External Towers Research Articles

An innovative twin-technology solar system design for electricity production

Traditional solar updraft power plants work during the daytime as it is dependent on solar radiation to generate electricity. Hence, energy productivity, efficiency, and performance are limited. This work presents a novel attempt to increase the productivity of a traditional solar updraft system by combining it with a downdraft technology in one system, the Twin-Technology Solar System (TTSS). The TTSS comprises two co-centric inner and external solar towers, turbines, water sprinklers, and a collector. The inner tower works as a traditional solar updraft system, where the air is heated under the collector due to irradiance and then moved up the chimney due to the pressure column. While the external tower creates a downdraft wind by spraying water at the hot ambient air at the top of the tower. The hot air instantly absorbs the water and descends the tower to interact with the turbines at the bottom to produce electricity. This mode is independent of solar irradiance and can operate day and night. Hence, the TTSS generates electricity, daytime and night. A mathematical simulation model was developed based on the proposed system's energy and mass balance equations to assess performance. The TTSS generated 752,763 kWh of electricity annually, 2.14 folds higher than a traditional solar updraft system. Consequently, a reduction of 677 tons of CO2 was achieved with production. The design is suitable for deployment in hot and dry weather areas, such as remote villages and deserts. Future work will investigate introducing other technologies to boost the TTSS performance.

Experimental study on earthquake‐induced pounding between steel structures

AbstractPounding between adjacent structures has been repeatedly observed during major earthquakes. The phenomenon may cause some local damage at the points of interactions, it may also lead to substantial destruction, permanent deformations or total collapse of colliding structures. The effects of earthquake‐induced structural pounding have been studied for more than three decades now. However, most of the studies concerned masonry as well as reinforced concrete structures and investigations on steel structures are very limited. The aim of the present paper is to show the results of the shaking table experimental investigation focused on earthquake‐induced pounding between three models of steel structures in a row. The models were constructed out of four steel columns made from rectangular box section with additional steel skew bracings so as to prevent transverse and torsional vibrations. To obtain different dynamic characteristics of the models, additional plates were added at the top of each tower. Two configurations were investigated. In the first one, two plates were mounted on the external structures and only one plate at the top of the middle tower. In the second configuration, only one plate was mounted at the top of external towers and two plates on the middle structure. Firstly, the free vibration tests were conducted. Then, the steel towers with different in‐between gap sizes were tested under different earthquakes. The results of the study confirm that interactions between insufficiently separated steel structures may significantly influence the structural behaviour during earthquakes. In most of the cases, pounding has resulted in the increase in the peak responses. In some cases, however, it has played a positive role leading to the decrease in the structural response under seismic excitation. Anyway, even if the response is reduced, interactions should be prevented at the design stage of steel structures since they may result in considerable damage at the points of impacts.

Emergency Messaging System using Chirp Spread Spectrum Protocol

Communication is essential for everyone. Its more essential when it comes to military operations, many of these operations takes place in remote areas which are off grid for network, this makes it harder to communicate with team members or base, using normal satellite calling in target areas may increase the risk of tracking by enemies, for basic communication army personnel use hand gestures this is not ideal when they are far away from line of sight. making it difficult to communicate properly in peak time. For solving this we propose you with our solution to make a device that can be used to communicate without need of external tower or satellite up to 18km

Coupling electrical resistivity methods and GIS to evaluate the effect of historic building features on wetting dynamics during wind-driven rain spells

• The usefulness of NDT improves by combining several methods and datasets over time. • The evaluation of evaporation areas improves the interpretation of ERT. • Results of NDT are represented in GIS considering building surfaces as a topography. • GIS improves the interpretation of NDT when using map algebra to combine sets of data. • Building features modify maximise local hydrometeorological anisotropy. Moisture is one of the most important factors causing building stone decay and rain penetration is one of the leading factors. Particularly, wind-driven rain spells, which are becoming increasingly common and seasonal as a result of climate change. Historic buildings' sometimes intricate design features can be a factor multiplying meteorological anisotropy, either shielding walls or increasing the surface that is affected by wind-driven rain spells. This paper aims to identify the effect of pilasters and tower buttresses on the wetting dynamics of a listed 9th Century historic building during a rain spell by means of electrical resistivity methods coupled with GIS mapping, paying special attention to how data representation and map algebra can improve the interpretation of several data sets of non-destructive testing. Results show how building features can modify deeply moisture dynamics and maximise local anisotropy. In the present case, a compound of an external tower buttress and an internal pilaster decreases moisture ingress through ground infiltration while increasing moisture retention into the wall due to its larger mass. This, in turn, multiplies the incidence of moisture-related processes inside the building. The presented data also highlight the usefulness of mapping over time (4D mapping) and of GIS to improve interpretations through map algebra. .

