39 research outputs found
Evaporation from a large lowland reservoir-observed dynamics and drivers during a warm summer
No full textWe study the controls on open water evaporation of a large lowland reservoir in the Netherlands. To this end, we analyse the dynamics of open water evaporation at two locations, Stavoren and Trintelhaven, at the border of Lake IJssel (1100ĝ€¯km2); eddy covariance systems were installed at these locations during the summer seasons of 2019 and 2020. These measurements were used to develop data-driven models for both locations. Such a statistical model is a clean and simple approach that can provide a direct indication of (and insight into) the most relevant input parameters involved in explaining the variance in open water evaporation, without making a priori assumptions regarding the process itself. We found that a combination of wind speed and the vertical vapour pressure gradient can explain most of the variability in observed hourly open water evaporation. This is in agreement with Dalton's model, which is a well-established model often used in oceanographic studies for calculating open water evaporation. Validation of the data-driven models demonstrates that a simple model using only two variables yields satisfactory results at Stavoren, with R2 values of 0.84 and 0.78 for hourly and daily data respectively. However, the validation results for Trintelhaven fall short, with R2 values of 0.67 and 0.65 for hourly and daily data respectively. Validation of the simple models that only use routinely measured meteorological variables shows adequate performance at hourly (R2Combining double low line0.78 at Stavoren and R2Combining double low line0.51 at Trintelhaven) and daily (R2Combining double low line0.82 at Stavoren and R2Combining double low line0.87 at Trintelhaven) timescales. These results for the summer periods show that open water evaporation is not directly coupled to global radiation at the hourly or daily timescale. Rather a combination of wind speed and vertical gradient of vapour pressure is the main driver at these timescales. We would like to stress the importance of including the correct drivers of open water evaporation in the parametrization in hydrological models in order to adequately represent the role of evaporation in the surface-Atmosphere coupling of inland waterbodies.Water Resource
Source partitioning of H2O and CO2 fluxes based on high-frequency eddy covariance data: a comparison between study sites
No full textFor an assessment of the roles of soil and vegetation in the climate system, a further understanding of the fluxcomponents of H2O and CO2 (e.g., transpiration, soil respiration) and their interaction with physical conditions andphysiological functioning of plants and ecosystems is necessary. To obtain magnitudes of these flux components, we appliedsource partitioning approaches after Scanlon and Kustas (2010; SK10) and after Thomas et al. (2008; TH08) tohigh-frequency eddy covariance measurements of 12 study sites covering different ecosystems (croplands, grasslands,and forests) in different climatic regions. Both partitioning methods are based on higher-order statistics of the H2O andCO2 fluctuations, but proceed differently to estimate transpiration, evaporation, net primary production, and soil respiration.We compared and evaluated the partitioning results obtained with SK10 and TH08, including slight modificationsof both approaches. Further, we analyzed the interrelations among the performance of the partitioning methods, turbulencecharacteristics, and site characteristics (such as plant cover type, canopy height, canopy density, and measurement height).We were able to identify characteristics of a data set that are prerequisites for adequate performance of the partitioningmethods.\\SK10 had the tendency to overestimate and TH08 to underestimate soil flux components. For both methods, the partitioningof CO2 fluxes was less robust than for H2O fluxes. Results derived with SK10 showed relatively large dependencieson estimated water use efficiency (WUE) at the leaf level, which is a required input. Measurements of outgoinglongwave radiation used for the estimation of foliage temperature (used in WUE) could slightly increase the qualityof the partitioning results. A modification of the TH08 approach, by applying a cluster analysis for the conditionalsampling of respiration–evaporation events, performed satisfactorily, but did not result in significant advantages comparedto the original method versions developed by Thomas et al. (2008). The performance of each partitioning approachwas dependent on meteorological conditions, plant development, canopy height, canopy density, and measurementheight. Foremost, the performance of SK10 correlated negatively with the ratio between measurement height and canopyheight. The performance of TH08 was more dependent on canopy height and leaf area index. In general, all site characteristicsthat increase dissimilarities between scalars appeared to enhance partitioning performance for SK10 and TH08
The Delft Fundamentals: integration of disciplines, projects and analysis
