Flow Past an Accumulator Unit of an Underwater Energy Storage System:Three Touching Balloons in a Floral Configuration

An LES simulation of flow over an accumulator unit of an underwater compressed air energy storage facility was conducted. The accumulator unit consists of three touching underwater balloons arranged in a floral configuration. The structure of the flow was examined via three dimensional iso surfaces of the Q criterion. Vortical cores were observed on the leeward surface of the balloons. The swirling tube flows generated by these vortical cores were depicted through three dimensional path lines. The flow dynamics were visualized via time series snapshots of two dimensional vorticity contours perpendicular to the flow direction; revealing the turbulent swinging motions of the aforementioned shedding-swirling tube flows. The time history of the hydrodynamic loading was presented in terms of lift and drag coefficients. Drag coefficient of each individual balloon in the floral configuration was smaller than that of a single balloon. It was found that the total drag coefficient of the floral unit of three touching balloons, i.e. summation of the drag coefficients of the balloons, is not too much larger than that of a single balloon whereas it provides three times the storage capacity. In addition to its practical significance in designing appropriate foundation and supports, the instantaneous hydrodynamic loading was used to determine the frequency of the turbulent swirling-swinging motions of the shedding vortex tubes; the Strouhal number was found to be larger than that of a single sphere at the same Reynolds number.     

Transport infrastructure provision and operations: Why should governments choose private–public partnership?

Recent transport sector liberalisation, as well as global economic crisis, is favouring the implementation of transport infrastructure projects through Public–Private Partnerships (PPP). However, there is a debate as to whether PPP schemes are a better option than conventional procurement. To this end, an evaluation framework is proposed, to assess which of these two alternative schemes for transport projects financing is preferable for the public. The proposed framework is complimentary to the Value for Money (VfM) approach and is based on a Multi Criteria Analysis (MCA). The first step is the estimation of the Public Sector Comparator (PSC) for the case of conventional procurement, dealing with construction, maintenance and operation costs revenues, as well as any costs associated with risks undertaken by the public. As for the PPP case, it includes any payments by the public sector and related risks costs. The MCA is then applied only if the PPP is found preferable for the public sector. The latter considers additional impacts, including among others the social attributes of a particular scheme, job creation, environmental impacts and safety and security aspects. The proposed framework was applied to a pilot Bus Rapid Transit (BRT) corridor infrastructure project in the city of Indore, India, in order to demonstrate its validity. The framework and its application could provide useful guidance when considering PPP for a transport project, since it demonstrates in a transparent way the society's attitude towards this project, something that is critical to its acceptance.     

Regulation,trust and contractual incentives around transport contracts – Is there anything bus operators can learn from public air service contracts?

This paper compares recent experiences in contract negotiation and subsequent commitment in public air services with the bus industry. The heart of the paper is a survey of European and Australian regional airlines, which we mirror with revealed experiences of bus operators. We aim to identify a number of elements in the contracting regimes that have exposed ambiguity and significant gaps in what the principal (e.g., transport department) expected, and what the agent (airline or bus operator) believed they were obliged to deliver. Ultimately airline and bus services are similar in that public authorities procure transport services that are desirable for the society but would be unprofitable without government involvement. In both sectors (theoretically fairly similar) public transport contracts are used, and those usually include obligations and performance measurements. In terms of similarities, one of the surveyed contract details that had a perceived high clarity in both industries was “payment procedures” and amongst those with rather poor clarity was also in both industries “incentives to improve performance and grow patronage”. We also show differences between regional air services and bus operations with regard to performance measurement and pre-specified obligations. Because of the strong safety culture around air services we find that regulation and trusting partnerships are even more important to aviation than to the bus sector. Because of the high level of trust but also because of simpler and more complete contracts in aviation, there is much less (re-)negotiation going on compared to the bus operations.     

