Hansen, Henriette I.

Thoft-Christensen, Palle

English

Hansen, H. I.

Wind Tunnel Testing of Active Control System for Bridges

This paper describes preparation of wind tunnel testing of the principle of using flaps to control the motion of suspension bridges. The experiment will take place at the Instituto Superior Technico Lisbon, Portugal. The bridge section model is constructed of foam with an aluminium frame. The flaps are regulated by servo motors. Neural networks are used to position the flaps in the optimal positions

    Aalborg UniversitetWind Tunnel Testing of Active Control System for BridgesHansen, Henriette I.; Thoft-Christensen, PallePublication date:1996Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Hansen, H. I., & Thoft-Christensen, P. (1996). Wind Tunnel Testing of Active Control System for Bridges. Dept.of Building Technology and Structural Engineering. Structural Reliability Theory Vol. R9662 No. 159General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: November 29, 2020INSTITUTTET FOR BYGNINGSTEKNIK DEPT. OF BUILDING TECHNOLOGY AND STRUCTURAL ENGINEERING AALBORG UNIVERSITET • · AAU • AALBORG • DANMARK STRUCTURAL RELIABILITY THEORY PAPER NO. 159 IABSE 15th Congress, Copenhagen, June 16-20, 1996 H. I. HANSEN & P. THOFT-CHRISTENSEN WIND TUNNEL TESTING OF ACTIVE CONTROL SYSTEM FOR BRIDGES DECEMBER 1996 ISSN 1395-7953 R9662 The STRUCTURAL RELIABILITY THEORY papers are issued for early disse~ina­tion of research results from the Structural Reliability Group at the Department of Buiiding Technology and Structural Engineering, University of Aalborg. These papers are generally submitted to scientific meetings, conferences or journals and should there-fore not be widely distributed. Whenever possible reference sh~mld be given to the final publications (proceedings, journals, etc.) and not to the Structural Reliability Theory papers . I Printed at Aalborg University I INSTITUTTET FOR BYGNINGSTEKNIK DEPT. OF BUILDING TECHNOLOGY AND STRUCTURAL ENGINEERING AALBORG UNIVERSITET • AAU • AALBORG • DANMARK STRUCTURAL RELIABILITY THEORY PAPER NO. 159 IABSE 15th Congress, Copenhagen, June 16-20, 1996 H. I. HANSEN & P. THOFT-CHRISTENSEN WIND TUNNEL TESTING OF ACTIVE CONTROL SYSTEM FOR BRIDGES DECEMBER 1996 ISSN 1395-7953 R9662 Wind Tunnel Testing of Active Control System for Bridges Henriette I. Hansen M.Sc., Ph.D.-Student Palle Thoft-Christensen Ph.D., Professor Aalborg University Department of Building Technology and Structur-al Engineering Sohngaardsholmsvej 57 DK-9000 Aalborg Denmark Summary Henriette I. Hansen, born 1966, got her M.Sc. in civil engineering in 1991 from Aalborg University. Be-fore she started as a Ph.D.-student in 1993 she worked as a research engineer for Computational Safety & Reliability in Aalborg. Palle Thoft-Christensen, born 1936, got his M.Sc. in civil engineering in 1960 and his Ph.D. in math-ematical plasticity theory in 1963 from the Tech-nical University of Den-mark. His main research areas are structural relia-bility and optimization. This paper describes preparation of wind tunnel testing of the principle of using flaps to control the motion of suspension bridges. The experiments will take place at the Instituto Superior' Tecnico in Lisbon, Portugal. The bridge section model is constructed of foam with an aluminium frame. The flaps are regulated by servo motors. Neural networks are used to position the flaps in the optimal positions. 