Abstract: Fuel and oxidant gas delivery plate, or fuel cell
plate, is a key component of a Proton Exchange Membrane (PEM)
fuel cell. To manufacture low-cost and high performance fuel cell
plates, advanced computer modeling and finite element structure
analysis are used as virtual prototyping tools for the optimization
of the plates at the early design stage. The present study examines
thermal stress analysis of the fuel cell plates that are produced
using a patented, low-cost fuel cell plate production technique
based on screen-printing. Design optimization is applied to
minimize the maximum stress within the plate, subject to strain
constraint with both geometry and material parameters as design
variables. The study reveals the characteristics of the printed
plates, and provides guidelines for the structure and material design
of the fuel cell plate.
Abstract: This paper presents a generalized formulation for the
problem of buckling optimization of anisotropic, radially graded,
thin-walled, long cylinders subject to external hydrostatic pressure.
The main structure to be analyzed is built of multi-angle fibrous
laminated composite lay-ups having different volume fractions of the
constituent materials within the individual plies. This yield to a
piecewise grading of the material in the radial direction; that is the
physical and mechanical properties of the composite material are
allowed to vary radially. The objective function is measured by
maximizing the critical buckling pressure while preserving the total
structural mass at a constant value equals to that of a baseline
reference design. In the selection of the significant optimization
variables, the fiber volume fractions adjoin the standard design
variables including fiber orientation angles and ply thicknesses. The
mathematical formulation employs the classical lamination theory,
where an analytical solution that accounts for the effective axial and
flexural stiffness separately as well as the inclusion of the coupling
stiffness terms is presented. The proposed model deals with
dimensionless quantities in order to be valid for thin shells having
arbitrary thickness-to-radius ratios. The critical buckling pressure
level curves augmented with the mass equality constraint are given
for several types of cylinders showing the functional dependence of
the constrained objective function on the selected design variables. It
was shown that material grading can have significant contribution to
the whole optimization process in achieving the required structural
designs with enhanced stability limits.
Abstract: Asiatic Houbara ( Chlamydotis macqueenii ) is a
flagship and vulnerable species. In-situ conservation of this
threatened species demands for knowledge of its habitat selection.
The aim of this study was to determine habitat variables influencing
birds wintering and breeding selection in semi- arid central Iran.
Habitat features of the detected nest and pellet sites were compared
with paired and random plots by quantifying a number of habitat
variables. In wintering habitat use at micro scale houbara selected
sites where vegetation cover was significantly lower compard to
control sites( p< 0.001). Areas with low number of larger plant
species (p=0.03) that were not too close to a vegetation
patch(p
Abstract: A novel path planning approach is presented to solve
optimal path in stochastic, time-varying networks under priori traffic
information. Most existing studies make use of dynamic programming
to find optimal path. However, those methods are proved to
be unable to obtain global optimal value, moreover, how to design
efficient algorithms is also another challenge.
This paper employs a decision theoretic framework for defining
optimal path: for a given source S and destination D in urban transit
network, we seek an S - D path of lowest expected travel time
where its link travel times are discrete random variables. To solve
deficiency caused by the methods of dynamic programming, such as
curse of dimensionality and violation of optimal principle, an integer
programming model is built to realize assignment of discrete travel
time variables to arcs. Simultaneously, pruning techniques are also
applied to reduce computation complexity in the algorithm. The final
experiments show the feasibility of the novel approach.
Abstract: This paper presents a unified approach based graph
theory and system theory postulates for the modeling and analysis
of Simple open cycle Gas turbine system. In the present paper, the
simple open cycle gas turbine system has been modeled up to its subsystem
level and system variables have been identified to develop the
process subgraphs. The theorems and algorithms of the graph theory
have been used to represent behavioural properties of the system like
rate of heat and work transfers rates, pressure drops and temperature
drops in the involved processes of the system. The processes have
been represented as edges of the process subgraphs and their limits
as the vertices of the process subgraphs. The system across variables
and through variables has been used to develop terminal equations of
the process subgraphs of the system. The set of equations developed
for vertices and edges of network graph are used to solve the system
for its process variables.