Fundamental studies of AVC with actuator dynamics

IMAC XXXIV: 34th Conference and Exposition on Structural Dynamics of Multiphysical Systems, 25 - 28 January 2016, Orlando, Florida, USAThis is the author accepted manuscript. The final version is available from the publisher.Active vibration control (AVC) of human-induced vibrations in structures with proof-mass actuators has been subject to much research in recent years. This has predominantly focussed on footbridges and floors and there is some evidence that this research is paving the way for commercial installations of AVC where traditional vibration control measures are not appropriate. However, the design of an AVC system is a complex task because of the influence of actuator dynamics, the contributions from higher frequency modes of vibration and the effect of low and high pass filters that are required to make the control algorithm implementable. This puts the AVC design process beyond the abilities of the vast majority of civil design engineers, even at a scheming stage to approximate what sort of reductions could be achieved by such a system. This paper considers a generalised system and investigates what sort of performance can be achieved in theory by a perfect AVC system, then considers the added complexity of actuator dynamics to demonstrate how this degrades the performance from optimal.The authors would like to acknowledge the financial support given by the UK Engineering and Physical Sciences Research Council through a responsive mode grant entitled Active Control of Human-Induced Vibration (Ref: EP/H009825/1) and Leadership Fellowship grant entitled Advanced Technologies for Mitigation of Human-Induced Vibration (Ref: EP/J004081/1)

Observer-based controller for floor vibration control with optimisation algorithms

Copyright © 2015 by SAGE PublicationsThis study presents the results of vibration suppression of a walkway bridge structure with a single actuator and sensor pair by using a proportional-integral (PI) controller and observer-based pole- placement controllers. From the results of experimental modal analysis (EMA), reduced order models of the walkway are identified. These are used for the design of a PI controller as well as for state estimation procedures that are necessary for development of reduced-order observer controllers. The respective orders of the latter are dependent on the number of plant modes used for their designs. They are formulated from plant and observer feedback gains that are obtained from specification of desired floor closed-loop eigenvalues and observer eigenvalues. There are numerous solutions possible with the observer-based controller design procedures whereas the PI controller defaults to a particular solution. There is also the flexibility for isolation and control of target vibration modes with the observer-based controllers for higher controller orders from a purely single-input single-output controller scheme as demonstrated in the analytical and experimental studies presented. Further, in this work, a design space of potential feedback gains is specified, where only a single plant mode has been used for the observer-based controller design process, and a multi-objective genetic algorithm optimisation scheme is used to search for an optimal solution within some pre-defined constraint conditions. The best solution here is regarded as one that offers the greatest vibration mitigation performance amongst the solutions identified.Engineering and Physical Sciences Research Council (EPSRC

Approximate pole-placement controller using inverse plant dynamics for floor vibration control

PublishedThis is the final version of the article. Available from SPIE via the DOI in this record.Past research and field trials have demonstrated the viability of active vibration control (AVC) technologies for the mitigation of human induced vibrations in problematic floors. They make use of smaller units than their passive counterparts, provide quicker and more efficient control, can tackle multiple modes of vibration simultaneously and adaptability can be introduced to enhance their robustness. Predominantly single-input-single-output (SISO) and multi-SISO collocated sensor and actuator pairs have been utilized in direct output feedback schemes, for example, with direct velocity feedback (DVF). On-going studies have extended such past works to include model-based control approaches, for example, pole-placement (PP), which demonstrate increased flexibility of achieving desired vibration mitigation performances but for which stability issues must be adequately addressed. The work presented here is an extension to the pole-placement controller design using an algebraic approach that has been investigated in past studies. An approximate pole-placement controller formulated via the inversion of the floor dynamics, considered as minimum phase, is designed to achieve target closed-loop performances. Analytical studies and experimental tests are based on a laboratory structure and comparisons in vibration mitigation performances are made with a typical DVF control scheme with inner loop actuator compensation. It is shown that with minimal compensation, primarily in the form of notch filters and gain adjustment, the approximate pole-placement controller scheme is easily formulated and implemented and offers good vibration mitigation performance as well as the potential for isolation and control of specific target modes of vibration. Predicted attenuations of 22dB and 12dB in both the first and second vibration modes of the laboratory structure were also realized in the experimental studies for DVF and the approximate PP controller. © 2013 SPIE

Findings with AVC design for mitigation of human induced vibrations in office floors

