Iranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321Effects of Geometrical Parameters of Gas Flow Channels on Polymer Electrolyte Membrane Fuel Cell PerformanceEffects of Geometrical Parameters of Gas Flow Channels on Polymer Electrolyte Membrane Fuel Cell Performance11310234610.30699/jsst.2022.1156FAHamed MoeiniMS.c., Department of Aerospace Engineering, Sharif University of Technology, Tehran, IranEbrahim AfshariAssociate Professor, Department of Mechanical Engineering, Faculty of Engineering, University of Isfahan, Isfahan, IranKarim MazaheriProfessor, Faculty of Aerospace Department, Sharif University of Technology, Tehran, IranJournal Article20181212In the present study, the effects of geometrical properties of gas flow channels on both current density and temperature distributions inside a polymer electrolyte membrane (PEM) fuel cell are investigated. The main purpose here is to clarify the effects of the variation of width, depth, and the ribs of flow channels on the fuel cell performance. To do this, the fuel cell is numerically simulated in two dimensions. The governing equations consist of the conservation of the electrical potential, Darcy’s law as alternative to the momentum equation, Maxwell-Stefan equation for mass transport, energy conservation, and electro-thermal equations along with the Butler–Volmer equation. Numerical results indicate that the width of channels and their ribs have more sensible effects than the depth of flow channels on the current density and temperature distributions and fuel cell performance. While the maximum temperature of the cell is increased by increasing the width of the flow channels, the current density distribution and fuel cell performance can be improved. By decreasing the width of their ribs or depth of channels, the performance of the fuel cell is improved and its maximum temperature is decreased.In the present study, the effects of geometrical properties of gas flow channels on both current density and temperature distributions inside a polymer electrolyte membrane (PEM) fuel cell are investigated. The main purpose here is to clarify the effects of the variation of width, depth, and the ribs of flow channels on the fuel cell performance. To do this, the fuel cell is numerically simulated in two dimensions. The governing equations consist of the conservation of the electrical potential, Darcy’s law as alternative to the momentum equation, Maxwell-Stefan equation for mass transport, energy conservation, and electro-thermal equations along with the Butler–Volmer equation. Numerical results indicate that the width of channels and their ribs have more sensible effects than the depth of flow channels on the current density and temperature distributions and fuel cell performance. While the maximum temperature of the cell is increased by increasing the width of the flow channels, the current density distribution and fuel cell performance can be improved. By decreasing the width of their ribs or depth of channels, the performance of the fuel cell is improved and its maximum temperature is decreased.https://jsst.ias.ir/article_102346_afe8f11660a9ca727ce096bd0f06ff98.pdfIranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321The Retrieval of Wet Refractivity Index by Tomography Using Spherical Cap HarmonicsThe Retrieval of Wet Refractivity Index by Tomography Using Spherical Cap Harmonics152410963910.30699/jsst.2022.1256FAMasoud DehvariM.Sc., School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran, Tehran, IranSaeed FarzanehAssociate Professor, School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran,, Tehran, IranMohammad Ali SharifiAssociate Professor, School of Surveying and Geomatics Engineering, Faculty of Engineering, University of Tehran,, Tehran, IranJournal Article20200102In this research, three-dimensional and four-dimensional tomography is used to demonstrate the distribution of wet refractivity index of the troposphere. In this model, spherical cap harmonics are used for the horizontal distribution of the wet refractivity index, and empirical orthogonal functions are used for the vertical distribution of the index. The region of study is in the west California State, and the wet refractivity index is retrieved from the wet tropospheric delay measurements. to validate the results, radiosonde profiles were compared to the tomographically retrieved profiles. The result shows that wet refractivity indices can be retrieved using functional models with RMSE about 2.4 ppm till 3.9 in four-dimension method. The comparisons show that the four-dimensional retrieved profiles shows improvement up to 34 and 42 percentage in mid-day tomography epochs compare to three-dimensional tomography results. Also it can be seen that in mid-night epochs three-dimensional tomography has higher accuracy compare to four-dimension method because of low variation of wet refractivity indicesIn this research, three-dimensional and four-dimensional tomography is used to demonstrate the distribution of wet refractivity index of the troposphere. In this model, spherical cap harmonics are used for the horizontal distribution of the wet refractivity index, and empirical orthogonal functions are used for the vertical distribution of the index. The region of study is in the west California State, and the wet refractivity index is retrieved from the wet tropospheric delay measurements. to validate the results, radiosonde profiles were compared to the tomographically retrieved profiles. The result shows that wet refractivity indices can be retrieved using functional models with RMSE about 2.4 ppm till 3.9 in four-dimension method. The comparisons show that the four-dimensional retrieved profiles shows improvement up to 34 and 42 percentage in mid-day tomography epochs compare to three-dimensional tomography results. Also it can be seen that in mid-night epochs three-dimensional tomography has higher accuracy compare to