1 Introduction The purpose of the wind tunnel testing of active control of suspension bridges described in this paper is primarly to investigate the principle to use flaps to control the bridge excitation. Suggestions for implementation of active control surface systems are given by Ostenfeld & Larsen [4] . To investigate this principle a bridge section model equipped with flaps is constructed. In a real bridge approximately lj3 of the central span will be equipped with flaps. The bridge section model is dimensioned to fit in a wind tunnel where the entrance to the test section is 1.5 m x 1.5 m and the maximum wind speed is 40 m/s- The bridge section model investigated is realistic compared to a real bridge, but no specific bridge is investigated. The bridge section model is equipped with a flap in each side, each flap is able to rotate 20° in both directions. It is very important that the flaps can be regulated independently as the effect of two flaps instead of one is essential. The purpose of the flap in the leading edge is primarly to introduce a load on the bridge opposite to the motion of the bridge. The purpose of the flap in the trailing edge is primarly to change the direction of the wake. Flaps with different lengths compared to the width of the bridge section are investigated. The wind tunnel is described in section 2. The bridge section model and the regulation system are described in section 3. The neural networks used to calculate the optimal positions of the flaps are described in section 4. 2 Wind Tunnel The wind tunnel for building aerodynamics at the Instituto Superior Tecnico in Lisbon, Portugal is described in the ROLLAB Report RR 079 [1], see figure 1. The tunnel is of the open return type and has a test section size of 1.5 m x 1.5 m x 5.0 m (nominal values). The maximum speed is 40 m;s. The floor is horisontal so the side walls and the ceiling alone are compensated with regard to the boundary layer growth along the wetted surfaces of the test section. 16800 r-~ f-.-_ --- -- - - - --- -=~ -a I- -. rh -r- 0 0 m tn ('(') --- ---- u -- u -u u· -- - --- --- u Figure 1: General layout of the wind tunnel. All lengths in mm, {1}. A collector (a funnel) will duct the air to a settling chamber where a honeycomb and two gauzes are installed. Thereafter a contraction unit (ratio 5.44:1) takes the air to the test section. The nominal dimensions of the entrance to the test section is 1.5 m x 1.5 m. It is as-sumed that the boundary layer displacement thickness at this station is 1.7 mm. This is in agreement with experienced values. The test section steel "cage" will be mounted on separate steel frames bolted on concrete pads in the floor . Between the long top beams of the cage there are also short cross beams to make the test section rigid. After the test section there is a diffuser /transition unit. At the end of the transition unit (from square to circular) a safety gauze has been installed so that the fan will be protected from loose elements or tools which may be forgotten in the test section. In order to accommodate the ceiling to the top wall of the diffuser a special overbridging link must be introduced between the test section and the diffuser. After the fan a diffuser will terminate the wind tunnel leg. Experimentally it has been demonstrated that fully turbulent flow could be assumed at a Reynolds Number R = 106 . In this case the calculated Reynolds Number R = 1.32 · 106 (based on a speed of 40 m;s and a characteristic length of 0.5 m). 3 Description of Bridge Section Model To get both a realistic weight of the model incl. flaps and regulation system depending on the model laws and a stiff model, the model is made of foam with an aluminium frame, see figure 2. ---1 .. , . ' -- - u - I r------ -- I I I wind tunnel wall -- ~ I " I / -. " 11 1·· .. . ·· ---I " .· .· : I -- --I i I IU I - - ~ - - .