PublishedTopics in Dynamics of Civil Structures, Volume 4; Part of the series Conference Proceedings of the Society for Experimental Mechanics Series pp 37-44This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.In recent years, there have been extensive active vibration control (AVC) studies for the mitigation of human induced vibrations in a series of office floors, in which such vibrations are deemed to be 'problematic' and have been found to affect only certain sections of the floors. These floors are predominantly open-plan in layout and comprise of different structural configurations for their respective bays and this influences their dynamic characteristics. Most of the AVC studies have comprised extensive analytical predictions and experimental implementations of different controller schemes. The primary measures of vibration mitigation performance have been by frequency response function (FRF) measurements, responses to controlled walking tests, and in-service monitoring, all tests with and without AVC. This paper looks at AVC studies in three different office floor case studies in past field trials. Some of the estimated modal properties for each of these floors from experimental modal analysis (EMA) tests are shown as well as some selected mode shapes of fundamental modes of vibration. These reflect the variability in their dynamic characteristics by virtue of their different designs and thus the potential for their 'liveliness' under human induced excitation. An overview of some of the controller schemes pursued in the various field trials are mentioned as well as a brief insight being provided into some challenges encountered in their designs and the physical siting of the collocated sensor and actuator pairs used in the field trials. The measure for the vibration mitigation performances in this work is in the form of uncontrolled and controlled point accelerance FRFs which show attenuations in the target modes of vibration between 13 and 18 dB. These tests also show the variability in vibration mitigation performances between the various controllers. © The Society for Experimental Mechanics, Inc. 2013

Receptance based approach for control of floor vibrations

This is the author accepted manuscript. The final version is available from the publisher via the link in this record.Advances in design, materials and construction technologies, coupled with client and architectural requirements, are some of the drivers for light-weight and slender pedestrian structures, which are becoming increasingly susceptible to human induced vibrations. The use of active control techniques is progressively being viewed as a more feasible approach for suppressing such vibrations compared with traditional passive technologies. In this paper, the principles of the receptance based approach are exploited to design appropriate feedback gains that place the eigenvalues of selected vibration modes of an experimental footbridge structure at selected locations thereby enhancing its vibration performance. These studies are based on a single-input multiple-output (SIMO) controller structure comprising of a single control actuator and two sensors. It is seen that this has the potential to offer additional design freedoms beyond purely a direct velocity feedback (DVF) controller. A comparative study is carried out with a DVF controller implemented in a single-input single-output (SISO) scheme. This work presents the analytical determination of appropriate feedback gains from results of experimental modal analysis (EMA) on the structure and thereafter the experimental implementation of these feedback gains. Vibration mitigation performance is evaluated through both changes in measured transfer functions and reductions in response under single pedestrian excitation

Direct velocity feedback versus a geometric controller design of remotely located vibration control systems

Proceedings of the 5th International Conference on Structural Engineering, Mechanics and Computation, SEMC 2013The mitigation of human induced vibrations in floors continues to be a key area of research particularly as a result of advancement in material and design technologies enabling the design of light, slender and more open plan structures. These floors are typically characterised by low and close natural frequencies as well as low modal damping ratios, and these combinations of factors contribute to their increased susceptibility to human induced vibrations. Amongst the remedial measures pursued to enhance their vibration serviceability performance, active vibration control (AVC) technologies are emerging as a viable technology and predominantly direct output feedback approaches have been pursued in past analytical studies and field trials. It has often been assumed that actuators and sensors can be located where vibration attenuation is desired and this may not always be feasible. The research work presented in this paper compares the vibration mitigation performances of the direct velocity feedback scheme that has been extensively used in past floor vibration control researches against a geometric controller design approach that has been developed to provide a design freedom for reducing vibration in both local and remote locations. The geometric controller design approach assumes the inability to locate the actuators and sensors at the remote location but acknowledges that this measurement can be obtained during the commissioning stage and used during the design phase to enhance both local and remote locations. All the analytical and experimental studies are based on a laboratory structure. The work demonstrates comparable vibration mitigation performances of the dominant mode of vibration of the laboratory structure for both approaches but also demonstrates potential for additional enhancement to the second vibration mode of the laboratory structure with the geometric controller design approach. Approximately 20-25 dB attenuation in the first and second vibration modes of the laboratory structure were achieved. © 2013 Taylor & Francis Group, London, UK.The authors would like to acknowledge the financial assistance provided by the UK Engineering and Physical Sciences Research Council (EPSRC) through a responsive mode grant entitled “Active Control of Human-Induced Vibration” (Ref: EP/H009825/1), Leadership Fellowship grant entitled “Advanced Technologies for Mitigation of Human-Induced Vibration” (Ref: EP/J004081/1) and Platform Grant entitled “Dynamic Performance of Large Civil Engineering Structures: An Integrated Approach to Management, Design and Assessment” (Ref: EP/G061130/1)

