Vibration Analysis and Control – New Trends and Developments 90 Fig. 15. Root locus of the total transfer function G T for CAFC on the footbridge. (×) pole; (ο) zero; (F) footbridge; (A) actuator −λ A F F Active Control of Human-Induced Vibrations Using a Proof-Mass Actuator 91 Uncontrolled (m/s 2 ) Controlled (m/s 2 ) Reduction (%) Mass displacement (m) Walking at 1.75 Hz 0.39 0.04 89 ± 0.034 Running at 3.50 Hz 6.16 3.75 40 ± 0.022 Table 3. Simulation performance assessment for the footbridge using the peak acceleration for walking and running excitation Walking and running tests are carried out to assess the efficacy of the AVC system. The walking tests consist of walking at 1.75 Hz such that the first vibration mode of the structure (3.5 Hz) could be excited by the second harmonic of walking. A frequency of 3.5 Hz is used for the running tests so that the structure is excited by the first harmonic of running. The walking/running tests consisted of walking/running from one end of Span 2 to the other and back again. The pacing frequency is controlled using a metronome set to 105 beats per minute (bpm) for 1.75 Hz and to 210 bpm for 3.5 Hz. Each test is repeated three times. Uncontrolled Controlled Reduction (%) Walking at 1.75 Hz Peak acceleration (m/s 2 ) 0.41 0.16 70 MTVV (1) (m/s 2 ) 0.21 0.06 67 Running at 3.50 Hz Peak acceleration (m/s 2 ) 3.34 1.19 64 MTVV (m/s 2 ) 2.20 0.69 68 Table 4. Experimental performance assessment for walking and running excitation. (1) Maximum Transient Vibration value defined as the maximum value of 1s running RMS acceleration The results are compared by means of the maximum peak acceleration and the MTVV computed from the 1 s running RMS acceleration. Table 4 shows the result obtained for the uncontrolled and controlled case. It is observed that the AMD designed (with a moving mass of 30 kg) performs well for both excitations, achieving reductions of approximately 70 %. Fig. 16 shows the response time histories (including the 1 s RMS) uncontrolled and controlled for a walking test. Fig. 17 shows the same plots for a running test. Vibration Analysis and Control – New Trends and Developments 92 Fig. 16. Walking test on the footbridge. a) Uncontrolled 2 MTVV 0.207 m s= . b) Controlled 2 MTVV 0.067 m s= a) b) Active Control of Human-Induced Vibrations Using a Proof-Mass Actuator 93 Fig. 17. Running test on the footbridge. a) Uncontrolled 2 MTVV 2.198 m s= . b) Controlled 2 MTVV 0.773 m s= a ) b ) Vibration Analysis and Control – New Trends and Developments 94 6. Conclusion The active cancellation of human-induced vibrations has been considered in this chapter. Even velocity feedback has been used previously for controlling human-induced vibrations, it has been shown that this is not a desirable solution when the actuator dynamics influence the structure dynamics. Instead of using velocity feedback, here, it is used a control scheme base on the feedback of the acceleration (which is the actual measured output) and the use of a first-order compensator (phase-lag network) conveniently designed in order to achieve significant relative stability and damping. Note that the compensator could be equivalent to an integrator circuit leading to velocity feedback, depending on the interaction between actuator and structure dynamics. Moreover, the control scheme is completed by a phase- lead network to avoid stroke saturation due to low-frequency components of excitations and a nonlinear element to account for actuator overloading. An AVC system based on this control scheme and using a commercial inertial actuator has been tested on two in-service structures, an office floor and a footbridge. The floor structure has a vibration mode at 6.4 Hz which is the most likely to be excited. This mode has a damping ratio of 3% and a modal mass of approximately 20 tonnes. Reductions of approximately 60 % have been observed in MTVV and cumulative VDV for controlled walking tests. For in-service whole-day monitoring, the amount of time that an R-factor of 4 is exceeded, which is a commonly used vibration limit for high quality office floor, is reduced by over 97 %. The footbridge has a vibration mode at 3.5 Hz which is the most likely to be excited. This mode has a damping ratio of 0.7 % and a modal mass of approximately 18 tonnes. Reductions close to 70 % in term of the MTVV has been achieved for walking and running