Torsional and coupled vibrations of embedded footings     

M. Novak  K. Sachs 《地震工程与结构动力学》1973,2(1):11-33

An approximate analytical solution is presented for torsional vibrations of footings partially embedded into a semi-infinite medium or a stratum. Simple formulas derived for pure torsional motion make it possible to apply a correction for the effect of embedment to the known solutions of surface footings. The solution completes an approach to the analysis of all modes of footing vibrations, including the coupled modes. The approach to coupled modes is illustrated by the solution of coupled response involving horizontal translation, rocking and torsion. Formulas are presented for stiffness and damping coefficients that can be used in the analysis of embedded footings or structures supported by such footings Field experiments were conducted with concrete footings featuring circular, square and rectangular bases and variable embedment depths. The experimental results were compared with theoretical predictions of pure torsional vibrations.  相似文献   

Turbulent heat transfer from a sparsely vegetated surface: Two-component representation     

J. Otterman  M. D. Novak  D. O. C. Starr 《Boundary-Layer Meteorology》1993,64(4):409-420

The conventional calculation of heat fluxes from a vegetated surface, involving the coefficient of turbulent heat transfer, which increases logarithmically with surface roughness (commonly taken as about 0.12 of the plant height), appears inappropriate for highly structured surfaces such as desertscrub or open forest. An approach is developed here for computing sensible heat flux from sparsely vegetated surfaces, where the absorption of insolation and the transfer of absorbed heat to the atmosphere are calculated separately for the plants and for the soil. This approach is applied to a desert-scrub surface for which the turbulent transfer coefficient of sensible heat flux from the plants is much larger than that from the soil below, as shown by an analysis of plant, soil and air temperatures measured in an animal exclosure in the northern Sinai. The plant density is expressed as the sum of products (plant-height) x (plant-diameter) of plants per unit horizontal surface area (the dimensionless silhouette parameter of Lettau). The solar heat absorbed by the plants is assumed to be transferred immediately to the airflow. The effective turbulent transfer coefficientk _g-eff for sensible heat from the desert-scrub/soil surface computed under this assumption increases sharply with increasing solar zenith angle, as the plants absorb a greater fraction of the incoming irradiation. The surface absorptivity (the co-albedo) also increases sharply with increasing solar zenith angle, and thus the sensible heat flux from such complex surfaces (which include open forests) is a much broader function of time of day than when computed under constantk _g-eff and constant albedo assumptions. The major role that desert-fringe plants play in the genesis of convection and advection cannot be evaluated properly in the conventional calculations....you know not the way of the wind... Ecclesiastes, Ch. XI, verse 5  相似文献   

Comparative performance study of diesel and electric face-haulage vehicles     

Thomas Novak  A. J. Gregg  H. L. Hartman 《Geotechnical and Geological Engineering》1987,5(4):405-417

Summary Results of a performance study of diesel ram-dump cars and electric cable-reel shuttle cars, conducted at an underground coal mine in the Warrior Basin of Alabama, are presented. Time-study data, obtained over a one-year period, show that the average load and discharge times of the diesel cars are slightly less than those of the electric cars, while the average travel-loaded, travel-empty, in, and out speeds of the diesel cars are slightly greater.Computer simulations, based on frequency distributions from the cycle-time data, show average shift productions for both vehicle types to be very close for two-car and three-car configurations with a haul distance of two crosscuts. However, as the haul distance increases, the diesel cars outproduce the electric cars.Results of a maintenance-cost comparison are presented for the sake of general interest and should not be considered as valid comparison, since the electric cars are approximately three years older than the diesel cars. The results show preventive maintenance costs to be much greater for a diesel car on both permonth and per-ton bases, and the total maintenance cost for a diesel car to be significantly higher on a permonth basis, but significantly less on a per-ton basis.  相似文献   