Ritual Inscriptions from Uzundara

The paper presents three Greek votive graffiti from the excavations of citadel of Fortress Uzundara (Uzbekistan) and describes their archaeological context. This fortress is located on the North-West Border of Ancient Bactria, and represents the crucial point in the tens–kilometers long borderline fortification system in this area. It is built at altitude of 1700 meters above the sea level. The fortress stands on the narrow (220 meters) neck between the precipitous walls of the natural boundary Kara-Kamar and the canyon Uzundara, and locks the pass for the equestrian troops intent to bypass the borderline wall of Darband in 7 kilometers northward. It consists of the principal rhomboid castle, a detached and adjacent triangular citadel, same sections of the external walls, and of three external towers. The main goal of this fortress was the warning of the sudden attack of nomads from the Karshin steppes. A military garrison was stationed in the Uzundara fortress – a Seleucid frurion in the first quarter of the 3rd century BC. Apparently at this time it consisted of Macedonians and Greeks. This is clearly evidenced by archaeological materials, including epigraphic ones. We analyze three artefacts voted to Demeter of the Mountains and the Borderline, Zeus–Mitra, and Zoroastrian Deity Srosh. The most complete inscription – votive to Demeter – persists on the three fragments of tagora (luterium) which could be used for the ritual ablution. They were founded in different years and in different places around the ovoid cellar on the rocky complex of the citadel Uzundara.

Heliostat aiming point optimization for external tower receiver

Abstract Reduction of peak fluxes on solar receiver is an important research topic because peak minimization can lead to lower receiver temperatures with advantages in terms of thermal efficiency and mechanical stresses. This work proposes different approaches for the minimization of the heat flux on external tower receiver with surround field. The mathematical formulation is implemented in Matlab, while Delsol is used for the heliostat field modeling. Since the number of variables is very high, branching the original optimization problem in a set of sub-problems is a beneficial technique. Four approaches, based on this concept, are here proposed: they differ for the number of field sectors considered in the optimization process and on the heliostat projection modeling. The best approach, which considers the overlapping effect between adjacent sectors, can reduce the peak flux down to 770 kW/m 2 in 120 s of computational time. This value is about 15% lower than reference aiming strategies available in literature. The optimized flux is almost flat in the central part of the receiver while it has significant gradient at the lower and upper border. Finally, a sensitivity analysis shows that the proposed approaches work well at any given solar position and with different heliostat assumptions (i.e. curvature and errors).

Comparison of Different Strategies for Heliostats Aiming Point in Cavity and External Tower Receivers

This paper investigates different strategies for the reduction of peak heat fluxes on the receiver of a solar tower plant through the variation of the heliostats aiming points. The analysis is performed for two different solar tower receivers and heliostat field layouts. The innovative aspect of the work is in the methodology proposed: the effect of different aiming points is evaluated at different sun positions, and the yearly optical efficiency is calculated to determine drawbacks in terms of energy production. The optical simulation of the solar plant is performed with delsol through a matlab suite to easily manage the input and output. Preliminary assessments showed that the most important displacement is the vertical one, and the variation of the aiming point is important for the rows that are closer to the tower. With the appropriate strategy, the peak heat flux can be reduced by about 40% with limited spillage increase compared to the reference case. This result is similar for the two investigated plants, and it is confirmed also at different sun positions. The yearly optical efficiency with the optimal aiming strategy is reduced by less than 0.5% points. Future analysis will assess potential cost reductions and thermal efficiency increase brought about by the proposed strategies.

Des tours internes aux sanctuaires suburbains. Regards occidentaux sur des questions chypriotes

The sanctuary at Kition-Bamboula was bordered to the South by a fortification reinforced by a tower turned towards the North, that is towards the sanctuary. If the fortification was designed to defend the sanctuary, it must be admitted that it possessed “ internal” towers, turned towards the site that it defended, which would thus constitute an almost unicum. The interpretation relies on two parallels : Idalion (acropolis and “ palace”) and Palaepaphos (fortification at Marchello). We try to show, on the basis of West Mediterranean parallels, that for these two sites such an interpretation is, if not impossible, at least difficult to substantiate. The Bamboula walls must therefore have had external towers, as is the rule in the Greek and Phoenician worlds. It implies either that the fortification defended a building located further South, completely distinct from the sanctuary, or that it was part of the city walls, in which case the sanctuary was suburban, perhaps linked to the port activities.