No full textAs part of the renewal in 2013/2014 of the bachelor education curriculum in the Faculty of Architecture and the Built Environment, Delft University of Technology, a new study programme was prepared on the Fundamentals (in Dutch: Grondslagen) of spatial design. The teaching approach, visually presented by some examples and explained in this paper, consists of three closely related elements: (a) lectures and readings on basic concepts of architectural, urban and landscape architectural design, (b) a canon of 160 projects illustrating these concepts and (c) a typomorphological project analysis exercise. This new, integrated programme was the follow-up of three former, separate study programmes, Basic Concepts of Architectural Design, Basic Concepts of Urban Design, and History of Architecture, Urbanism and Art. The faculty had serious doubts about the educational quality of those study programmes, consisting of 11 small courses of only one or two EC. The curriculum renewal brought a fresh look at study contents, teaching approach and assessment strategies, based on the didactic principles of integrated learning.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.OLD Urban DesignOLD Urban CompositionsSpatial Planning and StrategyOLD History of Architecture & Urban PlanningOLD Interio
Land Cover Control on the Drivers of Evaporation and Sensible Heat Fluxes: An Observation-Based Synthesis for the Netherlands
No full textLand cover controls the land-atmosphere exchange of water and energy through the partitioning of solar energy into latent and sensible heat. Observations over all land cover types at the regional scale are required to study these turbulent flux dynamics over a landscape. Here, we aim to study how the control of daily and midday latent and sensible heat fluxes over different land cover types is distributed along three axes: energy availability, water availability and exchange efficiency. To this end, observations from 19 eddy covariance flux tower sites in the Netherlands, covering six different land cover types located within the same climatic zone, were used in a regression analysis to explain the observed dynamics and find the principle drivers. The resulting relative position of these sites along the three axes suggests that land cover partly explains the variance of daily and midday turbulent fluxes. We found that evaporation dynamics from grassland, peatland swamp and cropland sites could mostly be explained by energy availability. Forest evaporation can mainly be explained by water availability, urban evaporation by water availability and exchange efficiency, and open water evaporation can almost entirely be explained by exchange efficiency. We found that the sensible heat flux is less sensitive to land cover type. This demonstrates that the land-atmosphere interface plays an active role in the shedding of sensible heat. Our results contribute to a better understanding of the dynamics of evaporation over different land cover types and may help to optimize, and potentially simplify, models to predict evaporation.Water Resource
Assessing the uncertainty of estimated annual totals of net ecosystem productivityAssessing the uncertainty of estimated annual totals of net ecosystem productivity: A practical approach applied to a mid latitude temperate pine forest
No full textValues for annual NEP of micrometeorological tower sites are usually published without an estimate of associated uncertainties. Few authors quantify total uncertainty of annual NEP. Moreover, different methods to assess total uncertainty are applied, usually addressing only one aspect of the uncertainty. This paper presents a robust and easy to apply method to quantify uncertainty of annual totals of Net Ecosystem Productivity (NEP), related to multiple factors involved therein. The method was applied to NEP observations for a Scots pine forest (Loobos) in the Netherlands. Total uncertainty of annual NEP for the Loobos site was on average ±32 g C m-2 a-1 (±8% of NEP), which is a quarter of the standard deviation of annual NEP (127 g C m-2 a-1). Highlights - ¿ A robust method is presented to quantify uncertainty of annual totals of net ecosystem productivity (NEP). ¿ The method contains uncertainty estimates for the most important known components of the total uncertainty: measurement error and flux calculation uncertainty, self-heating correction uncertainty, u* threshold uncertainty, statistical selection uncertainty and gap-filling uncertainty. ¿ The uncertainties associated with the friction velocity threshold criterion and measurement error and flux calculation are substantial and much higher than the other uncertainties. ¿ Total uncertainty of NEP for the Loobos site was on average ±32 g C m-2 a-1 (±8% of NEP). Abbreviations - NEP, annual net ecosystem productivity (g C m-2 a-1 positive values represent accumulation of carbon by the ecosystem); Fec, eddy-covariance flux (µmol m-2 s-1 positive values represent carbon released to the atmosphere); Fs, storage flux (µmol m-2 s-1 positive values represent carbon released to the atmosphere); NEE, net ecosystem exchange (µmol m-2 s-1 positive values represent carbon released to the atmosphere
Resilient places? The healthcare gardens and the Maggie's Centres
No full textThis thesis takes as its focus the Maggie’s Cancer Centres exploring for the first time the impact of their designed gardens. This research is situated within the immediate context of Maggie’s ambitions as an organisation and looks closely at their design process. It is also set within the wider debates about the effects of green space on health and the historical context of the restorative garden. By exploring both historical and contemporary examples, it argues that a healthcare garden may be a space for transformation.
Using four different Maggie’s gardens as case studies, the research seeks to investigate the role of these outdoor spaces and their impact on users. Through ethnographic and sensory methods, each garden is considered and mapped. It looks at the design brief and the intentions of the designers’, but the core work is an exploration of the experiences of staff and visitors. The focus is on the everyday use of these gardens as well as the design historiography. The experiences of gardens within healthcare are examined in order to expose the ways in which gardens, people, health and care are entwined.
