Presence Of Strong Winds Research Articles

Safety assessment of caisson transport on a floating dock by frequency- and time-domain calculations

When caissons are mounted on a floating transportation barge and towed by a tug boat in waves, motion of the floating dock creates inertia and gravity induced slip forces on the caisson. If its magnitude exceeds the corresponding friction force between the two surfaces, a slip may occur, which can lead to an unwanted accident. In oblique waves, both pitch and roll motions occur simultaneously and their coupling effects for slip and friction forces become more complicated. With the presence of strong winds, the slip force can appreciably be increased to make the situation worse. In this regard, the safety of the transportation process of a caisson mounted on a floating dock for various wind-wave conditions is investigated. The analysis is done by both frequency-domain approach and time-domain approach, and their differences as well as pros and cons are discussed. It is seen that the time-domain approach is more direct and accurate and can include nonlinear contributions as well as viscous effects, which are typically neglected in the linear frequency-domain approach.

Experiments on wind-perturbed rogue wave hydrodynamics using the Peregrine breather model

Being considered as a prototype for description of oceanic rogue waves, the Peregrine breather solution of the nonlinear Schrödinger equation has been recently observed and intensely investigated experimentally in particular within the context of water waves. Here, we report the experimental results showing the evolution of the Peregrine solution in the presence of wind forcing in the direction of wave propagation. The results show the persistence of the breather evolution dynamics even in the presence of strong wind and chaotic wave field generated by it. Furthermore, we have shown that characteristic spectrum of the Peregrine breather persists even at the highest values of the generated wind velocities thus making it a viable characteristic for prediction of rogue waves.

SEA SURFACE ALTIMETRY BASED ON AIRBORNE GNSS SIGNAL MEASUREMENTS

Abstract. In this study the focus is on ocean surface altimetry using the signals transmitted from GNSS (Global Navigation Satellite System) satellites. A low-altitude airborne experiment was recently conducted off the coast of Sydney. Both a LiDAR experiment and a GNSS reflectometry (GNSS-R) experiment were carried out in the same aircraft, at the same time, in the presence of strong wind and rather high wave height. The sea surface characteristics, including the surface height, were derived from processing the LiDAR data. A two-loop iterative method is proposed to calculate sea surface height using the relative delay between the direct and the reflected GNSS signals. The preliminary results indicate that the results obtained from the GNSS-based surface altimetry deviate from the LiDAR-based results significantly. Identification of the error sources and mitigation of the errors are needed to achieve better surface height estimation performance using GNSS signals.

Study of atmospheric stagnation, recirculation and ventilation potential at Narora Atomic Power Station NPP site

The atmosphere is an important pathway to be considered in assessment of the environmental impact of radioactivity releases from nuclear facilities. The estimation of concentration of released effluents in air and possible ground contamination needs an understanding of relevant atmospheric dispersion. This paper describes the meteorological characteristics of Narora Atomic Power Station (NAPS) Nuclear Power Project site by using the integral parameters developed by Allwine and Whiteman (Atmospheric Environment 28(4):713-721, 1994). Meteorological data measured during the period 2006-2010 were analysed. The integral quantities related to the occurrence of stagnation, recirculation and ventilation characteristics were studied for the NAPS site to assess the dilution potential of the atmosphere. Wind run and recirculation factors were calculated for a 24-h transport time using 5 years of hourly surface measurements of wind speed and direction. The occurrence of stagnation, recirculation and ventilation characteristics during 2006-2010 at the NAPS site is observed to be 33.8, 19.5 and 34.7 % of the time, respectively. The presence of strong winds with predominant wind direction NW and WNW during winter and summer seasons leads to higher ventilation (48.1 and 44.3 %) and recirculation (32.6 % of the summer season). The presence of more dispersed light winds during pre-winter season with predominant wind directions W and WNW results in more stagnation (59.7 % of the pre-winter season). Thus, this study will serve as an essential meteorological tool to understand the transport mechanism of atmospheric radioactive effluent release from any nuclear industry during the pre-operational as well as operational phase.

