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Ghatreh samani s., ,
Beheshti, H. ,
Akbarzadeh a.h., ,
Kiani y., International Journal of Structural Stability and Dynamics (02194554) 25(15)
In this paper, the free vibration of a sandwich plate with an anisogrid core and two face sheets reinforced with graphene platelets (GPLs) is investigated. A continuous approach is considered for the lattice core and the equivalent properties are calculated. Adopting the Halpin–Tsai micromechanics, the effective Young’s modulus of the nanocomposites/graphene platelets is extracted. Also, mass density and Poisson’s ratio are earned with the simple rule of mixtures. A quasi-3D theory is applied to model the kinematics of the sandwich plate with simply supported boundary conditions. Hamilton’s principle is implemented to obtain the equations of motion that are solved based on the Navier solution. The validity of the results of this study is confirmed by comparing the analytical results with those presented in other researches and also a finite element model. The effect of the parameters of the lattice core such as the width of ribs, the number of helical ribs in one direction, and the ratio of thickness of face sheets to core on the natural frequencies of the sandwich plate was investigated. Additionally, the impact of the pattern of graphene platelets and their weight fraction on the natural frequencies were investigated. The results show that by decreasing the ratio of the thickness of face sheets to the thickness of core and increasing the number of ribs and their width, the natural frequencies will decrease. Moreover, the patterns FG-V and FG-A have the highest and the lowest natural frequencies, respectively, among the other distribution of graphene platelets. © 2025 World Scientific Publishing Company.
Mechanics of Advanced Materials and Structures (15210596) 31(18)pp. 4295-4308
In this study, a novel micromechanics-based damage model is proposed for the damage evolution of a two-component microencapsulated-based self-healing polymer composite. In this way, a representative volume element (RVE) including an epoxy matrix with randomly distributed poly(methyl methacrylate) (PMMA) microcapsules is modeled in DigimatTM software and analyzed in Abaqus®. A new technique is developed to investigate the progressive damage by pre-inserted cohesive elements along all element boundaries of the epoxy matrix, PMMA shell, and capsule-matrix interfaces with the bilinear traction–separation law. Moreover, the impact of interface bonding strength, interface fracture energy, and PMMA microcapsules volume fraction on the load-carrying capacity of the RVEs under uniaxial tension loading was studied. The results indicated that the tensile strength of the self-healing polymer composite increased as the interfacial strength and fracture energy increased from 10 to 60 MPa and 100 to 1000 J/m2, respectively. Furthermore, the higher volume fraction of 5% PMMA microcapsules results in a lower load-carrying capacity of self-healing polymer composite with a strength of 4.9 N. A similar trend of Young’s modulus was observed for microcapsule-loaded epoxy composite compared to the pristine epoxy matrix. The micromechanical model has proper accuracy in predicting the tension behavior of self-healing composite in comparison to experimental results. Finally, two healing strategies are considered for the damaged RVE. © 2023 Taylor & Francis Group, LLC.
Journal of Composite Materials (00219983) 57(30)pp. 4675-4686
One of the most important applications of electromagnetic wave absorption is in stealth aircrafts and electromagnetic protection of avionic systems. The main limitations in the design of these structures are aerodynamics, thickness or weight, mechanical strength, manufacturing process, and reasonable cost. In this study, a novel three-layer woven fabric composite laminate (with a total thickness of about 3 mm) is proposed which each layer is reinforced by individual polyaniline, carbonyl iron, or (PANI + CI) core-shell fillers. The developed Non-dominated Sorting Genetic Algorithm II optimization algorithm suggests the stacking sequence of layers, the appropriate thickness of each layer, and the filler weight fraction in each layer to achieve a broadband absorption. Due to using both dielectric and magnetic absorbing fillers, this structure shows well-impedance matching and approximately absorbs 80% of the X-band (8-12 GHz) electromagnetic waves. The maximum reflection loss is about −14dB. Finally, the effect of the addition of absorbent particles on the mechanical properties has been investigated. Experimental results showed that the tensile modulus and strength decrease by about 21.5% and 20.6%, respectively, and the flexural modulus and strength reduce by 21.7% and 19.7%, respectively. However, the (PANI + CI) core-shell filler can be introduced as a high performance absorber filler because it suggests maximum reflection loss with low weight fraction compared to other fillers and consequently the minimum reduction in mechanical properties. © The Author(s) 2023.
