Windward Direction Research Articles

WINDWARD WINDBREAK EFFECTS ON AIRFLOW IN AND AROUND A SCALE MODEL OF A NATURALLY VENTILATED PIG BARN

Wind tunnel tests of 1:20scale windbreak models placed in a windward position from naturally ventilated pigbarns were performed to examine the capability of windbreaks to trap air contaminants emitted from livestock buildings. Theairflow surrounding the windbreak and the building was measured. Dispersion of air contaminants was predicted with theproposed parameters PU, PV, and PW, which are related to airflow momentum in the leeward direction and to horizontal andvertical plume sizes, respectively. Windbreaks included a solid wall, a net screen, and another pig barn. With a solid wall asa windbreak, air emitted from the building was exhausted in the windward direction. Compared to a net screen or anotherbarn, the solid wall resulted in the lowest airflow momentum. A highconcentration odorous area was predicted to be locatedbetween the windbreak and the building. Sprinklers in this area could possibly trap the air contaminants. When a buildingwas placed in the windward position as a wind barrier, the dispersion of odorous air behind the leeward building was predictedto be the smallest compared to a solid wall and a net; moreover, a smaller plume width was seen. When a net screen was used,the airflow between the wall and the building moved only in the leeward direction.

Impact of Urban Spaces and Building Height on Airflow Distribution: Wind Tunnel Testing of an Urban Setting Prototype in Abu-Dhabi City

This paper investigates the effect of changing design parameters such as building height, urban space width, and building cluster arrangement on airflow in typical urban settings in Abu-Dhabi. It focuses on the impact of these parameters on airflow pathlines and velocity and analyzes the results with regard to thermal comfort in outdoor urban spaces. The study concludes with some design guideline and recommendations such as the following: low-rise buildings in the urban context should face the windward direction to reduce wind shadow effect; staggered arrangements of buildings in urban context provide more effective passive cooling design than parallel arrangement because of its potential to cool building structures at night by natural convection and to reduce high levels of humidity.

Wind speeds within a single crown of Japanese black pine ( Pinus thunbergii Parl.)

Wind speed and crown thickness, which is defined as a horizontal distance from the observed point to outer edge of a crown in windward direction, were measured within a normal crown of a single tree of Japanese black pine ( Pinus thunbergii Parl.) at four vertical sections. Simultaneously, wind speed and direction were observed outside the crown. Regression analysis is used to obtain the wind profiles within the single crown. The results suggest that the crown features make a large influence on the wind profiles, therefore, the crown thickness as an indicator of crown feature is employed to develop the horizontal wind profile within the crown. A consistent relationship between relative wind speed and corresponding crown thickness is established for predicting wind speed at a horizontal plane. Additionally, vertical wind profile within the crown is also examined as literature suggested in exponential form. Within a single tree crown, where the distribution of leave and branch is essentially uniform with height, and the tree form is similar to Japanese black pine, the vertical wind profile can be derived from a single wind speed measurement outside the crown with using the parameter derived in this study. Based on the vertical and horizontal profiles, wind speed at any position in a plane within a crown at height z can be reasonably estimated if providing the crown thickness and wind data outside the crown. The wind profiles discussed here may be useful when discussing the ventilation of airflow at any level of a crown, analyzing the transfer processes for questions of disease and solving the problems of the tree damage by salty wind from the sea, etc.

Banded vegetation patterning in a subantarctic forest of Tierra del Fuego, as an outcome of the interaction between wind and tree growth

Abstract Banded patterns have been investigated in a Nothofagus betuloides primeval forest from Bahia del Buen Suceso, on the eastern edge of Tierra del Fuego island (Argentina). These forests grow on spodosols developed upon silicic shales, in a cold oceanic climate, with 5 °C mean annual temperature and 600 mm mean annual rainfall. Bands are oriented perpendicular to the prevailing wind direction, with older and dying trees in the windward edge and a seedling regrowth in the lee side of each band. Forest structure, species composition and relevant soil properties were sampled in a wind-affected forest and in an undisturbed stand. In the former, samples were obtained in transects across the banding and along a hill-slope gradient. Results show that wind causes about 50 % reduction of stand basal area and of size of overstorey trees. Stand growth processes, such as self-thinning, basal area and height growth, and specific composition of the understorey, occur in a windward direction, as well as changes in soil properties such as C/N ratio and redox potential increase. Based on field observations, we have developed an hypothesis of how wind is able to generate this pattern. Its core is that bands develop when vulnerability of trees to wind damage increases with age and with lack of protection from older windward trees. In such conditions, bands are the outcome of a tuning between tree growth rates and wind killing capacity. On the basis of this hypothesis, a simulation model, based on the cellular automata approach, was constructed. Simulated patterns that arise from heterogeneous forests with random age distributions match successfully with those observed in nature. Increasing tree growth rates lead to longer wavelengths and higher wave propagation rates, while increasing wind killing potential leads to shorter wavelengths and lower propagation rates. This interpretation of banded patterning involves a resonance between a directional disturbance and an oscillatory process, such as stand regeneration, growth and decay.

