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Energy Harvesting & Design Optimization Lab.

University of Maryland Baltimore County, Dept. of Mechanical Engineering

 

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Completed Topics – Energy Harvester / Topology Optimization / Shape Optimization / RBDO

 

1. Smooth boundary topology optimization:

A new topology optimization methodology, named smooth boundary topology optimization, is proposed to overcome the shortcomings of cell-based approaches, where the number of design variables tends to be too large, and a filtering process or an image process must be followed for an applicable result. The domain boundary is initially represented by a geometric function, B-spline curves composed of a number of control points, and the density of each finite element is not considered; only the location of the control point is considered. After calculating two kinds of design sensitivities, the topological sensitivity and the shape sensitivity of the B-spline’s control points, the design is improved by either creating a hole in the domain or moving control points to change the boundary, or both if necessary. These two kinds of design sensitivities are verified by comparing with the numerical sensitivity.

 

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Smooth boundary topology optimization:  Basic concept

Selection Criterion (SC)

 

Selection criterion, SC, is introduced to determine the moment of creating a hole. SC is defined as the sensitivity of an objective function divided by the sensitivity of a constraint function, and it means the ratio of improving the objective function to sacrificing the constraint function. Two kinds of SCs on creating a hole and moving boundary are calculated and compared to determine the direction of design modification. Once it is determined to create a hole, its boundary is represented by a new B-spline with a sufficient number of control points and recognized as a new boundary of the design domain. Additionally, some manipulative topics on programming are covered related to boundary rendering: the side constraints of each design variable (the location of control point) to prevent curve entangling phenomenon, and the hole merging functionality in case an intersection between two separate holes occurs. The feasibility of this methodology is shown with several applications where compliance or natural frequency is chosen as a performance measure.

Using this methodology, a new design of a hip prosthesis and a flexure stage are studied. It is shown that this method is a natural way of obtaining smooth boundary topology design effectively which combines computer graphics technique and design sensitivity analysis, and leads to good results with uniform density and smooth boundaries.

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Hip prosthesis design

Flexural stage design

 

 

2. Topology/shape design of energy harvesting skin:

Some drawbacks of cantilever type EH device (need of additional housing and possibility of vibration energy loss due to imperfect clamping condition) have motivated an innovative and practical “energy harvesting skin (EHS)”. In the EHS, thin piezoelectric patches are directly attached onto a vibrating shell structure to harvest electric power. I proposed a practical design method for piezoelectric patches to be segmented by inflection lines from multiple vibration modes in order to minimize voltage cancellation and utilize multiple vibration modes.

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Inflection line removal for preventing voltage cancellation

Optimization procedure for EH skin

 

Considering the practical use of EHS for providing an operating energy for wireless sensors, easily obtainable ambient vibration energy sources are employed in this research: outdoor unit and power transformer. Usually they are continuously operated and provide long-lasting ambient vibration energy with relative high-level vibration amplitude. For each case the top and front panel is chosen as design domain for additional piezoelectric patch and the power output of 4.8mW, 4.1mW has been obtained, respectively.

 

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Outdoor unit EH Skin design
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EH Skin design

 

 

 

3. Structural Network Synthesis for Passive Adaptive Shock Absorbing/Energy Harvesting System:

The increasing interest in engineering systems with excellent mitigation of vibration and shock has required novel design approaches which provide systems with passive adaptive performance across the different fields of engineering. In this research we present a novel modular design concept to synthesize passive adaptive structures upon a varied loading condition. This concept interconnects linear and nonlinear structural elements depending on the scale and performance requested to the final structural system. To realize this concept we developed a structural synthesis tool integrated with the genetic algorithm. The design optimization problem is formulated considering the prescribed design requirement on stiffness and damping performance. This tool optimally synthesizes the structural network by assembling the available constitutive elements in the set and successfully obtains passive adaptive assembly upon a varied loading condition in terms of vibration amplitude and frequency.

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Integration of modular structure for passive adapted dynamic performance

Periodic bistable vibration of snap through device

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Case study to synthesize three modular structures with linear/nonlinear joints

Loss factor plot for the cases on the left

 

 

 

 

 

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Energy Harvesting & Design Optimization Lab.

University of Maryland Baltimore County, Dept. of Mechanical Engineering

1000 Hilltop Circle, Baltimore, MD, 21250

© 2013