Journal of Reinforced Plastics and Composites (07316844) 42(9-10)pp. 430-445
The main challenge in the design of radar-absorbing composite structures (RASs) is that there is a variety of different parameters affecting the absorbing performance. In this study, these parameters are categorized into: (1) reinforcing materials including fabric types (i.e., glass fabric, carbon fabric, and 3D fabric) and filler types (i.e., carbon black, carbonyl iron, and polyaniline); (2) geometric parameters including layer thickness and stacking sequences; and (3) manufacturing methods. Up to now, the effect of all these parameters has not been simultaneously investigated and optimized on the X-band radar-absorbing feature of composite structures. Therefore, the influence of all these parameters is first experimentally investigated using waveguide tests; then, a new multi-objective optimization algorithm based on NSGA II technique is developed to simultaneously optimize the effective parameters for high-performance RAS with maximum average reflection loss and minimum weight, while considering structural limitations. Finally, the proposed algorithm is evaluated by experimental results. © The Author(s) 2022.
Smart Structures and Systems (17381584) 27(6)pp. 1001-1010
In this study, the effect of agitation speed as a key process parameter on the morphology and particle size of epoxy-Poly (methyl methacrylate) (PMMA) microcapsules was investigated. Thus, a new interpretation is presented to relate between the microcapsule size to rotational speed so as to predict the particle size at different agitation speeds from the initial capsule size. The PMMA shell capsules containing EC 157 epoxy and hardener as healing materials were fabricated through the internal phase separation method. The process was performed at 600 and 1000 rpm mechanical mixing rates. Scanning electron microscopy (SEM) revealed the formation of spherical microcapsules with smooth surfaces. According to static light scattering (SLS) results, the average diameter size of the epoxy/PMMA capsules at two mixing rates were 7.49 and 5.11 µm for 600 and 1000 rpm, respectively, indicating that the mean size increased as the mixing rates of the process increased. The D50, D90 and mean particle size values were the lowest for hardener/PMMA microcapsules at 1000 rpm. Moreover, the Fourier transform infrared (FTIR) spectroscopy was conducted to describe the chemical structure of epoxy and hardener PMMA capsules. To investigate the reinforcing role of microcapsules, they embedded in EPL-1012 epoxy resin with various amounts of 1 and 2.5 wt.% epoxy/PMMA capsules. The investigation also involved the effect of microcapsules on mechanical behavior as well as the reinforcement of polymer composite material. Experimental results showed that the tensile strength of the self-healing polymer composite slightly increased by 1 wt.% PMMA microcapsules prepared at 1000 rpm and then reduced with an increase in the concentration and mean size diameter of PMMA microcapsules. In addition, a similar trend of Young’s modulus was seen for pristine epoxy matrix and microcapsule-loaded epoxy composite. Copyright © 2021 Techno-Press, Ltd.
Mechanics of Advanced Materials and Structures (15210596) 28(24)pp. 2585-2594
Since lightweight and energy-absorbing materials have an effective role in occupant safety during accidents, the use of aluminum or composite tubes and their optimum designs are of great importance in crashworthiness. In this study, numerical simulation of crushing and multi-objective optimization of aluminum and composite cylinders are performed to evaluate the effects of tube thickness on the objective functions (the specific energy absorption and the peak force). Besides, the effects of annealing and tempering of ductile aluminum alloys (Al 6061) are investigated. The results show that annealing of ductile aluminum alloys yields a significant reduction in objective functions. With the same thickness of the aluminum and composite shell, the composite tube exhibits proper results in terms of both peak load and energy absorption. Finally, it seems that in the design of crash boxes, a thicker composite tube leads to more appropriate results than aluminum shell. © 2020 Taylor & Francis Group, LLC.
International Journal of Applied Mechanics (17588251) 12(4)
Since lightweight and energy-absorbing materials have an effective role in occupant safety during accidents, the use of hybrid aluminum-composite tubes and their optimum designs are of great importance in the crashworthiness. In this study, finite element simulation and multi-objective optimization of a hybrid aluminum-composite tube are performed under axial crushing to investigate the effect of metal volume fraction (MVF) on the objective functions, the specific energy absorption and the peak force. Besides, the effects of annealing and tempering of ductile aluminum alloys (Al-6061) as the base metal of hybrid tubes are investigated. The optimum values of the objective functions are obtained at MVF 0.5 (the same thickness of aluminum and composite). Also, annealing of ductile aluminum alloys has a negative effect on the objective functions. As a guideline for the design of fiber metal laminates under crushing, it is suggested to use tempered Al-6061 and increase the thickness of composite material so that MVF < 0.5. © 2020 World Scientific Publishing Europe Ltd.
