Search NASA⌕ Search

SEARCH · Search NASA

Results for “Computer simulations”

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.

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

At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Application of recursive manipulator dynamics to hybrid software/hardware simulation

Computer simulations of robotic mechanisms have traditionally solved the dynamic equations of motion for an N degree of freedom manipulator by formulating an N dimensional matrix equation combining the accelerations and torques (forces) for all joints. The use of an alternative formulation that is strictly recursive is described. The dynamic solution proceeds on a joint by joint basis, so it is possible to perform inverse dynamics at arbitrary joints. The dynamic formulation is generalized with respect to both rotational and translational joints, and it is also directly extendable to branched manipulator chains. A hardware substitution test is described in which a servo drive motor was integrated with a simulated manipulator arm. The form of the dynamic equation permits calculation of acceleration given torque or vice versa. Computing torque as a function of acceleration is required for the hybrid software/hardware simulation test described. For this test, a joint servo motor is controlled in conjunction with the simulation, and the dynamic torque on the servo motor is provided by a load motor on a common driveshaft.

Hill, Christopher J.↗
NASA NTRS1993

Evaporation kinetics of Mg2SiO4 crystals and melts from molecular dynamics simulations

Computer simulations based on the molecular dynamics (MD) technique were used to study the mechanisms and kinetics of free evaporation from crystalline and molten forsterite (i.e., Mg2SiO4) on an atomic level. The interatomic potential employed for these simulations reproduces the energetics of bonding in forsterite and in gas-phase MgO and SiO2 reasonably accurately. Results of the simulation include predicted evaporation rates, diffusion rates, and reaction mechanisms for Mg2SiO4(s or l) yields 2Mg(g) + 20(g) + SiO2(g).

Kubicki, J. D.↗
NASA NTRS1994

Computationally efficient multibody simulations

Computationally efficient approaches to the solution of the dynamics of multibody systems are presented in this work. The computational efficiency is derived from both the algorithmic and implementational standpoint. Order(n) approaches provide a new formulation of the equations of motion eliminating the assembly and numerical inversion of a system mass matrix as required by conventional algorithms. Computational efficiency is also gained in the implementation phase by the symbolic processing and parallel implementation of these equations. Comparison of this algorithm with existing multibody simulation programs illustrates the increased computational efficiency.

Ramakrishnan, Jayant↗
NASA NTRS2006

Micro-Energy Rates for Damage Tolerance and Durability of Composite Structures

In this paper, the adhesive bond strength of lap-jointed graphite/aluminum composites is examined by computational simulation. Computed micro-stress level energy release rates are used to identify the damage mechanisms associated with the corresponding acoustic emission (AE) signals. Computed damage regions are similarly correlated with ultrasonically scanned damage regions. Results show that computational simulation can be used with suitable NDE methods for credible in-service monitoring of composites.

Chamis, Christos C.↗
NASA NTRS1984

VLSI circuit simulation using a vector computer

Simulation of circuits having more than 2000 active devices requires the largest, fastest computers available. A vector computer, such as the CYBER 205, can yield great speed and cost advantages if efforts are made to adapt the simulation program to the strengths of the computer. ASPEC and SPICE (1), two widely used circuit simulation programs, are discussed. ASPECV and VAMOS (5) are respectively vector adaptations of these two simulators. They demonstrate the substantial performance enhancements possible for this class of algorithm on the CYBER 205.

Mcgrogan, S. K.↗
NASA NTRS1994

Numerical Simulation Of Cutting Of Gear Teeth

Shapes of gear teeth produced by gear cutters of specified shape simulated computationally, according to approach based on principles of differential geometry. Results of computer simulation displayed as computer graphics and/or used in analyses of design, manufacturing, and performance of gears. Applicable to both standard and non-standard gear-tooth forms. Accelerates and facilitates analysis of alternative designs of gears and cutters. Simulation extended to study generation of surfaces other than gears. Applied to cams, bearings, and surfaces of arbitrary rolling elements as well as to gears. Possible to develop analogous procedures for simulating manufacture of skin surfaces like automobile fenders, airfoils, and ship hulls.

Oswald, Fred B.↗
NASA NTRS1997

Closed-Loop HIRF Experiments Performed on a Fault Tolerant Flight Control Computer

ABSTRACT Closed-loop HIRF experiments were performed on a fault tolerant flight control computer (FCC) at the NASA Langley Research Center. The FCC used in the experiments was a quad-redundant flight control computer executing B737 Autoland control laws. The FCC was placed in one of the mode-stirred reverberation chambers in the HIRF Laboratory and interfaced to a computer simulation of the B737 flight dynamics, engines, sensors, actuators, and atmosphere in the Closed-Loop Systems Laboratory. Disturbances to the aircraft associated with wind gusts and turbulence were simulated during tests. Electrical isolation between the FCC under test and the simulation computer was achieved via a fiber optic interface for the analog and discrete signals. Closed-loop operation of the FCC enabled flight dynamics and atmospheric disturbances affecting the aircraft to be represented during tests. Upset was induced in the FCC as a result of exposure to HIRF, and the effect of upset on the simulated flight of the aircraft was observed and recorded. This paper presents a description of these closed- loop HIRF experiments, upset data obtained from the FCC during these experiments, and closed-loop effects on the simulated flight of the aircraft.

