Meters In Diameter Research Articles

Japanese activities related to (Radio) astronomy in the Antarctic

Japanese activities related to radio astronomy in Antarctica are briefly reviewed.The Japanese base, Showa, is located on the coast and is based on rocks rather than ice. A 10 metre diameter microwave antenna has been built at the Showa station and a series of VLBI experiments have been made between the Showa base and a station in Japan in 1988–1989. The experiments have been geophysically motivated and an accurate measurement of the location of the Showa base was determined relative to Japan, which has a well determined position relative to other continents.

Pipeline Induction Heat (PIH) complete tank life enhancement programme

Pipeline Induction Heat Ltd (PIH), Burnley — UK, has successfully completed a rehabilitation project for the British Pipeline Agency, UK. This work involved the internal cleaning and coating of a 36 metre diameter × 6 metre high semi‐buried aviation fuel tank. The tank was constructed approximately 50 years ago and has been in full service throughout this period.

A Continuum Vibrational Analysis for a Tetrahedral Space Platform

Antennas over 50 metres diameter are being considered for use in land mobile communication systems. As the satellite in geostationary orbit has an angular velocity equal to that of the earth, no tracking systems are necessary and low cost fixed ground antennas can be used. In addition, a typical early truss platform could possibly be a geostationary communication one of size up to 300m × 300m. In this paper structural stiffness, strength and dynamic characteristics of large skeletal frameworks for space applications are investigated by analysing the tetrahedral truss which is idealised as an equivalent continuum. Appropriate analytical relationships are presented in terms of the truss member properties which are taken as slender graphite/polyethersulphone composites. Fundamental and harmonic frequencies have been calculated and have been compared with those from a finite element skeletal analysis and a finite element plate analysis. It has been shown that the results of the simplified analysis technique are accurate to within 10 per cent of those of the analytical solutions provided the system is both large and flexible. In addition, the analysis provides a simple methodology for the preliminary assessment of vibration frequencies for large space structures.

A NONROTATING LIQUID MIRROR FOR ASTRONOMICAL TELESCOPES

ABSTRACT The author describes a new type of nonrotating liquid mirror based on GRIN (gradient index) optics. The mirror consists of a container at rest having a thin layer of mercury covered with a transparent liquid in which one has introduced a radial dependence of the index of refraction. This system can focus light like a mirror. The author considers a simple radial index dependence and some of the mechanisms that could be used to set up the index gradient. If working systems can be built, this type of mirror should have essentially no size limit and may be used to build optical telescopes having truly gigantic dimensions (hundreds of meters in diameter).

A radiation safety survey on a Clinac-20 linear accelerator

The radiation protection problems associated with a 20 MV linear accelerator are discussed, in particular those due to the considerable neutron production accompanying the 18 MV photon beam. These include the potential neutron dose to the patient, the special shielding requirements and the neutron activation of the accelerator and its surroundings. The results of the structural protection survey are described. In particular, the methods recommended by the NCRP for predicting the neutron dose equivalent at the end of a maze are shown to be reliable. Dose rates due to activation of the treatment room and various parts of the accelerator were measured, and potential doses to staff were assessed. Neutron dose equivalents were measured in the specified two metre diameter patient plane using the standard NRPB neutron badges and also with the recently developed CR-39 dosemeters. The latter appear to give sensible results.

Investigation of the aerodynamic performance and noise characteristics of a 1/5th scale model of the Dowty Rotol R212 propeller

SummaryAn investigation of the four-bladed Dowty Rotol R212 propeller (NACA 16 sections) has been made at l/5th scale (0·7 metre diameter) in the RAE 1·5 metre acoustic tunnel. Propeller power absorption and thrust have been measured over a range of rotational speeds up to 8000 rev/min at mainstream speeds from 15 m/s to 60 m/s for a range of blade settings. Slipstream wake surveys show outward movement of the position of the peak pressure as propeller loading is increased.Noise analysis demonstrates the predominance of multiple tones whose number and intensity increase with helical-tip Mach number. An empirical formula shows that the fundamental tone SPL varies with tip speed and power loading in an identical manner to that observed on a modern ARA-D section propeller.