tests. It has been shown that AVC could be a realistic and reasonable solution for flexible lightweight civil engineering structures such as light-weight floor structure or lively footbridges. In these cases, in which low control forces are required (as compared with other civil engineering applications such as high-rise buildings or long-span bridges), electrical actuators can be employed. These actuators present advantages with respect to hydraulic ones such as lower cost, maintenance and level of noise. However, AVC systems for human- induced vibrations needs much further research and development to jump into building and construction technologies considered by designers. With respect to passive systems, such as TMDs, cost is still the mayor disadvantage. However, it is expected that this technology will become less expensive and more reasonable in the near future. Research projects involving the development of new affordable and compact actuators for human-induced vibration control are currently on the go (Research Grant EP/H009825/1, 2010). 7. Acknowledgment The author would like to acknowledge the financial support of Universidad de Castilla-La Mancha (PL20112170) and Junta de Comunidades de Castilla-La Mancha (PPII11-0189-9979. The author would like to thank his colleagues Dr. Paul Reynolds and Dr Donald Nyawako from the University of Sheffield, and Mr Carlos Casado and Mr Jesús de Sebastián from CARTIF Centro Tecnológico for their collaboration in works presented in this chapter. Active Control of Human-Induced Vibrations Using a Proof-Mass Actuator 95 8. References APS. Instruction Manual Electro-Seis Model 400 Shaker, APS Dynamics, USA, available from http://www.apsdynamics.com Bachmann, H. (1992). Case studies of structures with man-induced vibrations. Journal of Structural Engineering, Vol.118, No.3, pp. 631-647, ISNN 0733-0445 Bachmann, H. (2002). Lively footbridges ⎯a Real Challenge, Proceedings of the International Conference on the Design and Dynamic Behaviour of Footbridges, OTUA, Paris, France, November 20-22 Balas, M.J. (1979). Direct velocity feedback control of large space structures, Journal of Guidance and Control, Vol.2, No.3, pp. 252–53 Bolton, W. (1998). Control engineering, Logman, ISBN 978-0-582-32773-3, United Kingdom Brownjohn, J.M.W., Pavic, A. & Omenzetter, P. (2004). A spectral density approach for modelling continuous vertical forces on pedestrian structures due to walking, Canadian Journal of Civil Engineering, Vol.31, No.1, pp. 65–77, ISSN 0315-1468 BS 6841. (1987). Measurement and evaluation of human exposure to whole-body mechanical vibration and repeated shock, British Standards Institution, ISBN 0-580-16049-1, United Kingdom BS 6472. (2008). Guide to evaluation of human exposure to vibration in buildings. Part 1: Vibration sources other than blasting, British Standards Institution, ISBN 978-0-580-53027-2, United Kingdom Caetano, E., Cunha, A., Moutinho, C. & Magalhães, F. (2010) Studies for controlling human- induced vibration of the Pedro e Inês footbridge, Portugal. Part 2: Implementation of tuned mass dampers, Engineering Structures, Vol.32, pp. 1082–1091, ISSN 0141- 0296 Chung, L.Y. & Jin, T.G. (1998). Acceleration feedback control of seismic structures, Engineering Structures, Vol.20, No.1, pp. 62–74, ISSN 0141-0296 Díaz, I.M. & Reynolds, P. (2010a). On-off nonlinear active control of floor vibrations, Mechanical Systems and Signal Processing, 24: 1711–1726, ISSN 0888-3270 Díaz, I.M. & Reynolds, P. (2010b). Acceleration feedback control of human-induced floor vibrations, Engineering Structures, Vol.32, No.1, pp. 163–173, ISSN 0141-0296 Ebrahimpour, A. & Sack, R.L. (2005). A review of vibration serviceability criteria for floor structures, Computers and Structures, Vol.83, pp. 2488–94, ISSN 0045-7949 FIB-Bulletin 32. (2005). Guidelines for the design of footbridges, International Federation for Structural Concrete, Lausanne, Switzerland Gómez, M. (2004). A new and unusual cable-stayed footbridge at Valladolid (Spain). Steelbridge 2004: Symposium International sur les Ponts Metálliques, Milau, France, June, pp. 23-25 Hanagan, L.M. & Murray, T.M. (1997) Active control for reducing floor vibrations, Journal of Structural Engineering, Vol.123, No.11, pp. 1497–1505, ISSN 0733-9445 Hanagan, L.M., Raebel, C.H. & Trethway, M.W. (2003a). Dynamic measurements of in-place steel floors to