SEARCH · Engineering Papers

Results for “modal model”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76

All sources NASA NTRS DOE OSTI

NASA NTRS1985

Direct model reference adaptive control of a flexible robotic manipulator

Quick, precise control of a flexible manipulator in a space environment is essential for future Space Station repair and satellite servicing. Numerous control algorithms have proven successful in controlling rigid manipulators wih colocated sensors and actuators; however, few have been tested on a flexible manipulator with noncolocated sensors and actuators. In this thesis, a model reference adaptive control (MRAC) scheme based on command generator tracker theory is designed for a flexible manipulator. Quicker, more precise tracking results are expected over nonadaptive control laws for this MRAC approach. Equations of motion in modal coordinates are derived for a single-link, flexible manipulator with an actuator at the pinned-end and a sensor at the free end. An MRAC is designed with the objective of controlling the torquing actuator so that the tip position follows a trajectory that is prescribed by the reference model. An appealing feature of this direct MRAC law is that it allows the reference model to have fewer states than the plant itself. Direct adaptive control also adjusts the controller parameters directly with knowledge of only the plant output and input signals.

Meldrum, D. R.↗

NASA NTRS2001

MPLM On-Orbit Interface Dynamic Flexibility Modal Test

Now that the International Space Station (ISS) is being constructed, payload developers have to not only verify the Shuttle-to-payload interface, but also the interfaces their payload will have with the ISS. The Multi Purpose Logistic Module (MPLM) being designed and built by Alenia Spazio in Torino, Italy is one such payload. The MPLM is the primary carrier for the ISS Payload Racks, Re-supply Stowage Racks, and the Resupply Stowage Platforms to re-supply the ISS with food, water, experiments, maintenance equipment and etc. During the development of the MPLM there was no requirement for verification of the on-orbit interfaces with the ISS. When this oversight was discovered, all the dynamic test stands had already been disassembled. A method was needed that would not require an extensive testing stand and could be completed in a short amount of time. The residual flexibility testing technique was chosen. The residual flexibility modal testing method consists of measuring the free-free natural frequencies and mode shapes along with the interface frequency response functions (FRF's). Analytically, the residual flexibility method has been investigated in detail by, MacNeal, Martinez, Carne, and Miller, and Rubin, but has not been implemented extensively for model correlation due to difficulties in data acquisition. In recent years improvement of data acquisition equipment has made possible the implementation of the residual flexibility method as in Admire, Tinker, and Ivey, and Klosterman and Lemon. The residual flexibility modal testing technique is applicable to a structure with distinct points (DOF) of contact with its environment, such as the MPLM-to-Station interface through the Common Berthing Mechanism (CBM). The CBM is bolted to a flange on the forward cone of the MPLM. During the fixed base test (to verify Shuttle interfaces) some data was gathered on the forward cone panels. Even though there was some data on the forward cones, an additional modal test was performed to better characterize its behavior. The CBM mounting flange is the only remaining structure of the MPLM that no test data was available. This paper discusses the implementation of the residual flexibility modal testing technique on the CBM flange and the modal test of the forward cone panels.

Bookout, Paul S.↗

DOE OSTI2015

SU-E-J-253: The Radiomics Toolbox in the Computational Environment for Radiological Research (CERR)

