Case Study: Modeling of Sediment Transport and Wind-Wave Impact in Lake Okeechobee

There are increasing demands for reliable engineering tools for sediment modeling and water resources management. The Lake Okeechobee environmental model (LOEM), which was calibrated and verified to simulate sediment resuspension and transport in Lake Okeechobee, Florida, is a dependable tool to meet those demands. The LOEM contains 2,126 horizontal grid cells and 5 vertical layers. The primary hydrodynamic and sediment transport driving forces are wind waves, surface wind stresses, and inflows/outflows. The LOEM was calibrated and verified, using two sets of observed data from May 16 to June 13, 1989 and January 17 to March 3, 2000, respectively. The model results indicate that sediment solids are resuspended primarily by wind–wave action and transported by lake circulation. The strong relationship between significant wave height and suspended sediment concentration in the lake indicates that sediment resuspension is primarily driven by wind-induced waves. To simulate this sediment resuspension, the processes of wind–wave- and current-induced bottom shear stresses on the lake bed were added to the LOEM. Once resuspended, the suspended sediment is transported to different areas of the lake by wind-induced currents. The importance of wind-wave, currents, and their interactions to sediment transport is included and discussed. By using the comprehensive data set for model calibration and verification, the LOEM model is proven to be a useful tool to water sources management in the lake.     

Modeling Artificial Aeration Kinetics in Ice-Covered Lakes

A lake hydrodynamic model has been enhanced to simulate ice cover and artificial aeration during ice cover periods. Artificial aeration using mechanical surface aerators (“splashers”) and point-source bubblers (“bubblers”) is examined. Applying the model to two lakes in Alberta, Canada, indicate the model's capacity to handle a range of lake conditions and aeration operations. The sediment bed is found to be an important source of both heat and biochemical oxygen demand to the water column, during both natural conditions and artificial mixing periods. The ice cover thickness is shown to be a function of snow weight and insulation effects. The effects of an opening in the ice cover are a net gain in dissolved oxygen and a net loss of heat. The design and placement of aerators in the lake, as well as their operation schedules, are shown to determine the volume of mixed water and aeration effectiveness. This model is suitable for designing lake aeration systems to prevent winterkill in subarctic lakes.     

Modeling Volatilization of MTBE from Standing Surface Waters

The discovery in California of methyl tertiary-butyl ether (MTBE) in surface waters used for recreational boating has raised concerns over the potential impact on drinking water quality. Concentrations of MTBE above the California secondary maximum contaminant level of 5 ppb have been reported. Here we present a model to predict the fate of MTBE in surface waters as a function of wind speed, water temperature, epilimnion depth, and lake surface area. The model was validated with MTBE concentration data from Lake Perris in southern California and Calero Reservoir in northern California. When applied to typical lake conditions in California [i.e., epilimnion depth <11 m (<35 ft) and water temperature >15°C], the maximum half-life for MTBE is <40 days for quiescent conditions, and as low as 6 days if the average wind speed is >4.5 m∕s (10 mi∕h). The model can be used for management of recreational boating based on a target MTBE concentration in the reservoir.     

Application of Three-Dimensional Hydrodynamic Model for Lake Okeechobee

A 3D hydrodynamic and heat transport model was developed for Lake Okeechobee. Continuity, momentum, and temperature transport equations were solved. Dynamically coupled transport equations for turbulent kinetic energy and turbulent scale also were solved. The numerical scheme used spatial finite differencing and a three-time-level, external-internal mode splitting procedure. A 28-day calibration was conducted, using measured bathymetry, rainfall, relative humidity, total solar radiation, wind velocity, inflow, and outflow data. During the calibration period, little rainfall occurred, and lake water levels receded. Water surface elevation, horizontal velocities, and temperature were computed. Agreement between observed and simulated values was based on graphical comparisons, minimizing mean absolute and root-mean-square errors, and spectral analysis. Comparisons showed that the model reproduced general observed trends and short-term fluctuations. The model's heat transport and turbulence closure schemes behaved as expected with regard to water column stratification and mixing. Simulation accuracy may potentially be improved by adding wind-wave and vegetation resistance algorithms to the model.     

