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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Joint University Program for Air Transportation Research, 1984

The research conducted during 1984 under the NASA/FAA sponsored Joint University Program for Air Transportation Research is summarized. The Joint University Program is a coordinated set of three grants sponsored by NASA Langley Research Center and the Federal Aviation Administration, one each with the Massachusetts Institute of Technology, Ohio University, and Princeton University. Completed works, status reports, and bibliographies are presented for research topics, which include navigation, guidance, control and display concepts. An overview of the year's activities for each of the schools is also presented.

Morrell, Frederick R.↗
NASA NTRS1986

Joint nonlinearity effects in the design of a flexible truss structure control system

Nonlinear effects are introduced in the dynamics of large space truss structures by the connecting joints which are designed with rather important tolerances to facilitate the assembly of the structures in space. The purpose was to develop means to investigate the nonlinear dynamics of the structures, particularly the limit cycles that might occur when active control is applied to the structures. An analytical method was sought and derived to predict the occurrence of limit cycles and to determine their stability. This method is mainly based on the quasi-linearization of every joint using describing functions. This approach was proven successful when simple dynamical systems were tested. Its applicability to larger systems depends on the amount of computations it requires, and estimates of the computational task tend to indicate that the number of individual sources of nonlinearity should be limited. Alternate analytical approaches, which do not account for every single nonlinearity, or the simulation of a simplified model of the dynamical system should, therefore, be investigated to determine a more effective way to predict limit cycles in large dynamical systems with an important number of distributed nonlinearities.

Mercadal, Mathieu↗
NASA NTRS1987

Response of joint dominated space structures

An efficient linearization method is presented for calculating the transient response of nonlinear systems due to initial disturbances. The method is an extension of the describing function approach in which the steady state response of the system is calculated by representing the nonlinear element, typically joints in the case of space structures, by impedances which are functions of the amplitude of response. Thus, the problem of solving the differential equation for the steady state response becomes one of solving a set of nonlinear algebraic equations involving the steady state amplitudes and phases of the system. It is shown that for the transient case the steady state impedances can be averaged over the range of responses in order to provide equivalent values of stiffness and damping that, for a given set of initial displacements, may be treated as being constant for purposes of calculating system response. Single degree of freedom system are used to demonstrate the method and to develop an approach for optimizing the joint's characteristics so as to minimize transient response times. The use of this method for response estimation and optimization in multiple degree of freedom systems is investigated.

Source record↗
NASA NTRS1987

Preloaded space structural coupling joints

A coupling device for tubular members of large truss structures with a locking collar being the only moving part is described. Each tubular member is constructed with an end bell section that has a belled flange with a mating face, and a necked area which is smaller in diameter than the tubular members to be joined. A split ring is affixed to each tubular member and is constructed so that when two tubular members are laterally moved into axial alignment and the collar is rotated over it, the split ring loads the joint with axial forces by pressing the belled flange mating surfaces together, and a preloading force is provided by the collar mating with a taper on the outside of the split rings. All free play is thereby removed by preloaded force. A major object is to provide an ability to remove and replace individual tubular members without disturbing other structural parts of a truss structure. An additional anticipated use of this joint is to couple high pressure fluid lines.

Rhodes, Marvin D.↗
NASA NTRS1986

Joint thunderstorm operations using the NASA F-106B and FAATC/AFWAL Convair 580 airplanes

During the 1985 thunderstorm season, three joint thunderstorm research flights were conducted within 100 n.mi. of NASA Langley by the NASA Storm Hazards F-106B and the FAA/USAF CV-580 research airplanes with ground-based weather radar measurements by NASA Wallops. This paper discusses the thunderstorm penetration capabilities of each airplane and the techniques used to safely place the two airplanes into the same thunderstorm cell for collection of correlated EM data. It is concluded that joint thunderstorm research operations of two aircraft with significantly dissimilar thunderstorm penetration capabilities are counterproductive to both airplanes.

Fisher, B. D.↗
NASA NTRS1986

Criterion for mixed mode fracture in composite bonded joints

A study was undertaken to characterize the debond growth mechanism of adhesively bonded composite joints under mode I, mixed mode I-II, and mode II static loadings. The bonded system consisted of graphite/epoxy (T300/5208) composite adherends bonded with a toughened epoxy (EC 3445) adhesive. The mode I, mode II and mixed-mode I-II fracture energies of the tested adhesive were found to be equal to each other. Furthermore, the criterion for mixed mode fracture in composite bonded joints was determined.

Mall, S.↗
NASA NTRS1987

Analytical formulation of orbiter-payload models coupled by trunnion joints with Coulomb friction

An orbiter and its payload substructure are linked together by five trunnion joints which have thirty degrees-of-freedom. Geometric compatibility conditions require fourteen of the interface physical coordinates of the orbiter and payload to be equal to each other and the remaining sixteen are free to have relative motions under Coulomb friction. The component modes synthesis method using fourteen inertia relief attachment modes for the formulation of the coupled system is presented. The exact nonlinear friction function is derived based on the characteristics of the joints. Formulation is applicable to an orbiter that carries any number of payload substructures.

Liu, Frank C.↗
NASA NTRS1988

Flexible Protective Shield For Newly Welded Joints

Simple device promotes defect-free welds in oxidation-prone metals. Welding torch pulls trailing shield behind to provide protective shield of argon gas over hot weld bead. Guide at front of torch holder feeds welding wire to joint. Shield bent or straightened to fit closely against weld joint.

Dyer, Gerald E.↗
NASA NTRS1988

Stiffening Rings For Rocket-Case Joints

Loss of seal preventable. Rotation of components joint reversed from that caused by normal outward bulge at joint, or else eliminated. Elimination or reversal of rotation by suitable amount prevents opening of gap on O-ring, thus preserving seal. Applicable to segmented terrestrial pressure vessels.

