
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