assess vibration performance, Journal of Performance of Constructed Facilities, Vol.17, pp. 126–135, ISSN - 0887-3828 Vibration Analysis and Control – New Trends and Developments 96 Hanagan, L.M., Murray, T.M. & Premaratne, K. (2003b). Controlling floor vibration with active and passive devices, The Shock and Vibration Digest, Vol.35, No.5, pp. 347–65, ISSN 0583-1024 Hanagan, L.M. (2005). Active floor vibration system, United States Patent 6874748 Moutinho, C., Cunha, A. & Caetano, E. (2010). Analysis and control of vibrations in a stress- ribbon footbridge, Structural Control and Health Monitoring, doi: 10.1002/stc.390 Nyawako, D. & Reynolds, P. (2007) Technologies for mitigation of human-induced vibration in civil engineering structures, The Shock and Vibration Digest, Vol.36, No.(6), pp. 465–93, ISSN 0583-1024 Occhiuzzi, A., Spizzuoco, M. & Ricciardelli, F. (2008). Loading models and response control of footbridges excited by running pedestrians, Structural Control and Health Monitoring, Vol.15, pp. 349–368, ISSN 1545-2263 Pavic, A. & Willford, M. (2005). Appendix G in Post-tensioned concrete floors design handbook– Technical Report 43, Concrete Society, Slough, United Kingdom Preumont, A. (1997). Vibration Control of Active Structures: An introduction, Kluwer Academic, Dordrecht, ISBN 1-4020-0496-9, The Netherlands Reiterer, M. & Ziegler, F. (2006). Control of pedestrian-induced vibrations of long-span bridges, Structural Control and Health Monitoring, Vol.13, pp. 1003–1027, ISSN 1545- 2263 Research Grant EP/H009825/1. (2010). Active control of human-induced vibration, PI: Dr Paul Reynolds, Engineering and Physical Sciences Research Council, 2010–2012, United Kingdom Reynolds, P., Díaz, I.M. & Nyawako, D.S. (2009). Vibration testing and active control of an office floor, Proceedings of the 27th International Modal Analysis Conference, Orlando, Florida, USA Setareh, M. & Hanson, R.D. (1992). Tuned mass damper to control floor vibration from humans, Journal of Structural Engineering, Vol.118, No.3, pp. 741–62, ISSN 0733-9445 Setareh, M. (2002). Floor vibration control using semi-active tuned mass dampers, Canadian Journal of Civil Engineering, Vol.29, No.1, pp. 76–84, ISSN 0315-1468 Slotine, J.J. & Li, W. (1991). Applied non linear control, Prentice-Hall, Chapter 5, ISBN 013- 040890-5, USA Wyatt, T.A. (1989). Design guide on the vibration of floors, The Steel Construction Institute, ISBN 1-870004-34-5, United Kingdom 5 Control Strategies for Vehicle Suspension System Featuring Magnetorheological (MR) Damper Min-Sang Seong 1 , Seung-Bok Choi 1 and Kum-Gil Sung 2 1 Inha University 2 Yeungnam College of Science and Technology Korea 1. Introduction Vehicle suspension is used to attenuate unwanted vibrations from various road conditions. So far, three types of suspension system have been proposed and successfully implemented; passive, active and semiactive. Though the passive suspension system featuring oil damper provides design simplicity and cost-effectiveness, performance limitations are inevitable due to the lack of damping force controllability. On the other hand, the active suspension system can provides high control performance in wide frequency range. However, this type may require high power sources, many sensors and complex actuators such as servovalves. Consequently, one way to resolve these requirements of the active suspension system is to adopt the semiactive suspension system. The semiactive suspension system offers a desirable performance generally enhanced in the active mode without requiring large power sources and expensive hardware. One of very attractive and effective semiactive vehicle suspension systems is to utilize magnetorheological (MR) fluid. MR fluids are currently being studied and implemented as actuating fluids for valve systems, shock absorbers, engine mounts, haptic systems, structure damper, and other control systems. The rheological properties of MR fluids are reversibly and instantaneously changed by applying a magnetic field to the fluid domain. Recently, a very attractive and effective semi-active suspension system featuring MR fluids has been researched widely. Carlson et al., 1996 proposed a commercially available MR damper which is applicable to on-and-off-highway vehicle suspension system. They experimentally demonstrated that sufficient levels of damping force and also superior control