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Papers by Zia ul Rehman Tahir

Research paper thumbnail of Numerical Buckling Of Composite Cylindrical Shells Under Axial Compression Using Asymmetric Meshing Technique (Amt)

This paper presents the details of a numerical study of<br> buckling and post buckling beha... more This paper presents the details of a numerical study of<br> buckling and post buckling behaviour of laminated carbon fiber<br> reinforced plastic (CFRP) thin-walled cylindrical shell under axial<br> compression using asymmetric meshing technique (AMT) by<br> ABAQUS. AMT is considered to be a new perturbation method to<br> introduce disturbance without changing geometry, boundary<br> conditions or loading conditions. Asymmetric meshing affects both<br> predicted buckling load and buckling mode shapes. Cylindrical shell<br> having lay-up orientation [0^o/+45^o/-45^o/0^o] with radius to thickness<br> ratio (R/t) equal to 265 and length to radius ratio (L/R) equal to 1.5 is<br> analysed numerically. A series of numerical simulations<br> (experiments) are carried out with symmetric and asymmetric<br> meshing to study the effect of asymmetric meshing on predicted<br> buckling behaviour. Asymmetric meshing techni...

Research paper thumbnail of A New Perturbation Technique In Numerical Study On Buckling Of Composite Shells Under Axial Compression

A numerical study is presented on buckling and post buckling behaviour of laminated carbon fiber ... more A numerical study is presented on buckling and post buckling behaviour of laminated carbon fiber reinforced plastic (CFRP) thin-walled cylindrical shells under axial compression using asymmetric meshing technique (AMT). Asymmetric meshing technique is a perturbation technique to introduce disturbance without changing geometry, boundary conditions or loading conditions. Asymmetric meshing affects predicted buckling load, buckling mode shape and post-buckling behaviour. Linear (eigenvalue) and nonlinear (Riks) analyses have been performed to study the effect of asymmetric meshing in the form of a patch on buckling behaviour. The reduction in the buckling load using Asymmetric meshing technique was observed to be about 15%. An isolated dimple formed near the bifurcation point and the size of which increased to reach a stable state in the post-buckling region. The load-displacement curve behaviour applying asymmetric meshing is quite similar to the curve obtained using initial geometric...

Research paper thumbnail of Artificial neural network prediction of buckling load of thin cylindrical shells under axial compression

Engineering Structures, 2017

Abstract Thin-walled circular cylindrical shells under axial compression are prone to buckling; t... more Abstract Thin-walled circular cylindrical shells under axial compression are prone to buckling; the reduction of buckling load from the theoretical estimation is considered primarily due to imperfection sensitivity. The buckling load from carefully conducted experiments using nominally similar shells falls below the prediction by the classical theory with substantial scatter. The current design recommendations apply highly conservative knockdown factors to the theoretical buckling loads to estimate the load carrying capacity of the shell structures. In this study, a systematic analysis of experimental data from the literature has been conducted using the artificial neural network (ANN). The networks were trained using Bayesian regularisation backpropagation training function. Two network models with eight and ten neurones were used to train, test and validate 390 sets of experimental data. The buckling loads predicted by the ANN models were compared with the design recommendations by National Aeronautics and Space Administration (NASA), Eurocode 3 (EC3) and the experimental buckling loads. The ANN models predict buckling load within 10% of the experimental buckling load and can be reliably used within the parametric range used in training. The NASA design recommendations provides 10–50% conservative estimates compared to the experimental loads while EC3 predictions are conservative by more than 50%.

Research paper thumbnail of Effect of asymmetric meshing on the buckling behavior of composite shells under axial compression

International Journal for Computational Methods in Engineering Science and Mechanics, 2017

Asymmetric meshing technique (AMT) is a perturbation method to introduce disturbances (i.e imperf... more Asymmetric meshing technique (AMT) is a perturbation method to introduce disturbances (i.e imperfections) in a finite-element model without changing geometry, boundary conditions or loading conditions. For cylindrical shells under axial compression, asymmetric meshing in the form of a square patch of three different surface areas and a band in axial and/or circumferential directions with different areas is discussed in the first half of the paper. The element size in the patch or band is lowered to a varying degree as compared to the rest of the shell in order to produce the asymmetry. The reduction in the buckling load was observed from 15% to 20% which depends mainly on the total area of asymmetric meshing, and less on the amplitude of asymmetry i.e., reduction in element size. While loading the shell an isolated dimple formed near the bifurcation point which increased in size to reach a stable state in the post-buckling region corresponding to the post-buckling plateau load. The load-displacement behaviour using asymmetric meshing is similar to the experimental results and the numerical results obtained by introducing initial geometric imperfections. Asymmetric meshing in the form of varying element size in both axial direction and circumferential direction of the shell is discussed in the second half of the paper. Asymmetric meshing showed reduction in the buckling load up to 7% with

Research paper thumbnail of Numerical Study on Buckling Behaviour of Composite Cylindrical Shells under Axial Compressive Load with Asymmetric Meshing Technique

