Available online at ScienceDirect. Procedia Engineering 111 (2015 )

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1 Aville online t ScienceDirect Procedi Engineering 111 (2015 ) XXIV R-S-P seminr, Theoreticl Foundtion of Civil Engineering (24RSP) (TFoCE 2015) Experimentl (OMA) nd numericl (FEM) modl nlysis of ll mill foundtions Zigniew Wójcicki *, Jcek Grosel, Wojciech Swicki, Krzysztof Mjcher, Wojciech Pkos - Astrct The pper presents the results of the modl nlysis of ll mill foundtion, n element of the processing technologicl line in n ore enrichment plnt in Polnd. The modl nlysis ws performed in two wys: numericlly, using FEM, nd experimentlly, using OMA. The nlyses results were vlidted nd the FEM model ws tuned ppropritely. The results show surprisingly good supporting structure design in n er when modern design methods, such s the FEM method, were not yet ville, i.e. in the 1960s. The study results ruled out the stte of the ground on which the foundtion rests s the cuse of lrge structure virtion. Insted, the poor technicl condition of the mchinery (ll mill erings) ws indicted s the min cuse The Authors. Pulished y Elsevier B.V Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of orgnizing committee of the XXIV R-S-P seminr, Theoreticl Foundtion of Civil Peer-review Engineering under (24RSP) responsiility of orgnizing committee of the XXIV R-S-P seminr, Theoreticl Foundtion of Civil Engineering (24RSP) Keywords: OMA; FEM; Bll mill; Foundtions 1. Short description of the prolem The immedite reson for the dynmic nlysis ws the occurrence of clerly perceivle virtion in the flottion nd mill hlls. The virtion ws lrge enough to concern the production supervisors nd the mintennce personnel working in these hlls. Some concerns even rose s to the stility of the hll constructions nd the conservtion of the foundtions of the mills nd other structures. * Corresponding uthor. Tel.: ; E-mil ddress: zigniew.wojcicki@pwr.edu.pl Pulished y Elsevier Ltd. This is n open ccess rticle under the CC BY-NC-ND license ( Peer-review under responsiility of orgnizing committee of the XXIV R-S-P seminr, Theoreticl Foundtion of Civil Engineering (24RSP) doi: /j.proeng

2 Zigniew Wójcicki et l. / Procedi Engineering 111 ( 2015 ) c Fig. 1. () view of mill hll; () reinforced concrete column; (c) steel column. The structure s whole is very lrge nd hevy, with dimensions of 351,0 88,1 30,5 m, nd would therefore seem to e immune to locl virtion cused y mchines functioning within it. However, with the lrge numer of devices cusing intense virtion (there re out 30 of the mills lone, Fig. 1), it ws decided tht study should e performed to estlish whether the virtion could led to destiliztion of the structures of the hlls nd of the engineering ojects within them. This ws especilly justified in tht the hll is multi-nve, reltively complex mixed structure prtilly mde of reinforced concrete (Fig. 1), prtilly of steel (Fig. 1c). As the cuse of the lrger virtion of some of the mill foundtions ws not known, the following were to e estlished: whether the dynmic chrcteristics of some of the mchine foundtions were different thn in other mchine foundtions (which would indicte they re dmged) whether some of the mchines generte greter virtion due to their worse technicl stte. 2. Brüel & Kjær s pltform for virtion nlysis System PULSE Dynmic mesurements were performed with the use of Brüel & Kjær 34 chnnel PULSE system, see Fig. 2. The PULSE system we used cn e divided into two independent prts, ech of 17 input chnnels, ll feturing the frequency rnge of DC to 25.6 khz. Becuse the 3560 PULSE mesurement system contins Dyn-X cquisition modules, ll inputs rech the dynmic rnge of 160 db with idel linerity nd phse mtching. The system hs een equipped with 17 input chnnels multi-nlyzer PULSE 3560-C (see Fig. 2) nd trnsducers intended for the purpose of experimentl Modl Anlysis set of 15 seismic high sensitivity ccelerometers DeltTron 8340 (Fig. 2). Ech ccelerometer DeltTron 8340 hs mss 775g nd sensitivity 1mV/ms -2. Fig. 2. System PULSE () multi-nlyzer PULSE 3560-C; () seismic ccelerometer DeltTron 8340.

3 860 Zigniew Wójcicki et l. / Procedi Engineering 111 ( 2015 ) Softwre Experimentl Opertionl Modl Anlysis (OMA) The OMA ppliction hs een equipped with ll of the newest chievements in the field, including utomtic serch nd detection of mode shpes, s well s utomtic detection nd removl of hrmonic contents in the mesured signl. The OMA pckge (Opertionl Modl Anlysis Pro developed y: Structurl Virtion Solutions A/S) pplied y the uthors contins 6 lgorithms for otining eigenfrequencies nd eigenforms: FDD (Frequency Domin Decomposition); EFDD (Enhnced Frequency Domin Decomposition); CFDD (Curve-Fit Frequency Domin Decomposition); SSI-UPC (Stochstic Suspce Identifiction-Unweighted Principle Components); SSI-PC (Stochstic Suspce Identifiction-Principle Components); SSI-CVA (Stochstic Suspce Identifiction-Cnonicl Vrite Anlysis). The first three lgorithms elong to frequency domin, the rest of the them to time domin nlyses [1]. The method is sed on the ide of replcing the response of discrete system with sum of responses of mny one-degree-of-freedom systems. In lgorithms 4-6, the stochstic suspce identifiction method is used. This method is sed on the eqution of stte of dynmic system nd its decomposition using Klmn filtrtion [2]. 3. Initil dynmic mesurements The initil dynmic mesurements were performer in order to identify the type, level nd energy of the virtion generted y the mchines functioning in the mill nd flottion hlls. To tht end, mesurements were tken on the columns supporting the hll structures. The mesurements were performed using the multi-nlyzer PULSE 3560-C, see Fig. 2, nd the Brüel & Kjær 8340 seismic ccelerometers, see Fig. 2. The trnsductors (ccelerometers) were mounted on the columns using especilly designed cues, which mke it possile to mesure virtion in one point nd in three directions perpendiculr to one nother, see Fig. 3. The nlysis results were presented in the form of the so-clled virtion mp. Fig. 3 presents exmples of RMS vlues of the mesured virtion levels in the horizontl direction x in the 1/3-octve nd with middle vlue of 2 Hz. The RMS vlues were nlyzed, since they re certin verging of the signl (while the mplitude vlue my distort the signl in non-sttionry virtion). There re mny different virtion sources within the hll, ll giving rise to excittion of differing frequencies. Therefore, the nrrow-nd nlysis (octves, 1/n-octves or Fourier s trnsforms) constitute etter pproch thn the wide-nd nlysis. The nrrow-nd pproch mkes it possile to extrct the signl components corresponding to ech excittion frequency which llows to estlish whether the registered virtion stems from one or more sources. The nlyses were performed in ccordnce with the norm [3] in the rnge Hz. The legend on the right side of Fig. 3 scries the vlues of the virtion ccelertions to chosen colors. The res of heightened virtion were determined using such mps nd the mills within those res (red color) were nlyzed in detil, see Fig. 3. m/s 2 Fig. 3. () mounting of the seismic ccelerometers DeltTron 8340; () mp of hll virtion in 1/3-octve nd with middle vlue of 2 Hz.

4 Zigniew Wójcicki et l. / Procedi Engineering 111 ( 2015 ) Dynmic nlysis of mills nd their foundtions 4.1. Numericl (FEM) modl nlysis T.1 shows the first 4 eigenfrequencies of the mill MK 221 determined using FEM lgorithms. Fig. 4 presents FEM scheme of mill with its foundtion, Fig. 4 n exmple of the first verticl eigenform of the foundtion. Tle 1.FEM nd OMA eigenfrequencies of mill MK 221 (mss 159,65 t) N o Description of eigenform Eigenfrequency FEM [Hz] Eigenfrequency OMA [Hz] 1 rottion round x xis 2, ,519 2 rottion round y xis 2,97202 _ 3 rottion round z xis 4,72485 _ 4 verticl virtions (long z xis) 5, ,886 Fig. 4. () FEM scheme of mill with its foundtion; () first verticl eigenform of the foundtion 5,08093Hz Opertionl modl nlysis (OMA) The min mesurements were performed for three mill foundtions, one hour for ech. The results presented here re for mill MK 221, which ws not functioning during the mesurements. The excittion ws due to the influence of other working mills nd mchines. However, the work of those mills nd mchines is of deterministic nture, not stochstic one. Therefore, the excittion of the nlyzed mill did not fully fulfill the sic ssumption of OMA excittion it is not white noise. Due to this difficulty, the nlysis ws limited to identifying two eigenforms: the first rottionl nd the first verticl ones. The verticl one ws used in FEM model vlidtion. The OMA mesurement scheme is presented in Fig. 5. The virtion ws mesured simultneously in four points nd in three directions in ech point. The closest cuoid represents the prt of the foundtion lock tht supports the engine, the ger trin nd the toothed-wheel rim; the frthest one the prt supporting the erings of the mill drum. The OMA results re presented in T. 1, nd the identified verticl eigenform is presented in Fig. 5. Fig. 5. () OMA scheme of the foundtion; () identified verticl eigenform 4,886.

5 862 Zigniew Wójcicki et l. / Procedi Engineering 111 ( 2015 ) Fig. 6. () Stiliztion Digrm of Stochstic Suspce Identifiction (SSI-CVA); () detection of hrmonic excittion using kurtosis All six OMA methods were used to determine the eigenfrequencies. The etter results were otined for stochstic lgorithms in time domin (SSI). An exemplry stiliztion digrm of the SSI-CVA method is shown in Fig. 6. Using kurtosis, hrmonic excittion ws detected (Fig. 6). The hrmonic excittions differed from the frequencies of the virtion registered in the erings nd foundtions. It ws therefore concluded tht the dominnt virtion ws not cused y rotting motion of the mill drum; insted, it ws minly due to the ger teeth engging ODS nlysis of exploittion virtion The mesurements for the ODS nlysis were tken using 17 ccelerometers, see Fig. 7. Green color mrks the concrete foundtions of the drum erings. Red color mrks the ering. During ODS nlysis, set of ODS Frequency Response Functions ws otined, which re presented in Fig. 8. For some frequencies, their vlues noticely pek. These frequencies nd the virtion forms corresponding to them were interpreted to e dominnt exploittion virtion forms. There re visile excittions with the 4 th, 8 th, 12 th etc. hrmonic of the sic frequency of the pinion shft, i.e., 11,1; 22,2 Hz etc., where 66,6 Hz is the frequency t which the gers engge. The figures elow present virtion forms corresponding to frequencies of 11,1Hz (Fig. 7) nd 66,6 Hz (Fig. 7c). c Fig. 7. () ODS scheme; () ODS form 11.1 Hz; (c) ODS form 66,6 Hz Fig. 8. () set of ODS Frequency Response Functions; () time history of erings L1 nd L2 virtions nd chrcteristic frequencies

6 Zigniew Wójcicki et l. / Procedi Engineering 111 ( 2015 ) Trnsient resonnce nlysis nd order trcking nlysis Fig. 8 presents the results of trnsient resonnce nlysis in the rnge Hz ([3]). Blue (L1) nd red (L2) mrk the virtion registered in the drum erings. A comprison etween the results shown in Fig. 8 nd Fig. 8 leds to the conclusion tht the fourth hrmonic of the pinion (11,1 Hz, Fig. 8) corresponds to the mplifiction of the virtion occurring for this frequency in the ODS function grphs (Fig. 8). Such n mplifiction is chrcteristic of dmge to the tooth clutch. Similr results were otined using order trcking nlysis, which is dignostic method tht llows to evlute the stte of mchine on the sis of the order spectrum. Tking mesurements is more difficult, s the rottionl speed must lso e registered using tcho proe. Exmples of virtion spectrogrms re presented in Fig. 9 nd Fig. 9 respectively. 5. Conclusions Fig. 9. () spectrogrm (frequency-time nlyses) of erings L1y ccelertions; () spectrogrm of erings L2y ccelertions It ws found tht: there is correltion etween lrge foundtion virtion nd the poor condition of the mchines the modl prmeters of the nlyzed foundtions were very similr, which mens there were no significnt dmges to ny of the foundtions the frequencies of the dominnt fundment virtion correspond to hrmonics of the shft nd enggement exceeding the normtive virtion levels on the erings of prcticlly ll the mills indictes their overlod, which ccelertes the rte of wer of the propulsion elements; this in turn cuses the virtion to increse, leding to progressive wer of the pinion teeth; the result is vicious circle of ongoing deteriortion Finlly, the lrge foundtion virtion of the mill MK 221 were dignosed to e cused y reducing the numer of pinion teeth from 27 to 24. This ltertion reduced the mill s power consumption, ut it ws detrimentl to the dynmics of the mill s propulsion system. At the engine s rottionl speed of 2,778 Hz, the sixth hrmonic frequency of the dmged clutch, i.e. 6 11,11 Hz = 66,67 Hz ecomes equl to the sic frequency of enggement which results from multiplying the rottionl speed of the pinion shft y the numer of pinion teeth, i.e. 24 2,778 Hz = 66,67 Hz. The frequency of the dmged clutch is four times greter thn the rottionl speed of the shft (4 th hrmonic, i.e. 4 2,778 Hz = 11,11 Hz). If the originl 27 teeth remined in the pinion, the sic frequency of enggement would e 27 2,778 Hz = 75,00 Hz nd would not e equl to the sixth hrmonic frequency of the dmged clutch, i.e. 66,67 Hz. References [1] R. Brincker, L. Zhng, P. Andersen, Modl Identifiction from Amient Responses using Frequency Domin Decomposition, Proceedings of the 18th Interntionl Modl Anlysis Conference (IMAC), Sn Antonio, Texs, 2000, p [2] M. Btel, Opertionl Modl Anlysis Another Wy of Doing Modl Testing. Sound nd Virtion, 2002, p [2] PN-85/B-02170,.