SEARCH · Engineering Papers

Results for “forces”

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 253 records · Page 14

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Quantifying CanESM5 and EAMv1 sensitivities to Mt. Pinatubo volcanic forcing for the CMIP6 historical experiment

Large volcanic eruptions reaching the stratosphere have caused marked perturbations to the global climate including cooling at the Earth's surface, changes in large-scale circulation and precipitation patterns and marked temporary reductions in global ocean heat content. Many studies have investigated these effects using climate models; however, uncertainties remain in the modelled response to these eruptions. This is due in part to the diversity of forcing datasets that are used to prescribe the distribution of stratospheric aerosols resulting from these volcanic eruptions, as well as uncertainties in optical property derivations from these datasets. To improve this situation for the sixth phase of the Coupled Model Intercomparison Project (CMIP6), a two-step process was undertaken. First, a combined stratospheric aerosol dataset, the Global Space-based Stratospheric Aerosol Climatology (GloSSAC; 1979–2016), was constructed. Next, GloSSAC, along with information from ice cores and Sun photometers, was used to generate aerosol distributions, characteristics and optical properties to construct a more consistent stratospheric aerosol forcing dataset for models participating in CMIP6. This “version 3” of the stratospheric aerosol forcing has been endorsed for use in all contributing CMIP6 simulations. Recent updates to the underlying GloSSAC from version 1 to version 1.1 affected the 1991–1994 period and necessitated an update to the stratospheric aerosol forcing from version 3 to version 4. As version 3 remains the official CMIP6 input, quantification of the impact on radiative forcing and climate is both relevant and timely for interpreting results from experiments such as the CMIP6 historical simulations. This study uses two models, the Canadian Earth System Model version 5 (CanESM5) and the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1), to estimate the difference in instantaneous radiative forcing in simulated post-Pinatubo climate response when using version 4 instead of version 3. Differences in temperature, precipitation and radiative forcings are generally found to be small compared to internal variability. An exception to this is differences in monthly temperature anomalies near 24 km altitude in the tropics, which can be as large as 3 °C following the eruption of Mt. Pinatubo.

58 GEOSCIENCES↗

DOE OSTI2023

Exploring ice sheet model sensitivity to ocean thermal forcing and basal sliding using the Community Ice Sheet Model (CISM)

Abstract. Multi-meter sea level rise (SLR) is thought to be possible within the next few centuries, with most of the uncertainty originating from the Antarctic land ice contribution. One source of uncertainty relates to the ice sheet model initialization. Since ice sheets have a long response time (compared to other Earth system components such as the atmosphere), ice sheet model initialization methods can have significant impacts on how the ice sheet responds to future forcings. To assess this, we generated 25 different ice sheet spin-ups, using the Community Ice Sheet Model (CISM) at a 4 km resolution. During each spin-up, we varied two key parameters known to impact the sensitivity of the ice sheet to future forcing: one related to the sensitivity of the ice shelf melt rate to ocean thermal forcing (TF) and the other related to the basal friction. The spin-ups all nudge toward observed thickness and enforce a no-advance calving criterion, such that all final spin-up states resemble observations but differ in their melt and friction parameter settings. Each spin-up was then forced with future ocean thermal forcings from 13 different CMIP6 models under the Shared Socioeconomic Pathway (SSP)5-8.5 emissions scenario and modern climatological surface mass balance data. Our results show that the effects of the ice sheet and ocean parameter settings used during the spin-up are capable of impacting multi-century future SLR predictions by as much as 2 m. By the end of this century, the effects of these choices are more modest, but still significant, with differences of up to 0.2 m of SLR. We have identified a combined ocean and ice parameter space that leads to widespread mass loss within 500 years (low friction and high melt rate sensitivity). To explore temperature thresholds, we also ran a synthetically forced CISM ensemble that is focused on the Amundsen region only. Given certain ocean and ice parameter choices, Amundsen mass loss can be triggered with thermal forcing anomalies between 1.5 and 2 ∘C relative to the spin-up. Our results emphasize the critical importance of considering ice sheet and ocean parameter choices during spin-up for SLR predictions and suggest the importance of including glacial isostatic adjustment in ice sheet simulations.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1974

Erosion in radial inflow turbines. Volume 2: Balance of centrifugal and radial drag forces on erosive particles

The particle motion in two-dimensional free and forced inward flowing vortices is considered. A particle in such a flow field experiences a balance between the aerodynamic drag forces that tend to drive erosive particles toward the axis, and centrifugal forces that prevent these particles from traveling toward the axis. Results predict that certain sizes of particles will achieve a stable orbit about the turbine axis in the inward flowing free vortex. In this condition, the radial drag force is equal to the centrifugal force. The sizes of particles that will achieve a stable orbit is shown to be related to the gas flow velocity diagram at a particular radius. A second analysis yields a description of particle sizes that will experience a centrifugal force that is greater than the radial component of the aerodynamic drag force for a more general type of particle motion.

