A study of jack-up leg drag coefficients

The accurate prediction of drag coefficients for truss-type jack-up legs is an important part of a unit's design. Over the past 14 years, a series of windtunnel tests have been conducted on both square and triangular cross-section leg configurations. A calculation method which closely fits the model test data has also been adopted. A previous paper described the early testing and the MMEC calculation method for square legs. Since then, testing and research have continued on both square and triangular leg designs. This paper describes the more recent testing performed on square legs, and it details the testing and the MMEC method for triangular legs. In addition, the effects of cornerpost design and surface roughness are discussed. Several example calculations are provided in Appendices.     

Ecology of bottom ice algae: II. Dynamics, distributions and productivity

Spring blooms of bottom ice algae are a common feature of landfast congelation ice in polar regions. Because ice algae are usually associated with a substrate, their population dynamics can be followed with considerable confidence. Although ice algal dynamics are closely related to irradiance, their dynamics and distributions are influenced by other abiotic and biotic factors. Ice algal abundance varies horizontally over all scales examined. Factors such as grazing and nutrient availability may contribute to local and geographic differences. Loss terms for most sea ice assemblages are largely unquantified. Ice algal biomass is most concentrated near the ice-water interface in spring.Environmental factors affecting ice algal abundance and productivity are considered here, emphasizing recent results from several well-studied sites. Biomass accumulation, growth rates and productivity have been documented for spring blooms of bottom interstitial and sub-ice assemblages. On an areal basis biomass accumulation in bottom ice assemblages can be comparable with planktonic systems. At low ambient temperatures and irradiances average specific growth rates (≤ 0.25 d⁻¹) and production rates (≤ 1.0 mg C mg Chl⁻¹ h⁻¹) for ice algae are low. Current methods of measuring productivity are compared. Results are consistently low but variable with little systematic difference among them. At present, apparent differences in productivity between bottom ice assemblages in the Arctic and Antarctic, or among different antarctic assemblages, are so confounded by methodological and other sources of variability that no firm differences can be detected.     

Waterproofing Underground Structures:Lessons from the Past,Systems for the Future

The paper describes some of the key issues that need to be addressed in the design and execution of underground structures to ensure their long term suitability as watertight units and outlines through practical examples of structures that have not achieved their design requirements which situations need to be considered. Waterproofing is not an exact science but a combination of theoretical knowledge and practical experience based on the five key factors: Environment, Design, Materials, Application and Use of the Structure.In conclusion the paper outlines the advances in crack control to date that can provide the necessary long term guarantees.The adoption of re - injectable crack inducers permitted the Client to save over 10% on construction costs and reduced the construction time by six months.     

Dedication to Peter Douglas (August 22, 1942–April 1, 2012)

Ecosystem management has been deemed a promising approach to environmental management in many settings. The ecosystem approach promises improved use of scientific information, better management coordination, and more meaningful public participation in environmental decision making. Yet, there is little evidence for how well ecosystem management efforts actually achieve their goals. This article presents an in‐depth analysis of one ecosystem management effort, the Albemarle‐Pamlico Estuarine Study (APES), which was part of the National Estuary Program. The APES failed to meet the objectives of ecosystem management in several visible ways. However, this case study reveals that the APES also had many positive results that were less visible to participants and observers. The performance of the APES is explained with reference to seven paradoxes inherent in the concept of ecosystem management. These findings have implications for appropriate expectations and evaluation of other ecosystem management efforts.     

The existence of an equilibrium solution to the traffic assignment problem when there are junction interactions

We consider a network with interactions and capacity constraints at each junction. We give conditions on the interactions and constraints which, if satisfied at each separate junction, ensure that any feasible assignment problem has an equilibrium solution. Two illustrative examples are provided; the first arises naturally and does not satisfy our conditions, while the second does satisfy our conditions but is somewhat unnatural.     

Preface and Acknowledgments

Abstract

The term “mitigation”; has been used in connection with habitat losses attributable to federal water projects as early as the Rivers and Harbors Act of 1899 and the Fish and Wildlife Coordination Act of 1934. Most of the current requirements to mitigate habitat losses associated with water development projects apply to wetlands, as they are biologically productive and have been destroyed at an increasing rate during recent years by developers seeking prime land in the coastal zone. A case study of the Port of Coos Bay and the City of North Bend, Oregon, provides an actual experience of estuarine mitigation in a dredging project and an airport fill. The case was developed as part of a larger curriculum research study for seaport management. This article is primarily written as a case with a brief introduction and discussion of mitigation requirements, followed by the text of the case and ending with a series of hypotheses for further research.     

Two-MPA Model for Siting a Marine Protected Area: Bahamian Case

This article recommends the parallel but separate modeling of nature-based and people-based marine protected areas (MPA) before the design and siting stages of establishing an MPA. Separate but simultaneous modeling of ideal nature and people MPAs permits each to be maximized for its own variables and subsequently compared to identify conflicts and agreements. The case that supports this recommendation is in the Commonwealth of the Bahamas, where the study conducted 572 interviews with people from six traditional settlements in the central Exumas Islands and Cays. The research is focused on why members of these settlements differentially responded to three nearby national MPA proposals.     

Achievable Dynamic Response for Automotive Active Suspensions *

A complete set of constraints is derived for the road disturbance transfer functions in a quarter car model of an automotive active suspension, for typical choices of measured outputs. It is shown that any road disturbance responses which are achievable using “full state feedback” can be achieved, to within an arbitrary small tolerance, using a dynamic compensator measuring suspension deflection only. Also considered are the disturbance responses to loads acting on the sprung mass, and a complete set of constraints is derived for these. It is shown that road disturbance and load disturbance responses can be determined independently if suspension deflection and sprung mass velocity are measured. Indeed, any responses achievable separately with “full measurements” can be approximated together to an arbitrary small tolerance. Certain integral relationships are shown to follow from the derived transfer function constraints. These relationships imply fundamental limitations for certain responses (e.g. tyre deflection) no matter what measurements are available for feedback.     

An algorithm for solving asymmetric equilibrium problems with a continuous cost-flow function

The paper gives two user objective functions for the asymmetric assignment problem, and an algorithm of descent type. The algorithm produces a sequence of flows which converges to the set of equilibria if the cost-flow function is continuous.