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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Advanced High-Temperature Engine Materials Technology Progresses

The objective of the Advanced High Temperature Engine Materials Technology Program (HITEMP) is to generate technology for advanced materials and structural analysis that will increase fuel economy, improve reliability, extend life, and reduce operating costs for 21st century civil propulsion systems. The primary focus is on fan and compressor materials (polymer-matrix composites--PMC's), compressor and turbine materials (superalloys, and metal-matrix and intermetallic-matrix composites--MMC's and IMC's) and turbine materials (ceramic-matrix composites--CMC's). These advanced materials are being developed by in-house researchers and on grants and contracts. NASA considers this program to be a focused materials and structures research effort that builds on our base research programs and supports component-development projects. HITEMP is coordinated with the Advanced Subsonic Technology (AST) Program and the Department of Defense/NASA Integrated High-Performance Turbine Engine Technology (IHPTET) Program. Advanced materials and structures technologies from HITEMP may be used in these future applications. Recent technical accomplishments have not only improved the state-of-the-art but have wideranging applications to industry. A high-temperature thin-film strain gage was developed to measure both dynamic and static strain up to 1100 C (2000 F). The gage's unique feature is that it is minimally intrusive. This technology, which received a 1995 R&D 100 Award, has been transferred to AlliedSignal Engines, General Electric Company, and Ford Motor Company. Analytical models developed at the NASA Lewis Research Center were used to study Textron Specialty Materials' manufacturing process for titanium-matrix composite rings. Implementation of our recommendations on tooling and processing conditions resulted in the production of defect free rings. In the Lincoln Composites/AlliedSignal/Lewis cooperative program, a composite compressor case is being manufactured with a Lewis-developed matrix, VCAP. The compressor case, which will reduce weight by 30 percent and costs by 50 percent, is scheduled to be engine tested in the near future.

Source record↗
NASA NTRS2000

Braided Carbon Fiber Rope Flow Characteristics

I am submitting the following technical subject for consideration as a thesis topic for the master degree: The reusable solid rocket motor (RSRM) nozzle internal joints are being evaluated for the incorporation of a carbon fiber rope (CFR) as a thermal barrier. The CFR is approximately 0.260 in. diameter and is composed of approximately 12,000 carbon fibers, woven in ten sheaths or layers. The CFR is manufactured by a sub-tier vendor and subsequently several of its manufacturing details are proprietary to that vendor. The CFR design intent is to prevent hot motor combustion products and slag from intruding into the joint scaling area while still approaching a vented joint design to avoid the detriments of gas jet impingement. As a member of the Heat Transfer section at Thiokol Propulsion, two main goals exist as part of this NASA funded design effort: (1) development of flow model through the CFR and (2) development of a heat transfer model through the CFR. While both models are needed and most probably interrelated, the gas flow model is being targeted as the subject matter. Essentially, the topic would be "Modeling of Gas Flow through a Braided Carbon Fiber Rope". An AIAA journal or conference paper is being considered through Thiokol/NASA as well. A sub-scale CFR flow test fixture was designed to simulate the relative levels of CFR compression. The test fixture provides the means to measure gas mass flow rate upstream of the CFR and the pressure and temperature both upstream and downstream of the CFR. The test fixture was designed to eliminate the possibility of dynamic gapping at the CFR location and provide minimal flow resistance to ambient for gases exiting the rope. The data collected in the experiment will be evaluated to define a permeability/flow resistance model. Two possibilities exist for the flow characteristics through the CFR from choked flow to strictly friction driven. A test matrix for evaluating the CFR has been compiled, which addresses both of these characteristics. The range of pressures to be tested covers a relatively low delta pressure where non-choked flow is impossible, while the high pressure shown is dictated by the RSRM joint operating pressure where choking is possible. The test matrix, was also designed for a range of rope compressions or test fixture gaps ranging from 0.025" to 0.070". These gaps are controlled by the range of RSRM full-scale hardware joint gaps that will be expected by virtue of the joint design.

