scholarly journals On the robustness of emptying filling boxes to sudden changes in the wind

2019 ◽  
Vol 868 ◽  
Author(s):  
John Craske ◽  
Graham O. Hughes
Keyword(s):  
Thermal Stratification ◽  
Temporal Variations ◽  
Transient Dynamics ◽  
Upper And Lower Bounds ◽  
Marginal Stability ◽  
Confined Space ◽  
Forward Displacement ◽  
Previous Formulation ◽  
Instantaneous Increase ◽  
Good Agreement

We determine the smallest instantaneous increase in the strength of an opposing wind that is necessary to permanently reverse the forward displacement flow that is driven by a two-layer thermal stratification. With an interpretation in terms of the flow’s energetics, the results clarify why the ventilation of a confined space with a stably stratified buoyancy field is less susceptible to being permanently reversed by the wind than the ventilation of a space with a uniform buoyancy field. For large opposing wind strengths we derive analytical upper and lower bounds for the system’s marginal stability, which exhibit a good agreement with the exact solution, even for modest opposing wind strengths. The work extends a previous formulation of the problem (Lishman & Woods, Build. Environ., vol. 44 (4), 2009, pp. 666–673) by accounting for the transient dynamics and energetics associated with the homogenisation of the interior, which prove to play a significant role in buffering temporal variations in the wind.

scholarly journals STH/CFD Coupled Simulation of the Protected Loss of Flow Accident in the CIRCE-HERO Facility

2020 ◽  
Vol 10 (20) ◽  
pp. 7032 ◽  
Author(s):  
Pucciarelli Andrea ◽  
Galleni Francesco ◽  
Moscardini Marigrazia ◽  
Martelli Daniele ◽  
Forgione Nicola
Keyword(s):  
Thermal Stratification ◽  
Outlet Section ◽  
Experimental Conditions ◽  
Ansys Fluent ◽  
Internal Loop ◽  
Fuel Pin ◽  
Mass Flow Rates ◽  
Computational Fluid Dynamics Cfd ◽  
The University ◽  
Good Agreement

The paper presents the application of a coupling methodology between Computational Fluid Dynamics (CFD) and System Thermal Hydraulic (STH) codes developed at the University of Pisa. The methodology was applied to the CIRCE-HERO facility in order to reproduce the recently performed experimental conditions simulating a Protected Loss Of Flow Accident (PLOFA). The facility consists of an internal loop, equipped with a fuel pin simulator and a steam generator, and an external pool. In this coupling application, the System code RELAP5 is adopted for the simulation of the internal loop while the CFD code ANSYS Fluent is used for the sake of simulating the pool. The connection between the two addressed domains is provided at the inlet and outlet section of the internal loop; a thermal coupling is also performed in order to reproduce the observed thermal stratification phenomenon. The obtained results are promising and a good agreement was obtained for both the mass flow rates and temperature measurements. Capabilities and limitations of the adopted coupling technique are discussed in the present paper also providing suggestions for improvements and developments to be achieved in the frame of future applications.

scholarly journals Contributions of Trans-boundary Transport to the Summertime Air Quality in Beijing, China

2016 ◽  
Author(s):  
Jiarui Wu ◽  
Guohui Li ◽  
Junji Cao ◽  
Naifang Bei ◽  
Yichen Wang ◽  
...  
Keyword(s):  
Air Quality ◽  
Control Strategies ◽  
Dominant Role ◽  
Fine Particulate Matter ◽  
Temporal Variations ◽  
Pollutant Emissions ◽  
Beijing China ◽  
Local Emissions ◽  
Factor Separation ◽  
Good Agreement

Abstract. In the present study, the WRF-CHEM model is used to evaluate the contributions of trans-boundary transport to the air quality in Beijing during a persistent air pollution episode from 5 to 14 July 2015 in Beijing-Tianjin-Hebei (BTH), China. Generally, the predicted temporal variations and spatial distributions of PM2.5 (fine particulate matter), O3 (ozone), and NO2 are in good agreement with observations in BTH. The WRF-CHEM model also reproduces reasonably well the temporal variations of aerosol species compared to measurements in Beijing. The factor separation approach is employed to evaluate the contributions of trans-boundary transport of emissions outside of Beijing to the PM2.5 and O3 levels in Beijing. On average, in the afternoon during the simulation episode, the pure local emissions contribute 22.4 % to the O3 level in Beijing, less than 36.6 % from pure emissions outside of Beijing. The O3 concentrations in Beijing are decreased by 5.1 % in the afternoon due to interactions of local emissions with those outside of Beijing. The pure emissions outside of Beijing play a dominant role in the PM2.5 level in Beijing, with a contribution of 61.5 %, much more than 13.7 % from pure Beijing local emissions. The emissions interactions enhance the PM2.5 concentrations in Beijing, with a contribution of 5.9 %. Therefore, the air quality in Beijing is primarily determined by the trans-boundary transport of emissions outside of Beijing during summertime, showing that the cooperation with neighboring provinces to mitigate pollutant emissions is a key for Beijing to improve air quality. Considering the uncertainties in the emission inventory and the meteorological field simulations, further studies need to be performed to improve the WRF-CHEM model simulations to reasonably evaluate trans-boundary transport contributions to the air quality in Beijing for supporting the design and implementation of emission control strategies.

