Active attenuation of the wave transmission through an L-plate junction

Active control is applied to an L-shaped plate in order to attenuate the flexural energy transmission from one plate to the other. The coupled plates are simply supported along two parallel sides, and free at the other two ends. Point forces are used to generate the primary and secondary excitation of the plates. The flexural wave coefficients are determined from the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction of the two plates. Bending, shearing, and longitudinal effects are taken into consideration at the corner junction. Under broadband frequency control at a discrete location in plate 2, both the control shaker and the error sensor are optimally located to achieve the best control performance. Results show that when the control force and error sensor are arbitrarily located, the control performance is dependent on the excitation frequency. When both the control force and error sensor are optimally located with respect to the primary shaker location in a symmetrical arrangement, the control performance is both maximized and independent of the excitation frequency. Using single-frequency control to attenuate the total vibrational response of the coupled plates, the error sensor location is strongly mode dependent. It is shown that using a single, properly located control force and a single, properly located error sensor, global attenuation of the L-shaped plate can be achieved

Active control of the plate energy transmission in a semi-infinite ribbed plate

Active control of the plate flexural wave transmission through the beam in a semi-infinite beam-reinforced plate is analytically investigated. The ribbed plate is modeled as a continuous system, using equations of motion to describe the plate in flexure and the beam in both flexure and torsion. The maximum transmission of the plate flexural waves through the reinforcing beam is found to occur at resonance frequencies corresponding to the optimal coupling between the plate flexural waves and the flexural and torsional waves in the beam. A single control force is applied to the beam, and a cost function is developed to attenuate the far-field flexural energy transmission. It can be observed that the transmission peaks corresponding to the flexural resonances in the beam are reduced. Similarly, the transmission peaks corresponding to the torsional resonance conditions in the beam can be attenuated using a single control moment applied to the beam. Significant attenuation of all the resonance peaks in the flexural wave transmission can also be achieved with the application of a single force and a single moment collocated on the beam. In this paper, the feasibility of attenuating the flexural wave transmission due to both the flexural and torsional resonance conditions by using a single point force and point moment collocated on the beam is demonstrated

Power transmission in L-shaped plates including flexural and in-plane vibration

In this paper, power flow propagation in plates connected in an L-joint is investigated in both the low and high frequency ranges. An exact solution is derived to describe the flexural, in-plane longitudinal and in-plane shear wave motion in the plates. The coupled plates are simply supported along two parallel sides, and free at the other two ends. A point force is used to generate flexural wave motion only. The flexural wave coefficients are determined from the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction of the plates. Structural intensity expressions are used to examine the structural noise transmission in the low and high frequency ranges. The contributions from the individual wave types are also examined

The effect of structural coincidences on the acoustic fields radiated from a ribbed plate under light fluid-loading

In this paper, the acoustic fields radiated from a ribbed plate under light fluid-loading are examined. In the ribbed plate system, the reinforcing beam affects both the propagation of the flexural waves in the plate, as well as the sound radiation from the structure. A subsonic incident flexural wave in the plate impinging on the beam discontinuity generates transmitted and reflected propagating waves, and transmitted and reflected near-field waves in the plate. The scattering of the structural wave field gives rise to supersonic wave number components of the plate vibration, which subsequently leads to sound radiation into the surrounding fluid field. Two structural coincidence conditions have been identified in this paper. Physically, they correspond to the optimal trace wave matching between the flexural waves in the plate and the flexural and torsional waves in the beam. This paper reports for the first time a new observation concerning the characteristics of the radiating sound fields that occur because of structural coincidence conditions

A hybrid approach to predict the vibration transmission in ship structures using a waveguide method and statistical energy analysis

Prediction of vibration transmission in ship structures is important, to design maritime vessels with greater power and\ud reduced weight, without increasing noise levels. As the frequency increases, and hence the number of modes increases, it is more practical to consider average responses and their distribution over the structure, using a technique such as Statistical Energy Analysis (SEA). Numerical results from an exact, analytical waveguide model are compared with those of conventional SEA models. These results include both response predictions and the SEA parameters. The theoretical estimation of the SEA parameters, namely the coupling loss factors, form the basis for the hybrid approach between the waveguide method and SEA technique. Results are presented for plate structures in an L, T and X-shaped configuration, and a complex built-up structure

An analytical investigation of single actuator and error sensor control in connected plates

Vibrations in structures travel in the form of flexural and extensional waves, and transfer energy to other components of the system coupled to the structure. This may result in an undesirable system response or sound radiation. This paper presents an analytical and computational investigation of active control of the dynamic response characteristics of a series of rectangular plates coupled together and subject to point force excitation. The idealized periodic point force may represent the actions of vibrating mounted machinery such as motors or engines. Feedforward active control of the flexural waves in the plate configurations is applied to actively attenuate the structural response. It is shown that for L, T and cross-shaped plates, global attenuation may be achieved using a single control source and a single error sensor

Active control of connected plates using single and multiple actuators and error sensors

Active control of the structure-borne vibration transmission in resonant, built-up structures which typically represent a ship hull is analytically and experimentally investigated. Using feedforward active control, the control performance is compared for both dependent and independent control force arrangements. Multiple actuator control forces and multiple error sensors are used to actively control the frequency response. The global response of the coupled plate structure is also presented for active control at discrete resonance frequencies

An analytical and experimental comparison of optimal actuator and error sensor location for vibration attenuation

Feedforward active control of the flexural waves in a single and L-shaped plate has been analytically and experimentally investigated. The plates are simply supported along two parallel edges, and free at the other two ends. Point forces were used to generate the primary and secondary plate excitations. The plate flexural displacement is described by a combination of a travelling wave solution and a modal expansion. The flexural wave coefficients were determined using the boundary conditions, continuity equations at the driving force locations, and continuity equations at the corner junction for the L-shaped plate. The control actuator and error sensor are optimally located in order to achieve the best control performance