International Journal Of Automotive And Mechanical Engineering (22298649) 16(2)pp. 6568-6587
Crash boxes play an important role in different industries as energy absorbers to reduce damage of accidents. An ideal crash box has lower maximum force and higher energy absorption. The aim of this study is to investigate the effect of various parameters such as geometry (diameter and thickness), triggering and filling with polymeric foam on axial crash behaviour of a composite cylindrical cash box. To this end, a composite crash box is modelled in a commercial finite element software, Abaqus, utilising the Hashin failure criterion to predict damage initiation. Linking damage initiation with material degradation rules provides the capability for damage evolution prediction on the basis of fracture energy of different failure modes. A new parameter (β) is defined to study the performance of a crash box with different geometries, triggers and foam-filling. The results show that three different triggering geometries (chamfer, fillet, and tulip) decrease the maximum load about 7-33%, and improved energy absorption about 40-86% compared to the crash box without trigger. Filling a triggered crash box with polymeric foam also improves energy absorption about 20%. Applying both triggering and foam-filling simultaneously on a crash box has a complementary role to receive a better performance. © Universiti Malaysia Pahang, Malaysia.
Emadi, M. ,
Beheshti, H. ,
Heidari-rarani, M. ,
Aboutalebi, F.H. Journal of Mechanical Science and Technology (1738494X) 33(5)pp. 2067-2074
Thin-walled aluminum tubes have been widely used in engineering structures, aerospace and transportation industries due to their excellent properties. In this paper, the effect of tempering and annealing on the crushing behavior of aluminum alloy tubes, in brittle or ductile manner, under quasi-static compression were investigated. The chemical composition, the Brinell hardness number and the tensile stress-strain curves of various types of Al alloys, i.e., Al 2024, Al 7075 and Al 6061 were obtained in both tempered and annealed state. Then, the axial compression tests were performed on the tubes by a universal testing machine at a controlled displacement rate of 5 mm/min. The crushing mode, load-displacement curve, and crashworthiness characteristics were achieved to obtain specifications of mentioned aluminum tubes. Annealing process, apart from changing the deformation mode and material strength, has often reduced energy absorption in the ductile alloy, Al 6061, and increased in brittle alloys, Al 2024-T3, T4 and Al 7075-T651. This process could also be used as a triggering mechanism to decrease the initial peak force. These experimental results give useful information regarding the material behavior of aluminum alloys to be utilized in the design process of crashworthy components. © 2019, KSME & Springer.
International Journal of Engineering, Transactions B: Applications (1728144X) 30(8)pp. 1260-1269
The aims of this study are to enhance the performance of a solar chimney power plant (SCPP), investigate utilization of thermal energy storage (TES) and analyze the environmental impact of the SCPP in providence of Isfahan, Iran. To achieve these goals, multi-stage numerical simulations during twenty-four hours of a day are performed in climate condition of Isfahan province (central region of Iran). Isfahan province has proper environmental condition for utilization of SCPP as a source of electricity and the environmental crises during the last decade in Iran have made utilization of green power plants a necessity. Performance enhancement of the SCPP is carried out by improvement in geometrical characteristics of collector and chimney of the SCPP. Considered factors for performance enhancement of SCPP are height, ceiling slop and radius of the collector as well as height, radius and throat shape of the chimney. Then a TES is employed to produce power in the absence of solar radiation in new proposed optimal configurations. In continue carbon dioxide emission and water consumption of enhanced configurations of SCPP are compared with shale gas, coal, hydroelectric and biomass power plants for same output power to investigate environmental impact of the SCPP. Results illustrate that improved collector of the SCPP increases the output power by almost 139% and enhanced chimney of the SCPP improves performance of the power plant by approximately 68.1%. Results also show that the SCPP with the TES would produce power during night hours in a stable range and TES has higher performance in SCPP with optimal proposed configurations. The results confirm that the SCPP is a proper choice for power generation in province of Isfahan (central region of Iran) and the enhanced SCPP with TES improves the output power range and environmental benefits considerably.
