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An Active Technology for Improving the Sound Transmission Loss of Glazed Facades

Robotics and automation in construction2 State of the art and the innovation provided by asAc systems for glassrly Active Noise Controse control was first introduced by Leug( Leug, 1936), whopresented a patent for a system implementing feed-forward active control of sound induct According to the patent, the sound field is detectedn a duct, resulting in destructive interference of the primary or noisee a feed-backgement was produced by Olson and May(Olson et al, 1953)ntrol system that is basedcting the offendingwith a microphone and feeding the signal back through a controller to a controloudspeaker located close to the microphone They also demonstrated good local reductionConover(Conover, 1955)ced thehich the radiatedmer was monitored and usedthe radiateddue to the use ofnalogue systems, particularly when the physical system was changing relatively rapidly1970s both(Kido, 1975)and(Chaplin et al

1976) began exploring theapplication of digitalprocessing techniques, demonstrating the feasible use of theirdigital active noise control approaches on a number of important applications, such as carexhaust noise, ship exhaust stack noise and active engine mountsActive control of structural vibrationsThe introduction of digital techniezoelectric actuators to vibratiBailey Hubbard (1985) considered feedback modal control of large structures BalasCanavin (1977) discussed feedback damping control of large spacecraft structures, Balas1978)applied theoretical modal control using velocity feed backsimple bearMeirovitch Oz(1980), with later work by Meirovitch and others (e g Meirovitch etwhere a coordinate transformationdecouple a complicated system into a set of independent second order systems in terms ofBaz poh(1988)made modifications to the IMSC method to minimize the effect of controllover(inadvertent localized increases in vibration levels due to constructive interferencecontrol fields) Mcomponents in noisy environments, pilot seat vibrations in helicoptersredoes and submarines23 Active Structural Acoustic Controdvances in active control of structural vibrationsbeen applied to develop analternative control method for enclosed noise fields, known as active structural acoustistructurally-basedon the radiating structure itself in order to minimize radiated sound (Ruckmanuller, 1995: Nelson Elliott, 1995; Fuller et al, 1996) The actuators are vibrationmic patches, etc which modify how a structure vibraltering the way it radiates noise

An Active Technology for Improving the Sound Transmission Loss of Glazed Facadesasymmetric disposal of Fig 7-a, the PZT patch excites the 2D structure with pureat can be simulated with the numerical model dRogers, 1991) It is assumed that the strain slope is continuous through the thickness of theass plate and of the PZT patch,which in turn are assumed parallel to the coordinate axes(the strain slopes are billed Cx andCu, The mathematical relation between strain and z-coordinatef the zhe middle of the plate thickness and e the strain Thetrained strain of the actuator (ep)along plate axes is dependent to the voltage appliedthe actuator thickness ( ta)and the PZT strain constant along x or y directions(d=dy)d vConsidering that the plate isure bending, no longitudinal waves will be excitednd by applying the momentum condition about the centre of the plate along x andn, 1997), assuming that the plate thickness is 2/b, theplate elastic modulus is Ep the actuator elastic modulus is Ep, and ve and vpe are the Poissonnts of the platethe x and y direcilled with mx and my) are present only under the PZT patch, andhe points ofdinates (xi, yn) and(x2, 12)(11eing H(x) the Heaviside function and C-EIK where I is the moment of inertia of the platerthen the equation of motion for plates subject to flexural waves can be writtenwhere p is an external uniform pressure applied on the plate

Eq (11), if written with theactuator induced moment, becomesm(,24m:0(13)oyhere m is the internal platent and m is the actuator induced bending moment; psurface of the plate; w is the displacementchange Assuming that thed substn be calculated by using the modal expansion of (3),which gives backwhere: P"cos(kmx)-cos(kmx2)

Robotics and automation in constructionEquation(14)can be written in terms of ( 3)and (5), defining the variablePpe(k m+k? b(15)Thus, given the properties of the PZt patches undernd theof the plate, (14together with (5)and (3)gives back theal displacehe 2D plated by PZt patch actuators with resped y coordinates, In the case shown in Figthe stack actuator has the task ofa punctual force, instead of a bendingained above, it is possible to calculthat describes the vibration field in terms of ()and(5)exploiting thefollowing relationthe force Fa is applied, that is the action provided by the stack actuator, which is dependentstem stiffness Assuming di the strain constant of the actuator adirection, its unconstrained displacement will be computed beight In fact the real displacement of the stack is lower than (16) because thereaction system has finite stiffness K, and the force effectively exerted by the stack along thed vKstiffness As in the previous case, the transverse vibration displacementof a 2D plate can be calculated by(14)with( 5)and (3)the disturbance is assumed to be a wave with frequency near the frequency of the mode ofvibration(2, 2)of a typical building facades panel, whose effect is compared with the ongiven by the use of the twementioned kinds of actuators The glazed paneIsupposed to be simply supported along the edges The two configurations of Fig 7arestudied analytically

