| 1. |
- Meng, Ziyang, et al.
(författare)
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Set target aggregation of multiple mechanical systems
- 2014
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - : IEEE conference proceedings. ; , s. 6830-6835
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Konferensbidrag (refereegranskat)abstract
- In this paper, we study the set target aggregation problem of multiple mechanical systems. Each system is modeled by a Lagrangian dynamical equation and observes a convex set as its local target. The objective of the group is to reach an aggregation towards these target sets.We propose a set target aggregation algorithm that is constructed based on each mechanical system's own target sensing and the exchange of its information with local neighbors. With necessary connectivity for both fixed and switching communication topologies, multiple mechanical systems are shown to converge to the intersection of all the local target sets while the vectors of generalized coordinate derivatives are driven to zero. Simulations are given to validate the theoretical results.
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| 2. |
- Peng, Ru, et al.
(författare)
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Influence of Dry Cut and Tool Wear on Residual Stresses in High Speed Machining of Nickel-Based Superalloy
- 2014
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Konferensbidrag (refereegranskat)abstract
- Machining induced residual stresses were investigated in Inconel 718 prepared by high speed turning under dry cut condition. The influence of cutting tool wear and the use of cutting fluid were studied. By x-ray diffraction measurements, characteristic residual stress distributions with tensile stresses in the top layer and compressive stresses in the layer below were found in all the investigated samples. The magnitude of surface tensile stresses and size of the tension as well as compression zones varied depending on the cutting condition. The application of cutting fluid for turning using new tool has a minor effect, giving a somewhat larger subsurface compressive zone but reducing the surface tensile stresses. Tool flank wear has shown a much stronger effect. While a flank wear of VBmax=0.15 mm enhanced mostly the surface tensile residual stresses, a severer wear of VBmax=0.3 mm greatly increased the thickness of the subsurface compression zone and at the same time resulted in strong stress anisotropy. Microstructural study by electron channelling contrast imaging shows that the observed influence of tool flank wear or cutting fluid on residual stresses are related to different contributions from increased plastic deformation and cutting heat, which changed with the cutting conditions.
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| 3. |
- Peng, Ru, et al.
(författare)
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Residual Stresses in High Speed Turning of Nickel-Based Superalloy
- 2014
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Ingår i: HTM Journal of Heat Treatment and Materials. - : Carl Hanser Verlag GmbH. - 1867-2493 .- 2194-1831. ; 69:1, s. 46-53
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Tidskriftsartikel (refereegranskat)abstract
- Residual stresses induced by machining operations can be critical for the performance and lifetime of the machined components. This paper investigated the influence of cutting conditions, including the use of cutting fluid, cutting speed and tool flank wear, on the residual stresses in high speed turning of Inconel 718 alloy. X-ray diffraction measurements revealed characteristic residual stress distributions with tensile stresses in a thin surface layer and compressive stresses in a much thicker subsurface layer in all investigated samples. However, the magnitude of the surface tensile stresses and subsurface compressive stresses as well as the size of the tension and compression zone depended on the cutting parameters. Surface tensile residual stresses over 1600 MPa and 1400 MPa were induced by tool flank wear and increased cutting speed, respectively, in dry turning. The effect of cutting induced local plasticity and temperature increase on the observed residual stress distributions was analyzed based on microstructural study by electron channeling contrast imaging and electron backscatter diffraction
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| 4. |
- Swartling, J.O., et al.
(författare)
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Collective Circumnavigation
- 2014
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Ingår i: Unmanned Systems: Mission Critical. - 0892-4023. ; 2:3, s. 219-229
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Andreasson, Martin, 1987-, et al.
(författare)
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Control of MTDC Transmission Systems under Local Information
- 2014
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Ingår i: Decision and Control (CDC), 2014 IEEE 53rd Annual Conference on. - : IEEE conference proceedings. - 9781479977468 ; , s. 1335-1340
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Konferensbidrag (refereegranskat)abstract
- High-voltage direct current (HVDC) is a commonly used technology for long-distance electric power transmission, mainly due to its low resistive losses. In this paper a distributed controller for multi-terminal high-voltage direct current (MTDC) transmission systems is considered. Sufficient conditions for when the proposed controller renders the closed-loop system asymptotically stable are provided. Provided that the closed loop system is asymptotically stable, it is shown that in steady-state a weighted average of the deviations from the nominal voltages is zero. Furthermore, a quadratic cost of the current injections is minimized asymptotically.
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| 6. |
- Andreasson, Martin, et al.