International Journal of Exergy (17428297) 20(2)pp. 150-169
In this paper, thermodynamic analysis of the performance of a solar chimney power plant with different types of thermal energy storage systems is presented. Stone and water as cost effective and low-maintenance thermal energy storage mediums are compared in different configurations in terms of electric power generation during night and the rate of exergy loss. The hydrodynamic and heat transfer phenomena in the solar chimney are numerically simulated. Comparison of different thermal energy storage systems shows that combined water-stone storage medium leads to several advantages of better stabilisation of power generation rate during a day, lower exergy loss by almost 30%, and higher power generation at night by about 10%. It is also shown that the solar chimney power plant with thermal energy storage reduces almost 340 kg per day of carbon dioxide emissions and 590 kg per day water consumption comparing with steam power plants. Copyright © 2016 Inderscience Enterprises Ltd.
Science and Technology for the Built Environment (2374474X) 22(5)pp. 619-627
This article studies the effect of operating frequency and fill pressure on the performance of a high frequency miniature scale pulse tube cryocooler. Pulse tube cryocoolers are robust, rough cryocoolers without a moving component at their cold ends. They are usually used in cryogenic cooling of high-performance electronics in space applications where reliability is vital. Miniaturizing cryocoolers is vital because their minimal size and weight facilitates many applications such as space operations. In spite of extensive studies, the extent of possible pulse tube cryocooler miniaturization is not clear. For miniature cryocoolers, computational fluid dynamics modeling is the best available method to accurately represent the processes that occur in the device as the scale is reduced. The present computational fluid dynamics simulation results indicate the significant influence of the operating frequency on the performance of the miniature pulse tube cryocooler and slight improvement of the performance as the fill pressure increases. Copyright © 2016 ASHRAE.
Journal of Thermal Science and Engineering Applications (19485093) 8(2)
The focus of this study is on serial and parallel configurations of a multistage thermoacoustic engines (TAE). Thermoacoustics integrates fluid dynamics, thermodynamics, and acoustics to explain the interactions existing between heat and sound. Considerable amounts of waste heat are released to the environment in everyday industrial processes. This waste heat cannot be reused due to its low temperature. One way for reusing some of this waste heat is to employ a thermoacoustic heat pump. TAEs can be driven by waste heat and are capable of supplying the power to drive the thermoacoustic heat pumps. However, due to the low temperature of this waste heat, single-stage TAEs cannot provide the required temperature lifts. Multistage TAEs are advantageous because they can provide sufficient temperature lifts. In this study, a computational fluid dynamics (CFD) simulation is carried out to understand the conversion process of heat to sound and study the nonlinear conjugation of unsteady heat release and acoustic disturbances. The two main parameters evaluated in this simulation are the initial pressure disturbance and the stack's temperature gradient. Their effects on actuating limit cycle oscillations are examined in a 2D numerical model. The numerical simulation results indicate that the pressure amplitude varies through alteration made in these mentioned parameters. The present numerical results are validated by previously published data. © 2016 by ASME.
Journal of Non-Equilibrium Thermodynamics (03400204) 40(3)pp. 171-183
The performance of a pilot scale flat plate solar water heater system is investigated theoretically and experimentally. The effect of the operating conditions and characteristic factors of the collector on the system efficiency is studied. A conceptual mathematical model is developed in order to analyze the system behavior in different operating conditions by considering the physical and constructive aspects of the system. The accuracy of the model result is estimated by comparing the model results with the existing experimental data. The highest obtained system thermal efficiency is 45%, and the optimum local values for surface azimuth and tilt angles are obtained at 180 degrees from north and 33 degrees, respectively, for the constructed solar water heater in Isfahan, Iran, with the local latitude of 32.6333°N. © 2015 by De Gruyter 2015.
International Journal of Crashworthiness (15738965) 20(1)pp. 44-59
Tubular forms of crash elements such as crash boxes are widely applied in transportation industries, especially in automobile industry. A crash box is an element used in the frontal crash zones, generally inserted between chassis and bumper to reduce the amount of crash energy that is transmitted to the rest of the front safety zones. In this paper, first, square section crash boxes filled with functionally graded honeycomb (FGH) subjected to oblique impact loading is presented with the objective to improve crashworthiness. Then, some optimisation tools such as the weighted average method, the geometrical average method, and multi-design objective optimisation technique are utilised to optimise the crash box structures. The optimisation results reveal that the crashworthiness of the FGH filled box structures exposed to the oblique impact loading is improved, and also proves its superiority with respect to the uniform honeycomb filled box structures. Finally, the metallic honeycomb density exponent gradient is properly determined. © 2014 Taylor & Francis.