four-dimension method because of low variation of wet refractivity indiceshttps://jsst.ias.ir/article_109639_5306d4b19a1469bbfc1c7d45947a2bc3.pdfIranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321Drop Behavior on Micro-Structured Superhydrophobic CoatingDrop Behavior on Micro-Structured Superhydrophobic Coating253311929510.30699/jsst.2020.1241FARamin Kamali MoghadamAssociate Professor, Aerospace Research Institute, Ministry of Science, Research and Technology, Tehran, Iran0000-0002-0780-7689Mohammad Taeibi RahniProfessor, Department of Aerospace Engineering, Sharif University of Technology, Tehran, IranSalar Heyat DavoudianPh.D., Student, Department of Aerospace Engineering, Sharif University of Technology, Tehran, IranReinhard MillerProfessor, Max Planck Institute of Colloids and Interfaces, GermanyJournal Article20191104Superhydrophobic coatings can be made by creating a micro-sized structure on a surface providing super-repellent properties which has many applications in aerospace, defense, automotive, biomedical and engineering. Numerical simulation of drop dynamics and motion on a superhydrophobic surface helps us understand control and building surface textures and find optimum micro structured coatings of maximum hydrophobicity. In the present work, the dynamics of drops on superhydrophobic inclined micro-structured surfaces is studied, using a finite element method. Effect of microstructures on droplet behavior on a superhydrophobic surface is investigated using different microstructures. The governing equations and important dimensionless numbers are described and a numerical algorithm is introduced. The validation of the numerical algorithm is performed by simulation of drop motion attached to an inclined surface. In addition, droplet movement on the micro structured surface is numerically simulated on smooth and microstructure surfaces in the same conditions. Comparison of the results shows the effect of microstructure coating on the surface hydrophobicity properties.Superhydrophobic coatings can be made by creating a micro-sized structure on a surface providing super-repellent properties which has many applications in aerospace, defense, automotive, biomedical and engineering. Numerical simulation of drop dynamics and motion on a superhydrophobic surface helps us understand control and building surface textures and find optimum micro structured coatings of maximum hydrophobicity. In the present work, the dynamics of drops on superhydrophobic inclined micro-structured surfaces is studied, using a finite element method. Effect of microstructures on droplet behavior on a superhydrophobic surface is investigated using different microstructures. The governing equations and important dimensionless numbers are described and a numerical algorithm is introduced. The validation of the numerical algorithm is performed by simulation of drop motion attached to an inclined surface. In addition, droplet movement on the micro structured surface is numerically simulated on smooth and microstructure surfaces in the same conditions. Comparison of the results shows the effect of microstructure coating on the surface hydrophobicity properties.https://jsst.ias.ir/article_119295_9e6b20eeb9b67f47f9766e7664d08151.pdfIranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321Strap-On Boosters Separation Analysis Using Coupled Simulation of Constraint Dynamics and Time Dependent CFDStrap-On Boosters Separation Analysis Using Coupled Simulation of Constraint Dynamics and Time Dependent CFD354414879610.30699/jsst.2022.1169FAMostafa JafariFaculty New Technologies and Aerospace Engineering, Shahid Beheshti University, Tehran IranAlireza ToloeiAssociate Professor, Faculty of New Technologies and Aerospace Engineering, Shahid Beheshti University, Tehran Iran0000-0002-1927-1412Journal Article20190225A numerical dynamic-aerodynamic interface for simulating the separation dynamics of constrained strap-on boosters jettisoned in the atmosphere is presented. Two commercial solvers: a 6DOF multi-body dynamic solver and a numerical time-dependent flow solver are integrated together with an interface code to constitute a package that presents real-time dynamic/aerodynamic coupled analysis. Dynamic unstructured mesh approach is employed using local remeshing methods in respect of bodies motion with a second-order upwind accurate 3D Euler solver. This interface can simulate multi body separation dynamics interaction with aerodynamic effects to complete separation mechanisms like springs, thrusters, joints and so on. The flow solver is validated by the Titan IV launch vehicle experimental data. The separation integration is used for a typical launch vehicle with two strap-on boosters using spring ejector mechanism and spherical constraint joints acting in the dense atmosphere. Hence, the aim of the presented interface is to facilitate the integration of complicated separation mechanisms with a full numerical CFD aerodynamic solver.A numerical dynamic-aerodynamic interface for simulating the separation dynamics of constrained strap-on boosters jettisoned in the atmosphere is presented. Two commercial solvers: a 6DOF multi-body dynamic solver and a numerical time-dependent flow solver are integrated together with an interface code to constitute a package that presents real-time dynamic/aerodynamic coupled analysis. Dynamic unstructured mesh approach is employed using local remeshing methods in respect of bodies motion with a second-order upwind accurate 3D Euler solver. This interface can simulate multi body separation dynamics interaction with aerodynamic effects to complete separation mechanisms like springs, thrusters, joints and so on. The flow solver is validated by the Titan IV launch vehicle experimental data. The separation integration is used for a typical launch vehicle with two strap-on boosters using spring ejector mechanism and spherical constraint joints acting in the dense