Publication Date: 2022
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025pp. 539-545
In this article, a super-twisting algorithm-based ADRC structure is proposed. This structure contains three parts, a super twisting sliding mode controller, an extended state estimator, and an optimal tracking differentiator. This proposed ADRC is employed to control the Delta parallel robot both numerically, in MATLAB, and experimentally. In numerical simulations, the robustness of the proposed ADRC is verified by applying various external disturbances. Both the numerical and experimental results show the ability of the proposed ADRC structure in controlling the Delta robot in the presence of disturbances and uncertainties. © 2022 IEEE.
Abdolmohammad-Zadeh, Hossein,
Jouyban, Abulghasem,
Amini, Roghayeh,
Sadeghi, G. Publication Date: 2013
Microchimica Acta (14365073)(7-8)
We have used a nano-structured nickel-aluminum layered double hydroxide (Ni-Al LDH) for the extraction of trace levels of selenium prior to its determination by continuous-flow hydride generation atomic absorption spectrometry. Extraction is based on the adsorption of Se(IV) anions on the Ni-Al-nitrate LDH, and/or their exchange with the nitrate anions in the LDH interlayer. The effects of pH value, amount of nanosorbent, eluent type and concentration, sample volume and flow rate were optimized. No appreciable matrix effects were observed. Under optimum conditions, the limit of detection (defined as three times the standard deviation of the blank signal divided by the slope of the calibration plot) is 10 pg mL-1, and the relative standard deviation is 2.8 %. The sorption capacity and preconcentration factor are 10 mg g-1 and 33, respectively. The method was successfully applied to the determination of Se(IV) in tap water, river water, well water, wastewater and oyster tissue (certified reference material, CRM 1566b). © 2013 Springer-Verlag Wien.
Abdolmohammad-Zadeh, Hossein,
Naseri, Abdolhossein,
Sadeghi, G. Publication Date: 2013
Journal of the Serbian Chemical Society (03525139)(1)
A simple micelle-mediated phase separation method has been developed for the pre-concentration of trace levels of iron as a prior step to its determination by flame atomic absorption spectrometry (FAAS). The method is based on the cloud point extraction (CPE) of iron using the non-ionic surfactant poly(ethyleneglycol-mono-p-nonylphenylether) (PONPE 7.5) without the addition of any chelating agent. Several variables affecting the extraction efficiency were studied and optimized utilizing a central composite design (CCD) and a three-level full factorial design. Under the optimum conditions, the limit of detection (LOD), limit of quantification (LOQ) and preconcentration factor were 1.5 μg L-1, 5.0 μg L-1 and 100, respectively. The relative standard deviation (RSD) for six replicate determinations at 50 μg L -1 Fe(III) level was 1.97 %. The calibration graph was linear in the range of 5-100 μg L-1, with a correlation coefficient of 0.9921. The developed method was validated by the analysis of two certified reference materials and applied successfully to the determination of trace amounts of Fe(III) in water and rice samples.
Publication Date: 2012
Talanta (00399140)
A simple solid phase extraction system based on the applying the nickel-aluminum layered double hydroxide (Ni-Al LDH) as a nano-sorbent was developed for the speciation analysis of chromium and manganese by flame atomic absorption spectrometry (FAAS). The method is based on the fact that Cr(VI) and Mn(VII) oxyanions could be adsorbed on the Ni-Al(NO3-) LDH and/or exchanged with LDH interlayer NO3- ions at pH 6.0, whereas Cr(III) and Mn(II) cations pass through the LDH-packed column without retention. The determinations of total Cr and Mn, and hence indirectly Cr(III) and Mn(II), involve the pre-oxidations of Cr(III) and Mn(II) to Cr(VI) and Mn(VII) with H2O2 and acidic solution of KIO4, respectively. Several important factors affecting the retention efficiency were investigated and optimized. In the optimum experimental conditions, the limits of detection (3Sb/m) for Cr(VI) and Mn(VII) were 0.51 and 0.47 ng mL-1, and the relative standard deviations were 2.5 and 3.2% (C = 30.0 ng mL-1, n = 6), respectively. The presented method was validated by the analysis of a certified reference material, and applied to the speciation of Cr and Mn in drinking waters, surface waters and industrial wastewater effluents. © 2012 Elsevier B.V. All rights reserved.
