In this paper, the active vibrational structural intensity (VSI) in, and the radiated acoustic power from an infinite elastic plate in contact with a heavy fluid is modeled by the Mindlin plate theory. The plate is excited by a point force, which generates a vector-active VSI field in the plate. The resulting acoustic radiation generates an active acoustic intensity (AI) in the fluid medium. The displacement, shear deformation, VSI vector map, radiated acoustic pressure, and the AI vector map are computed. One, two, or four synchronous point controllers are placed symmetrically with respect to the point force on the plate. Minimization of either the structural intensity at a reference point or the total radiated acoustic power is achieved. Below coincidence, a significant portion of the point force input power is trapped in the plate in the form of VSI. The total radiated power is calculated by use of the input power from the source, the controllers, and the VSI. Above coincidence, a significant portion of the input source power is leaked to the fluid in the form of AI, so that the acoustic radiated power is equal to the input power from the source and the controllers.

In this paper, the active vibrational structural intensity (VSI) in and the radiated acoustic intensity (AI) from an infinite elastic plate in contact with a heavy fluid is modeled by the Mindlin plate theory. This theory includes the shear deformation and rotatory inertia in addition to flexure. The plate is excited by a point force, which generates a vector active VSI field in the plate. The active VSI has two components; one depends on the shear force, and the other depends on the moment. The resulting acoustic radiation generates an active AI in the fluid medium. First, the Green’s functions for the plate with and without fluid loading were developed. These were then used to develop expressions for VSI and AI vector fields. The displacement, shear deformation, VSI vector map, radiated acoustic pressure, and the AI vector map are computed for frequencies below and above the coincidence frequency. Below coincidence, a significant portion of the point force input power is trapped in the plate in the form of VSI. Above coincidence, a significant portion of the input source power is leaked to the fluid in the form of AI, with a small portion propagating to the far-field VSI.

In this study, the active control of active vibrational structural intensity (SI) in an infinite elastic plate is discussed. The plate is excited by mechanical noise sources, which generate a vector active SI field in the plate. A set of control actuators made up of point forces and point moments are located judiciously on the plate. The vibrational active SI-vector components are quadratic functions of the mechanical noise sources and control actuators magnitudes and phases. Thus the magnitude-squared active vector-SI at a sensor point is an expression with up to fourth power in the sources and actuators magnitudes and phases. An algorithm is developed to minimize the active SI using steepest descent on the gradient of the magnitude-squared total SI to obtain optimum values for magnitudes and phases of the control point actuators. Test cases are discussed to exhibit the influence of excitation structural wavelength, relative location of the control actuators to the mechanical noise source region, the orientation of the point moments, and the optimum combination of point forces and moments to minimize the total intensity in the near and far field. An attempt is made to explore actuators configurations that result in efficient local or global control. a)Currently Visiting Scholar at Penn State.

In a previous paper, the active control of active structural intensity (SI) in an infinite elastic plate was discussed. The plate is excited by mechanical noise sources, which generate a vector active SI field in the plate. A colocated point force and a point moment actuator at an arbitrary location on the plate were used. An algorithm was developed to minimize the active SI at a reference point on the plate. The control strategy was aimed at minimization of only the SI at a reference point. In this paper, the active control of SI in a desired zone or a large global area of the plate is explored through the use of multiple controllers spread over the plate. Furthermore, the cost function to be minimized also includes the required power injected by the controllers. Thus the minimization algorithm minimizes both the total SI in a zone as well as the total injected power by the controllers. The influence of the number and type of controllers, and the location of these controllers relative to the source region for the minimization of both the total SI in a region and the input mechanical power of these controllers, is explored. a)Currently Visiting Scholar at Penn State Univ.

The active control of power flow in a T beam was presented at the 134th Meeting of the Acoustical Society of America. In that paper, the mechanical noise source was a shear force in the plane of the T beam. In this paper, the active control of structural intensity in the T beam is achieved for a general shear mechanical noise source that has in-plane and out-of-plane components. The reduction of the total power flow at a control point located midway in the vertical leg of the T beam is achieved through control actuators that are located at one end of the straight part of the T beam. The vector control actuators have components in three-dimensional space in various combinations of normal forces, shear forces, torques, and moments. The efficiency of the structural intensity reduction is considered for local versus global control. Various control strategies are compared which are also aimed at minimizing the cost function that represents the total power requirement for the control process versus the noise input power.