Neural Computing And Applications (09410643) 24(5)pp. 1123-1133
The superposition of work roll initial crown, the work roll bending and flattening crown, the work roll wearing crown and the work roll thermal crown makes the final hot strip. In this paper, new models based on numerical method have been obtained to predict the roll force, the work roll wearing crown and the work roll thermal crown utilizing experimental data provided by Mobarake Steel Complex. Meanwhile, the work roll bending and flattening crown has been obtained from finite element method as well as elasticity approach. Then, a computer programing has been written to obtain the work roll initial crown in order to get desired strip profile. This program is called Initial Crown Prediction Software (ICPS). Finally, the obtained initial crowns from ICPS were applied for different stands of hot strip mill of Mobarake Steel Complex, and the strip profile shows a good agreement with the desired one for the mentioned mill. © 2013 Springer-Verlag London.
Journal of Mechanical Science and Technology (1738494X) 28(5)pp. 1741-1752
Metallic foams as a filler in thin-walled structures can improve their crashworthiness characteristics. In this article, nonlinear parametric finite element simulations of FGF foam-filled conical tube are developed and the effect of various design parameters such as density grading, number of grading layers and the total mass of FGF tube on resulting mode shapes, specific energy absorption and initial peak load is investigated. Multi design optimization (MDO) technique and the geometrical average method, both are based on FE model are applied to maximize the specific energy absorption and minimize the impact peak force by estimating the best wall thickness and gradient exponential parameter "m" that controls the variation of foam density. The results obtained from the optimizations indicated that functionally graded foam material, with graded density, is a suitable candidate for enhancing the crashworthiness characteristics of the structure compared to uniform density foam. © 2014 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Central European Journal of Engineering (18961541) 2(4)pp. 562-577
Aircraft occupant crash-safety considerations require a minimum cushion thickness to limit the relative vertical motion of the seat-pelvis during high vertical impact loadings in crash landings or accidents. In military aircraft and helicopter seat design, due to the potential for high vertical accelerations in crash scenarios, the seat system must be provided with an energy absorber to attenuate the acceleration level sustained by the occupants. Because of the limited stroke available for the seat structure, the design of the energy absorber becomes a trade-off problem between minimizing the stroke and maximizing the energy absorption. The available stroke must be used to prevent bottoming out of the seat as well as to absorb maximum impact energy to protect the occupant. In this study, the energy-absorbing system in a rotorcraft seat design is investigated using a mathematical model of the occupant/seat system. Impact theories between interconnected bodies in multibody mechanical systems are utilized to study the impact between the seat pan and the occupant. Experimental responses of the seat system and the occupant are utilized to validate the results from this study for civil and military helicopters according to FAR 23 and 25 and MIL-S-58095 requirements. A model for the load limiter is proposed to minimize the lumbar load for the occupant by minimizing the relative velocity between the seat pan and the occupant's pelvis. The modified energy absorber/load limiter is then implemented for the seat structure so that it absorbs the energy of impact in an effective manner and below the tolerable limit for the occupant in a minimum stroke. Results show that for a designed stroke, the level of occupant lumbar spine injury would be significantly attenuated using this modified energy-absorber system. © Versita sp. z o.o.
Steel Research International (16113683) pp. 39-42
The final hot strip profile is a superposition of the roll initial crown, the roll bending and flattening crown, the roll wearing crown and the roll thermal crown. In this research, linear regression models were proposed to predict the roll wearing crown and the roll thermal crown utilizing experimental data provided by Mobarake Steel Complex. The ABAQUS 6.9 software based on finite element method was also used to simulate the rolling process and to predict the roll force and the roll bending and flattening crown. This simulation was confirmed comparing the obtained roll force with the measured one. The borrowed initial crowns for seven stands of an actual roll schedule for hot strip mill of Mobarake Steel Complex were then used and the strip profile was measured. The predicted strip profile showed a good agreement with the measured one for the mentioned mill. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
In this study the effect of earth reflective coefficient on the maximum solar radiation reached to a solar collector surface was investigated by the mathematical KT and Hay models. The results showed that the maximum total radiation on the collector inclined at optimum angles increases due to increasing the earth reflective coefficient. The results also showed that neglecting the earth reflection decreases the maximum solar radiation on the collector. © 2011 Amirkabir Univ of Tech.