scholarly journals A novel rapid method of purely elastic solution correction to estimate multiaxial elastic-plastic behaviour

2019 ◽  
Vol 6 (3) ◽  
pp. 269-283
Author(s):  
Nicolas Antoni
Keyword(s):  
Three Dimensional ◽  
Elastic Solution ◽  
Upper And Lower Bounds ◽  
Efficient Design ◽  
Effective Parameters ◽  
Relative Deviation ◽  
Elastic Plastic ◽  
Plastic Behaviour ◽  
A New Technique ◽  
Good Agreement

Abstract In structural analysis, it is of paramount importance to assess the level of plasticity a structure may experience under monotonic or cyclic loading as this may have a significant impact, particularly in fatigue analysis for singular areas. For efficient design analyses, it is often searched for a compromise in accuracy that consists in correcting a purely elastic analysis, generally simpler and faster to obtain compared to a full non-linear Finite Element (FE) analysis involving elastic-plastic behaviour, to estimate the actual elastic-plastic solution. There exists a great number of correction techniques in the literature among which the most famous and commonly used are Neuber and ESED energy-based methods. Nonetheless, both of them are known to provide respectively upper and lower bounds of the exact solution in most cases, with a relative deviation depending on the level of multiaxiality and on the amount of stress redistribution due to yielding. The new methodology presented in this paper is based on the well-known multiaxial Radial Return Method (RRM) revisited using effective parameters approach. By essence, it is fast and can be applied either to analytical elastic problems or to more complex three-dimensional elastic FE analyses. The accuracy of the proposed method is assessed by direct comparison with results from Neuber and ESED methods on various examples. It is also shown for each of them that this new method is very good agreement with the exact elastic-plastic solution. Highlights A new technique of purely elastic solution correction is presented and evaluated. The proposed method relies on the modification of Return Radial Method (RRM) considering effective parameters in lieu of initial elastic tensor. The obtained equation preserves the simplicity and efficiency of other well-known energy-based methods such as Neuber and ESED. It is shown on several examples that the proposed technique is in very good agreement with the exact or FE elastic-plastic solution, with very low relative deviation.

Analytical solutions for tsunami runup on a plane beach: single waves, N-waves and transient waves

2010 ◽  
Vol 645 ◽  
pp. 27-57 ◽  
Author(s):  
PER A. MADSEN ◽  
HEMMING A. SCHÄFFER
Keyword(s):  
Solitary Waves ◽  
Analytical Solutions ◽  
Kdv Equation ◽  
Deep Ocean ◽  
Temporal Variations ◽  
Convolution Integral ◽  
Transient Waves ◽  
Horizontal Length ◽  
Sloping Beach ◽  
Good Agreement

In the literature it has so far been common practice to consider solitary waves and N-waves (composed of solitary waves) as the appropriate model of tsunamis approaching the shoreline. Unfortunately, this approach is based on a tie between the nonlinearity and the horizontal length scale (or duration) of the wave, which is not realistic for geophysical tsunamis. To resolve this problem, we first derive analytical solutions to the nonlinear shallow-water (NSW) equations for the runup/rundown of single waves, where the duration and the wave height can be specified separately. The formulation is then extended to cover leading depression N-waves composed of a superposition of positive and negative single waves. As a result the temporal variations of the runup elevation, the associated velocity and breaking criteria are specified in terms of polylogarithmic functions. Finally, we consider incoming transient wavetrains generated by monopole and dipole disturbances in the deep ocean. The evolution of these wavetrains, while travelling a considerable distance over a constant depth, is influenced by weak dispersion and is governed by the linear Korteweg–De Vries (KdV) equation. This process is described by a convolution integral involving the Airy function. The runup on the plane sloping beach is then determined by another convolution integral involving the incoming time series at the foot of the slope. A good agreement with numerical model results is demonstrated.

