External Wind Conditions Research Articles

Fire safety case study of a railway tunnel: Smoke evacuation

When a fire occurs in a tunnel, it is of great importance to assure the safety of the occupants of the tunnel. This is achieved by creating smoke-free spaces in the tunnel through control of the smoke gases. In this paper, results are presented of a study concerning the fire safety in a real scale railway tunnel test case. Numerical simulations are performed in order to examine the possibility of natural ventilation of smoke in inclined tunnels. Several aspects are taken into account: the length of the simulated tunnel section, the slope of the tunnel and the possible effects of external wind at one portal of the tunnel. The Fire Dynamics Simulator of the National Institute of Standards and Technology, USA, is applied to perform the simulations. The simulations show that for the local behavior of the smoke during the early stages of the fire, the slope of the tunnel is of little importance. Secondly, the results show that external wind and/or pressure conditions have a large effect on the smoke gases inside the tunnel. Finally, some idea for the value of the critical ventilation velocity is given. The study also shows that computational fluid dynamics calculations are a valuable tool for large scale, real life complex fire cases. .

REAL-TIME CLIMATE CONTROL IN A COMPLEX GREENHOUSE

This paper describes the development of an embedded real-time system devoted to climate control in a complex greenhouse. The control system is capable of managing multiple, independent polytunnels units (PTUs). Both the internal temperature and humidity of PTUs as well as the external temperature, rain fall and wind conditions are monitored and regulate decisions of the control system. The realization depends on the use of Java technologies and on a general methodology suited to the development of real-time systems. The approach is based on hierarchical state machines extended with timing constraints, and a supporting toolbox which enables graphical modelling, automatic code generation, simulation and real-time execution of a system. The paper discusses design and implementation aspects of the control system and reports information about its real operation.

Proton aurora in the cusp during southward IMF

One of the most distinct aurorae in the high‐latitude dayside region occurs at the footprint of the cusp. The Spectrographic Imager SI‐12 channel on the IMAGE spacecraft allows for long‐duration observations of the proton aurora in this region and thus enables morphological and quantitative studies of the behavior of the proton aurora under different external solar wind conditions. Here we extend an earlier study of the proton aurora in the cusp during northward interplanetary magnetic field (IMF) conditions [Frey et al., 2002] to southward IMF conditions. We find a very similar dependence of the cusp aurora's location in magnetic local time (MLT) on the IMF By component, with locations at prenoon for negative By and postnoon for positive By. We also confirm the previously established dependence of the proton aurora brightness on the solar wind dynamic pressure. However, for similar solar wind pressures the proton aurora is brighter for the southward IMF case than for the northward IMF case. The other major difference between southward and northward IMF conditions is the very strong dependence of the latitude location on the magnitude of the IMF Bz for southward IMF. We discuss both differences in terms of the location of the reconnection site at the magnetopause that is connected to the ionosphere along cusp magnetic field lines.

Lee-side Ventilation-induced Air Movement in a Large-scale Multi-span Greenhouse

Lee-side ventilation-induced air movement was experimentally investigated in a 1728 m2multi-span glasshouse. Air velocity measurements were performed by means of a customized multi-point two-dimensional sonic anemometer system which simultaneously measured the horizontal air velocity components parallel and normal to the ridge at 3 Hz frequency. The airflow pattern in the horizontal plane of a greenhouse was analysed qualitatively under different external wind conditions. The experimental results show both the vertical and the horizontal profiles of the normalized interior air speed as a function of the measurement height, the external wind speed and opening angle were acceptably presented by the simple linear functions. The airflow in the horizontal plane was of low turbulence with large eddies.