Numerical Simulation of Fluxes Generated by Inhomogeneities of the Underlying Surface over the Jinta Oasis in Northwestern China

Using land-use types derived from satellite remote sensing data collected by the EOS Moderate Resolution Imaging Spectroradiometer (EOS/MODIS),the mesoscale and turbulent fluxes generated by inhomogeneities of the underlying surface over the Jinta Oasis,northwestern China,were simulated using the Regional Atmospheric Modeling System (RAMS4.4).The results indicate that mesoscale circulation generated by land-surface inhomogeneities over the Jinta Oasis is more important than turbulence.Vertical heat fluxes and water vapor are transported to higher levels by mesoscale circulation.Mesoscale circulation also produces mesoscale synoptic systems and prevents water vapor over the oasis from running off.Mesoscale circulation transports moisture to higher atmospheric levels as the land-surface moisture over the oasis increases,favoring the formation of clouds,which sometimes leads to rainfall.Large-scale wind speed has a significant impact on mesoscale heat fluxes.During the active phase of mesoscale circulation,the stronger large-scale winds are associated with small mesoscale fluxes; however,background wind seems to intensify the turbulent sensible heat flux and turbulent latent heat flux.If the area of oasis is enlarged properly,mesoscale circulation will be able to transport moisture to higher levels,favoring the formation of rainfall in the oasis and protecting its "cold island" effect.The impact of irrigation on rainfall is important,and increasing irrigation across the oasis is necessary to protect the oasis.     

Pool boiling cooling for melt spinning quench wheels

The production of rapidly quenched metal ribbons by melt spinning on a cylinder produces very high average heat fluxes through the cylinder. The problem of maintaining a low average casting surface temperature can be solved by boiling on the plain interior of the cylinder. An experimental, boiling cooled, amorphous iron alloy ribbon casting wheel was constructed to verify the concept and expand the available data on boiling heat transfer. Experiments were performed with water, near atmospheric pressure, in pools less than 0.03 m deep and at accelerations between 100 and 200 times earth gravity. Heat fluxes between 0.6 and 3.5 million W/m² were achieved. Heat transfer coefficients up to 0.1 million W/m² • K were measured. A loss of cooling occurred in a number of instances, at heat fluxes well below the predicted critical heat flux, and at heat flux conditions which were duplicated or exceeded in the remaining experiments. These conditions, possibly precipitated by local variations in the boiling heat transfer coefficient, are not considered to represent new boiling phenomena associated with high acceleration.     

Steel Flow into a Mold from a Submerged Nozzle with Eccentric Outputs

The flow of steel melt into a mold has not been adequately studied. In general, analysis of the melt flow is a complex mathematical problem, and accordingly numerical modeling is employed. The present work employs Odinokov’s numerical method, which is based on a finite-difference form of the initial system of equations. This method has been successfully employed in continuum mechanics; in casting to determine the stress–strain state of shell-type molds; and in solving other technological problems. That suggests its universality. In the present work, it is applied to the hydrodynamic fluxes of liquid metal when steel is cast in a mold of rectangular cross section. The use of a submerged nozzle with eccentric holes for steel supply requires a three-dimensional mathematical model describing the metal fluxes into the mold. Odyssey software is used to simulate the processes in the mold. The calculation is based on the fundamental hydrodynamic equations and the proposed numerical model. The solution is obtained numerically and takes the form of a system of differential equations. The region of interest is divided into finite elements, and the system of equations is written in difference form for each element. The result obtained is the field of metal flow velocities into the mold. A numerical approach and a corresponding algorithm are developed for solution of the system of algebraic equations obtained and are incorporated in a computation program written in Fortran-4. By means of the mathematical model, the geometric dimensions of the mold and the cross section of the exit holes in the submerged nozzle may be varied. The model clarifies the pattern of metal flows, which affects the heat transfer by the mold walls, and permits determination of the optimal parameters of metal exit from the submerged nozzle in different casting conditions. As an example, the model is applied to steel casting in a mold of rectangular cross section (height 100 cm, horizontal dimensions 2000 × 40 cm). Steel flow from the submerged nozzle is eccentric in two directions within the horizontal plane. The results of solution are presented in graphic form. The pattern of metal fluxes into the mold is shown, and the magnitude and intensity of the fluxes is determined.     

Antiepileptic drug utilization in out-patients--a prescribing pattern study

Antiepileptic drug utilization for the treatment of different epileptic seizures had been investigated for 10 years in Bulgaria (1985-1994). The data were collected from ambulatory cards of 10,132 epileptic out-patients as well as from pharmacists' sales records. The results were expressed in DDD/1,000 inhabitants/year. During the period 1985-1989 the drug mostly prescribed had been phenobarbital both in mono- and polytherapy, but during the second period (1990-1994) it had been replaced to a high extent by carbamazepine and valproates. Polytherapy had given up its place to monotherapy in all forms of epileptic seizures during the 10-year period of investigation.     