atmosphere. Hence, the aim of the presented interface is to facilitate the integration of complicated separation mechanisms with a full numerical CFD aerodynamic solver.https://jsst.ias.ir/article_148796_a056c9001c3354410ddab02d07d80e62.pdfIranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321Evaluation of Diversity Effects on Increasing the Reliability of Space SystemsEvaluation of Diversity Effects on Increasing the Reliability of Space Systems455312953510.30699/jsst.2021.1283FAGhasem KaheAssistant Professor, Aerospace Research Institute, Ministry of Science, Research and Technology, Tehran, Iran0000-0001-5511-2171Mehdi Alemi RostamiAssistant Professor, Aerospace Research Institute, Ministry of Science, Research and Technology, Tehran, Iran0000-0003-4609-3954Journal Article20200602Diversity in both hardware and software plays an essential and unmatched role in increasing the reliability of redundant systems, especially in safety and mission critical applications. The onboard computer of satellites and the flight computer of spacecrafts, which are ultra-reliable systems, utilize various hardware platforms for their redundant architecture to resolve a common cause failure (CCF) problem. Furthermore, the software is also developed by separate teams based on different software platforms to mitigate the specification and design flaws, and implementation mistakes. This paper focuses on modelling the diversity of redundant architectures in space systems using CCF modelling and Markov reliability analyzing. The proposed scheme is explored in two types of applications: mission critical applications (with long mission time) and safety critical applications (with short mission time). Analytical and simulation results show the effectiveness of diversity in increasing the reliability of these systems. Since a significant percentage of all failures appear as common cause failures, which restrict reliability improvement through similar redundant modules, achieving ultra-reliability necessitates considering diversity in these systems.Diversity in both hardware and software plays an essential and unmatched role in increasing the reliability of redundant systems, especially in safety and mission critical applications. The onboard computer of satellites and the flight computer of spacecrafts, which are ultra-reliable systems, utilize various hardware platforms for their redundant architecture to resolve a common cause failure (CCF) problem. Furthermore, the software is also developed by separate teams based on different software platforms to mitigate the specification and design flaws, and implementation mistakes. This paper focuses on modelling the diversity of redundant architectures in space systems using CCF modelling and Markov reliability analyzing. The proposed scheme is explored in two types of applications: mission critical applications (with long mission time) and safety critical applications (with short mission time). Analytical and simulation results show the effectiveness of diversity in increasing the reliability of these systems. Since a significant percentage of all failures appear as common cause failures, which restrict reliability improvement through similar redundant modules, achieving ultra-reliability necessitates considering diversity in these systems.https://jsst.ias.ir/article_129535_7088778fd7e86335e1506b8224a342f6.pdfIranian Aerospace Society -Aerospace Research InstituteSpace Science and Technology2008-456015English Special Issue20220321Design, Construction and Performance Evaluation of a Cold Gas Thruster Test StandDesign, Construction and Performance Evaluation of a Cold Gas Thruster Test Stand556413280510.30699/jsst.2021.1305FAَAlireza AlikhaniAssociate Professor, Aerospace Research Institute, Ministry of Science, Research and Technology, Tehran, Iran0009-0002-5658-1433Mohammad Reza SalimiAssistant Professor, Aerospace Research Institute, Ministry of Science, Research and Technology, Tehran, Iran0000-0003-2127-2921Journal Article20200928The cold gas thruster is one of the significant components of a satellite and its application possesses a marked impact on the entire system performance. The nonlinear function and order of magnitude, lead to increasing the importance of thruster function. Therefore, pre-mission performance assessment has a considerable effect on the risk reduction of space missions. In this article, an uncomplicated and efficient pendulum scheme for development and implementation of a Thruster Test Stand (TTS), to measure the thrust produced at the end of the nozzle is proposed. The TTS is capable of measuring thrust levels in the range of 0.1Newtons to 3N with operating frequencies up to 50 Hz which is used by various satellite ranges. The experimental results demonstrate that although the designed device is less sophisticated than other test devices, it is capable of measuring the produced thrust very precisely and with less than 15mN.The cold gas thruster is one of the significant components of a satellite and its application possesses a marked impact on the entire system performance. The nonlinear function and order of magnitude, lead to increasing the importance of thruster function. Therefore, pre-mission performance assessment has a considerable effect on the risk reduction of space missions. In this article, an uncomplicated and efficient pendulum scheme for development and implementation of a Thruster Test Stand (TTS), to measure the thrust produced at the end of the nozzle is proposed. The TTS is capable of measuring thrust levels in the range of 0.1Newtons to 3N with operating frequencies up to 50 Hz which is used by various satellite ranges. The experimental results demonstrate that although the designed device is less sophisticated than other test devices, it is capable of measuring the produced thrust very precisely and with less than 15mN.https://jsst.ias.ir/article_132805_d4ea1b40fe2c7c291a921d042e42753f.pdf