Thompson, Bryce W.↗
NASA NTRS1988

Improved Robot-Joint Calculations

Modified Denavit-Hartenberg parameters better for locating successive joint-axis systems. Modification results from insistence that transverse vector between successive joint rotational axes be perpendicular to one of rotational axes instead of both axes. Useful in industrial calibration of robot arms.

Barker, L. Keith↗
NASA NTRS1987

Design of source coders and joint source/channel coders for noisy channels

A theory behind a proposed joint source/channel coding approach is developed and a variable rate design approach which provides substantial improvement over current joint source/channel coder designs is obtained. The Rice algorithm as applied to the output of the Gamma Ray Detector of the Mars Orbiter is evaluated. An alternative algorithm is obtained which outperforms the Rice both in terms of data compression and noisy channel performance. A high-fidelity low-rate image compression algorithm is developed which provides almost distortionless compression of high resolution images.

Sayood, Khalid↗
NASA NTRS1984

Structural tests and development of a laminar flow control wing surface composite chordwise joint

The dramatic increases in fuel costs and the potential for periods of limited fuel availability provided the impetus to explore technologies to reduce transport aircraft fuel consumption. NASA sponsored the Aircraft Energy Efficiency (ACEE) program beginning in 1976 to develop technologies to improve fuel efficiency. The Lockheed-Georgia Company accomplished under NAS1-16235 Laminar-Flow-Control (LFC) Wing Panel Structural Design and Development (WSSD); design, manufacturing, and testing activities. An in-depth preliminary design of the baseline 1993 LFC wing was accomplished. A surface panel using the Lockheed graphite/epoxy integrated LFC wing box structural concept was designed. The concept was shown by analysis to be structurally efficient and cost effective. Critical details of the surface and surface joint was demonstrated by fabricating and testing complex, concept selection specimens. The Lockheed-Georgia Company accomplishments, Development of LFC Wind Surface Composite Structures (WSCS), are documented. Tests were conducted on two CV2 panels to verify the static tension and fatigue strength of LFC wing surface chordwise joints.

Lineberger, L. B.↗
NASA NTRS1988

The Joint NASA/Goddard-University of Maryland Research Program in Charged Particle and High Energy Photon Detector Technology

Having recognized at an early stage the critical importance of maintaining detector capabilities which utilize state of the art techniques, a joint program was formulated. This program has involved coordination of a broad range of efforts and activities including joint experiments, collaboration in theoretical studies, instrument design, calibrations, and data analysis. Summaries of the progress made to date are presented. A representative bibliography is also included.

Source record↗
NASA NTRS1988

Robotic joint experiments under ultravacuum

First, various aspects of a robotic joint development program, including gearbox technology, electromechanical components, lubrication, and test results, are discussed. Secondly, a test prototype of the joint allowing simulation of robotic arm dynamic effects is presented. This prototype is tested under vacuum with different types of motors and sensors to characterize the functional parameters: angular position error, mechanical backlash, gearbox efficiency, and lifetime.

Borrien, A.↗
NASA NTRS1988

Ammonia transfer across rotating joints in space

Thermal control of future large space facilities, such as the space station, will require the transfer of anhydrous ammonia across rotating joints with near zero leakage. Anhydrous ammonia is the primary heat transfer fluid aboard the station, providing critical thermal management of habitat and payload systems. The solar radiator joints, as well as the various payload pointing systems, are obvious examples of the need for a reliable fluid transfer device. Low weight, tight temperature control, low parasitic drag torque, long life, and high reliability, in addition to near zero leakage, are important characteristics necessary for the successful operation of such a device. In late 1986, Lockheed initiated a project to develop a Rotary Transfer Coupling (RTC) directed toward space station requirements. Fabrication and assembly of this device is now complete and testing is scheduled. The design and development of the face seal-type rotary fluid coupling that utilizes a unique cover gas concept (an inert gas such as nitrogen) to provide full containment of the ammonia was addressed.

Warner, Mark H.↗
NASA NTRS1988

Investigation of Super*Zip separation joint

An investigation to determine the most likely cause of two failures of five tests on 79 inch diameter Lockheed Super*Zip spacecraft separation joints being used for the development of a Shuttle/Centaur propulsion system. This joint utilizes an explosively expanded tube to fracture surrounding prenotched aluminum plates to achieve planar separation. A test method was developed and more than 300 tests firings were made to provide an understanding of severance mechanisms and the functional performance effects of system variables. An approach for defining functional margin was developed, and specific recommendations were made for improving existing and future systems.

Bement, Laurence J.↗
NASA NTRS1988

Joint University Program for Air Transportation Research, 1986

The research conducted under the NASA/FAA sponsored Joint University Program for Air Transportation Research is summarized. The Joint University Program is a coordinated set of three grants sponsored by NASA and the FAA, one each with the Mass. Inst. of Tech., Ohio Univ., and Princeton Univ. Completed works, status reports, and bibliographies are presented for research topics, which include computer science, guidance and control theory and practice, aircraft performance, flight dynamics, and applied experimental psychology. An overview of activities is presented.

Morrell, Frederick R.↗
NASA NTRS1988

Kinematics of Hooke universal joint robot wrists

The singularity problem associated with wrist mechanisms commonly found on industrial manipulators can be alleviated by redesigning the wrist so that it functions as a three-axis gimbal system. This paper discussess the kinematics of gimbal robot wrists made of one and two Hooke universal joints. Derivations of the resolved rate motion control equations for the single and double Hooke universal joint wrists are presented using the three-axis gimbal system as a theoretical wrist model.

Mckinney, William S., Jr.↗