Purpose: To present an open source and free platform to facilitate radiomics research — The “Radiomics toolbox” in CERR. Method: There is scarcity of open source tools that support end-to-end modeling of image features to predict patient outcomes. The “Radiomics toolbox” strives to fill the need for such a software platform. The platform supports (1) import of various kinds of image modalities like CT, PET, MR, SPECT, US. (2) Contouring tools to delineate structures of interest. (3) Extraction and storage of image based features like 1st order statistics, gray-scale co-occurrence and zonesize matrix based texture features and shape features and (4) Statistical Analysis. Statistical analysis of the extracted features is supported with basic functionality that includes univariate correlations, Kaplan-Meir curves and advanced functionality that includes feature reduction and multivariate modeling. The graphical user interface and the data management are performed with Matlab for the ease of development and readability of code and features for wide audience. Open-source software developed with other programming languages is integrated to enhance various components of this toolbox. For example: Java-based DCM4CHE for import of DICOM, R for statistical analysis. Results: The Radiomics toolbox will be distributed as an open source, GNU copyrighted software. The toolbox was prototyped for modeling Oropharyngeal PET dataset at MSKCC. The analysis will be presented in a separate paper. Conclusion: The Radiomics Toolbox provides an extensible platform for extracting and modeling image features. To emphasize new uses of CERR for radiomics and image-based research, we have changed the name from the “Computational Environment for Radiotherapy Research” to the “Computational Environment for Radiological Research”.

60 APPLIED LIFE SCIENCES↗

DOE OSTI2015

MO-AB-BRA-02: A Novel Scatter Imaging Modality for Real-Time Image Guidance During Lung SBRT

Purpose: A novel scatter imaging modality is developed and its feasibility for image-guided radiation therapy (IGRT) during stereotactic body radiation therapy (SBRT) for lung cancer patients is assessed using analytic and Monte Carlo models as well as experimental testing. Methods: During treatment, incident radiation interacts and scatters from within the patient. The presented methodology forms an image of patient anatomy from the scattered radiation for real-time localization of the treatment target. A radiographic flat panel-based pinhole camera provides spatial information regarding the origin of detected scattered radiation. An analytical model is developed, which provides a mathematical formalism for describing the scatter imaging system. Experimental scatter images are acquired by irradiating an object using a Varian TrueBeam accelerator. The differentiation between tissue types is investigated by imaging simple objects of known compositions (water, lung, and cortical bone equivalent). A lung tumor phantom, simulating materials and geometry encountered during lung SBRT treatments, is fabricated and imaged to investigate image quality for various quantities of delivered radiation. Monte Carlo N-Particle (MCNP) code is used for validation and testing by simulating scatter image formation using the experimental pinhole camera setup. Results: Analytical calculations, MCNP simulations, and experimental results when imaging the water, lung, and cortical bone equivalent objects show close agreement, thus validating the proposed models and demonstrating that scatter imaging differentiates these materials well. Lung tumor phantom images have sufficient contrast-to-noise ratio (CNR) to clearly distinguish tumor from surrounding lung tissue. CNR=4.1 and CNR=29.1 for 10MU and 5000MU images (equivalent to 0.5 and 250 second images), respectively. Conclusion: Lung SBRT provides favorable treatment outcomes, but depends on accurate target localization. A comprehensive approach, employing multiple simulation techniques and experiments, is taken to demonstrate the feasibility of a novel scatter imaging modality for the necessary real-time image guidance.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1987

The effect of nonlinearities on the dynamic response of a large shuttle payload

The STS Centaur was designed to be a high energy upper stage for use with the Space Shuttle. Two versions were designed under development when the program was cancelled. The first version, designated G-prime, was for planetary missions. The second version, designated G, was to place spacecraft in geosynchronous orbit. As a part of the STS Centaur finite-element model verification effort, test articles of both versions were subjected to a series of static tests. In addition the Centaur G-prime test article was subjected to a series of dynamic tests including a modal survey. Both the static and dynamic tests showed that nonlinearities existed in the Centaur and its support system. The support system included flight-like latches. The nonlinearities were particularly apparent in tests that loaded the forward support structure of the Centaur. These test results were used to aid in the development of two improved finite-element models. The first was a linear model, while the second contained nonlinear elements at the boundaries. Results from both models were compared with the transient response obtained from a step-relaxation or twang test. The linear model was able to accurately match the low frequency response found in the test data. However, only the nonlinear model was able to match higher frequency response that was present in some of the test data. In addition the nonlinear model was able to predict other nonlinear behavior such as the dynamic jump that occurs in systems with nonlinear stiffness.

