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During the past two decades the occurrence of ice accretion within commercial high bypass aircraft turbine engines under certain operating conditions has been reported. Numerous engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion such as degraded engine performance, engine roll back, compressor surge and stall, and even flameout of the combustor. As ice crystals are ingested into the engine and low pressure compression system, the air temperature increases and a portion of the ice melts allowing the ice-water mixture to stick to the metal surfaces of the engine core. The focus of this paper is on estimating the effects of ice accretion on the low pressure compressor, and quantifying its effects on the engine system throughout a notional flight trajectory. In this paper it was necessary to initially assume a temperature range in which engine icing would occur.

Unlike a terrestrial electric utility which can purchase power from a neighboring utility, the Space Station Freedom (SSF) has strictly limited energy resources; as a result, source control, system monitoring, system protection and load management are essential to the safe and efficient operation of the SSF Electric Power System (EPS). These functions are being evaluated in the DC Power Management and Distribution (PMAD) Testbed which NASA LeRC has developed at the Power System Facility (PSF) located in Cleveland, Ohio. The testbed is an ideal platform to develop, integrate, and verify power system monitoring and control algorithms. State Estimation (SE) is a monitoring tool used extensively in terrestrial electric utilities to ensure safe power system operation.

The process of reducing a physical system to a mathematical representation is a prevalent task mutual to all fields of analysis. Sometimes the system of equations, or mathematical model as commonly known, will be modified on a trial and error basis to make the model respond in some predetermined fashion or react so as to match behavioral data obtained from the actual physical system. This paper presents a survey of activities to produce logically based schemes to generate mathematical models by making use of experimentally derived information. Primary attention is given to modeling of mechanical structures for purposes of dynamic analysis. Emphasis is given to current effort at Goddard and in particular to the recent studies designed to verify the practical effectiveness of a specific modeling scheme. Strengths and weaknesses of the various modeling schemes are discussed.