The effect of friction in the hold down post spherical bearings on hold down post loads

The effect of friction at the connection of the Solid Rocket Booster (SRB) aft skirt and the mobile launch platform (MLP) hold down posts was analyzed. A simplified model of the shuttle response during the Space Shuttle Main Engine (SSME) buildup was constructed. The model included the effect of stick-slip friction for the rotation of the skirt about the spherical bearing. Current finite element models assume the joint is completely frictionless in rotation and therefore no moment is transferred between the skirt and the hold down posts. The model was partially verified against test data and preliminary parameter studies were performed. The parameter studies indicated that the coefficient of friction strongly influenced the moment on the hold down posts. The coefficient of friction had little effect on hold down post vertical loads, however. Further calibration of the model is necessary before the effect of friction on the hold down post horizontal loads can be analyzed

Using probabilistic analysis to assess the reliability of predicted SRB aft-skirt stresses

Probabilistic failure analysis is a tool to predict the reliability of a part or system. Probabalistic techniques were used to predict critical stresses which occur in the solid rocket booster aft-skirt during main engine buildup, immediately prior to lift-off. More than any other hold down post (HDP) load component, the Z loads are sensitive to variations in strains and calibration constants. Also, predicted aft-skirt stresses are strongly affected by HDP load variations. Therefore, the instrumented HDP are not effective load transducers for Z loads, and, when used with aft skirt stress indicator equations, yield estimates with large uncertainty. Monte Carlo simulation proved to be a straight forward way of studying the overlapping effects of multiple parameters on predicted equipment performance. An advantage of probabilistic analysis is the degree of uncertainty of each parameter as stated explicitly by its probability distribution. It was noted, however, that the choice of parameter distribution had a large effect on the simulation results. Many times these distributions must be assumed. The engineer who is designing the part should be responsible for the choice of parameter distribution

REGIONAL COTTON ACREAGE RESPONSE

An econometric model of cotton acreage response was estimated for four distinct production regions in the United States. This work builds on previous work in the area of supply response under government farm programs and provides up-to-date regionalized estimates of own-price elasticity of cotton acreage supply. The own-price variable used in this study is a weighted combination of expected market price and government policy variables. Results indicate regional similarity in response to own price but differences with respect to the prices of alternative enterprises. Differences in regional response to paid diversion are also indicated.Crop Production/Industries,

EFFECTS OF ALTERNATIVE FARM PROGRAMS AND LEVELS OF PRICE VARIABILITY ON TEXAS COTTON FARMS

This study examines the effects of alternative government farm programs and hypothetical price variability levels on two Texas cotton farms which were simulated stochastically over a 10-year period. Results indicate that a combination of high price variability and participation in government programs stimulates growth and wealth accumulation.Public Economics,

DISTRIBUTION CHOICE UNDER NULL PRIORS AND SMALL SAMPLE SIZE

Defining appropriate probability distributions for the variables in an economic model is an important and often arduous task. This paper evaluates the performance of several common probability distributions under different distributional assumptions when sample sizes are small and there is limited information about the data.Research Methods/ Statistical Methods,

ECONOMETRIC MODEL OF THE U.S. SHEEP INDUSTRY FOR POLICY ANALYSIS

The U.S. sheep inventory has been declining for many years. To further investigate this trend, an econometric sector model using single demand equations was developed to analyze the impacts of two alternative levels of wool marketing loan rates.Marketing,

INCORPORATING GOVERNMENT PROGRAM PROVISIONS INTO A MEAN-VARIANCE FRAMEWORK

E-V studies traditionally have relied on historical data to calculate returns and variance. Historical data may not fully reflect current conditions, particularly when decisions involve government-supported crops. This paper presents a method for calculating mean and variance using subjectively-estimated data. The method is developed for both government-supported and non-program crops. Comparisons to alternative methods suggest the approach provides reasonable accuracy.Agricultural and Food Policy,