Minimum-Cost Cruise at Constant Altitude of Commercial Aircraft Including Wind Effects

A IRCRAFT trajectory optimization is a subject of great importance in air traffic management from the point of view of defining optimal flight procedures that lead to energy-efficient flights. In practice, the airlines consider a cost index (CI) and define the direct operating cost (DOC) as the combined cost of fuel consumed and flight time weighted by the CI. Their goal is to minimize the DOC. However, in the presence of unexpected winds, the flight timemay differ considerably from the scheduled time, which leads to an arrival-error cost that can be added to the DOC to obtain the total cost (TC). Minimum-DOC trajectories have been studied by different authors [1–6]. The related problem of minimum fuel with fixed final time has been analyzed as a minimum-DOC problem with free final time in [3,5,7] (the problem is to find the time cost for which the corresponding free final time DOC-optimal trajectory arrives at the assigned time); this same problem is addressed in [8], analyzing the effects of mismodeled winds in a scenario formed by the final cruise and descent segments. The problem of minimum-cost flight, considering not only the DOC but also the arrival-error cost, is analyzed in [9,10], taking into account factors such as crew overtime cost, passenger dissatisfaction cost, and losses due to missed connections. In this Note, the problem of minimum-cost cruise at constant altitude in the presence of strong winds, including the arrival-error cost, is analyzed, considering the general unsteady problem, with variable aircraft mass, and without any restriction on cruise altitude. The main objective is to analyze the optimal trajectories that lead to minimum cost, defined as optimal speed laws (speed as a function of aircraft mass). The analysis is made using the theory of singular optimal control (see [11]), which has the great advantage of providing feedback control laws (control variables as functions of the state variables) that can be directly used to guide the aircraft along the optimal path. These optimal control laws are analyzed as well. In this work, the initial and final speeds are given, so that the optimal control is of the bang-singular-bang type, and the optimal paths are formed by a singular arc and two minimum/maximumthrust arcs joining the singular arc with the given initial and final points (see [6,12]). In previous work related to optimum cruise at constant altitude [13,14], only the singular arc was studied; hence, a more general formulation of the optimal problem is addressed now, apart from considering the arrival-error cost and including wind effects (average horizontal winds). In this analysis of the minimum-TC problem, the arrival-error cost depends on the difference between the actual and the scheduledflight times, and it is defined to be positive, so that both late and early arrivals are penalized (the objective is to achieve high arrival-time accuracy). It will be shown that, for some values of the parameters of the problem, minimum cost is obtained when the final time coincides with the scheduled time of arrival; that is, when the arrival-error cost is zero. This critical case is in fact a problem with fixed final time. Results are presented for a model of a Boeing 767-300ER.

Relative importance of dust inputs and aquatic biological production as sources of lake sediments in an oligotrophic lake in a semi‐arid area

AbstractThe dustfall (DF) and mass sedimentation rate (MSR) in Lake Alchichica, Central Mexico, were studied from June 2006 to June 2008. DF ranged between 0·11–0·93 g m−2 d−1 in the warm and rainy season and 0·54–1·21 g m−2 d−1 in the cold and dry season. MSR varied from 0·52–2·40 g m−2 d−1 in the stratification season to 1·14–5·07 g m−2 d−1 in the circulation season. The timing of the highest fluxes of DF and MSR is most likely a product of several factors coinciding during the cold and dry season: (a) availability of dust sources and the presence of strong winds (>7·5 m s−1) in the DF case, and (b) the circulation period of the lake and the availability of nutrients in the MSR case. As expected, the DF in Alchichica was high and similar to that found in other arid and semi‐arid areas. However, the MSR was higher than that reported for other oligotrophic lakes. Particles captured in the aerial traps consisted mainly of detrital minerals; in contrast, particles found in the water traps were mostly biogenic and, to a lesser extent, detrital minerals. The MSR was one to seven times higher than the DF. In spite of the oligotrophic status of Lake Alchichica, the large size of the settled phytoplankton (autochthonous, waterborne) is what leads to the high MSR, which surpasses the DF (allochthonous, airborne) derived from whirlwinds originating in easily eroded terrains that are characteristic of arid/semi‐arid areas. Our results indicate that caution must be taken in considering that the DF amount measured through DF collectors located at the lake shore does actually represent the DF entering into the lake. Copyright © 2010 John Wiley & Sons, Ltd.

A New Vertical Diffusion Package with an Explicit Treatment of Entrainment Processes

