127 research outputs found
Using light to improve ornamental plant propagation in controlled environments
No full textLight-emitting diodes (LEDs) can provide different spectrum and spectral combinations. This thesis investigated the effects of different monochromatic light spectra on seed germination of some commercially important ornamental plants, explored optimal light recipes for gerbera seedling production, and investigated the effects of dynamic red (R) and blue (B) lighting to improve campanula stock plant morphology and cutting quality. Generally, the monochromatic lights did not affect the seed germination response compared to darkness. Among the monochromatic lights, R, G, and UVB were the most promotive. Gerbera seedlings grown under RB-LED had as good a quality as those under fluorescent light and including a third light spectrum did not affect their growth and morphology. Dynamic R and B lighting can promote plant elongation without negatively affecting cutting quality, and with a mix of photoperiods, can be used as an effective lighting strategy for producing campanula stock plants for machine-harvest of cuttings
Cylindrical symmetry: II. The Green's function in 3+ 1 dimensional curved space
No full textAn exact solution to the heat equation in curved space is a much sought after; this report presents a derivation wherein the cylindrical symmetry of the metric gμν in 3 + 1 dimensional curved space has a pivotal role. To elaborate, the spherically symmetric Schwarzschild solution is a staple of textbooks on general relativity; not so perhaps, the static but cylindrically symmetric ones, though they were obtained almost contemporaneously by H. Weyl, Ann. Phys. Lpz. 54, 117 (1917) and T. Levi-Civita, Atti Acc. Lincei Rend. 28, 101 (1919). A renewed interest in this subject in C.S. Trendafilova and S.A. Fulling, Eur.J.Phys. 32, 1663(2011) - to which the reader is referred to for more references - motivates this work, the first part of which (cf.Kamath, PoS (ICHEP2016) 791) reworked the Antonsen-Bormann idea - arXiv:hep-th/9608141v1 - that was originally intended to compute theheat kernel in curved space to determine - following D.McKeon and T.Sherry, Phys. Rev. D 35, 3584 (1987) - the zeta-function associated with the Lagrangian density for a massive real scalar field theory in 3 + 1 dimensional stationary curved space to one-loop order, the metric for which is cylindrically symmetric. Using the same Lagrangian density the second part reported here essentially revisits the second paper by Bormann and Antonsen - arXiv:hep 9608142v1 but relies on the formulation by the author in S. G. Kamath, AIP Conf.Proc.1246, 174 (2010) to obtain the Green's function directly by solving a sequence of first order partial differential equations that is preceded by a second order partial differential equation
The Social Context of Technological Experiences: Three Studies from India
No full textThis book demonstrates how technology and society shape one another and that there are intrinsic connections between technological experiences and social relationships. It employs an array of theoretical concepts and methodological tools to examine the technology–society nexus among three urban groups in India (traditional caste-based handloom weavers, subaltern Dalit communities, and informal female labour).
It provides evidence of how innovations such as industrial technologies, communication technologies, and workplace technologies are not only about strides in science and engineering but also about politics and sociology on the ground. The book contributes to the growing research in innovation studies and technology policy that establishes how technological processes and outcomes are contingent on complex sociological variables and contexts. The author offers an inclusive, holistic, and interdisciplinary approach to understanding the field of innovation and technological change and development by involving various methodologies (network analysis, archival work, oral histories, focus group discussions, interviews).
The book will serve as reference for researchers and scholars in social sciences, especially those interested in development studies, science and technology policy and innovation studies, information and communication technology (ICT) policy, public policy, management, social work and research methods, economics, sociology, social exclusion and subaltern studies, women’s studies, and South Asian studies. It will also be useful to nongovernmental organisations, activists, and policymakers
Blue versus Red Light Can Promote Elongation Growth Independent of Photoperiod: A Study in Four Brassica Microgreens Species
No full textGrowth and morphological responses of gerbera seedlings to narrow-band lights with different light spectral combinations as sole-source lighting in a controlled environment
No full textTo optimize light-emitting diode (LED) spectral recipes for gerbera (Gerbera jamesonii) seedling propagation, seed germination and seedling morphology, biomass, flowering, and storage quality were observed in four cultivars, ‘Midi Dark Purple’, ‘Majorette Red Dark Eye’, ‘Maxi Pink’, and ‘Maxi White’, under six spectrum treatments: (1) FL, cool white fluorescent light; (2) RB, a photon flux ratio of 85% red and 15% blue (RB-LED); (3) RB + UVB, RB-LED combined with 0.5 mol m-2 s-1 of ultraviolet-B; (4) RB + UVA, RB-LED combined with 9.6 mol m-2 s-1 of ultraviolet-A; (5) RB + G, a photon flux ratio of 60% red, 15% blue, and 25% green; (6) RB + FR, RB-LED combined with 17.3 mol m-2 s-1 of far-red. For all treatments, the photosynthetic photon flux density was 165 mol m-2 s-1 under a 16-h photoperiod. Seedling growth and morphology were similar under FL and RB for all cultivars, except for a wider canopy of ‘Majorette Red Dark Eye’ under RB. Each of the tri-chromatic light treatments (i.e., RB + UVB, RB + UVA, RB + G or RB + FR) showed similar effects as RB, except for thicker ‘Maxi Pink’ stems under RB + FR. Furthermore, the quality index, an integrated evaluation of seedling quality, was similar under all the treatments for each cultivar. Given similar seedling quality and the advantages of LEDs, RB-LED can potentially replace FL for controlled-environment gerbera seedling production, but the tri-chromatic lights tested in this study appear to be unnecessary.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Seed germination responses to low-level narrow-band light spectra for 14 ornamental plant genotypes