Construction of a radio beacon (DVOR/DME) for aircraft traffic in Arta/Mallorca/Spain

A radio beacon is just a reference point, a station that sends out radio signals to help planes to find their way. This station requires the construction of a platform of 40 metres diameter, generally sited in mountain heights or in places free from interferences. In this work, the radio beacon recently built in Arta, at the Northeastern end of Mallorca by Dragados & Construcciones S. A. is described, developing the most representative of the construction: the concrete structure and the setting of the iron structure because of its special characteristics of form and dimensions.

Calibration of the Pointing System of a Radio-Telescope Using an Electronic Theodolite

Abstract The 26 metre diameter radio-telescope at the University of Tasmania makes use of synchro resolvers to determine the direction in which it points. These were calibrated with a Wild T2000 theodolite. By carefully aligning the equipment and removing random noise from the data an accuracy of better than ±3 seconds of arc was achieved.

TRIBOLOGY CHECK‐UP FOR WEAR IN OIL RIG BEARINGS

INVESTIGATIONS carried out by The National Centre of Tribology, at Risley, Warrington, into causes of wear and failure of large bearings (up to 6 metres diameter) used on oil rigs, cranes and mooring points in the North Sea, has generated data that is proving invaluable to designers and operators. As a result, the life of bearings may now be predicted much more accurately, and there is a corresponding improvements in the operational safety.

Groundwater Control in Complex Ground Conditions

Abstract Two fifteen metre diameter ten metre deep underground tanks were constructed immediately alongside each other by sinking bolted segmental caissons and casting the secondary lining in situ . Preliminary site investigation indicated difficult ground conditions with a high risk of base failure for excavation in the dry. Wet construction of the base slab would avoid base instability but not the problem of hydrostatic uplift of the partially completed structures. Further investigation revealed a complex sequence of interbedded sands, silts and clays of alluvial and glacial origins. The granular horizons comprised a small number of thicker continuous bands, one occurring immediately below the proposed formation levels for the tank floor slabs, and several thinner irregular bands grading laterally into silts and clays. Piezometers in the more critical granular horizons indicated artesian and sub-artesian groundwater levels. Temporarily disconnecting at ground level the piezometer showing artesian conditions and measuring the resulting water flow indicated a granular body of restricted size or limited recharge. The absence of any effect on other piezometers offered confirmation of isolated granular bodies. Despite obvious difficulties in predicting the effectiveness of a groundwater lowering installation the significant advantages of constructing in the dry over wet construction mitigated in favour of dewatering. Sixteen deep pumped wells were installed around the circumference of the tanks to form a figure of eight pattern for the wells. To reduce the risk of a base failure due to artesian groundwater in any lobes of granular material encroaching within the plan excavation but not intersected by the pumped wells, four internal relief wells per tank were installed. Successful construction was achieved, although a minor interruption to the pumping clearly demonstrated the prudence of the internal relief well installation. The paper comments on some aspects of BS 5930 in relation to the construction described.

Effect of Phosphorus Addition on Treatment Efficiency of a Lab Scale Anaerobic Filter, Treating Landfill Leachate

Abstract Sanitary landfill leachate has been a source of environmental concern due to its high organic strength and chemical diversity. A number of lab-scale and pilot scale studies have indicated that the anaerobic filter is highly competitive with other forms of biological treatment and has distinct economic advantages. While there have been a number of studies based on a general overall approach to leachate treatment by the anaerobic filter, limited information is available on the role played by essential nutrients like nitrogen and phosphorus in the biological treatment process. Laboratory studies were conducted at room temperature (22 °C) to study the effect of nutrient addition (specifically, phosphorus, the deficient constituent of leachate) on treatment efficiency of landfill leachate by the upflow anaerobic filter. Two anaerobic filters (0.975 metres x 0.15 metres diameter) were constructed using plexiglass pipes and packed with strips of corrugated fibre-glass sheets in four layers to form the filter bed. Leachate collected from a nearby landfill was applied at moderate organic loadings (1.8-4.0 kg COD/m3/day) to the two units maintaining a HRT of 0.987 days. Results indicate phosphorus addition may be made to organically diverse wastes such as landfill leachate with distinct advantages.