Abdolmohammad-Zadeh, Hossein,
Rezvani Z.,
Sadeghi, G.,
Zorufi E. Publication Date: 2011
Analytica Chimica Acta (18734324)(2)
The nickel-aluminum layered double hydroxide (Ni-Al LDH) was synthesized by a simple co-precipitation method with controlled pH and followed by hydrothermal treatment. The obtained nano-structured inorganic material was employed, for the first time, as a new solid-phase extraction (SPE) sorbent for the extraction and pre-concentration of trace levels of fluoride ions from aqueous solutions. An indirect method was used for monitoring of extracted fluoride ions. The method is based on the quenching effect of extracted fluoride ions upon the fluorescence intensity of Al-oxine complex via the forming of AlF63-, which was determined spectrofluorometrically at λem=510nm with excitation at λex=404nm. The effect of several parameters such as type of interlayer anion in Ni-Al LDH structure, pH, sample flow rate, elution conditions, amount of nano-sorbent, sample volume and co-existing ions on the extraction efficiency of the analyte were investigated. The results showed that fluoride ions could be retained on the Ni-Al (NO3-) LDH at pH 6.0 and stripped by 1.2mL of 3.0molL-1 NaOH. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 9.0ngmL-1 and 50, respectively. The optimized method was successfully applied to the determination of fluoride concentration in various water samples. The results obtained from the proposed method were successfully compared with those provided by standard SPADNS method. © 2010 Elsevier B.V.
Publication Date: 2010
Talanta (00399140)(3)
In this research, we combined ionic liquid-based dispersive liquid-liquid micro-extraction (IL-based DLLME) with stopped-flow spectrofluorometry (SFS) to evaluate the concentration of aluminum in different real samples at trace level. 1-Hexylpyridinium hexafluorophosphate [Hpy][PF6] ionic liquid and 8-hydroxyquinoline (oxine), which forms a highly fluorescent complex with Al3+, were chosen as the extraction solvent and chelating agent, respectively. The hydrophobic Al-oxine complex was extracted into the [Hpy][PF6] and separated from the aqueous phase. Then, the concentration of the enriched aluminum in the sediment phase was determined by SFS. Some effective parameters that influence the SFS signals and the micro-extraction efficiency, such as the suction and sending time, the concentration of the chelating agent, pH, the amount of the ionic liquid, the type of disperser solvent and diluting agent, ionic strength, extraction time, equilibration temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and enrichment factor were 0.05 μg L-1 and 100, respectively. The relative standard deviation (RSD) for six replicate determinations of 6 μg L-1 Al was 1.7%. The calibration graph using the pre-concentration system was linear in the range of 0.06-15 μg L-1 with a correlation coefficient of 0.9989. The developed method was validated by the analysis of certified reference materials and applied successfully to the determination of aluminum in several water, fruit juice and food samples. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2009
Analytica Chimica Acta (18734324)(2)
A simple dispersive liquid-liquid microextraction methodology based on the application of 1-hexylpyridinium hexafluorophosphate [HPy][PF6] ionic liquid (IL) as an extractant solvent was proposed for the preconcentration of trace levels of zinc as a prior step to determination by flame atomic absorption spectrometry (FAAS). Zinc was complexed with 8-hydroxyquinoline (oxine) and extracted into ionic liquid. Some effective factors that influence the microextraction efficiency such as pH, oxine concentration, amount of IL, ionic strength, temperature and centrifugation time were investigated and optimized. In the optimum experimental conditions, the limit of detection (3 s) and the enhancement factor were 0.22 μg L-1 and 71, respectively. The relative standard deviation (RSD) for six replicate determinations of 13 μg L-1 Zn was 1.92%. In order to validate the developed method, a certified reference material (NIST SRM 1549) was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the trace determination of zinc in water and milk samples. © 2009 Elsevier B.V. All rights reserved.