(författare)
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Distributed Control of Networked Dynamical Systems : Static Feedback, Integral Action and Consensus
- 2014
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Ingår i: IEEE Transactions on Automatic Control. - 0018-9286 .- 1558-2523. ; 59:7, s. 1750-1764
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Tidskriftsartikel (refereegranskat)abstract
- This paper analyzes distributed control protocols for first- and second-order networked dynamical systems. We propose a class of nonlinear consensus controllers where the input of each agent can be written as a product of a nonlinear gain, and a sum of nonlinear interaction functions. By using integral Lyapunov functions, we prove the stability of the proposed control protocols, and explicitly characterize the equilibrium set. We also propose a distributed proportional-integral (PI) controller for networked dynamical systems. The PI controllers successfully attenuate constant disturbances in the network. We prove that agents with single-integrator dynamics are stable for any integral gain, and give an explicit tight upper bound on the integral gain for when the system is stable for agents with double-integrator dynamics. Throughout the paper we highlight some possible applications of the proposed controllers by realistic simulations of autonomous satellites, power systems and building temperature control.
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| 7. |
- Andreasson, Martin, et al.
(författare)
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Distributed PI-Control with Applications to Power Systems Frequency Control
- 2014
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Ingår i: American Control Conference (ACC), 2014. - : IEEE conference proceedings. - 9781479932740 ; , s. 3183-3188
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Konferensbidrag (refereegranskat)abstract
- This paper considers a distributed PI-controller for networked dynamical systems. Sufficient conditions for when the controller is able to stabilize a general linear system and eliminate static control errors are presented. The proposed controller is applied to frequency control of power transmission systems. Sufficient stability criteria are derived, and it is shown that the controller parameters can always be chosen so that the frequencies in the closed loop converge to nominal operational frequency. We show that the load sharing property of the generators is maintained, i.e., the input power of the generators is proportional to a controller parameter. The controller is evaluated by simulation on the IEEE 30 bus test network, where its effectiveness is demonstrated.
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| 8. |
- Andreasson, Martin, 1987-, et al.
(författare)
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Distributed Voltage and Current Control of Multi-Terminal High-Voltage Direct Current Transmission Systems
- 2014
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Ingår i: Proceedings of the 19th IFAC World Congress, 2014. - : IFAC Papers Online. ; , s. 11910-11916
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Konferensbidrag (refereegranskat)abstract
- High-voltage direct current (HVDC) is a commonly used technology for long-distance power transmission, due to its low resistive losses and low costs. In this paper, a novel distributed controller for multi-terminal HVDC (MTDC) systems is proposed. Under certain conditions on the controller gains, it is shown to stabilize the MTDC system. The controller is shown to always keep the voltages close to the nominal voltage, while assuring that the injected power is shared fairly among the converters. The theoretical results are validated by simulations, where the affect of communication time-delays is also studied.
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| 9. |
- Aragues, Rosario, et al.
(författare)
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Distributed algebraic connectivity estimation for undirected graphs with upper and lower bounds
- 2014
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 50:12, s. 3253-3259
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Tidskriftsartikel (refereegranskat)abstract
- The algebraic connectivity of the graph Laplacian plays an essential role in various multi-agent control systems. In many cases a lower bound of this algebraic connectivity is necessary in order to achieve a certain performance. Lately, several methods based on distributed Power Iteration have been proposed for computing the algebraic connectivity of a symmetric Laplacian matrix. However, these methods cannot give any lower bound of the algebraic connectivity and their convergence rates are often unclear. In this paper, we present a distributed algorithm for estimating the algebraic connectivity for undirected graphs with symmetric Laplacian matrices. Our method relies on the distributed computation of the powers of the adjacency matrix and its main interest is that, at each iteration, agents obtain both upper and lower bounds for the true algebraic connectivity. Both bounds successively approach the true algebraic connectivity with the convergence speed no slower than O(1/k).
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| 10. |
- Do-Quang, Minh, et al.
(författare)
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Simulation of finite-size fibers in turbulent channel flows
- 2014
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 89:1, s. 013006-
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Tidskriftsartikel (refereegranskat)abstract
- The dynamical behavior of almost neutrally buoyant finite-size rigid fibers or rods in turbulent channel flow is studied by direct numerical simulations. The time evolution of the fiber orientation and translational and rotational motions in a statistically steady channel flow is obtained for three different fiber lengths. The turbulent flow is modeled by an entropy lattice Boltzmann method, and the interaction between fibers and carrier fluid is modeled through an external boundary force method. Direct contact and lubrication force models for fiber-fiber interactions and fiber-wall interaction are taken into account to allow for a full four-way interaction. The density ratio is chosen to mimic cellulose fibers in water. It is shown that the finite size leads to fiber-turbulence interactions that are significantly different from earlier reported results for point like particles (e.g., elongated ellipsoids smaller than the Kolmogorov scale). An effect that becomes increasingly accentuated with fiber length is an accumulation in high-speed regions near the wall, resulting in a mean fiber velocity that is higher than the mean fluid velocity. The simulation results indicate that the finite-size fibers tend to stay in the high-speed streaks due to collisions with the wall. In the central region of the channel, long fibers tend to align in the spanwise direction. Closer to the wall the long fibers instead tend to toward to a rotation in the shear plane, while very close to the wall they become predominantly aligned in the streamwise direction.
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