The properties of the glazed plate used for these simulations are listeuencies of vibration are given by(6)results are listed in Tab 3 for the smallemodes; so the frequency of the disturbanal to 78 Hz In the firstFig 7-a, the behaviour of the panel of Tab 1 is simulated when equipped with twe26 patches equally distributed 005 m far from the panel edges

An Activenology for Improving the Sound Transmission Loss of Glazed FacadesEach rectangular shaped patch measures (005 x 004)m Fig 8 shows the distribution of they-l/2 One of the diagrams is referred to the effect due to the disturbancege of 150 v(that is the highest limit for lotvoltage actuators) PZT patches can generate vibration fields far lower than the onerated by the disturbance子手Fig 8 Amplitude displacement along the y=l/2 axis due to the positioning of PZT patchesactuators, normalized with respect to thedisturbance valueFig 7-b In Fig

9 such vibration amplitudes are drawn with depeto the volded to stack actuators, It is assumed that the panelipped with 3 actuators(002 msectional area) per each side, equally spaced and at a 003 mdistance from the two edges; the stiffness of the reaction system is assumed equal to 200N/um, Fig 9 shows that, regardless of the small rigidity of the reaction system, the stackdisturbance witP onlv a voltage of 100 vputuue comparSymbolUnits of mment valueEp Modulus of elasticityde lengthTab 1 Glazed plates propertiesSymboUnits of mvalKg/md31 Expansion constant-0000000000166Tab 2 PZT patch's properti

Robotics and automation in constructionMode FREQl(Hz) Mode Frequency(Hz)(1,1)824(33)Tab 3 Natural frequencies of vibrationVibration amplitude200∈+41Fig 9 Amplitude displacement along the y=l/ 2 axis due to the positioning of stack stiffenedactuators, normalized with respect to thedisturbance valueTherefore, given the high controllability provided by stack actuators, they have beenbeen of theperimental campaign and technologic development carried out in this research

5 the case study: An Active Structural Acoustic control for a window pane51 The components of ASAC System for glazed facadeicrophone This solution seaestheticalthe feedback arrangement is preferred by the authors and detaiThe components of a feedback ASAC system for glazed facades are(Fig 10)rs for detecting vibration(eg, strain gaugeselectronic filters for analyzing signals from sensors in order to check the vibration fieldinduced by disturbanand compute the mostthe actuators levelg secondary actuators on glazed panelsctuators for controlling the vibration field of glazed panels,t kinds of actuattch and stackFor building applications, feasibility and aesthetical considerations suggest thatstack actuators are preferred, as their smaller size interferes less with visibility andtransparency and allow them to be easily mounted and dismantled from glass surface

An Activenology for Improving the Sound Transmission Loss of Glazed FacadesPZTActuwtwr>Fig 10 Layout of the ASAC control system for glazed facade52 The functioning of ASAC System for glazed facadesSignal coming from the sensors is elaborated by charge amplifiers, that convertsignals into physical variables like displacements, velocity and accelerationsdisturbance from the other connected with the action of secondary sources The electronireceiving room and then computes the opportune voltage to be supplied to positions of thecontroller, starting from the error signal, estimates the radiated field in some positions of theorder to reduce the panel's acoustic efficiency

Signal amplifiers provide for necessaryThe optimization of the actuators actions, in order tonumber and the size ofed sensors and actuators, is derived froalgorithms implemented inthe controller like the onented in (Clark Fullesed on the quadratic linearthe determination of actuator size and location and the second to sensors In both parts, thutes the yreduce glasshile the rest ofdefines the best actuators configu53Tholution developed as test-caseof the stiffener, according to its position on the glass surface, may also determineterference problewith the aearance of the glass panel whichdisregarded First of all, in order to minimize the radiation efficiency of the vibrating glaface, the correct positioning of stack actuators has to be studied Two are the possible

Robotics and automation in constructionby decreasing the vibratede of flexural waves(Fig 11-a)y changing the original vibraorder to obtain a vibration field where onlv evenmodes dominate( Fig 11-bFig 11