Applied Mechanics and Materials, 2013

AMT is a perturbation technique to introduce disturbance in the model without changing geometry, ... more AMT is a perturbation technique to introduce disturbance in the model without changing geometry, boundary conditions or loading conditions. Asymmetric meshing technique is employed in the form of a band along circumferential direction of the shell model. The elements size in the band is reduced as compared with the rest of shell to produce asymmetry in the meshing and four magnitudes of asymmetry in meshing are used. Asymmetric meshing affects predicted buckling load, buckling mode shape and post-buckling behaviour. The reduction in the buckling load using AMT was observed to be about 20%. An isolated dimple formed near the bifurcation point and the size of which increased to reach a stable state in the post-buckling region. The load-displacement curve behaviour applying asymmetric meshing is quite similar to the curve obtained by introducing initial geometric imperfection in the shell model.

Research paper thumbnail of Thermal performance enhancement of nanofluids based parabolic trough solar collector (NPTSC) for sustainable environment

Alexandria Engineering Journal, 2022

Research paper thumbnail of Wind energy potential and economic assessment of four locations in Sistan and Balouchestan province in Iran

Renewable Energy, 2017

Utilization of wind turbines to produce energy has been increasing in recent years, due to techno... more Utilization of wind turbines to produce energy has been increasing in recent years, due to technology advancement, cost stability and environmental issues. In this paper, the wind resource and economic feasibility have been studied to avoid investment risk in cites of Zabol, Zahak, Zahedan and Mirjaveh in Sistan and Balouchestan province of Iran. The Weibull distribution function has been applied to estimate the wind power and energy density, using meteorological data. Determination of coefficient, root mean square error, mean bias error and mean bias absolute error are also calculated to ensure the accuracy of the statistical analysis of fitted distribution. Windographer software has been employed to investigate the prevailing wind direction. The estimated annual energy densities are 2495.36, 2355.69, 1265.24 and 1214.01 kWh/m 2 /year, and the annual mean power densities are 284.97, 269.02, 144.49 and 138.64 W/ m 2. It is found that Zabol and Zahedan are suitable for large scale power generation. The results indicate that using DW61-900 kW wind turbines are highly beneficial for Zabol and Zahak, while for Zahedan, DW52/54-250 kW wind turbine is more appropriate for generating electricity. However, Mirjaveh is suitable for off-grid applications. It should be noted that in this analysis, monetary units are presented in 2016 U.S. dollar.

Research paper thumbnail of Numerical Buckling Of Composite Cylindrical Shells Under Axial Compression Using Asymmetric Meshing Technique (Amt)

This paper presents the details of a numerical study of<br> buckling and post buckling beha... more This paper presents the details of a numerical study of<br> buckling and post buckling behaviour of laminated carbon fiber<br> reinforced plastic (CFRP) thin-walled cylindrical shell under axial<br> compression using asymmetric meshing technique (AMT) by<br> ABAQUS. AMT is considered to be a new perturbation method to<br> introduce disturbance without changing geometry, boundary<br> conditions or loading conditions. Asymmetric meshing affects both<br> predicted buckling load and buckling mode shapes. Cylindrical shell<br> having lay-up orientation [0^o/+45^o/-45^o/0^o] with radius to thickness<br> ratio (R/t) equal to 265 and length to radius ratio (L/R) equal to 1.5 is<br> analysed numerically. A series of numerical simulations<br> (experiments) are carried out with symmetric and asymmetric<br> meshing to study the effect of asymmetric meshing on predicted<br> buckling behaviour. Asymmetric meshing techni...

Research paper thumbnail of A New Perturbation Technique In Numerical Study On Buckling Of Composite Shells Under Axial Compression

A numerical study is presented on buckling and post buckling behaviour of laminated carbon fiber ... more A numerical study is presented on buckling and post buckling behaviour of laminated carbon fiber reinforced plastic (CFRP) thin-walled cylindrical shells under axial compression using asymmetric meshing technique (AMT). Asymmetric meshing technique is a perturbation technique to introduce disturbance without changing geometry, boundary conditions or loading conditions. Asymmetric meshing affects predicted buckling load, buckling mode shape and post-buckling behaviour. Linear (eigenvalue) and nonlinear (Riks) analyses have been performed to study the effect of asymmetric meshing in the form of a patch on buckling behaviour. The reduction in the buckling load using Asymmetric meshing technique was observed to be about 15%. An isolated dimple formed near the bifurcation point and the size of which increased to reach a stable state in the post-buckling region. The load-displacement curve behaviour applying asymmetric meshing is quite similar to the curve obtained using initial geometric...