Abstract This paper proposes a revised vertical diffusion package with a nonlocal turbulent mixing coefficient in the planetary boundary layer (PBL). Based on the study of Noh et al. and accumulated results of the behavior of the Hong and Pan algorithm, a revised vertical diffusion algorithm that is suitable for weather forecasting and climate prediction models is developed. The major ingredient of the revision is the inclusion of an explicit treatment of entrainment processes at the top of the PBL. The new diffusion package is called the Yonsei University PBL (YSU PBL). In a one-dimensional offline test framework, the revised scheme is found to improve several features compared with the Hong and Pan implementation. The YSU PBL increases boundary layer mixing in the thermally induced free convection regime and decreases it in the mechanically induced forced convection regime, which alleviates the well-known problems in the Medium-Range Forecast (MRF) PBL. Excessive mixing in the mixed layer in the presence of strong winds is resolved. Overly rapid growth of the PBL in the case of the Hong and Pan is also rectified. The scheme has been successfully implemented in the Weather Research and Forecast model producing a more realistic structure of the PBL and its development. In a case study of a frontal tornado outbreak, it is found that some systematic biases of the large-scale features such as an afternoon cold bias at 850 hPa in the MRF PBL are resolved. Consequently, the new scheme does a better job in reproducing the convective inhibition. Because the convective inhibition is accurately predicted, widespread light precipitation ahead of a front, in the case of the MRF PBL, is reduced. In the frontal region, the YSU PBL scheme improves some characteristics, such as a double line of intense convection. This is because the boundary layer from the YSU PBL scheme remains less diluted by entrainment leaving more fuel for severe convection when the front triggers it.

Constraining Reionization with the Evolution of the Luminosity Function of Lyα Emitting Galaxies

At redshifts beyond z 6, as the mean fraction of neutral hydrogen xH i in the intergalactic medium (IGM) increases, the line flux of Lyα emitters can be significantly attenuated, which can result in a decrease in the observed number of emitters at a given Lyα flux. However, cosmological H II regions surrounding the Lyα emitting galaxies alleviate these effects. We use simple models of the Lyα line attenuation that incorporate the presence of H II regions to predict the overall effect of the Lyα absorption on the Lyα luminosity function (LF). We find, in agreement with other recent studies, that a fully neutral IGM is inconsistent with the Lyα LF remaining unchanged from z = 5.7 to z = 6.5, as suggested by recent observations. However, the presence of local H II regions prohibits placing a tight constraint on the mean neutral fraction. We find x 0.25; the presence of strong winds and/or the clustering of ionizing sources would further weaken this constraint. We conclude that the evolution of the Lyα LF is consistent with reionization occurring near this redshift, as suggested by other observations. Finally, we suggest that a measurement of observed Lyα line width as a function of the Lyα luminosity, in a future, larger sample of Lyα emitters, may serve as a robust diagnostic of the neutral fraction in the IGM.

On the Relationship between the Optical Emission‐Line and X‐Ray Luminosities in Seyfert 1 Galaxies

We have explored the relationship between the [O?III] ?5007 and the 2-10 keV luminosities for a sample of broad- and narrow-line Seyfert 1 galaxies (BLSy1s and NLSy1s, respectively). We find that both types of Seyfert galaxies span the same range in luminosity and possess similar [O?III]/X-ray ratios. The NLSy1s are more luminous than BLSy1s when normalized to their central black hole masses, a fact attributed to higher mass accretion rates. However, we find no evidence for elevated [O?III]/X-ray ratios in NLSy1s, which would have been expected if they had excess extreme-ultraviolet (EUV) continuum emission compared to BLSy1s. Also, other studies suggest that the gas in narrow-line regions (NLRs) of NLSy1s and BLSy1s spans a similar range in ionization, contrary to what is expected if those of the former are exposed to a stronger flux of EUV radiation. The simplest interpretation is that, like BLSy1s, a large EUV bump is not present in NLSy1s. However, we show that the [O III]/X-ray ratio can be lowered as a result of absorption of the ionizing continuum by gas close to the central source, although there is no evidence that intrinsic line-of-sight absorption is more common among NLSy1s, as would be expected if there were a larger amount of circumnuclear gas. Other possible explanations include (1) anisotropic emission of the ionizing radiation; (2) higher gas densities in the NLRs of NLSy1s, resulting in lower average ionization; or (3) the presence of strong winds in the nuclei of NLSy1s that may drive off much of the gas in the NLR, resulting in lower cover fraction and weaker [O III] emission.

