Analytical Prediction of Tubular Light-Pipe Performance Under Arbitrary Sky Conditions

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Jaromír Petržala ◽  
Ladislav Kómar
Keyword(s):  
Analytical Solution ◽  
Light Guide ◽  
Analytical Prediction ◽  
Optical Efficiency ◽  
Deep Interior ◽  
Wide Range ◽  
The Mean ◽  
Light Guides ◽  
Sky Conditions ◽  
Good Agreement

The tubular light guides are devices allowing deliverance of solar light into deep interior rooms, offices, or underground spaces. Due to considerable costs of such systems, the reasonable assessment of their lighting performance is desirable. To predict accurately their efficiency, precise numerical computations have to be performed. Such computations may be strongly time consuming, mainly when mass calculations are required as it is in case of the so-called climate-based daylight modeling. This paper presents an analytical solution to the optical efficiency of cylindrical straight pipes that is applicable over a wide range of pipe’s parameters and under arbitrary sky luminance conditions. The proposed method gives results in good agreement with ray-tracing numerical simulations—the mean absolute percentage errors are less than 3%—but unlike them, the calculations are much faster. Therefore, it appears to be convenient for daylight modeling, which takes into account utilization of tubular light guide systems in buildings.

An equation to predict the leaching of surface-applied nitrate

1975 ◽  
Vol 85 (3) ◽  
pp. 443-454 ◽  
Author(s):  
I. G. Burns
Keyword(s):  
Soil Profile ◽  
Field Capacity ◽  
Weather Conditions ◽  
Published Data ◽  
Wide Range ◽  
The Mean ◽  
New Equation ◽  
Image Position ◽  
Good Agreement

SUMMARYThe fraction (f) of surface-applied nitrate leached below any depth h cm in a uniform soil profile may be calculated from the equationwhere P is the quantity of water draining through the soil (in cm) and Vm is the percentage volumetric field capacity. The fraction of nitrate retained is then (1—f).This equation has been tested using published data. Values of h corresponding to the mean displacement (f = 0·5) were calculated for a wide range of soil and weather conditions and the results compared with mean displacements measured in the field. Similar comparisons were made with the leaching equation of Rousselle (1913) and Levin (1964). The new equation gives good agreement with the observed data, whereas the Rousselle-Levin equation generally overestimates the mean displacement of nitrate. Methods of applying the equations to field situations are discussed.

scholarly journals Convective Heat Transfer in a Rotating Cylindrical Cavity

1982 ◽  
Author(s):  
J. M. Owen ◽  
H. S. Onur
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Gap Ratio ◽  
Wide Range ◽  
The Mean ◽  
Radial Outflow ◽  
Good Agreement

In order to gain an understanding of the conditions inside air-cooled gas-turbine rotors, flow visualization, laser-doppler anemometry and heat-transfer measurements have been made in a rotating cavity with either an axial throughflow or a radial outflow of coolant. For the axial throughflow tests, a correlation has been obtained for the mean Nusselt number in terms of the cavity gap ratio, the axial Reynolds number and rotational Grashof number. For the radial outflow tests, velocity measurements are in good agreement with solutions of the linear (laminar and turbulent) Ekman layer equations, and flow visualization has revealed the destabilizing effect of buoyancy forces on the flow structure. The mean Nusselt numbers have been correlated, for the radial outflow case, over a wide range of gap ratios, coolant flow rates, rotational Reynolds numbers and Grashof numbers. As well as the three (forced convection) regimes established from previous experiments, a fourth (free convection) regime has been identified.

scholarly journals An Accurate Prediction of Daylight Pipe Harvesting of Interior Space

2019 ◽  
Vol 9 (17) ◽  
pp. 3552
Author(s):  
Ladislav Kómar ◽  
Miroslav Kocifaj
Keyword(s):  
Light Guide ◽  
Specific Property ◽  
Empirical Models ◽  
Interior Space ◽  
Optical Efficiency ◽  
Atmospheric Turbidity ◽  
Illumination Method ◽  
Light Guides ◽  
First Time

The performance of a light guide under arbitrary meteorological conditions is difficult to predict numerically because none of the present methods can account for the random configuration of clouds. Although, partly cloudy skies typically occur very frequently in many regions over the globe, the effects of cloud sizes, distributions, or altitudes on the luminous effectiveness of a light guide remain virtually unknown. The physical installation of light guides does not allow for a controlled experiment in which a single parameter can be varied within a defined range, while holding all other parameters constant. Numerical modeling is the only practical way to provide deep insights on the role of a specific property, such as cloud coverage, and its importance relative to all others (e.g., atmospheric turbidity). We have developed a unique solution through linking the UniSky simulator and HOLIGILM (hollow light guide interior illumination method) tool, while providing for the first time a powerful method that can provide accurate predictions and understanding of the fundamental differences of light guide behaviors under homogeneous and inhomogeneous sky states. The use of homogeneous skies in low-accuracy empirical models often results in overestimated/underestimated effectiveness of some light-guide systems. The model we have developed can predict complex optical signatures that are normally impossible to reproduce using up-to date empirical models (e.g., the illuminance patterns due to isolated clouds or clouds traversing across the sky). The optical efficiency, average cosine and working-place illuminance are analyzed and compared in order to demonstrate the model capabilities.

Convective Heat Transfer in a Rotating Cylindrical Cavity

1983 ◽  
Vol 105 (2) ◽  
pp. 265-271 ◽  
Author(s):  
J. M. Owen ◽  
H. S. Onur
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Laser Doppler Anemometry ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Gap Ratio ◽  
Wide Range ◽  
The Mean ◽  
Radial Outflow ◽  
Good Agreement

In order to gain an understanding of the conditions inside air-cooled, gas-turbine rotors, flow visualization, laser-doppler anemometry, and heat-transfer measurements have been made in a rotating cavity with either an axial throughflow or a radial outflow of coolant. For the axial throughflow tests, a correlation has been obtained for the mean Nusselt number in terms of the cavity gap ratio, the axial Reynolds number, and rotational Grashof number. For the radial outflow tests, velocity measurements are in good agreement with solutions of the linear (laminar and turbulent) Ekman layer equations, and flow visualization has revealed the destabilizing effect of buoyancy forces on the flow structure. The mean Nusselt numbers have been correlated, for the radial outflow case, over a wide range of gap ratios, coolant flow rates, rotational Reynolds numbers, and Grashof numbers. As well as the three (forced convection) regimes established from previous experiments, a fourth (free convection) regime has been identified.

Impact Behavior of Square Crash Box Structures Having Holes at Corners

2014 ◽  
Vol 660 ◽  
pp. 613-617 ◽  
Author(s):  
Nguyen Chanh Nghia ◽  
Tatacipta Dirgantara ◽  
Sigit P. Santosa ◽  
Annisa Jusuf ◽  
Ichsan Setya Putra
Keyword(s):  
Theoretical Prediction ◽  
Impact Behavior ◽  
Analytical Prediction ◽  
Axial Crushing ◽  
Safe Level ◽  
Crushing Force ◽  
Box Structures ◽  
The Mean ◽  
The One ◽  
Good Agreement

In this paper, an analytical prediction and numerical simulation of the behavior of square crash box structures having hole at corners on dynamic axial crushing are studied. The focus of the present theoretical prediction is to calculate the mean crushing force and maximum crushing force during the folding process subjected to axial impact loading. Then, the effect of hole size to the crushing response of square crash box structures was also evaluated. For validation, an explicit non-linear commercial finite element code LS-DYNA was used to predict the response of the structures subjected to axial crushing. It was found that results of numerical method and theoretical prediction were in good agreement. The results showed that, by inserting holes at corners, the folding can be controlled to be always started from the hole, and peak crush load on the first fold can be reduced significantly. Meanwhile, the decreasing of mean crushing force is insignificant compared to the one without holes. Hence, the characteristic of impact energy absorption in a progressive buckling can be improved, the damage in passenger compartment can be minimized, and the deceleration level can be kept in safe level to prevent injury of the passenger.

scholarly journals Experimental and Simulation Study of n-Heptane Adsorption on Rutile

2007 ◽  
Vol 25 (7) ◽  
pp. 517-530 ◽  
Author(s):  
G.U. Rakhmatkariev ◽  
A.J. Palace Carvalho ◽  
J.P. Prates Ramalho
Keyword(s):  
Bulk Liquid ◽  
Grand Canonical Monte Carlo ◽  
Differential Heat ◽  
Wide Range ◽  
Adsorption Entropy ◽  
The Mean ◽  
Differential Heat Of Adsorption ◽  
Grand Canonical ◽  
Good Agreement

The adsorption of n-heptane on microcrystalline rutile has been studied experimentally by thermodynamic techniques (adsorption isotherms and microcalorimetry) over a wide range of coverage at 303 K and complemented by Grand Canonical Monte Carlo simulations. The differential heat of adsorption exhibited three descending segments corresponding to the adsorption of n-heptane on three types of surfaces. The mean molar adsorption entropy of n-heptane in the monolayer was less than the entropy of the bulk liquid by ca. −23 J/(mol K), thus revealing a hindered state of motion for the n-heptane molecules on the surface of rutile. Simulations of the adsorption of n-heptane were performed on the three most abundant crystallographic faces of rutile. The adsorption isotherm obtained from the combination of the isotherm for each face weighted by the respective abundance was found to be in good agreement with experimental data. A structural characterization of n-heptane near the surface was also conducted which indicated that the substrate strongly perturbed the distribution of the n-heptane conformations relative to the situation found for the gaseous phase. Adsorbed molecules are predominantly orientated with their long axes, with the zig-zag planes of their backbones parallel to the surface and preferentially aligned along the five-fold cus Ti4+ ions of the faces. Fewer gauche conformations were observed for molecules near the surface than was characteristic of the bulk phase.

scholarly journals Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

2011 ◽  
Vol 11 (11) ◽  
pp. 5457-5469 ◽  
Author(s):  
G. G. Palancar ◽  
R. E. Shetter ◽  
S. R. Hall ◽  
B. M. Toselli ◽  
S. Madronich
Keyword(s):  
Three Dimensional ◽  
Transport Models ◽  
Model Calculations ◽  
Actinic Flux ◽  
Clear Sky ◽  
Photolysis Rates ◽  
Wide Range ◽  
Sensitivity Studies ◽  
Sky Conditions ◽  
Good Agreement

Abstract. Ultraviolet (UV) actinic fluxes measured with two Scanning Actinic Flux Spectroradiometers (SAFS) aboard the NASA DC-8 aircraft are compared with the Tropospheric Ultraviolet-Visible (TUV) model. The observations from 17 days in July-August 2004 (INTEX-NA field campaign) span a wide range of latitudes (28° N–53° N), longitudes (45° W–140° W), altitudes (0.1–11.9 km), ozone columns (285–353 DU), and solar zenith angles (2°–85°). Both cloudy and cloud-free conditions were encountered. For cloud-free conditions, the ratio of observed to clear-sky-model actinic flux (integrated from 298 to 422 nm) was 1.01±0.04, i.e. in good agreement with observations. The agreement improved to 1.00±0.03 for the down-welling component under clear sky conditions. In the presence of clouds and depending on their position relative to the aircraft, the up-welling component was frequently enhanced (by as much as a factor of 8 relative to cloud-free values) while the down-welling component showed both reductions and enhancements of up to a few tens of percent. Including all conditions, the ratio of the observed actinic flux to the cloud-free model value was 1.1±0.3 for the total, or separately 1.0±0.2 for the down-welling and 1.5±0.8 for the up-welling components. The correlations between up-welling and down-welling deviations are well reproduced with sensitivity studies using the TUV model, and are understood qualitatively with a simple conceptual model. This analysis of actinic flux observations illustrates opportunities for future evaluations of photolysis rates in three-dimensional chemistry-transport models.

On the Influence of Friction in the Calculation of Conical Disk Springs

1999 ◽  
Vol 121 (4) ◽  
pp. 622-627 ◽  
Author(s):  
G. Curti ◽  
R. Montanini
Keyword(s):  
Finite Element ◽  
Friction Coefficient ◽  
Analytical Solution ◽  
Maximum Error ◽  
Accurate Estimate ◽  
Analytical Prediction ◽  
Numerical Examples ◽  
Finite Element Calculations ◽  
New Formulation ◽  
Good Agreement

An analytical solution is proposed by the authors in order to take into account the effects of friction in the calculation of conical disk springs. The new formulation allows a more accurate estimate of the load corresponding to a given displacement, but it implies the knowledge of the friction coefficient f between the spring and the supporting surfaces. The reported numerical examples show that, disregarding friction effects, the maximum error committed in the evaluation of the load is in the range 2–5%, with f = 0.14 (average friction coefficient value determined experimentally on commercial conical disk springs with different geometry). Comparison with both experimental and finite element calculations show a very good agreement of the analytical prediction.

scholarly journals Ultraviolet actinic flux in clear and cloudy atmospheres: model calculations and aircraft-based measurements

2011 ◽  
Vol 11 (1) ◽  
pp. 3321-3354 ◽  
Author(s):  
G. G. Palancar ◽  
R. E. Shetter ◽  
S. R. Hall ◽  
B. M. Toselli ◽  
S. Madronich
Keyword(s):  
Three Dimensional ◽  
Transport Models ◽  
Model Calculations ◽  
Actinic Flux ◽  
Clear Sky ◽  
Photolysis Rates ◽  
Wide Range ◽  
Sensitivity Studies ◽  
Sky Conditions ◽  
Good Agreement

Abstract. Ultraviolet (UV) actinic fluxes measured with two Scanning Actinic Flux Spectroradiometers (SAFS) aboard the NASA DC-8 aircraft are compared with the Tropospheric Ultraviolet-Visible (TUV) model. The observations from 17 days in July–August 2004 (INTEX-NA field campaign) span a wide range of latitudes (27.5° N–53.0° N), longitudes (45.1° W–139.5° W), altitudes (0.1–11.9 km), ozone columns (285.4–352.7 DU), and solar zenith angles (1.7°–85°). Both cloudy and cloud-free conditions were encountered. For cloud-free conditions, the ratio of observed to clear-sky-model actinic flux (integrated from 298 to 422 nm) is 1.01±0.04, i.e. in good agreement with observations. The agreement improves to 1.00±0.03 for the down-welling component under clear sky conditions. In the presence of clouds, both down-welling and up-welling components show reductions or enhancements from clear sky values, depending on the position of the airplane relative to clouds. The correlations between up-welling and down-welling deviations are well reproduced with sensitivity studies using the TUV model, and are understood qualitatively with a simple conceptual model. This analysis of actinic flux observations illustrates opportunities for future evaluations of photolysis rates in three-dimensional chemistry-transport models.

Compression of a Single Transverse Ridge in a Circular Elastohydrodynamic Contact

2003 ◽  
Vol 125 (2) ◽  
pp. 275-282 ◽  
Author(s):  
R. P. Glovnea ◽  
J. W. Choo ◽  
A. V. Olver ◽  
H. A. Spikes
Keyword(s):  
Thin Film ◽  
Film Thickness ◽  
Local Perturbation ◽  
Local Pressure ◽  
Numerical Predictions ◽  
Pure Rolling ◽  
Wide Range ◽  
The Mean ◽  
Theoretical Results ◽  
Good Agreement

A detailed experimental study has been made of the behavior of a 100 nm high transversely oriented ridge in an elastohydrodynamic (EHD) contact. Ultra-thin film interferometry has been used to measure film profiles accurately over a very wide range of lubricant film thicknesses, from a few nanometers up to nearly one micron. This enables the recovery of the amplitude of the inlet perturbation geometry with increasing EHD film thickness to be quantified and compared with numerical predictions. In pure rolling under very thin film conditions, corresponding to a smooth surface EHD film thickness of 10 nm, the surfaces near the ridge were squashed down, leading to a constriction in the film of only about 9 percent of the height of the un-deformed ridge. As the EHD film thickness increased, this deformation recovered until the ridge constriction regained about 90 percent of its original height at film thicknesses of about 1 μm. However this relatively rapid recovery only occurred in pure rolling and is attributed to the local perturbation of film convergence which the ridge generates while in the inlet region. This propagates through the contact at the mean speed of the surfaces and—in pure rolling—acts to diminish the effect of local squeeze. When sliding was present, the ridge remained almost fully deformed even when the mean film thickness was as much as twice the height of the original ridge. In this case, the ridge travels through the contact at a different speed from the mean of the two surfaces. The consequent decoupling of the ridge and the convergence perturbation results in a large local pressure due to squeeze which acts to inhibit recovery of the ridge. The general trend of the behavior of the lubricated ridge is shown to be in good agreement with earlier theoretical results.

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