Developing a Spatially Enabled Inventory of Recreational Boats Using Vessel Registration Data

Effective waterway management requires information on the characteristics and locations of boats. A field-based boat census—a traditional method to obtain spatially accurate information—is relatively expensive, time-consuming, and restrictive in scope. Vessel registration data, maintained by all U.S. states, is potentially a more robust information source. This research evaluated the accuracy and reliability of vessel registration data to supply location and attribute information for boats. The study premise was to use vessel registration data, which includes the mailing address of registered boat owners, to develop a spatially enabled inventory of boats. The study area comprised 12,064 salt-water accessible property parcels in two Florida counties. An on-water census (OWC) provided location and characteristics for 5,023 vessels, which were compared to 8,681 vessel registration records linked to the study area. Discrepancies between the OWC and vessel registration data were explained by a stratified, random sample of 485 telephone survey respondents. Study results show that vessel registration data accurately located and characterized roughly 81% of the boat population; in contrast, the OWC accurately located less than 56%. A conclusion is that state vessel registration data is a better alternative than an OWC for locating and characterizing boats kept along waterways.     

Book reviews

Coastal Resources Management: Beyond Market and Bureaucracy by Robert B. Ditton, John L. Seymour, and Gerald C. Swanson. Published by D. C. Heath and Company, Lexington, Massachusetts, 1977, 191 pp., 6 figures.

The Urban Sea: Long Island Sound by Lee E. Koppelman, Peter K. Weyl, M. Grant Gross, and DeWitt S. Davies. Published by Praeger Publishers, 1976. 209 pp., 81 figures, 42 tables.     

Management of corals and coral ecosystems in the United States

Abstract

Corals and coral communities provide substantial societal benefits by virtue of their recreational and esthetic appeal, the habitat provided for commercially harvested fish and shellfish, the structural foundation provided for productive coastal ecosystems, and the market value of harvested coral specimens. Coral resources are subject to adverse effects from pollution, dredging, specimen collecting, anchor damage, commercial fishing, overharvesting, and activities related to offshore petroleum development. Management programs which protect coral resources in the United States comprise a patchwork of separate federal and state programs. They attempt to adapt broad regulatory authorities for parks, fisheries, offshore mineral resources, and other subjects for the purpose of coral conservation. These programs embody species‐specific, area‐specific, and generic approaches to coral management. This paper traces the evolution of U.S. coral management programs and comments on their respective strengths and weaknesses. Alternative approaches for strengthening management systems could include new coordinating committees, legislation, memoranda of agreement between involved agencies, and others.     

Northern Abalone: Using an Invertebrate to Focus Marine Conservation Ideas and Values

Marine invertebrate species have usually been overlooked in favor of high-profile vertebrate species for facilitating dialogue towards area conservation. The northern abalone (Haliotis kamtschatkana) is proposed as a focal ("flagship") species whose protection and recovery could concentrate public concern for abalone and its associated kelp forest ecosystems in Haida Gwaii (Queen Charlotte Islands), British Columbia. I explain how issues of culture, commerce, and conservation unite to create a strong role for northern abalone in preparations for creating a large marine conservation area within Haida Gwaii. Culture is relevant, as local indigenous people (the Haida) are currently denied access to constitutionally established subsistence fishing rights for northern abalone. Commerce is involved as ongoing kelp forest-associated fisheries co-occur with northern abalone. Finally, this is a challenging precedent in Canadian marine conservation, as restoring two "listed" species- at risk (northern abalone and their predator, the sea otter (Enhydra lutris)) is potentially mutually exclusive. As part of the forthcoming public consultations towards establishing a marine conservation area, the opportunity provided by northern abalone to focus ideas and values should be seized.     

On the axial force induced on a duct by a propulsor

The axial force induced on a duct (duct thrust) which surrounds a propulsor is, by means of an energy conservation argument, expressed in terms of the thrust and power of the propulsor and the kinetic energy losses per unit of time of the propulsor and the duct. Emphasis is put on the linear theory of an axisymmetric ducted actuator disk, where it is shown that the work done by the duct thrust is equal to the extra work done by the actuator disk when it is surrounded by the duct. This simplified model gives more insight into the interaction between the propeller and the duct and on the limits of linearization.     