Belcastro, Celeste M.↗
NASA NTRS1978

Employing static excitation control and tie line reactance to stabilize wind turbine generators

An analytical representation of a wind turbine generator is presented which employs blade pitch angle feedback control. A mathematical model was formulated. With the functioning MOD-0 wind turbine serving as a practical case study, results of computer simulations of the model as applied to the problem of dynamic stability at rated load are also presented. The effect of the tower shadow was included in the input to the system. Different configurations of the drive train, and optimal values of the tie line reactance were used in the simulations. Computer results revealed that a static excitation control system coupled with optimal values of the tie line reactance would effectively reduce oscillations of the power output, without the use of a slip clutch.

Hwang, H. H.↗
NASA NTRS2010

Computational Aerodynamic Simulations of a Spacecraft Cabin Ventilation Fan Design

Quieter working environments for astronauts are needed if future long-duration space exploration missions are to be safe and productive. Ventilation and payload cooling fans are known to be dominant sources of noise, with the International Space Station being a good case in point. To address this issue cost effectively, early attention to fan design, selection, and installation has been recommended, leading to an effort by NASA to examine the potential for small-fan noise reduction by improving fan aerodynamic design. As a preliminary part of that effort, the aerodynamics of a cabin ventilation fan designed by Hamilton Sundstrand has been simulated using computational fluid dynamics codes, and the computed solutions analyzed to quantify various aspects of the fan aerodynamics and performance. Four simulations were performed at the design rotational speed: two at the design flow rate and two at off-design flow rates. Following a brief discussion of the computational codes, various aerodynamic- and performance-related quantities derived from the computed flow fields are presented along with relevant flow field details. The results show that the computed fan performance is in generally good agreement with stated design goals.

Tweedt, Daniel L.↗
NASA NTRS1995

Spectral variation of high power microwave pulse propagating in a self-generated plasma

A systematic study to understand the spectral variation of a high power microwave pulse propagating in a self-generated plasma is carried out. It includes the theoretical formulation, experimental demonstration, and computer simulations and computer experiments. The experiment of pulse propagation is conducted in a vacuum chamber filled with dry air (approximately 0.2 torr); the chamber is made of a 2 ft. cube of Plexiglas. A rectangular microwave pulse (1 microsec pulse width and 3.27 GHz carrier frequency) is fed into the cube through an S band microwave horn placed at one side of the chamber. A second S-band horn placed at the opposite side of the chamber is used to receive the transmitted pulse. The spectra of the incident pulse and transmitted pulse are then compared. As the power of the incident pulse is only slightly (less than 15%) above the breakdown threshold power of the background air, the peak of the spectrum of the transmitted pulse is upshifted from the carrier frequency 3.27 GHz of the incident pulse. However, as the power of the incident pulse exceeds the breakdown threshold power of the background air by 30%, a different phenomenon appears. The spectrum of the transmitted pulse begins to have two peaks. One is upshifted and the other one downshifted from the single peak location of the incident pulse. The amount of frequency downshift is comparable to that of the upshifted frequency. A theoretical model describing the experiment of pulse propagation in a self-generated plasma is developed. There are excellent agreements between the experimental results and computer simulations based on this theoretical model, which is also used to further carry out computer experiments identifying the role of plasma introduced wave loss on the result of frequency downshift phenomenon.

Ren, A.↗
NASA NTRSDate not supplied

A Methodology for Actuating RCS Jets in a Continuous, Time-Accurate CFD Simulation

Computational fluid dynamics simulations of Mars entry vehicle reaction control systems have been used to gain a better understanding of the wide range of flow phenomena encountered during various phases of flight. One aspect of this is simulating the system during controlled flight. Current practices model the system in a continuously actuated state, but this methodology is unable to accurately model the dynamic behavior of the system during EDL. One method to improve this is to create a coupled CFD-RBD-Control simulation. The first step to this is establishing a method of accurately actuating an RCS jet during a time accurate CFD simulation. This paper presents a method to achieve this actuation. There are three phases to the methodology: establishing the off state, creating a ramping function that will initialize the jet flow, and establishing the on state. A test case of a jet in a supersonic crossflow is implemented to establish the success of the methodology in being able to actuate a jet in the midst of an ongoing CFD simulation. It shows significant improvement in boundary condition responsiveness for linear and exponential ramping functions in comparison to the step function. A preliminary demonstration of the methodology is presented for the MSL vehicle which shows significant advantages for the implementation of a linear ramping function over a step function.

Alexandra Hickey↗
NASA NTRSDate not supplied

A Methodology for Actuating RCS Jets in a Continuous, Time-Accurate CFD Simulation

Computational fluid dynamics simulations of Mars entry vehicle reaction control systems have been used to gain a better understanding of the wide range of flow phenomena encountered during various phases of flight. One aspect of this is simulating the system during controlled flight. Current practices model the system in a continuously actuated state, but this methodology is unable to accurately model the dynamic behavior of the system during EDL. One method to improve this is to create a coupled CFD-RBD-Control simulation. The first step to this is establishing a method of accurately actuating an RCS jet during a time accurate CFD simulation. This paper presents a method to achieve this actuation. There are three phases to the methodology: establishing the off state, creating a ramping function that will initialize the jet flow, and establishing the on state. A test case of a jet in a supersonic crossflow is implemented to establish the success of the methodology in being able to actuate a jet in the midst of an ongoing CFD simulation. It shows significant improvement in boundary condition responsiveness for linear and exponential ramping functions in comparison to the step function. A preliminary demonstration of the methodology is presented for the MSL vehicle which shows significant advantages for the implementation of a linear ramping function over a step function.

Alexandra Hickey↗