Theoretical values of daily atmospheric and soil thermal admittances     

Michael D. Novak 《Boundary-Layer Meteorology》1986,34(1-2):17-34

Effective daily atmospheric and soil thermal admittances were calculated using harmonic solutions to the one-dimensional heat transfer equation for a semi-infinite medium. The thermal properties of both media were assumed to be power functions of depth only and it was shown how to calculate the parameters in these functions. The admittances critically depended on the manner in which the thermal properties varied near the surface.  相似文献   

Theoretical determination of the surface energy balance and thermal regimes of bare soils   总被引：1，自引：0，他引：1  

M. D. Novak  T. A. Black 《Boundary-Layer Meteorology》1985,33(4):313-333

An analytical theory that determines the thermal regimes in the soil and the thermal and moisture regimes in the atmosphere for bare surfaces is derived. Both soil and atmospheric thermal properties are assumed to be power functions of depth and height, respectively. Evaporation is determined using a surface resistance to vapour flow. Fourier superposition is used to represent nonsinusoidal variations in time due to effects such as variable cloud cover. The theory is in acceptable agreement with micrometeorological measurements made at two bare soil sites of contrasting surface bulk density. It is concluded that the surface resistance model for evaporation is applicable to bare soils which remain wet at depth, particularly if their surface is loosened. The theory is used to predict the diurnal thermal regimes of saturated and dry sand, loam, and peat soils.  相似文献   

Heavy metals in sediments as evidence for recent pollution and quasi-estuarine processes: an example from Lake Druzno,Poland   总被引：1，自引：0，他引：1  

Wojciech Tylmann  Roman Gołębiewski  Piotr Paweł Woźniak  Karolina Czarnecka 《Environmental Geology》2007,53(1):35-46

This article presents the results of a geochemical investigation of sediments from Lake Druzno (northern Poland), a reservoir fed by freshwater from the catchment, with periodic input of brackish water from Vistula Lagoon. This study analyzed the spatial variation in heavy metal content in surface sediments as well as the temporal changes in metal content in two sediment cores dated using the ²¹⁰Pb method. In the surface sediments, the highest metal concentrations were recorded in the northern part of the lake, with lower concentrations in the central and southern parts. Absolute values of metal concentrations in the cores were low, but normalization with respect to Al showed an increase during the second half of the 20th century. Mean enrichment factors (EF) in sediments from the second half of the 20th century ranged from insignificant (1–1.2) for Fe to (1.55–3.3) for Cu, Cd, Pb and Zn. The sediments deposited before 1950 had lower EF values (>1.5) and had low variability. Results from both the surface sediments and the cores indicate that the main source of lake pollution is brackish water intrusion from the Vistula Lagoon via the contaminated River Elbląg.  相似文献   

Early spring turbulent mixing in an ice-covered Arctic fjord during transition to melting     

Ilker Fer  Karolina Widell 《Continental Shelf Research》2007

Observations are presented of currents, hydrography and turbulence in a jet-type tidally forced fjord in Svalbard. The fjord was ice covered at the time of the experiment in early spring 2004. Turbulence measurements were conducted by both moored instruments within the uppermost 5 m below the ice and a microstructure profiler covering 3–60 m at 75 m depth. Tidal choking at the mouth of the fjord induces a tidal jet advecting relatively warmer water past the measurement site and dominating the variability in hydrography. While there was no strong correlation with the observed hydrography or mixing and the phase of the semidiurnal tidal cycle, the mean structure in dissipation of turbulent kinetic energy, work done under the ice and the mixing in the water column correlated with the current when conditionally sampled for tidal jet events. Observed levels of dissipation of turbulent kinetic energy per unit mass, 1.1×10⁻⁷ W kg⁻¹, and eddy diffusivity, 7.3×10⁻⁴ m² s⁻¹, were comparable to direct measurements at other coastal sites and shelves with rough topography and strong forcing. During spring tides, an average upward heat flux of 5 W m⁻² in the under-ice boundary layer was observed. Instantaneous (1 h averaged) large heat flux events were correlated with periods of large inflow, hence elevated heat fluxes were associated with the tidal jet and its heat content. Vertical heat fluxes are derived from shear-probe measurements by employing a novel model for eddy diffusivity [Shih et al., 2005. Parameterization of turbulent fluxes and scales using homogeneous sheared stably stratified turbulence simulations. Journal of Fluid Mechanics 525, 193–214]. When compared to the direct heat flux measurements using the eddy correlation method at 5 m below the ice, the upper 4–6 m averaged heat flux estimates from the microstructure profiler agreed with the direct measurements to within 10%. During the experiment water column was stably, but weakly, stratified. Destabilizing buoyancy fluxes recorded close to the ice were absent at 5 m below the ice, and overall, turbulence production was dominated by shear. A scaling for dissipation employing production by both stress and buoyancy [Lombardo and Gregg, 1989. Similarity scaling of viscous and thermal dissipation in a convecting boundary layer. Journal of Geophysical Research 94, 6273–6284] was found to be appropriate for the under-ice boundary layer.  相似文献   