Research paper thumbnail of Artificial neural network prediction of buckling load of thin cylindrical shells under axial compression

Engineering Structures, 2017

Abstract Thin-walled circular cylindrical shells under axial compression are prone to buckling; t... more Abstract Thin-walled circular cylindrical shells under axial compression are prone to buckling; the reduction of buckling load from the theoretical estimation is considered primarily due to imperfection sensitivity. The buckling load from carefully conducted experiments using nominally similar shells falls below the prediction by the classical theory with substantial scatter. The current design recommendations apply highly conservative knockdown factors to the theoretical buckling loads to estimate the load carrying capacity of the shell structures. In this study, a systematic analysis of experimental data from the literature has been conducted using the artificial neural network (ANN). The networks were trained using Bayesian regularisation backpropagation training function. Two network models with eight and ten neurones were used to train, test and validate 390 sets of experimental data. The buckling loads predicted by the ANN models were compared with the design recommendations by National Aeronautics and Space Administration (NASA), Eurocode 3 (EC3) and the experimental buckling loads. The ANN models predict buckling load within 10% of the experimental buckling load and can be reliably used within the parametric range used in training. The NASA design recommendations provides 10–50% conservative estimates compared to the experimental loads while EC3 predictions are conservative by more than 50%.

Research paper thumbnail of Effect of asymmetric meshing on the buckling behavior of composite shells under axial compression

International Journal for Computational Methods in Engineering Science and Mechanics, 2017

Asymmetric meshing technique (AMT) is a perturbation method to introduce disturbances (i.e imperf... more Asymmetric meshing technique (AMT) is a perturbation method to introduce disturbances (i.e imperfections) in a finite-element model without changing geometry, boundary conditions or loading conditions. For cylindrical shells under axial compression, asymmetric meshing in the form of a square patch of three different surface areas and a band in axial and/or circumferential directions with different areas is discussed in the first half of the paper. The element size in the patch or band is lowered to a varying degree as compared to the rest of the shell in order to produce the asymmetry. The reduction in the buckling load was observed from 15% to 20% which depends mainly on the total area of asymmetric meshing, and less on the amplitude of asymmetry i.e., reduction in element size. While loading the shell an isolated dimple formed near the bifurcation point which increased in size to reach a stable state in the post-buckling region corresponding to the post-buckling plateau load. The load-displacement behaviour using asymmetric meshing is similar to the experimental results and the numerical results obtained by introducing initial geometric imperfections. Asymmetric meshing in the form of varying element size in both axial direction and circumferential direction of the shell is discussed in the second half of the paper. Asymmetric meshing showed reduction in the buckling load up to 7% with

Research paper thumbnail of Numerical Study on Buckling Behaviour of Composite Cylindrical Shells under Axial Compressive Load with Asymmetric Meshing Technique

Applied Mechanics and Materials, 2013

AMT is a perturbation technique to introduce disturbance in the model without changing geometry, ... more AMT is a perturbation technique to introduce disturbance in the model without changing geometry, boundary conditions or loading conditions. Asymmetric meshing technique is employed in the form of a band along circumferential direction of the shell model. The elements size in the band is reduced as compared with the rest of shell to produce asymmetry in the meshing and four magnitudes of asymmetry in meshing are used. Asymmetric meshing affects predicted buckling load, buckling mode shape and post-buckling behaviour. The reduction in the buckling load using AMT was observed to be about 20%. An isolated dimple formed near the bifurcation point and the size of which increased to reach a stable state in the post-buckling region. The load-displacement curve behaviour applying asymmetric meshing is quite similar to the curve obtained by introducing initial geometric imperfection in the shell model.

Research paper thumbnail of Thermal performance enhancement of nanofluids based parabolic trough solar collector (NPTSC) for sustainable environment

Alexandria Engineering Journal, 2022

Research paper thumbnail of Wind energy potential and economic assessment of four locations in Sistan and Balouchestan province in Iran

Renewable Energy, 2017

Utilization of wind turbines to produce energy has been increasing in recent years, due to techno... more Utilization of wind turbines to produce energy has been increasing in recent years, due to technology advancement, cost stability and environmental issues. In this paper, the wind resource and economic feasibility have been studied to avoid investment risk in cites of Zabol, Zahak, Zahedan and Mirjaveh in Sistan and Balouchestan province of Iran. The Weibull distribution function has been applied to estimate the wind power and energy density, using meteorological data. Determination of coefficient, root mean square error, mean bias error and mean bias absolute error are also calculated to ensure the accuracy of the statistical analysis of fitted distribution. Windographer software has been employed to investigate the prevailing wind direction. The estimated annual energy densities are 2495.36, 2355.69, 1265.24 and 1214.01 kWh/m 2 /year, and the annual mean power densities are 284.97, 269.02, 144.49 and 138.64 W/ m 2. It is found that Zabol and Zahedan are suitable for large scale power generation. The results indicate that using DW61-900 kW wind turbines are highly beneficial for Zabol and Zahak, while for Zahedan, DW52/54-250 kW wind turbine is more appropriate for generating electricity. However, Mirjaveh is suitable for off-grid applications. It should be noted that in this analysis, monetary units are presented in 2016 U.S. dollar.