Browsing by Subject "wire"
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Item Experimental examination of wire mesh dampers subjected to large amplitude displacements(2009-06-02) Jones, Adam MatthewWire mesh dampers are under investigation because they are seen as replacements for squeeze film dampers as a source of direct stiffness and damping at bearing locations. There are several advantages of wire mesh dampers over squeeze film dampers, including: temperature insensitivity, oil-free operation, and the ability to contain large amplitude vibrations. Furthermore, due to their direct damping and lack of cross-coupled stiffness, the wire mesh reduces the response to imbalance and increases the stability of the system. The objective of this research was to determine the properties of wire mesh dampers under large amplitude vibrations. Impact testing was first conducted on the wire mesh as a means of obtaining the large amplitudes that were of interest. Next, to verify the results, a second methodology was employed using shaker testing. It was found that both the stiffness and hysteretic damping decrease with increasing displacement. However, they both approached asymptotes around 2 mils of displacement, and further increases in displacement had significantly less effect on the properties. Once the results were verified to be consistent, equations were obtained to describe the response of the wire mesh dampers. These equations were then used to create a new design workbook, which would allow an engineer to determine the properties of wire mesh dampers under conditions that they might experience.Item Exploiting level sensitive latches in wire pipelining(Texas A&M University, 2005-02-17) Seth, VikramThe present research presents procedures for exploitation of level sensitive latches in wire pipelining. The user gives a Steiner tree, having a signal source and set of destination or sinks, and the location in rectangular plane, capacitive load and required arrival time at each of the destinations. The user also defines a library of non-clocked (buffer) elements and clocked elements (flip-flop and latch), also known as synchronous elements. The first procedure performs concurrent repeater and synchronous element insertion in a bottom-up manner to find the minimum latency that may be achieved between the source and the destinations. The second procedure takes additional input (required latency) for each destination, derived from previous procedure, and finds the repeater and synchronous element assignments for all internal nodes of the Steiner tree, which minimize overall area used. These procedures utilize the latency and area advantages of latch based pipelining over flip-flop based pipelining. The second procedure suggests two methods to tackle the challenges that exist in a latch based design. The deferred delay padding technique is introduced, which removes the short path violations for latches with minimal extra cost.Item Structural Thermomechanical Models for Shape Memory Alloy Components(2014-04-18) Rao, AshwinThermally responsive shape memory alloys (SMA) demonstrate interesting properties like shape memory effect (SME) and superelasticity (SE). SMA components in the form of wires, springs and beams typically exhibit complex, nonlinear hysteretic responses and are subjected to tension, torsion or bending loading conditions. Traditionally, simple strength of materials based models/tools have driven engineering designs for centuries, even as more sophisticated models existed for design with conventional materials. In light of this, an effort to develop strength of materials type modeling approach that can capture complex hysteretic SMA responses under different loading conditions is undertaken. The key idea here is of separating the thermoelastic and the dissipative part of the hysteretic response by using a Gibbs potential and thermodynamic principles. The dissipative part of the response is later accounted for by a discrete Preisach model. The models are constructed using experimentally measurable quantities (like torque?twist, bending moment?curvature etc.), since the SMA components subjected to torsion and bending experience an in-homogeneous non-linear stress distribution across the specimen cross-section. Such an approach enables simulation of complex temperature dependent superelastic responses including those with multiple internal loops. The second aspect of this work deals with the durability of the material which is of critical importance with increasing use of SMA components in different engineering applications. Conventional S-N curves, Goodman diagrams etc. that capture only the mechanical loading aspects are not adequate to capture complex thermomechanical coupling seen in SMAs. Hence, a novel concept of driving force amplitude v/s number of cycles equivalent to thermodynamical driving force for onset of phase transformations is proposed which simultaneously captures both mechanical and thermal loading in a single framework. Recognizing the paucity of experimental data on functional degradation of SMAs (especially SMA springs), a custom designed thermomechanical fatigue test rig is used to perform user defined repeated thermomechanical tests on SMA springs. The data from these tests serve both to calibrate the model and establish thermodynamic driving force and extent of phase transformation relationships for SMA springs. A drop in driving force amplitude would suggest material losing its ability to undergo phase transformations which directly corresponds to a loss in the functionality/smartness of SMA component. This would allow designers to set appropriate driving force thresholds as a guideline for analyzing functional life of SMA components.