2,003 research outputs found
Linear and nonlinear parametric hydrodynamic models for wave energy converters identified from recorded data
Ocean waves represent an important resource of renewable energy, which can provide a significant
support to the development of more sustainable energy solutions and to the reduction ofCO2 emissions.
The amount of extracted energy from the ocean waves can be increased by optimizing the
geometry and the control strategy of the wave energy converter (WEC), which both require mathematical
hydrodynamic models, able to correctly describe the WEC-fluid interaction. In general,
the construction of a model is based on physical laws describing the system under investigation.
The hydrodynamic laws are the foundation for a complete description of the WEC-fluid interaction,
but their solution represents a very complex and challenging problem. Different approaches
to hydrodynamic WEC-fluid interaction modelling, such as computational fluid dynamics (CFD)
and linear potential theory (LPT), lead to different mathematical models, each one characterised
by different accuracy and computational speed. Fully nonlinear CFD models are able to describe
the full range of hydrodynamic effects, but are very computationally expensive. On the other hand,
LPT is based on the strong assumptions of inviscid fluid, irrotational flow, small waves and small
body motion, which completely remove the hydrodynamic nonlinearity of the WEC-fluid interaction.
Linear models have good computational speed, but are not able to properly describe nonlinear
hydrodynamic effects, which are relevant in some WEC power production conditions, since
WECs are designed to operate over a wide range of wave amplitudes, experience large motions,
and generate viscous drag and vortex shedding. The main objective of this thesis is to propose
and investigate an alternative pragmatic framework, for hydrodynamic model construction, based
on system identification methodologies. The goal is to obtain models which are between the CFD
and LPT extremes, a good compromise able to describe the most important nonlinearities of the
physical system, without requiring excessively computational time. The identified models remain
sufficiently fast and simple to run in real-time. System identification techniques can ‘inject’ into
the model only the information contained in the identification data; therefore, the models obtained
from LPT data are not able to describe nonlinear hydrodynamic effects. In this thesis, instead
of traditional LPT data, experimental wave tank data (both numerical wave tank (NWT), implemented
with a CFD software package, and real wave tank (RWT)) are proposed for hydrodynamic
model identification, since CFD-NWT and RWT data can contain the full range of nonlinear hydrodynamic
effects. In this thesis, different typologies of wave tank experiments and excitation
signals are investigated in order to generate informative data and reduce the experiment duration.
Indeed, the reduction of the experiment duration represents an important advantage since, in the
case of a CFD-NWT, the amount of computation time can become unsustainable whereas, in the
case of a RWT, a set of long tank experiments corresponds to an increase of the facility renting
costs
Conditional sign flip via teleportation
We present a model to realize a probabilistic conditional sign flip gate
using only linear optics. The gate operates in the space of number state qubits
and is obtained by a nonconventional use of the teleportation protocol. Both a
destructive and a nondestructive version of the gate are presented. In the
former case an Hadamard gate on the control qubit is combined with a projective
teleportation scheme mixing control and target. The success probability is 1/2.
In the latter case we need a quantum encoder realized via the interaction of
the control qubit with an ancillary state composed of two maximally entangled
photons. The success probability is 1/4
Can Tidal Current Energy Provide Base Load?
Tidal energy belongs to the class of intermittent but predictable renewable energy
sources. In this paper, we consider a compact set of geographically diverse locations, which
have been assessed to have significant tidal stream energy, and attempt to find the degree to
which the resource in each location should be exploited so that the aggregate power from all
locations has a low variance. An important characteristic of the locations chosen is that there
is a good spread in the peak tidal flow times, though the geographical spread is relatively
small. We assume that the locations, all on the island of Ireland, can be connected together
and also assume a modular set of tidal turbines. We employ multi-objective optimisation to
simultaneously minimise variance, maximise mean power and maximise minimum power.
A Pareto front of optimal solutions in the form of a set of coefficients determining the degree
of tidal energy penetration in each location is generated using a genetic algorithm. While
for the example chosen the total mean power generated is not great (circa 100 MW), the
case study demonstrated a methodology that can be applied to other location sets that exhibit
similar delays between peak tidal flow times
Routing quantum information in spin chains
Two different models for performing efficiently routing of a quantum state
are presented. Both cases involve an XX spin chain working as data bus and
additional spins that play the role of sender and receivers, one of which is
selected to be the target of the quantum state transmission protocol via a
coherent quantum coupling mechanism making use of local/global magnetic fields.