Heman, J. R. C.↗
NASA NTRS2001

Environmental Barrier Coatings for Silicon-Based Ceramics

Silicon-based ceramics, such as SiC fiber-reinforced SiC (SiC/SiC ceramic matrix composites (CMC) and monolithic silicon nitride (Si3N4), are prime candidates for hot section structural components of next generation gas turbine engines. Silicon-based ceramics, however, suffer from rapid surface recession in combustion environments due to volatilization of the silica scale via reaction with water vapor, a major product of combustion. Therefore, application of silicon-based ceramic components in the hot section of advanced gas turbine engines requires development of a reliable method to protect the ceramic from environmental attack. An external environmental barrier coating (EBC) is considered a logical approach to achieve protection and CP long-term stability. The first generation EBC consisted of two layers, mullite (3Al2O3-2SiO2) bond coat and yttria-stabilized zirconia (YSZ, ZrO2-8 Wt.% Y2O3) top coat. Second generation EBCs, with substantially improved performance compared with the first generation EBC, were developed in the NASA High Speed Research-Enabling Propulsion Materials (HSR-EPM) Program. The first generation EBC consisted of two layers, mullite (3Al2O3-2SiO2) bond coat and yttria-stabilized zirconia (YSZ, ZrO2-8 wt.% Y2O3) top coat. Second generation EBCs, with substantially improved performance compared with the first generation EBC, were developed in the NASA High Speed Research-Enabling Propulsion Materials (HSR-EPM) Program (5). They consist of three layers, a silicon first bond coat, a mullite or a mullite + BSAS (BaO(1-x)-SrO(x)-Al2O3-2SiO2) second bond coat, and a BSAS top coat. The EPM EBCs were applied on SiC/SiC CMC combustor liners in three Solar Turbines (San Diego, CA) Centaur 50s gas turbine engines. The combined operation of the three engines has accumulated over 24,000 hours without failure (approximately 1,250 C maximum combustor liner temperature), with the engine in Texaco, Bakersfield, CA, accumulating about 14,000 hours. As the commercialization of Si-based ceramic components in gas turbines is on the horizon, a major emphasis is placed on EBCs for two reasons. First, they are absolute necessity for the protection of Si-based ceramics from water vapor. Second, they can enable a major enhancement in the performance of gas turbines by creating temperature gradients with the incorporation of a low thermal conductivity layer. Thorough understanding of current state-of-the-art EBCs will provide the foundation upon which development of future EBCs will be based. Phase stability and thermal conductivity of EPM EBCs are published elsewhere. This paper will discuss the chemical/environmental durability and silica volatility of EPM EBCs and their impact on the coating's upper temperature limit.

Lee, Kang N.↗
NASA NTRS2004

Vibration Characteristics Determined for Stainless Steel Sandwich Panels With a Metal Foam Core for Lightweight Fan Blade Design

The goal of this project at the NASA Glenn Research Center is to provide fan materials that are safer, weigh less, and cost less than the currently used titanium alloy or polymer matrix composite fans. The proposed material system is a sandwich fan construction made up of thin solid face sheets and a lightweight metal foam core. The stiffness of the sandwich structure is increased by separating the two face sheets by the foam layer. The resulting structure has a high stiffness and lighter weight in comparison to the solid facesheet material alone. The face sheets carry the applied in-plane and bending loads (ref. 1). The metal foam core must resist the transverse shear and transverse normal loads, as well as keep the facings supported and working as a single unit. Metal foams have ranges of mechanical properties, such as light weight, impact resistance, and vibration suppression (ref. 2), which makes them more suitable for use in lightweight fan structures. Metal foams have been available for decades (refs. 3 and 4), but the difficulties in the original processes and high costs have prevented their widespread use. However, advances in production techniques and cost reduction have created a new interest in this class of materials (ref. 5). The material chosen for the face sheet and the metal foam for this study was the aerospace-grade stainless steel 17-4PH. This steel was chosen because of its attractive mechanical properties and the ease with which it can be made through the powder metallurgy process (ref. 6). The advantages of a metal foam core, in comparison to a typical honeycomb core, are material isotropy and the ease of forming complex geometries, such as fan blades. A section of a 17-4PH sandwich structure is shown in the following photograph. Part of process of designing any blade is to determine the natural frequencies of the particular blade shape. A designer needs to predict the resonance frequencies of a new blade design to properly identify a useful operating range. Operating a blade at or near the resonance frequencies leads to high-cycle fatigue, which ultimately limits the blade's durability and life. So the aim of this study is to determine the variation of the resonance frequencies for an idealized sandwich blade as a function of its face-sheet thickness, core thickness, and foam density. The finite element method is used to determine the natural frequencies for an idealized rectangular sandwich blade. The proven Lanczos method (ref. 7) is used in the study to extract the natural frequency.