Sullivan, Timothy L.↗

NASA NTRS1987

The effect of nonlinearities on the dynamic response of a large Shuttle payload

The STS Centaur was designed to be a high energy upper stage for use with the Space Shuttle. Two versions were designed and under development when the program was cancelled. The first version, designated G-prime, was designed for planetary missions. The second version, designated G, was designed to place spacecraft in geosynchronous orbit. As a part of the STS Centaur finite-element model verification effort, test articles of both versions were subjected to a series of static tests. In addition the Centaur G-prime test article was subjected to a series of dynamic tests including a modal survey. Both the static and dynamic tests showed that nonlinearities existed in the Centaur and its support system. The support system included flight-like latches. The nonlinearities were particularly apparent in tests that loaded the forward support structure of the Centaur. These test results were used to aid in the development of two improved finite-element models. The first was a linear model, while the second contained nonlinear elements at the boundaries. Results from both models were compared with the transient response obtained from a step-relaxation or twang test. The linear model was able to accurately match the low frequency response found in the test data. However, only the nonlinear model was able to match higher frequency response that was present in some of the test data. In addition the nonlinear model was able to predict other nonlinear behavior such as the dynamic 'jump' that occurs in systems with nonlinear stiffness.

Sullivan, Timothy L.↗

DOE OSTI2015

Opportunities and Challenges in the Design and Analysis of Biomass Supply Chains

The biomass supply chain is one of the most critical elements of large-scale bioenergy production and in many cases a key barrier for procuring initial funding for new developments on specific energy crops. Most productions rely on complex transforming chains linked to feed and food markets. The term 'supply chain' covers various aspects from cultivation and harvesting of the biomass, to treatment, transportation, and storage. After energy conversion, the product must be delivered to final consumption, whether it is in the form of electricity, heat, or more tangible products, such as pellets and biofuels. Effective supply chains are of utmost importance for bioenergy production, as biomass tends to possess challenging seasonal production cycles and low mass, energy and bulk densities. Additionally, the demand for final products is often also dispersed, further complicating the supply chain. The goal of this paper is to introduce key components of biomass supply chains, examples of related modeling applications, and if/how they address aspects related to environmental metrics and management. The paper will introduce a concept of integrated supply systems for sustainable biomass trade and the factors influencing the bioenergy supply chain landscape, including models that can be used to investigate the factors. Our paper will also cover various aspects of transportation logistics, ranging from alternative modal and multi-modal alternatives to introduction of support tools for transportation analysis. Lastly, gaps and challenges in supply chain research are identified and used to outline research recommendations for the future direction in this area of study.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2021

Structural color from a coupled nanowire pair beyond the bonding and antibonding model

Optical resonances in nanostructures can be harnessed to produce a wide range of structural colors. Conversely, the analysis of structural colors has been used to clarify the nature of optical resonances. Here, we show that silicon nanowire (NW) pairs can display a wide range of structural colors by controlling their radiative coupling. This is accomplished by exciting a series of Fabry–Pérot-like modes where light is repeatedly scattered between two NWs. These modes are beyond the expectation from the conventional chemical bonding model under a quasi-electrostatic approximation, in which only bonding and antibonding modes can be formed in a pair system through modal hybridization. The additional eigenmodes found in a two-resonator system originate from the nonlinear, frequency-dependent coupling strength derived from the radiative nature of low- Q resonators. The Fabry–Pérot modes can be tuned across the entire visible frequency range by varying the distance between two NWs, leading to what we believe is a new type of universal building blocks that can provide structural color within a subwavelength footprint. The presented results pave the way toward the design and usage of highly tunable resonances that exploit the radiative coupling of high-index nanostructures.

Li, Qitong↗

NASA NTRS1971

Synthesis of stiffness and mass matrices from experimental vibration modes.