Lightning protection of overhead transmission lines using external ground wires

In this paper, a new kind of overhead transmission line (OHL) lightning protection system based on external ground wires is analyzed. Instead of a standard ground wire, two ground wires placed at the top of separate external towers located at both sides of the protected line are used. This type of protection should be applied in specific circumstances for protection of short OHL sections which are highly endangered by lightning. The distance between external protection system and OHL is calculated by using EMTP-ATP. Calculations are performed in order to avoid flashovers from the point where lightning strikes the external protection system to the protected OHL. A rolling sphere method is used to calculate the height of external ground wires above OHL phase conductors to avoid shielding failures. An experiment in a high voltage laboratory is performed to verify the dimensions of the external protection system from the aspect of shielding failures. According to the results of simulation and experiment, the optimal dimensions of the external protection system are determined.

Studies on Suitability of Heat Exchangers for Solar Receivers-Experimental Simulation and Numerical Investigation

The development of efficient solar receivers for different types of solar collectors such as point focusing, line focusing and external towers have received major attention in solar thermal power conversion process. The point focusing or parabolic concentrators need the receiver with internal cavity absorber and heat transfer system design with limited length and diameter. The line focusing collectors are not limited by its receiver length with respect to the trough. In this regard an experimental simulation was carried out to enhance the overall heat transfer coefficient by effective design of shell and helical tube heat exchanger using silver (Ag) Nano particles with water as Heat Transfer Fluid (HTF), which reduces the length of the receiver in point focusing collector. The line focusing collector was analysed by 3D numerical model with porous discs of top half, bottom half, combination of top & bottom half and full shape with silicon carbide ceramic foam as a material to evaluate the performance of the receiver to suit for line focusing collectors. The results obtained with porous disc are compared with plain tube line receiver.

Recursos formales y constructivos en la arquitectura militar almohade de al-Andalus

El presente artículo trata sobre algunos aspectos especialmente característicos de la construcción militar almohade (Siglos XII y XIII), que venían a definir una imagen clara y propagandista del poderoso promotor que había detrás. En concreto, hablaremos de la terminación de los muros de hormigón de cal encofrado, puertas de acceso a las fortificaciones y torres poligonales y albarranas. Afrontaremos el trabajo mediante el estudio de diversos ejemplos, que nos permitirán rastrear, igualmente, la existencia de equipos de constructores itinerantes que cumplirían las órdenes de las autoridades almohades.

The South Gate and Defences ofVenta Icenorum: Professor Atkinson's Excavations, 1930 and 1934

ABSTRACTThis paper describes the hitherto unpublished South Gate of the Roman city at Caistor St Edmund, Norfolk, which was excavated by Donald Atkinson in 1934; it discusses the implications both of the adjacent two kinds of external towers and of his trench through the rampart behind the city's north wall, dug in 1930 but not previously published.

Screenhouse Microclimate and Ventilation: an Experimental Study

A field experiment was carried out to study the microclimate and air exchange rate of an insect-exclusion fine-mesh 60 m by 110 m by 3·2 m commercial screenhouse for pepper cultivation in central Israel. Diurnal courses of plant transpiration, and internal temperature and humidity at three heights were measured at two locations (northern and middle sites) across the screenhouse. Two external towers measured conditions outside the screenhouse. The water vapour mass balance, based on measurements of plant transpiration and internal and external humidity, was used to calculate the air exchange rate and resistance to mass transfer of the screenhouse. Plant transpiration was measured by the heat-pulse technique. Results show that the upper region of the screenhouse interacted strongly with the ambient air, but that during most of the day a temperature inversion inside the screenhouse stabilised the air and reduced mixing. Humidity and temperature profiles show that within the screenhouse temperature increased and absolute humidity decreased with increasing height. Air exchange rates were between 7 and 33 h −1 for windspeeds between 1·5 and 3·5 m s −1 at the two locations measured in the screenhouse. The rate of increase of air exchange rate with windspeed was 7·7 and 3·2 h −1 (m s −1) −1 at the north and middle of the screenhouse, respectively. The higher rate at the northern side demonstrated the influence of wind entering through the sidewalls. Ventilation rates were compared to a theoretical calculation for an open pepper field. For external wind speeds between 1·5 and 3·5 m s −1 covering the field with a screenhouse would reduce ventilation rates by 51–71% in the middle site, respectively, and for the north site by 60–64%. The ventilation rates were higher than those reported for similar size greenhouses, which implies lower resistance to transport in screenhouses as compared with greenhouses of the same size.

