IMAT graphics manual

The Integrated Multidisciplinary Analysis Tool (IMAT) consists of a menu driven executive system coupled with a relational database which links commercial structures, structural dynamics and control codes. The IMAT graphics system, a key element of the software, provides a common interface for storing, retrieving, and displaying graphical information. The IMAT Graphics Manual shows users of commercial analysis codes (MATRIXx, MSC/NASTRAN and I-DEAS) how to use the IMAT graphics system to obtain high quality graphical output using familiar plotting procedures. The manual explains the key features of the IMAT graphics system, illustrates their use with simple step-by-step examples, and provides a reference for users who wish to take advantage of the flexibility of the software to customize their own applications

Rate of Swelling of Vacuum-Impregnated Wood

The swelling rate of wood wafers vacuum-impregnated with water and other swelling agents was measured by a videotaping technique. After an initial period of inhibited swelling, the rate of swelling could be described quantitatively by a simple membrane Fickian diffusion model for solvent penetration into the wood cell walls. Diffuse porous aspen swelled more slowly than red pine as a result of differences in initial distribution of solution in the wood tissue. In red pine, swelling rate increased with increasing degree of saturation of the wood void space, while in aspen the swelling rate was not related to solution absorption. Wood relative density did not affect swelling rate significantly over the range of densities tested. Increased solution temperature had the expected effect of increased swelling rate. The estimated activation energy for bound water diffusion inducing swelling depended on the direction of swelling and the treating solution and ranged from 26.4 to 41.6 kJ/mole. Treatment with 8% monoammonium phosphate (MAP) resulted in slower swelling rates compared to water and 10% polyethylene glycol (PEG) treated wafers under most conditions. The organic swelling solvents dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) initially swelled wood much more slowly than water

Sensitivity of Space Station alpha joint robust controller to structural modal parameter variations

The photovoltaic array sun tracking control system of Space Station Freedom is described. A synthesis procedure for determining optimized values of the design variables of the control system is developed using a constrained optimization technique. The synthesis is performed to provide a given level of stability margin, to achieve the most responsive tracking performance, and to meet other design requirements. Performance of the baseline design, which is synthesized using predicted structural characteristics, is discussed and the sensitivity of the stability margin is examined for variations of the frequencies, mode shapes and damping ratios of dominant structural modes. The design provides enough robustness to tolerate a sizeable error in the predicted modal parameters. A study was made of the sensitivity of performance indicators as the modal parameters of the dominant modes vary. The design variables are resynthesized for varying modal parameters in order to achieve the most responsive tracking performance while satisfying the design requirements. This procedure of reoptimization design parameters would be useful in improving the control system performance if accurate model data are provided

Multidisciplinary analysis of actively controlled large flexible spacecraft

The control of Flexible Structures (COFS) program has supported the development of an analysis capability at the Langley Research Center called the Integrated Multidisciplinary Analysis Tool (IMAT) which provides an efficient data storage and transfer capability among commercial computer codes to aid in the dynamic analysis of actively controlled structures. IMAT is a system of computer programs which transfers Computer-Aided-Design (CAD) configurations, structural finite element models, material property and stress information, structural and rigid-body dynamic model information, and linear system matrices for control law formulation among various commercial applications programs through a common database. Although general in its formulation, IMAT was developed specifically to aid in the evaluation of the structures. A description of the IMAT system and results of an application of the system are given

Structural dynamic interaction with solar tracking control for evolutionary Space Station concepts

The sun tracking control system design of the Solar Alpha Rotary Joint (SARJ) and the interaction of the control system with the flexible structure of Space Station Freedom (SSF) evolutionary concepts are addressed. The significant components of the space station pertaining to the SARJ control are described and the tracking control system design is presented. Finite element models representing two evolutionary concepts, enhanced operations capability (EOC) and extended operations capability (XOC), are employed to evaluate the influence of low frequency flexible structure on the control system design and performance. The design variables of the control system are synthesized using a constrained optimization technique to meet design requirements, to provide a given level of control system stability margin, and to achieve the most responsive tracking performance. The resulting SARJ control system design and performance of the EOC and XOC configurations are presented and compared to those of the SSF configuration. Performance limitations caused by the low frequency of the dominant flexible mode are discussed

Effects of CCA-C Preservative Retention and Wood Species on Fixation and Leaching of CR, CU, and AS