Measurements, simulations, and analyses of instantaneous heat fluxes from solidifying steels to the surfaces of twin roll casters and of aluminum to plasma-coated metal substrates

Using implanted thermocouples, and an inverse heat-transfer technique, heat fluxes and associated heat-transfer coefficients during the solidification of steel in a pilot scale 0.6-m-diameter twin roll caster, whose copper contact surfaces had been treated with a propriety coating, were measured. It was found that heat fluxes during initial contact of liquid steel with the rolls were low, rising to maximum values of about 5 to 6 MW per square meter halfway down the sump of liquid steel, but then diminishing toward zero as the strip approached the roll nip. These results corresponded to roll speeds of some 7 m/min, strip thicknesses of 7 mm, and a roll separating force of 20 kN. For higher speeds and thinner strip, a secondary peak in the heat flux was observed. Associated microstructures revealed acicular ferrite, large prior austenite grains, and secondary dendrite arm spacings in keeping with measurements. In parallel experiments simulating a single belt horizontal caster, heat fluxes from strips of various aluminum alloys to coated and uncoated steel and copper substrates were measured. Under these conditions, peak heat fluxes were recorded during the period of initial contact, and depending on the coating characteristics, these reduced to a lower plateau before declining, or continuously decreased toward zero, corresponding to complete solidification of the strip. A theoretical analysis of the maximum heat-transfer rates that can be expected given perfect thermal contact of metal with the rolls, and its moderations by gas films, and substrate coatings illustrates the dominant role of the gas film and the need for dynamic heat flux measurements for quantitative modeling of fluid flows and solidification phenomena in thin strip casting operations. A model for air gap formation is proposed, based on viscous laminar flows within the gas films. Predicted thicknesses are in reasonable accord with those deduced on the basis of heat flux measurements. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS.     

Estimating Regional Evapotranspiration Using Remote Sensing: Application to Sone Low Level Canal System, India

Remote sensing-derived spectral data have been used in the past to partition net radiation, soil heat, and sensible heat fluxes for estimating latent heat flux as a residual of surface energy balance, and thus regional evapotranspiration. Attempts to provide a simplified procedure for estimating sensible heat flux at a regional scale have not been successful because of the relatively strong dependence of the heat transfer coefficient on the land–atmosphere boundary condition. This paper presents a remote sensing-based procedure to estimate the sensible heat flux incorporating the local meteorological conditions, and in turn to determine the regional evapotranspiration. The model utilizes satellite-derived surface albedo, surface temperature, and leaf area index along with a very few agrometeorological data as inputs. The proposed procedure has been tested on a part of the Western Yamuna Canal system, India, and is found to be computationally simple as well as stable. For a well-watered wheat crop, the average evapotranspiration by the proposed model is estimated to be 2.05?mm?d?1 on January 30, 1996, whereas it is estimated to be 1.89?mm?d?1 using the Penman-Monteith equation, indicating a difference of less than 10%. The model is subjected to sensitivity analysis for uncertainties in the observed wind velocity and the computed leaf area index (by ±20%) to estimate sensible heat flux. Results reveal that the percentage change in mean sensible heat flux for the image is less than 5% in all cases, thus indicating the acceptability of the model against the uncertainties. Further, the model has been applied to three sets of Landsat-TM data covering the Sone Low Level Canal system, India, to demonstrate its usefulness in evaluating water delivery performance.     

Periodic Diffusional Mass Transfer near Sediment/Water Interface: Theory

Time-variable (periodic) flow over a lake bed, and the associated boundary layer development, have the potential to control or at least influence rates of mass transfer across the sediment/water interface. An analysis for instantaneous and time averaged flux of a material across the sediment/water interface for infinite supply in the water and infinite sink in the sediment is presented. The water flow above the interface is characterized by the shear velocity (U?) which is a periodic function of time with a maximum amplitude of (U?0) as may be typical of an internal seiche (internal standing wave) motion in a density stratified lake. The relationship between the shear velocity on the lake bed and the wind shear on the lake surface is illustrated for an extremely simplified two-layered lake of constant depth. For a less restrictive analysis, shear velocities on a lake bed have to be obtained either from field measurements or from a three-dimensional lake circulation model driven by atmospheric forcing including wind. Smaller and wind-sheltered lakes will have lower (U?0) and periodicities (T). The response of the diffusive boundary layer was related to the period of the periodic motion (T), Schmidt number (Sc), and shear velocity (U?). The vertical diffusive flux at the sediment/water interface was expressed by a Sherwood number (Sh), either instantaneous or time averaged. The mean Sherwood number (Shave) varies with shear velocity of the wave motion over the sediment bed, Schmidt number (Sc) and the period (T) due to the response of the diffusive boundary layer to the time variable water velocity. Effective diffusive boundary layers develop only at low shear velocities. Where they do, maximum and minimum boundary layer thickness depends on all three independent variables (T, Sc, and U?0). The diffusive boundary layer strongly affects sediment/water mass transfer, i.e., Sherwood numbers. Mass transfer averaged over a period can be substantially less than that produced by steady-state flow at the same U?0 and Sc. At Sc = 500, typical for dissolved oxygen, the mass transfer ratio can be reduced to 60% of steady state, depending on the internal wave period (T).     

