ECONOMIC, ENVIRONMENTAL AND ENERGY USE IMPLICATIONS OF SHORT-SEASON COTTON PRODUCTION: TEXAS LOWER RIO GRANDE VALLEY

Crop Production/Industries,

Assessment of Buffet Forcing Function Development Process Using Unsteady Pressure Sensitive Paint

A wind tunnel test was conducted at the Ames Unitary Plan Wind Tunnel to characterize the transonic buffet environment of a generic launch vehicle forebody. The test examined a highly instrumented version of the Coe and Nute Model 11 test article first tested in the 1960s. One of the measurement techniques used during this test was unsteady pressure sensitive paint (uPSP) developed at the Arnold Engineering Development Complex. This optical measurement technique measured fluctuating pressures at over 300,000 locations on the surface of the model. The high spatial density of these measurements provided an opportunity to examine in depth the assumptions underpinning the development of buffet forcing functions (BFFs) used in the development of the Space Launch System vehicle. The comparison of discrete-measurement-based BFFs to BFFs developed by continuous surface pressure integration indicates that the current BFF development approach under predicts low frequency content of the BFFs while over predicting high frequency content. Coherence-based adjustments employed to reduce over prediction in the surface integration of discrete pressure measurements contribute to the inaccuracy of the BFFs and their implementation should be reevaluated

Irrigation- Oriented ET Models for the Great Plains

An evapotranspiration (ET) model is a mathematical expression relating the major climate, crop, and soil variables to ET. Modeling is a systematic and organized approach to solving a problem. It requires a look at the "whole picture" and not just the segments of interest. It also requires work on the entire system under natural environments and not segments of the system under artificial environments. Modeling enables researchers to develop more rigorous hypotheses before establishing experiments, thereby minimizing wasted effort and replowing old ground. The experience a researcher gains in developing a basic model for a segment of his work is invaluable since modeling requires establishing quantitative relationships, a consideration of all major variables, and long-range planning. Finally, contrary to popular opinions, models need not be extremely complex to be useful

The Importance of Large Scale Advection in Evapotranspiration from Irrigated Crops in Southern Idaho

Intensive measurements of evapotranspiration during two growing seasons show that large scale advected sensible heat is a significant source of energy to evaporation from irrigated crops in southern Idaho. Even though the site of the study was several miles from the boundary of the irrigated areas and the surrounding desert, measured latent heat flux exceeded net radiation by as much as 25%. Inversion conditions near the surface of well-watered crops having complete cover were typical throughout the day in mid- summer. The results emphasize the importance of developing a meaningful concept and measure of potential evapotranspiration for irrigated areas in arid regions and for the development of reliable methods of predicting the evapotranspiration from various crops throughout the season as the stage of maturity and crop cover changes under these arid, climatic conditions

Comparison of Estimated and Measured Daily Evapotranspiration from Irrigated Crops in Southern Idaho

Irrigation scheduling using climate-crop-soil data requires accurate estimates of daily evapotranspiration. Extensive application of this method of irrigation scheduling also requires the use of standard or readily available meteorological data. Experience in southern Idaho indicates that daily net radiation can be estimated within 10% using observed solar radiation, maximum and minimum air temperatures, and a single observation of dew point temperature. Observed versus cloudless day solar radiation for the area is used to adjust the net longwave radiation for cloud cover effects. Estimates of daily evapotranspiration with adequate soil moisture and nonlimiting leaf area generally also are within 10% when using a combination energy balance-aerodynamic equation. Several equations for estimating potential evapotranspiration will be compared with measured values

The Role of Evapotranspiration Models in Irrigation Scheduling

MOST evapotranspiration (El) models are based on physical principles controlling evaporation and the conservation of mass and energy, and use daily climatic data. ET models coupled with irrigation models are valuable tools because they enable trained and experienced irrigation specialists to provide irrigation scheduling services at a reasonable cost. Estimated standard deviations of mean daily ET for 1- to 30-day periods (S-et) at Akron, Colorado; Davis, California; Kimberly, Idaho; and Lompoc, CA varied from 0.9 to 1.3 mm/day. S-et decreased to 0.4 to 0.7 mm/day for 15- to 30-day periods. Standard errors of. ET estimates (Sy,x) with a combination equation based on 243 days of data from Kimberly, ID were normally distributed. The Sy,x for daily values was 1.0 mm/day. The Sy,x decreased inversely with the square root of the number of days for up to 30 days and was similar to those reported for other areas using models that operate on daily climatic data. A summary of factors affecting confidence levels in irrigation scheduling is presented along with the expected standard deviations. Generally, the error in estimating irrigation applications exceeds estimated ET errors. The error in measuring soil moisture is generally smaller than estimated ET and irrigation application errors

Development and Evaluation of Evapotranspiration Models for Irrigation Scheduling

EVAPOTRANSPIRATION (ET) data for irrigated crops in southern Idaho were used to develop relationships for estimating net radiation and potential ET for the USDA-ARS Computerized Irrigation Scheduling Program. ET estimated with the initial relationships compared well with recent measurements obtained with two sensitive weighing lysimeters. The:average daily measured Et for alfalfa for 128 days when there was full cover was 7.23 mm, while the average daily estimated ET was 7.15 mm. Crop curve relationships were developed from the ET results for snap beans (Phaseolus vulgaris L). The depletion of soil water was predicted for two years of irrigated beans with the scheduling program using the improved crop curves and compared with the measured as a test of its performance. The standard deviation of the difference between predicted and measured was about 0.95 mm/day from planting until harvest. The results also demonstrated the importance of obtaining representative meteorological data for irrigation scheduling

Peak Water Requirements of Crops in Southern Idaho

Peak water requirements for crops in southern Idaho were determined from frequency distributions of evapotranspiration rates for 1-day, 3-day, 7-day, 15-day, and 30-day averaging periods. Daily evapotranspiration for a well watered reference crop (alfalfa), measured with a precision weighing lysimeter, and meteorological data were used to verify the calculations of daily evapotranspiration. Previously, peak water requirements for crops in southern Idaho were determined from soil sampling data which represented averages of 10-day to 20-day periods. The frequency analysis of daily evapotranspiration (ET) presented in this paper provides the probable or expected peak water requirements for irrigation intervals of 1 day to 30 days

Verification of a mathematical model for layered T-beams

CER73-74MLK-MEC-JRG-JB-EGT-MDV28.March 1974.Includes bibliographical references.An experimental program and the verification of a mathematical model for layered T-beams, developed assuming small deflection theory and including effects of interlayer slip, are described in this report. This research is a part of an overall program to develop a verified analysis procedure for wood joist floor systems. After a description of the construction and load-testing of 14 two-and three-layered T-beams, a brief discussion on the mechanical properties of the materials used is given. The deflections observed in the loading tests are then compared with the predicted deflections given by the mathematical model, which used a finite element solution technique. These comparisons for the fourteen T-beams, including two and three-layered systems, formed the primary basis for the verification of the mathematical model. Test results provided by a manufacturer of joist systems were also compared to the mathematical model. Good agreement between the observed and theoretical values were obtained for all tests. These favorable results show the validity of this general layered beam theory