Propellant-powered actuator for gas generators

Hydrazine operated monopropellant generators are used for spacecraft rocket engines and propellant pressurization systems. Measured work output of monopropellant actuators compares favorably with output of squib-type actuators

Ferromagnetic-fluid logic devices

Logic element switches flows of low pressure process control fluid in fluidics assemblies. Device operates both electrically and fluidically and is controlled by passing permanent magnet or electromagnet over elements, thus providing proximity switching functions

Nitrogen tetroxide flow decay study for the Orbital Workshop Propulsion System Final report

Flow decay of nitrogen tetroxide in Orbital Workshop Propulsion Syste

HOPDM Modular Solver for LP Problems User's Guide to version 2.12

The paper provides a description of HOPDM, a library of routines for solving large scale linear programming problems and its implementation at IIASA. HOPDM stands for Higher Order Primal Dual Method. The algorithm implemented in HOPDM is a new variant of a primal-dual logarithmic barrier method that uses multiple correctors of centrality. The newest version of the library -- HOPDM 2.12 -- is a robust and efficient LP code that compares favorably with the up to date commercial solvers. The paper contains an outline of the algorithm implemented in HOPDM and information about results of tests done with large LP problems developed at IIASA. Finally, the paper provides with details of the implementation of HOPDM and its use at IIASA, as well as with information about availability of the portable version of the HOPDM library

SAP- Modular Tool for Specification and Analysis of User Preferences in Multiple-Criteria Model Analysis

Model based Decision Support Systems (DSS) often use multiple-criteria optimization for selecting Pareto-efficient solutions. Such a selection is based on interactive specification of user preferences. This can be done by specification of aspiration and reservation levels for criteria. Diverse graphical user interface could be used for specification of these levels as well as for interpretation of results. In the approach presented in this paper the specified aspiration and reservation levels are used for generation of component achievement functions for corresponding criteria. Such functions can be interpreted as fuzzy membership functions or as functions, which reflect the degree of satisfaction with given values of criteria. The paper outlines the methodological background and modular structure of a DSS shell for multiple-criteria analysis of decision problems that can be represented as Linear Programming (LP) or Mixed Integer Programming (MIP) problems. The DSS shell has been used at IIASA for analysis of decision problems in water quality management and land use for sustainable development planning. The pilot implementation of one component of that DSS, namely the modular software tool for interactive specification of user preferences is described in more detail. The tool has been also used as in a DSS for analysis of non-linear problems in several engineering applications

Solving a Class of LP Problems with a Primal-Dual Logarithmic Barrier Method

Applying a higher order primal-dual logarithmic barrier method for solving large real-life linear programming problems is addressed in this paper. The efficiency of interior point algorithm on these problems is compared with the one of the state-of-the-art simplex code MINOS version 5.3. Based on such experience, a wide class of LP problems is identified for which logarithmic barrier approach seems advantageous over the simplex one. Additionally, some practical rules for model builders are derived that should allow them to create problems that can easily be solved with logarithmic barrier algorithms

Multicriteria Methodology for the NEEDS Project

This report begins with an overview of multicriteria analysis methods, and the basic principles of developing mathematical models for such analysis. An overview of various representation of user preferences is then presented, including methods based on pairwise comparisons of criteria and those based on scalarizing functions. This is followed by a summary of structures of criteria and alternatives. Next, basic properties of multi-criteria analysis are discussed, followed by a more detailed presentation of the similarities of and differences between the main methods based on scalarizing functions. This report concludes that existing methods do not best meet the needs of the NEEDS project, presents the reasons, and proposes a new methodology for development. Depending upon the development and testing of this new methodology, an existing method will also be chosen as a backup for comparative or alternate use

Multicriteria Methodology for the NEEDS Project

This report begins with an overview of multicriteria analysis methods, and the basic principles of developing mathematical models for such analysis. An overview of various representation of user prefereces is then presented, including methods based on pairwise comparisons of criteria and those based on scalarizing functions. This is followed by a summary of structures of criteria and alternatives. Next, basic properties of multi-criteria analysis are discussed, followed by a more detailed presentation of the similarities of and differences between the main methods based on scalarizing function. This report concludes that existing methods do not best meet the needs of the NEEDS project, presents the reasons, and proposes a new methodology for development. Depending upon the development and testing of this new methodology, an existing method will also be chosen as a backup for comparative or alternate use

Multiple Criteria Analysis of Discrete Alternatives with a Simple Preference Specification: Pairwise-outperformance based Approaches

Many methods have been developed for multiple criteria analysis and/or ranking of discrete alternatives. Most of them require complex specification of preferences. Therefore, they are not applicable for problems with numerous alternatives and/or criteria, where preference specification by the decision makers can hardly be done in a way acceptable for small problems, e.g., for pair-wise comparisons. In this paper we describe several new methods implemented for a real-life application dealing with muti-criteria analysis of future energy technologies. This analysis involves large numbers of both altrnatives and criteria. Moreover, the analysis was made by a large number of stakeholders without expeience in analytical methods. Therefore, a simple method for interactive preference specification was a condition for the analysis. The paper presents a number of new methods based on the developed out performance aggregations that take into account inter-alternative factors. Finally, a comparison of methods and experience of using them is discussed

User Guide to MCA: Multiple Criteria Analysis of Discrete Alternatives with a Simple Preference Specification

This report provides detailed information about using the MCA, which is the Web-based application formultiple criteria analysis of discrete alternatives with a simple preference specification. MCA in its currently available version supports analysis of a set of discrete alternatves, defined either interactively or through a prepared file. Each alternative is characterized by several attributes (indicators) that serve for specification of criteria. MCA has been designed for problems having large numbers of alternatives and of criteria. However, it can also be used for problems with small numbers of criteria and/or alternatives. The report is composed of two main parts. The first one provides an overview of the MCA and summarize the methodology of multiple criteria analysis implemented in the MCA. The second part consists of the step-by-step detailed tutorial to the MCA organized into three stages corresponding to (1) basic funtions of the MCA, (2) specification of problems, instances, and analyses, and (3) interactive multiciteria analysis process