With highly complex structures, it is sometimes desirable to derive a dynamic model of the system from experimental vibration data. This paper presents algorithms for synthesizing the mass and stiffness matrices from experimentally derived modal data in a way which preserves the physical significance of the individual mass and stiffness elements. The synthesizing procedures allow for the incorporation of other mass and stiffness data, whether empirical or based on the analyst's insight. The mass and stiffness matrices are derived for a cantilever beam example and are compared with those obtained using earlier techniques.

Ross, R. G., Jr.↗

NASA NTRS1977

Experimental studies of the Space Shuttle payload acoustic environment

Two series of experiments were conducted to reduce the uncertainties concerning the Space Shuttle payload bay acoustic environment. Tests using a one-fifth scale model showed large changes in level below 125 Hz with the introduction of typical payloads. The changes were associated with particular acoustic modal behavior and were sensitive to the type of acoustic excitation. Another series of experiments evaluated the noise reduction of the first orbiter vehicle (OV-101). The results showed consistently greater noise reduction for grazing excitation than for diffuse excitation. The results were extrapolated to OV-102 using mass law relations and acceleration measurements.

Piersol, A. G.↗

NASA NTRS1979

Thrust oscillations of the Space Shuttle solid rocket Booster motor during static tests

Thrust oscillations have occurred during static tests of Space Shuttle Booster solid rocket motors. These oscillations in measured axial thrust occurred primarily near 15 Hz; these oscillations late in the motor burn reach magnitudes up to approximately + or - 3% of motor thrust. The phenomenon has consistently occurred on the four demonstration motors which have been static tested and appears to be associated with small amplitude, 15 Hz pressure oscillations inside the motor. The source of the pressure oscillations is thought to be associated with the fundamental longitudinal acoustic resonance of the motor at 15 Hz. These thrust oscillations potentially can impact the design of the Space Shuttle vehicle structure. The demonstration motors have been instrumented with an array of transducers to aid in understanding the phenomenon. In addition to measuring axial and lateral thrust of the motor, pressure transducers were located to measure chamber pressure oscillations at the forward dome. Accelerometers and extensometers have measured motions of the structure. A modal survey was conducted on a fired motor to identify its structural dynamic characteristics, and these data were used to validate mathematical models of the motor in the static test facility.

Mason, D. R.↗

NASA NTRS1984

Flutter of swept fan blades

The effect of sweep on fan blade flutter is studied by applying the analytical methods developed for aeroelastic analysis of advance turboprops. Two methods are used. The first method utilizes an approximate structural model in which the blade is represented by a swept, nonuniform beam. The second method utilizes a finite element technique to conduct modal flutter analysis. For both methods the unsteady aerodynamic loads are calculated using two dimensional cascade theories which are modified to account for sweep. An advanced fan stage is analyzed with 0, 15 and 30 degrees of sweep. It is shown that sweep has a beneficial effect on predominantly torsional flutter and a detrimental effect on predominantly bending flutter. This detrimental effect is shown to be significantly destabilizing for 30 degrees of sweep.

Kielb, R. E.↗

NASA NTRS1985

Flutter of swept fan blades

Kielb, R. E.↗

NASA NTRS1989

Static and dynamic deflection studies of the SRM aft case-nozzle joint

The redesign of the joints on the solid rocket motor (SRM) has prompted the need for analyzing the behavior of the joints using several different types of analyses. The types of analyses performed include modal analysis, static analysis, transient response analysis, and base driving response analysis. The forces used in these analyses to drive the mathematical model include SRM internal chamber pressure, nozzle blowout and side forces, shuttle vehicle lift-off dynamics, SRM pressure transient rise curve, gimbal forces and moments, actuator gimbal loads, and vertical and radial bolt preloads. The math model represented the SRM from the aft base tangent point (1,823.95 in) all the way back to the nozzle, where a simplified, tuned nozzle model was attached. The new design used the radial bolts as an additional feature to reduce the gap opening at the aft dome/nozzle fixed housing interface.