No full textTo investigate whether low-level lighting is necessary and which narrow-band light spectra are effective in seeds germination, seeds of 14 genotypes from begonia, echinacea, gerbera, petunia, and vinca were germinated under ultraviolet-B (UVB), blue (B), green (G), red (R), far-red (FR) light, or darkness. Light-emitting diode (LED) fixtures provided all spectrum treatments except for UVB, which was provided by a narrow-band fluorescent light. The photon flux density at seed level was ≈18 mol m-2 s-1 for B, G, R, and FR, and 0.4 mol m-2 s-1 for UVB. Based on daily germination observations, final germination percentage, germination onset time, germination time spread, and germination speed were compared among different spectrum treatments for each of the plant genotypes. There were no promotive effects on final germination percentage, germination onset time, and germination time spread under the narrow-band lights compared to darkness. For all plant genotypes, B had a similar effect as darkness on seed germination. FR inhibited seed germination relative to darkness by reducing final germination percentage by 31–88%, delaying germination onset time by 30–40%, and decreasing germination speed by 11–48% in some genotypes. Under R, G, and UVB compared to darkness, germination speed was promoted for begonia ‘Apricot Shade’, a light-requiring genotype, and inhibited for vinca ‘Burgundy’, a light-inhibited genotype. Therefore, lighting at low levels used in our study is unnecessary for seed germination of the tested species except light-requiring genotypes, where R, G, and UVB are the most promotive among the tested narrow-band lights.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
A new CFD-based framework for modelling the interaction of open ocean aquaculture structures and complex free surface hydrodynamics
No full textThe work presented in this PhD thesis provides the first numerical framework for the detailed simulation of open ocean aquaculture structures in the sea environment. It enables the simulation of the fluid-structure interaction of rigid floating structures and nets with a viscous fluid including a free surface. As part of the thesis, new approaches for modelling mooring dynamics, dynamics of nets and the rigid body dynamics of floating structures as well as their interaction with the fluid are developed by the author. All models are integrated into the viscous two-phase Computational fluid dynamics (CFD) solver REEF3D. This is in contrast to existing numerical approaches which either neglect important non-linearities or the interaction between the structures and the fluid.
The Reynolds-averaged Navier-Stokes equations including a free surface are solved as the basis of the two-phase numerical wave tank REEF3D. Here, a k-w turbulence model including an additional source term for the free surface treatment is applied. The equations are solved on a staggered rectilinear grid using finite differences. The convection terms are discretised using fifth-order accurate weighted essentially non-oscillatory (WENO) schemes. An incremental pressure-correction algorithm is added by the author for handling the pressure-velocity coupling. The free surface is represented implicitly by the zero level set of a smooth signed distance function. This function is propagated in time and space by solving the linear advection equation. Waves are generated at the inlet using the relaxation method, and a numerical beach prevents excessive reflections at the end of the tank. Full parallelisation is enabled using a ghost-point approach and the message passing interface (MPI) protocol.
An improved version of a continuous direct forcing immersed boundary method is derived in this thesis for modelling rigid floating objects in the three-dimensional numerical wave tank. It is based on a new implicit representation of the body on a stationary grid using a level set function. The motion of the rigid body is described using Euler parameters and Hamiltonian mechanics. The dynamic boundary conditions are enforced by coupling the conservation laws of fluid and rigid body dynamics at the interface between fluid and structure. This effectively avoids computationally expensive reconstruction processes as used in existing approaches and enables the application to large three-dimensional structures.
In addition, a new quasi-static mooring model is presented. Here, each mooring cable is divided into finite truss elements, and the static force equilibria are solved at each knot in each time step. Thus, the steady-state solution for the shape of an elastic cable and the tension force distribution under consideration of hydrodynamic loads is found. A successive approximation is applied to the resulting system of equations which leads to a significant reduction of the matrix size in comparison to the usage of Newton-Raphson methods. Here, the unknown internal and external forces are separated, and the system is corrected iteratively using the intermediate results for the unit vectors until convergence is reached. The resulting model presents a novel compromise between dynamic and analytical solutions for mooring lines because it combines the flexibility of a generically formulated numerical approach with similar efficiency and simplicity as an analytical solution.