Finite temperature effects on the evolution of ionospheric barium clouds in the presence of a conducting background ionosphere: 1. The simplest case: Incompressible background ionosphere, equipotential magnetic field lines, and an altitude‐invariant neutral wind

We postulate that under realistic ionospheric conditions, barium ion clouds hundreds of meters in diameter can be long‐lived, quasi‐stable, nonbifurcating structures. These structures may resemble “tadpoles,” with a dense head, steep density gradients at the front, and a long, less dense tail. We assume that these structures are the final products of the recursive bifurcation of a considerably larger barium ion cloud, i.e., striations. The realistic ionospheric conditions to which we refer consist of a barium ion cloud with ion temperatures Ti of approximately 1000°K, coupled electrically to a background ionosphere of lower compressibility than itself, i.e., an F region. We show analytically that this combination of finite Ti and relatively incompressible background, combined with the simplifying assumptions of equipotential magnetic field lines and of a uniform, altitude‐invariant neutral wind, results in an effective diffusion of barium plasma but more importantly of total magnetic‐field‐line‐integrated Pedersen conductivity Σp. The diffusion coefficient has a special form which allows the inner portions of the cloud to diffuse slowly, giving the cloud a long lifetime, and allows the outer, less dense portions of the cloud to diffuse rapidly, preventing cloud bifurcation. Numerical simulations of the full nonlinear dynamics are then used to show that this diffusion does in fact give rise to quasi‐stable barium striations hundreds of meters in diameter. These findings are consistent with the linear analysis of Francis and Perkins (1975). The consequences of relaxing the above simplifying assumptions will be treated in subsequent papers in this series.

Design of a 5.5 metre diameter superconducting solenoid for the Delphi particle physics experiment at LEP

A magnet comprised of a superconducting solenoid surrounded by an iron yoke is required to produce 1.2 Tesla in a room temperature volume of 5.2 metres diameter by 6.8 metres long. A single layer main coil is wound with pure aluminium clad Nb-Ti conductor on the inside of a support cylinder. Series connected field correction coils are located at each end of the main coil. The operational current is 5kA. The coil is indirectly cooled with pumped two-phase 4.5K He and is suspended within an 80K gas cooled radiation shield inside a stainless steel vessel. The paper covers the design concept, field and force computations, coil winding and bonding R&D, plus the fabrication proposals.

LARGE DIAMETER POLYETHYLENE SUBMARINE OUTFALLS

This paper presents the state of the art that has now evolved in Australia and shows the trend towards using high density polyethylene pipes for submarine conditions and the varying techniques and materials utilised. Prior to 1981 High Density Polyethylene (H.D.P.E.) was not produced in Australia in diameters larger than 630mm and even in the available sizes submarine outfalls were in the main constructed of mild steel or concrete pipes. In 1980 the Gold Coast City Council called tenders for the supply and installation of a 1500 metre, 1 metre diameter, outfall across the Southport Broadwater which is an active tidal estuary area. The proposed route crossed a main navigation channel and required trenching up to 8 metres into sand and sandstone. After consideration of the special requirements and high tender prices for conventional materials, Council constructed a temporary 400mm diameter H.D.P.E. outfall while the design of the permanent outfall was re-evaluated. The outfall was eventually constructed by day labour utilising a 1 metre diameter H.D.P.E. at a cost saving of approximately $1.5 million over the lowest tender price utilising steel pipes. Manufacturing facilities were imported into Australia for this job and now other large diameter submarine H.D.P.E. outfalls have been constructed in Australia and this material is now gaining acceptance.

Two methods of concrete lining machine bored tunnels : Nelsen, A A Paper to 3rd Australian Tunnelling Conference, Sydney, 12–15 Sept 1978, 6P

The Melbourne and Metropolitan Board of Works has constructed over 30 kilometres of various sized machine bored rock tunnels in the last 10 years. All of these tunnels for sewerage have been temporarily supported during excavation and completed by placing an insitu concrete lining. Two methods of constructing the concrete lining have evolved. For smaller sewers, 1.8 metres diameter when lined, the full circle bulkheaded pour method is used and for larger tunnels from 2.59 metres to 3.51 metres diameter when lined, the full circle continuous pouring method is used. The paper explains both methods and gives important details such as, concrete mixes, formwork, plant and equipment for transporting and placing the concrete, crew requirements and production achieved.

