Iranian Aerospace Society
Journal of Aerospace Science and Technology
1735-2134
2345-3648
3
4
2006
12
01
An Introduction to a New Criterion Proposed for Stopping GA Optimization Process of a Laminated Composite Plate
167
176
EN
A.
Abedian
abedian@sharif.edu
Several traditional stopping criteria in Genetic Algorithms (GAs) are applied to the optimization process of a typical laminated composite plate. The results show that neither of the criteria of the type of statistical parameters, nor those of the kinds of theoretical models performs satisfactorily in determining the interruption point for the GA process. Here, considering the configuration of the history curve of the maximum objective or fitness value with generation number, a Logarithmic Performance Criterion (LPC) is introduced as a stopping criterion for optimization of composite plates. The results highlight the advantages of LPC in performing sufficiently smooth (no noise), requiring reasonable number of generations, less parameter dependency, lower need for conservative assumption, on-line controllability, wide scope applicability, and reasonably easy application in engineering decision-making problems.
Genetic algorithm,optimization,Stopping Criterion,Laminated Composite Plate
https://jast.ias.ir/article_51523.html
https://jast.ias.ir/article_51523_0bfcaa670927cc5ffa78f22568d5a8ef.pdf
Iranian Aerospace Society
Journal of Aerospace Science and Technology
1735-2134
2345-3648
3
4
2006
12
01
outflow Boundary Codition Issues in Direct Numerical Simulation of Three- Dimensional Plane Wake Flow
177
183
EN
M.J.
Maghrebi
javad@shahroodut.ac.ir
https://jast.ias.ir/article_51524.html
https://jast.ias.ir/article_51524_8592da2700935cfef736fd7b2aa667dd.pdf
Iranian Aerospace Society
Journal of Aerospace Science and Technology
1735-2134
2345-3648
3
4
2006
12
01
Mixed-mode I/II Interlaminar Fracture of CF/PEI Composite Material
185
193
EN
Naghdali
Choupani
choupani@sut.ac.ir
Failures in composite materials occur mainly due to interlaminar fracture, also called delamination, between laminates. This indicates that characterizing interlaminar fracture toughness is the most effective factor in the fracture of composite materials. This study reports investigation on mixed-mode interlaminar fracture behaviour in woven carbon fibre/polyetherimide (CF/PEI) thermoplastic composite material based on experimental and numerical analyses. Experiments were conducted using the special test loading device. By varying the loading angle,? from 0? to 90?, pure mode-I, pure mode-II and a wide range of mixed-mode data were obtained experimentally. Using the finite-element results, geometrical factors were applied to the specimen. Based on experimentally measured critical loads, mixed-mode interlaminar fracture toughness for the composite under consideration determined. The fracture surfaces were examined by scanning electron microscopy to gain insight into the failure responses.
https://jast.ias.ir/article_51525.html
https://jast.ias.ir/article_51525_02c4b068d2d6d2f8489771d9ae7d375b.pdf
Iranian Aerospace Society
Journal of Aerospace Science and Technology
1735-2134
2345-3648
3
4
2006
12
01
MULTI FRACTURE/DELAMINATION ANALYSIS OF COMPOSITES SUBJECTED TO IMPACT LOADINGS
195
204
EN
Soheil
Dr. Mohammadi
University of Tehran
smoham@ut.ac.ir
A combined finite/ discrete element method is presented for modelling of composite specimens subjected to dynamic/impact loadings. The main task is set on developing an algorithm for simulation of potential bonding and debonding/delamination phenomena during impact or general dynamic loading conditions. In addition, full fracture analysis can also be performed. The proposed approach adopts a general node to face nonlinear frictional contact algorithm to enforce bonding/debonding constraints between composite plies. The method is also capable of analysing progressive fracture and fragmentation behaviour as well as potential post cracking interactions caused by the newly created crack sides and segments. A local remeshing technique is adopted every time a new crack is formed, while an overall remeshing is performed anytime a certain criterion of error estimation is violated. The special local remeshing technique is designed to model geometrically an individual crack by splitting the element, separating the failed node, creating new nodes and dividing the neighbouring elements to preserve the compatibility conditions. The same procedure is capable of modelling application of fibre reinforced polymer (FRP) layers to other engineering structures in order to improve their flexible behaviour in static and dynamic loading conditions.
Composites,debonding,Delamination,discrete element method,Impact,Cracking
https://jast.ias.ir/article_51526.html
https://jast.ias.ir/article_51526_64f1c4fe46e51a6617755f6b4934d96b.pdf
Iranian Aerospace Society
Journal of Aerospace Science and Technology
1735-2134
2345-3648
3
4
2006
12
01
On the Dependence of Soot Formation and Combustion on Swirling Combustion Furnaces: Measurement and Simulation
205
212
EN
K.
Bashirnezhad
bashirnezhad@yahoo.com
Soot concentration distribution is investigated both numerically and experimentally in methane-air diffusion flame. The experimental work is conducted with a cylindrical swirl stabilized combustor. Filter paper technique is used to measure soot volume fraction inside the combustor. The numerical simulation is based on the solution of the fully-coupled conservation equations for swirling turbulent flow, chemical species kinetic modeling, fuel combustion and soot formation and oxidation. The soot particle number density and the mass density based on the acetylene concentrations are used to model the soot emission in confined swirling turbulent diffusion flame. The comparison between predictions and measurement results over a range of different swirl numbers shows good agreement. The results reveal the significant influence of swirl intensity on combustion characteristics and soot formation in diffusion flames. An increase in swirl number enhances the mixing rate, peak temperature, and soot volume fraction inside the flame zone. The locations to give the maximum temperature and soot concentration shift to backward (close to combustor inlet) with increase in swirl number.
soot formation/combustion,Swirling flow,methane flame,turbulent flame
https://jast.ias.ir/article_51527.html
https://jast.ias.ir/article_51527_cdcdf96c1e9195da3d259181269a380e.pdf