DHI Water and Environment Pte. Ltd

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Singapore, Singapore
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Drillet G.,Technical University of Denmark | Drillet G.,Roskilde University | Drillet G.,DHI Water and Environment Pte. Ltd | Hansen B.W.,Roskilde University | Kiorboe T.,Technical University of Denmark
Limnology and Oceanography | Year: 2011

Three populations of the copepod Acartia tonsa two from the Baltic Sea and one from the U.S. East Coast were compared for resting egg production at conditions of saturating and limiting food availability. All three populations produced eggs that hatched within 72 h when incubated at 17°C (subitaneous eggs) but the two Baltic populations in addition produced eggs that hatched at a much slower rate in the course of a month (delayed hatching eggs [DHE]). Such eggs were not produced by the U.S. population. The fraction of DHE increased when food was limiting. Females from a Baltic population that were incubated individually all produced subitaneous eggs but about half the females consistently also produced DHE. Cold storage that mimicked boreal winter conditions synchronized the hatching of DHE after extended storage indicating that spring hatching of DHE might seed the water column with nauplii as an adaptation to match the timing of the spring bloom in boreal marine ecosystems. Low food availability promotes the production of resting eggs in marine copepods. © 2011 by the Association for the Sciences of Limnology and Oceanography Inc.


Leschka S.,DHI Wasy GmbH | Oumeraci H.,TU Braunschweig | Larsen O.,DHI Water and Environment Pte. Ltd.
Journal of Earthquake and Tsunami | Year: 2014

In tsunami hazard assessment, usually depth-averaged flow models are applied which use the quadratic friction law with Manning's coefficients to describe the surface roughness of the bottom. Large roughness elements such as buildings and tree vegetation, which are too small to be resolved by the grid of the bottom topography, are mainly considered by using purely empirical Manning coefficients. This approach, however, is not physically sound and may thus result in very large uncertainties in inundation modeling. A more physically-based approach is to determine prediction formulae for the hydraulic resistance of large roughness elements, considering for example different shapes, sizes and types of arrangement which can then be directly implemented in depth-averaged models such as nonlinear shallow water (NLSW) models. Such prediction formulae can be determined on the basis of systematic simulations using a well-validated 3D numerical model. To better understand complex flow phenomena involved in tsunami inundation, three vertical emerged cylinders have been arranged in four different configurations with four different distances between each other and subject to a solitary wave and to a bore. A validated three-dimensional two-phase Reynolds-averaged Navier-Stokes (RANS) model with the volume of fluid (VOF) method has been used to assess flow velocities and water levels near the cylinders. In this study, the validation of the numerical model by data obtained from large-scale model tests in the Large Wave Flume (GWK) Hanover, the flume at the Leichtweiss Institute for Hydraulic Engineering and Water resources (LWI) and the wave tank of the University of Washington is presented and the effects types of cylinder arrangement and distances between the cylinders on the flow induced by a solitary wave and a bore in the near field are discussed. © 2014 World Scientific Publishing Company.


Drillet G.,DHI Water and Environment Pte Ltd. | Drillet G.,Roskilde University | Frouel S.,Danisco | Sichlau M.H.,Technical University of Denmark | And 5 more authors.
Aquaculture | Year: 2011

Copepods are important crustaceans studied because of their key role in ecology, trophic biology, fisheries management, in modeling the flow of energy and matter, ecotoxicology, aquaculture and aquarium trade. This paper discusses various aspects of the state of knowledge of copepod culture at large scales and provides the scientific community with ideas and concepts that could improve and quicken the development of copepod mass cultures. As a framework for discussion, we use a conceptual scheme from Teece (1988) and adapted it to our goal: 'how to capture value from a copepod product'. The suggestions include: 1) optimize cultures by automation and implement recirculation technology for improving water quality; 2) use harpacticoid and cyclopoid copepods in industries that can produce large amounts of these prey on site at any given time; but use calanoid copepods for industries limited in production time and those that export copepod products (e.g. eggs); 3) select preferentially local copepod species and if possible species with lipid conversion capabilities; 4) optimize sex ratio and selection/cross-breeding to develop suitable copepod strains for aquaculture; 5) explore the use of probiotics for improving the fitness of copepod cultures; and 6) encourage copepod producers/retailers to use/develop an efficient sales and marketing strategy. © 2011 Elsevier B.V.

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