Use of a tunnel boring machine on a coal mine decline : White, S B Paper to 3rd Australian Tunnelling Conference, Sydney, 12–15 Sept 1978, 5P

A Calweld 5.1 metre diameter full face tunnel boring machine was used by the Allied Codelfa Joint Venture to excavate a 1600 metre long decline for Coal Cliff Collieries Pty. Ltd. at their new West Cliff Mine on the southern coalfields of New South Wales. This was the first time in Australia that such equipment had been used on a 1 in 3 gradient. The tunnel boring machine owned by Codelfa Construction Pty. Limited had to be modified firstly to accommodate the 1 in 3 slope and secondly to comply with the electrical requirements of the Coal Mines Regulation Act. The decline traverses horizontally bedded sedimentary strata over a vertical distance of 530 metres from the surface to the Bulli coal seam. Ingress of ground water from the overlying Hawkesbury sandstone caused problems during the initial drivage and necessitated alterations to construction methods. Adverse geological conditions in the interbedded shale and sandstone below the Hawkesbury sandstone gave rise to unstable roof conditions which considerably reduced the rate of advance. Notwithstanding the problems encountered on this project, experience has shown that a tunnel boring machine could be successfully used on a 1 in 3 decline. However the high initial cost of providing and installing the equipment may well limit its application to coal mine declines.

Measurement ofG/Tfor ESCES Antenna System Using Moon

G/T of 14 metre diameter cassegrain antenna at ESCES, Ahmedabad has been measured using moon as the source. The measured results agree closely with the theoretical value.

Large diameter thin superconducting solenoid magnets

High energy physics experiments on the latest generation colliding beam machines require large superconducting solenoid magnets. The Lawrence Berkeley Laboratory is developing a new generation of high current density (∼ 10 9 A m −2) superconducting solenoid magnets which are thin from a radion standpoint. To meet our design objectives, an integrated magnet and cryostat design has been evolved. Recent tests of one metre diameter prototype magnets show that our design concepts are technically viable. The results of the one metre magnet test are reported here.

Mechanisms and dynamics of strombolian activity

Strombolian explosions at Heimaey and Stromboli are described. Two main components of activity within a typical strombolian explosion are distinguished: an initial, high velocity, gas thrust part due to gas decompression and a subsequent convective part. Initial gas velocities at Heimaey averaged 157 m/s (standard deviation 28 m/s from 15 observations) and at Stromboli 31 m/s (standard deviation 12 m/s from 8 observations) for one vent and 56 m/s for a second vent. Velocities decreased approximately exponentially with height, and decelerations of up to 50 gravities were observed during the gas thrust events. A model of the gas thrust process is developed and values are deduced for the gas/solid mass ratio in the ejected material. Evidence is resented for the several-foId concentration of gas into that part f the magma expelled explosively, and a model in which large bursting gas bubbles are responsible for the explosions is shown to be compatible with the observations. Excess pressure within such bubbles is found to be of order 2.5 × 10 4 N/m (0.25 atmospheres) at Heimaey and 600N/m 2 (0.006 atmospheres) at Stromboli. Pressures inside bubbles of a few metres diameter are found to be of comparable magnitudes. Average gas release rates of 3 to 6 × 10 3 kgm/s at Heimaey and at least 0.13 kgm/s at Stromboli are indicated.

Reduction of fan noise by annulus boundary layer removal

Much of the noise produced by a fan is due to varying forces caused by the unsteady flow field through which it passes. In the absence of inlet guide vanes, support struts and other mechanical obstructions, the flow irregularities are caused by large scale intake turbulence and temporal and spatial variations in the annulus boundary layer. In many cases the most effective source is the annulus boundary layer, as this interacts with the blade tip which is the fastest part of the blade and is therefore the most effective noise source. This noise can be reduced if the annulus boundary layer is smoothly bled away from the rotor so that the blade tip sees a thin, uniform boundary layer. A one metre diameter ventilation fan has been run in a duct with and without a boundary layer bleed system and a reduction of far field sound power of approximately 5 dB has been obtained for a bleed of 5 % of the main flow with some far field tone reductions of more than 15 dB. Measurements of far field directivities, in-duct acoustic modes and aerodynamic distortions have confirmed the suggested explanation for this phenomenon. The tests have shown that great care must be taken in the design of a bleed system so that residual boundary layer distortions are not in the correct wavelength range to produce propagating acoustic waves at important blade passing harmonic frequencies. If such distortions are present, the far field noise can increase instead of decrease.