Tahir Sultan

UNIVERSITY OF POONCH RAWALAKOT, Sociology, Graduate Student

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Effects of Selective Laser Melting additive manufacturing parameters of Inconel 718 on porosity, microstructure and mechanical properties

Materials Science and Engineering: A, 2018

The effect of SLM parameters on porosity, microstructure and mechanical properties is studied. To... more The effect of SLM parameters on porosity, microstructure and mechanical properties is studied. To this purpose, the Selective Laser Melting (SLM) technology is applied to manufacture Inconel 718 specimens. The material, the manufacturing process, the Hot Isostatic Pressure (HIP), heat treatment, observation procedures and characterisation of mechanical properties are presented. A columnar-dendritic microstructure was observed on all the SLM specimens and a Volumetric Energy Density (VED) effect on the latter was also noted. The rate of porosity varies in relation to the VED and is considerably reduced after HIP. The heat treatment erases the dendritic microstructure, significantly enhances microhardness and confers on the alloy tensile mechanical properties comparable to forged Inconel 718.

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Model Analysis for the Implementation of a Fast Model Predictive Control Scheme on the Absorption/Stripping CO2 Capture Plants

ACS Omega, 2022

The purpose of this paper is to investigate the possible implementation of the Fast model predict... more The purpose of this paper is to investigate the possible implementation of the Fast model predictive control (MPC) scheme for chemical systems. Due to the difficulties associated with complicated dynamic behavior and model sensitivity, which results in considerable offsets, the Fast MPC controller has not been implemented on the CO 2 capture plant based on the absorption/stripping system. The main objective of this work is to evaluate the most appropriate model for implementing the Fast MPC control strategy, which results in fast output responses, negligible offsets, and minimum errors. The steady-state and dynamic simulation models of the CO 2 capture plant are designed in Aspen PLUS. In the System Identification Toolbox, multiple state-space models are identified to achieve a highly accurate model for the Fast MPC controller. The Fast MPC controller is then implemented to evaluate the performance under a setpoint tracking mode with ±5 and ±15% step changes. The results showed that the Fast MPC based on the statespace prediction focus model has on average 7.9 times lower offset than the simulation focus model and 10.4 times lower integral absolute error values. The comparison study concluded that the Fast MPC control strategy performs efficiently using prediction-based focus state-space models for CO 2 capture plants using the absorption/stripping system with minimum offsets and errors.

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Performance evaluation of the fast model predictive control scheme on a CO2 capture plant through absorption/stripping system

Process Safety and Environmental Protection, 2022

Influence of Different Additives on Cold Recycled Mixes at Environmental Conditions of Pakistan

As with the passage of time, natural resources become extinct. Different recycling techniques are... more As with the passage of time, natural resources become extinct. Different recycling techniques are being developed for the use of recycled materials. Reclaimed asphalt pavement materials (RAP) have been used in cold in place recycled pavements worldwide from early nineties. The performance of CIPR technique varies in different zones of the world and up till now its mix design is under development stage. This research work is done to evaluate the behavior of CIPR mixes using different additives keeping in view the local conditions of Pakistan. For this purpose resilient modulus and static creep test has been performed on Marshall Samples of CIPR mixes using UTM- 5P with foam and emulsified bitumen as additives. It was concluded that samples with foam bitumen showed more structural adequacy as compare to emulsified bitumen samples at various temperatures and loading frequencies according to Pakistani traffic conditions. (Khan K M , Ahmed S , Ali F , Sultan T , Kiffayat Ullah. Influence...

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Performance Evaluation of Cold Recycled Asphalt Mixes at Different Temperatures and Loading Rates

Pakistan Journal of Engineering and Applied Sciences, 2016

Nowadays recycling is one of the most advance and interesting technique for the rehabilitation of... more Nowadays recycling is one of the most advance and interesting technique for the rehabilitation of road pavements. In recent years the increased interest in this process, has led to the development of various alternative methods for the recovery and the reuse of road bituminous materials. Cold recycling allows the recovery of bituminous material from an existing pavement without the addition of heat, whilst ensuring the strength of high quality bound base layers. Resilient behavior, rutting resistance and moisture susceptibility of five different cold recycled asphalt mixes have been investigated using UTM-5P. RAP was used as controlled mix to compare with four other mixes having variable binding material types and percentages. Mixes were evaluated at 40 °C and 50 °C under varying loading conditions of 150 ms and 450 ms. Resilient modulus decreases with increase in type and time of loading for all mixes. Both emulsified bitumen with cement and 100% RAP, and 100% RAP performed excelle...