Clevenger, W. B., Jr.↗

NASA NTRS1981

Axial force and efficiency tests of fixed center variable speed belt drive

An investigation of how the axial force varies with the centerline force at different speed ratios, speeds, and loads, and how the drive's transmission efficiency is affected by these related forces is described. The tests, intended to provide a preliminary performance and controls characterization for a variable speed belt drive continuously variable transmission (CVT), consisted of the design and construction of an experimental test rig geometrically similar to the CVT, and operation of that rig at selected speed ratios and power levels. Data are presented which show: how axial forces exerted on the driver and driven sheaves vary with the centerline force at constant values of speed ratio, speed, and output power; how the transmission efficiency varies with centerline force and how it is also a function of the V belt coefficient; and the axial forces on both sheaves as normalized functions of the traction coefficient.

Bents, D. J.↗

NASA NTRS1987

Structural frequency functions for an impulsive, distributed forcing function

The response of a penetrator structure to a spatially distributed mechanical impulse with a magnitude approaching field test force levels (1-2 Mlb) were measured. The frequency response function calculated from the response to this unique forcing function is compared to frequency response functions calculated from response to point forces of about 2000 pounds. The results show that the strain gages installed on the penetrator case respond similiarly to a point, axial force and to a spatially distributed, axial force. This result suggests that the distributed axial force generated in a penetration event may be reconstructed as a point axial force when the penetrator behaves in linear manner.

Bateman, Vesta I.↗

NASA NTRS1988

Electrostatic forces in planetary rings

The average charge on a particle in a particle-plasma cloud, the plasma potential inside the cloud, and the Coulomb force acting on the particle are calculated. The net repulsive electrostatic force on a particle depends on the plasma density, temperature, density of particles, particle size, and the gradient of the particle density. In a uniformly dense ring the electrostatic repulsion is zero. It is also shown that the electrostatic force acts like a pressure force, that even a collisionless ring can be stable against gravitational collapse, and that a finite ring thickness does not necessarily imply a finite velocity dispersion. A simple criterion for the importance of electrostatic forces in planetary rings is derived which involves the calculation of the vertical ring thickness which would result if only electrostatic repulsion were responsible for the finite ring thickness. Electrostatic forces are entirely negligible in the main rings of Saturn and the E and G rings. They may also be negligible in the F ring. However, the Uranian rings and Jupiter's ring seem to be very much influenced by electrostatic repulsion. In fact, electrostatic forces could support a Jovian ring which is an order of magnitude more dense than observed.

Goertz, C. K.↗

NASA NTRS1987

Rotordynamic forces on centrifugal pump impellers

The asymmetric flow around an impeller in a volute exerts a force upon the impeller. To study the rotordynamic force on an impeller which is vibrating around its machine axis of rotation, the impeller, mounted on a dynamometer, is made to whirl in a circular orbit within the volute. The measured force is expressed as the sum of a steady radial force and an unsteady force due to the eccentric motion of the impeller. These forces were measured in separate tests on a centrifugal pump with radically increased shroud clearance, a two-dimensional impeller, and an impeller with an inducer, the impeller of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine). In each case, a destabilizing force was observed over a region of positive whirl.

Franz, R.↗

NASA NTRS1988

Turbomachinery rotor forces

The fluid-induced forces, both steady and unsteady, acting upon an impeller of a centrifugal pump, and impeller blade-diffuser vane interaction in centrifugal pumps with vaned radial diffusers were evaluated experimentally and theoretically. Knowledge of the steady and unsteady forces, and the associated rotordynamic coefficients are required to effectively model the rotor dynamics of the High Pressure Fuel Turbopump (HPFTP) of the Space Shuttle Main Engine (SSME). These forces and rotordynamic coefficients were investigated using different impellers in combination with volutes and vaned diffusers, and axial inducers. These rotor forces are global. Local forces and pressures are also important in impeller-diffuser interaction, for they may cause cavitation damage and even vane failures. Thus, in a separate investigation, impeller wake, and impeller blade and diffuser vane pressure measurements were made. The nature of the rotordynamic forces is discussed, the experimental facility is described, and the measurements of unsteady forces and pressure are reported together with a brief and incomplete attempt to calculate these flows.