capability of the damping force by applying control magnetic field. Spencer Jr. et al., 1997 proposed dynamic model for the prediction of damping force of a MR damper. They compared the measured damping forces with the predicted ones in time domain. Kamath et al., 1998 proposed a semi-active MR lag mode damper. They proposed dynamic model and verified its validity by comparing the predicted damping force with the measured one. Yu et al., 2006 evaluated the effective performance of the MR suspension system by road testing. Guo & Hu, 2005 proposed nonlinear stiffness model of a MR damper. They proposed nonlinear stiffness model and verified it using simulation and experiment. Du et al., 2005 Vibration Analysis and Control – New Trends and Developments 98 proposed H-infinity control algorithm for vehicle MR damper and verified its effectiveness using simulation. Shen et al., 2007 proposed load-levelling suspension with a magnetorheological damper. Pranoto et al., 2005 proposed 2DOF-type rotary MR damper and verified its efficiencies. Ok et al., 2007 proposed cable-stayed bridges using MR dampers and verified its effectiveness using semi-active fuzzy control algorithm. Choi et al., 2001 manufactured an MR damper for a passenger vehicle and presented a hysteresis model for predicting the field-dependent damping force. Hong et al., 2008 derived a nondimensional Bingham model for MR damper and verified its effectiveness through experimental investigation. Yu et al., 2009 developed human simulated intelligent control algorithm and successfully applied it to vibration control of vehicle suspension featuring MR dampers. Seong et al., 2009 proposed hysteretic compensator of MR damper. They developed nonlinear Preisach hysteresis model and hysteretic compensator and demonstrated its damping force control performance. As is evident from the previous research work, MR damper is very effective solution for vibration control of vehicle suspension system. So in this chapter, we formulate various vibration control strategies for vibration control of MR suspension system and evaluate their control performances. In order to achieve this goal, material characteristics of MR fluid are explained. Then the MR damper for vehicle suspension system is designed, modelled and manufactured. The characteristics of manufactured MR damper are experimentally evaluated. For vibration control, the quarter vehicle suspension system featuring MR damper is modelled and constructed. Then, various vibration control strategies such as skyhook control, PID control, LQG control, H ∞ control, Sliding mode control, moving sliding mode control and fuzzy moving sliding mode control are formulated. Finally, control performances of the proposed control algorithms are experimentally evaluated and compared. 2. Suspension modelling 2.1 MR fluid Since Jacob Rabinow discovered MR fluid in the late 1940s, of which yield stress and viscosity varies in the presence of magnetic field, various applications using MR fluid have been developed such as shock absorbers, clutches, engine mounts, haptic devices and structure dampers, etc (Kim et al., 2002). Physical property changes of MR fluid are resulted from the chain-like structures between paramagnetic MR particles in the low permeability solvent. At the normal condition, MR fluid shows the isotropic Newtonian behavior because the MR particles move freely as shown in Fig. 1 (a). However, when the magnetic field applied to the MR fluid, MR fluid shows the anisotropic Bingham behavior and resist to flow or external shear force because the MR particles make a chain structure as shown in Fig. 1 (b). From this property, force or torque of application devices can be easily controlled by the intensity of the magnetic field. 2.2 MR damper The schematic configuration of the cylindrical type MR damper proposed in this work is shown in Fig. 2. The MR damper is composed of the piston, cylinder and gas chamber. The floating piston between the cylinder and the gas chamber is also used in order to compensate for the volume induced by the motion of the piston. Also the gas chamber [...]... 