Ghosn, Louis J.↗
NASA NTRS2012

NASA Tech Briefs, September 2012

Topics covered include: Beat-to-Beat Blood Pressure Monitor; Measurement Techniques for Clock Jitter; Lightweight, Miniature Inertial Measurement System; Optical Density Analysis of X-Rays Utilizing Calibration Tooling to Estimate Thickness of Parts; Fuel Cell/Electrochemical Cell Voltage Monitor; Anomaly Detection Techniques with Real Test Data from a Spinning Turbine Engine-Like Rotor; Measuring Air Leaks into the Vacuum Space of Large Liquid Hydrogen Tanks; Antenna Calibration and Measurement Equipment; Glass Solder Approach for Robust, Low-Loss, Fiber-to-Waveguide Coupling; Lightweight Metal Matrix Composite Segmented for Manufacturing High-Precision Mirrors; Plasma Treatment to Remove Carbon from Indium UV Filters; Telerobotics Workstation (TRWS) for Deep Space Habitats; Single-Pole Double-Throw MMIC Switches for a Microwave Radiometer; On Shaft Data Acquisition System (OSDAS); ASIC Readout Circuit Architecture for Large Geiger Photodiode Arrays; Flexible Architecture for FPGAs in Embedded Systems; Polyurea-Based Aerogel Monoliths and Composites; Resin-Impregnated Carbon Ablator: A New Ablative Material for Hyperbolic Entry Speeds; Self-Cleaning Particulate Prefilter Media; Modular, Rapid Propellant Loading System/Cryogenic Testbed; Compact, Low-Force, Low-Noise Linear Actuator; Loop Heat Pipe with Thermal Control Valve as a Variable Thermal Link; Process for Measuring Over-Center Distances; Hands-Free Transcranial Color Doppler Probe; Improving Balance Function Using Low Levels of Electrical Stimulation of the Balance Organs; Developing Physiologic Models for Emergency Medical Procedures Under Microgravity; PMA-Linked Fluorescence for Rapid Detection of Viable Bacterial Endospores; Portable Intravenous Fluid Production Device for Ground Use; Adaptation of a Filter Assembly to Assess Microbial Bioburden of Pressurant Within a Propulsion System; Multiplexed Force and Deflection Sensing Shell Membranes for Robotic Manipulators; Whispering Gallery Mode Optomechanical Resonator; Vision-Aided Autonomous Landing and Ingress of Micro Aerial Vehicles; Self-Sealing Wet Chemistry Cell for Field Analysis; General MACOS Interface for Modeling and Analysis for Controlled Optical Systems; Mars Technology Rover with Arm-Mounted Percussive Coring Tool, Microimager, and Sample-Handling Encapsulation Containerization Subsystem; Fault-Tolerant, Real-Time, Multi-Core Computer System; Water Detection Based on Object Reflections; SATPLOT for Analysis of SECCHI Heliospheric Imager Data; Plug-in Plan Tool v3.0.3.1; Frequency Correction for MIRO Chirp Transformation Spectroscopy Spectrum; Nonlinear Estimation Approach to Real-Time Georegistration from Aerial Images; Optimal Force Control of Vibro-Impact Systems for Autonomous Drilling Applications; Low-Cost Telemetry System for Small/Micro Satellites; Operator Interface and Control Software for the Reconfigurable Surface System Tri-ATHLETE; and Algorithms for Determining Physical Responses of Structures Under Load.