Arndt, Norbert↗

NASA NTRS1991

Effects of surface temperature and clouds on the CO2 forcing

The effects of surface temperature and clouds on the CO2 forcing are studied, based on use of the Colorado State University GCM. Results are reported from a pair of perpetual July simulations in which the sea surface temperatures differ by 4 K. The precipitable water is about 1.5 times larger in the warm run. The increased water vapor concentration amplifies the radiative effects of CO2, leading to greater CO2 forcing in the warm run. In the colder run the globally averaged reduction in upward longwave radiation due to a doubling of CO2 is 4.3 W/sq m at the level of maximum forcing, or the 'CO2 tropopause'. Above and below this level the CO2 forcing decreases, resulting in a net tropospheric warming of 0.033 K/day and a net stratospheric cooling. In the warm run the CO2 forcing at the CO2 tropopause is 4.6 W/sq m, and is associated with a tropospheric warming of 0.04 K/day. The clear-sky CO2 forcing at the CO2 tropopause is 5.0 W/sq m in the cold run, and 5.2 W/sq m in the warm run. By blocking infrared radiation that would otherwise be blocked by CO2, the clouds reduce the CO2 forcing of the surface-troposphere system by 0.66 W/sq m in the cold run, and by 0.59 W/sq m in the warm run.

Schmitt, Christina↗

NASA NTRS1992

Evaluation of force-torque displays for use with space station telerobotic activities

Recent experiments which addressed Space Station remote manipulation tasks found that tactile force feedback (reflecting forces and torques encountered at the end-effector through the manipulator hand controller) does not improve performance significantly. Subjective response from astronaut and non-astronaut test subjects indicated that force information, provided visually, could be useful. No research exists which specifically investigates methods of presenting force-torque information visually. This experiment was designed to evaluate seven different visual force-torque displays which were found in an informal telephone survey. The displays were prototyped in the HyperCard programming environment. In a within-subjects experiment, 14 subjects nullified forces and torques presented statically, using response buttons located at the bottom of the screen. Dependent measures included questionnaire data, errors, and response time. Subjective data generally demonstrate that subjects rated variations of pseudo-perspective displays consistently better than bar graph and digital displays. Subjects commented that the bar graph and digital displays could be used, but were not compatible with using hand controllers. Quantitative data show similar trends to the subjective data, except that the bar graph and digital displays both provided good performance, perhaps do to the mapping of response buttons to display elements. Results indicate that for this set of displays, the pseudo-perspective displays generally represent a more intuitive format for presenting force-torque information.

Hendrich, Robert C.↗

NASA NTRS1992

Climate forcing by anthropogenic aerosols

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol, in particular, has imposed a major perturbation to this forcing. Both the direct scattering of short-wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

Charlson, R. J.↗

NASA NTRS1992

Stress observations and driving force models for the South American plate

A comparison of stress observations to predictions of driving force models for the South American plate is presented. Conditions for dynamical equilibrium are used to estimate the magnitudes of forces as a function of age, with ridge push and slab pull as active forces, and plate drag and slab resistance as passive forces. The results are consistent with earlier published models, and it is found that the primary balance for an oceanic plate is between slab pull and the resisting drag forces. The model is generalized for the possible forces driving the South American plate, and it is compared with observed stress measurements and kinematics. The plate balance is found to be largely between ridge push and plate drag. The magnitude of a possible trench suction force is estimated using a model with an eddy between the Nazca slab and the overlying South American plate.

Stefanick, Michael↗

NASA NTRS1992

A new scheme of force reflecting control

A new scheme of force reflecting control has been developed that incorporates position-error-based force reflection and robot compliance control. The operator is provided with a kinesthetic force feedback which is proportional to the position error between the operator-commanded and the actual position of the robot arm. Robot compliance control, which increases the effective compliance of the robot, is implemented by low pass filtering the outputs of the force/torque sensor mounted on the base of robot hand and using these signals to alter the operator's position command. This position-error-based force reflection scheme combined with shared compliance control has been implemented successfully to the Advanced Teleoperation system consisting of dissimilar master-slave arms. Stability measurements have demonstrated unprecedentedly high force reflection gains of up to 2 or 3, even though the slave arm is much stiffer than operator's hand holding the force reflecting hand controller. Peg-in-hole experiments were performed with eight different operating modes to evaluate the new force-reflecting control scheme. Best task performance resulted with this new control scheme.

Kim, Won S.↗

NASA NTRS1993

Two techniques for measuring locomotion impact forces during zero G

A load-cell-instrumented treadmill mated to a Kistler force plate was used to investigate two methods of force measurement instrumentation during treadmill ambulation in zero g, created by parabolic flight on NASA's KC-135 aircraft. Current spaceflight treadmills do not have adequate instrumentation to determine the resultant foot impact force applied during restrained ambulation. Accurate measurement of foot-ground reaction forces is critical in attaining proper one-g loading, therefore ensuring proper musculoskeletal conditioning. Treadmill instrumentation and force plate measurements were compared for frequency response and linearity. Locomotion impact data were also collected under one-g laboratory settings and in Keplerian flight. The first resonant frequency for both techniques was found to be well above the primary frequency content of the locomotive forces. Peak impact forces measured by the two systems compared to within 10 percent.