Temporal Trends in the Rates of Multiple Maternities in England and Wales

2007 ◽  
Vol 10 (4) ◽  
pp. 626-632 ◽  
Author(s):  
Aldur W. Eriksson ◽  
Johan Fellman
Keyword(s):  
Maternal Age ◽  
Temporal Trends ◽  
Developed Countries ◽  
Temporal Variations ◽  
Steady Increase ◽  
Delayed Childbearing ◽  
England And Wales ◽  
Older Mothers ◽  
Continuous Decrease ◽  
Good Agreement

AbstractAfter a long continuous decrease, the twinning and higher multifetal rates in many developed countries have increased during the last 2 to 3 decades. This change has been attributed to delayed childbearing and to increased use of subfertility treatments, particularly in women over 35 years of age. In this study we analyze how these new trends depend on changes in the effect of maternal age on the rates of multiple maternities. Our study is based on data for England and Wales for the period 1938 to 2003. The temporal variations show a decreasing trend to a trough around 1980 and after that a steady increase. This increase was more marked for higher multifetal rates and was particularly high for quadruplets. Furthermore, we identified changes in the age-specific rates resulting in increased levels for older mothers. These findings are in good agreement with our results from Nordic populations.

scholarly journals Diagnosing Ocean Stirring: Comparison of Relative Dispersion and Finite-Time Lyapunov Exponents

2012 ◽  
Vol 42 (7) ◽  
pp. 1173-1185 ◽  
Author(s):  
Darryn W. Waugh ◽  
Shane R. Keating ◽  
Mei-Lin Chen
Keyword(s):  
Lyapunov Exponents ◽  
Finite Time ◽  
Temporal Variations ◽  
Uniform Strain ◽  
Upper And Lower Bounds ◽  
Relative Dispersion ◽  
Integration Time ◽  
Finite Time Lyapunov Exponents ◽  
Wide Range ◽  
Analytical Expressions

Abstract The relationship between two commonly used diagnostics of stirring in ocean and atmospheric flows, the finite-time Lyapunov exponents λ and relative dispersion R2, is examined for a simple uniform strain flow and ocean flow inferred from altimetry. Although both diagnostics are based on the separation of initially close particles, the two diagnostics measure different aspects of the flow and, in general, there is not a one-to-one relationship between the diagnostics. For a two-dimensional flow with time-independent uniform strain, there is a single time-independent λ, but there is a wide range of values of R2 for individual particle pairs. However, it is shown that the upper and lower limits of R2 for individual pairs, the mean value over a large ensemble of pairs, and the probability distribution function (PDF) of R2 have simple relationships with λ. Furthermore, these analytical expressions provide a reasonable approximation for the R2–λ relationship in the surface ocean flow based on geostrophic velocities derived from satellite altimeter measurements. In particular, the bimodal distribution, upper and lower bounds, and mean values from the ocean flow are similar to the analytical expressions for a uniform strain flow. How well, as well as over what integration time scale, this holds depends on the spatial and temporal variations within the ocean region being considered.

A Mathematical Model for Recurrent Twinning

1990 ◽  
Vol 39 (3) ◽  
pp. 307-316 ◽  
Author(s):  
J.O. Fellman ◽  
A.W. Eriksson
Keyword(s):  
Temporal Variations ◽  
Likelihood Method ◽  
Demographic Information ◽  
Poor Agreement ◽  
Expected Number ◽  
Sibship Size ◽  
Considerable Excess ◽  
The Mean ◽  
Crude Estimate ◽  
Good Agreement

AbstractIn an attempt to improve our understanding of the factors that affect human twinning, we further developed the models given by Hellin (1895) and Peller (1946). The connection between these models and our own model (“Fellman's law”) were studied. These attempts have resulted in a more general model, which was then applied to data from Åland Islands (1750-1939), Nîmes (1790-1875), Stuttgart (about 1790-1900) and Utah (1850-1900). The product of the mean sibship size and the total twinning rate can be considered as a crude estimate of the expected number of sets of twins in a sibship. The same can be said about the twinning parameter in our model. These estimates are in good agreement. If we consider twinning data only, we obtain the geometric distribution, and log (Nk), where Nk is the number of mothers with k twin maternities, is a linear function of the number of recurrences. Graphically, this property can easily be checked. For sibships containing three or more sets of twins, all four populations show higher values than expected, particularly the populations from Stuttgart and Utah, which data also show poor agreement according to a χ2-test. A more exact model would demand more detailed demographic information, such as distribution of sibship sizes, age-specific twinning rates and temporal variations in twinning.The osberved number of mothers in Åland with several recurrences of multiple maternities shows a considerable excess over the expected number as predicted by Peller's rule. The parameters in our model can be estimated by the maximum likelihood method and the obtained model fits the data better then Peller's model.

