Empirical Design Equations Research Articles

Comparison of performances of rotating perforated tubes and rotating biodiscs biofilm reactors for wastewater treatment

Wastewater treatment performance of a novel biofilm reactor named as rotating perforated tubes biofilm reactor (RPT) was investigated and compared with a rotating biodisc reactor (RBD) under the same conditions. The effects of major process variables such as feed wastewater flow rate, COD concentration and loading rate on COD removal performances of both reactors were evaluated. Rotating perforated tubes biofilm reactor was found to be more advantageous as compared to rotating biodisc system for COD removal efficiency. This difference becomes more significant at low A/ Q ratios. Empirical design equations were developed for both systems to quantify the systems' performance as a function of major process variables.

Wastewater Treatment Performance of Rotating Perforated Tubes Biofilm Reactor with Liquid Phase Aeration

A novel biofilm reactor named as `rotating perforated tubes biofilm reactor' was used for treatment of synthetic wastewaterwith and without liquid phase aeration. Effects of major processvariables such as feed wastewater flow rate, COD concentration and loading rate, liquid phase aeration on the rate and extent ofCOD removal were investigated. Liquid phase aeration was provento be advantageous especially for high strength wastewaters at highCOD loading rates. Kinetics of COD removal was investigated andkinetic constants were determined by using the experimental data.An empirical design equation was developed to quantify the system's performance as a function of major process variables.

Rotating-Perforated-Tubes Biofilm Reactor for High-Strength Wastewater Treatment

A rotating-perforated-tubes biofilm reactor was used for treatment of synthetic wastewater at different operating conditions. The biofilm reactor consisted of two sections each having 25 perforated tubes mounted on three perforated discs. The battery of the tubes was rotated with the aid of a shaft and a motor. Effects of major process variables such as feed wastewater flow rate and COD concentration on the system performance were investigated. Kinetics of COD removal was investigated and kinetic constants determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of major process variables.

Short-cut design of small hydroelectric plants

The problem of designing small hydroelectric plants has been properly analysed and addressed in terms of maximizing the economic benefits of the investment. An appropriate empirical model describing hydroturbine efficiency was developed. An overall plant model was introduced by taking into account their construction characteristics and operational performance. The hydrogeographical characteristics for a wide range of sites have been appropriately analyzed and a model that involves significant physical parameters has been developed. The design problem was formulated as a mathematical programming problem, and solved using appropriate programming techniques. The optimization covered a wide range of site characteristics and three types of commercially available hydroturbines. The methodology introduced an empirical short-cut design equation for the determination of the optimum nominal flowrate of the hydroturbines and the estimation of the expected unit cost of electricity produced, as well as of the potential amount of annually recovered energy.

FDTD Characterization of Meander Line Antennas for Rf and Wireless Communications

Printed small antennas are becoming the main subject of investigations for improved performance of personal wireless communication systems. In recent presentations a new type of printed meander line antenna was introduced. In this paper, the analysis of this type of antenna with dual sleeves is performed using the finite difference time domain technique. Empirical design equations are obtained for the resonant (operating) frequency and the corresponding input impedance. Samples of the new design provide antennas with good matching impedance to a 50 system, a dual band operation, and wider bandwidth.

Single-angle compression members welded by one leg to a gusset plate. II. A parametric study and design equation

Single-angle compression members are complex members to analyze and design. The two generally accepted design procedures, the simple-column and the beam-column approaches, in general, underestimate the load-carrying capacity of single-angle compression members welded by one leg to a gusset plate fixed to a rigid support. One of the reasons is that these approaches do not properly account for the end constraint provided by the gusset plate. The effective length factor can be adjusted, but this is difficult to do as the end restraint is not easy to evaluate in many practical cases. Another reason is that these approaches are not based on a rational understanding of the failure mechanism of these members. An experimental program confirmed that the finite element method can be used, with a reasonable degree of accuracy, to predict the behavior and load-carrying capacity of single-angle compression members welded by one leg to a gusset plate fixed to a rigid support. The finite element method was used to study some 1800 different combinations of parameters. It was found that out-of-straightness, residual stresses in the angle section, Young's modulus of elasticity, and the unconnected gusset plate length do not have a great effect on the load-carrying capacity. The most significant parameter is the gusset plate thickness with the gusset plate width being the second most important parameter. An empirical design equation is proposed.Key words: angles, buckling, columns (structural), compressive resistance, design equation, gusset plates.

