Controlling flexible structures: A survey of methods

Most of the presently available control system design techniques applicable to flexible structure problems were developed to design controllers for rigid body systems. Although many of these design methods can be applied to flexible dynamics problems, recently developed techniques may be more suitable for flexible structure controller design. The purpose of this presentation is to examine briefly the peculiarities of the dynamics of flexible structures and to stimulate discussion about top level controller design approaches when designing controllers for flexible structures. Presented here is a suggestion of a set of categories of design methods for designing controllers for flexible structures as well as a discussion of the advantages and disadvantages of each category. No attempt has been made herein to select one category of design techniques as the best for flexible structure controller design. Instead, it is hoped that the structure suggested by these categories will facilitate further discussion on the merits of particular methods that will eventually point to those design techniques suitable for further development

Modeling and control system design and analysis tools for flexible structures

Described here are Boeing software tools used for the development of control laws of flexible structures. The Boeing Company has developed a software tool called Modern Control Software Package (MPAC). MPAC provides the environment necessary for linear model development, analysis, and controller design for large models of flexible structures. There are two features of MPAC which are particularly appropriate for use with large models: (1) numerical accuracy and (2) label-driven nature. With the first feature MPAC uses double precision arithmetic for all numerical operations and relies on EISPAC and LINPACK for the numerical foundation. With the second feature, all MPAC model inputs, outputs, and states are referenced by user-defined labels. This feature allows model modification while maintaining the same state, input, and output names. In addition, there is no need for the user to keep track of a model variable's matrix row and colunm locations. There is a wide range of model manipulation, analysis, and design features within the numerically robust and flexible environment provided by MPAC. Models can be built or modified using either state space or transfer function representations. Existing models can be combined via parallel, series, and feedback connections; and loops of a closed-loop model may be broken for analysis

Design of integrated pitch axis for autopilot/autothrottle and integrated lateral axis for autopilot/yaw damper for NASA TSRV airplane using integral LQG methodology

Two designs are presented for control systems for the NASA Transport System Research Vehicle (TSRV) using integral Linear Quadratic Gaussian (LQG) methodology. The first is an integrated longitudinal autopilot/autothrottle design and the second design is an integrated lateral autopilot/yaw damper/sideslip controller design. It is shown that a systematic top-down approach to a complex design problem combined with proper application of modern control synthesis techniques yields a satisfactory solution in a reasonable period of time

Theta Dependence In The Large N Limit Of Four-Dimensional Gauge Theories

The theta dependent of pure gauge theories in four dimensions can be studied using a duality of large N gauge theories with string theory on a certain spacetime. Via this duality, one can argue that for every theta, there are infinitely many vacua that are stable in the large N limit. The true vacuum, found by minimizing the energy in this family, is a smooth function of theta except at theta equal to pi, where it jumps. This jump is associated with spontaneous breaking of CP symmetry. Domain walls separating adjacent vacua are described in terms of wrapped sixbranes.Comment: 8 p

Systematic Approach To Case Recertification

LecturePg. 133-138Turbomachinery life expectancy, economic conditions, and plant capacity enhancements have created a need for vintage compressors to be reevaluated and re-engineered for operational parameters that may not have been incorporated in the original design. Aerodynamic revamps have been standard practice for optimizing flow conditions to today's processes. These changeouts have traditionally been limited to manipulation within designed pressure ratings. Recently, in addition to the aerodynamic enhancements, processes are requiring increased pressure levels. These new requirements and requests have posed questions and concerns which have not been of predominant importance previously. Integrity of the containment vessel, leakage of process gases, condition, and life expectancy at above design conditions must be addressed to make an informed comparison between a rerate and purchase of replacement equipment. The hazards and possible expenses of operating turbomachinery above rated pressures without a systematic and consistent verification process should be avoided. Hence, a new field has been undertaken by OEMs driven by equipment user request, to certify existing casings at increased levels in the safest and most reliable manner. The following guidelines have been produced to conduct such rerates with minimal risk to the compressor case and thus, the processes in which these machines play an intricate part: • Specific case testing history • Examine records and designs to determine if the casing has been hydrotested previously, or has been hydrotested to appropriate new condition levels. • Review of similar vintage machinery • Review designs of similar machines built in the same era to determine if ratings have ever been within appropriate levels. • Analyze the specific case design • Analyze the case with the use of modem and proven finite element methods to verify the integrity of the case design at elevated pressures based on blueprint dimensions. Review data with the user, discussing concerns of both parties and come to a consensus whether a hydrotest is feasible. • Inspect and review • Inspect the case per manufacturing blueprints to verify thickness and overall condition of the case and continuity of FEA model. With the use of magnetic particles, inspect the casing for indications and discontinuities which could endanger the casing during the hydrotest. Review the data and determine if continuation of testing is feasible. • Strain gauge casing • Place strain gauge equipment at key high stress locations based on FEA model to protest casing during hydrotesting. • Hydrotest case • With online strain readings, hydrotest casing to the appropriate levels. Carefully monitor the strain data to protect the casing from going beyond prescribed stress levels at the desired pressure levels. If stress levels appear to be approaching recommended limits, consensus should be made on whether to continue. • Recertification • After a successful hydrotest, rerate the compressor name plate and records for the new pressure level. The following paper will use a case history as a step by step example to show how case recertification has been accomplished in the safest possible manner with minimal risk to equipment

Systematic review of prediction models for gestational hypertension and preeclampsia.