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Plant-wide MPC control scheme for CO2 absorption/stripping system

Materials Today: Proceedings, 2020

Abstract The high contents of CO2 in natural gas processing industries cause various issues in th... more Abstract The high contents of CO2 in natural gas processing industries cause various issues in the operation, and it is essential to reduce the amount of CO2 using amine-based absorption processes. An efficient and flexible control strategy is highly desirable for CO2 removal in CO2 absorption/stripping system. The excellent performance of Model Predictive Control (MPC) in setpoint tracking and disturbance rejection scenarios could make it a better option for the flexible controllability of a CO2 absorption/stripping plant. MPC performance depends significantly on the accuracy of the identified mathematical model of the plant. The state-space model is believed as the better option for MPC as it represents the plant model with true dynamics. Therefore, this study is focused on the design of the 2 × 2 MPC control strategy in MATLAB® MPC Designer Toolbox using 2nd order continuous-time state-space model. The main aim of this study is to develop a plant-wide control scheme based on MPC for the natural gas absorption/striping system. Step changes in the CO2 composition of sweet gas (±5%) and stripper temperature (±15%) have been introduced in the absorption/stripping simulation model. The results show that the MPC controller has achieved the new setpoint of CO2 composition within 0.5 sec in the setpoint tracking scenario. Similarly, the MPC controller has been able to reject the disturbances successfully introduced as ± 15% step change in stripper temperature within 7.5 sec. Hence, the performance of the MPC controller using the state-space model at higher step changes is adequate with no peak, closer to the setpoint, and no overshoot in the output.

Optical and dielectric spectroscopic analysis of SmMn2O5

Physica Scripta, 2020

Polycrystalline SmMn2O5 has been synthesized by using sol-gel auto combustion tecnique. X-ray dif... more Polycrystalline SmMn2O5 has been synthesized by using sol-gel auto combustion tecnique. X-ray diffraction (XRD) pattern reflects the single phase formation of orthorhombic structure with Pbam space group. In the frequency range of (30–1000 cm−1) reflectivity spectrum reveals the 14 infrared active phonons out of 36, which are already pridicted theoretically. We have estimated the optical energy band gap (E g ) ≃ 1.5 eV from UV–visible absorption spectrum. Temperature dependent (293-533 K) DC electrical characterization up to 40 V suggests semiconducting nature of the material. The temperature dependent impedance spectroscopy within a broader frequency range of (20 Hz—3 GHz) shows decreasing behavior of dielectric constant and tangent loss while AC conductivity increasing with the rise in frequency and temperature suggest the strong frequency dispersion and relaxational behavior of the material. The activation energy calculation from AC conductivity is in good agreement with semicond...

Impact of rare earth substitution on structural and optical properties of multiferroic La2−xGdxNiMnO6

Materials Research Express, 2019

Polycrystalline La2-XGdXNiMnO6 (x = 0.0, 0.5 and 1.0) double perovskites were synthesized by auto... more Polycrystalline La2-XGdXNiMnO6 (x = 0.0, 0.5 and 1.0) double perovskites were synthesized by auto combustion sol-gel method. The prepared samples have monoclinic phase with space group P21/n, revealed by Rietveld analysis of X-ray diffraction (XRD) pattern. The analysis of reflectivity spectrum showed well resolved infrared (IR) active phonon modes. We discuss the results in terms of different phonon bands originated as a result of atomic vibrations. Optical energy band gap (Eg) has been estimated from optical conductivity (1 ()) spectrum and UV-visible absorption spectrum. Temperature dependent resistivity measurements suggest variable range hopping conduction mechanism in these multiferroics.

Input Selection of Wavelet-Coupled Neural Network Models for Rainfall-Runoff Modelling

Water Resources Management, 2018

The use of wavelet-coupled data-driven models is increasing in the field of hydrological modellin... more The use of wavelet-coupled data-driven models is increasing in the field of hydrological modelling. However, wavelet-coupled artificial neural network (ANN) models inherit the disadvantages of containing more complex structure and enhanced simulation time as a result of use of increased multiple input sub-series obtained by the wavelet transformation (WT). So, the identification of dominant wavelet sub-series containing significant information regarding the hydrological system and subsequent use of those dominant sub-series only as input is crucial for the development of wavelet-coupled ANN models. This study is therefore conducted to evaluate various approaches for selection of dominant wavelet sub-series and their effect on other critical issues of suitable wavelet function, decomposition level and input vector for the development of wavelet-coupled rainfall-runoff models. Four different approaches to identify dominant wavelet sub-series, ten different wavelet functions, nine decomposition levels, and five different input vectors are considered in the present study. Out of four tested approaches, the study advocates the use of relative weight analysis (RWA) for the selection of dominant input wavelet sub-series in the development of wavelet-coupled models. The db8 and the dmey (Discrete approximation of Meyer) wavelet functions at level nine were found to provide the best performance with the RWA approach.

