1,720,963 research outputs found
Exploring the limits of a deflection-based method for the estimation of dynamic stress in beams
No full textEstimation of the dynamic stress in structures, such as beams and plates, has previously been made using the relationship between stress and velocity spatial maxima based on farfield assumptions. This paper presents a method for the estimation of dynamic stress in a beam using Euler-Bernoulli beam theory, where deflection data from a grid of measurement points on the surface of the beam is used to estimate the dynamic bending stress in the structure. The limitations of the method are investigated via response data provided by a numerical model of a free-free beam. A non-dimensional wavenumber analysis is used to determine the number of points required for an accurate estimate of stress. Beams with a range of material and geometric parameters are modelled in order to explore the limits of the estimation method, and parameters representative of several real-world materials are used to assess the suitability of the method for practical applications
Experimental measurements of stress in an Acoustic Black Hole using a laser doppler vibrometer
No full textAcoustic Black Holes (ABHs) make use of modifications to a structure to effectively decrease the structural wavespeed, thus increasing the effect of damping material applied in the ABH taper region, resulting in greater vibration attenuation. The most common way in which this is implemented is by gradually reducing the thickness of the structure over a finite interval, to a very thin tip. The focusing effect of the ABH results in high amplitude vibrations occurring in the thin part of the structure, resulting in high stresses and raising significant concerns about fatigue life. This paper presents an experimental assessment of stress in the taper section of an ABH used to terminate a uniform beam, using laser doppler vibrometer measurements to avoid the mass loading associated with accelerometers or strain gauges. A calculation of stress using Euler-Bernoulli beam theory is then presented, and the validity of this approach is assessed for a thick damping layer applied to a thin structure. A comparison is then made to predictions from a numerical model, in order to validate the results from the experimental measurements
Optimisation of a modified acoustic black hole profile for the reduction of dynamic stress
No full textAcoustic Black Holes (ABHs) make use of structural modifications to effectively reduce the wave speed of vibration in a structure. This increases the effectiveness of damping material applied to the ABH and results in more effective vibration control. The most common realisation of an ABH is to gradually taper the thickness of a structure, resulting in a very thin tip when realised as a structural termination. The ABH effect causes an increase in energy density as structural thickness decreases, resulting in a large amount of energy being focused within the thin section of the ABH. This raises concerns around high levels of dynamic stress in the structure. This paper presents a modified ABH taper profile that aims to reduce the level of dynamic stress in the structure while maintaining ABH performance. The parameters defining the modified ABH profile are optimised to reduce dynamic stress in the taper while maintaining ABH performance, and the optimised profile is compared to the conventional ABH for both performance measures
Modified acoustic black hole profile for improved fatigue performance
No full textAcoustic black holes (ABHs) are realised via modifications to a structure that effectively reduce the structural wave speed; this increases the effect of damping treatments and thus enhances the achievable vibration attenuation. ABHs are commonly designed using a tapering thickness profile and this leads to part of the ABH being very thin. Due to the focusing effect of the ABH, the thin section of the taper is also exposed to high amplitude vibrations and this raises concerns relating the vibration fatigue of the structure. This paper investigates the fatigue life of an ABH taper used to terminate a beam using a numerical model, before a modified taper profile is proposed that aims to reduce the fatigue, while maintaining ABH performance. The effect of the power law used in the taper profile on the fatigue life is investigated and the potential trade-off between performance and fatigue life is explored for both the unmodified and modified profiles
An investigation of structural stress in active acoustic black holes
No full textAcoustic Black Holes (ABHs) are structural features that enable a notable level of vibration control by introducing a spatial variation in either the thickness or material properites of a structure, leading to a significant reduction in the wave speed and resultingly an increase in the efficiency of an applied damping treatment. There are two key potential limitations associated with ABHs – firstly, due to the focusing of structural waves into the ABH feature they can increase the structural stresses; and secondly, their performance at low frequencies is limited by the size of the ABH feature. It has previously been shown that through the integration of active control it is possible to enhance the lowfrequency performance of ABHs, however, the effect that this has on the resulting stress has not been previously explored. This paper presents an investigation into the change in structural stress due to the integration of active control into an ABH terminated beam. A feedforward wave-based controller is utilised, which aims to minimise the wave reflected from the ABH termination using a piezoelectric patch actuator attached to the ABH feature. This demonstrates that a conventional active ABH introduces a significant stress enhancement and, therefore, a modified control strategy is explored in which the stress measured in the ABH is included in the cost function being minimised