Publication Date: 2024
Journal of Vibration Engineering and Technologies (25233920)12(Suppl 1)pp. 985-996
Objective: In this paper, the nonlinear flutter of the wing is investigated under the influence of aerodynamic control surfaces. Methods: The wing aerodynamic loads are determined using Peter’s unsteady aerodynamic model, and the aerodynamic loads of the control surface are added with quasi-steady relations in the interior of the equations. The governing aeroelastic equations are presented in the structure of fully intrinsic and these equations are discretized using the finite difference method. Results: The effects of the presence of an aerodynamic control surface have been investigated based on the analytical-experimental relationships and considering the nonlinear effects of high control surface deflections. Furthermore, investigation of the effects of some important parameters such as deflections, location, chord size, and length of the control surface on the speed and frequency of flutter instability, is another achievement of this article. Conclusions: The results show that based on aeroelastic considerations, the deflection angle of the control surface has an important effect on the aeroelastic stability. Also, by bringing the control surface closer to the wing tip, increasing the thickness ratio and the chord ratio in accordance with other effective parameters, flutter suppression can be caused. © Springer Nature Singapore Pte Ltd. 2024.
Publication Date: 2024
Applied Soft Computing (1568-4946)165
The use of multiple fixed-wing unmanned aerial vehicles in search and rescue missions after natural disasters has become of great interest as they can search large areas and find survivors as quickly as possible. This paper discusses a minimum time cooperative search scheme that utilizes ant colony optimization and new heuristic functions to tackle various constraints in a dynamic environment. The study makes novel use of Dubins curves in the heuristic functions to consider the kinematic limitations of fixed-wing UAVs when planning tangent continuity paths. Furthermore, a novel probabilistic approach is introduced to model the uncertainties induced by dynamic obstacles and determine optimal search paths that are safe and practical in a grid search environment. The performance of the proposed search algorithm is tested through two-dimensional and three-dimensional simulations, statistical analysis, and comparison with other well-known optimization algorithms. To randomize the simulated cooperative search, different search scenarios with static and dynamic obstacles are run several times. © 2024 Elsevier B.V.
Publication Date: 2024
Soft Computing (14327643)28(17-18)pp. 10601-10628
A real-time wind velocity vector and parameters estimation and wind model identification approach using a machine learning technique is addressed in this paper. The proposed method uses only the state measurements of an aircraft and does not require control commands, air data systems, or satellite-based data. Small unmanned aerial vehicles (UAVs) can benefit from this method, since it relies solely on measurement results from the common sensors as an attitude and heading reference system. The independence of external sources of information made estimations resistant to intentional errors. This algorithm uses long short-term memory neural networks (LSTM NNs) in a two-step deep learning process involving classification and regression. A classification NN was trained with four different labeled wind models, while individual regression NNs were trained to estimate the velocity vector and parameters of each wind model. The linear acceleration, angular velocity, and Euler angle measurements were used as the inputs of trained networks. The algorithm suggests in its first step identifying the exact wind model, and in its second step estimating the wind velocity vector and parameters using a properly assigned estimation from a trained network. A nonlinear six-degree-of-freedom simulation of straightforward and level turn maneuvers of a fixed-wing UAV in the presence of different wind models served as the dataset in the learning process. Monte Carlo simulations proved the accuracy and rapidity of the proposed algorithm in identifying the wind model and estimating three-dimensional wind velocity vector and parameters. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Publication Date: 2023
Advances in Space Research (02731177)71(12)pp. 5337-5359
