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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.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Identification and structural analysis of a thermophilic β-1,3-glucanase from compost

β-1,3-glucanase can specifically hydrolyze glucans to oligosaccharides and has potential applications in biotechnology. We used the metatranscriptomic technology to discover a thermophilic β-1,3-glucanase from compost. The phylogenetic study shows that it belongs to the family 16 glycoside hydrolase (GH16) and is most homologous with an enzyme from Streptomyces sioyaensis, an actinobacterium. It has the activity of 146.9 U/mg in the optimal reaction condition (75 °C and pH 5.5). Its catalytic domain was crystallized and diffracted to 1.14 Å resolution. The crystal structure shows a sandwich-like β-jelly-roll fold with two disulfide bonds. After analyzing the occurring frequencies of these cysteine residues, we designed two mutants (C160G and C180I) to study the role of these disulfide bonds. Both mutants have decreased their optimal temperature from 75 to 70 °C, which indicate that the disulfide bonds are important to maintain thermostability. Interestingly, the activity of C160G has increased ~ 17% to reach 171.4 U/mg. We speculate that the increased activity of C160G mutant is due to increased dynamics near the active site. Our studies give a good example of balancing the rigidity and flexibility for enzyme activity, which is helpful for protein engineering.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1973

Statistical identification of structures.

A method is formulated for systematically using experimental measurements of the natural frequencies and mode shapes of a structure to modify stiffness and mass characteristics of a finite element model. Throughout the modification process, which does not require complete data, the finite element model remains consistent. An additional feature is that the engineer's confidence in the modeling of the various finite elements is quantified and incorporated into the revision procedure. Examples demonstrate the convergence and versatility of the method.

Collins, J. D.↗
NASA NTRS1974

Identification of structural parameters from helicopter dynamic test data

A method is presented for obtaining the mass, stiffness, and damping parameters of a linear mathematical model, having fewer degrees of freedom than the structure it represents, directly from dynamic response measurements on the actual helicopter without a priori knowledge of the physical characteristics of the fuselage. The only input information required in the formulation is the approximate natural frequency of each mode and mobility data measured proximate to these frequencies with sinusoidal force excitation applied at only one point on the vehicle. The practicality and numerical soundness of the theoretical development was demonstrated through a computer simulation of an experimental program.

Giansante, N.↗
NASA NTRS1977

The use of random decrement technique for identification of structural modes of vibration

An algorithm is developed to obtain the free responses of a structure from its random responses due to some unknown or known random input or inputs, using the random-decrement technique without changing time correlation between signals. The algorithm is tested using random responses from a 'generalized payload' model and from the 'Space Shuttle' model. The resulting free responses are then used to identify the modal characteristics of the two systems.

Ibrahim, S. R.↗
NASA NTRS1977

Modal identification of structures from the responses and random decrement signatures

The theory and application of a method which utilizes the free response of a structure to determine its vibration parameters is described. The time-domain free response is digitized and used in a digital computer program to determine the number of modes excited, the natural frequencies, the damping factors, and the modal vectors. The technique is applied to a complex generalized payload model previously tested using sine sweep method and analyzed by NASTRAN. Ten modes of the payload model are identified. In case free decay response is not readily available, an algorithm is developed to obtain the free responses of a structure from its random responses, due to some unknown or known random input or inputs, using the random decrement technique without changing time correlation between signals. The algorithm is tested using random responses from a generalized payload model and from the space shuttle model.

Brahim, S. R.↗
NASA NTRS1990

A global approach for the identification of structural connection properties

A general procedure is developed for identifying properties of structural joints. The procedure, which uses experimental response data, is considered general because it is applicable to any size or type of structural system. The present procedure, which identifies characteristics such as damping and stiffness, accommodates both linear and nonlinear joint properties and may process test data measured at arbitrary stations on the structural system. The method identifies joint characteristics by performing a global fit between predicted and measured data. It overcomes limitations of previous methods in that it can better deal with parameter-dependent constraints (e.g., gaps). The method is demonstrated with a simplified model of a bladed disk assembly having friction damping and mistuning.

Lawrence, Charles↗
NASA NTRS1991

Structural damage identification using mathematical optimization techniques

An identification procedure is proposed to identify damage characteristics (location and size of the damage) from dynamic measurements. This procedure was based on minimization of the mean-square measure of difference between measurement data (natural frequencies and mode shapes) and the corresponding predictions obtained from the computational model. The procedure is tested for simulated damage in the form of stiffness changes in a simple fixed free spring mass system and symmetric cracks in a simply supported Bernoulli Euler beam. It is shown that when all the mode information is used in the identification procedure it is possible to uniquely determine the damage properties. Without knowing the complete set of modal information, a restricted region in the initial data space has been found for realistic and convergent solution from the identification process.

Shen, Mo-How Herman↗
NASA NTRS1992

Laboratory for Engineering Man/Machine Systems (LEMS): System identification, model reduction and deconvolution filtering using Fourier based modulating signals and high order statistics

Several important problems in the fields of signal processing and model identification, such as system structure identification, frequency response determination, high order model reduction, high resolution frequency analysis, deconvolution filtering, and etc. Each of these topics involves a wide range of applications and has received considerable attention. Using the Fourier based sinusoidal modulating signals, it is shown that a discrete autoregressive model can be constructed for the least squares identification of continuous systems. Some identification algorithms are presented for both SISO and MIMO systems frequency response determination using only transient data. Also, several new schemes for model reduction were developed. Based upon the complex sinusoidal modulating signals, a parametric least squares algorithm for high resolution frequency estimation is proposed. Numerical examples show that the proposed algorithm gives better performance than the usual. Also, the problem was studied of deconvolution and parameter identification of a general noncausal nonminimum phase ARMA system driven by non-Gaussian stationary random processes. Algorithms are introduced for inverse cumulant estimation, both in the frequency domain via the FFT algorithms and in the domain via the least squares algorithm.

