Donald L. Reddell

The Laplace Transform Finite Difference Method for Simulation of Flow Through Porous Media

A new numerical method, the Laplace transform finite difference (LTFD) method, was developed to solve the partial differential equation (PDE) of transient flow through porous media. LTFD provides a solution which is semianalytical in time and numerical in space by solving the discretized PDE in the Laplace space and numerically inverting the transformed solution vector. The effects of the traditional treatment of the time derivative on accuracy and stability are rendered irrelevant because time is no longer a consideration. For a single time step, LTFD requires no more than eight matrix solutions and an execution time eight times longer than the analogous finite difference (FD) requirement without an increase in storage. This disadvantage is outweighed by an unlimited time step size without any loss of accuracy, a superior accuracy, and a stable, nonincreasing round off error. Thus, a problem in standard FD format may require several hundred time steps and matrix inversions between the initial condition and the desired solution time, but LTFD requires only one time step and no more than eight matrix inversions to achieve a more accurate result.

Field Measurement of Ambient Odors with a Butanol Olfactometer

ABSTRACT A1-butanol olfactometer was used to measure ambient odor intensities at feedlots, meat packing and rendering plants, oil refineries, and other sources. The ambient odor intensities determined by odor panels using the butanol olfactometer were equivalent to 1.25 and 56.6 ppm of 1-butanol vapor in air. The precision of ambient odor measurements was within one-half step on the butanol scale. The method is precise enough for most odor investigations and abatement research.

Odor Intensities at Cattle Feedlots

ABSTRACT ODOR intensities measured at two cattle feedlots in Texas ranged from 1.5 to 170 dilutions to threshold (DT), which covers the measurement range of the Barnabey-Cheney Scentometer. The average odor reading at the surface of a 4000 head feedlot, determined by monitoring four randomly selected pens for 7 mo, was 31 DT. The run-off settling basin and retention pond averaged 68 and 46 DT. Half of the odor intensities were more than 23 DT, which exceeds the odor standards in several states. Odor intensities were diluted to 1.5 to 2 DT within 380 to 500 m (1250 to 1650 ft) downwind of the feedlot. At a 12,000 head feedlot, calcium ben-tonite was fed as a ration supple-ment at the following levels: 0.0, 0.8 and 2.0 percent. The 2 percent ben-tonite treatment resulted in a reduction in odors. Bentonite also improved average daily gain of cattle during the first 21 days.

Secondary Water Recovery by Air Injection: 1. The Concept and the Mathematical and Numerical Model

An air-driven secondary water recovery operation was proposed in order to recover water stored in the unsaturated zone of depleted aquifers and currently unavailable with conventional techniques. The operation employed a single-well serving as both a production and injection facility and consisted of three stages: (1) an air injection stage, (2) a “recovery” stage, and (3) a “production” (pumping) stage. The concept of the operation was based on the hysteretic behavior of the capillary pressures and the relative permeabilities of air and water. Hysteresis was counted upon to prevent water, forced into the saturated zone during injection, from migrating back to the unsaturated zone. A general mathematical model was developed and numerically approximated using a simultaneous two-phase, three-dimensional finite difference model in both Cartesian and cylindrical coordinates. Two types of nonlinearities were identified: (1) pressure-related weak nonlinearities and (2) saturation-related strong nonlinearities. Techniques to alleviate the resulting instabilities, as well as methods for the establishment of stable initial conditions and the treatment of boundary conditions, were developed.

Land application of thin stillage from a grain sorghum feedstock

Abstract Thin stillage, the wastewater from ethyl alcohol production after separation of wet solids, has high concentrations of organic solids, nitrogen and potassium and may be utilized in a land application system. Thin stillage from a grain sorghum feedstock was applied weekly using sprinkler irrigation to common bermudagrass ( Cynodon dactylon L.) on a sandy loam soil and was surface irrigated on grain sorghum ( Sorghum bicolor L.) followed by winter wheat ( Triticum aestivum L.) on fine-silty, mixed, thermic Fluventic Ustochrept in one growing season. Stillage application rates on soil varied from 15 to 60 mm year −1 which added 334–1040 kg N ha −1 year −1 . The rate of mineralization of stillage organic N was investigated in a non-leaching, 16-week incubation test. Excessive nutrient accumulations in common bermudagrass forage were not observed with stillage applications as high as 60 mm year −1 . Stillage additions increased nutrient levels in the soils, particularly N, P, and K, but toxic levels were not reached. However, the potential for nitrate and salt build-up in the long term was indicated. Approximately 27% of the stillage-applied organic N was potentially mineralizable. Thin stillage produced grain sorghum and wheat yields equal to or higher than yields obtained from ammonium fertilizer. Land application of thin stillage from grain sorghum may be a viable treatment alternative.