Reduction of theIn the first cashoulddle in thehe alternatives listed corresponds a different positioning of actuathave to be installed in the points where maximum vibration awhile, in the second one, theyalong the border lines, with lessglass panel's appearance Starting from thossible technological solutions are depicted(Naticchia and Carbonari, 2007citicthe centralusually characterized bamplitude vibrations, and stiffened by a metal profile(approach 1)b stack actuators installed alongrder of the panel and stiffened brofile(approachstack actuators placed close to the borded stiffened witht reactiapproach 3)b)Figsuggested for the installation of actuatorsFurtherals for technological solhave been advanced, where the actuatoreaction system directly attached to the glas surface for thisof two different kinds of metallic profiles have been hypothesized: in Figcircular-shaped profitrasting a stack actuator is depicted in a 3-D view and a

An Activenology for Improving the Sound Transmission Loss of Glazed Facadescross-sectionFig 13-b represents a similar solution realized with a z-shapedrofile bothes seem to be advantageous fromnce with visibility through the glass, and should be studied relativeprofile characteristics and to the stress induced in correspondence of the connection poibetween the same profile and the glass panea-1: 3D view a-2 Sectionb)Fig 13 Further hypotheses of point reaction systems: circular-shaped profile(a-1; a-2): Z-and discussed in this chapthe effectiveness of the purposed technology over the limits imposed by the choice of onestack actuator, stiffened by a mass, realized with a cylinder of metallic material overlappedd connected to the free extreme of the actuator, as will be detailed in paragraph 6

26 Experimental analysisIn the following paragraphs, the results of experimental ancarried outto evaluate acoustic improvementgested activecontrol technology will be presented(Carbonari and Spadexperimental prototypehas been simulated with a 017, Kg weightedreme of theactuator(Fig 15-e and 15-f)61 Theg of the experimental prototypearding the realization of the prototype was the simulation of a simply supportingndary constraint: ittion of two cylindricalbetween the glass panel and the two window frame profiles,guaranteect between the glass and the Teflon bars The wlthe influence of external actions on the glass's vibrations, establishing the simplestpoint grid was defined on the panel, in order toentity measurement marks

An Activenology for Improving the Sound Transmission Loss of Glazed FacadesIn 1990 Jones and Fuller proposed an initial work where electromagnetic shakers were usedtrol inprploitedicrophones placed in the cylinder interior, such that interior soundhe control ofctural vibration Thisnstrated thatin general, fewer control actuators are required by the ASAC approach as compared to ANC( Acti

ve Noise Control)techniques Also, control spillover in the interior acoustic space waswhere only the few dominant radiating modes are reduced in amplitude Other structurales that are poorly coupled with the noise field may be left unchanged by the controlSimpson, et al (1991)performed control experiments in a test section comprising the aftrtion of a furnished DC-9 aircraft Using a typical feed-forward controller arrangementconfigurations of 7 error microphonesBecause point forcesspectrally whiteontrolling forcesSAC work can lead to undesired spillomany structural vibration modes In seekingcontrol actuator with more distributed forcing properties, mresearchers recentlyivestigated the use of piezoceramic materials for applying bending moments or in-planetitanate(PZT) materialshave been widely used in ASAC work, providing sufficient forcing capabilities with thebenefit of greatly reducedd space requirementsused ancylindrical test section withdirectly to the cylinder surface and the system was acoustically excited with an exteriorloudspeaker neUsing two miethe ASAC systemprovided global attenuations on the order of 10 dB in the cylinder interiorRecently, ASAC testsselage, a typical mid-sized business jet In thebutge gldB was measureddditionalhones Controhe off

gnificantly reduced, with reductions of 2-10 dB at the error seSome past work has addressed actuator position optimization via analyticalal, 1992; Wang et al, 1994; Burdissfinite element model has shown the importance of position optimization to glolperformance, made by (Yang et al 1995)Spatially averaged reductions of acousgy of up to 14 db have been predicted using 16 optimally-located point forces, whileresult in overall global sound increas2 4 Active Noise Control in glazed enclosuresTo the authors knowledge, no ASAC application has been performed on glazed structuresOther works by(Kaiser et al, 2003)suggest an ANC approach through the positioninginside air cavities; and(Zhu et al, 2004)place monitorisors outside windows Instead, most of the recent research was developed to verify theperformances of the control provided by PZT patch actuators on opaque surfaces, both forbuilding walls and for helicopter and airplane envelopes: in the