The influence of aurora on ionospheric electron content

1981 ◽  
Vol 59 (8) ◽  
pp. 1089-1096 ◽  
Author(s):  
P. A. Forsyth ◽  
J. A. Fulford ◽  
J. Hofstee ◽  
G. F. Lyon
Keyword(s):  
Relaxation Times ◽  
Temporal Variations ◽  
Optical Data ◽  
Electron Content ◽  
Model Calculations ◽  
Ionospheric Electron Content ◽  
Temporal And Spatial ◽  
Sensitive Structure ◽  
Small Change ◽  
Good Agreement

The ionospheric electron content was measured at La Ronge, Sask. for a variety of auroral conditions during the Pulsating Aurora Campaign in February of 1980. The two-frequency differential phase technique was used with the NNSS satellite beacons. Comparisons of optical data and the radio results indicate that for quite strong pulsations the electron content is modulated by less than 2%. Even this small change is somewhat larger than the purely temporal variations to be expected on the basis of currently accepted relaxation times in the ionosphere. If the observed fluctuations are interpreted as representing both temporal and spatial variations, good agreement is obtained with model calculations. For irregularity sizes and strengths to which the experiment is sensitive, structure was present in diffuse or patchy aurora but absent from at least some well defined forms. This suggests that the technique can be used to explore the mechanism of formation of the irregularities.

Numerical Simulation of Thermal Stratification in the Upper Plenum of Fast Reactor

2013 ◽  
Author(s):  
Seok-Ki Choi ◽  
Tae-Ho Lee
Keyword(s):  
Experimental Data ◽  
Steady State ◽  
Thermal Stratification ◽  
Numerical Solutions ◽  
Steady State Solution ◽  
Temporal Variations ◽  
State Solution ◽  
Thermal Mixing ◽  
Commercial Code ◽  
Inlet Conditions

A numerical analysis of the thermal stratification in the upper plenum of the MONJU fast breeder reactor was performed. Calculations were performed for a 1/6 simplified model of the MONJU reactor using the commercial code, CFX-13. To better resolve the geometrically complex upper core structure of the MONJU reactor, the porous media approach was adopted for the simulation. First, a steady state solution was obtained, and the transient solutions were then obtained for the turbine trip test conducted in December 1995. The time dependent inlet conditions for the mass flow rate and temperature were provided by JAEA. Good agreement with the experimental data was observed for the steady state solution. The numerical solution of the transient analysis shows the formation of thermal stratification within the upper plenum of the reactor vessel during the turbine trip test. The temporal variations of temperature were predicted accurately by the present method in the initial rapid coastdown period (∼300 seconds). However, the transient numerical solutions show a faster thermal mixing than that observed in the experiment after the initial coastdown period. A near homogenization of the temperature field in the upper plenum is predicted after about 900 seconds, which is a much shorter-term thermal stratification than the experimental data indicates.

scholarly journals The circulation of the Persian Gulf: a numerical study

Ocean Science ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 27-41 ◽  
Author(s):  
J. Kämpf ◽  
M. Sadrinasab
Keyword(s):  
United Arab Emirates ◽  
Persian Gulf ◽  
Thermal Stratification ◽  
Numerical Study ◽  
Three Dimensional ◽  
Mass Properties ◽  
Inverse Estuary ◽  
The Persian Gulf ◽  
Autumn And Winter ◽  
Good Agreement

Abstract. We employ a three-dimensional hydrodynamic model (COHERENS) in a fully prognostic mode to study the circulation and water mass properties of the Persian Gulf – a large inverse estuary. Our findings, which are in good agreement with observational evidence, suggest that the Persian Gulf experiences a distinct seasonal cycle in which a gulf-wide cyclonic overturning circulation establishes in spring and summer, but this disintegrates into mesoscale eddies in autumn and winter. Establishment of the gulf-wide circulation coincides with establishment of thermal stratification and strengthening of the baroclinic exchange circulation through the Strait of Hormuz. Winter cooling of extreme saline (>45) water in shallow regions along the coast of United Arab Emirates is a major driver of this baroclinic circulation.

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