In this paper, the previous work of the authors on Subspace Predictive Control (SPC) in the context of spacecraft roto-translational relative motion is pursued, and the introduced novel SPC-based approach to fault-tolerant control (FTC) of nonlinear time-variant systems is further investigated. Firstly, the effectiveness of the proposed SPC-based framework for adaptive control allocation is exploited. Subsequently, separating nonlinear control and control allocation blocks yields a new layered SPC-based control scheme. Furthermore, designating a dedicated controller for each of the coupled motions leads to a novel distributed SPC-based architecture. Accordingly, three complete model-free fault-tolerant controllers for coupled nonlinear time-variant plants are developed, which solely need the knowledge of the occurrence time of faults as prerequisite. An internal fault diagnosis capability is also introduced, which makes the framework completely self-sufficient. Finally, the proposed framework is verified by challenging simulated scenarios. © 2023
Publication Date: 2023
Aut Journal Of Mechanical Engineering (25882937)7(3)pp. 297-316
Planning the flight path for a fleet of fixed-wing unmanned aerial vehicles during search and rescue operations poses a significant challenge as it requires minimizing search time and optimizing the formation of the unmanned aerial vehicles. This paper proposes a novel integration of a leader-follower formation flight technique for multiple fixed-wing unmanned aerial vehicles with a minimum-time search path planning algorithm. In the first step, the proposed algorithm, based on continuous ant colony optimization, plans a sequence of safe and feasible waypoints for the leader while determining appropriate azimuth angles for the followers. In the next step, the algorithm utilizes a nonlinear three-degree-of-freedom model, developed based on a leader-follower formation flight technique, to plan the followers’ flight paths. Applying Dubins curves based on kinematic constraints of the unmanned aerial vehicles not only reduces computational time but also ensures the feasibility of the best search paths between planned waypoints. Furthermore, in the presence of static obstacles, a developed function in the planning process addresses collision and obstacle avoidance constraints. The effectiveness and performance of the suggested method in detecting targets in minimum-time search missions and the ability of the planner to reconfigure the formation of unmanned aerial vehicles in cluttered environments are demonstrated through comprehensive simulation studies and Monte Carlo analysis. © 2023, Amirkabir University of Technology. All rights reserved.
Publication Date: 2022
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (09544100)236(7)pp. 1295-1303
For more than a decade, the multi-state constraint Kalman filter is used for visual-inertial navigation. Its advantages are the light-weight calculations, consistency, and similarity to the current mature GPS/INS Kalman filters. For using it in an airborne platform, an important deficiency exists. It diverges while the object stops moving. In this work, this deficiency is accounted for, by changing the state augmentation and measurement update policy from a time-based to horizontal travel-based scheme, and by reusing the oldest tracked point over and over. Besides the computational savings, it works infinitely with no extra errors in full-stops and with minor error build up in very low speeds. © IMechE 2022.
Publication Date: 2021
Journal of Aerospace Engineering (08931321)34(6)
The problem of controlling coupled six-degrees-of-freedom (6-DOF) relative motion of an integrated-actuation spacecraft in the presence of actuator faults, and especially failures, is investigated in this paper. Considering the complications and limitations of the common control paradigm (which requires a mathematical model of a plant), a novel data-driven control framework is proposed. Specifically, the subspace predictive control (SPC) approach (which is an elegant data-driven framework based on a special combination of the model predictive control method and the subspace system identification technique) is developed and extended to control nonlinear plants and to tolerate abrupt and severe faults. Accordingly, a model-free fault-tolerant control method for coupled nonlinear time-variant plants is provided, such that its only fault diagnostic requirement is detection of the occurrence time of faults. Furthermore, a fully decentralized multispacecraft strategy is proposed and formulated that is quite suitable for a data-driven cooperative control approach. The effectiveness of the developed framework is demonstrated via simulation. © 2021 American Society of Civil Engineers.
