Structural design for dynamic response reduction

A computer program for redesigning structural modes to reduce response has been initiated. The linear regulator approach in modal coordinates has been implemented. It is noted that the transformation of solution to physical structure is a major problem. It is concluded that the solution of stiffness equations and damping equations can be done separately as NXN set of (matrix Riccati) equations

Structures and Materials Working Group report

The appropriateness of the selection of four issues (advanced materials development, analysis/design methods, tests of large flexible structures, and structural concepts) was evaluated. A cross-check of the issues and their relationship to the technology drivers is presented. Although all of the issues addressed numerous drivers, the advanced materials development issue impacts six out of the seven drivers and is considered to be the most crucial. The advanced materials technology development and the advanced design/analysis methods development were determined to be enabling technologies with the testing issues and development of structural concepts considered to be of great importance, although not enabling technologies. In addition, and of more general interest and criticality, the need for a Government/Industry commitment which does not now exist, was established. This commitment would call for the establishment of the required infrastructure to facilitate the development of the capabilities highlighted through the availability of resources and testbed facilities, including a national testbed in space to be in place in ten years

Closed-form solutions for linear regulator design of mechanical systems including optimal weighting matrix selection

Vibration in modern structural and mechanical systems can be reduced in amplitude by increasing stiffness, redistributing stiffness and mass, and/or adding damping if design techniques are available to do so. Linear Quadratic Regulator (LQR) theory in modern multivariable control design, attacks the general dissipative elastic system design problem in a global formulation. The optimal design, however, allows electronic connections and phase relations which are not physically practical or possible in passive structural-mechanical devices. The restriction of LQR solutions (to the Algebraic Riccati Equation) to design spaces which can be implemented as passive structural members and/or dampers is addressed. A general closed-form solution to the optimal free-decay control problem is presented which is tailored for structural-mechanical system. The solution includes, as subsets, special cases such as the Rayleigh Dissipation Function and total energy. Weighting matrix selection is a constrained choice among several parameters to obtain desired physical relationships. The closed-form solution is also applicable to active control design for systems where perfect, collocated actuator-sensor pairs exist

Myth Protagonist X

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The Influence of Dams on Downstream Larval and Juvenile Fish and Benthic Macroinvertebrate Community Structure and Associated Physicochemical Variables

The Influence of Dams on Downstream Larval and Juvenile Fish and Benthic Macroinvertebrate Community Structure and Associated Physicochemical Variables R. Daniel Hanks The influence of dams on downstream biotic and abiotic components of aquatic ecosystems has been largely studied within the context of the River Continuum (RCC) and Serial Discontinuity Concepts (SDC). Few of these studies have sufficiently studied how these variables change along the longitudinal gradient below the impoundments in a systematic manner, comparing equal distances below both epilimnetic and hypolimnetic dams to a reference condition. This is especially true of early life stages of fish (i.e., larval and juvenile stages) and macroinvertebrate functional groups. Here, we systematically evaluated the effects of dams at 16 sites downstream of dams for their impact on physicochemical (instream habitat [e.g., substrate, flow, etc.] and water quality [i.e., DO, pH, conductivity, and temperature], and landcover [i.e., % forested land, % developed land, and % grassland]) and various metrics for larval and juvenile fish and benthic macroinvertebrates.;Effective capture of larval and juvenile fish was paramount for the evaluation of dam influences on larval and juvenile. Sampling larval fish at various life stages can be difficult in shallow, structurally and spatially diverse streams. We evaluated three commonly employed methods (light traps, drift nets, and spot-and-sweep) for sampling larval fish in these systems. We found the spot-and-sweep method captured a higher abundance of larvae than either drift nets or light traps during both daytime and nighttime hours. Additionally the spot-and-sweep method captured as many different taxa as drift nets and more than light traps. The coefficient of variation was lower for spot-and-sweep than for either drift nets or light traps for both taxa richness and larval abundance. Richness for daytime and nighttime spot-and-sweep sampling was equal. Mean richness was also equal between the two periods, and mean CPUE was not significantly different between periods. The coefficient of variation was lowest for daytime spot-and-sweep sampling, suggesting it was less variable than nighttime sampling. The spot-and-sweep method showed promise for determining taxa presence and relative abundance. Discrepancies in the ability of personnel while performing spot-and-sweep sampling was investigated and found to be insignificant. Of the three methods evaluated for sampling structurally complex and spatially heterogeneous streams the spot-and-sweep method was found to be the most effective. We investigated the effects of dams on downstream larval and juvenile fish. Generalized additive models indicated that there was a general increase in abundance, genus richness, and Shannon diversity associated with increasing distance from dams. Principal component analysis (PCA) indicated three influential PC\u27s that were structured by landcover, habitat and water quality, and disturbance. Nonmetric multidimensional scaling (NMDS) indicated larval and juvenile fish communities were structured differently between epilimnetic and hypolimnetic releases and that habitat variables structuring those communities were more variable in epilimnetic releases than hypolimnetic releases. We systematically evaluated both the abiotic and biotic (i.e., benthic macroinvertebrates at the family level) along the stream continuum below impoundments with both epilimnetic and hypolimnetic releases and compared those findings to a reference stream. Generalized additive models (GAMs) identified six habitat variables (i.e., substrate coarseness, substrate diversity, pH, temperature, stream width, and stream depth) as significantly related to distance from dam. GAMs also indicated that abundance was not significantly related to distance from dam but both family level richness and Shannon diversity exhibited significant increases with increasing distance from dams. We evaluated patterns of changes in physicochemical and macroinvertebrate functional group components of aquatic systems along the longitudinal gradient below dams and compared changes in these variables to an undammed reference stream. Generalized additive models indicated that genus richness, functional richness, tolerance, dispersal, percent five dominant genera, EPT, and GLIMPSS were lower in dammed streams than in our reference stream. Genus and functional richness, percent 5 dominant genera, EPT, and GLIMPSS all increased as distance from dams increased while they remained relatively consistent within our reference stream. Tolerance and dispersal changed with distance from dams in dammed streams but showed little change in our reference stream. Percent composition of functional groups was different between dammed and reference streams; in dammed streams the percent composition changed with increasing distance from dams, but remained relatively stable in our reference stream. Genus and functional richness also exhibited two distinct gradients within the 5,100-m that we sampled below dams where a short, rapidly changing gradient existed immediately below dams to approximately 2,000-m, followed by a more gradual steadily increasing gradient that appeared to continue beyond our most distant sampling location below dams (i.e., 5,100-m). Important explanatory variables that varied in statistical significance between response variables but were commonly significant with distance from dams was substrate coarseness and percent forested land. Eighty five percent of our measured abiotic variables below dams had higher r values where curvilinear relationships were modeled as compared to linear relationships; whereas only 46% of the biotic variables had higher r values with curvilinear models. Nonmetric multidimensional scaling (NMDS) confirmed our GAM results indicating benthic macroinvertebrates below dams show structural changes along the stream continuum.;In all cases (larval and juvenile fish, family level aquatic macroinvertebrates, and genus level aquatic macroinvertebrate metrics) our findings generally agreed with the SDC but future studies should aim to sample in a spatially systematic manner, as this will improve our understanding of how dams influence abiotic and biotic components of aquatic systems. Additionally, our studies consistently indicated two gradients existed for most biotic measures. We believe further studies are required to understand the two recovery gradients that exist below dams and the extent of dam influences along the stream continuum