Robotics and automation in constructional, 2003)and(Bao and Pan, 1997) it is shown that using ANC control systems for doublhichanels Preliminary results in Wenli(2001)show that PZT laminated(multi-layer) patchesubstantially with the primal function of the window, namely to look through it, they mayt be considered an option5ovided by the proposed ASAC systemhis chapter proposes an original approach foruant the problif considerably reducedred to thelaminated patch actuatorsThe application of ASAC systems on glazed panels is particularly critical, as there are nns of efficientlyall the acoustic spectrum, as will be explaineparagraphn in thef 1500 to 6000 Hz whilef1500 Hz theSound Transmission Loss remains significantly low Furthermore, the double glazingapproach provides appreciablereduction just in the frequency range above 500 Hzof the ASAC technology seems to be the only one capable of increasingglazed facades STL over all the acoustic spectrum In thisrnal facades, even in very harsh areas, such as in proximity ofrts, railwds

Additionally, the problems connected with the applof actuatorsparent facades will be tackled for the first time3 Adoption of active means for controlling acoustic and vibration behaviour31 Adoptioctive means for STLonsidering that for buildings, the main type of disturbingered glass prodinances that dramatically decrease its STL Above thelaw of acoustics and is dictated by theof glass Hfrequency at which the speed of incidenttches thatglass bending wave and acoustic waveffective at causing glavibrate, which makes the vibrating glass an effradiator at that specific frequency and above As a result, the first critical point for a singleass panel is in corresuntil the critical effect causes another drop of STL, due to the matching betwhe wavelength of flexural vibrations propagating through the glassfficiency of the glass panel The latter effect may be solved through the adoption of

An Activenology for Improving the Sound Transmission Loss of Glazed Facadesth pvBall flexural stiffness olaminated panels, shifting up the critical frequency (fc), out of the audible range, But nprovides an ayof Stl (mer in the middle freg between the two glass panelsnd theposition depends on the thickness and typol34) An illustrative example from measurements is presented in FtHarris, 1994): three double glass panelsmpared in ordereven if the air layer is further widened, the low frequency STL is still lep which persists even if a much higher air thickness equal to 005 m is providedSound Transmission Loss for several glass panelsFig 1

Sound Transmission Loss curves for single, double and laminated glass panels(a); thefor double glass panels(bthat traffic noise levels are usually very high in the low frequ(IMAGINE, 2003), it fethat other solutionsrequiredbuildings(as illustrated in Fig 2)導品網需導器器號2 Equivalent omni-directional sound power level of road traffic noise as function of a

Robotics and automation in construction987)and they are induced in plates by external disturbances, itanalyticallydescribe the flexural respaimply supported plata harmonic excitation ofbitrary distribution like f(x, y, t)=F(x,y) elot (where a= 2mv, v is the excitation frequency,F(x,y) is the excitation amplitude), obtaining the equilibrium model introduced byKirchhoff-Love(Timoshenko and Woinolowsky-Krieger, 1959ax+ ax2ay2 ay#lutions of eq (1)for the formalization of the transverse displacementobtaineddescribing it as the superposition of infinite modes of the free response of the plate, which isvibrating at the forcing frequencyde(m, )on the plate, while the exponential term is aimed at describing the dependenceth the timethe influence of disturbing frequency Io study theersaldisplacement motion of a plate whose side lengths are a and b, it is necessary to compute thedisplacement distribution field given by an incident plane wave Eq

(2)is generallyapproximated in another form, which considers only the superposition of a finite number ofby the combination of two finite numbersthe approximation is dependent on the choice of these twe2 Thus the displacementdistribution is given by(Fuller et al, 1Substituting eq (3)in eq (1)we can find the solution ason,

An Activenology for Improving the Sound Transmission Loss of Glazed Facadesussos,1985)an analytical solution for the generic case of a planeimply supported plate, like in Fig 3, is detailedFig 3 Angles individuating the direction of incidence of an acoustic plane wave into aglazed plate4 The41 Active Structural Acoustic Cches by Leug's patent in 1936 and (Olson May, 1953)are the firstANC feed-feontrol, when prior knowledge of the noiseobtained with aneam microphone, and ANC feed back arrangement, where the detection microphone isclose to the active secondary source respectively

