791 research outputs found
Drone-based Data Collection, Analysis & Visualisation for Greenhouse Growth Analysis
No full textCurrently, the mapping of a greenhouse is done by hand, rendering it cost and time intensive. A drone could optimise this process by autonomously mapping the greenhouse. Moreover, data such as imaging, humidity and temperature could be collected by the drone whilst navigating in a greenhouse. This data proves to be insightful for the horticulturist as well as a consultant. We have created a prototype drone which can navigate through a greenhouse, collecting, analysing and visualising crop growth data. This report will give an insight into the process of creating such a prototype. A suitable drone for this task has been selected with the appropriate obstacle sensing sensors for indoor flight. An algorithm to explore the greenhouse has been constructed to navigate through a greenhouse, con- sisting of four states. The drone first searches the wall of the greenhouse, to consequently follow the wall so it can determine the perimeter. Next the drone searches for posts. If the perimeter is determined and if the posts are located, a map of the greenhouse can be generated. Information about the posts and walls is collected using ultrasonic and imaging sensors. Using image recognition techniques post can be detected and with the use of ultrasonic data distance to the posts and walls is determined. Our prototype could be extended with additional sensors to create more insight into greenhouse crop growth. A lot of potential exists in further development of the project, as the market is waiting for a scalable solution like this.Electrical Engineering, Mathematics and Computer ScienceComputer scienc
Stribeck Curve for Starved Concentrated Contacts
No full textThis paper discusses a mixed lubrication model in order to predict the Stribeck curve for starved lubricated line contacts. Themodel is an extension of themixed lubrication model of Gelinck and Schipper [1]. In order to build the starved Stribeck curve model, the contact model of Greenwood and Williamson [2] and the EHL film thickness for starved line contacts making use of the assumption of Johnson et al. [3] is combined. The starved solution to be implemented in the EHL component is obtained by fitting numerical data of Wolveridge et al. [4] who computed the starved film thickness for smooth line contacts. Calculations are presented for different oil supply layer thickness over roughness values. For values of oil layer thickness over roughness ratio (h oil/σ s) larger than approximately 6, the Stribeck curve and separation do not change. If the oil layer thickness over roughness ratio is in the range of 6 to 0.7 friction starts to increase and the film thickness decreases. When the oil layer thickness over roughness ratio is less than approximately 0.7 the Stribeck curve tends to transform into a straight line and separation stays on the same value as in the BL regime
Long term nitrate removal in a denitrification wall
No full textNitrogen (N) inputs to groundwater are one of the most widespread environmental problems globally. However, as N is important for crop production to support the current global population, it is difficult to limit N input to an extent where groundwater contamination is completely avoided. Researchers have been testing new ways to remove N (in the form of nitrate (NO3-)) from groundwater, primarily through enhancing microbial denitrification. One technology utilizing this microbial process is a denitrification wall, which is an inexpensive, low-maintenance technology compared to other options to treat NO3--contaminated groundwater. Denitrification walls have been shown to be effective for removing NO3- from groundwater through denitrification for seven years in New Zealand, nine years in Iowa, and 15 years in Canada; however, long-term data on the efficacy of denitrification walls remain limited. In order to understand how these systems function in the long term, the performance of a New Zealand denitrification wall installed in 1996 was examined. Field sampling was carried out during the winter of 2010 at the denitrification wall at Bardowie Farm in Cambridge, New Zealand. This farm had received relatively high N inputs from spray-irrigation of effluent from the nearby Hautapu Dairy Factory for over 30 years. The denitrification wall was originally constructed by mixing 40 m3 Pinus radiata sawdust with soil down to a depth of 1.5 m where it intercepted groundwater flow. Groundwater samples were collected from wells installed upslope and within the wall and samples were analyzed for NO3- concentrations on five occasions. Soil samples were collected on four occasions from below the water table and analyzed for denitrifying enzyme activity (DEA), total carbon (C), available C, and microbial biomass C. Results were compared to previous measurements. Groundwater NO3- concentrations entering the wall averaged 2.6 mg N L-1, which was a decrease from 2002 where NO3- entered the wall at an average of 9 mg N L-1. Despite this decrease, NO3- concentrations within the wall averaged 0.2 mg N L-1, which corresponded to 92% NO3- removal. DEA rates in the wall were nearly as high as the first year of construction. In contrast, total C and microbial biomass C had decreased by half, while available C remained the same as measured two years after construction. Denitrification in the wall remained NO3- limited suggesting that C was still sufficiently available to the denitrifiers. These data indicated that the denitrification wall was still effective after 14 years. To predict denitrification wall longevity, a first-order decay curve was fitted to the total C data through time (R2 = 0.92; p < 0.05). The decay curve was used to predict the time until total C reached 0.1%, although it is unclear at what %C denitrification will become C limited. Using this decay curve, it was estimated that C in the wall would not be depleted for 66 years, although it is possible that C will become limiting to denitrifiers before that time. This long-term study suggested that denitrification walls are cost-effective solutions to removing NO3- from groundwater as they can be effective for a number of years without any maintenance
Feasibility of Concrete Shells using Flexible Mould Prefabricated Concrete Elements
No full textShell structures appear quite often in our daily life. From aircraft fuselages to storage silos and boat hulls, these structures are employed for their structural efficiency and the aesthetics they provide. They are characterised by a small thickness in comparison to their other dimensions and by curvature in their unstressed state. Despite their structural efficiency transferring loads in their plane, thin concrete shells are not employed quite often. The traditional construction method is a labour intensive process which includes the fabrication of a formwork system, usually made out of plywood, on which concrete is cast. The necessary reinforcement in the form of bars although it is quickly placed, it has the drawback of requiring frequent joints and overlapping. Its bending and assembling is also considered difficult for curved shapes like shells. As it can be seen, great costs emerge from this process and this was a trigger factor for the formation of the research question. A different approach for the construction of shells employs prefabricated elements which are connected on site and create the complete thickness of the concrete shell. Although high construction speed and high quality are achieved with this method, significant reduction of costs is still not feasible, as the formwork is very expensive and re-use of it, is only occasionally possible. However, an adjustable mould can produce elements of different dimensions, shape and curvature, decreasing substantially the formwork costs which comprise large part of the total shell construction costs. The flexible mould method and the principle of deformation after casting that were introduced by Prof. R.H. Schipper find application in this project. This project aims to answer whether it is possible to construct a concrete shell using the flexible mould prefabricated elements, without putting aat risk the stability of the structure. A comparison between the structural feasibility of a monolithic shell and the one of a segmented prefabricated shell is the method that will be utilised to answer the research question.Civil Engineering | Building Engineerin
Assessment of effects of chemical contaminants in dredged material on marine ecosystems and human health
No full textOm te voorkomen dat scheepvaartroutes dichtslibben moeten waterwegen en havens in deltagebieden regelmatig worden gebaggerd. Wereldwijd worden op jaarbasis honderden miljoenen tonnen baggerspecie en sediment verwijderd. Nederland verspreidt jaarlijks meer dan 25 miljoen kubieke meter gebaggerd sediment in de Noordzee. Hierbij is het van belang te kunnen bepalen wat de risico's zijn voor het ecosysteem. Het in sediment identificeren van chemische stoffen die een potentieel risico vormen voor het ecosysteem of voor de menselijke gezondheid is dan ook het onderwerp van veel studies. Dit proefschrift onderzoekt de toepasbaarheid van in vitro, in vivo bioassays en bio-indicatoren als mogelijke beoordelingsinstrument voor het vaststellen van de schadelijke effecten op zeeorganismen van complexe chemische verbindingen in sedimen
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