INTRODUCTION: Prediction models for gestational hypertension and preeclampsia have been developed with data and assumptions from developed countries. Their suitability and application for low resource settings have not been tested. This review aimed to identify and assess the methodological quality of prediction models for gestational hypertension and pre-eclampsia with reference to their application in low resource settings. METHODS: Using combinations of keywords for gestational hypertension, preeclampsia and prediction models seven databases were searched to identify prediction models developed with maternal data obtained before 20 weeks of pregnancy and including at least three predictors (Prospero registration CRD 42017078786). Prediction model characteristics and performance measures were extracted using the CHARMS, STROBE and TRIPOD checklists. The National Institute of Health quality assessment tools for observational cohort and cross-sectional studies were used for study quality appraisal. RESULTS: We retrieved 8,309 articles out of which 40 articles were eligible for review. Seventy-seven percent of all the prediction models combined biomarkers with maternal clinical characteristics. Biomarkers used as predictors in most models were pregnancy associated plasma protein-A (PAPP-A) and placental growth factor (PlGF). Only five studies were conducted in a low-and middle income country. CONCLUSIONS: Most of the studies evaluated did not completely follow the CHARMS, TRIPOD and STROBE guidelines in prediction model development and reporting. Adherence to these guidelines will improve prediction modelling studies and subsequent application of prediction models in clinical practice. Prediction models using maternal characteristics, with good discrimination and calibration, should be externally validated for use in low and middle income countries where biomarker assays are not routinely available

Developing a pressure ulcer risk factor minimum data set and risk assessment framework

AIM: To agree a draft pressure ulcer risk factor Minimum Data Set to underpin the development of a new evidenced-based Risk Assessment Framework.BACKGROUND: A recent systematic review identified the need for a pressure ulcer risk factor Minimum Data Set and development and validation of an evidenced-based pressure ulcer Risk Assessment Framework. This was undertaken through the Pressure UlceR Programme Of reSEarch (RP-PG-0407-10056), funded by the National Institute for Health Research and incorporates five phases. This article reports phase two, a consensus study.DESIGN: Consensus study.METHOD: A modified nominal group technique based on the Research and Development/University of California at Los Angeles appropriateness method. This incorporated an expert group, review of the evidence and the views of a Patient and Public Involvement service user group. Data were collected December 2010-December 2011.FINDINGS: The risk factors and assessment items of the Minimum Data Set (including immobility, pressure ulcer and skin status, perfusion, diabetes, skin moisture, sensory perception and nutrition) were agreed. In addition, a draft Risk Assessment Framework incorporating all Minimum Data Set items was developed, comprising a two stage assessment process (screening and detailed full assessment) and decision pathways.CONCLUSION: The draft Risk Assessment Framework will undergo further design and pre-testing with clinical nurses to assess and improve its usability. It will then be evaluated in clinical practice to assess its validity and reliability. The Minimum Data Set could be used in future for large scale risk factor studies informing refinement of the Risk Assessment Framework

Scanning Electron Microscopy Analysis of Polyethylene Oxide Hydrogels for Blood Contact

Hydrogels are a class of synthetic material, composed of a polymer-water matrix and have been proposed as tissue substitutes and drug delivery vehicles. Polyethylene oxide (PEO) hydrogels were synthesized and used to produce coated wires and conduits for baboon blood compatibility studies. Blood-material interactions were studied both by Scanning Electron Microscopy (SEM) and 111In labeled platelet deposition. SEM processing modifications were first evaluated in order to reduce shrinkage and surface distortion incurred during sample preparation of these high water content materials. Pretreatment with 1% tannic acid reduced bulk shrinkage associated with critical point drying by 10-20%. This effect is small, nevertheless, it prevented major sample disruption. Coated guidewires were exposed to baboon blood for one hour in the inferior vena cava and conduits were placed for either 30 or 60 minutes in an ex vivo femoral arteriovenous shunt. Reference materials included Gore-tex®, polyethylene and silica-free polydimethyl siloxane (PDMS). In the guidewire studies, 111In labeled platelet levels were highest on Gore-tex® (6568.97 platelets/ 1000 μm2) and large thrombotic deposits were well visualized by SEM. Formulations containing PEO had low levels of platelet deposition and little evidence of platelet activation was noted by SEM. Shunt studies demonstrated that materials of high PEO content and molecular weight had the lowest levels of platelet deposition. After 60 minutes of blood flow, mean platelet deposition on PDMS and Gore-tex® was 50 and 1000 fold higher than on a network composed of 65% PEO 20,000 (p \u3c 0.05). SEM confirmed these findings

Salamanders

12 p. : ill. ; 24 cm.Includes bibliographical references (p. 11-12)