Source record↗
NASA NTRSDate not supplied

A New Concurrent Engineering Tool for the New Mission Design Center at NASA Ames Research Center

The NASA Ames Mission Design Center (MDC) has undergone a significant transformation process in recent years, culminating in becoming a true Concurrent Engineering Center. The underlying goal of this transformation is to better serve the Ames PI community in a cost-effective and rapidly-responsive way, providing quality products pivotal to the decision-making proposal strategy of our center. The four pillars of the change focus on four areas: personnel, physical places, tools, and training. Personnel: the MDC switched from using a dedicated pool of engineers—mostly entry-level career—for a matrixed approach with more experienced Subject Matter Experts, usually involved in spaceflight projects. These SMEs get detailed to the MDC for the duration of the study on a part-time or full-time basis. Physical places: The physical aspect pertains mostly to the layout of the new Engineering building and the dedicated concurrent engineering layout to foster collaboration. The current plan includes a dedicated space for concurrent engineering sessions as well as dedicated project rooms for concept studies. Tool: the MDC team is developing a new in-house concurrent engineering tool to facilitate concurrent engineering sessions. The team leveraged the many lessons learned and insight gained from using the current concurrent engineering tool, in use since 2007. SMEs have been involved throughout its design and development, ensuring accuracy and providing validity to the implementation approach. This new tool is database-driven and allows a team to work concurrently on the same model of a mission concept. “Workspaces” are provided for each of the traditional spacecraft mission design disciplines, including cost accounting and systems engineering. There are multiple tiers of fidelity available within each workspace, which can be completed parametrically or independently from the other disciplines as needed or synchronously with the other disciplines. A “commit” step synchronizes a workspace with the mission database and identifies any potential conflicts, along with the user who entered the conflicting data. A Mission Summary workspace enables a Study Lead to run an effective CE session, displaying key graphics, workspace status information, and technical and monetary budget information. This new CE tool will be undergoing Beta Testing with its primary user base and a limited Parts database in the summer of 2020. The team plans to release the first fully operational version in December 2020. Training: working in early concept development and maturation for a space mission requires a unique mindset and being comfortable with uncertainties in an environment where requirements are not yet fully developed, and where changes and trade-offs happen at a high tempo. The MDC started a weekly training program to ensure a common knowledge base on how do develop and mature early concept studies, as well as how to operate in a concurrent engineering environment. In conclusion, the MDC transformation will provide the overall PI community focused on cost-effective small satellite scientific missions with a powerful tool to address and mature early concepts more effectively and efficiently.

David Mauro↗
NASA NTRS2004

Inducer Hydrodynamic Forces in a Cavitating Environment

Marshall Space Flight Center has developed and demonstrated a measurement device for sensing and resolving the hydrodynamic loads on fluid machinery. The device - a derivative of the six-component wind tunnel balance - senses the forces and moments on the rotating device through a weakened shaft section instrumented with a series of strain gauges. This rotating balance was designed to directly measure the steady and unsteady hydrodynamic loads on an inducer, thereby defining the amplitude and frequency content associated with operating in various cavitation modes. The rotating balance was calibrated statically using a dead-weight load system in order to generate the 6 x 12 calibration matrix later used to convert measured voltages to engineering units. Structural modeling suggested that the rotating assembly first bending mode would be significantly reduced with the balance s inclusion. This reduction in structural stiffness was later confirmed experimentally with a hammer-impact test. This effect, coupled with the relatively large damping associated with the rotating balance waterproofing material, limited the device s bandwidth to approximately 50 Hertz Other pre-test validations included sensing the test article rotating assembly built-in imbalance for two configurations and directly measuring the assembly mass and buoyancy while submerged under water. Both tests matched predictions and confirmed the device s sensitivity while stationary and rotating. The rotating balance was then demonstrated in a water test of a full-scale Space Shuttle Main Engine high-pressure liquid oxygen pump inducer. Experimental data was collected a scaled operating conditions at three flow coefficients across a range of cavitation numbers for the single inducer geometry and radial clearance. Two distinct cavitation modes were observed symmetric tip vortex cavitation and alternate-blade cavitation. Although previous experimental tests on the same inducer demonstrated two additional cavitation modes at lower inlet pressures, these conditions proved unreachable with the rotating balance installed due to the intense dynamic environment. The sensed radial load was less influenced by flow coefficient than by cavitation number or cavitation mode although the flow coefficient range was relatively narrow. Transition from symmetric tip vortex to alternate-blade cavitation corresponded to changes in both radial load magnitude and radial load orientation relative to the inducer. Sensed moments indicated that the effective load center moved downstream during this change in cavitation mode. An occurrence of "higher+rdex cavitation" was also detected in both the stationary pressures and the rotating balance data although the frequency of the phenomena was well above the reliable bandwidth of the rotating balance. In summary the experimental tests proved both the concept and device s capability despite the limitations and confirmed that hydrodynamically-induced forces and moments develop in response to the unbalanced pressure field, which is, in turn, a product of the cavitation environment.

