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Full-Text Articles in Engineering
An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich
An Experimental Investigation Of Residual Stress Development During Selective Laser Melting Of Ti-6al-4v, Nathan Charles Levkulich
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Selective laser melting (SLM) is an additive manufacturing (AM) process that gives rise to large thermal gradients and rapid cooling rates that lead to the development of undesirable residual stress and distortion. In this work, a number of different techniques (i.e., x-ray-diffraction, hole-drilling, layer-removal, and contour) were utilized to establish the effect of process parameters on residual stress development during SLM of Ti-6Al-4V. The measurements indicated that higher laser power, slower scan speed, smaller stripe width, reduced substrate overhang, and reduced build plan area each reduce the level of residual stress. In addition, the correlation between microstructure, crystallographic texture, and …
Low Velocity Impact And Rf Response Of 3d Printed Heterogeneous Structures, Sandeep Keerthi
Low Velocity Impact And Rf Response Of 3d Printed Heterogeneous Structures, Sandeep Keerthi
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Three-dimensional (3D) printing, a form of Additive manufacturing (AM), is currently being explored to design materials or structures with required Electro-Mechanical-Physical properties. Microstrip patch antennas with a tunable radio-frequency (RF) response are a great candidate for 3D printing process. Due to the nature of extrusion based layered fabrication; the processed parts are of three-layer construction having inherent heterogeneity that affects structural and functional response. The purpose of this study is to identify the relationship between the anisotropy in dielectric properties of AM fabricated acrylonitrile butadiene styrene (ABS) substrates in the RF domain and resonant frequencies of associated patch antennas and …
Synthesis And Characterizations Of Lithium Aluminum Titanium Phosphate (Li1+Xalxti2-X(Po4)3) Solid Electrolytes For All-Solid-State Li-Ion Batteries, Jianping Yang
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New-generation low-emission transportation systems demand high-performance lithium ion (Li-ion) batteries with high safety insurance at broad operable temperatures. Highly conductive solid electrolyte is one of the key components for such applications. The objective of this thesis is to synthesize and characterize aluminum doped lithium titanium phosphate, i.e. Li1+xAlxTi2-x(PO4)3 (LATP), one of the solid-state electrolytes for potential applications to all solid-state lithium-ion batteries. In this research, sol-gel method and one step solid-state reaction approaches were explored and critical processes were optimized towards maximizing lithium ion conductivities at room temperature. The impacts of the processing conditions on the structures, morphologies, compositions of …
Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali
Friction Stir Welding Between Similar And Dissimilar Materials, Khaled Yousif Ali
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This thesis focuses on the friction stir welding (FSW) between similar and dissimilar alloys. FSW is a solid state joining process that welds the work-pieces through a combination of heat generated by friction and mechanical stirring of the metals in the region of the joint. Being a solid state process, FSW can be used to weld alloys with significantly different melting points. This provides a significant benefit over traditional fusion welding process in a variety of applications in automotive, biomedical, aerospace, nuclear and petroleum industries. Two materials - an aluminum alloy (6061-T6, m.p. 582 - 652°C) and a steel (SAE …
Modeling Two Phase Flow Heat Exchangers For Next Generation Aircraft, Hayder Hasan Jaafar Al-Sarraf
Modeling Two Phase Flow Heat Exchangers For Next Generation Aircraft, Hayder Hasan Jaafar Al-Sarraf
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Two-phase heat exchangers offer the potential of significant energy transfer by taking advantage of the latent heat of vaporization as the working fluid changes phase. Unfortunately, the flow physics of the phase change process is very complex and there are significant gaps in the fundamental knowledge of how several key parameters are affected by the phase change process. Therefore, an initial investigation modeling a two-phase flow heat exchanger has been accomplished. Many key assumptions have been defined which are critical to modeling two-phase flows. This research lays an initial foundation on which further investigations can build upon. Two-phase heat exchangers …
Studies Of Ionic Liquid Hybrids: Characteristics And Their Potential Application To Li-Ion Batteries And Li-Ion Capacitors, Mengxin Liu
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Ionic liquids (ILs) have attracted much attention in electrochemical energy storage systems for their advantageous properties over traditional lithium salt/carbonate solvent electrolyte in terms of higher electrochemical potential windows, comparable ionic conductivity, negative vapor pressure and non-flammability. Ionic liquids can be used as the solvent-free electrolyte in electrochemical double layer capacitors (EDLCs) or can act as the important additives to the carbonate electrolyte in lithium ion batteries (LIBs). Recently, lithium ion capacitors (LICs) have emerge as a novel energy storage system to satisfy the demands for higher energy density and higher power density in portable and transportation systems. This Master …
Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi
Processing Of Ultra-Thin Film Of Un Modified C60 Fullerene Using The Langmuir-Blodgett Technique. Effect Of Structure On Stiffness And Optoelectric Properties, Hasanain Basim Altalebi
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Monolayer films of C60 fullerene were for the first time produced successfully by using the Langmuir-Blodgett technique. The processing parameters were optimized and the structure of these films has been investigated using Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM). Film stiffness was measured to be in the range of 15 MPa to 32 MPa depending on the nature of the solvent used to process the films. Optical transparency and electrical performance have been measured and correlated to the film structure. While 100% transparent, the film measured conductivity was in the range of 1013 S/m, that is orders of …
Ab Initio Study Of The Effects Of Humidity On Perovskite Based Hybrid Solar Cell Interfaces, Shantanu Rajendra Rachalwar
Ab Initio Study Of The Effects Of Humidity On Perovskite Based Hybrid Solar Cell Interfaces, Shantanu Rajendra Rachalwar
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Despite the impressive success of perovskite-based hybrid solar cells, their widespread usage has been limited partially owing to stability issues under working environmental conditions. Among these, the effects of humidity are some of the most significant. Water intercalation generally degrades the material, shortens its useful life, and reduces the efficiency of photovoltaic energy conversion. Understanding the reasons for these effects can be achieved through detailed and accurate atomic-scale analysis. Here, we study water intercalation at the interfaces of perovskite-based hybrid solar cell material and TiO2 electrode. Accurate ab initio computer simulations are used to obtain structural and electronic properties. We …
Development Of Computer Program For Wind Resource Assessment, Rotor Design And Rotor Performance, Valentina Jami
Development Of Computer Program For Wind Resource Assessment, Rotor Design And Rotor Performance, Valentina Jami
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People understand and have seen that renewable energy has many advantages over conventional energy sources. Because of these advantages, more and more emphasis has been given to generating electrical energy with renewable sources. Among the many renewable and conventional ways currently available for a society to generate electrical power, wind turbines are one of the cheapest ways of doing this. The main objective of this thesis work is to develop a computer program that assesses the wind resource at a given location, designs a wind turbine rotor for optimum power capture for one wind speed, and analyzes the performance of …
Development Of Guidance Laws For A Reduced Order Dynamic Aircraft Model, Jack W. Brendlinger
Development Of Guidance Laws For A Reduced Order Dynamic Aircraft Model, Jack W. Brendlinger
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A set of guidance control laws has been developed for enabling three distinct modes of operation of a reduced order dynamic aircraft model. These include 1) a waypoint following control law, 2) a trajectory tracking control law, and 3) a set of kinematically constrained control laws for reaching a commanded altitude, speed or heading. The formulation of the reduced order model is presented so that the capabilities and limitations of the model are understood, and so that the interface architecture between the controllers and the plant is clearly defined. The controller formulations are then presented, together with sample results. The …
An Automated Controller Design Methodology For Six Degree-Of-Freedom Aircraft Models, Dominic J. Dierker
An Automated Controller Design Methodology For Six Degree-Of-Freedom Aircraft Models, Dominic J. Dierker
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This thesis presents an automated design methodology for development of six degree-of-freedom aircraft controllers. The essential functions required of the controller design are 1) to provide sufficient inner loop compensation to guarantee dynamic stability and acceptable handling qualities over the full flight envelope, and, 2) to enable automated mission following capabilities through implementation of outer loop trackers. A hierarchical control architecture consisting of nested nonlinear dynamic inversion control loops is proposed as a means of achieving these top level objectives. Gain tuning based on an automated linearization methodology is then suggested. Next, an automated optimal control allocation algorithm is tested …
Configuration And Electronic Properties Of The Interface Between Lead Iodide Hybrid Perovskite And Self-Assembled Monolayers In Solar Cells, Parin Divya Amlani
Configuration And Electronic Properties Of The Interface Between Lead Iodide Hybrid Perovskite And Self-Assembled Monolayers In Solar Cells, Parin Divya Amlani