Observation and analysis of selected IMP 8 and WIND bow shock crossings in late 1994

Nine bow shock crossings from late 1994 are examined using data from the IMP 8 spacecraft as input to the Rankine‐Hugoniot (RH) conservation equations. In addition, two crossings from the same time period are examined using WIND spacecraft data. A nonlinear chi‐square minimization method is used to obtain the best fit bow shock (BS) normal and speed for each crossing. The shock normals and speeds are also calculated neglecting temperature, as well as using only the magnetic coplanarity and velocity coplanarity techniques. All of the methods generally give mutually consistent results. The orientations of the shock normals are consistent with the nominal bow shock shape. The shocks were expected to move according to a simple “breathing model in which the bow shock moves inward and outward from Earth according to changes in external solar wind conditions. However, the results show outward motion of the bow shock for all but one of all the crossings considered. Moreover, the direction of motion of the BS depends on the exact choice of the shock normal so that a slightly different shock normal can give a different sense of motion of the BS. We conclude that the RH equations that we use may be missing some terms which would provide an accurate description of the balance on both sides of the BS. In particular, the BS acceleration at its flanks is not taken into account by these equations.

Observations of bow shock motion during times of variable solar wind conditions

We examine seven periods during which IMP 8 made multiple crossings of Earth's bow shock during times when IMP 7 data were available to monitor external solar wind conditions. The positions of the bow shock encounters are consistent with reference shock shape models normalized to the solar wind conditions. We find that multiple crossings can usually be interpreted as being due to changes in the external solar wind parameters. We also find that inward motion of the shock is accompanied by large magnetosheath densities just before the shock sweeps across the spacecraft. We perform a chi‐square minimization analysis using a limited set of Rankine‐Hugoniot conditions across the bow shocks in order to determine their speeds and normals; we find that the shock velocities are generally consistent with the postulated inward and outward bow shock motions. Whether the crossings are observed on the dawnside or the duskside, most of the bow shock structures are quasi‐perpendicular due to changes in the external field orientation just upstream of the shock. The orientations of the normals are consistent with a model in which effects of changes in external conditions propagate as shock shape deformations which move downstream from the nose to the flanks.

The challenge of fire modelling

Fire presents a formidable challenge to the modeller. Not only are the underlying physical processes difficult to model (turbulent buoyant convection, radiative heat transfer, combustion) but imponderables such as the location of the fire within its enclosure, the configuration of ventilation openings and the external wind conditions will all affect the outcome. A variety of models have been developed over the years and have now matured to the point at which they are enjoying increasing popularity in practical design. This paper explores the current state of art in the development of modelling, and highlights successes, areas of particular difficulty and work currently in progress to meet the challenges posed by the needs of Fire Safety Engineering.

Magnetospheric substorms

Magnetospheric substorms encompass a myriad of dynamical phenomena resulting from the coupling of the solar wind with the Earth’s magnetic field and the ionosphere. Although external solar wind conditions conducive to substorm development are generally regarded as identified, the precise cause for substorm onset remains an outstanding unresolved problem. The contending theories include externally driven magnetic reconnection, magnetosphere–ionosphere coupling, thermal catastrophe, macro- and microinstabilities (such as interchange/ballooning, Kelvin–Helmholtz, tearing, lower-hybrid drift, modified two-stream, and ion-Weibel instabilities). The conventional approach to substorm modeling is to describe the entire substorm episode on the basis of a single mechanism. After a brief review and critique of existing substorm models, a new paradigm is introduced in which compatible features among different models are synthesized into a single one which is superior to any individual model in consistency with observations. This new paradigm advocates that substorms may be triggered by more than one mechanism and also that the full set of substorm phenomena may only be accounted for by more than one physical process. Some unresolved substorm problems amenable to immediate future investigation are also identified.

Large amplitude substorm motion of the magnetotail boundary

During a period of several days when the solar wind was relatively quiet, the magnetotail boundary near lunar distance swept back and forth past Explorer 33 as the spacecraft traveled through a distance perpendicular to the Earth‐sun line of about 17 Re. The boundary crossings are remarkably well‐correlated with peaks in the AE index, even though the magnitudes of the peaks are only on the order of 200 nT. Examination of the regions of multiple crossings on other Explorer 33 and 35 orbits reveals that they commonly cover large distances perpendicular to the Earth‐sun line, although correlation with AE is often obscured, probably by external solar wind conditions. We conclude that a substantial fraction of the scatter in published statistical plots of boundary crossing positions can be accounted for in terms of an internal substorm‐related motion with an amplitude of 5‐8 Re. The data suggest that the motion takes the form of a compressional deformation wave convecting down the tail.