Skelley, Stephen E.↗
NASA NTRS2015

Ultra High Temperature (UHT) SiC Fiber (Phase 2)

Silicon-carbide fiber-reinforced silicon-carbide ceramic matrix composites (SiCSiC CMC) are emerginglightweight re-usable structural materials not only for hot section components in gas turbine engines, but also for controlsurfaces and leading edges of reusable hypersonic vehicles as well as for nuclear propulsion and reactor components. Ithas been shown that when these CMC are employed in engine hot-section components, the higher the upper usetemperature (UUT) of the SiC fiber, the more performance benefits are accrued, such as higher operating temperatures,reduced component cooling air, reduced fuel consumption, and reduced emissions. The first generation of SiCSiC CMC with a temperature capability of 2200-2400F are on the verge of being introduced into the hot-section components ofcommercial and military gas turbine engines.Today the SiC fiber type currently recognized as the worlds best in terms ofthermo-mechanical performance is the Sylramic-iBN fiber. This fiber was previously developed by the PI at NASA GRC using patented processes to improve the high-cost commercial Sylramic fiber, which in turn was derived from anotherlow-cost low-performance commercial fiber. Although the Sylramic-iBN fiber shows state-of-the art creep and rupture resistance for use temperatures above 2550oF, NASA has shown by fundamental creep studies and model developmentthat its microstructure and creep resistance could theoretically be significantly improved to produce an Ultra HighTemperature (UHT) SiC fiber.This Phase II Seedling Fund effort has been focused on the key objective of effectively repeating the similar processes used for producing the Sylramic-iBN fiber using a design of experiments approach to first understand the cause of the less than optimum Sylramic-iBN microstructure and then attempting to develop processconditions that eliminate or minimize these key microstructural issues. In so doing, it is predicted that that theseadvanced process could result in an UHT SiC fiber with 20 times more creep resistance than the Sylramic-iBN fiber,which in turn would allow SiCSiC CMC to operate up to 2700oF and above, thereby further enhancing the performancebenefits of SiCSiC components in aero-propulsion engines. It was also envisioned that the fiber processes developedduring Phase II efforts would not only reduce production costs for the UHT fiber by using low-cost precursor fibers andcombined processes, but also allow the UHT fibers to be directly produced in preforms of the precursor fibers, possibly atthe facilities of the CMC fabricator.

SiC Ceramic Fiber↗
NASA NTRS2007

Improved Underwater Excitation-Emission Matrix Fluorometer

A compact, high-resolution, two-dimensional excitation-emission matrix fluorometer (EEMF) has been designed and built specifically for use in identifying and measuring the concentrations of organic compounds, including polluting hydrocarbons, in natural underwater settings. Heretofore, most EEMFs have been designed and built for installation in laboratories, where they are used to analyze the contents of samples collected in the field and brought to the laboratories. Because the present EEMF can be operated in the field, it is better suited to measurement of spatially and temporally varying concentrations of substances of interest. In excitation-emission matrix (EEM) fluorometry, fluorescence is excited by irradiating a sample at one or more wavelengths, and the fluorescent emission from the sample is measured at multiple wavelengths. When excitation is provided at only one wavelength, the technique is termed one-dimensional (1D) EEM fluorometry because the resulting matrix of fluorescence emission data (the EEM) contains only one row or column. When excitation is provided at multiple wavelengths, the technique is termed two-dimensional (2D) EEM fluorometry because the resulting EEM contains multiple rows and columns. EEM fluorometry - especially the 2D variety - is well established as a means of simultaneously detecting numerous dissolved and particulate compounds in water. Each compound or pool of compounds has a unique spectral fluorescence signature, and each EEM is rich in information content, in that it can contain multiple fluorescence signatures. By use of deconvolution and/or other mixture-analyses techniques, it is often possible to isolate the spectral signature of compounds of interest, even when their fluorescence spectra overlap. What distinguishes the present 2D EEMF over prior laboratory-type 2D EEMFs are several improvements in packaging (including a sealed housing) and other aspects of design that render it suitable for use in natural underwater settings. In addition, the design of the present 2D EEMF incorporates improvements over the one prior commercial underwater 2D EEMF, developed in 1994 by the same company that developed the present one. Notable advanced features of the present EEMF include the following: 1) High sensitivity and spectral resolution are achieved by use of an off-the-shelf grating spectrometer equipped with a sensor in the form of a commercial astronomical- grade 256 532-pixel charge-coupled-device (CCD) array. 2) All of the power supply, timing, control, and readout circuits for the illumination source and the CCD, ancillary environmental monitoring sensors, and circuitry for controlling a shutter or filter motor are custom-designed and mounted compactly on three circuit boards below a fourth circuit board that holds the CCD (see figure). 3) The compactness of the grating spectrometer, CCD, and circuit assembly makes it possible to fit the entire instrument into a compact package that is intended to be maneuverable underwater by one person. 4) In mass production, the cost of the complete instrument would be relatively low - estimated at approximately $30,000 at 2005 prices.