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To Investigate the Flow Structure of Discontinuous Vegetation Patches of Two Vertically Different Layers in an Open Channel

Water, 2018

In the present study, the flow structure of discontinuous double-layered vegetation patches was i... more In the present study, the flow structure of discontinuous double-layered vegetation patches was investigated using a 3D Reynolds stress turbulence model (RSM). The channel domain was built using GAMBIT (Geometry and Mesh Building Intelligent Toolkit). For the simulation and postprocessing, FLUENT (ANSYS) was used to analyze the distribution of the mean velocity, Reynolds stresses, and other flow properties against two different flow conditions. The results captured by the turbulence model at specific locations and the cross section are presented in the form of various velocity profiles and contour plots. In the gap portion, the velocity was visibly lower than that in the vegetation areas, while the influence of patch distribution was not visible in the overlying flow layer. The velocity profiles at critical locations were categorized by numerous modulation points and velocity projections close to the bed, principally for positions straight after the vegetation structures. A distinction in the velocity at the topmost of the smaller vegetation structure was prominent. Reynolds stresses, turbulent kinetic energy, and turbulence intensity exhibited large fluctuations inside the vegetation regions and just behind the vegetation structures compared with in the gap regions.

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Effect of Sr2+ doping on the structural, electrical and optical properties of BiFeO3

Chinese Journal of Physics, 2018

Abstract Multiferroic nanoparticles of Bi 1 − x SrxFeO3 (x = 0.00, 0.05, 0.10, 0.15, 0.20) were ... more Abstract Multiferroic nanoparticles of Bi 1 − x SrxFeO3 (x = 0.00, 0.05, 0.10, 0.15, 0.20) were prepared by sol–gel route and the effect of Sr 2 + concentration on the structural, electrical and optical properties have been studied. The average crystallite size of bismuth ferrite calculated from XRD result was 29–50 nm and is consistent with the scanning electron microscopy (SEM). The lattice constants, unit cell volume and porosity are found to increase with the increase in x. Moreover, the dc electrical resistivity was found to decrease with the increase of temperature reflecting the semiconducting nature of the material. Remarkably, the doping of Sr 2 + ions are considered to originate small polaron which grows in size with x and reflects a structural distortion at x  >  0.15. Infrared reflectivity (30–1000 cm − 1 ) was used to study the phonon contribution to the intrinsic structural response of the system. Interestingly structural distortion is evident for x  >  0.15 as observed through high frequency phonon shifts .

Frequency shifts of infrared active phonon modes in orthorhombic Dy 1 − x Y x Mn 2 O 5

Physica B: Condensed Matter, 2017

Abstract A systematic investigation of infrared active phonon excitations in the orthorhombic Dy ... more Abstract A systematic investigation of infrared active phonon excitations in the orthorhombic Dy 1 - x Y x Mn 2 O 5 with x=0, 0.2, 0.4, 0.6, 0.8, and 1 was carried out at room temperature. A detailed analysis towards the correlation between both local structural response and local lattice distortion has been undertaken. Frequency shifts of several phonons were observed, which strongly depends on the Y concentration and are likely to be associated with the electron–phonon coupling. A strong evidence for structural distortions of MnO6 and MnO5 has been observed in the high frequency range. The optical band gap has also been determined through optical conductivity and UV-visible absorption spectra, indicating semiconducting behavior of all members of the series Dy 1 - x Y x Mn 2 O 5 .

A Comparative Study of Various Hybrid Wavelet Feedforward Neural Network Models for Runoff Forecasting

Water Resources Management, 2017

Considering network topologies and structures of the artificial neural network (ANN) used in the ... more Considering network topologies and structures of the artificial neural network (ANN) used in the field of hydrology, one can categorize them into two different generic types: feedforward and feedback (recurrent) networks. Different types of feedforward and recurrent ANNs are available, but multilayer perceptron type of feedforward ANN is most commonly used in hydrology for the development of wavelet coupled neural network (WNN) models. This study is conducted to compare performance of the various wavelet based feedforward artificial neural network (ANN) models. The feedforward ANN types used in the study include the multilayer perceptron neural network (MLPNN), generalized feedforward neural network (GFFNN), radial basis function neural network (RBFNN), modular neural network (MNN) and neuro-fuzzy neural network (NFNN) models. The rainfallrunoff data of four catchments located in different hydro-climatic regions of the world is used in the study. The discrete wavelet transformation (DWT) is used in the present study to decompose input rainfall data using db8 wavelet function. A total of 220 models are developed in this study to evaluate the performance of various feedforward neural network models. Performance of the developed WNN models is compared with their counterpart simple models developed without applying wavelet transformation (WT). The results of the study are further compared with-multiple linear regression (MLR) model which suggest that the WNN models outperformed their counterpart simple models. The hybrid wavelet models developed using MLPNN, the GFFNN and the MNN models performed best among the six selected data driven Water Resour Manage

