Finite element modeling of truss structures with frequency-dependent material damping

A physically motivated modelling technique for structural dynamic analysis that accommodates frequency dependent material damping was developed. Key features of the technique are the introduction of augmenting thermodynamic fields (AFT) to interact with the usual mechanical displacement field, and the treatment of the resulting coupled governing equations using finite element analysis methods. The AFT method is fully compatible with current structural finite element analysis techniques. The method is demonstrated in the dynamic analysis of a 10-bay planar truss structure, a structure representative of those contemplated for use in future space systems

Transfer having a coupling coefficient higher than its active material

A coupling coefficient is a measure of the effectiveness with which a shape-changing material (or a device employing such a material) converts the energy in an imposed signal to useful mechanical energy. Device coupling coefficients are properties of the device and, although related to the material coupling coefficients, are generally different from them. This invention describes a class of devices wherein the apparent coupling coefficient can, in principle, approach 1.0, corresponding to perfect electromechanical energy conversion. The key feature of this class of devices is the use of destabilizing mechanical pre-loads to counter inherent stiffness. The approach is illustrated for piezoelectric and thermoelectrically actuated devices. The invention provides a way to simultaneously increase both displacement and force, distinguishing it from alternatives such as motion amplification, and allows transducer designers to achieve substantial performance gains for actuator and sensor devices

Model reduction for analysis of cascading failures in power systems

In this paper, we apply a principal-orthogonal decomposition based method to the model reduction of a hybrid, nonlinear model of a power network. The results demonstrate that the sequence of fault events can be evaluated and predicted without necessarily simulating the whole system

Wind Energy Workforce Development: Engineering, Science, & Technology

Broadly, this project involved the development and delivery of a new curriculum in wind energy engineering at the Pennsylvania State University; this includes enhancement of the Renewable Energy program at the Pennsylvania College of Technology. The new curricula at Penn State includes addition of wind energy-focused material in more than five existing courses in aerospace engineering, mechanical engineering, engineering science and mechanics and energy engineering, as well as three new online graduate courses. The online graduate courses represent a stand-alone Graduate Certificate in Wind Energy, and provide the core of a Wind Energy Option in an online intercollege professional Masters degree in Renewable Energy and Sustainability Systems. The Pennsylvania College of Technology erected a 10 kilowatt Xzeres wind turbine that is dedicated to educating the renewable energy workforce. The entire construction process was incorporated into the Renewable Energy A.A.S. degree program, the Building Science and Sustainable Design B.S. program, and other construction-related coursework throughout the School of Construction and Design Technologies. Follow-on outcomes include additional non-credit opportunities as well as secondary school career readiness events, community outreach activities, and public awareness postings

DETC2006-99439 HINGED BEAM ELEMENTS FOR THE TOPOLOGY DESIGN OF COMPLIANT MECHANISMS USING THE GROUND STRUCTURE APPROACH

ABSTRACT The design obtained from a topology optimization problem can largely depend on the type of the ground structure used. A new type of ground structure containing hinged beam elements is described in this paper that reduces the dependence of the optimal design on the ground structure. Apart from the beam and truss elements that have traditionally been used, two new types of elements are introduced: 1) a beam with a hinge on one end and a solid connection on the other end, 2) beam element with hinges on both ends. These elements are particularly useful when applied to a compliant mechanism design using a truss/beam type ground structure. A couple of compliant mechanism problems are solved to demonstrate the effectiveness of these elements