Fire-induced Winds In The 20 October 1991 Oakland Hills Fire

The winds generated at 11:45 a.m. by 38 fires and at 12:OO p.m. by 259 fires for the 20 October 1991 Oakland Hills Fire are simulated using the Baum and McCaffrey mass fire model. Each house is modeled as having a 50 MW heat release rate at the time of the computation. For each single fire, the flame tip is 15 m high, the maximum vertical velocity is 16 m/s and the maximum radial velocity is 2.4 m/s. At 11:45 a.m., for the mass fire the maximum induced wind is 2.6 m/s. The maximum vertical velocity is 14 m/s. At 12:OO p.m., the maximum horizontal velocity is 13 m / ~ . The maximum vertical velocity is 26 m / ~ . Results indicate that the strong fire-induced winds at and after 12:OO p.m. contributed to the post-noon decrease in the fire spread rate in the ambient windward direction.

Above- and below-ground characteristics associated with wind toppling in a young Populus plantation

Damage from a dormant-season windstorm in a 3-year-old Populus research trial differed among four clones and three spacings and between monoclonal and polyclonal plots. Clonal differences in susceptibility to toppling (or leaning) were associated with both above- and below-ground characteristics. Susceptible clones had less taper in the lower stem and more weight in branches on the upper stem. The most susceptible clone also had the most above-ground biomass per unit of cross-sectional root area. The other susceptible clone had the least root system development in the windward quadrants. Wind toppling was least at the closest spacing. Apparently, mutual support was more important than individual tree characteristics from which the most damage would be expected at the closest spacing. Differences between paired trees of the same clone and spacing which did or did not topple were primarily associated with distribution of root systems by compass quadrant or depth. At the closest spacing where crown sway would have been minimized, trees which did not topple had greater cross-sectional root area in the windward direction than trees which did topple. At the widest spacing where crown sway would have been greatest, windfirm trees had greater cross-sectional root area than non-windfirm trees in both the windward and leeward directions. Toppling was reduced in polyclonal plots; this reduction may have been the result of more rapid stand differentiation in the polyclonal plots or reduction in the “domino effect” by inclusion of more windfirm clones in the mixture.

Model studies of the motion response of a damaged four column semisubmersible in regular and irregular waves

A brief review of the stability requirements of semisubmersibles is presented. Results of the dynamic response of a damaged, twin pontoon, four column semisubmersible at a scale of 1:100 are discussed. The tests involved both regular and irregular waves with the model oriented in head, beam and quartering directions for both intact as well as damage conditions. Four damage conditions representing partial damage to one column were simulated: two in windward (positive) direction and two in leeward (negative). The “light damage” condition represented about 9% flooding of the damaged column, while for the “moderate damage” the flooding was equivalent to about 18%. For moderate damage conditions, regular wave studies showed that the motions are essentially nonlinear, although for light damage conditions this cannot be said with certainty. Model tests showed certain asymmetry in the motions of the damage semisubmersible with respect to the position of the damaged column. Moderate damage conditions seemed to produce significant subharmonic response of the vessel in a frequency range which is twice the natural frequency of the vessel in heave. These observations were confirmed from the results of irregular wave studies. Irregular wave studies showed that the quartering sea pitch and roll motions in windward damage conditions are as significant as those in the leeward conditions which was not the case for regular wave studies. The energy due to the motion of the semisubmersible was concentrated in the frequency of 0.7–1.3 Hz, which corresponds to the energetic range of the normal sea state. The natural frequencies of the vessel in damaged condition in pitch, roll and heave are higher than the corresponding frequencies in the intact condition of the vessel. The natural frequency in heave, for both intact and damage conditions, is higher than either those of pitch and roll in similar conditions. These natural frequencies in pitch and roll begin to approach that of the natural frequency in heave as the damage condition increases. This is true irrespective of the position of the damaged column or the sea state. The value of the natural frequency in heave itself increased much more slowly with increase in damage condition. It was inferred that the nonlinear wave pressure term played only a minor role in the asymmetry of motions of the vessel, while the mooring characteristics had a more dominant influence.

Gas screening effect caused by steam curtains

Steam curtain equipment is used to prevent leaking flammable gases from reaching ignition sources, such as furnaces. However, steam curtains are sometimes designed badly and are ineffective for preventing the leaking gas from spreading in the windward direction. The leaked gas may pass on either side of the stream curtain, it may pass between the nozzles, or it may pass on the upper side of the stream curtain. At present, data to design the best stream curtains are quite rare. It is necessary to obtain fundamental data on the entrainment of air by steam jet and on the inclination of the steam curtain caused by the strong wind. Therefore, a series of experiments to investigate the entrained air and the inclination of the steam curtain were performed, in addition to further theoretical considerations. Thus, fundamental data useful for the design of the steam curtain equipment have been obtained.