Fixation of chromated copper arsenate (CCA-C) preservative was investigated using ground sapwood of trembling aspen, red pine, and red maple at treatment retentions of 4.0, 6.4, 9.6, and 30 kg/m3 at 30°C. The fixation of (CCA) wood preservative differed considerably among the wood species and was affected by treatment retention, resulting in differences in subsequent leaching of the "fixed" components. For the wood species considered, the fixation times increased with increasing retention for the Cr and Cu components but decreased with increasing retention for As. Red pine and aspen had similar fixation patterns and similar leaching trends and levels of leaching losses. Red maple had significantly faster CCA fixation than red pine and aspen but had elevated Cr and As leaching. These fixation anomalies decreased with an increase in treatment retention, and after removal of hot-water-soluble extractives. It is postulated that extractives impair the quality of fixation owing to their high reducing capacity toward Cr(VI) and capability to complex Cu(II) and Cr(III). Irregular CCA fixation in red maple results in incomplete fixation of As due to reduced availability of Cr in a form that can complex As

The Incidence of Low-Metallicity Lyman-Limit Systems at z~3.5: Implications for the Cold-Flow Hypothesis of Baryonic Accretion

Cold accretion is a primary growth mechanism of simulated galaxies, yet observational evidence of "cold flows" at redshifts where they should be most efficient ($z=2$-4) is scarce. In simulations, cold streams manifest as Lyman-limit absorption systems (LLSs) with low heavy-element abundances similar to those of the diffuse IGM. Here we report on an abundance survey of 17 H I-selected LLSs at $z=3.2$-4.4 which exhibit no metal absorption in SDSS spectra. Using medium-resolution spectra obtained at Magellan, we derive ionization-corrected metallicities (or limits) with a Markov-Chain Monte Carlo sampling that accounts for the large uncertainty in $N_{\rm HI}$ measurements typical of LLSs. The metal-poor LLS sample overlaps with the IGM in metallicity and is best described by a model where $71^{+13}_{-11}\%$ are drawn from the IGM chemical abundance distribution. These represent roughly half of all LLSs at these redshifts, suggesting that 28-40$\%$ of the general LLS population at $z\sim3.7$ could trace unprocessed gas. An ancillary sample of ten LLSs without any a priori metal-line selection is best fit with $48^{+14}_{-12}\%$ of metallicities drawn from the IGM. We compare these results with regions of a moving-mesh simulation; the simulation finds only half as many baryons in IGM-metallicity LLSs, and most of these lie beyond the virial radius of the nearest galaxy halo. A statistically significant fraction of all LLSs have low metallicity and therefore represent candidates for accreting gas; large-volume simulations can establish what fraction of these candidates actually lie near galaxies and the observational prospects for detecting the presumed hosts in emission.Comment: 19 pages, 17 figures; Submitted to ApJ; Corrected figure 16

Interaction Of Wood-Protecting Anions With The Wood Cell Wall

Under normal treating conditions, anionic components of wood preservatives and fire retardants, such as arsenates and phosphates, equilibrate at much lower concentrations in the cell-wall bound water than in the free solution in the cell lumens. A degree of anion exclusion is expected in wood due to the Donnan membrane effect. Fixed anions in the wood cell wall are not free to diffuse into the lumens, resulting in limited migration of the mobile anions into the cell wall. The observed exclusion, measured as "solute free water" (δ), decreases with increasing solute concentration, as expected from Donnan exclusion effects. However, the expected pH dependence (increased exclusion with increased pH) is not observed in ammoniacal solutions. In fact, there is an apparent anomalous effect of high cell-wall penetration or reaction with basic solutions containing ammonium hydroxide. Dichromate solutions are more or less depleted from the free lumen solution, depending on the initial pH of the solution as the hexavalent chromium is reduced and fixed to the cell-wall material

Kinetic Model of CCA Fixation on Wood. Part I. The Initial Reaction Zone

The fixation process for chromated copper arsenate (CCA-C) preservative treated wood has at least two distinctly different zones. One of these is a fast "Initial Reaction," characterized by a rapid increase in pH and a decrease in available hexavalent chromium (Crvi). In the present study we develop a mathematical model that describes the initial reaction kinetics for red pine (Pinus resinosa Ait.) treated with 1% CCA-C. The results show that the initial fixation reactions follow pseudo 10th order kinetics. The activation energy and pre-exponential factors were found to be 37.8 kj.mol-1 and 8.7 X 10-19 h-1 mol-9 I9, respectively. At all treatment temperatures tested, the initial reaction resulted in approximately 47% chromium reduction. At 4° the time required to complete the initial reaction is approximately 4.5 h; at room temperature the initial reaction is complete in about 1.7 h. At 50° the initial reaction is complete in about 25 min. The complete model incorporates the rate equation, Arrhenius temperature dependence, and the fixation definition into a single equation that expresses % chromium fixation as a function of initial chromium concentration in the treating solution and time and temperature history of the wood following treatment.This model can also be used as an integral part of an overall fixation model that can be used to predict the percent fixation at a given treatment condition based on knowledge of the temperature history of the wood during fixation