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Hybrid perovskite photovoltaic materials are currently the most promising functional materials for solar cell applications with efficiency reaching to those of more conventional materials such as silicon. Using self-assembled monolayers between photovoltaic materials and electrodes is a method for improving the stability and functionality. Recent experiments have shown that using 4-mercaptobenzoic acid and pentafluorobenzenethiol monolayers bridging lead iodide hybrid perovskite photovoltaic materials and electrodes result in improved stability and efficiency. The details of monolayer assembly, molecular adsorption configuration, and resulting modification of electronic properties are important characteristics related to solar cell performance. These characteristics can be obtained through accurate computer …
Computational Modeling Of A Williams Cross Flow Turbine, Sajjan Pokhrel
Computational Modeling Of A Williams Cross Flow Turbine, Sajjan Pokhrel
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Hydropower is not only the most used renewable energy source in the United States, but in the world. While it is well known that large hydropower facilities, like the Hoover Dam, provide large amounts of electrical power, there is also a tremendous opportunity for hydroelectric power generation from small scale facilities that has largely been overlooked. The work being presented here studies a new cross flow turbine called the Williams Cross Flow Turbine (WCFT), which was designed to extract electric energy from low head, run-of-the-river, small hydropower sites. To spur the implementation of the WCFT in small hydropower applications, and …
Analysis And Sensitivity Study Of Zero-Dimensional Modeling Of Human Blood Circulation Network, Roussel Rahman
Analysis And Sensitivity Study Of Zero-Dimensional Modeling Of Human Blood Circulation Network, Roussel Rahman
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The systemic circulation has a large number of vessels; therefore, 3-D simulation of pulse-wave propagation in the entire cardiovascular system is difficult and computationally expensive. Zero-Dimensional (Zero-D) and One-Dimensional (1-D) models are simplified representations of the cardiovascular network; they can be coupled as supplements to regional 3-D models for closed-loop multi-scale studies or be simulated as self-sufficient representations of the blood-flow network. Unlike Zero-D models, 1-D models can provide linear space-wise information for the vessels. However, Zero-D models can prove to be more useful in particular cases; as flexibility in adjusting parameters facilitate in tailoring the model to specific needs. …
Design And Testing Of Scalable 3d-Printed Cellular Structures Optimized For Energy Absorption, Sagar Dilip Sangle
Design And Testing Of Scalable 3d-Printed Cellular Structures Optimized For Energy Absorption, Sagar Dilip Sangle
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Sandwich panel structures are widely used due to their high compressive and flexural stiffness and strength-to-weight ratios, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures that are often based upon honeycomb topologies. Interest in additive manufacturing (AM), popularly known as 3D printing (3DP), has rapidly grown in past few years. The 3DP method is a layer-by-layer approach for the fabrication of 3D objects. Hence, it is very easy to fabricate complex structures with complex internal features that cannot be manufactured by any other fabrication processes. Due to the …
An Investigation On The Stress Intensity Factor Of Surface Micro-Cracks, Sirisha Divya Arli
An Investigation On The Stress Intensity Factor Of Surface Micro-Cracks, Sirisha Divya Arli
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The contact fatigue failure in the form of micro or macro-scale pitting is an important failure mode for rolling mechanical elements, such as bearings and gears that are widely used in the automotive, aerospace and wind turbine fields. The micro-pitting process in some cases, gradually removes the surface material through fatigue wear, altering the geometry of the contact surfaces to alleviate the contact pressure decelerating the continued pitting rate. The propagation of the micro-cracks in other cases, goes deep into the material along a shallow angle, turns parallel to the surface at a certain depth, where the maximum shear or …
One Dimensional Computer Modeling Of A Lithium-Ion Battery, Ashwin S. Borakhadikar
One Dimensional Computer Modeling Of A Lithium-Ion Battery, Ashwin S. Borakhadikar
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Renewable energy storage is vitally important to many applications for which batteries are the finest choice. As energy storage technology may be applied to a number of areas that differ in power and energy requirements, modeling of battery performance is required. In recent years, a lot of research has been done in this area but, the earliest model was designed by Marc Doyle, T. F. Fuller, and J. Newman in 1993. This work involves the development of a one-dimensional computer model of a lithium-ion battery which consists of three domains: the negative electrode, the separator, and the positive electrode. The …
Structure Stability And Optical Response Of Lead Halide Hybrid Perovskite Photovoltaic Materials: A First-Principles Simulation Study, Siddharth Narendrakumar Rathod
Structure Stability And Optical Response Of Lead Halide Hybrid Perovskite Photovoltaic Materials: A First-Principles Simulation Study, Siddharth Narendrakumar Rathod