Full-Scale Experiments and Analyses of Cellular Hull Sections in Compression

Abstract Compression tests were conducted on high-strength single-cell and multiple-cell box sections with plate width-to-thickness (b/t) ratios ranging from 48 to 96. Local plate buckling occurred at stresses as low as 5 percent of the yield stress, whereas the ultimate compression stress ranged from 38 to 72 percent of the yield stress. These critical stresses were not significantly affected by the length of the specimen, the number of cells, the boundary conditions, or lateral load. Simple empirical design equations based only on b/t gave estimates of the collapse strength within five percent in all cases. Finite-element analyses were able to predict the significant reserve load-carrying capacity and ductility after ultimate load, which was dependent on the length of the specimen as well as the b/t ratio.

Design of Rigid Overlays for Airfields

Current airfield overlay design generally uses empirical methods developed in the 1940s and 1950s. This paper presents a mechanistic overlay design procedure based on layered elastic theory as an alternative to the empirical design procedure. The layered elastic model is capable of analyzing layered structures with different material properties and interface conditions. It is also compatible with many current evaluation techniques using falling weight deflectometers. This mechanistic design approach includes the effects of fatigue and structural damage to the base pavement before overlay, progressive cracking of the base pavement after overlay, and substandard load transfer at joints. The proposed design procedure was checked against the results of the accelerated traffic tests originally used to develop the empirical overlay design equations, and comparative designs were also made using the proposed design procedure and the empirical equations. The proposed procedure generally gave good and reasonable co...

Superposition of microconvective and macroconvective mass transfer at gas-evolving electrodes—a theoretical attempt

For mass transfer at gas-evolving electrodes with superimposed electrolyte flow through the interelectrode gap a mathematical model is developed and discussed. The resulting equation for the combined mass transfer coefficient takes account of the individual mass transfer coefficients. The new equation can be satisfactorily approximated by an older empirical design equation.

Support capacity and roof behaviour at longwall faces with shield supports

Field investigations on seven U.S. longwall coal faces were carried out to examine the behaviour and interaction of roof, floor and support on longwall faces equipped with hydraulic powered supports. The most important factor in determining face stability was found to be periodic weighting and an empirical design equation was developed for support capacity. The interaction of various elements in the face system is examined and discussed.

Polychrest: A development system for radio-frequency-coupled implants

Inductively-coupled neurological prosthetic implants may employ RF coils of unusual design (for example ‘square’ spiral inductors printed in thick-film ink on both sides of the alumina substrate) for which published empirical design equations are hard or impossible to find ‘Polychrest’ enables the rapid experimental generation of ad hoc design data for RF-coupled energy-transfer systems, leading quickly to a working model which can be thoroughly studied and understood.

Velocity Calculation for Local Exhaust Inlets — Empirical Design Equations

Several studies have determined empirical design equations for calculating centerline velocities of local exhaust inlets. Significant differences exist with the earliest findings, obtained over forty years ago and still in use today, and also with recent findings. Principal considerations include the formulation and accuracy of the equations and the effects of inlet factors including flanging, width-to-length ratio, and face velocity. All equations provide useful approximations, with variable complexity, accuracy, and extent of application.

Velocity Calculation for Local Exhaust Inlets — Empirical Design Equations

Several studies have determined empirical design equations for calculating centerline velocities of local exhaust inlets. Significant differences exist with the earliest findings, obtained over forty years ago and still in use today, and also with recent findings. Principal considerations include the formulation and accuracy of the equations and the effects of inlet factors including flanging, width-to-length ratio, and face velocity. All equations provide useful approximations, with variable complexity, accuracy, and extent of application.

Velocity Calculation for Local Exhaust Inlets — Graphical Design Concepts

Graphical design concepts are useful for approximating airflow characteristics of local exhaust inlets. They may be applied for situations which are significantly different from those which have been studied experimentally. Simple inlet configurations may be combined as “building blocks” to represent more complex configurations, including obstructive surfaces near an inlet opening. Streamlines and velocity potentials are two-dimensional airflow characteristics which may be applied for design purposes in different ways. These methods include freehand sketching, vector addition, imaginary inlets, conformal mapping, and area/velocity change. Graphical methods are enhanced by application of empirical design equations for certerline velocity gradients. Modern computers can facilitate inlet design by performing complex calculations and graphical representations with relative ease.

