Thrust Estimation of Quadrotor UAV using Adaptive Neural Network Observer

Asad Ullah Awan,Hyoun Jin Kim 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.11

In this work, we present an application of an adaptive neural network observer for estimating the thrust that is generated by individual rotors of a quadrotor UAV with uncertain actuator dynamics. In most of the previous works aimed at controlling quadrotor UAV, the controller implementation is based on the assumption of a static relationship between the input to the motors and the resulting force generated by the rotor-propeller subsystem. However variations in this relation can result in performance degradation of the closed-loop system. Using a nonlinear observer, the estimated thrust can be used in feedback control of UAV, making the closed-loop system more robust to such variations. We consider a nonlinear model of the quadrotor with unknown actuator dynamics and we use an adaptive neural network observer with adaptation laws, derived using Lyapunov stability analysis, to estimate unknown dynamics. The resulting adaptation laws guarantee that the error between actual and estimated thrust produced by each individual rotor is bounded. Simulation results show the estimated thrust values match the actual thrust values with satisfactory accuracy.

Adaptive Control of a Shape Memory Alloy Actuator using Neural-Network Feedforward and RISE Feedback

Asad Ullah Awan,박재만,김현진,류정현,조맹효 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.4

This paper presents a position tracking control system for a shape memory alloy (SMA) actuator using neural network (NN) feedforward and robust integral of signum of error (RISE) feedback. Nonlinear control of SMA actuators is difficult due to model uncertainties and unknown disturbances. Discontinuous control techniques such as sliding mode control have conventionally been used to achieve asymptotic tracking in the presence of model uncertainties. However, such discontinuous controllers usually result in increased power loss due to high frequency switching. With the recent development of the continuous RISE feedback control, semiglobal asymptotic tracking can be achieved. Furthermore, the NN-RISE control leads to better tracking performance and lower power losses caused by input signal switching/chattering when compared to discontinuous controllers. In order to apply the NN-RISE, a state-space model of the SMA actuator is derived, which has been overlooked in many previous works, using Taylor series expansion and exploiting the nature of SMA dynamics. Experimental results show that the proposed control system works well even in the absence of an accurate model of the SMA actuator.

Thrust Estimation of Quadrotor UAV using Adaptive Observer

Asad Ullah Awan,Jaemann Park,Hyoun Jin Kim 제어로봇시스템학회 2011 제어로봇시스템학회 국제학술대회 논문집 Vol.2011 No.10

In this work, we apply an adaptive observer for estimating the thrust generated by the individual rotors of a quadrotor UAV with uncertain actuator parameters, using a linear dynamic model of the system. In most of the previous works, the implementation of quadrotor control is based on the assumption of a known static relationship between the voltage signal to the motors and the thrust generated by the actuator-propeller assembly. However, due to variations in this voltage-to-thrust relationship, this approach may lead to undesirable results in practice. Feedback of the quadrotor thrust in the control system can provide more robustness to the system. In the absence of accurate knowledge of the actuator parameters, we use an adaptive observer for thrust estimation in this work. An adaptive observer is an algorithm for joint estimation of states and unknown parameters of a dynamical system. We use the adaptive Luenberger observer using two different cost functions, and apply a genetic algorithm to select the design parameters of the observer. We use low- and higher-order models for the actuator with the adaptive observer, and compare their performance. The results show that the estimates from the adaptive observer used with a low-order actuator model match the thrust values obtained from measurements with good accuracy.

Performance and energy cost evaluation of an integrated NH₃-based CO₂ capture-capacitive deionization process

Ullah, Asad,Saleem, Muhammad Wajid,Kim, Woo-Seung Elsevier 2017 International journal of greenhouse gas control Vol.66 No.-

