Spelling suggestions: "subject:"eigenfrequencies""
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Frequency analysis of accelerometer measurements on trainsMajala, Jonas January 2017 (has links)
No description available.
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Determining the Optimal Orientation of Orthotropic Material for Maximizing Frequency BandgapsHaystead, Dane 20 November 2012 (has links)
As the use of carbon fiber reinforced polymers (CFRP) increases in aerospace struc-
tures it is important to use this material in an efficient manner such that both the weight
and cost of the structure are minimized while maintaining its performance. To com-
bat undesirable vibrational characteristics of a structure an optimization program was
developed which takes advantage of the orthotropic nature of composite materials to
maximize eigenfrequency bandgaps. The results from the optimization process were then
fabricated and subjected to modal testing. The experiments show that local fiber angle
optimization is a valid method for modifying the natural frequencies of a structure with
the theoretical results generally predicting the performance of the optimized composite
plates.
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Determining the Optimal Orientation of Orthotropic Material for Maximizing Frequency BandgapsHaystead, Dane 20 November 2012 (has links)
As the use of carbon fiber reinforced polymers (CFRP) increases in aerospace struc-
tures it is important to use this material in an efficient manner such that both the weight
and cost of the structure are minimized while maintaining its performance. To com-
bat undesirable vibrational characteristics of a structure an optimization program was
developed which takes advantage of the orthotropic nature of composite materials to
maximize eigenfrequency bandgaps. The results from the optimization process were then
fabricated and subjected to modal testing. The experiments show that local fiber angle
optimization is a valid method for modifying the natural frequencies of a structure with
the theoretical results generally predicting the performance of the optimized composite
plates.
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Detection of defects in timber using dynamic excitation and vibration analysisMoshiri, Farzad, Mobasher, Bahareh, Talib Issa, Osama January 2009 (has links)
This thesis evaluates the possibility to detect natural defects, such as knots, in timber boards using dynamic excitation test and ABAQUS software. In the study the edgewise bending direction were compared with axial direction. Dynamic excitation and modal analysis were used to extract the natural frequencies of several sound and artificially defected boards with the help of Signalcalc. Mobylizer software. By using the first edgewise natural frequency, modulus of elasticity (MOE) was calculated. An ABAQUS 2D Finite Element model was utilized to model the board and to extract the frequencies for the six first mode shapes in both axial and edgewise directions. The extracted frequencies from the model were compared with the frequencies from the tests. The analytical and experimental results, from the homogeneous boards, in edgewise direction has similar frequency variations. The defects in the timber boards decreased the natural frequencies. The bending modes with more curvature at the location of the artificial defect displayed more frequency deviation in that mode. The variation in response frequencies for uniform and defected boards was more noticeable in edgewise bending modes than in longitudinal modes.
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Evaluation of different support conditions when measuring eigenfrequencies of wooden boardsShaikh, Abdul Qadir, Min, Hu, Arvidsson, Irawati January 2009 (has links)
No description available.
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Modal Analysis of Continuous Structrual System with Tapered Cantilevered MembersKim, Yoon Mo 2011 December 1900 (has links)
Analytical Model of Traffic Signal Structures (TSS) is developed based on a continuous system method to observe dynamic characteristics of the structures. Conventional and basic continuous system method can show the approximate dynamic characteristics of the TSS, but the discretized continuous analytical model is proposed to get more accurate and realistic results of the TSS. In addition, the discretized continuous model can alternatively analyze the effect of the tapered cross-sectional members which are real model of TSS. For the verification of the analytical model, the dynamic characteristics of the numerical solutions by modal analysis in ABAQUS and the results of experimental measurements are provided. Compared with the numerical solutions and the experimental results, the analytical solution for each member shows its considerable accuracy. In addition, it will be also able to accurately express the effects of the linearly tapered cross-sectional member with more discretized continuous structural system. Moreover, the discretized analytical model of the TSS has the usability to observe the effects of boundary flexibility.
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Evaluation of different support conditions when measuring eigenfrequencies of wooden boardsShaikh, Abdul Qadir, Min, Hu, Arvidsson, Irawati January 2009 (has links)
No description available.
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Detection of defects in timber using dynamic excitation and vibration analysisMoshiri, Farzad, Mobasher, Bahareh, Talib Issa, Osama January 2009 (has links)
<p>This thesis evaluates the possibility to detect natural defects, such as knots, in timber boards using dynamic excitation test and ABAQUS software. In the study the edgewise bending direction were compared with axial direction. Dynamic excitation and modal analysis were used to extract the natural frequencies of several sound and artificially defected boards with the help of Signalcalc. Mobylizer software. By using the first edgewise natural frequency, modulus of elasticity (MOE) was calculated. An ABAQUS 2D Finite Element model was utilized to model the board and to extract the frequencies for the six first mode shapes in both axial and edgewise directions. The extracted frequencies from the model were compared with the frequencies from the tests. The analytical and experimental results, from the homogeneous boards, in edgewise direction has similar frequency variations. The defects in the timber boards decreased the natural frequencies. The bending modes with more curvature at the location of the artificial defect displayed more frequency deviation in that mode. The variation in response frequencies for uniform and defected boards was more noticeable in edgewise bending modes than in longitudinal modes.</p>
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Vertical Axis Wind Turbines : Tower Dynamics and NoiseMöllerström, Erik January 2015 (has links)
Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research. The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires. This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied. The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied. The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.
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Vertical Axis Wind Turbines : Tower Dynamics and NoiseMöllerström, Erik January 2015 (has links)
Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research. The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires. This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied. The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied. The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.
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