Damping Models for Shear Beams With Applications to Spacecraft Wiring Harnesses

Presented on September 20, 2012 from 3:30-4:30 pm in Guggenheim 442.Dr. Georgia Lesieutre is Professor and Head of the Deparment of Aerospace Engineering and Director of the Center for Acoustics and Vibration at Penn State. He earned a B.S. in Aeronautics and Astronautics from MIT, and a PhD in Aerospace Engineering from UCLA. Prior to joining Penn State, he held positions at SPARTA, Rockwell Satellite Systmes, Allison Gas Turbines, and Argonne National Lab. His research interests include structural dynamics of aerospace systems, including passive damping, active structures, and energy harvesting. Dr. Lesieutre served as PI of several major DARPA programs in adaptive structures, and has received five society best paper awards. He is a Fellow of AIAA, and serves on the AIAA Board of Directors. He was a member of the Materials Panel of the recent National Research Council study of the NASA (Space) Technology Roadmaps. He once paddled a canoe from Montreal to the Gulf of Mexico as part of a historical reenactment, and more recently ran a 50-mile ultramarathon.Runtime: 58:53 minutes.Damping is an important aspect of aerospace sturctures designed to operate in dynamic environments. Wiring harnesses can significantly affect the dynamics of spacecraft structures. High-fidelity models of the coupled structure-cable dynamic system are needed to accurately predict launch loads and potential control system interactions. A beam model including first-order transverse shear can accurately capture the effects of cable mass and stiffness on dynamic response and provide insight into structural behavior. However, available time-domain damping models are inadequate for use in such a model- common proportional damping models predict modal damping that depends strongly and unrealistically on frequency. Inspired by a geometirc rotation-based viscous damping model that provides frequency-independent modal damping in an Euler-Bernoulli beam model, several time-domain viscous damping models are presented that exhibit weaker frequency dependence than proportional damping models. At low frequencies (bendingdominated modes), the models provide modal damping that is either directly or inversely proportional to the mode number. Model predictions compare favorably to available experimental data

Damping Models For Timoshenko Beams With Applications To Spacecraft Wiring Harnesses

Power and data cabling are attached to a spacecraft bus structure at many points and can account for a significant fraction of a spacecraft\u27s dry mass. This combination leads to coupled spacecraft and cable dynamics that require a model to predict the effects of this interaction. While current models can accurately predict vibration frequencies, typical proportional damping models are inadequate. Instead, a viscous damping model that produces approximately frequency-independent modal damping in Euler-Bernoulli and shear beams is considered. The relevant viscous damping terms (as well as those commonly employed in proportional damping approaches) are extended and modified for application to Timoshenko beams. The inclusion of rotary inertia does add some frequency-dependence; however, careful selection of damping coefficients can produce a large range of approximately frequency-independent modal damping. As transverse shear and rotary inertia effects become large, this range decreases, with the terms producing modal damping values that increase or decrease with mode number in a fashion similar to typical proportional damping models, but at a much lower rate. When transverse shear and rotary inertia effects approach zero, collapses to the one that provides frequency-independent modal damping for the Euler-Bernoulli beam. © 2013 by Jeffrey L. Kauffman and George A. Lesieutre

\u27Geometric\u27 Viscous Damping Model For Nearly Constant Beam Modal Damping

This paper considers the damped transverse vibration of flexural structures. Viscous damping models available to date, such as proportional damping, suffer from the deficiency that the resulting modal damping is strongly frequency dependent, which is a situation not representative of experiments with built-up structures. The focus model addresses a viscous geometric damping term in which an internal resisting shear force is proportional to the time rate of change of the slope. Separation of variables does not lead directly to a solution of the governing partial-differential equation, although a boundary-value eigenvalue problem for free vibration can nevertheless be posed and solved. For small damping the method of weighted residuals provides an alternate approach to the development of approximate modal equations of motion and estimation of modal damping. In a discretized finite-element context the resulting damping matrix resembles the geometric stiffness matrix used to account for the effects of membrane loads on lateral stiffness. For beams having any combination of hinged and guided boundary conditions this model yields constant modal damping that is independent of frequency as well as real mode shapes. For more general boundary conditions modal damping varies somewhat, approaching the expected constant value with increasing mode number; furthermore, the mode shapes are complex. This viscous damping model should prove useful to researchers and engineers who need a simple time-domain damping model that exhibits more realistic variation of damping with frequency than the alternatives. Copyright © 2013 by Christopher Porter, R. Mark Rennie, Eric J. Jumper