Energy Sources, Part A: Recovery, Utilization and Environmental Effects (15567230) 33(24)pp. 2319-2319
Journal of Mechanical Science and Technology (1738494X) 25(7)pp. 1675-1685
Impact is very common source of noise in the industries. The impacts can be visible, such as forging, and can be invisible, such as impacts due to clearance of hinges. As a result of this generality, the control of impact noise needs more attention. Reduction of this tiresome noise needs enough perception about the impact. A study of this noise sources presents difficult problems both theoretically and experimentally. This is partly due to the many complex interconnected mechanical phenomena that occur and partly due to the fact that usual steady-state techniques of analysis cannot be applied. In such complex problems numerical techniques can help to acousticians. To gain some insight into this source of sound, in this paper collision of two steel spheres are studied with finite element method (FEM). Then the FEM results were compared with experiments to show authority of this numerical method to simulate impact noises. FEM results show that if the vibrational modes are excited by impact, the vibrational modes can be as effective as rigid body motion. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Salvatipour h.s., ,
Abdolzadeh m., ,
Beheshti, H. ,
Rahnama m., Energy Sources, Part A: Recovery, Utilization and Environmental Effects (15567230) 33(17)pp. 1625-1635
In this study, a mathematical model was used for estimating the total (global) solar radiation on an inclined surface faced to the south, and to determine the optimum slope angle for the solar collectors in Isfahan (central part of Iran) based on experimental data for a horizontal surface. The monthly, seasonal, and yearly optimum slope angles were found. Effect of earth reflection on the maximum total solar radiation was investigated. The results showed that neglecting the earth reflection decreases the optimum slope angle. The results also indicated that changing the monthly, seasonal, and yearly optimum slope angles causes to achieve a significant yearly gain in the solar radiation for the region under investigation. Copyright © Taylor & Francis Group, LLC.
Energy Sources, Part A: Recovery, Utilization and Environmental Effects (15567230) 33(13)pp. 1281-1290
In the present article, the optimum tilt and azimuth angles have been calculated utilizing non-isotropic Klein and Hay methods in Isfahan. This is to obtain the maximum monthly total solar energy during a year. In the first part, the optimum tilt angle of the panel with zero azimuth angle is obtained using the isotropic Liu model. The results showed that the yearly optimum slope angle is near the latitude angle of the region. Comparison between the total solar energy of a tilted panel at an optimum angle and a horizontal panel show that the tilted panel receives significantly more energy during the year. In the second part, the effects of an azimuth angle are considered using non-isotropic models. The results also show that the panel of optimum tilt and azimuth angles receives higher solar energy compared with the fixed panel. Finally, the results depict that the effect of setting the panel at the optimum angles is more significant in summer and winter compared to other seasons. Copyright © Taylor & Francis Group, LLC.