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A third-generation of solar cell is based on organic-inorganic hybrid perovskite materials. These have reached up to 22.1% conversion efficiency through exponential growth just within the last decade, compared to much longer improvement times for other photovoltaic technologies. Lead halide perovskites are among the most commonly used materials in this context. Despite the relatively large number of available works on some of these materials, in particular CH3NH3PbI3, others are less investigated. Here, we focused on CH3NH3PbCl3, CH3NH3PbBr3 and CH3NH3PbI3 for assessing structure stability and optical response. Using quantum-mechanics-based first principles approaches, we calculated the optimized structures of these three materials …
3d Cfd Investigation Of Low Pressure Turbine Aerodynamics, Jacob Andrew Sharpe
3d Cfd Investigation Of Low Pressure Turbine Aerodynamics, Jacob Andrew Sharpe
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A 3-D Reynolds-Averaged Navier Stokes (RANS) model of a highly-loaded blade profile has been developed using a commercial CFD code with an unstructured/structured grid and several different turbulence models. The ability of each model to predict total pressure loss performance is examined in terms of the spanwise loss distribution and the integrated total pressure loss coefficient. The flowfield predicted by each model is investigated through comparisons of isosurfaces of Q criterion to previous Implicit Large Eddy Simulation (ILES) results. The 3-equation k-kl-¿ model was shown to provide the most accurate performance predictions for a baseline 3-D LPT geometry, and was …
Turboelectric Distributed Propulsion System For Nasa Next Generation Aircraft, Hashim H. Abada
Turboelectric Distributed Propulsion System For Nasa Next Generation Aircraft, Hashim H. Abada
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Next generation aircraft, more specifically NASA aircraft concepts, will include new technologies and make many advancements in fuel economy and noise. However, there are some challenges associated with the latest technologies that NASA is planning to use for the next generation aircraft. For example, these aircraft concepts require large amounts of electrical power to generate the required thrust throughout a notional flight profile. One of the new technologies is using advanced propulsion systems, such as the Turboelectric Distributed Propulsion (TeDP) system, which is significantly different from current aerospace high bypass turbofan based propulsion system. The TeDP propulsion system replaces the …
A Look At The Optimum Slope Of A Fixed Solar Panel For Maximum Energy Collection For A One Year Time Frame, Salah Alhaidari
A Look At The Optimum Slope Of A Fixed Solar Panel For Maximum Energy Collection For A One Year Time Frame, Salah Alhaidari
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A rule-of-thumb for orientating fixed solar panels for optimum yearly collection of solar radiation that is not influenced by atmospheric effects is to face the panel due south in the Northern Hemisphere or due north in the Southern Hemisphere and to tilt the panel from the horizontal plane at an angle equal to the latitude of the location of the solar panel. The work presented in this thesis shows that this rule-of-thumb is an approximation for no-atmosphere, panel orientation; but not a precise value. This project presents a detailed method for determining the precise optimum tilt angle of a fixed …
Electrical Power And Storage For Nasa Next Generation Aircraft, Saif Al-Agele
Electrical Power And Storage For Nasa Next Generation Aircraft, Saif Al-Agele
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Next generation aircraft will incorporate more electrical power generation and storage for both a distributed electric propulsion system and onboard subsystems. The power generation in this type of aircraft will require orders of magnitude higher than today’s commercial aircrafts, thus producing many challenges. For this reason, a unique, high-powered electric propulsion system primarily powered by a turbo-generator system with electrical storage is being considered. A Simulink/Matlab model has bee created for the electrical power system of the next generation blended wing commercial aircraft proposed by NASA. The components of the electrical system include turbo-generators, generators, battery banks, and electrical distribution …
Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins
Investigation Of Residual Stresses In Melt Infiltrated Sic/Sic Ceramic Matrix Composites Using Raman Spectroscopy, Kaitlin Noelle Kollins
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Ceramic matric composites (CMCs) are being developed for use in extreme operating conditions. Specifically, there is interest to replace superalloys with Silicon Carbide/Silicon Carbide (SiC/SiC) CMCs in the hot section of gas turbine engines because of their lower densities, high temperature performance, and oxidation resistance. Residual stresses in SiC/SiC CMCs are a direct result of the high temperature processing conditions, a mismatch in the coefficients of thermal expansion between composite constituents, and silicon crystallization expansion upon cooldown. Understanding the residual stress state and magnitudes of these stresses will enable better prediction of behavior and life performance in application environments. This …
Low-Velocity Impact Behavior Of Sandwich Panels With 3d Printed Polymer Core Structures, Andrew Joseph Turner
Low-Velocity Impact Behavior Of Sandwich Panels With 3d Printed Polymer Core Structures, Andrew Joseph Turner