Buchbesprechungen     

B. M. Novak  Peter Perret 《Aquatic Sciences - Research Across Boundaries》1979,41(2):421-421

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The Czech Hydrometeorological Institute's severe storm nowcasting system     

Petr Novak   《Atmospheric Research》2007,83(2-4):450-457

To satisfy requirements for operational severe weather monitoring and prediction, the Czech Hydrometeorological Institute (CHMI) has developed a severe storm nowcasting system which uses weather radar data as its primary data source. Previous CHMI studies identified two methods of radar echo prediction, which were then implemented during 2003 into the Czech weather radar network operational weather processor. The applications put into operations were the Continuity Tracking Radar Echoes by Correlation (COTREC) algorithm, and an application that predicts future radar fields using the wind field derived from the geopotential at 700 hPa calculated from a local numerical weather prediction model (ALADIN).To ensure timely delivery of the prediction products to the users, the forecasts are implemented into a web-based viewer (JSMeteoView) that has been developed by the CHMI Radar Department. At present, this viewer is used by all CHMI forecast offices for versatile visualization of radar and other meteorological data (Meteosat, lightning detection, NWP LAM output, SYNOP data) in the Internet/Intranet environment, and the viewer has detailed geographical navigation capabilities.  相似文献   

Decomposing Malaria Mosquito Aquatic Habitat Data into Spatial Autocorrelation Eigenvectors in a SAS/GIS^® Module     

Benjamin G Jacob  Daniel A Griffith  Robert J Novak 《Transactions in GIS》2008,12(3):341-364

We present a geostatistical approach that accounts for spatial autocorrelation in malaria mosquito aquatic habitats in two East African urban environments. QuickBird 0.61 m data, encompassing visible bands and the near infra‐red (NIR) bands, were selected to synthesize images of Anopheles gambiae s.l. aquatic habitats in Kisumu and Malindi, Kenya. Field sampled data of An. gambiae s.l. aquatic habitats were used to determine which ecological covariates were associated with An. gambiae s.l. larval habitat development. A SAS/GIS^® spatial database was used to calculate univariate statistics, correlations and perform Poisson regression analyses on the An. gambiae s.l. aquatic habitat datasets. Semivariograms and global autocorrelation statistics were generated in ArcGIS^®. The spatially dependent models indicate the distribution of An. gambiae s.l. aquatic habitats exhibits weak positive autocorrelation in both study sites, with aquatic habitats of similar log‐larval counts tending to cluster in space. Individual anopheline habitats were further evaluated in terms of their covariations with spatial autocorrelation by regressing them on candidate spatial filter eigenvectors. This involved the decomposition of Moran's I statistic into orthogonal and uncorrelated map pattern components using a negative binomial regression. The procedure generated synthetic map patterns of latent spatial correlation representing the geographic configuration of An. gambiae s.l. aquatic habitat locations in each study site. The Gaussian approximation spatial filter models accounted for approximately 13% to 32% redundant locational information in the ecological datasets. Spatial statistics generated in a SAS/GIS^® module can capture spatial dependency effects on the mean response term of a Poisson regression analysis of field and remotely sampled An. gambiae s.l. aquatic habitat data.  相似文献