· • --- -- --11 --Figure 2: Illustration of bridge section model seen fmm above, visible aluminium is hatched. A long flap is shown in the left hand side, and a short flap is shown in the right hand side. The bridge section model is suspended as described by Hjorth-Hansen [3] . The model is connected to a horizontal extension rod in each side which is going through the wind tun-nel wall. The suspension system is the same in both sides. The extension rod is connected to an arm with dummy masses that can be moved on the arm so the model can represent the correct mass and mass inertia. Each side of the arm is suspended in two helical springs. The spring constant for each suspension point is adjusted so as the two-dimensional model has the same eigenfrequency and damping ratio as the lowest symmetric bending eigen-mode and the lowest torsion eigenmode of the real bridge, depending on the model laws. The damping of the model is ignored in the experiments. Additional damping can be made by letting a vane at each support plane shear through silicone oil as described by Hjorth-Hansen [3]. Each flap is positioned by a servo motor and reduction gear which are placed inside the bridge section model. The reduction gear is connected to the flap via a cable. The regu-lation system is dimensioned so the flaps are able to turn the possible 40° during lj5 of the torsional eigen period of the model. The bridge section model equipped with short flaps is shown in figure 3. Figure 3: Bridge section model with short flaps. 4 Active Control of Bridge Section Model Active control of a structure requires that the new (descretized) state vector of the struc-ture can be estimated based on the state vector, the load vector and the control force vector for the previous time step. Therefore, adaptive control algorithms must be used with simultaneous online structural system identification and vibration control. Unfortu-nately, there is no assurance of convergency for the extended Kalman filter even when it is used for linear problems. In the experiments the possibility of prediction of the state vector using neural networks is investigated. Further, the possibility for application of neural networks for estimation of optimal control forces is investigated. T . _,, < ~'---------~-~t_)_:_\_!._._~·-1 ----~ > Figure 4: Definition of positive directions . A (.1: 1 , x2 )-coordinate system is defined in the centre of mass gravity CG of the bridge sec-tion, see figure 4. The x2 axis is defined to be positive upwards. The x1 axis is defined to be positive in the direction of the trailing edge (in the direction of the mean wind velocity) . The wind velocity u ( k) with the composants u1 ( k) and u 2 ( k) in the directions of the coordinate system is measured in the undisturbed stream in front of the leading edge at the discrete times 't = k6.t, k = 0, 1, . . . The positions of the flaps are given by the vector (1) where a 1 ( k) and a 2 ( k) are the angles of the flaps at the leading edge and the trailing edge, respectively. The angles are measured at timet= k6.t and are both positive in the positive rotation direction of the plane. The bridge section is considered to be stiff and the motion in the direction of the x 1 axis is ignored. Thereby, the bridge section has two degrees of freedom, selected as the vertical motion v(k) in the x2-direction and the rotation in the positive rotation direction B(k) of the centre of mass gravity of the bridge section. The motion of the bridge section is then specified by the vector [ v(k) ] x(k) = B(k) (2) x(k) is measured at times t = k6.t, k = 0, 1, ... The following equation for the dynamic system is assumed x(k) = f(x(k- 1), ... , x(k -l), u(k- 1), .. . , u(k- m), o.(k -1), ... ,o.(k- n),w1) (3) The control law is in the same way given by o.(k) = g(x(k- 1), ... , x(k- l), u(k- 1), ... , u(k- m), o.(k- 1), . .. , o.(k- n), w 9 ) (4) The functions f (modelling the dynamic system) and g (modelling the controller) are approximated by neural networks. w I and w 9 are vectors of weights and thresholds of the selected neural network topologies, [2]. The size of the tapped-delay lines defined by l, m and n and the topology of the neural networks must be learned by experience from tests with the model. The primary aim is the design of the controller g, i.e. the specification of the control action (flap positions) at the time t = kb.t as a function of tapped delays of previous measured displacements, velocities and previous