Pan, Jianqiang↗
NASA NTRS1993

System identification and structural control on the JPL Phase B testbed

The primary objective of NASA's CSI program at JPL is to develop and demonstrate the CSI technology required to achieve high precision structural stability on large complex optical class spacecraft. The focus mission for this work is an orbiting interferometer telescope. Toward the realization of such a mission, a series of evolutionary testbed structures are being constructed. The JPL's CSI Phase B testbed is the second structure constructed in this series which is designed to study the pathlength control problem of the optical train of a stellar interferometer telescope mounted on a large flexible structure. A detailed description of this testbed can be found. This paper describes our efforts in the first phase of active structural control experiments of Phase B testbed using the active control approach where a single piezoelectric active member is used as an actuation device and the measurements include both colocated and noncolocated sensors. Our goal for this experiment is to demonstrate the feasibility of active structural control using both colocated and noncolocated measurements by means of successive control design and loop closing. More specifically, the colocated control loop was designed and closed first to provide good damping improvement over the frequency range of interest. The noncolocated controller was then designed with respect to a partially controlled structure to further improve the performance. Based on our approach, experimental closed-loop results have demonstrated significant performance improvement with excellent stability margins.

Chu, Cheng-Chih↗
NASA NTRS2021

Sublimation of Laboratory Ices Millimeter/Submillimeter Experiment (SubLIME): Structure-Specific Identifications of Products from UV-photolyzed Methanol Ice

Submillimeter/far-IR spectroscopy was used to detect and quantify organic molecules sublimated after the ultraviolet photolysis (at 12 K) and warm-up (up to 300 K) of a methanol (CH3OH) ice sample. Eleven sublimated photoproducts were uniquely identified: carbon monoxide (CO), formaldehyde (H2CO), ketene (C2H2O), acetaldehyde (CH3CHO), ethylene oxide (CH2OCH2), vinyl alcohol (CH2CHOH), ethanol (CH3CH2OH), dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), glycolaldehyde (HOCH2CHO), and acetone ((CH3)2CO). Two additional products were detected in the photolyzed ice by Fourier-transform infrared (FTIR) spectroscopy: carbon dioxide (CO2) and methane (CH4). The rotational temperatures and gas densities were calculated for the organics containing two or more C atoms via a rotation diagram analysis, and the gas-phase submillimeter/far-IR technique was used in tandem with mass spectrometry and FTIR spectroscopy of the ice during photolysis. The abundance ratios of the sublimated species (normalized to methanol) were compared to those observed in hot cores (Orion-KL, Sagittarius B2(N), and IRAS 16293-2422(B)) and in comets C/2014 Q2 (Lovejoy) and 67P/Churyumov–Gerasimenko.

K M Yocum↗
NASA NTRS2021

Sublimation of Laboratory Ices Millimeter/Submillimeter Experiment (SubLIME): Structure-Specific Identifications of Products from UV-photolyzed Methanol Ice

Submillimeter/far-IR spectroscopy was used to detect and quantify organic molecules sublimated after the ultraviolet photolysis (at 12 K) and warm-up (up to 300 K) of a methanol (CH3OH) ice sample. Eleven sublimated photoproducts were uniquely identified: carbon monoxide (CO), formaldehyde (H2CO), ketene (C2H2O), acetaldehyde (CH3CHO), ethylene oxide (CH2OCH2), vinyl alcohol (CH2CHOH), ethanol (CH3CH2OH), dimethyl ether (CH3OCH3), methyl formate (HCOOCH3), glycolaldehyde (HOCH2CHO), and acetone ((CH3)2CO). Two additional products were detected in the photolyzed ice by Fourier-transform infrared (FTIR) spectroscopy: carbon dioxide (CO2) and methane (CH4). The rotational temperatures and gas densities were calculated for the organics containing two or more C atoms via a rotation diagram analysis, and the gas-phase submillimeter/far-IR technique was used in tandem with mass spectrometry and FTIR spectroscopy of the ice during photolysis. The abundance ratios of the sublimated species (normalized to methanol) were compared to those observed in hot cores (Orion-KL, Sagittarius B2(N), and IRAS 16293-2422(B)) and in comets C/2014 Q2 (Lovejoy) and 67P/Churyumov–Gerasimenko.

K. M. Yocum↗
NASA NTRS1981

Algorithms for identification and analysis of large space structures

The identification of the mass, damping and stiffness matrix for the finite-element formulation of a structure will be given. It will be shown that the quadrature integration procedure can be used to find the desired matrices when reasonable assumptions hold. The mass, damping and stiffness matrices of the matrix polynomial are identified by the algorithm.

Denman, E. D.↗
NASA NTRS1984

Natural large-scale structures in the axisymmetric mixing layer

The present study is concerned with the optimization of conditional sampling techniques for eduction of naturally occurring large-scale structures in an axisymmetric mixing layer, and a comparison of the natural structure with that induced by means of controlled excitation. Questions regarding the sensitivity of the educed structure to the excitation amplitude are also explored. Aspects regarding the eduction with the high-speed-side reference signal are considered, taking into account structure identification, the smearing effect and a comparison with the structure under excitation, the effects of the threshold level, and the effect of a trigger-level window. Attention is given to structure characteristics and their dependence on Reynolds number and initial condition.

Zaman, K. B. M. Q.↗