Publication Date: 2021
Journal of Navigation (03734633)74(4)pp. 801-821
This paper describes a camera simulation framework for validating machine vision algorithms under general airborne camera imperfections. Lens distortion, image delay, rolling shutter, motion blur, interlacing, vignetting, image noise, and light level are modelled. This is the first simulation that considers all temporal distortions jointly, along with static lens distortions in an online manner. Several innovations are proposed including a motion tracking system allowing the camera to follow the flight log with eligible derivatives. A reverse pipeline, relating each pixel in the output image to pixels in the ideal input image, is developed. It is shown that the inverse lens distortion model and the inverse temporal distortion models are decoupled in this way. A short-time pixel displacement model is proposed to solve for temporal distortions (i.e. delay, rolling shutter, motion blur, and interlacing). Evaluation is done by several means including regenerating an airborne dataset, regenerating the camera path on a calibration pattern, and evaluating the ability of the time displacement model to predict other frames. Qualitative evaluations are also made. Copyright © The Royal Institute of Navigation 2021.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment (14750902)233(3)pp. 918-936
The design process of an autonomous underwater vehicle requires mathematical model of subsystems or disciplines such as guidance and control, payload, hydrodynamic, propulsion, structure, trajectory and performance and their interactions. In early phases of design, an autonomous underwater vehicle is often encountered with a high degree of uncertainty in the design variables and parameters of system. These uncertainties present challenges to the design process and have a direct effect on the autonomous underwater vehicle performance. Multidisciplinary design optimization is an approach to find both optimum and feasible design, and robust design is an approach to make the system performance insensitive to variations of design variables and parameters. It is significant to integrate the robust design and the multidisciplinary design optimization for designing complex engineering systems in optimal, feasible and robust senses. In this article, we present an improved multidisciplinary design optimization methodology for conceptual design of an autonomous underwater vehicle in both engineering and tactic aspects under uncertainty. In this methodology, uncertain multidisciplinary feasible is introduced as uncertain multidisciplinary design optimization framework. The results of this research illustrate that the new proposed robust multidisciplinary design optimization framework can carefully set a robust design for an autonomous underwater vehicle with coupled uncertain disciplines. © IMechE 2018.
Publication Date: 2018
Ocean Engineering (00298018)147pp. 517-530
Optimal design of an Autonomous Underwater Vehicle (AUV) consists of various subsystems and disciplines such as guidance and control, payload, hydrodynamics, power and propulsion, sizing, structure, trajectory and performance. The designed vehicle is also employed in an operational environment with tactical parameters such as distance to target, uncertainty in estimation of target position and target velocity. Multidisciplinary Design Optimization (MDO) is the best way for finding both optimum and feasible designs. In this paper, a new optimization design framework is proposed in which Multidisciplinary Feasible (MDF) as MDO framework and Particle Swarm Optimization (PSO) as optimizer were combined together for optimal and feasible conceptual design of an AUV. Initially, we found an optimal system design by using MDF-PSO methodology in engineering space for any single tactical situation (locally tactical parameters). Then the optimal off-design AUVs in tactical subspaces were found by minimizing the difference between the locally optimized objective function and sub-optimal objective function. In this framework, we have shown that not only is the tactical situation affected by AUV design parameters, but an optimal AUV for each tactical regions are also found. © 2017 Elsevier Ltd
Publication Date: 2017
Aeronautical Journal (20596464)121(1244)pp. 1561-1577
This paper attempts to develop an efficient online algorithm for terrain following in completely unknown rough terrain environments while incorporating aircraft dynamics in the guidance strategy. Unlike most existing works, the proposed algorithm does not generate the flight path directly. The algorithm employs acquired information from the vehicle onboard sensors and rapidly issues appropriate Guidance Commands (GCs) at every point along the way. A suitable dynamic model is developed which takes the lags in the vehicle dynamics into account. The flight path forms gradually as a result of applying the GCs to the vehicle dynamics. Terrain-conforming capability afforded by this approach allows for autonomous and safe low-level flight in unknown mountainous areas. It considerably enhances the autonomy level of the vehicle and in the case of manned aircraft could significantly lead to pilot workload reduction. The proposed scheme is proven to be promising for online applications. Copyright © Royal Aeronautical Society 2017.
Publication Date: 2017
Journal of Aerospace Engineering (08931321)30(5)
This research is aimed at developing an efficient online path planner for unmanned air vehicle guidance in completely unknown three-dimensional (3D) rough terrain environments. A novel algorithm is proposed that directly incorporates the vehicle dynamics in the guidance strategy. A suitable point mass dynamic model is also developed. The flight path forms gradually as a result of applying the guidance commands to the vehicle dynamics. A key feature of this approach is real-time assessment of terrain characteristics and using this information in the guidance procedure. The problem is considered within a fuzzy behavior-based framework. The guidance algorithm uses acquired information from the onboard sensors and rapidly issues commands that will guide the vehicle safely to an intermediate position within the sensor range. Two behaviors are introduced: go to target and 3D terrain following/terrain avoidance. The issued commands are then integrated with adjustable weighting factors. Simulation results demonstrate a significant enhancement in vehicle autonomy level. Intelligent decision-making capability afforded by this approach allows for autonomous and safe low-level flight in mountainous areas. © 2017 American Society of Civil Engineers.