Journal of Mechanical Science and Technology (1738494X) 24(5)pp. 1105-1110
This paper obtains a Mathematical Dynamic Model (MADYMO) for occupant lumbar load evaluation under CFR Part 23 and 25 at extreme ranges of temperature. The validation of results is performed by full scale sled test results. Aircraft industries are using viscoelastic polyurethane foams as seat cushion. Visco-elastic foams bring not only more comfort to the passengers in long term sitting but it also maintains more safety during unpredicted crashes and hard landings. Aircraft seat cushions are exposed to varying temperature ranges during their life time. This fact has motivated aircraft industries to evaluate the seat cushion dynamic behavior at extreme ranges of temperatures in addition to what is mentioned in Federal Aviation Administration (FAA) Regulations at room temperature. This research provides a methodology based on simulation and modeling to eliminate, or at least, minimize the number of full scale dynamic sled tests defined by regulations for aircraft seats at extreme ranges of temperature. © 2010 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering (03321649) 29(3)pp. 667-685
Purpose - The purpose of this paper is to present a 3D finite element model of the electromagnetic fields in an AC three-phase electric arc furnace (EAF). The model includes the electrodes, arcs, and molten bath. Design/methodology/ approach - The electromagnetic field in terms of time in AC arc is also modeled, utilizing a 3D finite element method (3D FEM). The arc is supposed to be an electro-thermal unit with electrical power as input and thermal power as output. The average Joule power, calculated during the transient electromagnetic analysis of the AC arc furnace, can be used as a thermal source for the thermal analysis of the inner part of furnace. Then, by attention to different mechanisms of heat transfer in the furnace (convection and radiation from arc to bath, radiation from arc to the inner part of furnace and radiation from the bath to the sidewall and roof panel of the furnace), the temperature distribution in different parts of the furnace is calculated. The thermal model consists of the roof and sidewall panels, electrodes, bath, refractory, and arc. The thermal problem is solved in the steady state for the furnace without slag and with different depths of slag. Findings - Current density, voltage and magnetic field intensity in the arcs, molten bath and electrodes are predicted as a result of applying the three-phaseACvoltages to theEAF. The temperature distribution in different parts of the furnace is also evaluated as a result of the electromagnetic field analysis. Research limitations/implications - This paper considers an ideal condition for the AC arc. Non-linearity of the arc during the melting, which leads to power quality disturbances, is not considered. In most prior researches on the electrical arc furnace, a non-linear circuit model is usually used for calculation of power quality phenomena distributions. In this paper, the FEM is used instead of non-linear circuits, and calculated voltage and current densities in the linear arc model. The FEM results directly depend on the physical properties considered for the arc. Originality/value - Steady-state arc shapes, based on the Bowman model, are used to calculate and evaluate the geometry of the arc in a real and practical three-phase AC arc furnace. A new approach to modeling AC arcs is developed, assuming that the instantaneous geometry of the AC arc at any time is constant and is similar to the geometry of a DC arc with the root mean square value of the current waveform of the AC arc. A time-stepping 3D FEM is utilized to calculate the electromagnetic field in the AC arc as a function of time. © Emerald Group Publishing Limited.
AC electric arc furnaces (EAFs) highly reduce power quality of the network by generating disturbances such as flicker and harmonics. These disturbances are due to the nonlinear electromagnetic and thermal field behaviors of the AC arcs. Analysis of these nonlinear behaviors is required for improving power quality in the network. This paper presents a three-dimensional finite element modeling of the electromagnetic fields in an AC three-phase electric arc furnace. The model includes the electrodes, arcs and molten bath. Current density, voltage and magnetic field intensity in the arcs, molten bath and electrodes are predicted as a result of applying the three-phase AC voltages to the EAF. This model does not consider the instantaneous geometry of the arc, instead a constant geometry, which is adjacent to the geometry of a DC arc with a DC current equal to the RMS value of the current waveform, is considered. Electromagnetic field of the AC arc in the time-domain is also modeled using the three-dimensional finite element method. ©2009 IEEE.
Occupant lumbar load under CFR Part 23 and 25 is being obtained by using different methodologies including hybrid dynamic modeling and MADYMO analysis. The output of these methods is validated with full scale sled tests results. A crashworthy structure is designed such that in the event of crash, it absorbs impact energy in a controlled manner. The main subsystems of an aircraft involved in crashworthiness are seat cushion, which is part of seat structure, restraints, fuselage and landing gear. Polyurethane foams are being used as acoustic purposes, as padding in the finished interior panels of the aircraft, and seat cushions. Their main application is mostly in seating purposes to provide comfort for occupant. All the seat cushions have to pass Federal Aviation Administration (FAA) Regulations before being installed on the seats. These regulations require a dynamic sled test of the entire seat system for certifying the seat cushions. This traditional dynamic testing is also required for replacing the deteriorated cushions with new buildup cushions which is time consuming and costly. This research provides methodologies based on simulation and modeling to eliminate, or at least, minimize the number of full scale dynamic sled tests defined by regulations for aircraft seats.