Design of a 1-Butanol Scale Dynamic Olfactometer for Ambient Odor Measurements

ABSTRACT A portable system has been developed for quantifying odors in atmospheric air. Panelists compare the intensity of ambient odors with the intensity of discrete levels of 1-butanol provided by the olfactometer. Range of delivered 1-butanol concentrations is 0 to 80 ppm in air at a flow rate of 15 L/min. Laboratory tests have been performed to ascertain precision, panelist response, variability between two olfactometers, and effect of delivery method (ascending, descending and random odor presentation). Nineteen panelists made determinations of comparative odor intensities from two identically constructed olfactometers, where one unit provided a set concentration of 1-butanol and the second provided variable concentrations to the panelists. At a given set concentration the panelist would be exposed to a sufficient number of intensities from the variable-output system such that a decision could be made on the match of intensities. Totally, 855 data points of matched intensities were acquired in the study. For the entire data set the mean value of the ratio of measured concentration to set concentration was 0.984. The geometric standard deviation of the concentration ratios was 1.44. INTRODUCTION Odor complaints are the most frequent problems for air pollution control agencies; for example, during 1981 the Texas Air Control Board received 1,467 complaints of which 51% were related to odors. Fourteen percent of these odor complaints were related to agricultural sources (Bradford, 1982). There are two techniques which agencies presently use.

Incorporating Crop Needs into Drainage System Design

ABSTRACT AN approach is proposed for incorporating crop drainage requirements into drainage design pro-cedures. The overall methodology links crop drainage re-quirements, climatological data, and drainage theory in-to a workable design method through incorporation of the stress-day index concept into the NCSU water management model.

Nonpoint Sources: State-of-the-Art Overview

ABSTRACT DURING the past few years, the term nonpoint pollution source has become exceedingly important to agriculture. In 1972, Federal legislation (Public Law 92-500) was passed bringing many forms of agricu-turally related nonpoint pollution under regulatory authority. Section 208 of Public Law 92-500 created a cooperative local/state/Federal system for areawide water quality planning. Nonpoint pollution sources are a major concern to these 208 planners. During the past, both basic and applied research have been conducted on such classical soil and water conservation topics as erosion control, sediment transport, soil chemistry and physics, crop production, range management, agricultural chemicals, animal science, and forestry. The challenge today is to locate, interpret, and compile this past knowledge into forms useful for Section 208 planners. This paper reviews the current knowledge concerning the occurrence of nonpoint pollution sources such as sediment, nutrients, pesticides, and fecal con-taminants. Sediment transport equations are reviewed and described and the pollution potential of range and pasture livestock production is discussed.

Time-Motion Analysis of Feedlot Manure Collection Systems

ABSTRACT MACHINE productivity, energy consumption and cost of feedlot manure collection were determined by time-motion analysis at four Texas cattle feedlots. Truck loading, hauling, and spreading time require-ments were also determined, as was the performance of wheel loader operators. The wheel loader/chisel plow combination produced the highest manure col-lection rate of 160 t (metric tons)/h (at 100 percent operating efficiency), followed in order by the ele-vating scraper, wheel loader, and wheel loader/roto-tiller. The most energy efficient collection system was the elevating scraper (0.88 kWh/t). Plowing of the manure pack before the wheel loader collection reduced overall energy consumption by 30 percent and increased the collection rate by 46 percent. The average rate of manure loading into spreader trucks was 186 t/h or 3.0 min per truck. Performance of wheel loader oper-ators varied by 85 percent. A prediction equation for spreader truck turn-around time versus haul distance was developed.

Secondary Water Recovery by Air Injection: 2. The Implicit Simultaneous Solution Method

The finite difference equations of air and water flow in air-driven secondary water recovery define a multidimensional strongly nonlinear system with sharp pressure and saturation fronts, large differences in the magnitude of flow coefficients, physical and mathematical discontinuities, sudden flow reversals, and high injection rates. The implicit simultaneous solution (SS) method, which solves simultaneously for the unknown pressures and saturation changes, was the sole method capable of handling these problems. Instabilities were alleviated by introducing implicit flow coefficients, implicit capillary pressures, and implicit accumulation terms. The treatment of hysteresis was based on petroleum engineering models. The concept of two separate air-water interfaces was introduced: (1) the “zero air saturatution interface,” which indicates the physical boundary of air discontinuity, and (2) the “zero capillary pressure interface,” defined as the upper boundary of a zero capillary pressure zone. A method for the numerical tracking of the two interfaces, necessary for the evaluation of the effectiveness of secondary water recovery, was also developed.