Quantum routing is achieved, in the first of the models considered, by weakly
coupling the sender and the receiver to the data bus. In the second model,
strong magnetic fields acting on additional spins located between the
sender/receiver and the data bus allow us to perform high fidelity routing.Comment: added references in v
Identification of Nonlinear Excitation Force Kernels Using Numerical Wave Tank Experiments
This paper addresses the mathematical modelling
of the relationship between the free surface elevation (FSE) and
the excitation force for wave energy devices (excitation force
model). While most studies focus on the model relating the
FSE to the device motion, the excitation force model is required
to complete the mathematical wave energy system description
and also plays an important role in excitation force observer
design. In the paper, a range of linear and nonlinear modelling
methodologies, based on system identification from numerical
wave tank tests, are developed for a range of device geometries.
The results demonstrate a significant benefit in adopting a
nonlinear parameterisation and show that models are heavily
dependent on incident wave amplitude
Optimising numerical wave tank tests for the parametric identification of wave energy device models
While linear and nonlinear system identification is a well established
field in the control system sciences, it is rarely used in
wave energy applications. System identification allows the dynamics
of the system to be quantified from measurements of the
system inputs and outputs, without significant recourse to first
principles modelling. One significant obstacle in using system
identification for wave energy devices is the difficulty in accurately
quantifying the exact incident wave excitation, in both
open ocean and wave tank scenarios. However, the use of numerical
wave tanks (NWTs) allow all system variables to be accurately
quantified and present some novel system tests not normally
available for experimental devices. Considered from a system
identification perspective, this paper examines the range of
tests available in a NWT from which linear and nonlinear dynamic
models can be derived. Recommendations are given as to
the optimal configuration of such system identification tests
Numerical wave tank identification of nonlinear discrete time hydrodynamic models
Hydrodynamic models are important for the design, simulation and control of wave energy
converters (WECs). Linear hydrodynamic models have formed the basis for this and have been well verified
and validated over operating conditions for which small amplitude assumptions apply. At larger amplitudes a
number of nonlinear effects may appear. One of these effects is due to the changing bouyancy force as the body
moves in and out of the water. In this paper we look at identifying a nonlinear static block to be added the linear
hydrodynamic model to account for this effect. The parameters for this nonlinear block are identified from WEC
experiments simulated in a numerical wave tank (NWT). The parameters for the linear hydrodynamic model are
also identified from NWT experiments. Here we explore the use of a discrete time linear hydrodynamic model
which is well suited to the identification procedur
Numerical wave tank identification of nonlinear discrete time hydrodynamic models
Hydrodynamic models are important for the design, simulation and control of wave energy
converters (WECs). Linear hydrodynamic models have formed the basis for this and have been well verified
and validated over operating conditions for which small amplitude assumptions apply. At larger amplitudes a
number of nonlinear effects may appear. One of these effects is due to the changing bouyancy force as the body
moves in and out of the water. In this paper we look at identifying a nonlinear static block to be added the linear
hydrodynamic model to account for this effect. The parameters for this nonlinear block are identified from WEC
experiments simulated in a numerical wave tank (NWT). The parameters for the linear hydrodynamic model are
also identified from NWT experiments. Here we explore the use of a discrete time linear hydrodynamic model
which is well suited to the identification procedur
Optimising numerical wave tank tests for the parametric identification of wave energy device models
While linear and nonlinear system identification is a well established
field in the control system sciences, it is rarely used in
wave energy applications. System identification allows the dynamics
of the system to be quantified from measurements of the
system inputs and outputs, without significant recourse to first
principles modelling. One significant obstacle in using system
identification for wave energy devices is the difficulty in accurately
quantifying the exact incident wave excitation, in both
open ocean and wave tank scenarios. However, the use of numerical
wave tanks (NWTs) allow all system variables to be accurately
quantified and present some novel system tests not normally
available for experimental devices. Considered from a system
identification perspective, this paper examines the range of
tests available in a NWT from which linear and nonlinear dynamic
models can be derived. Recommendations are given as to
the optimal configuration of such system identification tests
Mesoscopic continuous and discrete channels for quantum information transfer
We study the possibility of realizing perfect quantum state transfer in
mesoscopic devices. We discuss the case of the Fano-Anderson model extended to
two impurities. For a channel with an infinite number of degrees of freedom, we
obtain coherent behavior in the case of strong coupling or in weak coupling
off-resonance. For a finite number of degrees of freedom, coherent behavior is
associated to weak coupling and resonance conditions
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