Through the qualitative research process this thesis develops a new hypothesis as to how healthcare gardens may operate – offering a new definition for them as “resilient places”. Careful analysis of the data reveals the specific networks and affordances presented by these gardens. The thesis argues, based on the evidence of users, that healthcare gardens can uniquely embrace certain “essences” where essence is defined as conveying a quality or attribute. These garden essences are identified as thresholds, sensory richness, the density of time and homeliness. The thesis also argues that a healthcare garden can provide specific and unique opportunities for care and this, in turn, can enhance the healing ethos of an organisation such as Maggie’s
Carbon exchange of a maize (Zea mays L.) crop: Influence of phenology
No full textA study was carried out to quantify the carbon budget of a maize (Zea mays L.) crop followed by a rye cover crop in the Netherlands, and to determine the importance of the phenological phases and the fallow phase when modelling the carbon budget. Measurements were made of carbon fluxes, soil respiration, biomass and Plant Area Index (PAI). On the basis of PAI the annual cycle was subdivided into 5 phases: juvenile-vegetative, adult-vegetative, reproductive, senescence and fallow. To model the annual carbon budget, it should be sufficient to assess the light response in the juvenile-vegetative phase, the growing season and the fallow phase, combined with the length of these phases and the PAI development. We conclude that emphasis should be put on determining off-season fluxes while the growing season can be estimated from radiation only. During the cultivation period (from sowing to harvest) 5.97 tC ha−1 was sequestered by the maize crop. The amount of carbon exported from the field was 7.5 tC ha−1, and the estimated amount of carbon imported by organic fertilizer was 0.51 tC ha−1, resulting in a carbon loss of 1.02 tC ha−1 from the soil. The fallow phase, with a rye cover crop at the field, decreased the amount of carbon fixed in the cultivation period by 2.65 tC ha−1 (44% reduction). To enable determination of the carbon sequestration or emission of croplands, farmers should be required to analyze, apart from the nitrogen content, also the carbon content of organic fertilizers.A study was carried out to quantify the carbon budget of a maize (Zea mays L) crop followed by a rye cover crop in the Netherlands, and to determine the importance of the phenological phases and the fallow phase when modelling the carbon budget. Measurements were made of carbon fluxes, soil respiration, biomass and Plant Area Index (PAI). On the basis of PAI the annual cycle was subdivided into 5 phases: juvenile-vegetative, adult-vegetative, reproductive, senescence and fallow. To model the annual carbon budget, it should be sufficient to assess the light response in the juvenile-vegetative phase, the growing season and the fallow phase, combined with the length of these phases and the PAI development. We conclude that emphasis should be put on determining off-season fluxes while the growing season can be estimated from radiation only. During the cultivation period (from sowing to harvest) 5.97 tC ha(-1) was sequestered by the maize crop. The amount of carbon exported from the field was 7.5 tC ha(-1), and the estimated amount of carbon imported by organic fertilizer was 0.51 tC ha(-1), resulting in a carbon loss of 1.02 tC ha(-1) from the soil. The fallow phase, with a rye cover crop at the field, decreased the amount of carbon fixed in the cultivation period by 2.65 tC ha(-1) (44% reduction). To enable determination of the carbon sequestration or emission of croplands, farmers should be required to analyze, apart from the nitrogen content, also the carbon content of organic fertilizers. (C) 2010 Elsevier B.V. All rights reserved
Numerical modelling of composite laminates with through-thickness-reinforcements
No full textThe main objective of the present research study was to develop numerical models to investigate the mechanical properties and effectiveness of z-fibre reinforced laminates. A survey of relevant literature on through-thickness reinforcements (TTR) was undertaken and z-fibre pinning was chosen as the main topic of study. The development of numerical tools was mainly based on the finite element (FE) method and was carried out at different model scale levels.
At a micro-mechanical level of analysis, two models were presented. Firstly a unit cell FE model based on the actual geometric configuration of a z-pinned composite was used. Calculations were performed to understand how the through-thickness reinforcement modified the engineering elastic constants and local stress distributions.
Secondly the study of an analytical micro-mechanical model was undertaken. The model simulated a z-fibre bridging a delamination crack tinder mixed-mode loads. A constitutive law relating the z-pin bridging forces with the crack displacements was defined as the "bridging law". Numerical examples for z-fibre bridging laws under Mode I and Mode II loads were computed along with design evaluations of the effect of several micro-mechanical parameters on the bridging laws. This analytical model was then implemented into a MATLAB code specifically written by the author. The code generated constitutive relationship for interface elements simulating the bridging laws of a single z-pin to be used in a FE analysis.
A detailed numerical study of the mode I interlaminar fracture of composite laminates with z-pins was then carried out. AFL• model of a double cantilever beam (DCB) was developed. The numerical analysis focused on the large scale bridging (LSB) caused by z-pins mechanics, which increased the laminate resistance against delamination growth. The numerical results were validated against experimental data. Computational curves for the energy balance and energy rates were also determined showing that the LSB process consumed a significant amount of irreversible energy. The assumption made by the linear elastic fracture mechanics (LEFM) that all energy dissipations were included in the fracture energy and confined within the damage front, was not valid for z-pinned laminates.
The FE analysis was then extended to study a curved single-lap shear joint, to prove the effectiveness of TTR against debond failure of the joint. The presence of TTR was shown to delay the propagation of the debonding and generally to enhance the load carrying capability of the joint. TTR is proved to be more effective in reducing the Mode I component of debonding driving force than that of the Mode II.
Finally a global-local approach was proposed to implement the TTR elements into large composite stnictural FE models. Possible future studies for TTR numerical modelling were also addressed