Holocene reef sequences and geochemistry, Britomart Reef, central Great Barrier Reef, Australia

ABSTRACTHolocene reef development was investigated by coring on Britomart Reef, a mid‐shelf reef, 23 km long and 8 km wide situated 120 km north of Townsville in the central Great Barrier Reef (GBR). Two holes were drilled, Britomart 1 on a lagoon patch reef, and Britomart 2 on the windward reef crest. The Holocene reef (25·5 m) is the thickest yet recorded in the GBR and overlies an uneven substrate of weathered Pleistocene limestone.Mineralogical and geochemical analyses show that magnesian calcite and aragonite were converted to low Mg‐calcite below the Holocene‐Pleistocene disconformity. Corals above the interface have 7500–8500 ppm Sr, but 1650–1500 ppm just below it, decreasing to 400–800 ppm downwards. The intermediate Sr values could be due to partial replacement of aragonite by calcite or higher original Sr content in the corals.Three units are recognized in the Holocene: (1) coral boundstone unit, (2) coral framestone unit, and (3) coral rudstone unit. The coral boundstone unit forms the top 5 m of both cores and is algal‐bound coral rubble similar to the present reef top. The coral framestone unit is composed of massive head corals Diploastrea heliopora and Porites sp., and is currently forming in patch reefs situated in the lagoon and along the reef front. The coral rudstone unit comprises coral rudstone and floatstone with unabraded, and unbound, coral clasts in muddy matrix. This matrix may be up to 30% sponge chips.Radiocarbon dating indicates the reef grew more rapidly under the lagoon than under the reef front from 7000 to 5000 yr BP. The rate of reef growth matched existing estimates of sea‐level rise, but lagged approximately 1000 years (5–10 m) behind it. Most of the reef mass accumulated between 8500 and 5000 yr BP as a mound of debris, perhaps stabilized by seagrasses or algae. Accretion of the reef top in a windward direction between 5000 and 3000 yr BP created the present, steep reef‐front profile.

PREVAILING WIND OVER THE CITY AREA OF TOKAI, ESTIMATED FROM DUST DEPOSITS ON THE SURFACE OF LEAVES

The K amount of dust deposit on a leaf reflects wind direction, namely the amount of dust which adhered to the surface of the leaf facing windward direction is larger than that of any other direction. In this study, in order to clarify the distribution of the prevailing wind over the city area of Tokai, Aichi Prefecture, the authors investigated the amount o dust deposit on the surface of leaves. The results are summarized as follows: (1) Summer ( Fig. 2) (a) The southerly winds, summer monsoon, from the Mikawa Pay flow to the north along the Sakai River, and then the winds change their direction to the northwest in the southern and the eastern parts of city area. (b) The westerly winds which are considered to be sea breeze flow into the northern part and the coast area of city. (2) Winter (Fig. 3) The northwesterly winds, winter monsoon, prevail over the city area. (3) It is clear that the topography in local scale chang the wind direction, as shown in Figs. 2 and 3.

諏訪湖の溶存酸素と<i>Microcystis</i>の大発生の生態学的研究-II.

In the season of Microcystis bloom in Lake Suwa, both the horizontal and vertical distributions of dissolved oxygen around a floating net (9×9×1.5m) with about 7000 carps were studied. Oxygen concentration in the upper waters at the edge of the net or inside it was always lower than that at the control stations at a distance of 100 or 200m from the net, and the presence of nets caused the decrease of oxygen concentration up to the distance of about 50m from the net. The decrease in oxygen concentration was more prominent in the layer of 0 to 2m (32% saturation on Sept. 17), especially when the net was set in the windward direction. Oxygen consumption of bottom deposits around the net, up to a distance of about 20m, was much larger than that at the other stations located far away.

Effect of Wind on Dispersal of Trichogramma semifumatum12

The effect of wind on the dispersal of T. semifumatum (Perkins) was studied by releasing these parasitic wasps and then after 24 hours, recovering them at 4 heights on sticky posterboard panels circumscribing release points at 8 cardinal compass directions at 3 radii, 2, 4, and 8 ft. Recovery was recorded for 2 experiments with different wind conditions. Percentages of released wasps recovered in windward directions were compared with percentages recovered in directions perpendicular to the wind. Results indicated that wind influenced dispersal of T. semifumatum . Also, vertical and directional distribution data showed that the height of the plant canopy is the most favorable level for release if a perimetrical distribution pattern is desired.

