| 1. |
- Epperlein, Jonathan P., et al.
(författare)
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Control Laboratory Experiments in ThermoAcoustics Using the Rijke Tube
- 2014
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Ingår i: American Control Conference, 2014.
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Konferensbidrag (refereegranskat)abstract
- We report on experiments that investigate the dynamics, identification and control of thermoacoustic phenomena in a Rijke tube apparatus. These experiments are relatively simple to construct and conduct in a typical, well-equipped undergraduate controls laboratory, yet allow for the exploration of rich and coupled acoustic and thermal dynamics, the associated thermoacoustic instabilities, and the use of acoustic feedback control for their stabilization. We describe the apparatus construction, investigation of thermoacoustic dynamics and instabilities in both open-loop and closed-loop configurations, closed-loop identification of the underlying dynamics, as well as model validation. We also summarize a transcendental transfer function analysis that explains the underlying phenomena. These experiments are notable for the fact that rich thermoacoustic phenomena can be analyzed using introductory concepts such as the frequency response and root locus, and thus can be performed and understood by controls students with relatively little background in acoustics or heat transfer.
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| 2. |
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| 3. |
- Ranaweera, Aruna, et al.
(författare)
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Lateral Mean Exit Time of a Spherical Particle Trapped in an Optical Tweezer
- 2004
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Ingår i: Decision and Control, 2004. CDC. 43rd IEEE Conference on. - 0191-2216. - 0780386825 ; 5, s. 4891-4896
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Konferensbidrag (refereegranskat)abstract
- We apply the Fokker-Planck equation to analyze the stochastic behavior of a 1-micron diameter polystyrene bead trapped in water using an optical tweezer. Due to thermal noise, given enough time, a trapped particle will escape con nement from the trap. However, at biological temperatures, for laser powers of greater than approximately 5 milliwatts at the focus, the mean rst exit time in the lateral plane is extremely large, and unbounded for most practical purposes. We show that the mean exit time increases exponentially with laser power. Furthermore, for a trapped 9.6-micron diameter polystyrene bead, we show that experimental mean passage times within the linear trapping region are in close agreement with theoretical calculations.
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| 4. |
- Tegling, Emma, 1988-, et al.
(författare)
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On Fundamental Limitations of Dynamic Feedback Control in Regular Large-Scale Networks
- 2019
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Ingår i: IEEE Transactions on Automatic Control. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9286 .- 1558-2523. ; 64:12, s. 4936-4951
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study fundamental performance limitations of distributed feedback control in large-scale networked dynamical systems. Specifically, we address the question of whether dynamic feedback controllers perform better than static (memoryless) ones when subject to locality constraints. We consider distributed linear consensus and vehicular formation control problems modeled over toric lattice networks. For the resulting spatially invariant systems, we study the large-scale asymptotics (in network size) of global performance metrics that quantify the level of network coherence. With static feedback from relative state measurements, such metrics are known to scale unfavorably in lattices of low spatial dimensions, preventing, for example, a one-dimensional string of vehicles to move like a rigid object. We show that the same limitations in general apply also to dynamic feedback control that is locally of first order. This means that the addition of one local state to the controller gives a similar asymptotic performance to the memoryless case. This holds unless the controller can access noiseless measurements of its local state with respect to an absolute reference frame, in which case the addition of controller memory may fundamentally improve performance. In simulations of platoons with 20-200 vehicles, we show that the performance limitations we derive manifest as unwanted accordionlike motions. Similar behaviors are to be expected in any network that is embeddable in a low-dimensional toric lattice, and the same fundamental limitations would apply. To derive our results, we present a general technical framework for the analysis of stability and performance of spatially invariant systems in the limit of large networks.
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| 5. |
- Tegling, Emma, et al.
(författare)
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Scale fragilities in localized consensus dynamics
- 2023
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- We consider distributed consensus in networks where the agents have integrator dynamics of order two or higher (n≥2). We assume all feedback to be localized in the sense that each agent has a bounded number of neighbors and consider a scaling of the network through the addition of agents in a modular manner, i.e., without re-tuning controller gains upon addition. We show that standard consensus algorithms, which rely on relative state feedback, are subject to what we term scale fragilities, meaning that stability is lost as the network scales. For high-order agents (n≥3), we prove that no consensus algorithm with fixed gains can achieve consensus in networks of any size. That is, while a given algorithm may allow a small network to converge, it causes instability if the network grows beyond a certain finite size. This holds in families of network graphs whose algebraic connectivity, that is, the smallest non-zero Laplacian eigenvalue, is decreasing towards zero in network size (e.g. all planar graphs). For second-order consensus (n=2) we prove that the same scale fragility applies to directed graphs that have a complex Laplacian eigenvalue approaching the origin (e.g. directed ring graphs). The proofs for both results rely on Routh–Hurwitz criteria for complex-valued polynomials and hold true for general directed network graphs. We survey classes of graphs subject to these scale fragilities, discuss their scaling constants, and finally prove that a sub-linear scaling of nodal neighborhoods can suffice to overcome the issue.
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| 6. |
- Tegling, Emma, et al.
(författare)
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The Price of Synchrony : Evaluating the Resistive Losses in Synchronizing Power Networks
- 2015
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Ingår i: IEEE Transactions on Control of Network Systems. - : IEEE Press. - 2325-5870. ; 2:3, s. 254-266
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the resistive power losses that are incurred in keeping a network of synchronous generators in a synchronous state. These losses arise due to the transient power-flow fluctuations that occur when the system is perturbed from a synchronous state by a small transient event or in the face of persistent stochastic disturbances. We call these losses the "price of synchrony," as they reflect the real power-flow costs incurred in resynchronizing the system. In the case of small fluctuations at each generator node, we show how the total network's resistive losses can be quantified using an H-2 norm of a linear system of coupled swing equations subject to distributed disturbances. This norm is shown to be a function of transmission-line and generator properties, to scale unboundedly with network size, and to be weakly dependent on the network topology. This conclusion differentiates the price of synchrony from typical power systems stability notions, which show highly connected networks to be more coherent and, thus, easier to synchronize. In particular, the price of synchrony is more dependent on a network's size than its topology. We discuss possible implications of these results in terms of the design of future power grids, which are expected to have highly distributed generation resources leading to larger networks with the potential for greater transient losses.
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| 7. |
- Yi, Yuhao, et al.
(författare)
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Diffusion and Consensus in a Weakly Coupled Network of Networks
- 2021
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Ingår i: IEEE Transactions on Control of Network Systems. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2325-5870. ; 8:4, s. 1601-1612
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Tidskriftsartikel (refereegranskat)abstract
- We study diffusion and consensus dynamics in a network of networks model. In this model, there is a collection of subnetworks, connected to one another using a small number of links. We consider a setting where the links between networks have small weights, or are used less frequently than links within each subnetwork. Using spectral perturbation theory, we analyze the diffusion rate and convergence rate of the investigated systems. Our analysis shows that the first-order approximation of the diffusion and convergence rates is independent of the topologies of the individual graphs; the rates depend only on the number of nodes in each graph and the topology of the connecting edges. The second-order analysis shows a relationship between the diffusion and convergence rates and the information centrality of the connecting nodes within each subnetwork. We further highlight these theoretical results through numerical examples.
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