Biofilm architecture of Phanerozoic cryptic carbonate marine veneers

Thin (<150 μm) micritic veneers lining crypts in Paleozoic and Mesozoic reef, microbial, and bioclastic carbonates have the dimensions and architecture of modern uncalcified bacterial biofilm. Morphologic attributes include rounded aggregate nanofabric, internal channels, external towers, mushrooms, and plumes. All can be interpreted as characteristics of attached bacterial communities, i.e., aggregates as microcolonies, originally embedded in a matrix of extracellular polymeric substances; channels as water conduits and/or uncolonized nutrient-poor spaces; external protuberances as localized growths; and plumes as surface streamers. Cryptic habitat favored pristine biofilm preservation by precluding disturbance and overgrowth, and suggests aphotic and anoxic conditions. These examples provide diagnostic morphologic criteria for wider recognition of biofilm in Phanerozoic and older carbonates.

British Urban Defences in Earthwork

Urban defences in Roman Britain and the dates of their erection have been discussed by various writers during the last three decades, and the subject has received renewed attention in three recent publications. The last of these has put forward views concerning both date and motivation which a wider consideration of the evidence makes hard to accept. In general, however, the outline of events is clear. Although certain cities received earthworks in the first century or masonry defences from early in the second, the great majority remained open until, in the second half of the second century, a very large number of earth-work circuits was erected in what, all are agreed, must be either a concerted programme or a chain reaction. This embraced not only the cities (the civitas capitals) but also a great variety of minor centres. Beginning quite early in the third century, or even at its outset, and continuing for 70 or 80 years, a long series of towns was receiving walls in masonry. Where earth ramparts already existed the front was normally cut back to receive the wall; elsewhere fresh banks were piled behind the new work. Free-standing walls appeared only in the fourth century and are found at very few towns, for most were already defended. Another development of the same period was the addition of external towers to existing walls: most of these towers seem to date from the third quarter of the fourth century, but some were earlier, beginning, perhaps with Verulamium, c. 265–70.

A Group of Late Roman City Walls in Gallia Belgica

THE late Roman defences which are found in many of the chief cities of France have long been remarkable for similarities of design. In the northern and western parts of France many of the cities were protected by thick, high walls, built in rubble concrete with a facing of 'petit appareil', interspersed with rows of tiles usually in double or triple courses. The foundations were of large unmortared stone blocks, which were, as often as not, re-used from earlier buildings destroyed in the barbarian raids of the later third century or else deliberately demolished to provide a solid foundation for the new walls. The whole circuit was strengthened by the addition of external towers, usually of one build with the walls. Fortifications of this type are also found in other provinces of the western empire.' But despite this similarity of style, there are remarkable differences of building technique and planning. Studies of the fortifications have tended to show that the style described above is 'normal', but have not attempted to add much to that assertion. However, within this framework there is scope for much variation of detail. Differences in the town plans, for example, are well known: many of them are published in Blanchet's book, which despite its appearance as long ago as 1907 is still the only major work on the subject.z Construction methods, too, and details of the varying sizes of materials used, particularly of the tiles, though previously noted, have lacked specific comment on the relevance or usefulness of the information.3 Wall-thicknesses, shapes and types of towers, the number and width of tile-courses, all differ from one site to another, but although lack of evidence at some sites makes a comprehensive comparison impossible, there are cities where sufficient remains of the walls exist or demolished fragments have been recorded in enough detail to make the comparative study of such minutiae significant and valuable. The sites discussed in this paper, as a kind of pilot study in this field, are three cities of Belgica Secunda. Beauvais, the capital of the Bellovaci, has one of the best-preserved enceintes of France. Recent excavations in areas of the city near the

Excavations at Alchester, 1928

The primary object of the work of 1928 was to follow up the discovery in 1927 of the unexpectedly strong and heavy foundation underlying the north-east corner mound. As a result of this year's work it is evident that this corner mound represents some heavy structure which is best explained as a circular corner tower built into the town walls at their northeast angle; but even its foundations were so broken up that it was impossible to discover any outline or recover a complete ground plan. Oh the outside, instead of extending beyond the walls themselves, the circumference of the structure lay flush with the curved external angle of the walls, while on the inside its circumference projected slightly beyond the angle of the walls proper. It was thus rather an internal than an external tower, a fact which it is important to bear in mind.