Linearized Theory of a Partially Cavitating Plano-Convex Hydrofoil Including the Effects of Camber and Thickness

The linearized treatment of the flow over a partially cavitating single hydrofoil having a flat pressure surface and a circular-arc suction side is presented. The flow is treated as a two-dimensional, steady, inviscid flow. Further assumptions made are those of incompressibility and irrotationality. The results obtained are compared with experiment and generally good correlation is found for the ranges of validity of the linearization

MARKET STRUCTURE AND SPATIAL PRICE DYNAMICS

A method was developed with time series models to test hypotheses about the relationship between market structure and spatial price dynamics. Long-run dynamic multipliers measuring the magnitude of lagged adjustments for spatial milled rice prices were calculated from the time series model and used as the dependent variable in a regression model that included a number of factors expected to influence price determination. Results show that price adjustments were slower as regional submarket concentration increased and were faster in the regions with a higher market share. Arkansas, the state with the largest market share, was consistently a price leaderDemand and Price Analysis, Industrial Organization,

SOME EFFECTS OF RICE QUALITY ON ROUGH RICE PRICES

Quality discounts and premiums for rough rice in Texas rice bid/acceptance markets are analyzed. The most important quality factors determining the value of rough rice are head yield and peck. A one percentage point reduction in peck damage raises the price received per hundredweight of rough rice by $.13 to$.68 across markets and years. Since peck damage can be reduced by controlling the rice stinkbug, evaluation of alternative methods for better control of this pest in Texas rice fields is needed.Demand and Price Analysis,

The Value of Regional Annual Nitrogen Needs Information for Wheat Producers in Oklahoma

Crop producers are increasingly interested in reducing nitrogen use without sacrificing yield. Technology is available for precise application at the sub-field level, but adoption has been sluggish. This paper estimates the relative profitability of a field level annual predictor of mid-season N requirements and a regional predictor of the same.nitrogen seeds, nitrogen use efficiency, precision agriculture, wheat, Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,

The results of an agricultural analysis of the ERTS-1 MSS data at the Johnson Space Center

The initial analysis of the ERTS-1 multispectral scanner (MSS) data at the Johnson Space Center (JSC), Houston, Texas is discussed. The primary data set utilized was the scene over Monterey Bay, California, on July 25, 1972, NASA ERTS ID No. 1002-18134. It was submitted to both computerized and image interpretative processing. An area in the San Joaquin Valley was submitted to an intensive evaluation of the ability of the data to (1) discriminate between crop types and (2) to provide a reasonably accurate area measurement of agricultural features of interest. The results indicate that the ERTS-1 MSS data is capable of providing the identifications and area extent of agricultural lands and field crop types

IMPACTS OF PRICE VARIABILITY ON MARKETING MARGINS AND PRODUCER VIABILITY IN THE TEXAS WHEAT INDUSTRY

The effects on marketing margins and Texas what producers of shifting from a period with stable prices to a period without stable prices were investigated using both econometric and simulation techniques. Empirical evidence reveals wheat export firms are risk averse and that either futures markets were unable to absorb increased price risk or futures markets absorbed increased price risk at a cost of $0.054 per bushel. Increased variability in prices and reduced farm program benefits substantially reduced the probability of Texas wheat producers receiving a reasonable return on equity and a reasonable rate of asset accumulation.Crop Production/Industries, Marketing,

Experimental Study of Cavitating Hydrofoils in Cascade

Liquid filled hydraulic systems often operate in such a way that cavitation may take place in one or more of the components of the system. Most often the cavitation will take place in a pump or a turbine as the liquid velocity there is usually greatest in these devices. However, cavitation can also occur in bends or elbows or constrictions in the system, such as a venturi tube. When cavitation does take place, the region occupied by the cavitation process displaces liquid that was formerly there, creating in a sense a "reservoir", the volume of which depends upon the extent of the cavitation. In every case the amount of cavitation in any type of hydraulic device will increase as the system pressure is lowered. The liquid that has been displaced causes changes in the motion of the fluid throughout the system causing or requiring time-varying pressure gradients to occur. In most practical hydraulic systems in which cavitation can occur, these transient pressure changes die away and the liquid flow system operates about some steady mean value. Indeed, for some applications cavitation is deliberately introduced into the system in such a way as to cause the flowing system to operate at a steady, stable condition

Experimental Observations on the Flow Past a Plano-Convex Hydrofoil

Some new measurements and observations on the noncavitating and cavitating flow past a plano-convex hydrofoil are presented. Under some conditions of partial cavitation, strong, periodic oscillations both in the cavity length and forces exerted on the hydrofoil are observed. The reduced frequency of oscillation depends upon the cavitation number and angle of attack; it also depends somewhat on tunnel speed for the lower angles of attack but becomes substantially independent of speed for the highest angle. The peak-to-peak magnitude of the force oscillation can amount to about 20 percent of the average force

Investigation of Cavitating Cascades

Experiments on cavitating and noncavitating cascades were carried out in a conventional water tunnel modified for this purpose. The comparison of the experimental results with theory, in both the fully wetted and fully cavitating conditions, was found to be satisfactory

Selectively Ventilated Ring Wing Hydrofoils

Experiments were made on a ring wing having a chord-diameter ratio of one-half with a profile section consisting of a 10 percent Clark Y airfoil. Measurements were made of the force characteristics of this ring wing in fully wetted flow for several Reynolds numbers and angles of attack; in fully wetted flow these observations agreed with similar previous results on fully wetted ring wings. A portion of the circumference of the ring was also ventilated by the controlled injection of air to provide a cross-force. The magnitude of this cross-force varies with extent of ventilation and with the rate of injection of air. With less than approximately 11 percent of the trailing edge of the wing so ventilated, the cross-force corresponds to the wing in fully wetted flow having an angle of attack of nearly three degrees. Experiments were also made on the rapidity with which this cross-force could be built up at the start of injection or terminated after the ventilation had been established. The termination of the cross-force is very quick and amounts to a time approximately required for the flow to travel a distance of a few wing chords. The build-up process on the other hand is considerably slower, and it appears to be a dynamic one but the scaling laws for this phenomenon are not yet established