control actions. In principle control of the flaps could be determined from visual inspection of the displacements and velocities of the bridge via a joystick. Obviously, this is basically a closed-loop control of the bridge (the control action is only dependent on the present displacements and velocities). The digitalized control actions a(k) along with the measured displacements x(k) and velocities u(k) could then be used to train the neural network (4) without any resort to the dynamic model (3). However there is a number of difficulties with such an approach. First, the method can hardly be carried out from a practical point of view because the fundamental eigenperiod of the model is as low Tm ~ 0.57 s. Secondly, there is no guarantee, that any manual control is optimal in decreasing the vibrations. At least it seems likely that dif-ferent people will select different control actions to the same displacement state, resulting in different vibration performance. Optimal control can only be specified if the vibration level is defined by a performance index. The dependency of such a performance index on th~ control action is evaluated by a dynamic model such as (3) with explicit dependency on previous control actions. Hence, optimal control relies on simultaneous modelling of the structural system and the control action. Bibliography [1] Description of IST Wind Tunnel. ROLLAB Report RR 079. [2] H.I. Hansen, P.H. Kirkegaard, and S.R.K. Nielsen. Modelling of Deteriorating Re-Structures undeT Stochastic Dynamic Loading by Neural Networks. In Computational Stochastic Mechanics. P.D. Spanos (editor). Balkema, 1995. Proceedings Second Inter-national Conference on Computational Stochastic Mechanics, Athens, Greece, 12-15 June 1994, pp. 681-686. [3] E. Hjorth-Hansen. Section Model Tests. In Aerodynamics of Large Bridges. A. Larsen (editor) . Balkema, 1992. Proceedings of the First International Symposium on Aero-dynamics of Large BTidges, Copenhagen, Denmark, 19-21 February 1992, pp. 95-112 . [4] K.H. Ostenfeld and A. Larsen. Bridge Engineering and Aerodynamics. In Aemdy-namics of Large Bridges. A. Larsen (editor). Balkema, 1992. Proceedings of the First International Symposium on Aerodynamics of Large Bridges, Copenhagen, Denmark, 19- 21 February 1992, pp. 3-22. STRUCTURAL RELIABILITY THEORY SERIES PAPER NO. 132: I. B. Kroon: Decision Theory applied to Stntctural Engineering · Problems. Ph.D.-Thesis. ISSN 0902-7513 R9421. PAPER 133: H. U. Koyliioglu, S. R. K. Nielsen & A. S. Qakmak: Stochastic Dy-namics of Nonlinear Structures with Random Properties subject to Random Stationary Excitat?:on. ISSN 0902-7513 R9520. PAPER NO. 134: H. U. Koyliioglu, S. R. K. Nielsen & A. S- Qakmak: Solution of Random Structural System subject to Non-Stationary Excitation: Transforming the Equation with Random Coefficients to One with Deterministic Coefficients and Random Initial Conditions. ISSN 0902-7513 R9429. PAPER NO . 135: S. Engelund, J. D. S0rensen & S. Krenk: Estimation of the Time to Initiation of Corrosion in Existing Uncracked Concrete Structures. ISSN 0902-7513 R9438. PAPER NO. 136: H. U. Koyliioglu, S. R. K. Nielsen & A. S- Qakmak: - S ol1Ltion Methods for Structures with Random Properties subject to Random Excitation. ISSN 0902-;7513 R9444. PAPER NO. 137: J. D. S0rensen, M. H. Fabel" & I. B. Kroon.: Optimal Reliability-Based Planning of Experiments for POD Curves. ISSN 0902-7513 R9455. PAPER NO. 138: S.R.K. Nielsen & P.S. Skjrerbrek, H.U. Koyliioglu & A.S. Qakmak: Prediction of Global Damage and Reliability based 1Lpon Sequential Identification and Updating of RC Structures subject to Earthquakes. ISSN 0902-7513 R9505. PAPER NO. 139: R. IwaB,kiewiez, S. R. K. Nielsen & P. S. Skjrerbrek: Sensdivity of Reliability Estimates in Partially Damaged RC Structures subject to Earthquakes) using Reduced Hysteretic Models . ISSN 0902-7513 R9507. PAPER NO. 140: R. d. Micaletti, A. S- Qakmak, S. R. K. Nielsen & H. U. Koyliioglu: Error Analysis of Statist1:cal Linearization with Gaussian Closure fow Large Degree-of-Freedom Systems . ISSN 1395-7f)53 R9631. PAPER NO 141: H. U. KoyliiogJu, S. R. K. Nielsen & A. ~ - Qakmak: Uncertmin Buckling Load and Reliability of Columns with Uncertain Properties. IS'SN 0902-7513 R9524. PAPER NO. 142: S. R. K. Nielsen & R. Iwankiewicz: Response of Non-Linear Systems to Renewal Imp,ulses by Path Integration. JSSN 0902-7513 R9512. PAPER NO. 143: H. U. Koyliioglu, A. S- Qakmak & S. R K. Nielsen: Midbroken Re-inforced Concrete Shear Frames Due to Earth9uakes. - A Hys,ieretic Model to Qua.ntify Damage at the Storey Level. ISSN 1395-7953 R9630. PAPER NO. 145: H. U. Koyliioglu, S. R. K. Nielsen, Jamison Abbott & A. S- Qakmak: Local and Modal Damage Indicators for Reinforced Concrete Shear Frames subject to Earthquakes. ISSN 0902-7513 R9521 PAPER NO. 146: P. H. Kirkegaard, S. R. K. Nielsen, R. C. Micaletti & A. S- Qakmak: Identification of a Maximum Softening Damage Indicator of RC-Structures using Time-Frequency Techniques. ISSN 0902-7513 R9522. STRUCTURAL RELIABILITY THEORY SERIES PAPER NO. 147: R. C. Micaletti, A. ~· Qakmak, S. R. K. Nielsen & P. H. Kirkegaard: Construction of Tim e-Dependent Spectra using Wavelet Analysis for Determination of Global Damage. ISSN 0902-7513 R9517. PAPER NO. 148: H. U. Koyliioglu, S. R. K. Nielsen & A. ~ · Qakmak: Hysteretic MDOF Model to Quantify Damage for TC Shear Frames subject to Earthquakes. ISSN 1395-7953 R9601. PAPER NO. 149: P. S. Skjrerbrek, S. R. K. Nielsen & A. ~ · Qakmak: Damage Loca-tion of Severely Damaged RC-Structures based on Measured Eigenperiods from a Single Response. ISSN 0902-7513 R9518. PAPER NO . 150: S. R. K. Nielsen & H. U. Koyliioglu: Path Integration applied to Structural Systems with Uncertain Properties. ISSN 1395-7953 R9602. PAPER NO. 151: H. U. Koyliioglu & S. R. K. Nielsen: System Dynamics and Modified Cumulant Neglect Closure Schemes. ISSN 1395-7953 R9603. PAPER NO. 153: R. C. Micaletti, A.~ · Qakmak, S. R. K. Nielsen & H. U. Koyliioglu: A Sol1dion Method for Linear and Geometrically Nonlinear MDOF Systems with Random Properties subject to Random Excitation. ISSN 1395-7953 R9632. PAfER NO . 154: J . D. S0rensen, M. H. Faber, I. B. Kroon: Optimal Reliability-Based Planning of Experiments for POD Curves . ISSN 1395-7953 R9542. PAPER NO. 155: J. D. S0rensen, S. Engelund: Stochastic Finite Elements in Reliability-Based Structv.ral Optimization. ISSN 1395-7953 R9543 . PAPER NO. 156: C. Pedersen, P. Thoft-Christensen: Guidelines for Interactive Reliability-Based Structural Optimization using Quasi-Newton Algorithms. ISSN 1395-7953 R9615. PAPER NO . 157: P. Thoft-Christensen, F. M. Jensen, C. R. Middleton, A. Bla.ckmore: Assessment of the Reliability of Concrete Slab Bridges. ISSN 1395-7953 R9616 . PAPER NO. 159: H. I. Hansen, P. Thoft-Christensen: Wind Tunnel Testing of Active Control System joT Bridges. ISSN 1395-7953 R9662. PAPER NO 160: C. Pedersen: Interactive Reliability-Based Optimization of S'tructv.ral Systems. Ph.D .-Thesis. ISSN 1395-7953 R9638. PAPER NO. 161: S. Engelund, J . D. S!1lrensen: Stochastic Models for Chloride-initiated Corrosion in Reinforced Concrete.ISSN 1395-7953 R9608. PAPER NO. 165: P. H. Kirkegaard, F . M. Jensen, P. Thoft-Christensen: Modelling of StLrjace Ships using Artificial Neural Networks. ISSN 1593-7953 R9625. PAPER NO. 167: S.R.K. Nielsen, R. Iwankiewicz: Dynamic systems Driven by Non-Poissonian Impulses : M arkov Vector AppTOach. ISSN 1395-7953 R9705. Department of Building Technology and Structural Engineering Aalborg University, Sohngaardsholmsvej 57, DK 9000 Aalborg Telephone: +45 98 15 85 22 Telefax: +45 98 14 82 43 

https://vbn.aau.dk/ws/files/198623178/Wind_Tunnel_Testing_of_Active_Control_System_for_Bridges.pdf

Wind Tunnel Testing of Active Control System for Bridges

Abstract

Similar works

Full text

Available Versions

VBN

VBN