NASA'S controls-structures interaction program

A NASA program is about to start which has the objective to advance Controls-Structures Interaction (CSI) technology to a point where it can be used in spacecraft design for future missions. Because of the close interrelationships between the structure, the control hardware, and the analysis/design, a highly interdisciplinary activity is defined in which structures, dynamics, controls, computer and electronics engineers work together on a daily basis and are co-located to a large extent. Methods will be developed which allow the controls and structures analysis and design functions to use the same mathematical models. Hardware tests and applications are emphasized and will require development of concepts and test methods to carry out. Because of a variety of mission application problem classes, several time-phased, focus ground test articles are planned. They will be located at the Langley Researdh Center (LaRC), the Marshall Space Flight Center (MSFC) and at the Jet Propulsion Laboratory (JPL). It is anticipated that the ground tests will be subject to gravity and other environmental effects to the extent that orbital flights tests will be needed for verification of some technology items. The need for orbital flight experiments will be quantified based on ground test results and mission needs. Candidate on-orbit experiments will be defined and preliminary design/definition and cost studies will be carried out for one or more high-priority experiments

The Elmore Ranch and Superstition Hills earthquakes of 24 November 1987: Introduction to the special issue

On 24 November 1987, two significant earthquakes occurred along the southern San Jacinto fault zone and related structural elements in southern California, not far from the International Border. These two events, the Elmore Ranch earthquake (M = 6.2 at 0154 GMT) and the Superstition Hills earthquake (M = 6.6 at 1315 GMT, both moment magnitudes from Sipkin, 1989), and their aftershocks have yielded a rich harvest of geological, seismological, and engineering data pertinent to the cause and effect of earthquakes in this region, where the southern San Jacinto fault zone enters the Salton Depression from the Peninsula Ranges bordering it on the southwest (Fig. 1). This special issue of the Bulletin presents 18 geologic and seismologic investigations of these earthquakes, a collection of papers born in El Centro, California, on 8 and 9 February 1988 at a meeting attended by approximately 60 scientists interested in these earthquakes for one reason or another

Beyond Survival: Reshaping Entrepreneurial Vision In Successful Growing Ventures

This paper addresses the role of vision in the management of organization growth. Effective growth management requires that founders/executives envision the firm as a larger entity and anticipate critical changes which will need to occur. A five part strategy for expanding entrepreneurial vision in the growing firm is proposed. Elements of that strategy are as follows:  (a) get to know the territory, (b) recognize that change is inevitable, (c) revise your vision in· anticipation of increased size, (d) update your business plan, and (e) share the vision at every appropriate  opportunity