Category: Research Sponsored by GWRI

Principal Investigator: Charng Ning Chen (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1970-11-01; Completion Date: 1970-11-01;
Keywords:
Description:

The mechanics of the process by which a sediment particle is removed from a stream bed was investigated. An idealized model, consisting of a one-inch diameter sphere protruding through a flat plate, a sphere-supporting base, and two equal height sphere-restraining pins aligned perpendicular to the flow direction, was used to simulate the condition of a cohesionless particle lying on a stream bed. By means of this model, the statistical variables of the angle of repose, the protrusion condition, and the approach velocity distribution became controllable at deterministic values.

In spite of the replacement of most of the statistical variables by the deterministic variables, initial motion of the particle is a fluctuating phenomenon which must be described in probabilistic terms because the fluid-dynamic force is fluctuating in nature. The transition from a stationary state to the removal of the spherical particle was found to be gradual rather than instantaneous. The transition is characterized by the random rocking motion of the sphere. The initial stage of the transition is defined as the condition at which the cumulative per cent time of contact between the sphere and the base is 95 per cent. The final stage is defined as the condition at which the sphere would be rolled over definitely. The condition of initial stage is established by equating the static weight-restoring moment to a moment level which exceeds the fluctuating fluid-driving moment 95 percent of the time. The final stage is established by equating an additional impulsive moment to the difference of the driving moment and the restoring moment as used in establishing the initial stage. The flow condition associated with the transition is expressed in terms of the mean velocity at the height of the protruding sphere. The effect of nonuniform velocity distribution is accounted for by the use of a momentum correction coefficient.

The fluid-dynamic moments and forces were determined experimentally in air flow with both uniform and non-uniform approach velocity profiles. Since the transitional stage is associated with the balance of moments, a method has been developed using the weight-restoring moment at the transitional stage as a gauge to measure the unknown fluid-driving moment. The corresponding fluid-driving force pattern was then determined through a set of three algebraic equations defining the equilibrium of moments due to the driving force and the restoring force. Experimental results indicated that the ratio of the coefficient of lift to drag decreased from approximately 1.6 to 0.4 as the ratio of the protrusion height to the sphere diameter increased from 25 per cent to 100 per cent. Also, the resultant fluid driving force could be considered as passing through the centroid of the sphere for protrusion height equal to or less than 75 per cent of the sphere diameter.

Technical Report

Principal Investigator: William W. Hines (Georgia Institute of Technology)
Principal Investigator: John E. Knight (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1968-07-01; Completion Date: 1970-06-30;
Keywords:

Description:
The management and control of a region’s water quality are known to be greatly influenced by prevailing social, political, and economic conditions. Research into how these conditions and attitudes relate over time to result in water quality control has been inadequate to date. The main objective of this research has been to illustrate how these prevailing conditions and attitudes interrelate in an information feedback and control system to produce traditional modes of system response. Included are such considerations as the level of water standards legislation, public awareness to pollution concentrations, enforcement effort by an administrative agency, and ecological deterioration due to excessive pollution concentration levels.

More specifically, the research attempted to (1) identify and quantify some controlling feedback loops in the complex system which encompasses water quality control and response in a basin, and (2) test the generalized model under a wide range of policies and parameters to illustrate system response and sensitivity to these changes. Utilizing the understanding of the system structure and its response patterns, directions for effective policy formulations can be suggested and tested. The methodology and philosophy of Industrial Dynamics was utilized to model this high order, multi-loop, non-linear feedback system. The DYNAMO simulation language was used to program this model for digital computer simulation, testing, and experimentation.

Initial emphasis in the modeling phase was placed on isolation of important system variables and identification of their relative magnitudes, periods, and phasing in historically polluted watersheds. The understanding of the relationships between these social, political, and economic factors led to the postulation and testing of interrelated feedback loops thought responsible for identified modes of behavior. Following refinement of the model, different policies and parameters were tested to determine their overall effect on total system response.

The results of the research include a systematic analysis of important feedback loops within the total complex system identified. General response patterns of water quality crises are shown to be embedded in the system structure proposed. Within the complex structure, feedback loops were found to have greater importance in system behavior than did relationships between variables in feedback loops. In addition, gaining an understanding of when and how various loops gain dominance of the system was then found to be necessary for understanding system response. For example, the non-linear public awareness to perceived water pollution concentration levels created different response according to the loop’s ability to direct the system for an extended time.

In summary, the study conclusions demonstrate that water quality management and control is deeply embedded in a complex, information feedback system involving social, political and economic pressures and forces. Furthermore, the complex system response was shown to be highly insensitive to many parameter changes and also very unintuitive in behavior. However, some critical points do exist, and through programs directed at these points, significant changes occur in system response.

The results of the study would be applicable to high level, governmental planning agencies since effective understanding of the interactions creating historical, pollution-control response patterns would lead to more effective development of future control policies and programs. Specifically, the research provides some in sight into the total system response time as conditions of public awareness, enforcement effort, and legislative commitments change over time.

Technical Report

Principal Investigator: William E. Gates (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1965-05-03; Completion Date: 1969-06-30;
Keywords:

Description:

The problem of dynamic oxygen balances obtained under a variety of oxygenation and deoxygenation conditions was studied. Both laboratory studies using batch reactors and field studies using natural streams were conducted during the course of the project. It was determined that the Streeter-Phelps expression for the mathematical description of oxygen sag curves was inaccurate due to the inclusion of the first order expression for describing substrate utilization by bacteria. The Monod Equations were determined to be most appropriate for defining bacterial substrate utilization and protozoa bacterial utiliization. The nature of substrate utilization as determined by the COD test was found to be dependent on the time frame for sampling. The shorter the time frame, the greater the variances and apparent inconsistencies in the data. This situation was not totally resolved, but, probable explanations were developed. Techniques for determining the Monod Equation constants using batch reactor data and data obtained under continuous dilution in a natural stream were developed. In general, the results of the study indicate that the use of a laboratory system to evaluate the impact of alternative methods of water resource management on the oxygen resources of the receiving stream is an appropriate course of action.