Wind Energy Conversion Systems as a Distributed Source of Generation

As a result of the worldwide energy crisis, research and development activities in the field of wind energy have been gaining momentum for the last few years in many countries. Although this technology has been greatly improved during that time, the available technical know-how is not yet adequate to develop reliable wind energy converting systems for Indian conditions at low wind speeds. In spite of a few indigenous efforts, the developments of wind energy converting systems working at low wind speeds of 2–5 m/s, which is available for a considerable period of the year in the major part of the country, remain unfulfilled. This issue continues to be a matter of great concern for the Indian researchers. This paper introduces a new concept of amplifying the wind speed before it comes in contact with the rotor blades of a Savonius turbine by using a convergent nozzle. This novel work emphasizes the improvement of the efficiency of Savonius rotors, which normally extract less than 25% of the power in the wind and have been commercially unsuccessful. A research program involving wind tunnel tests of five different nozzle models has been conducted. Some necessary modifications in the design of the turbine have been suggested and verified practically with the help of working models. Analysis of different nozzle dimensions has also been outlined. The variation of the output speed with different values of input wind speed and different lengths placed at different distances from the wind tunnel are presented in the paper.     

Immunology and growth faltering of Anga children, Papua New Guinea: preliminary work

BACKGROUND: Between 1985 and 1989, only one centre in Sweden combined preoperative radiotherapy with total mesorectal excision (TME) in the primary treatment of rectal cancer. The aim of this study was to investigate whether this change in primary treatment had an impact on the outcome. METHOD: The survival rate of 94,262 patients with colorectal cancer from the total Swedish population between 1960 and 1989 was analysed. RESULTS: A continuous improvement in relative survival rate occurred during the first year of follow-up for both colonic and rectal cancer. Some improvement was also seen during follow-up years 2-5, but this was much more pronounced during the last period (1985-1989) for rectal cancer in the county of Uppsala. The improvement was particularly marked during follow-up years 3-5. CONCLUSION: There are strong indications from this study that altered primary treatment for rectal cancer results in improved long-term survival.     

Downscaling Model Resolution to Illuminate the Internal Wave Field in a Small Stratified Lake

This paper presents the application of hydrostatic and nonhydrostatic three-dimensional hydrodynamic models to a stratified lake. Focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20?m?s?1. Simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100×100 to 10×10?m. Results of the hydrostatic models were used to investigate the large-scale features of the internal wave motion. With the intent of investigating the high-frequency waves, observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids. Wavelength of the high frequency waves decreased with grid resolution. However, none of the uniform grids were sufficiently fine to capture the waves of the highest frequency. Simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field. The simulations showed that these waves were shear unstable modes and that their vertical and horizontal length scales were in close agreement with results from linear stability analysis.     

Mathematical modeling of postcombustion in a KOBM converter

A mathematical model has been developed to describe gas flow, combustion reactions, and heat transfer in converter-type steelmaking processes. Thek- ε two-equation turbulent model, a finite reaction model, and the DeMarco-Lockwood flux model have been incorporated in this model to deal with the turbulent flow, postcombustion reactions, and radiation heat transfer. Local gaseous flow patterns, temperature, and heat flux distributions were calculated for a 300 tonne Klöckner Oxygen Blowing Maximillanshuette (KOBM) converter. Comparison between the heattransfer fluxes calculated based on the model and those measured industrially indicates the validity of the model in this application. The postcombustion has been found to be determined by the decarburization rate (DCR) which is directly related to the hardness of blowing not by the entrainment of surrounding gas to the oxygen jet as previously reported. The model revealed that about 20 pct of what is normally considered to be recovered heat has actually been lost through the vessel wall and to the lance. It is shown that this model is useful in studying the detailed mechanisms of postcombustion to optimize operations in converter-type steelmaking processes.     