Greenisen, Michael C.↗

NASA NTRS1992

A teleoperation training simulator with visual and kinesthetic force virtual reality

A force-reflecting teleoperation training simulator with a high-fidelity real-time graphics display has been developed for operator training. A novel feature of this simulator is that it enables the operator to feel contact forces and torques through a force-reflecting controller during the execution of the simulated peg-in-hole task, providing the operator with the feel of visual and kinesthetic force virtual reality. A peg-in-hole task is used in our simulated teleoperation trainer as a generic teleoperation task. A quasi-static analysis of a two-dimensional peg-in-hole task model has been extended to a three-dimensional model analysis to compute contact forces and torques for a virtual realization of kinesthetic force feedback. The simulator allows the user to specify force reflection gains and stiffness (compliance) values of the manipulator hand for both the three translational and the three rotational axes in Cartesian space. Three viewing modes are provided for graphics display: single view, two split views, and stereoscopic view.

Kim, Won S.↗

NASA NTRS1992

Developments of new force reflecting control schemes and an application to a teleoperation training simulator

Two schemes of force reflecting control, position-error based force reflection and low-pass-filtered force reflection, both combined with shared compliance control, were developed for dissimilar master-slave arms. These schemes enabled high force reflection gains, which were not possible with a conventional scheme when the slave arm was much stiffer than the master arm. The experimental results with a peg-in-hole task indicated that the newly force reflecting control schemes combined with compliance control resulted in best task performances. As a related application, a simulated force reflection/shared compliance control teleoperation trainer was developed that provided the operator with the feel of kinesthetic force virtual reality.

Kim, Won S.↗

NASA NTRS1923

Notes on the N.A.C.A. control force recorder

Emphasized here is the desirability of using recording instruments in the investigation of the characteristics of airplanes with particular reference to the National Advisory Committee for Aeronautics (NACA) control force recorder. Given here are photographs, records, and a description of the instrument developed by NACA for investigations on different types of aircraft. Described here is an instrument for recording control forces. At present, this control force recorder registers only the forces exerted on the stick. However, attachments are being designed to enable the forces on the rudder bar also to be recorded. The instrument in its final form will consist of three parts, namely, the recorder, the controller for the stick, and the controller for the rudder. The first two are in use now. The theory of operation is simple. In the controller, which is slipped over and fastened to the stick, are small electrical resistances which vary with the force applied to the handle. The recording apparatus then consists of suitable variable resistances properly connected to galvanometers whose deflections are proportional to the forces applied to the stick.

Reeid, H J E↗

NASA NTRS1993

Flexure and the role of inplane force around coronae on Venus

Large coronae on Venus, such as Artemis and Latona, are rimmed by conspicuous trenches and associated outer rises. Sandwell and Schubert have observed that these systems resemble terrestrial subduction zones in planform and have succeeded in fitting an elastic plate bending equation to the inferred flexural topography. However, the first zero crossing bending moments required are -2.5 x 10(exp 17) N for Artemis and -5.0 x 10(exp 16) N for Latona. Since these moments are similar in magnitude to those of subducting slabs on Earth, a rollback subduction mechanism was proposed to explain the flexure around the largest coronae, although a differential thermal subsidence model is sufficient to account for the topography around some coronae. The purpose is to investigate the effect of inplane force as a possible alternative to large applied moments in producing flexure at Artemis and Latona. The close correlation of gravity to topography on Venus implies the absence of a low viscosity zone and the strong coupling of the lithosphere to mantle convection. If coronae are the surface manifestations of mantle plumes, they may be the sites of active convective stress coupling. As the upwelling reaches the lithosphere, it spreads radially outward, inducing shear tractions on the base of the plate. In addition, the hot, expanding corona may load the surrounding plate horizonally. Both the basal shear stresses and radial loading can be treated as an equivalent compressive inplane force in the mechanical lithosphere, which contributes to the bending of the outlying plate. Using a model that relates inplane force to the measured gravity anomalies, a rough value of the inplane force at Artemis was calculated. Recent Pioneer Venus spherical harmonic gravity models indicate a geoid anomaly of about 75 m over Artemis, which corresponds to an estimated inplane force on the order of -1x10(exp 13) N/m. The gravity model is unable to resolve Latona, but an inplane force of similar dimensions is assumed. The maximum possible inplane force based on the expected rheology can be constrained by using the approximate 5 K/km thermal gradient inferred from the best fit 30 km elastic plate at Artemis and Latona. For a dry olivine flow law in the upper mantle, the compressional load limit of the 60 km thick mechanical lithosphere is -4 x 10(exp 13) N/m. This value is equivalent to a load of -8 x 10(exp 13) N/m on a 30 km thick elastic plate.

Brown, C. David↗