Pb and Pu in the Northeast Water Polynya, Greenland: particle dynamics and sediment mixing rates

Distributions of the radionuclides ²¹⁰Pb and ^239,240Pu in sediment cores from the Northeast Water Polynya, Greenland, showed that these nuclides reached depths of 5–15 cm by particle mixing and sediment accumulation. End-member average values of the particle mixing coefficient and sediment accumulation rate were 0.13 cm² y⁻¹ and 0.06 cm y⁻¹, obtained from the ²¹⁰Pb profiles by assuming that each process is dominant relative to the other. Both ²¹⁰Pb and ^239,240Pu were measured on four cores; using the Pu data to constrain mixing rates produced corrected sediment accumulation rates that were 20–80% of the values calculated by neglecting mixing. Organic carbon burial in the polynya sediments was ≤0.4 mmol m⁻² d⁻¹, based on measured POC values at depth in the sediments and sediment accumulation rates corrected for mixing. This value is about 1% of the independently measured POC flux leaving the euphotic zone and compares with benthic carbon remineralization rates of 7% calculated by others from O₂ uptake in the sediments.The inventories of excess ²¹⁰Pb in the sediments ranged from 6 to 28 dpm cm⁻². Relative to the atmospheric input of ²¹⁰Pb and in situ production from decay of ²²⁶Ra, approximately 5 dpm cm⁻² of ²¹⁰Pb was being removed from the water column. The difference between the removal from the water column and sediment inventories suggests a net import of ²¹⁰Pb to the polynya. This may occur by input of dissolved ²¹⁰Pb from offshore waters or by input of ²¹⁰Pb carried by sea ice. Particulate matter in land-derived fast ice adjacent to the polynya contained 330 ± 14 dpm of excess ²¹⁰Pb g⁻¹. If particles transported in sea ice are comparable to those extracted from fast ice, then sea ice transport into the polynya followed by melting may be an important source of excess ²¹⁰Pb to the area. Fast ice also may contribute ²¹⁰Pb if portions break off and melt within the polynya, as occurred in 1993.     

Sediment geochemistry and mineralogy in Milos bay, SW Kyklades, Aegean Sea, Greece

This work aims at studying the geochemistry and mineralogy of Milos bay surface sediments. The bay forms an enclosed marine area, supplied totally by volcanic formations. Totally 16 samples were subjected to sedimentological (grain size), mineralogical (microscope examination and X-ray diffraction of the bulk sample and the pelitic fraction), and geochemical analyses (X-ray fluorescence in the pelitic fraction). Also the carbonate content was determined. Sediments were sandy with a high carbonate content (14–58%). The dominant minerals recognized in the pelitic fraction were smectite, kaolinite and illite, followed by chlorite, quartz, calcite, Mg-calcite and feldspars. In general, element concentrations appeared to be within the normal range, except Pb and Zn, which exhibited relatively high values. The Index of Geoaccumulation I_geo was computed, in order to investigate a possible enrichment of the surface sediments in metals. The analysis revealed again high values of I_geo class for both Pb and Zn. A careful study of the area, in relation to the quality of the catchment basins petrology, lead to a non-anthropogenic origin of these high concentrations. The enrichment of the surface sediments in Pb and Zn is attributed to the weathering of several mineral deposits, pyroclastic rocks and lavas, covering almost all Milos vicinity. A study of the geochemical data correlation coefficient matrix revealed three major groups of elements: (i) the elements of detrital origin represented by Si, Al, K and a part of the metals; (ii) the carbonates group; and (iii) a Fe–Mn oxyhydroxides–oxides group, which attracts a part of Pb, Cr and Ni.