含轴油承用作磨床主轴前轴承的运转试验

为提高磨床砂轮主轴的旋转精度以及改进轴承结构,杭州机床厂将原来使用的动压轴承改成预载荷弹性变形含油轴承并取得初步成效。根据对新轴承所进行的300多小时运转试验,测得摩擦系数为0.02-0.05,温升为20℃左右,其值介于一般的流体动压轴承和铁基含油轴承之间;磨损量为10μm左右;主轴启动扭矩约为动压轴承的两倍。试验还表明,保证充分供油和把磨削力控制在额定范围以内是保证弹性变形含油轴承正常运转的两个重要条件。     

Long-term follow-up on hydroxylapatite-coated cylindrical dental implants: a comparison between developmental and recent periods

PURPOSE: To compare success rates for dental implants placed from 1985 through 1988 and from 1989 through 1991, and to investigate the factors associated with success or failure. PATIENTS AND METHODS: All hydroxylapatite-coated cylindrical implants placed from 1985 through 1991 were followed yearly. Lifetable survival analyses compared implant success for a "developmental period" from 1985 through 1988 (4 to 8 years follow-up) and a "recent period" from 1989 through 1991 (1 to 4 years follow-up). Reasons for success or failure, time from implant placement to removal related to failure reason, outcome after implant removal, and a morbidity analysis are included. RESULTS: The 7 to 8-year cumulative success rate for all implants placed in the developmental period (maxilla and mandible combined) was 86.5%; it was 84.2% for all maxillary implants and 87.5% for all mandibular implants. The cumulative success rate for all implants placed in the recent period was 97.5%; it was 97.5% for all maxillary implants and 97.6% for all mandibular implants. The difference between the two periods was statistically significant only for the anterior maxilla. Regression analysis on the interval success rates indicates that interval failure did not follow a linear relationship with time. The most common reasons associated with failure were lack of keratinized gingiva, poor oral hygiene, mechanical overload, and malposition. CONCLUSION: Comparison with previously reported cumulative success rates indicated learning curve experiences comparable with other implant systems. Improvements in hardware, surgical and prosthetic techniques, and patient selection have led to an improvement in success rates with the recent period implants.     

Influence of Stratification and Shoreline Erosion on Reservoir Sedimentation Patterns

Sedimentation in the main pool of a deep (maximum depth: 50?m), 227?km2 hydropower reservoir was modeled using a three-dimensional numerical model of hydrodynamics and sedimentation for different wind, inflow, and outflow conditions. Short-term velocity measurements made in the reservoir were used to validate some aspects of the hydrodynamic model. The effects of thermal stratification on sedimentation patterns were investigated, since the reservoir is periodically strongly stratified. Stratification alters velocity profiles and thus affects sedimentation in the reservoir. Sedimentation of reservoirs is often modeled considering only the deposition of sediments delivered by tributaries. However, the sediments eroding from the shorelines can contribute significantly to sedimentation if the shorelines of the reservoir erode at sufficiently high rates or if sediment delivery via tributary inflow is small. Thus, shoreline erosion rates for a reservoir were quantified based on measured fetch, parameterized beach profile shape, and measured wind vectors, and the eroded sediments treated as a source within the sedimentation modeling scheme. The methodology for the prediction of shoreline erosion was calibrated and validated using digital aerial photos of the reservoir taken in different years and indicated approximately 1?m/year of shoreline retreat for several locations. This study revealed likely zones of sediment deposition in a thermally stratified reservoir and presented a methodology for integration of shoreline erosion into sedimentation studies that can be used in any reservoir.     

One-Dimensional Modeling of Dam-Break Flow over Movable Beds

A one-dimensional model has been established to simulate the fluvial processes under dam-break flow over movable beds. The hydrodynamic model adopts the generalized shallow water equations, which consider the effects of sediment transport and bed change on the flow. The sediment model computes the nonequilibrium transport of bed load and suspended load. The effects of sediment concentration on sediment settling and entrainment are considered in determining the sediment settling velocity and transport capacity. In particular, a correction factor is proposed to modify the Van Rijn formulas of equilibrium bed-load transport rate and near-bed suspended-load concentration for the simulation of sediment transport under high-shear flow conditions. The governing equations are solved by an explicit finite-volume method with the first-order upwind scheme for intercell fluxes. The model has been tested in two experimental cases, with fairly good agreement between simulations and measurements. The sensitivities of the model results to parameters such as the sediment nonequilibrium adaptation length, Manning’s roughness coefficient and the proposed correction factor have been verified. The proposed model has also been compared to an existing model and the results indicate the new model is more reliable.