Experimental validation of a modified acoustic black hole profile
No full textAcoustic Black Holes (ABHs) use modifications to a structure to reduce the structural wavespeed, which increases the effect of damping treatment applied in the ABH region, resulting in greater vibration attenuation. The most common type of ABH uses a gradually tapering thickness to reduce the wavespeed, resulting in part of the structure becoming very thin. Due to the focusing effects of the ABH, high amplitude vibrations occur in the thin part of the structure, and this raises concerns about vibration fatigue. This paper uses a numerical model to investigate the fatigue life of an ABH taper used to terminate a beam. A comparison is made between the results from a standard ABH taper and a modified ABH profile that aims to reduce fatigue while preserving vibration performance. Following this, the dynamic performance of both ABHs is assessed experimentally to validate the results from the numerical model
Fatigue analysis of acoustic black holes
No full textAcoustic black holes (ABHs) are realised via modifications to a structure that effectively reduce the structural wave speed, which increases the effect of damping treatments and thus enhances the achievable vibration attenuation. ABHs are commonly designed using a tapering thickness profile and this leads to part of the ABH being very thin. Due to the focusing effect of the ABH, the thin section of the taper is also exposed to high amplitude vibrations and this raises concerns relating to the vibration fatigue of the structure. This paper presents a numerical simulation based investigation into the fatigue life of an ABH taper used to terminate a beam. In particular, the effect of the power law used in the taper profile on the fatigue life is investigated and the potential trade-off between performance and fatigue life is explored
A parametric study of dynamic stress in acoustic black holes
No full textAcoustic Black Holes (ABHs) make modifications to a structure that act to reduce the speed of a wave travelling through the ABH region. The reduced wavespeed has a corresponding reduced wavelength which increases the effectiveness of damping treatment applied to the ABH. A common way in which the reduction of wavespeed can be achieved is by gradually reducing the thickness of a structure. This is commonly implemented as a beam termination, which results in a thin tip. In this case, the energy focusing effect of the ABH causes high amplitude vibrations to occur in the thin section of the structure, raising concerns about high levels of dynamic stress that could result in fatigue failure. This paper presents an investigation into the effect of changing the ABH taper length, tip height and power law on the dynamic stress in an ABH terminated beam. This is achieved via numerical model of the structure, which enables a full parametric analysis to be carried out. For each ABH parameterisation, the performance is also quantified in terms of reflection coefficient so that trade-offs between performance and stress can be observed
Design and analysis of Acoustic Black Holes for dynamic stress
No full textAcoustic Black Holes (ABHs) are lightweight, high-performance structures for the attenuation of vibration. However, the ABH effect is known to cause a large amount of energy to be directed at a thin structural section, resulting in very high amplitude vibration of the ABH tip. This raises concerns about the level of dynamic stress within ABH tapers, which could limit the practical applications for which they are suitable. This thesis, therefore, presents an exploration into the possibility of reducing the dynamic stress within an ABH taper using both passive and active strategies.Initially, an assessment of the dynamic stress and vibration attenuation of a conventional ABH profile is presented using numerical simulations, including an exploration of the effect that varying several geometric parameters has on the performance of the structure. Following this, a parametrically defined modified ABH profile is proposed that implements an increased structural thickness in areas of high stress in a conventional ABH. The parameters defining the profile are optimised, aiming to reduce ABH taper stress while maintaining the vibration attenuation performance of the conventional profile. In order to validate these findings, experimental measurements of both the reflection coefficient and the dynamic bending stress are taken.Following the assessment of the performance of the modified ABH profile, the possibility of reducing the ABH taper stress using active control strategies is considered. Initially, the ABH taper stress is assessed for a feedforward wave-based active control strategy that has previously been shown to achieve good vibration attenuation performance. Following this, an active control strategy that aims to reduce the ABH taper stress is implemented, and its effect on the vibration attenuation performance of the ABH structure is assessed. Finally, the possibility of a combined control strategy that includes both the reflection coefficient and the ABH taper stress in the cost function is considered
Acoustic black hole, structure damper structurally damped structure and method
No full textThere is provided an acoustic black hole comprising: in a first axis, a taper from a first thickness to a second thickness, along a line; in a second axis perpendicular to the first axis, and away from the line, one or more regions of different spatial property relative to a spatial property of the ABH at the line
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