International Journal of Crashworthiness (15738965) 11(1)pp. 27-35
The main subsystems of an aircraft involved in crashworthiness are the seat cushion, which is part of the seat structure, as well as the restraints, fuselage, and landing gear. A crashworthy structure is designed so that in the event of a crash, it will absorb impact energy in a controlled manner. All energy absorption materials such as honeycombs, polyurethane foams, polymer foams, metallic foams, etc. are being used in aircraft structures, to ensure a safe and survivable trip for passengers, and even in packaging applications for sensitive instruments, equipment, and computers. Polyurethane foams are being used for acoustic purposes, as padding in the finished interior panels of the aircraft, and seat cushions, but they are primarily used in seating applications. The fact that a direct interaction exists between the occupant's body and the seat cushion means that the seat cushion must be ergonomically comfortable in addition to providing safety for passengers. All seat cushions must pass Federal Aviation Administration regulations prior to installation. These regulations require a dynamic sled test of the entire seat system in order to certify it. This traditional testing is also required for replacing old, deteriorated cushions with new buildup cushions, which is time-consuming and costly. Much effort has been taken to obtain reliable modeling in terms of substituting dynamic full-scale sled testing with a cheaper and simpler method of certification. The Advanced General Aviation Transportation Experiments (AGATE) group has proposed a methodology using quasi-static testing instead of full-scale sled testing. In this study, AGATE methodology was validated with experimental results from full-scale sled testing and quasi-static testing. Rate sensitivity of foams was investigated and a criterion using stress-relaxation testing techniques is proposed. This paper addresses full-scale sled testing and quasi-static testing of aircraft seat cushions. This investigation recommends that full-scale sled testing used for seat cushion certification be replaced with quasi-static testing. © Woodhead Publishing Ltd.
Seat cushion is in the primary load path between the seat and the occupant, and the potential for injuries to an occupant in an accident highly depends on it. The seat cushion is able to dissipate the kinetic energy due to impact in a controlled manner. Wide varieties of energy absorbing materials are used in aircraft interiors for occupant safety and ergonomic purposes. Flexible polyurethane foams are one among those used in seat cushions. Although comfort and aesthetics play an important role in the seat cushion design, safety is among the top criteria. Studies on seat cushions have demonstrated that the seat cushions generally amplify the lumbar/pelvis transmitted load to the occupant, making the seat cushion design further complicated for crashworthy design. The certification of seat cushion requires that their performance be demonstrated by dynamic full scale sled testing. Due to the high costs involved in dynamic testing, a mathematical hybrid multi-body model is developed in this study to simulate the dynamic responses of a bare iron seat, the seat cushion and the occupant represented by crash test dummy. The model is utilized to predict the lumbar load sustained when subjected to the FAR Part 23 and 25 dynamic test conditions for transport and general aviation category aircraft. The model is also used to determine the relative displacement and velocity of occupant against the seat pan. The results from the dynamic model are validated with full-scale sled tests performed at the National Institute for Aviation Research (NIAR), and hence can be utilized as a design tool for the selection of proper seat cushions. Copyright © 2005 by ASME.
Alshaer b.j., ,
Nagarajan h., ,
Beheshti, H. ,
Lankarani, H.M. ,
Shivaswamy s., Journal of Mechanical Design (10500472) 127(3)pp. 493-498
Clearances exist in kinds of joints in multibody mechanical systems, which could drastically affect the dynamic behavior of the system. If the joint is dry with no lubricant, impact occurs, resulting in wear and tear of the joint. In practical engineering design of machine, joints are usually designed to operate with some lubricant. Lubricated journal bearings are designed so that even when the maximum load is applied, the joint surfaces do not come into contact with each other. In this paper, a general methodology for modeling lubricated long journal bearings in multibody mechanical systems is presented. This modeling utilizes a method of solving for the forces produced by the lubricant in a dynamically loaded long journal bearing. A perfect revolute joint in a multibody mechanical system imposes kinematic constraints, while a lubricated journal bearing joint imposes force constraints. As an application, the dynamic response of a slider-crank mechanism including a lubricated journal bearing joint between the connecting rod and the slider is considered and analyzed. The dynamic response is obtained by numerically solving the constraint equations and the forces produced by the lubricant simultaneously with the differential equations of motion and a set of initial conditions numerically. The results are compared with the previous studies performed on the same mechanism as well a dry clearance joint. It is shown that in a multibody mechanical system, the journal bearing lubricant introduces damping and stiffness to the system. The earlier studies predict that the order of magnitude of the reaction moment is twice that of a perfect revolute joint. The proposed model predicts that the reaction moment is within the same order of magnitude of the perfect joint simulation case. Copyright © 2005 by ASME.