Evolución de un evento de surgencia frente a punta Curaumilla, Valparaíso

The beginning, maturity and relaxation phases of a coastal upwelling event (16 to 20 January 1986), off punta Curaumilla (33°06'S), were characterized. This characterization was based on the spatial and time distribution of temperature, salinity, dissolved oxygen, nutrients (nitrate, phosphate and silicate), wind and Ekman transport. Satellite images of sea surface temperature were used as complementary information. The results showed that the winds were fluctuating and mainly blowing from the south and southwest, so it was possible to observe the initial and mature phases and the beginning of the relaxation phase. The initial phase was characterized by an increase of the south and southwest wind and the Ekman transport, a rise of the seasonal thermocline at the coast and the presence of a cold surface water plume 45-55o towards the left of the coastline. The mature phase was characterized by the presence of strong winds (>10 m·s -1 ), high mean Ekman transport (>1,000 m 3 ·s -1 per 1,000 m of coast), a lowering of the temperature ( 34.4 psu) and nutrients (phosphate >2.0 µM; nitrate >15 µM; silicate >10 µM ) at the coastal margin. The declination phase was partially observed, because the wind did not relax enough during the sampling period. However, the surface temperature satellite images on 23 and 24 January, clearly showed a decrease of the area covered with cold upwelled water. The water mass displaced towards the ocean had Subantarctic characteristics and the water mass upwelled to the surface, had Equatorial Subsurface characteristics.

Interaction of accretion shocks with winds

Accretion shocks are known to oscillate in presence of cooling processes in the disk. This oscillation may also cause quasi-periodic oscillations of black holes. In the presence of strong winds, these shocks have oscillations in vertical direction as well. We show examples of shock oscillations under the influence of both the effects. When the shocks are absent and the flow is cooler, the wind becomes weaker and the vertical oscillation becomes negligible.

An Extraordinary Accretion Event Detected on DF Tauri

We report on the detection of an extreme flarelike event on DF Tauri during a spectroscopic monitoring program of some classical T Tauri stars known to show hot spots on their surfaces. These observations were performed on a nightly basis within roughly one rotational period of DF Tau between 2000 January 7 and 14. The estimated amplitude of variation during this time reached up to 6 mag in the B band. Significant inverse P Cygni profiles in high Balmer lines—evidence of mass accretion—dominated the spectrum obtained on January 8, when the brightness of DF Tau was approaching its maximum. The flux in the ultraviolet dropped dramatically on the following day. Ca II H and K emission lines, the indicator of chromospheric activity, turned into deep, wide absorption, and all other emission lines in the blue end were also absent (filled in or weak absorption), suggesting severe absorption in the line of sight possibly caused by a transient envelope produced in the process of a violent accretion shock. The effect of veiling decreased rapidly from January 10, and normal P Cygni profiles, indicating the presence of strong wind, began to appear. Based on the unique features displayed, we propose that the spectroscopic record of this flarelike brightening on DF Tau, believed to be due to episodic mass accretion accompanied by the release of gravitational energy, might actually be taken as an isolated, snapshot view of the YY Orionis phenomenon.

Advection Distance of Water Droplets in Strong Winds

As part of a study on wind effects on runup and overtopping of coastal structures, advection distances for water droplets of various sizes were measured in a wind/wave flume. The study found that advection distances were considerably greater than would be expected from wind forces acting on spherical droplets. Flattening of the windward face of water droplets from splash and spray in the presence of strong wind was found to increase the drag of droplets in this study and possibly add a lifting force, thereby increasing the distances droplets were carried. Results of this study indicate that splash and spray may be carried over a coastal structure considerably farther than may be expected, which in turn may contribute to higher overtopping rates.

Experimental study of atmospheric gravity waves and visibility oscillations in a fog episode

A fog episode characterized by quasi-periodic oscillations in visibility is described. Gravity waves are also present, and frequencies at which pressure and transparency fluctuate are compared. The existence of intervals during which they are synchronized and the presence of strong winds aloft suggest that shear instabilities in the troposphere can influence the fog behaviour at ground.

Frost-bite: Treatment by passive vascular exercise: Report of cases

Frost-bite is a prevailing pathological entity not uncommonly found among outdoor workers during the cold winter months, especially at temperatures below 8 ° f., or between 8 ° and 14 ° f. in the presence of strong winds. The underlying pathology results in the disturbance in the blood supply to the part by a marked vasospasm producing ischemia and anesthesia and if this vasospasm is not relieved within a period of twenty-four hours actual gangrene may result. Prophylaxis is the most important factor in reducing the incidence of occurrence. A comparatively new method of conservative therapy is offered in the alleviation of frost-bite, by the rapid relief of pain and the rapid restoration of circulation of the relaxation of vasospasm with a complete recovery in cases treated early. Late cases that have actual gangrene are relieved of pain and require less extensive surgery and a more useful limb therefore. Tendon injuries are not necessarily of a permanent nature. Epithelialization is rapid. Hospital stay is remarkably lessened as an added economic factor. The passive vascular exercise therapy in frost-bite will enable the surgeon to change from the placid role of waiting for a time to amputate to an active role of trying to tide these sufferers through to a stage of actual healing by restoring their circulatory balance in a rapid and sound way.