111 112 16 Uncontrolled Skyhook LQG Hinf 14 2 PSD of SM Acc ((m/s) /Hz) Vibration Analysis and Control – New Trends and Developments 12 10 8 6 4 2 0 0 .5 1 50 10 16 Uncontrolled SMC MSMC FMSMC 14 2 PSD of SM Acc ((m/s) /Hz) Frequency (Hz) 12 10 8 6 4 2 0 0 .5 1 10 50 Frequency (Hz) Fig 17 Random responses of the quarter vehicle MR suspension system (72km/h) RMS of Vertical Acc 1 .5 1.0 0 .5 0.0 UC SkyH... suspension system and hence increase the stability of the system 4 Control performances Vibration control performances of the quarter vehicle MR suspension system are evaluated under two types of excitation (road) conditions The first excitation, normally used to reveal the transient response characteristic, is a bump described by 110 Vibration Analysis and Control – New Trends and Developments = 1... resistance is given by (Liu et al., 2006; White, 1994) = 8η (1) ⁄ 100 Vibration Analysis and Control – New Trends and Developments (a) MR damper (b) piston (3-D view) Fig 2 Schematic configuration of the proposed MR damper and where η is the viscosity of the MR fluid and is the length of the annular duct are the inner radius of the outer piston and outer radius of the inner piston respectively By assuming... Vibration Analysis and Control – New Trends and Developments 3.6 Fuzzy moving sliding mode controller (FMSMC) The fuzzy moving sliding mode controller, which can change the coefficients and intercepts of sliding surface by fuzzy tuning which takes into account for location of reaching phase, is developed Fig 13 presents the block diagram of the proposed FMSMC The basic configuration of fuzzy control. .. shows the conceptual scheme of sliding mode control algorithm After the initial reaching phase, the system states slides along the sliding surface The first step to formulate the SMC is to design a stable sliding surface The stable sliding surface for the control system is defined as follows: s= + + + + (13) 106 Vibration Analysis and Control – New Trends and Developments zr System B u(t) -KLQG x C y(t)... presented 102 Vibration Analysis and Control – New Trends and Developments in Table 1 Fig 4 presents the measured and analysed damping force FD characteristics of the MR damper with respect to the piston velocity at various magnetic fields This is obtained by calculating the maximum damping force at each velocity The piston velocity is changed by increasing the excitation frequency from 0 .5 to 4.0Hz,... mid-sized passenger vehicle, and listed in Table 2 3 Control strategies In order to evaluate vibration control performance of the quarter vehicle MR suspension system, various control strategies are formulated and experimentally implemented 3.1 Skyhook controller Skyhook controller is simple but very effective control algorithm It is well known that the logic of the skyhook controller is easy to implement... estimated state Control gain is set as −1248.3 1 150 .3 −4121.8 15. 5 0.4 in this work 3.3 H∞ controller In reality, the sprung mass of the vehicle is varied by the loading conditions such as the number of riding persons and payload And it makes the pitch and roll mass moment of inertia to be changed Therefore, in order to successfully control the vibration, a robust control algorithm is required by considering... quarter vehicle suspension system was then constructed and its governing equations of motion were derived In order to obtain a favourable control performance of the MR suspension system, skyhook controller, LQG controller, H∞ controller, sliding mode controller, moving sliding mode controller and fuzzy moving sliding mode controller were designed and experimentally realized to the quarter vehicle MR... stiffness of the tire, and , and are the vertical displacements of sprung mass, unsprung mass and road excitation respectively The state space equation of proposed quarter vehicle suspension can be expressed using dynamic equation (Lee et al., 2011): = + + , = (7) 104 Vibration Analysis and Control – New Trends and Developments where = 0 = 1 0 0 0 1 −1 0 1 − − 0 0 − 0 ( 0 + ) 0 − 0 = 0 0 0 0 1 , 0 , (8) . (including the 1 s RMS) uncontrolled and controlled for a walking test. Fig. 17 shows the same plots for a running test. Vibration Analysis and Control – New Trends and Developments 92 . (2003b). Controlling floor vibration with active and passive devices, The Shock and Vibration Digest, Vol. 35, No .5, pp. 347– 65, ISSN 058 3-1024 Hanagan, L.M. (20 05) . Active floor vibration. floors to assess vibration performance, Journal of Performance of Constructed Facilities, Vol.17, pp. 126–1 35, ISSN - 0887-3828 Vibration Analysis and Control – New Trends and Developments