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On the optimal design of pipes conveying fluid.
KTH, Superseded Departments, Aeronautical Engineering.
1998 (English)In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 12, no 3, 353-365 p.Article in journal (Refereed) Published
Abstract [en]

The stability and optimal design of a beam subject to forces induced by fluid flow through attached pipes is investigated. The structure is assumed to have the same dynamics as a fluid-conveying pipe, and the dynamic stability is analysed using a finite element formulation of the linear equation of motion. The optimal design problem of minimizing the structural mass at fixed critical flow speed is solved. The numerical results are compared to experiments with satisfactory agreement, provided that the lower bounds of the beam dimensions are properly chosen. The influence of structural damping on the critical flow speed is significant, and is found to be strongly design-dependent.

Place, publisher, year, edition, pages
1998. Vol. 12, no 3, 353-365 p.
Identifiers
URN: urn:nbn:se:kth:diva-12425DOI: 10.1006/jfls.1997.0135OAI: oai:DiVA.org:kth-12425DiVA: diva2:311333
Note
QC 20100421Available from: 2010-04-21 Created: 2010-04-21 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Control and optimization of structures with fluid interaction
Open this publication in new window or tab >>Control and optimization of structures with fluid interaction
2000 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Various problems on the optimal design of elastic structures subject to nonconservative fluid-dynamic forces are considered. The optimal design problem istypically posed as minimizing structural weight subject to constraints on structural stability. Traditionally, structural dimensions and orientations of fibercomposite materials are common design variables. It is demonstrated that the structural weight can be reduced further by including the design of a stabilizingcontrol system in the structural design optimization, giving an integrated optimization problem where both structural and control system parameters are used as design variables. The integrated approach may result in a design with significantly improved performance compared to traditional methods, both in terms of reduced structural weight and control system performance. Using optimization for design of mechanical systems with nonconservative external load tends to increase the likelihood of obtaining a design which is very sensitive to imperfections. As a result, the predicted performance of the optimal design may not be achieved in practice. The importance of this fundamental difficulty is emphasized throughout the thesis by comparing numerically obtained results to experiments.

The first part of the thesis is concerned with the stability and optimal design of a beam subject to forces induced by fluid flow through attached pipes. A nozzle control system deflecting the fluid jet at the beam tip is used to improve the stability of the system. The simultaneous design of the control system and the beam shape minimizing structural mass is performed using numerical optimization. The inclusion of the control system in the optimization gives a considerable reduction of the beam weight but results in an optimal design which is very sensitive to imperfections. An optimal design with improved robustness is obtained by solving a modified optimization problem. The stability of a flexible wing structure with a controllable trailing edge flap is investigated. Due to uncertainties in the numerical stability analysis, the wing is predicted to become unstable at a significantly higher speed than what is observed in wind tunnel tests. Two different approaches to stabilize the wing in flutter is demonstrated. First, numerical optimization is used to design a controller which at each flow speed maximizes the damping of the flutter mode observed in the wind tunnel experiment. Second, an integrated approach is adopted, where a simultaneous mass balancing and control law design is performed. It is argued that a two-step procedure may be required to obtain a design with minimum weight and a control law that is well-defined for all operating conditions.

Place, publisher, year, edition, pages
Stockholm: KTH, 2000. 8 p.
Series
Report. Department of Aeronautics, 2000:1
Identifiers
urn:nbn:se:kth:diva-2956 (URN)993-261067-4 (ISBN)
Public defence
2000-05-12, 00:00 (English)
Note
QC 20100421 NR 20140805Available from: 2000-05-11 Created: 2000-05-11 Last updated: 2010-04-28Bibliographically approved
2. Control and optimization of pipes conveying fluid
Open this publication in new window or tab >>Control and optimization of pipes conveying fluid
1998 (English)Licentiate thesis, comprehensive summary (Other scientific)
Place, publisher, year, edition, pages
Stockholm: KTH, 1998. 21 p.
Series
Report. Department of Aeronautics, 98:1
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-784 (URN)
Presentation
(English)
Note
QC 20100429Available from: 2000-09-26 Created: 2000-09-26 Last updated: 2010-04-29Bibliographically approved

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