The structural dynamics of large tensile and flexible structures undergoing large motions and deformations, such as nets, are solved with a novel approach based on the lumped mass method. The discrete structure is represented by several elastic bars and knots connecting up to four bars. Non-linear material laws are incorporated which is in contrast to previous models for this type of structures. An implicit system of equations is derived from the fundamental relations of dynamics, kinematics and material laws. It is solved using an improved Newton’s method. Hence, a robust model is derived which can be easily coupled to any fluid dynamics solver without restricting the general time step criterion.
In contrast to common tensile structures such as membranes, the considered nets are characterised by high porosities and consist of a large number of individual twines. The length scale of the flow around each twine is significantly smaller than the length scale of the flow around the whole floating structure. This prevents the resolution of the net on the same numerical grid as the fluid domain, and an alternative representation of the fluid-structure interaction between net and fluid has to be introduced. Within this thesis, the author presents a new Lagrangian approach to account for this coupling. The model is based on solving the momentum equations for the fluid on the Eulerian grid and including a source term to account for the disturbances due to the presence of the net. These disturbances represent the momentum transfer between fluid and net and are calculated from the acting forces on the structure. The forces are approximated using a screen force model on Lagrangian points discretising the surface of the net. A suitable interpolation kernel is applied to distribute the forcing term on the fluid domain. In comparison to approaches based on porous media representations, the new model is based on a physical derivation and is suitable for arbitrary geometries and large motions.
Multiple validation cases are presented for the different modules in the course of establishing the framework. It includes the simulation of current flows and wave propagation through fixed and flexible nets as well as the analysis of moored-floating objects in waves with and without nets attached. Finally, a semi-submersible and a mobilefloating open ocean aquaculture structure are investigated to highlight the possibilities of the numerical approach for future applications in this field
Calculation of Wave Forces using REEF3D
No full textNon-breaking wave forces on a cylindrical pile are calculated numerically by solving the three-dimensional Navier Stokes equations in the numerical wave tank of REEF3D. Initially, the numerical wave tank is validated by comparison of the numerical results with the analytical solutions for varying grid density, time step size, numerical beach width, wave amplitude, numerical methods- time and spatial discretization, relaxation method and wave type. The performance of the wave tank under the aforementioned various conditions is observed. As a result the appropriate parameters to be used for the numerical experiment are obtained. Finally, simulations are carried out to calculate the wave forces on a cylindrical pile and the numerical results are compared to the results obtained using the Morison formula. During validation, it is observed that the wave tank gives good results with an error of 0.24% in the wave amplitude at a grid density of 100 cells per wavelength and CFL number 0.1 for a fifth order Stokes wave of amplitude 0.05m and wavelength 2m. A recent study using a different approach reported a requirement of 200 cells per wavelength. Thus, the performance of the wave tank in this study is considered very good. The calculation of wave forces also shows promising results. The wave forces from REEF3D seem to be slightly under estimated compared to the Morison force in the four numerical experiments carried out. There exists a possibility of erroneous calculation of the Morison force. There were no instabilities in the solution from the numerical calculations. Due to the absence of simple experimental data for wave force on a cylinder and time constraints, validation is attempted only through Morison formula by adding the formula in the code. The validation of wave force calculation could not be deemed conclusive.CoMEM - Coastal and Marine Engineering and ManagementHydraulic EngineeringCivil Engineering and Geoscience
Overall design optimization of offshore wind farms
No full textThe objective of this thesis is to build an optimization algorithm with the aim of optimizing layouts for two objective functions - Annual Energy Production (AEP) and Levelized Cost of Energy (LCoE), for large offshore wind farms. The algorithm considers the four main factors that are taken into account when creating a preliminary system design for an offshore wind farm. They are - the geographical location of the turbines, the hub height of the turbines, the type of the turbine, and the total number of turbines in the design space.The annual energy production (AEP) of the wind farm is calculated using PyWake which uses the simple NOJDeficit wake model combined with the required superposition and blockage models to resolve wind turbine wakes. This AEP is then fed into TOPFARM, an economic solver developed at DTU which uses scaling factors to derive the total cost of the wind farm. Constant factors such as the discount rate, distance from shore, foundation type, and drivetrain type are also considered when deriving the total cost of the wind farm.The results of this process are used to determine whether a system design is better than another. Several constraints are applied when changing each optimization variable to keep each iteration as realistic as possible. The boundary is assumed to be a square. Both algorithms arrive at similar results, with random search providing a much better solution with approximately a 40\% reduction in LCoE.European Wind Energy Masters (EWEM
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