In this paper the attitude determination of a micro-satellite is handled applying two different state identification methods. The point-by-point or deterministic method solves the so-called Wahba's problem analytically by means of Davenport's q-method and the recursive or stochastic method estimates the attitude mean and covariance of the satellite's states using Extended Kalman Filter (EKF). The comparative results of two methods for the attitude determination of a micro-satellite in Low Earth Orbit (LEO) show the proficiency of the study. © 2017 IEEE.
Publication Date: 2017
Journal of Aerospace Technology and Management (21759146)9(1)pp. 71-82
The optimum design of a solid propulsion system consists of optimization of various disciplines including structure, aerothermodynamics, heat transfer, and grain geometry. In this paper, an efficient model of every discipline has been developed, and a suitable framework is introduced for these hard-coupled disciplines. Hybrid optimization algorithm is used to find the global optimum point including genetic algorithm and sequential quadratic programing. To show the performance of the proposed algorithm, the required correction factor values have been carefully derived using comparison between more than 10 real solid propulsion systems and the proposed algorithm results. According to the results, the derived correction factors are close to 1, with scattering level better than 0.97. In addition, it is shown that the proposed algorithm (errors < 8%) is more accurate in comparison with the conventional approach (errors < 17%). Then, for a case study, multidisciplinary analysis has been done based on 3 general objectives including dry mass, total mass, and specific impulse. It means that the optimum specific impulse is not the maximum value and the optimum dry mass is not the minimum value. Finally, the proposed algorithm can be used to directly derive the optimum configuration for every mission requirement. © 2017, Journal of Aerospace Technology and Management. All rights reserved.
Publication Date: 2017
International Journal Of Technology (20869614)8(3)pp. 376-386
In this study, a method was developed for tuning moments of inertia for a free-flying dynamically similar/scaled model of an aircraft. For this method, the simulated annealing optimization algorithm was used to obtain similar mass-inertial properties of the model and the full-scale aircraft utilizing ballast weights. For a scaled model of a Su-27 fighter, the ballast arrangement were designed and weights were determined to achieve the required center of gravity position and the moments of inertia based on the similitude requirements. A computer code was developed, and the task of tuning inertia properties was performed. The results showed that the proposed optimization approach was successfully used to determine a feasible ballast weight and position. Moreover, the ballast weight reduced from 8.66 kg to 4.86 kg using the proposed technique, and the inertia characteristics' non-similarity was minimized. © 2017 IJTech.
Publication Date: 2016
Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (09544100)230(6)pp. 1103-1113
This paper presents continuous curvature paths for unmanned vehicles such as robots and unmanned aerial vehicles. The importance of these paths is that both upper-bounded curvature and upper-bounded curvature derivatives are included in the path. The approach is based on replacement of the Dubins line with the quintic PH Bezier curves by computing a shape parameter by considering the kinematic constraints of the path. Since these paths are Dubins-based paths, their lengths are close to the minimum length. The effectiveness and sub-optimality of the proposed paths are demonstrated through fully nonlinear simulation. © 2015 Institution of Mechanical Engineers.
Publication Date: 2016
Sadhana - Academy Proceedings in Engineering Sciences (09737677)41(1)pp. 87-96
Reduction of costs is a main consideration in every space mission, and propulsion system is an important subsystem of those missions where orbital maneuvers are considered. Lighter propulsions with higher performance are necessary to reduce the mission costs. Bipropellant propulsions have been widely used in launch vehicles and upper-stages as well as deorbit modules because of better performances in comparison with other propulsion systems. Unfortunately heat transfer and thermal control limit bipropellant propulsion performance and maximum performance cannot be achieved. Well-known cooling methods such as regenerative and film cooling increase the cost using extra equipment and high temperature materials. In this paper, a new approach for cooling is presented based on combined ablative and radiative cooling. Governing equations are derived for two or three layers of thermal protection system (TPS) to optimize the TPS mass. The first layer is used as an ablative layer to control the temperature where the second and third layers are used as an insulator to control the heat fluxes. Proposed cooling method has been applied for two real bipropellant thrusters. According to the results, the presented algorithm can suitably predict the heat fluxes and satisfy the wall temperature constraint. Then, the algorithm has been used to minimize the wall temperatures as low as possible and replace high temperature materials (platinum alloy) with common materials (composite or steel). It is shown that selection of TPS materials affects the TPS mass and Isp simultaneously, but conversely. Best solution should be derived by trading off between structure temperature (cost), Isp (performance), and TPS thicknesses (geometry). Multidisciplinary approach to TPS and structure material selection of a bipropellant thruster is presented for a case study. It has been shown that mass and performance penalties of using TPS are acceptable, considering the advantages of using steel alloy instead of platinum alloy. © 2016, Indian Academy of Sciences.
Publication Date: 2015
Acta Astronautica (00945765)114pp. 174-183
Abstract Optimum design of an upper-stage with bipropellant propulsion system consists of optimization of three major subsystems including thruster, feeding subsystem, and propellant tanks. Optimization of such a complex system involved in optimization of many disciplines including structure, heat transfer, aerothermodynamics, guidance and control, trajectory and propulsion. Hard coupling of the disciplines increase the optimization processing times. Multidisciplinary design optimization algorithm can derive the optimum configuration but more elapsed time is needed for single-level methods such as all at once (AAO) and lower feasibility occurred in multi-level methods such as collaborative optimization (CO). In this paper, a new multidisciplinary design optimization framework is proposed for such coupled disciplines with concentrating on the propulsion system. The proposed framework uses Combined Single-level and Bi-level Optimizations (CSBO) frameworks to minimize numbers of design variables and system constraints when feasibility is increased. For this goal, modeling of every discipline is introduced and the design algorithm validated by redesigning of two real bipropellant thrusters. Three MDO frameworks are applied for our problem including AAO, CO and CSBO. Comparisons between the results show that CSBO can find the optimum solution in shorter elapsed time with lower F-count. Therefore, CSBO is more efficient for complex systems with coupled disciplines. © 2015 IAA.
Publication Date: 2015
International Journal of Intelligent Unmanned Systems (20496427)3(2-3)pp. 156-170
Purpose – For complex engineering problems, multidisciplinary design optimization (MDO) techniques use some disciplines that need to be run several times in different modules. In addition, mathematical modeling of a discipline can be improved for each module. The purpose of this paper is to show that multi-modular design optimization (MMO) improves the design performances in comparison with MDO technique for complex systems. Design/methodology/approach – MDO framework and MMO framework are developed to optimum design of a complex system. The nonlinear equality and inequality constrains are considered. The system optimizers included Genetic Algorithm and Sequential Quadratic Programming. Findings – As shown, fewer design variables (optimization variables) are needed at the system level for MMO. Unshared variables are optimized in the related module when shared variables are optimized at the system level. The results of this research show that MMO has lower elapsed times (14 percent) with lower F-count (16 percent). Practical implications – The monopropellant propulsion upper-stage is selected as a case study. In this paper, the efficient model of the monopropellant propulsion system is proposed. According to the results, the proposed model has acceptable accuracy in mass model (error <2 percent), performance estimation (error <6 percent) and geometry estimation (error <10 percent). Originality/value – The monopropellant propulsion system is broken down into the three important modules including propellant tank (tank and propellant), pressurized feeding (tank and gas) and thruster (catalyst, nozzle and catalysts bed) when chemical decomposition, aerothermodynamics, mass and configuration, catalyst and structure have been considered as the disciplines. The both MMO and MDO frameworks are developed for the monopropellant propulsion system. © 2015, © Emerald Group Publishing Limited.