Moore, Casey↗
NASA NTRS2009

Radar Differential Phase Signatures of Ice Orientation for the Prediction of Lightning Initiation and Cessation

The majority of lightning-related casualties typically occur during thunderstorm initiation (e.g., first flash) or dissipation (e.g., last flash). The physics of electrification and lightning production during thunderstorm initiation is fairly well understood. As such, the literature includes a number of studies presenting various radar techniques (using reflectivity and, if available, other dual-polarimetric parameters) for the anticipation of initial electrification and first lightning flash. These radar techniques have shown considerable skill at forecasting first flash. On the other hand, electrical processes and lightning production during thunderstorm dissipation are not nearly as well understood and few, if any, successful techniques have been developed to anticipate the last flash and subsequent cessation of lightning. One promising approach involves the use of dual-polarimetric radar variables to infer the presence of oriented ice crystals in lightning producing storms. In the absence of strong vertical electric fields, ice crystals fall with their largest (semi-major) axis in the horizontal associated with gravitational and aerodynamic forces. In thunderstorms, strong vertical electric fields (100-200 kV m(sup -1)) have been shown to orient small (less than 2 mm) ice crystals such that their semi-major axis is vertical (or nearly vertical). After a lightning flash, the electric field is typically relaxed and prior radar research suggests that ice crystals rapidly resume their preferred horizontal orientation. In active thunderstorms, the vertical electric field quickly recovers and the ice crystals repeat this cycle of orientation for each nearby flash. This change in ice crystal orientation from primarily horizontal to vertical during the development of strong vertical electric fields prior to a lightning flash forms the physical basis for anticipating lightning initiation and, potentially, cessation. Research has shown that radar reflectivity (Z) and other co-polar back-scattering radar measurements like differential reflectivity (Z(sub dr)) typically measured by operational dual-polarimetric radars are not sensitive to these changes in ice crystal orientation. However, prior research has demonstrated that oriented ice crystals cause significant propagation effects that can be routinely measured by most dual-polarimetric radars from X-band (3 cm) to S-band (10 cm) wavelengths using the differential propagation phase shift (often just called differential phase, phi(sub dp)) or its range derivative, the specific differential phase (K(sub dp)). Advantages of the differential phase include independence from absolute or relative power calibration, attenuation, differential attenuation and relative insensitivity to ground clutter and partial beam occultation effects (as long as the signal remains above noise). In research mode, these sorts of techniques have been used to anticipate initial cloud electrification, lightning initiation, and cessation. In this study, we develop a simplified model of ice crystal size, shape, orientation, dielectric, and associated radar scattering and propagation effects in order to simulate various idealized scenarios of ice crystals responding to a hypothetical electric field and their dual-polarimetric radar signatures leading up to lightning initiation and particularly cessation. The sensitivity of the K(sub dp) ice orientation signature to various ice properties and radar wavelength will be explored. Since K(sub dp) is proportional to frequency in the Rayleigh- Gans scattering regime, the ice orientation signatures should be more obvious at higher (lower) frequencies (wavelengths). As a result, simulations at radar wavelengths from 10 cm down to 1 cm (Ka-band) will be conducted. Resonance effects will be considered using the T-matrix method. Since most K(sub dp) Vbased observations have been shown at S-band, we will present ice orientation signatures from C-band (UAH/NASA ARMOR) and X-bd (UAH MAX) dual-polarimetric radars located in Northern Alabama. Issues related to optimal radar scanning for the detection of oriented ice will be discussed. Preliminary suggestions on how these differential phase signatures of oriented ice could contribute to lightning initiation and cessation algorithms will be presented.