<P><B>Abstract</B></P> <P>A capacitive deionization (CDI) device was proposed for NH<SUB>3</SUB>-based CO<SUB>2</SUB> absorption-desorption process, to reduce the stripper regeneration energy. A rate-based model, RateFrac, was developed for the absorber, along with an equilibrium-based model, RadFrac, for the stripper. The model was verified, and the results have shown good agreement with experimental data. The CO<SUB>2</SUB> capture process, which is integrated with CDI, was simulated and compared with a non-CDI CO<SUB>2</SUB> capture process based on regeneration energy. Operating parameters such as flow rate, lean CO<SUB>2</SUB> loading, and ammonia concentration in the lean solvent were used to analyze the integrated model. Stripper regeneration energy can be reduced by as much as 37.5% by using the CDI setup. Moreover, energy cost estimation was performed using two heat sources (natural gas and coal). CDI saved a maximum of 31% of the energy costs for a natural gas–fired boiler and 12.3% of the energy costs for a coal-based boiler.</P> <P><B>Highlights</B></P> <P> <UL> <LI> NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture process integrated with Capacitive deionization device was proposed to reduce regeneration energy. </LI> <LI> The model was verified and the results show good agreement with the experimental data. </LI> <LI> Main operating parameters of the CO<SUB>2</SUB> capture process were analyzed to check their effects on regeneration energy. </LI> <LI> Energy Cost estimation of CO<SUB>2</SUB> capture process both with and without capacitive deionization was performed. </LI> <LI> Regeneration energy reduced up to 37.5% by integrating capacitive deionization device. </LI> </UL> </P>

Ammonia-based CO₂ capture parameters optimization and analysis of lean and rich vapor compression processes

Ullah, Asad,Soomro, Mujeeb Iqbal,Kim, Woo-Seung Elsevier 2019 Separation and purification technology Vol.217 No.-

<P><B>Abstract</B></P> <P>Carbon dioxide (CO<SUB>2</SUB>) capture through chemical solvent absorption process is the most favourable and well-proven technique to reduce CO<SUB>2</SUB> emission. However, in this technique, the energy penalty correlated with absorbent regeneration is a critical challenge. To reduce energy consumption, the operating parameters in NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture process were optimized. Then flowsheet modifications including rich vapor compression (RVC) and lean vapor compression (LVC) were proposed for the first time in the NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture process. Both the LVC and RVC schemes were combined with cold solvent split (CSS) process to further reduce the energy requirements. Moreover, the LVC and RVC processes of this study were also compared with the advanced NH<SUB>3</SUB>-based and MEA-based LVC and RVC processes with respect to energy reduction. The optimized process was considered as a base process and it was compared with the modified processes. The RVC and LVC combined with CSS process reduced the reboiler duty by 26.7% and 19%, respectively. These energy savings are much higher than that of 11.6% and 8.26% energy savings of the advanced NH<SUB>3</SUB>-based rich split and inter-heating processes, respectively. The total equivalent energy savings of LVC, RVC, LVC with CSS, and RVC with CSS processes in this study were about 6.4%, 18.1%, 3.4%, and 15%, respectively, which are higher than 3.4% and 8.5% energy savings of MEA<B>-</B>based LVC with CSS and RVC with CSS processes, respectively. Furthermore, these combined processes can also avoid the use of a condenser.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Parameters optimization and process modifications were proposed for NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture process. </LI> <LI> RVC and LVC combined with CSS process reduce the reboiler duty by about 26.7% and 19%, respectively. </LI> <LI> The total equivalent energy of 18.1% and 15% can be saved by using the RVC and LVC schemes, respectively. </LI> </UL> </P>

Investigating the long-term behavior of creep and drying shrinkage of ambient-cured geopolymer concrete

Asad Ullah Qazi,Ali Murtaza Rasool,Iftikhar Ahmad,Muhammad Ali,Fawad S. Niazi 국제구조공학회 2024 Structural Engineering and Mechanics, An Int'l Jou Vol.89 No.4

This study pioneers the exploration of creep and shrinkage behavior in ambient-cured geopolymer concrete (GPC), a vital yet under-researched area in concrete technology. Focusing on the influence of sodium hydroxide (NaOH) solution concentration, the research utilizes low calcium fly ash (Class-F) and alkaline solutions to prepare two sets of GPC. The results show distinct patterns in compressive strength development and dry shrinkage reduction, with a 14 M NaOH solution demonstrating a 26.5% lower dry shrinkage than the 16 M solution. The creep behavior indicated a high initial strain within the first 7 days, significantly influenced by curing conditions and NaOH concentration. This study contributes to the existing knowledge by providing a deeper understanding of the time-dependent properties of GPC, which is crucial for optimizing its performance in structural applications.

Solvent Effects on the Porosity and Size of Porous PLGA Microspheres Using Gelatin and PBS as Porogens in a Microfluidic Flow-Focusing Device

Ullah, Asad,Kim, Chul Min,Kim, Gyu Man American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.10

<P>In this study, we analyzed the effects of four solvents-dimethylcarbonate (DMC), ethylacetate (EA), dichloromethane (DCM), and chloroform (CH)-on the porosity and size of porous PLGA microspheres produced using aqueous gelatin and phosphate-buffered saline (PBS) as porogens in a microfluidic flow-focusing (MFF) device. Relatively water soluble solvent such as DMC and EA miscible with aqueous porogen solution/porogen, did not produce porous microspheres, while poor water soluble solvents such as DCM and CH produced highly porous microspheres. Furthermore, as the immiscibility of the polymer solution and porogen increased, the porosity and pore size also increased. Similarly, the highly volatile solvents (DCM and CH) resulted in smaller microspheres than EA and DMC, which are less volatile. The porosity of porous microspheres also depended on the porogen. Aqueous gelatin produced highly porous microspheres, while PBS resulted in smaller pore sizes.</P>

Analysis of a rich vapor compression method for an ammonia-based CO₂ capture process and freshwater production using membrane distillation technology

Ullah, Asad,Soomro, Mujeeb Iqbal,Kim, Woo-Seung Elsevier 2019 Chemical engineering research & design Vol.147 No.-

<P><B>Abstract</B></P> <P>Post-combustion capturing of CO<SUB>2</SUB> through chemical solvent absorption is a promising technique for reducing the CO<SUB>2</SUB> emissions from fossil fuel power plants. However, the energy penalty associated with the absorbent regeneration continues to be a critical challenge in the chemical solvent absorption process. In this study, the operating parameters of ammonia-based CO<SUB>2</SUB> capture were optimized to reduce the energy penalty. This optimized process was considered a base process to which process modifications were added, with the goal of further reducing the energy consumption. These process modifications included absorber inter-cooling and rich vapor compression (RVC) combined with cold solvent split (CSS) processes. The combined RVC and CSS process was compared with the base process and advanced NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture processes, such as the rich split process and the inter-heating process. Compared to the base process, the combined process reduced the energy requirements by 20.2%, which was higher than the 11.6% and 8.26% energy reductions obtained via the rich split and inter-heating processes, respectively. The combined process was also compared with MEA-based process modifications. The energy savings from the combined process were higher than those of the MEA-based process modifications. To estimate the trade-offs between the energy savings resulting from the combined process vs. the capital cost of the additional equipment required, the Aspen Capital Cost Estimator (ACCE) was used. The results showed that the combined process saved $0.707 million per year. Furthermore, a membrane distillation (MD) technology was integrated with the CO<SUB>2</SUB> capture unit to produce freshwater. This additional process produced freshwater at a rate of 719.240 m<SUP>3</SUP>/day at a feed stream temperature to the MD unit of 35.66 ℃.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Process modifications were proposed for NH<SUB>3</SUB>-based CO<SUB>2</SUB> capture process. </LI> <LI> RVC combined with CSS process can reduced the reboiler duty by 20.2%. </LI> <LI> Intercooling process can reduce the absorber packing height by 25%. </LI> <LI> RVC combined with CSS process can save $0.707 million from the total cost per year. </LI> <LI> The freshwater was produced at a rate of 719.240 m<SUP>3</SUP>/day at feed temperature of 35.66 ℃ to the MD unit. </LI> </UL> </P>

Amplitude Damping Loss in Quantum Consensus Algorithms

Muhammad Asad Ullah,Hyundong Shin 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.6

The ex-ante Effect of Law and Judicial Efficiency on Borrower Discouragement: An International Evidence

Safi Ullah Khan,Naimat Ullah Khan,Asad Ullah 한국증권학회 2021 Asia-Pacific Journal of Financial Studies Vol.50 No.2

We investigate whether cross-country differences in the legal system influence demand-side credit constraints. We explore the notion of discouraged borrowers — firms that choose not to apply for bank credit because they anticipate rejection. Employing survey data from 46 economies, we find that rapid and less costly court proceedings, lower procedural complexity in court processes, and higher recovery rates under bankruptcy lead to the lower likelihood of borrower discouragement. These results are more pronounced in countries with strong creditor protections in relation to company reorganization and liquidation. The results corroborate the supply-side view that strong creditor rights and their efficient enforceability alleviate banks’ participation constraints in the loan market, thereby encouraging small and medium-sized enterprises to apply for credit in the first place. We also find that differences in institutional settings, such as higher regulatory quality, better control of corruption, and the rule of law, lead to lower rates of credit self-rationing in the loan market.