AIR AND SAND MOVEMENTS TO THE LEE OF DUNES1

SUMMARYThe large and extensive transverse and barchane dunes of coastal South West Africa are strongly oriented under the influence of predominantly southerly winds. During periods of strong winds (40–50 miles/h) deposition occurs on the lee slope in three ways: (1) sand is blown over the crest of the dune and falls on the lee slope; (2) rapid deposition near the dune crest results in periodic slumps and slides down the lee slope; (3) eddy currents developed to the lee of the dune pick up sand from the surface downwind from the dune and transport it to the lee slope.The size and strength of the lee eddy is surprising. With winds in the 40–50 miles/h range frequent gusts lift fine sand from the downwind surface to a height of several feet. Less frequently sand is picked up from a low position on the lee slope and redeposited higher on the slope. The addition of material to the lee slope by the eddy is much less volumetrically than the contribution directly over the dune crest from the windward direction; however, with strong winds the removal and transportation of sand from the area downwind of the lee slope back to the lee slope appears to be important in the deflation of this surface. The width of the area influenced by the lee eddy during strong winds is about equal to the height of the dune.Observations in low dunes from 1 to 20 ft. high at Sapelo Island, Ga., U.S.A., confirm the presence of a well developed eddy to the lee of these dunes during strong and moderate winds (20–50 miles/h).

STRUCTURES OF DUNES AT WHITE SANDS NATIONAL MONUMENT, NEW MEXICO (AND A COMPARISON WITH STRUCTURES OF DUNES FROM OTHER SELECTED AREAS)1

SUMMARYThe type, scale, and relative abundance of sedimentary structures in four kinds of dunes at White Sands National Monument, New Mexico, were determined by examination of vertical sections on walls of trenches cut through the dunes both in a windward direction and at right angles to this direction. Analysis of cross‐stratification in all dunes examined indicated certain common features: sets of cross‐strata mostly are medium‐ to large‐scale; nearly all laminae dip downwind at high angles (not uncommonly at 30°‐34°); most bounding surfaces between sets of cross‐strata are nearly horizontal on the upwind side, but have progressively steeper dips to lee, downwind; and individual sets of cross‐strata tend to be thinner and the laminae flatter near the top than at the bottom of a dune in vertical section.Sparse but distinctive structural features that are characteristic of the four types of dunes are varieties of contorted bedding, rare ripple laminae, and either local scour‐and‐fill bedding, or festoon bedding. Other structures, apparently limited to either one or two types of dunes, are the concave‐downward foresets in some parabolic dunes; the low‐angle reverse dips of upwind strata on high transverse dunes; and the almost horizontal laminae which represent apparent dip in sections normal to wind direction in dome‐shaped and transverse dunes.Describing cross‐stratification in terms of three dimensions, dune structure at White Sands consists dominantly of the tabular planar sets, with units thickest near the dune base, thinner above. To a lesser extent the sets are of simple (non‐erosion) tabular form and relatively uncommonly, of the trough type. Wedge planar forms are scarce. The planar forms characteristically are of two classes in nearly equal proportions: those in which bounding surfaces are virtually horizontal and those in which they dip at moderate to high degree.A brief comparison is made between the structures of dunes that are characteristic of one effective wind direction, as at White Sands, and certain others formed by winds of two or more directions. Seif dunes of Libya, reversing dunes of the San Luis Valley, Colorado, and star dunes in Saudi Arabia are discussed as examples of complex dunes formed by multi‐directional winds.

A Study of the Relation Between Growth Form and Exposure on Monte Maiella, Italy

In an earlier paper (Whitehead, 1951) the vegetation of the altipiano of Monte Maiella was described. A number of community types were distinguished, and it was established that there exists a relationship between plant height and the roughness of the ground surface. This was calculated from measurements of the wind velocity at different heights above ground level and expressed as the parameter Z0 (Whitehead, 1951). The difference in physiognomy of these communities was so striking that further investigations were carried out in 1951. The four community types referred to as areas A, E, G and H in the earlier work were selected as representing a graded series of communities varying from extreme exposure in A to maximum shelter in H. Quadrats were mapped in detail in each community, the height of each plant, the percentage cover and the growth form of each species being recorded. Growth form is here used in the original sense as proposed by Warming (1909) and as redefined by Du Rietz (1931). The anemometer used to determine Z0 was of the whirling-cup type (cup size 3cm.), electrically recording and made to a design modified from that described by Sheppard (1940). It was set up on the leeward edge of each quadrat, and the wind speed was measured simultaneously at three heights above the surface over a period of at least 3 min. The quadrats were so chosen that the vegetation for the operative distance (c. 30 m.) in the windward direction was as homogeneous as possible. The vegetation data for these quadrats are given in Table 1. The growth-form classification used in this investigation does not belong to any system in particular, but where similar growth forms have already been described, this is indicated in brackets in the list of definitions below: