Isolating Damping Tuning. Spring Devices. Viscoelastic Dampers. Elastomeric Devices. Tuned Mass Dampers. Active Damping Devices

Transcription

1 Isolating Daping Tuning Spring Devices Viscoelastic Dapers Elastoeric Devices Tuned Mass Dapers Active Daping Devices

2 2 For each vibration proble the optiu solution!

3 Content Technical bacground Vibration control principles Isolation Daping Dissipation De-tuning Energy transfer to a coupled oscillating syste Absorption Active vibration control Spring devices Viscoelastic dapers Elastoeric devices Tuned ass dapers Active daping devices Plant engineering Seisic protection Daping Spring devices Elastoeric devices Viscoelastic dapers Tuned ass dapers Active daping devices Hydraulic devices Shoc transission units Bridge bearings Isolating Railways VICODA solutions provide: SafeTY for personnel, facilities and environent AVAILABILITY for plants, installations and construction LongeVity for the aortization of investents Buildings Tuning Bridges 3

4 Technical Bacground Fig. F I F D F E = inertia force [N] = daping force [N] = elastic force [N] F(t) = excitation force [N] x ẋ ẍ d t = displaceent [] = velocity [/s] = acceleration [/s²] = ass [g] = stiffness [N/] = daping paraeter [N/(/s)] = tie [s] Haronic excitation force F(t) = F 0 sin(2πf E t) = force aplitude F 0 Natural angular frequency [/s]: ω 0 = Natural frequency : f 0 = 2π = 2π ω 0 f E x = excitation frequency Frequency ratio []: η = ω E ω 0 = f E f 0 Modal daping ratio []: d D = 2 ω 0 d F(t) Basic physical odel Systes with vibration probles often are very coplex. However, ost of the fundaental effects ay be discussed using a siple syste with only one degree of freedo. Coplex systes can be transferred into a set of these siple systes (odal reduction). The basic odel for an excited and daped oscillator with one degree of freedo is shown in Fig.. An external force F(t) acts on the ass that is connected to a spring with a stiffness. The resulting otion of the ass is daped due to a daping device with a daping paraeter d. Starting fro the equilibriu of the acting forces in the syste F I + F D + F E = F(t) the differential equation describing the otion of the ass is given by ẍ + dẋ + x = F(t) In case of no external excitation but an initial displaceent of the ass leading to an elastic force of the spring, the solution of the equation describes a free, daped oscillation the ass oscillates with its natural angular frequency ω 0 i.e. its natural frequency f 0. In case of a sinusoidal (haronic) excitation force with a frequency f E the change in axiu displaceent of the syste (aplitude aplification) is given by V = ( ( f E f0 ) 2 ) 2 + (2D f E f0 ) 2 = ( η 2 ) 2 + (2Dη) 2 For slow excitations (f E 0, η 0, f E << f 0 ) the syste response is quasi-static i.e. the otion of the ass directly follows the excitation force. There is practically no increase of the aplitude of the oscillation copared to the static displaceent (Fig. 2). For excitations with high frequencies (f E, η, f E >> f 0 ) the syste cannot follow the excitation force. Therefore the aplitude of the oscillation is reduced and approaches zero (Fig. 2). If the frequency of the excitation force f E is close to the natural frequency of the syste (η, f E f 0 ) the otion of the ass is increased significantly. This effect is called resonance. The increase of the aplitude is depending on the daping paraeter of the syste, creating different aplitude aplification functions for different daping paraeters (Fig. 2). In general the aplification function can be divided into two areas. For η > 2 the aplitude is always reduced even without a daping eleent this area often is called isolation area. The odal daping ratio D describes the daping in a syste. In case of a vibratory syste as shown in Fig. without external excitation but an initial displaceent and D = 0 the ass will continue oscillating lie in an undaped syste, D the syste will be strongly daped so that the ass will return to its rest position without any overshoot, Aplitude aplification V 2,5 2,5 0,5 No daping Isolation D = 0% D = 30% D = 50% 0 < D < the ass will oscillate with a decreasing aplitude and finally coe to rest. Fig Frequency ratio η 4

5 Vibration control principles In order to control the effects of unwanted vibrations in plants, achines or structures in general there are the following fundaental principles:.) isolation 2.) daping Dissipation 3.) de-tuning 4.) energy transfer to a coupled oscillating syste Absorption 5.) active vibration control ISOLATIon In case of vibration control by isolation it is avoided that energy fro the source of vibration (exciter) is transferred to the vibratory syste. Due to the reduced energy transfer the vibratory syste will oscillate with a saller aplitude copared to the non-isolated situation. A good and siple odel to discuss vibration isolation is given in Fig. 3. The odel describes a daped oscillator with base excitation i.e. an induced otion of the base that was considered fixed in the odel described in Fig.. The differential equation describing the otion of the ass is given by ẍ + dẋ + x = dṡ + s = F(s(t)) In case of haronic base excitation s(t) the solution of the equation is very siilar to the results discussed for the basic physical odel above. The aplitude aplification function is given by V = + ( 2D f E f0 ) 2 ( ( f E f0 ) 2 ) 2 + 2D ( f E f0 ) 2 Lie in the basic physical odel the aplitude is significantly reduced for high frequency ratios η or f E >>f 0. The syste can be considered isolated fro the base exciting. However, in cases where the frequency f E of the base otion is close to the natural frequency f 0 of the vibratory syste there will be resonance. In order to achieve isolation in this case a soft coupling has to be introduced between the syste and the base as shown in Fig. 4. In fact the vibration proble is now a proble with two degrees of freedo as a second syste has been introduced. However, if the stiffness is uch saller than the stiffness of the original syste i.e. <<, the two asses * and can be considered as rigidly connected. Therefore the odel can be siplified to the odel shown in Fig. 5. The natural frequency f 0 of the siplified syste is defined by the total ass = * + and. For a good isolation the coupling has to be defined in a way that the resulting natural frequency f 0 is uch lower than the excitation frequency f E of the base otion. The aplitude aplification function of the siplified syste has its axiu at the new natural frequency f 0 (Fig. 6). Copared to the original syste the aplitude aplification (Fig. 6) can be significantly reduced. Isolation is a very effective way to avoid unwanted vibrations, as energy transfer fro the exciter to the vibratory syste is syste - atically prevented. However, in order to apply isolation as an approach to control vibrations it is often a prerequisite to consider it during the design of the syste, e.g. during the design of a achine or a building and its foundation. A later ipleentation of an isolation solution to reduce unwanted vibrations is often costly. Aplitude aplification V Fig. 6 2,5 2,5 0,5 0 ' f 0 ' >> ' Frequency f E Fig. 3 s ṡ x s Fig. 4 Fig. 5 x' s ' ' = displaceent of base [] * ' d = velocity of base [/s] x s ' = + * f 0 ' = η' = 2π f 0 ' f E ' ' d d' Paraeters of coupling syste: * = ass [g] ' = stiffness [N/] d' = daping paraeter [N/(/s)] d' 5

6 DAMping DISSIPATION Fig. 7 x x d' > d d d' F (t) F (t) In case of vibration control by daping energy fro an oscillating syste is dissipated by a daping eleent (Fig. 7). In contrast to isolation here the syste is excited first i.e. there is an energy transfer fro the exciter to the vibratory syste. Within the daping eleent a portion of inetic energy of the vibration is converted into another for of energy lie heat, thus reducing the aplitude of the oscillation. Daping is only an effective ethod to reduce vibrations in the range of the syste s natural frequency f 0 i.e. around resonance (Fig. 2). By increasing the daping paraeter the aplitude of the syste in that area can be significantly reduced. The related change of the aplitude aplification function is shown in Fig. 8. Daping eleents have to be designed in a way that they efficiently dissipate energy in that frequency range. Other than in the case of isolation daping can often be applied as a retrofit easure to control vibrations. Viscoelastic dapers are a typical exaple for a daping device that can easily be added to e.g. an installed piping syste. Aplitude aplification V Fig. 8 2,5 2,5 0,5 0 f 0 d < d' Frequency f E De-tuning Fig. 9 x x ' F (t) d f 0 ' > f 0 F (t) ' d f 0 = f 0 ' = 2π 2π ' ' The basic characteristics of a vibratory syste are defined by the oscillating ass, the daping as well as the elastic properties of the syste. In case of an excitation around the natural frequency of the syste, i.e. around resonance, the resulting aplitude of the oscillation is specifically high (Fig. 2). When changing the size of the oscillating ass or the elastic properties of the syste the natural frequency of the syste will change as well (Fig. 9). By that change it can be achieved that the nat ural frequency of the syste and the exc it ation frequency are no longer in the sae range i.e. the syste is no longer in resonance for the given excitation frequency and the apli tude of the oscillation is reduced. In fact the aplitude aplification function will shift depending on the natural frequency (Fig 0). De-tuning can be done by changing the ass or the typical approach by stiff - ening the syste i.e. increasing the stiffness. Obviously with the new natural freq uency resonance will occur at another excitation frequency. Therefore it has to be ade sure that the new natural frequency is not atching any other possible excitation frequency. Lie daping de-tuning can be applied as a retrofit easure. However, sig - nificant de-tuning is often only possible in a narrow frequency range as Aplitude aplification V Fig. 0 2,5 2,5 0,5 0 f 0 f 0 ~ f 0 ' = f 0 ' 2π ' ' > f 0 = 2π Frequency f E 6

7 Energy transfer to a coupled oscillating syste ABsorption A special way of reducing the aplitude of an oscillating syste is to couple it to another vibratory syste, the tuned ass daper (TMD), and tune the characteristics of this coupled syste i.e. its ass, daping properties and stiffness so that it efficiently gets energy transferred fro the original syste (Fig. ). original syste. The daping eleent of the TMD, e.g. a viscoelastic or eddy current daper, allows the use of the TMD in a wider frequency range. TMDs often are a good retro fit easure, as they can easily be ounted on vibrating structures without any abutent. Fig. d F (t) x As a result the TMD will oscillate while the vibration of the original syste is significantly reduced (Fig. 2). Vibration energy of the original syste is absorbed by the tuned ass daper. Passive TMDs are to be designed in a way that they efficiently absorb energy fro the original syste when it is oscillating at its natural frequency. The level of absorption depends on the initial daping of the Aplitude aplification V Fig Syste without TMD Syste with TMD f 0 Frequency f E ' ' d' d F (t) x Active vibration control Fig. 3 F (t) x A very special and unconventional approach to control vibrations is to couple an active syste to the original syste (Fig. 3). These active systes are equipped with sensors and actuators and can counteract the oscillation of the original syste. By superposition of the vibrations of both systes the initial vibration of the original syste can be significantly reduced. Different fro TMDs active devices can be adjusted to changing excitation frequencies. They are also a good retrofit easure e.g. for vibration probles in piping systes, as they can be easily ounted onto the piping syste and significant vibration reduction can be achieved with only little ass ' of the active syste. x' ' F (t) x ' d' d d c b c With all the above ethods unwanted vibrations can be controlled and significantly reduced. The design of the best solution is an optiizing tas for the VICODA engineers. Due to the coprehensive portfolio of vibration control products lie spring eleents or elastoeric bearings for isolation, viscoelastic dapers for daping, spring eleents or rigid steel struts for de-tuning, TMDs or active devices, they are not liited to a certain ethod to solve a vibration proble but can choose the optiu solution and support it with the optiu products. a Actuator b Controller c Sensor 7

8 SPRING DEVICes Isolation Spring devices are the prototype product to isolate a vibratory syste fro a source of vibration. They are to be positioned between the syste and the source in order to iniize the energy transfer fro the source to the syste. The natural frequency of the vibratory syste f 0, defined by the spring devices and the load they carry, has to be designed in a way that it is significantly lower than the ain natural frequency f E of the vibration source. Field of application Spring devices can be used for solving a wide range of vibration isolation probles. A typical industrial application is the base isolation of heavy duty achinery lie presses or forge haers. In power plants spring devices are installed to isolate coal ills, gas- or diesel engines, turbines, pups or condensers. Copressors or big fans are other exaples where the isolation with spring devices avoids that the vibration induced by this equipent the source of the vibration is transitted to the environent (isolation at source). Spring devices can also be used to isolate a vibratory syste against vibrations induced by the environent (isolation of recipient). Exaples for this are the base isolation of precision equipent or structures lie buildings against vibrations induced e.g. by traffic. In any case base isolation with spring devices is a state of the art approach to reduce the effects of unwanted vibrations thus allowing: protection against shocs and continuous excitation for an, achines, structures and building control of operational vibrations within the adissible liits reduction of wear and tear of achines, equipent and structures. As a consequence, with a good base isolation concept for e.g. a big hydraulic press, the foundation of the achine ay be designed in a significantly lighter way (Fig. 4). This concept allows the installation of vibrating equipent in alost every location and it allows to considerably reduce the cost of the foundation itself. Fig. 4 - Different base isolation concepts for a hydraulic press The above exaple shows that the range of applications of spring devices is big and so is the related product portfolio. 8

9 Design The basic design of a spring device consists of a set of helical coil steel copression springs connected to a top and botto plate (Fig. 5). These plates are fixed to the vibra t- ory syste and the vibration source through different anchor systes or by screwless fastening. For screwless fastening the spring devices ay be fitted using adhesive pads that in addition allow the decoupling of the syste fro structure-borne noise. Springs The springs are the core eleents of a VICODA spring device. Being an affiliate of LISEGA, the world aret leader for pipe supports, VICODA benefits fro LISEGA s ore than 50 years of experience in the design and anufacturing of spring based constant and spring hangers. The full portfolio of standardized, high quality LISEGA springs is available for VICODA s design engineers. However, to coply with all the typical requireents of base isolation additional standardized springs were added. Over tie especially under higher loads and at higher teperatures the stiffness of conventional helical coil springs ay decrease (spring relaxation). In order to avoid any negative effects due to that effect VICODA uses pre-relaxed springs guaranteeing the constant functionality of springs over their lifetie. In order to ensure high quality corrosion protection VICODA springs are given a special surface treatent based on a cathodic iersion process (CIP) that was adopted fro autootive industry: first the peeled surface of springs is steel ball blasted and then zinc-phosphated, subsequently a 2-coponent epoxy resin coating is applied by electro-iersion and burnt in at ~200 C. In order to cover the wide range of applications VICODA has developed a odular approach for the design of spring devices using a liited nuber of standardized springs. As discussed in the technical bacground the natural frequency f 0 of a vibratory syste is given by f 0 = 2π Applying this to the syste defined by the spring device and the ass it carries, it can be concluded that the natural frequency of the syste is directly depending on the spring copression (travel) due to the weight of the ass (dead load): f 0 = 2π = 2π g x 2 x Therefore, only by checing the travel of a spring device at dead load the natural frequency of the syste can be deterined (Fig. 6). For good base isolation this natural frequency has to be significantly lower than the ain frequencies of the vibration source. x[] x f Fig. 6 - Travel of a spring device at dead load and the resulting natural frequency a b c Fig. 5 a Top plate b Helical coil c Botto plate 9

10 Fig. 7 - Spring device type SL Fig. 8 - Spring device type SM Fig. 9 - Spring device type SH Daping Eleents In general spring devices only have very low daping properties due to natural aterial daping of steel coponents. Whenever higher daping characteristics are needed, viscoelastic daping eleents can be integrated into the spring devices. Typical exaples for the need of higher daping characteristics are ipulsive excitations as induced e.g. by forge haers. In this case a daping eleent is needed to quicly convert the significant inetic energy of the haer into heat thus rapidly stopping the otion of the haer. Another exaple is the existence of dif fe r- ent operational conditions of the vibration source leading to changing frequencies f E, e.g. during rap-up of a turbine. Starting fro a rotation frequency of 0Hz the turbine will accelerate up to its continuous operational frequency. As a base isolation spring device is designed in a way that the vibratory syste has a natural frequency that is lower than the continuous operational fre q uency the syste will be exposed to frequencies close to its natural frequency f 0 during the rap-up phase. In order to avoid significant resonance effects during that phase a safety daping eleent has to be added. In this case the energy to be converted into heat is significantly saller than in the case of the forge haer. Preloading and locing of spring devices An iportant feature of spring devices is the function of locing the at any spring copression (Preloading). Preloaded spring devices are installed in a loced position by that acting as solid supports. At the end of the installation which ay be the in s t- allation of heavy achinery or the erection of a building the spring devices are activated i.e. they are unloced. Fro that oent on the devices act as vibration control eleents. This feature of spring devices allows for an easy adjustent or aintenance, as it is not necessary to lift the supported achine, structure or building. For any alignent, aintenance or replaceent of spring devices without that feature it is indispensable to first lift the supported achines or structure leading to significantly higher related cost. Basic types of spring devices VICODA spring devices are designed based on a odular approach allowing for costeffective anufacturing and quic delivery ties. The fundaental types of VICODA spring devices are: Spring devices without daping eleents type SL The design of these spring devices consists of a set of springs connected to a top and botto plate (Fig. 7). By cobining VICODA standard springs these devices allow an optiu adjustent of the natural frequency of the vibratory syste and by that effective base isolation for a given excitation frequency of the vibration source. Spring devices with safety daping eleents type SM Different fro the spring devices of Type SL, the springs of the devices of type SM are ebedded in a highly viscous fluid (Fig. 8). This adds a safety daping characteristic to these devices. Spring devices with viscoelastic daping eleents type SH These spring devices provide a visco - elastic daping eleent (Fig. 9) coparable to the standard VICODA viscoelastic dapers. These daping eleents allow a significantly higher daping than the safety daping eleents. 0

11 VICODA spring devices are available with or without the feature of preloading. All spring devices are delivered with high quality corrosion protection in line with international standards. For extree operational conditions VICODA can provide adequate special surface protection using its surface treatent center. Configuration of spring devices The basic paraeters needed for the definition of a base isolation solution with spring devices are: the load [N], given by the weight of the supported achine, structure or building and the load distribution, the ain excitation frequencies of the vibration source, Testing, installation and aintenance All VICODA spring devices are subject to a final test before shipent. LISEGA, VICODA s parent copany an experienced designer and anufacturer of dynaic and static test stands, has provided all the now-how for the related test equipent and processes. Installation of spring devices can be supported and supervised by experienced VICODA service personnel. Due to the high quality of the spring dev ices they can be considered aintenancefree in case of noral operating conditions and the typical lifeties of the supported structures. However, when equipped with daping eleents a visual inspection every 0 years is recoended. For these aintenance inspections, for replaceents in general and for any ind of base isolation related trouble shooting the VICODA experts are available. operating teperatures [ C] in case of daping eleents, installation diensions [] and geoetrical liitations. Even though the definition of the general solution is rather siple the any cobinations of different nubers of standardized springs and daping eleents ae it hard for a non-expert to define the optiu solution for his specific proble. That is why VICODA engineers are available to help you configure the optiu solution using the VICODA odular syste. If and to what extend unwanted vibrations ay affect a syste can be deterined at a rather early stage in new built projects. As good base isolation can reduce the stress on a structure significantly, the structure itself ight be designed in a uch lighter way. Therefore an early discussion of your proble with VICODA engineers and their early involveent in the process can help you to identify cost-effective overall solutions. Assebly of spring device - type SM

12 Spring Devices Types SL, SM, SH Standard springs The standardized VICODA spring portfolio covers ost of the typical applications of base-isolating spring devices. Typical natural frequencies of the isolated syste consisting of the spring device and the supported achine, structure or building are in the range of up to 8Hz. By cobining a set of standardized VICODA springs in a device an optiu device for a vibration isolation tas ay be configured. Starting fro the given dead load of the syste the set of standard springs has to be chosen in a way that the total stiffness of the device will create the intended natural frequency. As discussed the total stiffness of the spring device, its travel under dead load and natural frequency are lined. The standardized VICODA spring devices cover all the typical applications as shown in Fig. 20. As an exaple when using a spring device of type SL , consisting of 2 standard springs with a total stiffness of 47.76N/ to support a syste with a dead load of 955N, the syste will have a natural frequency of 3.5Hz and the travel under dead load will be 20. Another option to carry the sae load can be the use of spring type SL which will provide a natural frequency of 2.8Hz. For even higher isolation, spring device SL can be used, ensuring a natural frequency of 2.46Hz. In ost of the cases there will not be one single device to support and isolate a syste but a set of spring devices. In this case of course the natural frequency of the syste will be defined by the totality of spring devices used. In order to find the best solution to a given vibration isolation proble an optiization has to be done with regard to the nuber of standard spring devices and the type of standard spring devices i.e. the nuber of springs used per device. As the nuber of possible cobinations of standard springs and standard spring dev - ices is rather high VICODA engineers are ready to help you with the identification of the optiu solution. Based on the general configuration paraeters defined on page, they will configure a solution using the odular VICODA spring device portfolio based on standardized springs. Natural frequency Load [N] SL SL SL SL SL SL Fig Standard VICODA spring device specifications and selection of device SL Spring travel []

13 The odular VICODA spring device portfolio is optiized with regard to anufacturing thus allowing quic delivery ties and cost effective production. As a prerequisite for that the coplete technical docuentation including design and production drawings, bill of aterials, special certifications as well as custoer docuentation is ade available in the VICODA IT systes. As an exaple the typical technical datasheets for spring devices of type SL 02, SL 07 and SL 08 are shown in Fig. 2. Fig. 2 3

14 VISCoelastiC DAMpers Daping DISSIPATION Viscoelastic dapers reduce vibrations by converting inetic energy into heat thus daping the otion of the syste. Daping, as a ethod to reduce unwanted vibrations, is ost effective in cases where the vibratory syste is excited with a fre - quency close to its natural frequency. VICODA s viscoelastic da p ers are designed in a way that they can be used in a wide frequency range. Field of application Viscoelastic dapers ay be used to solve very different vibration probles. A typical exaple is the daping of operational vibra tions in an industrial piping syste e.g. in a power plant. Whenever the piping sys - tes cannot be isolated fro the source of vibration, daping ight be an adequate easure to reduce the otion of the piping to an acceptable level. Another exaple is the daping of shoclie forces induced e.g. by a large forge haer. In this case the daping device needs to absorb a significant aount of energy in a very short tie, so that the syste coes to rest as quicly as possible allowing the start of the next operation of the haer with iniu recovery tie. Viscoelastic dapers ay also be used together with spring devices e.g. for the base isolation of a saller diesel engine foundation in a power plant (Fig. 22). During start-up, the engine will continuously increase its speed up to the operational frequency. Spring devices are designed in a way that at operational frequency the surroundings are well isolated fro the vibration of the rotating achine. In fact the natural frequency of the syste consisting of engine, foundation and spring devices has to be uch lower than the operational frequency. Therefore when starting up the turbine it will increase its frequency fro zero to the operational frequency thus passing the resonance range of the syste around its natural frequency that is where it needs a viscoelastic daping eleent to dap the otion of the syste. Unfortunately soeties dapers are pr o - posed as an alternative to shoc arresters (snubbers). The typical function of shoc arresters is to ae sure that echanical connections are protected in case of shoclie forces acting on these connections. Therefore these devices have to provide a rigid lin parallel to the connection to be protected that can transit these forces instead of the connection. An exaple for this is e.g. the connection of a stea gen - erator in a nuclear plant to the piping that ust be protected in case of a seisic event. Here viscoelastic dapers are not the right choice to protect the connection as they do not provide the necessary rigidity with the nec essary reaction tie. Fig Diesel engine supported by spring devices and viscoelastic dapers 4

15 Design VICODA viscoelastic dapers consist of a etal housing that is filled with a viscous fluid (Fig. 23). The piston which is connected to the top plate can ove in all directions within the housing (Fig. 24). Either top or botto plate of a VICODA viscoelastic daper can be connected to the vibra ting syste. The respective other plate has to be ounted on a rigid abutent. Because of this viscoelastic dapers do not statically support the syste that they are conn ected to, but they allow that by ove - ent of the piston within the viscous fluid inetic energy is dissipated i.e. transferred into heat. This free oveent of piston / top connection plate against housing / botto con nection plate aes it possible that viscoelastic dapers can follow sall theral displaceents (travel) of the syste they are connected to. In addition, they allow daping of vibrations in all six degrees of freedo i.e. of all linear and torsional vibrations. The odel of the ideal daper is a siple but in ost cases an adequate way to describe viscoelastic dapers. In this odel the da - ping force F D, that the viscoelastic daper develops to counteract the oveent of the piston, is directly lined to the velocity of the piston F D = dẋ Typically the daping paraeter d is depending on the frequency the syste is vibrating with i.e. d = d(f). The frequency dependence iniu vertical daping paraeter d [Ns/] frequency Fig Miniu daping paraeter as a function of operational frequency for different VICODA viscoelastic dapers of the daping paraeter of a daper is deterined by tests (Fig. 25). Due to the design of VICODA viscoelastic dapers vertical and horizontal daping paraeters are different. The odel iplies that slow oveents of the piston only lead to sall daping forces. Therefore slow displaceents of the piston due to e.g. theral extensions lead to negligible daping forces. However, continuous operational vibrations leading to a displac e - ent x of the piston lead to continuous energy dissipation during every cycle of an oscillation (Fig. 26). VD VD VD VD VD VD VD FD VD x Fig Hysteresis of a viscoelastic daper Installed viscoelastic daper in a nuclear plant a c d e b Fig. 23 a g e f b Fig. 24 a Top connection plate b Botto connection plate c Serial nuber plate d Position indicator e Housing f Fluid g Piston 5

16 Fig Viscoelastic daper with locing device (red) in neutral (above) and in offset position (below) Viscous fluids and basic types Apart fro the piston design the ost i - portant eleent to define the daping characteristics of a viscoelastic daper is the selection of the fluid. In general the viscosity of fluids is teperature dependent. Hence for an optiu design of a viscoelastic daper the operational teperatures of the daper have to be considered. The operational teperature will always be a result of the expected abient teperatures during operation and the heat that will be created within the daper due to its operation. VICODA is providing three types of fluids with different characteristics depending on teperature and frequency: Viscoelastic dapers type VD with bituen based fluids allowing high daping paraeters (up to d = 554Ns/ at 5Hz) for operational teperatures fro +20 C to 80 C in a liited teperature range of T = 0 C Viscoelastic dapers type VM with polybuten based fluids allowing ediu daping paraeters (up to d = 438Ns/ at 5Hz) for operational teperatures fro 0 C to +40 C Configuration of viscoelastic dapers The basic paraeters needed for the definition of an adequate daping solution with VICODA s viscoelastic dapers are: operating teperatures [ C] i.e. the highest and lowest expected operational teperature the doinant resonance frequencies of the vibrating syste the daping paraeters [Ns/] required travel [] between installation and operating condition installation diensions [] and geoetrical liitations. With these paraeters a viscoelastic daper fro VICODA s standard portfolio ay be identified using the tables in the following section. In order to choose the optiu solution for each proble and to identify the ost suitable daping device VICODA engineers are available to help you. Viscoelastic dapers type VL with silicone oil based fluids allowing lower daping paraeters for operational teperatures of 30 C to +0 C All VICODA viscoelastic dapers are delivered with high quality corrosion protection in line with international standards. For extree operational conditions VICODA can provide adequate special surface protection using its surface treatent center. Testing, installation and aintenance All VICODA viscoelastic dapers have been thoroughly tested during their design phase. On request final testing before shipent is possible in the VICODA test labs. All VICODA viscoelastic dapers are delivered with a transport locing device that has to be reoved during its installation and before putting it into operation (Fig. 27). 6

17 In cases where a significant travel between installation and operational condition is to be expected the daper can be delivered in an offset position. By this it can be achieved that the daper will operate in a centric po - sition (Fig. 28). It has to be ade sure that the dapers are always handled in an upright position to avoid leaage of the fluid. Instal - lation of the dapers on site can be supported and supervised by experienced VICODA service personnel. Especially dapers using bituen as viscous ediu ay have a significantly higher viscosity at installation teperature than at operating teperature. In order to allow sooth travel fro installation to operational position of the daper heating eleents ay be added to heat up the fluid during installation and by that reduce its viscosity. Although they do not statically support the vibratory syste, viscoelastic dapers need a rigid abutent. There are any ways of installing the, connecting either top or botto plate of the daper to the vibrating syste (Fig. 29). Special coponents to connect the viscoelastic daper, e.g. to piping, ay be designed and delivered as required (Fig. 30). Due to the high quality of VICODA s viscoelastic dapers they can be considered aintenance-free for 40 years. During this period of tie the fluids can be considered as non-aging in case of noral operating conditions. However a visual inspection every year and after exceptional operating conditions e.g. higher operating teperatures over a longer period of tie is recoended. For these aintenance inspections, for replaceents in general or for any ind of related troubleshooting VICODA experts are available. Fig Viscoelastic daper in neutral and offset position Fig Installation exaples Fig Special connection eleents Daping of horizontal piping Daping of horizontal piping Daping of vertical piping 7

18 VISCoelastiC DAMpers TYPE VD All daping paraeters have been deterined based on the high requireents of the geran standard for nuclear plants (KTA3205.3). Noinal load, diensions, weight Noinal E B C s a b Weight Type load [N] [] [] [] [] [] [] M [g] VD VD VD VD M6 3 VD M6 5 VD M6 84 VD M6 09 VD M6 49 VD M6 9 VD M6 246 M = transport thread Noinal load = axiu force that the daper can transfer at operational teperature Vertical daping paraeter [Ns/] Type Noinal load [N] VD VD VD VD VD VD VD VD VD VD Maxiu offset to neutral position is 40 for all viscoelastic dapers of type VD shown here. Specifications for dapers with larger offsets are available upon request. Horizontal daping paraeter [Ns/] Type Noinal load [N] VD VD VD VD VD VD VD VD VD VD

19 ViscoElastic Dapers Type VM All daping paraeters have been deterined based on the high requireents of the geran standard for nuclear plants (KTA3205.3). Noinal load, diensions, weight Noinal E B C s a b Weight Type load [N] [] [] [] [] [] [] M [g] VM M6 2 VM M6 30 VM M6 48 VM M6 06 VM M6 93 VM M6 288 Maxiu offset to neutral position is 30 for all viscoelastic dapers of type VM shown above. Noinal load, diensions, weight Noinal E B C s a b Weight Type load [N] [] [] [] [] [] [] M [g] VM M6 39 VM M6 49 VM M6 07 VM M6 58 VM M6 282 VM M6 489 Maxiu offset to neutral position is 50 for all viscoelastic dapers of type VM shown above. Specifications for dapers with larger offsets are available upon request. Vertical and horizontal daping paraeters are the sae for VM and VM Vertical daping paraeter [Ns/] Type Noinal load [N] VM VM VM VM VM VM Horizontal daping paraeter [Ns/] Type Noinal load [N] VM VM VM VM VM VM In general offset is possible in vertical and horizontal directions. 9

20 Elastoeric Devices a b c Fig. 3 a Top plate b Rubber iddle section c Botto plate Isolation Siilar to spring devices, elastoeric dev - i ces are products used for the isolation of a vibratory syste fro the source of vibration. A special characteristic of elastoeric devices is that they always provide soe internal daping. Lie spring devices they are to be positioned between the vibratory syste and the source of vibration. For an efficient isolation the natural frequency of the vibratory syste, defined by the elastoeric devices and the load they carry, has to be significantly lower than the ain excitation frequency of the vibration source. The protection of coplete building struc t - ures against seisic events lie earthquaes is also possible with special elastoeric devices. The design of these devices requires a thorough upfront analysis of the situation. Because of the vibrational characteristics of the VICODA elastoeric aterials, the natural frequencies of the typical vibratory systes defined by the elastoeric devices and the load they carry are in the range of 6 to 20Hz, thus above the range of spring devices. This difference in natural frequency often is decisive when choosing the appropriate product for an isolation proble. Field of application There are any applications where elastoeric devices represent the ost efficient way to solve a given vibration isolation proble. A typical exaple is the isolation of an eergency power generator of a building lie a hospital that is located at the top of building (isolation at source). The bacup power supply will be instantly started when a power cut occurs. During the startup and the operation of the generator the isolation by elastoeric devices has to ae sure that the operational vibration of the generator is not transitted to the building thus not ipairing the functioning of sensitive edical instruents or laboratory equipent. Elastoeric devices are also frequently used to isolate coplete roos or even buildings fro external excitations (isolation of rec i p ient). Exaples range fro sall roos with sens - itive production or easureent equipent to coplete concert halls that are isolated against e.g. the vibrations induced by nearby railway tracs. Another big area of application is the isol a tion of production equipent such as achine tools. Here the use of sall standard elastoeric devices provides a very siple and cost efficient isolation solution. Design Lie all VICODA products, also VICODA elastoeric devices are based on a odular design approach. The basic design of an elastoeric device consists of a rubber pad that is vulcanized to an upper and a lower steel plate. For the anchoring of the devices the plates ay be equipped with threaded holes or bolts (Fig. 3). Rubber aterials The vertical stiffness of an elastoeric device and its daping characteristics are depending on the rubber aterial and its thicness. The typical VICODA rubber copound used for the elastoeric devices of type RR has a Shore A Hardness of 55 and a related daping ratio D of 4-5%. However, in order to cover the wide spectru of elastic as well as daping requireents other synthetic or caoutchouc based rubber aterials are available. In aggressive weather environents chloroprene rubber provides the required resistance. When resistance against oil or grease is required acrylonitrile butadiene based rubber is available. 20

21 Arrangeent of elastoeric devices VICODA standard elastoeric devices ay be used to create very different elastic properties. Lie in the case of spring devices in a parallel arrangeent of elastoeric devices the total stiffness of the syste will be the su of the stiffnesses of all devices in the arrangeent (Fig. 32). In a serial arrangeent the (vertical) thicness of the syste is increased thus reducing the total stiffness of the arrangeent (Fig. 33). With these data an elastoeric device so l u- tion for a vibration isolation proble can be defined using the odular VICODA product portfolio. However, lie in the case of spring devices the large nuber of different possible rubber aterials, loads etc. aes it hard for a non-expert to define the optiu solution for his specific proble. Therefore VICODA experts are available to help you configure the optiu solution. A typical configuration process for the VICODA elastoeric devices of type RR is described on page 23. Parallel arrangeent of elastoeric devices: Total stiffness tot : tot = Deflection: x = F F = tot F Installation and aintenance Fig. 32 Configuration of elastoeric devices For the definition of the vibration isolation solution using VICODA standard elastoeric devices the following paraeters are neces s ary: the load [N] given by the weight of the supported achine, structure or building and the load distribution When all relevant requireents have been taen into account during the configuration process, VICODA elastoeric devices do not require any aintenance during their typical service life. However, as the rubber aterial is subject to aging, a regular visual inspection of the devices is recoended. The intervals are depending on the rubber aterial used and the environental conditions that the devices are exposed to. For the installation of elastoeric devices, for inspections and for any ind of replaceent wor, VICODA experts are available. Serial arrangeent of elastoeric devices: Total stiffness tot : tot = Deflection: x = F = F + F + F + F tot F the ain excitation frequencies of the vibration source Fig installation diensions [] and geoetrical liitations special environental requireents lie exposure to sunlight, ozone, oil or grease operating teperatures [ C] special dynaic requireents. 2

22 Elastoeric devices type RR VICODA offers a wide variety of elastoeric devices with different sizes and characteristics. As an exaple the below table shows the standard devices of type RR. For the VICODA elastoeric devices of type RR a standard rubber copound with a Shore A Hardness of 55 is used. They are avail able in 6 different widths fro 40 to 200 and with thicnesses ranging fro 20 to 0. The length of a device is adjustable to the required loads. w t h Elastoeric Devices Type RR Values are valid for 0 length Natural Diensions Stiffness Max. load freq. at F z Hardness Vicoda w h l t x.y z F x.y F z f 0 Ref. [] [] [] [] [N/] [N/] [N] [N] [Shore A] RR RR RR RR RR RR RR RR RR RR RR RR RR RR RR RR Cut to needed length; IMPORTANT: data on stiffness. ax. load and in. natural frequency relate to 0 length) RR RR RR RR RR RR RR RR RR RR RR RR w = Width h = Height l = Length t = Thicness of top and botto plate x,y = Stiffness in horizontal direction z = Stiffness in vertical direction 22

23 Configuration exaple A rotating achine running at 3,000rps (50Hz) with a ass of 2,000g is to be supported by four elastoeric devices of type RR, so that the surroundings are isolated fro the vibration of the achine. The load distribution on the four devices is assued to be even. Because of geoetrical liitations the height of the devices should be less than 50. The expected load on every device is: F = 2,000 4 g 9.8 s 2 = 4.9N Due to the geoetrical liitation only the devices with a height of up to 45 are suitable for this specific application. When choosing a device RR.2009 with a axiu load capacity of 800N per 0 length, the required length of the device is I = 4.9N 800N / 0 = 6.25 the total stiffness of this device is = ,376 N = 8,428 N and the related deflection of the device will be x = F = 0.58 The resulting natural frequency would be f 0 = 2π = 20.7Hz As desired the natural frequency is significantly lower than the excitation frequency of 50Hz induced by the rotating achine. When choosing a device RR.409 with a axiu load capacity of 520N per 0 length of the device the related date would be: l = 94 = 2.45N / x = 2 f 0 =.2Hz In this case the natural frequency of the syste is lower than in the case of the RR.2009 devices. The softer support of the achine provides an even better isolation. The final choice of the elastoeric device will be driven by the geoetrical liitations and the reachable natural frequencies. Elastoeric devices under a test bench 23

24 Tuned Mass Dapers a b Fig Tuned ass daper a Oscillating unit b Standard connection eleents Fig Oscillating unit Fig Eddy current daping eleent Energy transfer to a coupled oscillating syste ABSORPTION Tuned ass dapers (TMDs) are systes that can be coupled to a vibrating syste and efficiently absorb energy fro it. By that the vibration aplitude of the original syste can be reduced significantly. TMDs are designed in a way that they efficiently absorb energy of vibrations around the natural frequency f 0 of the vibrating syste. They are passive vibration control products as they only follow the otion of the original syste. Field of application There are applications for tuned ass dapers in any industries fro plant construction to civil engineering. A typical application in plant engineering is the vibration control of piping systes in power plants or industrial plants oscillating e.g. because of rotating pups. An exaple taen fro civil engineering is the control of vibrations of high-rise buildings or towers induced by wind. Another application is the control of vibrations of wind turbine generators that are due to the rotation of their blades. These very different vibration control probles show that TMDs often are products that are specially designed for a specific application. Design Tuned ass dapers in general are vibratory systes consisting of a ass, an elastic and a daping eleent being coupled to the original vibrating syste. The process to design a TMD always follows a siilar logic. However, depending on the specific application the size of the ass, as well as the sizes of the elastic and daping eleent of the TMD can vary in a broad range. VICODA can provide TMD solutions for all typical applications. Depending on the vib r a- tion proble different designs lie trolley type TMDs or pendulu TMDs are available. td type TP Especially for the vibration control of piping systes a TMD has been developed consisting of an oscillating unit and standard connection eleents to the pipe (Fig. 34). Oscillating unit There are two preconfigured standard oscil l- ating units available allowing to control alost all typical industrial piping vibration probles (Fig. 35). Due to the odular design of the oscillating units its ass, its elastic and its daping paraeter are adjustable. The saller unit provides a ass of up to 00g, the bigger unit a ass up to 350g. Final fine-tuning of all paraeters can easily be done during coissioning on site by VICODA experts thus allowing a precise calibration of the TMD and by that a highly effective reduction of the pipe vibration. Daping eleents Daping of the TMD is provided by an eddy current daping unit (Fig. 36). Copared to conventional daping eleents eddy current dapers have a nuber of special advantages: daping is independent fro environental conditions especially fro teperature daping is independent fro specific vibration characteristics of the piping syste allowing efficient daping also in different operating conditions due to contactless energy transfer to the daping eleent the oscillating unit is durable, aintenance free and highly reliable. 24

25 Connection eleents LISEGA, VICODA s parent copany, is the world-aret leader of pipe support systes. Therefore, VICODA is benefitting fro LISEGA s ore than 50 years of experience in design and production of all types of pipe surrounding connection parts. Standard connection parts are available for pipe diaeters fro 00 to With one VICODA TMD a one or two-diensional vibration can be controlled. For threediensional vibrations two tuned ass dapers are required. An iportant advantage of the TMD is that it can be ounted directly onto the pipe with - out any rigid abutent lie it is needed for e.g. a viscoelastic daper (Fig. 37). Due to this feature the tuned ass daper does not interfere with theral oveents of the piping syste. It is also due to that feature that it can be perfectly used as a retrofit easure. Configuration of tuned ass dapers For the definition of a vibration control sol - ution using VICODA TMDs the support of VICODA s engineers is andatory. The first step in the solution process is always a de - tailed analysis of the vibration proble. In case of retrofit easures additional on-site esureents are recoended. Wölfel Beratende Ingenieure, a founding partner of VICODA has provided the respective now-how. The optiu design will then be defined in close cooperation with the custoer. Installation and aintenance Installation of VICODA TMDs can be provided by VICODA s experienced service staff. Within their noral service life tuned ass dapers are aintenance-free. The VICODA TMD is designed to efficiently reduce vibrations with typical frequencies in the range of 2 25Hz and it is reliably oper a t - ing in the teperature range fro 40 C up to +80 C. As pure echanical products without any electrical coponents tuned ass dapers are suitable for application in areas where explosion prevention is andatory. As pas s ive vibration control eleents not depending on power supply TMDs eep their functionality also in situations where this supply cannot be reliably secured e.g. in case of a seisic event. For aggressive environental conditions e.g. in a cheical plant VICODA TMDs can be delivered with special durable paints and coatings. Fig TMDs installed on a piping syste 25

26 Active Daping Devices Active vibration control Active daping devices are coupled to a vibrating syste and counteract the otion of this syste. In contrast to passive vibration control the otion of an active daping device is created by acceleration of its reac - tion ass through actuators causing reaction forces in the original vibrating syste thus reducing the vibration. Vibration aplitude [] ---- without Active Daping Device ---- with Active Daping Device Fig. 39 Frequency Field of application x x' ' ' d' d c VICODA has developed a standard active daping device for vibration control in indust rial piping systes. These devices are especially suitable in cases where the vibrat - ion of the syste needs to be reduced at various frequencies, e.g. due to different operational conditions of the plant. Design The VICODA standard active daping device is equipped with sensors detecting the otion of a vibrating syste and with powerful linear actuators accelerating the reaction ass of the devices (Fig. 38). Daping effect of reaction forces on piping syste Actuators ove reaction ass In the control unit of the device the actuator is continuously and autoatically calc ulated based on the sensor signal thus sec uring an efficient counteraction of the daping device and reduction of the vibration. An exaple for the efficient vibration reduction over a wide frequency range is shown in Fig. 39. Fig Functional principle of an active daping device 26

27 Fig. 4 - Active vibration control in one, two or three diensions With one basic odule of the VICODA active daping device (Fig. 40) it is possible to create counteracting otion in one diension. Therefore ulti-diensional vibration probles require the respective nuber of odules (Fig. 4, 42). Lie a tuned ass daper, VICODA active daping devices can be ounted directly onto the pipe without any rigid abutent (Fig. 43) lie it is needed for e.g. a viscoelastic daper. Therefore they do not interfere with theral oveents of the piping syste. It is also due to that feature that they can be easily used as a retrofit easure. Because of its special design using powerful actuators the ass of an active daping device is uch lighter than the ass typically used in a coparable passive tuned ass daper. The robust control cycle of the devices allows an easy adaptation to changing operational conditions in the plant. If required the detected inforation about the vibration can be transitted to a central onitoring or control syste. For aggressive environental conditions e.g. in a cheical plant VICODA active daping devices can be delivered with special durable paints and coatings. Devices to be used in environents where explosion prevention is copulsory are available upon request. Configuration of active daping devices The definition of a vibration control solution using active daping devices requires the support of VICODA s experienced engineers. A detailed analysis of the vibration proble and in case of retrofit easures on-site easureents are always the first step in the solution process. The optiu design will then be defined in close cooperation with the custoer Installation and aintenance Installation and aintenance of VICODA active daping devices can be provided by VICODA s experienced service staff. Maintenance requireents depend on the specific operating conditions of the active daping device. Fig Active daping device installed directly on a gas piping syste Fig One basic odule of an active daping device Fig Active daping device for vibration control in two diensions 27

28 VICODA GbH Gerhard-Liesegang-Straße Zeven Gerany Tel. +49 (0) 42 8/ Fax +49 (0) 42 8/ A copany of the LISEGA Group MouseDesign 205