Mehmet Bulent Ozer

Extending Den Hartog's vibration absorber technique to multi-degree-of-freedom systems

The most common method to design tuned dynamic vibration absorbers is still that of Den Hartog, based on the principle of invariant points. However, this method is optimal only when attaching the absorber to a single-degree-of-freedom undamped main system. In the present paper, an extension of the classical Den Hartog approach to a multi-degree-of-freedom undamped main system is presented. The Sherman-Morrison matrix inversion theorem is used to obtain an expression that leads to invariant points for a multi-degree-of-freedom undamped main system. Using this expression, an analytical solution for the optimal damper value of the absorber is derived. Also, the effect of location of the absorber in the multi-degree-of-freedom system and the effect of the absorber on neighboring modes are discussed.

Boundary element model for simulating sound propagation and source localization within the lungs

An acoustic boundary element (BE) model is used to simulate sound propagation in the lung parenchyma. It is computationally validated and then compared with experimental studies on lung phantom models. Parametric studies quantify the effect of different model parameters on the resulting acoustic field within the lung phantoms. The BE model is then coupled with a source localization algorithm to predict the position of an acoustic source within the phantom. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm does not perform as well if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. The BE model and source localization procedure are then applied to actual lung geometry taken from the National Library of Medicines Visible Human Project. These numerical studies are in agreement with the studies on simpler geometry in that use of a BE model in place of the free field assumption alters the predicted acoustic field and source localization results. This work is relevant to the development of advanced auscultatory techniques that utilize multiple noninvasive sensors to construct acoustic images of sound generation and transmission to identify pathologies.

Experimental and Computational Models for Simulating Sound Propagation Within the Lungs

An acoustic boundary element model is used to simulate sound propagation in the lung parenchyma and surrounding chest wall. It is validated theoretically and numerically and then compared with experimental studies on lung-chest phantom models that simulate the lung pathology of pneumothorax. Studies quantify the effect of the simulated lung pathology on the resulting acoustic field measured at the phantom chest surface. This work is relevant to the development of advanced auscultatory techniques for lung, vascular, and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.

Modeling the effect of piezoceramic hysteresis in structural vibration control

Dielectric hysteresis in piezoceramic transducers can degrade their performance in structural vibration control applications. Different hysteresis models have been applied to piezoelectric transducers, including those based on Preisach, Jiles-Atherton and Ishlinskii concepts. Relationships between these and other models, new experimental identification schemes and multi-term describing function representations of some of them are reviewed. Then, system equations that incorporate the hysteretic behavior are formulated for two pedagogical smart structural systems: a passively shunted / actively driven PZT wafer on (1) a simply supported thin plate and (2) a simply supported thin beam. The effect of PZT hysteresis on optimized passive and hybrid vibration control strategies is evaluated.

Experimental and Computational Models for Simulating Sound Propagation and Acoustic Source Localization Within the Lungs

An acoustic boundary element (BE) model for porous compliant material like the lung parenchyma is developed and validated theoretically and experimentally. This BE model is coupled with a source localization algorithm to predict the position of an acoustic source within a lung phantom. The BE model is also coupled with a finite element (FE) model to simulate the surrounding shell-like chest wall. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm fails if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. This research is relevant to the development of advanced auscultatory techniques for lung, vascular and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.Copyright

Applications of the Sherman-Morrison matrix inversion formula in linear and non-linear vibrations, controls and acoustics

Applications of the Sherman-Morrison matrix inversion formula are reviewed and demonstrated for several problems in sound and vibration control. The inversion formula enables one to easily separate the effect of a perturbation or subcomponent on the dynamic behavior of the overall system. Applications of this technique that are demonstrated here include: identifying optimal PZT electrical shunt parameter values to minimize sound radiation from a PZT-plate structure, identifying the optimal location and parameter values of a tuned dynamic vibration absorber attached to a multi-degree of freedom, damped system, and identifying and quantifying an isolated non-linearity in an otherwise linear system. Extensions to active control system design are also discussed.Copyright