Carey, L.D.↗
NASA NTRS2009

Modeling and Simulation of Variable Mass, Flexible Structures

The advent of the new Ares I launch vehicle has highlighted the need for advanced dynamic analysis tools for variable mass, flexible structures. This system is composed of interconnected flexible stages or components undergoing rapid mass depletion through the consumption of solid or liquid propellant. In addition to large rigid body configuration changes, the system simultaneously experiences elastic deformations. In most applications, the elastic deformations are compatible with linear strain-displacement relationships and are typically modeled using the assumed modes technique. The deformation of the system is approximated through the linear combination of the products of spatial shape functions and generalized time coordinates. Spatial shape functions are traditionally composed of normal mode shapes of the system or even constraint modes and static deformations derived from finite element models of the system. Equations of motion for systems undergoing coupled large rigid body motion and elastic deformation have previously been derived through a number of techniques [1]. However, in these derivations, the mode shapes or spatial shape functions of the system components were considered constant. But with the Ares I vehicle, the structural characteristics of the system are changing with the mass of the system. Previous approaches to solving this problem involve periodic updates to the spatial shape functions or interpolation between shape functions based on system mass or elapsed mission time. These solutions often introduce misleading or even unstable numerical transients into the system. Plus, interpolation on a shape function is not intuitive. This paper presents an approach in which the shape functions are held constant and operate on the changing mass and stiffness matrices of the vehicle components. Each vehicle stage or component finite element model is broken into dry structure and propellant models. A library of propellant models is used to describe the distribution of mass in the fuel tank or Solid Rocket Booster (SRB) case for various propellant levels. Based on the mass consumed by the liquid engine or SRB, the appropriate propellant model is coupled with the dry structure model for the stage. Then using vehicle configuration data, the integrated vehicle model is assembled and operated on by the constant system shape functions. The system mode shapes and frequencies can then be computed from the resulting generalized mass and stiffness matrices for that mass configuration. The rigid body mass properties of the vehicle are derived from the integrated vehicle model. The coupling terms between the vehicle rigid body motion and elastic deformation are also updated from the constant system shape functions and the integrated vehicle model. This approach was first used to analyze variable mass spinning beams and then prototyped into a generic dynamics simulation engine. The resulting code was tested against Crew Launch Vehicle (CLV-)class problems worked in the TREETOPS simulation package and by Wilson [2]. The Ares I System Integration Laboratory (SIL) is currently being developed at the Marshall Space Flight Center (MSFC) to test vehicle avionics hardware and software in a hardware-in-the-loop (HWIL) environment and certify that the integrated system is prepared for flight. The Ares I SIL utilizes the Ares Real-Time Environment for Modeling, Integration, and Simulation (ARTEMIS) tool to simulate the launch vehicle and stimulate avionics hardware. Due to the presence of vehicle control system filters and the thrust oscillation suppression system, which are tuned to the structural characteristics of the vehicle, ARTEMIS must incorporate accurate structural models of the Ares I launch vehicle. The ARTEMIS core dynamics simulation models the highly coupled nature of the vehicle flexible body dynamics, propellant slosh, and vehicle nozzle inertia effects combined with mass and flexible body properties that vary significant with time during the flight. All forces that act on the vehicle during flight must be simulated, including deflected engine thrust force, spatially distributed aerodynamic forces, gravity, and reaction control jet thrust forces. These forces are used to excite an integrated flexible vehicle, slosh, and nozzle dynamics model for the vehicle stack that simulates large rigid body translations and rotations along with small elastic deformations. Highly effective matrix math operations on a distributed, threaded high-performance simulation node allow ARTEMIS to retain up to 30 modes of flex for real-time simulation. Stage elements that separate from the stack during flight are propagated as independent rigid six degrees of freedom (6DOF) bodies. This paper will present the formulation of the resulting equations of motion, solutions to example problems, and describe the resulting dynamics simulation engine within ARTEMIS.

Tobbe, Patrick A.↗