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Energy Harvesting & Design Optimization Lab. |
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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.
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.
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.
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.
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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Energy Harvesting & Design Optimization
Lab. University of Maryland Baltimore County,
Dept. of Mechanical Engineering 1000 Hilltop Circle, Baltimore, MD, 21250 © 2013 |
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