Inhibited Shaped Charge Launcher Testing of Spacecraft Shield Designs

This report describes a test program in which several orbital debris shield designs were impact tested using the inhibited shaped charge launcher facility at Southwest Research Institute. This facility enables researchers to study the impact of one-gram aluminum projectiles on various shielding designs at velocities above 11 km/s. A total of twenty tests were conducted on targets provided by NASA-MSFC. This report discusses in detail the shield design, the projectile parameters and the test configuration used for each test. A brief discussion of the target damage is provided, as the detailed analysis of the target response will be done by NASA-MSFC

Inhibited Shaped Charge Launcher Testing of Spacecraft Shield Designs

This report describes a test program in which several orbital debris shield designs were impact tested using the inhibited shaped charge launcher facility at Southwest Research Institute. This facility enables researchers to study the impact of one-gram aluminum projectiles on various shielding designs at velocities above 11 km/s. A total of twenty tests were conducted on targets provided by NASA-MSFC. This report discusses in detail the shield design, the projectile parameters and the test configuration used for each test. A brief discussion of the target damage is provided, as the detailed analysis of the target response will be done by NASA-MSFC

Anchored Bulkhead Failure on the Arabian Gulf

A 1500-m long anchored bulkhead with a height of 20m exhibited a localized failure in the form of broken and overstressed anchors several months after construction. The wall had not yet been subjected to its full design loadings. The soil conditions in the failure area differ from those occurring along the rest of the quay wall by the presence of a very soft silt/clay layer, and during construction the wall had been strengthened in this area. Post-failure analysis of the anchored bulkhead indicated that the primary cause of the failure was overly optimistic design assumptions for the strength of the silt/clay layer and mobilization of passive pressure. The effects of certain construction methods employed and the settlement of the silt/clay were contributing factors in the failure. A relieving platform constructed one year after the failure was designed for the original undrained strength of the silt/clay, without taking into account the effects of soil consolidation and strength gains which had occurred

Feasibility study for a Scanning Celestial Attitude Determination System /SCADS/ for three axis attitude determination at a Command and Data Acquisition /CDA/ station Final report

Scanning Celestial Attitude Determination System /SCADS/ for three axis attitude determination at Command and Data Acquisition /CDA/ statio

Rubber friction on wet and dry road surfaces: the sealing effect

Rubber friction on wet rough substrates at low velocities is typically 20-30% smaller than for the corresponding dry surfaces. We show that this cannot be due to hydrodynamics and propose a novel explanation based on a sealing effect exerted by rubber on substrate "pools" filled with water. Water effectively smoothens the substrate, reducing the major friction contribution due to induced viscoelastic deformations of the rubber by surface asperities. The theory is illustrated with applications related to tire-road friction.Comment: Format Revtex 4; 8 pages, 11 figures (no color); Published on Phys. Rev. B (http://link.aps.org/abstract/PRB/v71/e035428); previous work on the same topic: cond-mat/041204

Rubber friction on (apparently) smooth lubricated surfaces

We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short wavelength roughness, which may give the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the substrate surface asperities. The presented results are of great importance for rubber sealing and other rubber applications involving (apparently) smooth surfaces.Comment: 7 pages, 15 figure

Rubber friction on smooth surfaces

We study the sliding friction for viscoelastic solids, e.g., rubber, on hard flat substrate surfaces. We consider first the fluctuating shear stress inside a viscoelastic solid which results from the thermal motion of the atoms or molecules in the solid. At the nanoscale the thermal fluctuations are very strong and give rise to stress fluctuations in the MPa-range, which is similar to the depinning stresses which typically occur at solid-rubber interfaces, indicating the crucial importance of thermal fluctuations for rubber friction on smooth surfaces. We develop a detailed model which takes into account the influence of thermal fluctuations on the depinning of small contact patches (stress domains) at the rubber-substrate interface. The theory predicts that the velocity dependence of the macroscopic shear stress has a bell-shaped f orm, and that the low-velocity side exhibits the same temperature dependence as the bulk viscoelastic modulus, in qualitative agreement with experimental data. Finally, we discuss the influence of small-amplitude substrate roughness on rubber sliding friction.Comment: 14 pages, 16 figure

Blending HF Radar and Model Velocities in Monterey Bay Through Normal Mode Analysis

Nowcasts of the surface velocity field in Monterey Bay are made for the period August 1-9, 1994, using HF radar observations blended with results from a primitive equation model. A spectral method called normal mode analysis was used. Objective spatial and temporal filtering were performed, and stream function, velocity potential, relative vorticity, and horizontal divergence were calculated over the domain. This type of nowcasting permits global spectral analysis of mode amplitudes, calculation of enstrophy, and additional analyses using tools like empirical orthogonal functions. The nowcasts reported here include open boundary flow information from the numerical model. Nowcasts using no open boundary flow information, however, still provide excellent results for locations within the observation footprint. This method, then, is useful for filtering high-resolution data like HF radar observations, even when open boundary flow information is unavailable. Also, since the nowcast velocity gradient fields were much less noisy than the observations, this may be an effective method for preconditioning high-resolution observation sets for assimilation into a numerical model. Copyright 2000 by the American Geophysical Union

Numerical Simulation of Mixing Enhancement in a Hot Supersonic Jet

Experimental observations show that the presence of small tabs on the edge of a hot, compressible jet exiting into a slower moving, colder ambient flow can increase the rate of spreading of the jet. This suggests that the rate of mixing of the jet and the ambient fluid is also increased. In order to elucidate the physical mechanism responsible for the increased spreading rate a set of calculations were carried out within the framework of the compressible three dimensional Navier-Stokes equations. A series of grid refinements were made to assess the accuracy of the results. The first simulated the flow without the tabs, obtaining reasonable agreement with experimental measurements of the velocity. We then simulated the flow, without tabs, over a range of values of the convective Mach number in order to determine the dependence of the mixing on this parameter. Simulations with modeled tabs were also carried out. In these calculations the effect of the tabs on the flow was modeled by pairs of counter rotating vortices. The results of these calculations indeed show that the presence of the tabs increase the spreading rate of the jet. The basic physical mechanism responsible for the enhanced spreading rate is discussed and qualitative comparisons with flow visualizations are made