Christian, David C.↗

NASA NTRS1993

Model reduction results for flexible space structures

This paper describes the novel subsystem balancing technique for obtaining reduced-order models of flexible structures, and investigates its properties fully. This method can be regarded as a combination of the best features of modal truncation (efficiency) and internal balancing (accuracy); it is particularly well suited to the typical practical case of structures which possess clusters of close modes. Numerical results are then presented demonstrating the results obtained by applying subsystem balancing to the Air Force Phillips Laboratory ASTREX testbed, the Jet Propulsion Laboratory antenna facility, and the NASA Marshall Space Flight Center ACES structure.

Williams, Trevor↗

NASA NTRS1993

Vibration suppression for large scale adaptive truss structures using direct output feedback control

In this article, the vibration control of adaptive truss structures, where the control actuation is provided by length adjustable active members, is formulated as a direct output feedback control problem. A control method named Model Truncated Output Feedback (MTOF) is presented. The method allows the control feedback gain to be determined in a decoupled and truncated modal space in which only the critical vibration modes are retained. The on-board computation required by MTOF is minimal; thus, the method is favorable for the applications of vibration control of large scale structures. The truncation of the modal space inevitably introduces spillover effect during the control process. In this article, the effect is quantified in terms of active member locations, and it is shown that the optimal placement of active members, which minimizes the spillover effect (and thus, maximizes the control performance) can be sought. The problem of optimally selecting the locations of active members is also treated.

Lu, Lyan-Ywan↗

NASA NTRS1989

Propagation and scattering of elastic waves in fiber-reinforced plates

The objectives of this program are as follows: modelling of guided waves in fiber-reinforced plates in terms of different modes; and analysis of scattering by transverse cracks using modal representation. A hybrid numerical method combining the finite element representation of a region around the crack with the modal representation in the exterior region will be used in this program. Modes will be obtained using the through-the-thickness discretization of the displacement field.

Bratton, Robert L.↗

NASA NTRS2008

The LHT (Lunar Highlands Type) Regolith Simulant Series

Three NU-LHT (NASA/USGS-Lunar Highlands Type) regolith simulants have been produced to date: NU-LHT-1M, -ID, and -2M. A fourth simulant is currently in production: NU-LHT-3C. The "M" (medium) designation indicates a simulant with a grain size of <1 mm, "D" (dust) a simulant with a grain size of <36 microns, and "C" (coarse) a simulant with a 10 cm maximum particle size. The composition of these simulants is based on a NASA average Apollo 16 regolith chemical composition, However, the mixing model used to create our simulants is based on cationic nonnative mineral proportions derived from the target chemical composition to approximate lunar modal mineralogy rather than chemical composition per se. Accordingly, the amount of plagioclase, pyroxenes, olivine, and trace minerals in the simulant crystalline fraction approximates that of the lunar regolith. We also added synthetic agglutinate in amounts approximate for low-medium regolith maturity. A pure glass fraction was also added to simulate other types of lunar glasses present in the regolith. In addition, the 3C simulant will include synthetic impact melt breccia clasts for the >1 cm particles. The bulk raw materials used to create these simulants include clinopyroxene-norite, anorthosite, hartzburgite and noritic mill waste from the Stillwater Mine, Nye, MT, and olivine from the Twin Sisters dunite, WA. Added trace minerals include beach sand ilmenite, chromite, synthetic p-tricaicium phosphate (whitiockite), gem grade fluor-apatite, and pyrite. The agglutinate, glasses, and synthetic breccia were designed and prepared at an industrial plasma melting facility in Boulder, CO, using Stillwater mill waste feedstock for the melt. These simulants do not include nanophase-feO. The M and C simulant grain size distribution (down to 0.4 microns) approximates that of Apollo 16 regolith and the regolith in general.

Stoeser, Douglas↗