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Sandwich panel structures are widely used in aerospace, marine, and automotive applications because of their high flexural stiffness, strength-to-weight ratio, good vibration damping, and low through-thickness thermal conductivity. These structures consist of solid face sheets and low-density cellular core structures, which are often based upon honeycomb topologies. The recent progress of additive manufacturing (AM) (popularly known as 3D printing) processes has allowed lattice configurations to be designed with improved thermal-mechanical properties. The aim of this work is to design and print lattice truss structures (LTS) keeping in mind the flexible nature of AM. Several 3D printed core structures were created …
Mathematical Modeling Of A P-N Junction Solar Cell Using The Transport Equations, Surjeet Singh
Mathematical Modeling Of A P-N Junction Solar Cell Using The Transport Equations, Surjeet Singh
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While analytical models are limited in the situations that they can simulate, they are generally easier to implement than numerical models and provide a rapid view of the variables which affect a certain quantity. Analytical models are also very useful in educational situations; such as a graduate class on photovoltaics. The modeling of the interior workings of a solar cell can be complex and involved; and some of the equations can become quite lengthy. A focus of this thesis work is the derivation of the minority carrier density and minority current density equations for a p-n junction solar cell. The …
Dynamic Modeling And Simulation Of A Variable Cycle Turbofan Engine With Controls, Robert W. Buettner
Dynamic Modeling And Simulation Of A Variable Cycle Turbofan Engine With Controls, Robert W. Buettner
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Next generation aircraft (especially combat aircraft) will include more technology and capability than ever before. This increase in technology comes at the price of higher electrical power requirements and increased waste heat that must be removed from components to avoid overheating induced shutdowns. To help combat the resulting power and thermal management problem, a vehicle level power and thermal management design and optimization toolset was developed in MATLAB®/Simulink®. A dynamic model of a three-stream variable cycle engine was desired to add to the capabilities of the power and thermal management toolset. As an intermediate step to this goal, the dynamic …
Resilience And Toughness Behavior Of 3d-Printed Polymer Lattice Structures: Testing And Modeling, Mohammed Al Rifaie
Resilience And Toughness Behavior Of 3d-Printed Polymer Lattice Structures: Testing And Modeling, Mohammed Al Rifaie
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This research focuses on the energy absorption capability of additively manufactured or 3D printed polymer lattice structures of different configurations. The Body Centered Cubic (BCC) lattice structure is currently being investigated by researchers for energy absorption applications. For this thesis, the BCC structure is modified by adding vertical bars in different arrangements to create three additional configurations. Four designs or sets of the lattice structure are selected for comparison including BCC, BCC with vertical bars added to all nodes (BCCV), BCC with vertical bars added to alternate nodes (BCCA), and BCC with gradient arrangements of vertical bars (BCCG). Both experimental …
A Numerical And Experimental Investigation Of Steady-State And Transient Melt Pool Dimensions In Additive Manufacturing Of Invar 36, Chigozie Nwachukwu Obidigbo
A Numerical And Experimental Investigation Of Steady-State And Transient Melt Pool Dimensions In Additive Manufacturing Of Invar 36, Chigozie Nwachukwu Obidigbo
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The use of additive manufacturing (AM) in tooling enables low production components to be fabricated with lower costs, reduced waste, increased design flexibility and reduced lead time. Invar 36 is a popular metal tooling material known for its low coefficient of thermal expansion. This work uses thermal finite element (FE) modeling as a tool to determine the feasibility of using Invar 36 in AM and to investigate the transient effect from common scanning strategies. Results show that the steady-state melt pool dimensions behave similar to traditional AM materials for varying process parameters. Transient results show that the melt pool response …
Dynamic Modeling Of Thermal Management System With Exergy Based Optimization, Marcus J. Bracey
Dynamic Modeling Of Thermal Management System With Exergy Based Optimization, Marcus J. Bracey
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System optimization and design of aircraft is required to achieve many of the long term objectives for future aircraft platforms. To address the necessity for system optimization a vehicle-level aircraft model has been developed in a multidisciplinary modeling and simulation environment. Individual subsystem models developed exclusively in MATLAB-SimulinkTM, representing the vehicle dynamics, the propulsion, electrical power, and thermal systems, and their associated controllers, are combined to investigate the energy and thermal management issues of tactical air vehicle platforms. A thermal vehicle level tip-to-tail model allows conceptual design trade studies of various subsystems and can quantify performance gains across the aircraft. …