Both approaches relate to the main conceptof ANC, and hold its drawbacks: when applied to buildings' glazed facades, they need aexternal microphone for disturbance monitoring, and internal error sensors andspeakersthis reason some attempts at inserting all the systemtoo difficul t in thetheir narrow air laherefore, the ASAC system should be preferred for this kind of application, because bothand actuators are placed on the same glazed panelquired for thelementation of a feedback controller Fig 4-a and fig 4b resirward and feed-back arrangements of an ASAC configuration for glazed facades controIn both cases, actuators are positioned on the vibrating surface, which is theose vibratiits finaI stLasac does not require the use of loudspeakers ormicrophones in the receivingt,however optimum positioning ofand PZT actuators on the vibratingurface must beconclusions: only the most efficient meneed to betrolled rather thanthe relative phases and amplitudes of multi-modalponse can be adjusnterfere destructiveThe feed-forward control of Fig 4-a requires knowledge of the primary disturbance, whichunpractical, because it would require the installation of a microphone on the exterior of the

Robotics and automation in constructionindow which for functional and aesthetic issues, is not feasible Therefore, the feed backype controller depicted in Fig, 4b seems to be opportune and is detailed subsequentlyFig 4 Feed-forwarda)and feedback(case b) ASAC systems for glazed facadis based on the reduction of structura(transmitted and reflected)assurfaces ASAC can be easily integrated into buildings, as it dtheudspeakersnones in the receivinglust be elaborated by chargend accelerations), and electronic filters thattaskto separate the contribution to the total vibration field due to the primary disturbanceto compute the radiated field in some positions of the receiving room, to calculate the(difference between reference value and actual value of the radiated neThe controller, starting from the error signals, computes the opportune voltage to bepplied to thehose electric power is provided by the amplifiersgorithm calculates the controgeneral, it has the task of changing the distributed mass, stiffness and damping of thethe internalent, determined mainlyes which need to be decreased by the control plant for thn

thecomplexity of the algorithm derives from the fact that reference and control sensors apositioned at the same place, therefore electronic filters are necessary The controller musttrol is thetable for ASAC systems: it has the advantage that the choice in theprescribed change of the dynamic properties is motivated by its aim to reduce structuralradiatedparameters directly minimizing a cost function of performance which is proportional to theired methe system' s response For the sake of computational efficiency, itenient to definfunction that is quadratically dependent on the response,amplifying the optimization problem One of the possible solutions can be the one proposedby(Fuller et al, 1997), where the cost function is given by

An Activenology for Improving the Sound Transmission Loss of Glazed Facadesbeing the totalair; Pi thepointbut computed from the signals deriving from the refer(through the use of filters) Thus, the structural-acoustic coupling is inherent in thedefinition of the cost function It was demonstrated by(Fuller et al

, 1997)and(NelsonElliott, 1992) that substituting the opportune expression of radiated sound pressure, givenmFig 5 Scheme of an ASAC system for glazed panels integrated in buildingsby the superposition of thentributions of both the disturbance and thethe cost function is scalar It can be converted into a quadratic expreand itdemonstrated that this function hasuThe generalto be minimized becomesnput disturbances, h is the vector of transfer functionsassociated with these dces: c is the control transfer function vector and w is theOnce the transfer functions between the reference signal deriving from referencediated noise is known for aystem, the control plant will automaticallyexecute all these steps, minimizing the radiated noisependent input disturbances, giving back an automated glazed facade, that actively changesting this control system, it issary to calculate the control transfers,which requirereliminary stage, thehoice of the opportune kind of secondary sources, carried out in theHowever, the analytical modela series ofimplifications, which appear difficult to apply in terms of the actual situations that one caome across in the building field

Robotics and automation in constructionsimple support boundary constraints, whereas in fact, constraint situations are moremore similar to afixed or yielding joint;pplications of only point forces, without the association of mathe realwhen controffected through theactuators contrasted by stiffeningstructuresGiven the above considerations, it has been established that the nuheory of Kirchhoff-Love, willtituted by a model buprogramsABTM), which allows overcoming the simplificationsd to the analytic modelPiezoelectric actuatorTwo main types of actuators, suitable for glazed facadely marketed( Fig 6)Piezoelectric(PZT) patch actuators providing bending actions to excite structures;PZT stack actuators providing point forces to excite structuresFig 6 PZT patch(a)and stack actuators for glazed facades(b)The first type is usually bonded to a surface while the second needs a stiffening structure tofix it and make it transfer follingpable of generating hightony applications, however they have not been tested in applications on glazed facades,nd most of the experimentsin the automotive and aeronautic fields ofresearch

As far as concerns the choice of actuators, the first rectangular shaped patch mainterfere with visibility(Fig 7-a); the stack one instead is very small but needs a stiffener inperly(Fig 7-b)Fig 7 PZT patches(a)and PZT stack actuators(b), as applied on a glass