Fuzzy Logic Controller Scheme for Floor Vibration Control

© 2015 Owned by the authors, published by EDP Sciences. The design of civil engineering floors is increasingly being governed by their vibration serviceability performance. This trend is the result of advancements in design technologies offering designers greater flexibilities in realising more lightweight, longer span and more open-plan layouts. These floors are prone to excitation from human activities. The present research work looks at analytical studies of active vibration control on a case study floor prototype that has been specifically designed to be representative of a real office floor structure. Specifically, it looks at tuning fuzzy control gains with the aim of adapting them to measured structural responses under human excitation. Vibration mitigation performances are compared with those of a general velocity feedback controller, and these are found to be identical in these sets of studies. It is also found that slightly less control force is required for the fuzzy controller scheme at moderate to low response levels and as a result of the adaptive gain, at very low responses the control force is close to zero, which is a desirable control feature. There is also saturation in the peak gain with the fuzzy controller scheme, with this gain tending towards the optimal feedback gain of the direct velocity feedback (DVF) at high response levels for this fuzzy design.The authors would like to acknowledge the financial assistance provided by the UK Engineering and Physical Sciences Research Council (EPSRC) through a responsive mode grant (Ref. EP/H009825/1), a Platform Grant (Ref. EP/G061130/2) and a Leadership Fellowship Grant (Ref. EP/J004081/2). Also acknowledged are the British Council (UK) through the Researcher Links programme and Brazilian institutions CNPq and CAPES financial support

Damage detection in concrete precast slabs: A quick assessment through modal tests

© 2015 Owned by the authors, published by EDP Sciences. The use of modal tests for detecting damage in reinforced concrete precast slabs is evaluated. A set of eight slabs were tested, each belonging to flats constructed for residential use. Two groups of slabs were identified and, in each group, both cracked and uncracked slabs were found. This made it possible to compare the responses of the slabs when subjected to modal tests. The tests were carried out employing an instrumented hammer and heel drops as excitation sources. Responses were measured using an accelerometer. The lowest natural frequencies of the slabs could be identified and after filtering the results, plots indicating the variation of the lowest natural frequency versus the number of cycles of free decay were obtained for each slab. Such a plot is of more general use than the value of the natural frequency by itself, as it does not depend on slab configuration. It was observed that the cracked slabs presented a similar pattern of variation of the natural frequencies throughout the decay, being distinctive from the pattern observed for their uncracked counterparts. This provided evidence that a quick assessment of the structural condition of such slabs through the use of the tests were feasible.The authors acknowledge both Brazilian institutions CNPq and CAPES, and the British Council (UK) through the Researcher Links programme, for the financial support for this research work

Dynamic Compensators for Floor Vibration Control

Conference paperIn recent years, active control of flexible structures has been studied extensively. The motivation for continual studies with this approach is that the vibration performance of flexible structures can be improved significantly via control. For example, the performance of civil engineering floor structures, which the present research work is based on, is increasingly being governed by meeting permissible vibration serviceability limits depending upon their respective usages, and this can usually be enhanced via active control. This then offers designers increased flexibility to realise more lightweight, longer span and open-plan floor layouts that are in tune with the advancements in material and design technologies as well as meeting the challenges for reduced carbon footprint of new constructions. The work presented here focuses on active control of human-induced vibrations in floor structures using dynamic compensators. These are formulated from reduced order plant models and vary in complexity depending on the number of plant modes of vibration used for their respective designs. It is demonstrated that there are increased options offered by higher dynamic compensator orders with respect to realising various vibration mitigation performance objectives: for example, the isolation and targeting of specific vibration modes. These compensators are found to possess desirable stability margins and are much less sensitive to disturbances at lower frequencies in comparison with direct velocity feedback (DVF). A study of the robustness of the dynamic compensators designed here to changes in structural properties, for example, that would arise under human-structure interaction is also presented. It is found that the performance of dynamic compensator performance can be sensitive to changes in structural dynamic properties as compared with a direct velocity feedback scheme, as seen in the closed-loop stability properties, which is not so obvious from a study of the disturbance rejection properties.Engineering and Physical Sciences Research Council (EPSRC

Investigation of transmission of pedestrian-induced vibration into a vibration-sensitive experimental facility

This is the author accepted manuscript. The final version is available from Springer via the DOI in this record.Conference Proceedings of the Society for Experimental Mechanics Series book series (CPSEMS)This paper is based on field measurements that were undertaken in a facility housing ultra-low level vibration sensitive equipment. The aim of these tests was to better understand the vibration transmission from an overhead pedestrian footbridge to a pile supported experimental floor and the supported vibration sensitive equipment. The results of experimental measurements to estimate the as-built modal properties (natural frequencies, modal damping ratios and mode shapes) of the footbridge structure are presented as well as response measurements at selected locations on the footbridge and experimental floor from controlled walking tests. These series of measurements indicate that vibrations are transmitted from the footbridge to the experimental floor as well as to the supported equipment. This is verified through transmissibility checks which also indicate that vibrations from the experimental floor are transmitted onto the supported equipment over the frequency bandwidth considered. The assessment of vibration levels using vibration criteria curves for response measurements on the experimental floor and the supported equipment for ambient (quiet conditions) and controlled walking excitations on the footbridge structure are also providedThe authors would like to acknowledge the financial assistance provided by the UK Engineering and Physical Sciences Research Council (EPSRC) through a responsive mode grant (Ref. EP/H009825/1), and a Leadership Fellowship Grant (Ref. EP/J004081/