Tony J. Anderson

Large-deformation tests and total-Lagrangian finite-element analyses of flexible beams

Presented here is a total-Lagrangian displacement-based finite-element formulation for general anisotropic beams undergoing large displacements and rotations. The theory fully accounts for geometric nonlinearities (large rotations), general initial curvatures, and extensionality by using Jaumann stress and strain measures, an exact coordinate transformation, and a new concept of orthogonal virtual rotations. Moreover, transverse shear deformations are accounted for by using a first-order shear-deformation theory. To verify the accuracy of the finite-element model, two test fixtures have been built for bending and twisting experiments. Large static deformation tests of beams with different loading conditions have been performed. The finite-element results agree closely with the experimental results and numerically exact solutions obtained by using a multiple shooting method to solve for post-buckling deformations of highly flexible beams undergoing large static rotations and displacements in three-dimensional space.

Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial life

BackgroundDetecting microbial life in extraterrestrial locations is a goal of space exploration because of ecological and health concerns about possible contamination of other planets with earthly organisms, and vice versa. Previously we suggested a method for life detection based on the fact that living entities require a continual input of energy accessed through coupled oxidations and reductions (an electron transport chain). We demonstrated using earthly soils that the identification of extracted components of electron transport chains is useful for remote detection of a chemical signature of life. The instrument package developed used supercritical carbon dioxide for soil extraction, followed by chromatography or electrophoresis to separate extracted compounds, with final detection by voltammetry and tandem mass-spectrometry.ResultsHere we used Earth-derived soils to develop a related life detection system based on direct observation of a biological redox signature. We measured the ability of soil microbial communities to reduce artificial electron acceptors. Living organisms in pure culture and those naturally found in soil were shown to reduce 2,3-dichlorophenol indophenol (DCIP) and the tetrazolium dye 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). Uninoculated or sterilized controls did not reduce the dyes. A soil from Antarctica that was determined by chemical signature and DNA analysis to be sterile also did not reduce the dyes.ConclusionObservation of dye reduction, supplemented with extraction and identification of only a few specific signature redox-active biochemicals such as porphyrins or quinones, provides a simplified means to detect a signature of life in the soils of other planets or their moons.

Response prediction of switched inductor/piezoelectric vibration suppression

Switched electromechanical shunts have been proposed as a method to suppress vibrations of a mechanical structure. In this method, a piezoelectric patch is attached to the vibrating structure. An inductor and series switch are shunted across the electrodes of the piezoelectric patch. At maximum and minimum displacements, the polarity of the charge on the patch is changed by closing the switch that shunts a piezoelectric element to ground through an inductor. The method is similar to an active velocity feedback technique where the forces from the piezoelectric patch to the structure always oppose the velocity. Previous work used numerical simulation to demonstrate the degree of vibration suppression that can be obtained with the switched electromechanical shunts method. In this paper, a novel and transparent algebraic closed-form expression is derived. This algebraic expression predicts the displacement amplitude of the vibrating structure with a switched shunt in terms of the mechanical properties of the structure, the electromechanical coupling coefficient, and the shunt parameters. The closed-form expression clearly shows which system parameters need to be changed to optimize the performance of this vibration suppression method. Experiments were performed that verified the theoretical closed-form expression for displacement amplitude. It was shown that the maximum suppression that can be obtained with this method is determined by the allowable voltage drop across the piezoelectric element.

Passive vibration suppression using nonlinear electromechanical coupling

The development of a new class of passive vibration and acoustic suppression systems is presented. The approach is to transfer the energy from one mechanical system to another using reversible piezoelectric transducers connected with a passive electric circuit. Response of the first system is suppressed while exciting the response of the second system. The two mechanical systems can be physically separated structures, or different mechanical modes of a single structure. The passive electric circuit is a network containing diodes and/or transistors switched from the piezoelectric voltages. Reductions of 25% in the response of the directly excited system have been shown. This approach is an improvement over a passive shunt technique in that the typically heavy inductor in the electrical shunt is replaced with an existing system mechanical impedance. It also has the advantage over active control techniques in that an external power source is not required and there is no possibility to add energy to the syste...

Large torsional deformation of a circular band

A total-Lagrangian displacement-based finite-element model of initially curved beams undergoing large displacements and rotations is derived using a beam theory that fully accounts for large rotations and extensionality by using Jaumann stress and strain measures. To verify the accuracy of the finite-element model, a test fixture has been built and used to test the large twisting of a circular band. The finite-element results agree closely with the experimental results.

Tuned passive vibration suppression using linear electro‐mechanical coupling

One proposed method to suppress vibrations of a mechanical structure is to couple the energy of vibration to an external electric shunt circuit. Coupling of the mechanical energy to the electric circuit is accomplished with a piezoelectric transducer attached to the structure. Significant amounts of mechanical energy can be dissipated by the shunt, but a large inductor is required. In this presentation, we describe an alternative approach that replaces the shunt with a linear passive electric circuit that is connected to another piezoelectric transducer attached to the structure. Even though the electric circuit does not contain an inductor, it is still possible to dissipate significant amounts of mechanical energy in the connecting circuit. The mechanism of energy dissipation in the electric circuit is similar to, but not identical to, that exploited by a tuned electric shunt. Inductance, however, is provided by mutual coupling of piezoelectric transducers on the structure.

Application of system identification to ultrasonic waveforms

In the context of NonDestructive Evaluation (NDE), system identification is a process that can be used to extract sample properties from ultrasonic waveforms. Usually, system identification is applied directly to time series data. We describe a novel application of system identification. The process is applied to ultrasonic data in the frequency domain. Some investigators have pointed out that useful information can be obtained from the cepstral analysis of frequency domain data. Our approach further generalizes this practice, to the point that frequency domain data are identically mapped to a linear system, with frequency playing the role of time. We believe that our approach can be used to extract material properties, provide sensitive measures to flaws, return detailed information about flaws, extrapolate the bandwidth of ultrasonic measurements, and provide avenues for data compression.