Velocity Calculation for Local Exhaust Inlets — Graphical Design Concepts

Graphical design concepts are useful for approximating airflow characteristics of local exhaust inlets. They may be applied for situations which are significantly different from those which have been studied experimentally. Simple inlet configurations may be combined as “building blocks” to represent more complex configurations, including obstructive surfaces near an inlet opening. Streamlines and velocity potentials are two-dimensional airflow characteristics which may be applied for design purposes in different ways. These methods include freehand sketching, vector addition, imaginary inlets, conformal mapping, and area/velocity change. Graphical methods are enhanced by application of empirical design equations for certerline velocity gradients. Modern computers can facilitate inlet design by performing complex calculations and graphical representations with relative ease.

Weight of X-Ray Shields for Interceptor Missiles

A decision to shield interceptor propulsion systems from x-rays emitted by a nuclear weapon during a nuclear engagement results in significant increases in system weight. Shielding is one alternative available to the designer to reduce the x-ray dose in the solid-propellant grain component of the propulsion system. Exposure to x-ray emissions can result in system failure by inducing unacceptable changes in the solid-propellant ballistic and mechanical properties, or premature ignition, or both. The magnitude of the shield weight required to protect the solid-propellant grain from x-rays has been determined for various motor case materials, nuclear weapon spectra, and nuclear fluence levels. The study was conducted by determining the shield thickness required to reduce the x-ray dose in the propellant to 2 cal/g. An empirical design equation suggested by Watcher was investigated and found to yield incorrect results when compared with results obtained using an energy deposition computer code. Graphite, fiberglass, and Kevlar motor case materials were studied in typical interceptor designs. Both equal-thickness and equal-strength designs were considered. Weapon spectra with blackbody temperatures ranging from 2 to 15 keV and fluence levels up to 100 cal/cm were studied. The x-ray shield material was tantalum carbide. For a motor case thickness of 1.27 cm, shield weights of approximately 1.6 g/cm are required to protect the solid propellant. For a typical interceptor design, this translates into a total weight penalty of approximately 129 kg (285 Ib).

Determinate Hydraulic Geometry of River Channels

Natural channels have the ability to adjust their flow and bankfull hydraulic geometry in response to flow conditions. Nine governing equations are necessary to define the complete adjustment process and relate channel response to discharge, sediment load, bed, and bank sediment, and the valley slope. A preliminary analysis enables the nature of this process-response model to be identified although insufficient information is known about all the processes for it to be used for design purposes. The necessary dependent and independent variables for the development of empirical design equations are identified by the model and it also confirms the determinate nature of alluvial channels.

Interesting Aspects of the Empirical Wall Design Equation

Interesting Aspects of the Empirical Wall Design Equation

Diaphragms for Curved Box Beam Bridges

A finite difference procedure is used to determine the response of a single span curved single box beam bridge with any number of interior diaphragms. The bending and torsional distortions as well as cross-sectional distortions can then be determined throughout the curved box girder. The forces that are determined include bending moment and shear, pure torsion, warping torsion, and bimoment. These forces, in addition to distortional functions, yield resulting normal bending, normal warping, and normal distortional stresses. The technique is then used to determine the dead-load and live-load response of a series of typical curved box beams. A study of the data has resulted in a series of empirical design equations.

Drying of Sand-Digested Sludge Mixtures

An empirical design equation has been developed to estimate the drying rate during the falling rate drying period of a mixture of sand and centrifuged digested primary domestic sewage sludge to be used as a fill material. The drying rate is required to calculate the average moisture content of the mixture while drying. The design equation was developed from data collected over a nine-month period using three different sands with sand-to-sludge dry solids ratios from 0:1 to 30:1. The primary variables considered are sand-to-sludge dry weight ratio, ambient temperature, and ambient relative humidity. Mixture depth and sand particle size were not found to affect drying rates for ranges and distributions tested. The design equation has not been verified for polymer-treated sludges.