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Lattice Dynamics and Transport Properties of Multiferroic DyMn2O5

Advances in Condensed Matter Physics, 2017

We have investigated the optical and electrical properties of polycrystalline DyMn2O5synthesized ... more We have investigated the optical and electrical properties of polycrystalline DyMn2O5synthesized by sol-gel method. Analysis of the reflectivity spectrum has led to the observation of 18 infrared (IR) active phonon modes out of 36 predicted ones. We discuss the results in terms of different phonon bands originated as a result of atomic vibrations. Moreover, the optical energy band gap ofEg(OC)~1.78 eV has been estimated from optical conductivity(σ1(ω))spectrum. The energy band gap and optical transitions were also determined from UV-visible absorption spectrum and band gap ofEg(UV)~1.57 eV was estimated. Moreover, DC electrical resistivity shows the p-type polaronic conduction above room temperature.

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Rutting performance of Polyethylene, Lime and Elvaloy modified Asphalt Mixes performance of Polyethylene modified, Lime modified and Elvaloy modified Asphalt Mixes Life Sci J

Life Science Journal

A key element in the performance of asphalt is its resistance to rutting. Many modifiers can be u... more A key element in the performance of asphalt is its resistance to rutting. Many modifiers can be used to improve the properties of asphalt and to enhance its rut resistance. This research is aimed to evaluate the effectiveness of Polyethylene modified, Lime modified and Elvaloy modified asphalt mixes in improving the performance of asphaltic concrete regarding rutting resistance and to compare it with the performance of conventional NHA (National Highway Authority Pakistan) Class-A mix. In this study the compacted asphalt mixes were tested for resistance to rutting by subjecting all the specimens to 10,000 repetitions of a loaded wheel and the rut depth for each specimen was determined using wheel tracking machine. Polyethylene modified mixes showed better resistance to rutting than all the other mixes and the conventional NHA class-A mix showed the poorest performance. The order of performance is polyethylene modified mix performed best, then lime modified mix, then elvaloy modified...

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Experimental study to compare the effects of Gradation, Additives and Filler Materials on performance of CIR Mixes study to compare the effects of Gradation, Additives and Filler Materials on performance of CIR Mixes Life Sci J

Life Science Journal

Road transport is one of the major components in economic and social development of a country, es... more Road transport is one of the major components in economic and social development of a country, especially in developing countries like Pakistan. In Pakistan, 95% of the total freight movement throughout the country takes place through roads. Infrastructure development is one of the costlier processes and consumes a lot of national budget and then to maintain the infrastructure, again a considerable budget is required. There are various maintenance and rehabilitation techniques developed so far, with the modernization and new construction mechanical instruments and machines developed, cold recycling is a new, environmentally friendly and cost effective rehabilitation technique. The performance of Recycled mixes is still unknown as the recycled pavements behaves differently at different temperatures and in different regions of the world. Laboratory investigation of various stabilizing agents and recycling agent and amount of RAP and New Aggregates to be used is yet to be analyzed. Hen...

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Performance Comparison of Cold in Place Recycled and Conventional HMA Mixes

IOSR Journal of Mechanical and Civil Engineering, 2012

Cold In-Place Recycling (CIR) of flexible pavements has been experimented and executed worldwide ... more Cold In-Place Recycling (CIR) of flexible pavements has been experimented and executed worldwide during the past twenty years. The performance of CIR projects is inconsistent in different parts of the world; furthermore its mix design is still under development. In local traffic and climatic conditions of Pakistan, this research work was focused to evaluate the structural performance of cold in-placed recycled mixes. This will assist the highway agencies of the country for making decision regarding future utilization of cold recycling technology, especially in the conditions of budgetary constraints for maintenance and rehabilitation and expanding highway network. For the structural evaluation of CIR pavements, Resilient Modulus Test and Static Creep test was performed on Marshall Samples of CIR mixes using UTM-5P with Cement and Lime being used as an additive at various temperatures and loading Frequencies and their strength was compared with conventional HMA mixes. It was concluded that the performance of cold recycling and conventional rehabilitation was nearly the same and the cement added cold recycled mixes were found better than lime added.

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