Large-eddy simulation of a mildly curved open-channel flow

After validation with experimental data, large-eddy simulation (LES) is used to study in detail the open-channel flow through a curved flume. Based on the LES results, the present paper addresses four issues. Firstly, features of the complex bicellular pattern of the secondary flow, occurring in curved open-channel flows, and its origin are investigated. Secondly, the turbulence characteristics of the flow are studied in detail, incorporating the anisotropy of the turbulence stresses, as well as the distribution of the kinetic energy and the turbulent kinetic energy. Moreover, the implications of the pattern of the production of turbulent kinetic energy is discussed within this context. Thirdly, the distribution of the wall shear stresses at the bottom and sidewalls is computed. Fourthly, the effects of changes in the subgrid-scale model and the boundary conditions are investigated. It turns out that the counter-rotating secondary flow cell near the outer bank is a result of the complex interaction between the spatial distribution of turbulence stresses and centrifugal effects. Moreover, it is found that this outer bank cell forms a region of a local increase of turbulent kinetic energy and of its production. Furthermore, it is shown that the bed shear stresses are amplified in the bend. The distribution of the wall shear stresses is deformed throughout the bend due to curvature. Finally, it is shown that changes in the subgrid-scale model, as well as changes in the boundary conditions, have no strong effect on the result

Impuls nodig voor veredeling van weinig eisende rassen'

Het onderzoeksprogramma Groene Veredeling is van start gegaan. Biologische en gangbare veredelingsbedrijven werken samen met onderzoekers aan de veredeling van rassen die geschikt zijn voor low input teelt en/of teelt onder suboptimale omstandigheden. Een interview met Margreet Hofstede van het ministerie EL&I

Scalar dispersion in strongly curved open-channel flows

River hydrodynamicsTurbulent open channel flow and transport phenomen

New bird records for the island of Lombok

Seventeen species are recorded for the first time from the island of Lombok. Nine of these are maritime birds on passage and four are widely occurring migrant shore and land birds. Gallirallus striatus may be a local migrant, Chrysococcyx basalis is a visitor from Australia, and Anthreples malaccensis is presumed to be either a previously overlooked resident or a recent colonist. Hemiprocne longipenis, previously unrecorded from the Lesser Sundas, appears to be a recent colonist

Scalar dispersion in strongly curved open-channel flows

Large-eddy simulations (LES) and Reynolds-averaged numerical simulations (RANS) are performed for the flow and scalar dispersion through a strongly curved open-channel bend. The aim of the study is to investigate the performance of both LES and RANS as regards the reproduction of the key bend flow features and the associated prediction of scalar spreading along the flume. In this respect, three different issues are addressed. Firstly, the influence of the water depth on the flow behavior as computed by LES and RANS is considered. Secondly, the plume statistics of the case with a continuous vertical line source is investigated. And thirdly, the dispersion behavior of a scalar tracer is studied by means of the case in which a blob of the scalar tracer is instantaneously injected. It is found that the LES computations fairly well reproduce the main flow features, whereas RANS computations experience severe difficulties in predicting the flow field. Moreover, it was found that the gradient-hypothesis of diffusion is only limitedly valid; even counter-gradient diffusion is observed. In addition, the residence time characteristics of the instantaneously injected blob of the scalar tracer in the bend are addressed as well

Zeven teelten in praktijk : teelthandleidingen voor biologisch geteelde gewassen

Teelthandleidingen voor biologisch geteelde consumptieaardappelen, granen, ijsbergsla, peen, prei, sluitkool en spruitkool. Het laatste hoofdstuk van het boek bestaat uit saldoberekeningen voor pootaardappel uit kleigebieden, vroege aardappelen, consumptieaardappelen uit kleigebieden, wintertarwe uit kleigebieden, zomertarwe uit kleigebieden, wintergerst uit kleigebieden, zomergerst uit kleigebieden, haver uit zandgebieden, winterrogge uit zandgebieden, triticale uit zandgebieden, ijssla (zomerteelt), bospeen (zomerteelt), grove peen (b-peen, bewaring), prei (vroeg herfst), witte kool (bewaring), witte kool (industrie), rode kool (bewaring), rode kool (industrie) en spruitkool (middenvroeg)

Two decades of numerical modelling to understand long term fluvial archives: Advances and future perspectives

The development and application of numerical models to investigate fluvial sedimentary archives has increased during the last decades resulting in a sustained growth in the number of scientific publications with keywords, 'fluvial models', 'fluvial process models' and 'fluvial numerical models'. In this context we compile and review the current contributions of numerical modelling to the understanding of fluvial archives. In particular, recent advances, current limitations, previous unexpected results and future perspectives are all discussed. Numerical modelling efforts have demonstrated that fluvial systems can display non-linear behaviour with often unexpected dynamics causing significant delay, amplification, attenuation or blurring of externally controlled signals in their simulated record. Numerical simulations have also demonstrated that fluvial records can be generated by intrinsic dynamics without any change in external controls. Many other model applications demonstrate that fluvial archives, specifically of large fluvial systems, can be convincingly simulated as a function of the interplay of (palaeo) landscape properties and extrinsic climate, base level and crustal controls. All discussed models can, after some calibration, produce believable matches with real world systems suggesting that equifinality - where a given end state can be reached through many different pathways starting from different initial conditions and physical assumptions - plays an important role in fluvial records and their modelling. The overall future challenge lies in the development of new methodologies for a more independent validation of system dynamics and research strategies that allow the separation of intrinsic and extrinsic record signals using combined fieldwork and modelling

Bodemindicatoren in BASIS : Identificatie van de belangrijkste biologische en chemische bodemparameters (“bodemindicatoren”) in het project BASIS over de periode 2009-2016

In deze studie is nagegaan welke gemeten chemische en biologische bodemparameters het beste onderscheid maken tussen de verschillende grondbewerkingssystemen en teeltsystemen in de systeemproef BASIS in Lelystad. Met variantieanalyse en multivariate statistische technieken zijn bodemparameters in BASIS geanalyseerd. Samenvattend blijkt potentieel mineraliseerbare stikstof (PMN) en de N-totaal de beste bodemindicatoren te zijn om verschillen tussen systemen van hoofdgrondbewerking (ploegen versus niet-kerende bewerkingen) en verschillen tussen teeltsystemen (biologisch versus gangbaar) weer te geven. Daarnaast zijn HWC, biomassa schimmels, biomassa bacteriën en borium- en magnesiumgehalte goede bodemindicatoren om deze verschillen te duiden. De correlatie tussen PMN en organische stof en de correlatie tussen HWC en organische stof blijkt goed te zijn. Vanwege de hoge correlatie tussen HWC en PMN en de hoge prijs van de PMN meting heeft HWC de voorkeur. Aanbevolen wordt de analyse te gebruiken in de ontwikkeling van de BLN en vergelijkbare analyses te doen voor andere maatregelen en andere systeemproeven