© Acta hydrotechnica 23/38 (2005), Ljubljana ISSN 1581-0267 39 UDK/UDC: 531.7:56.535.001.5 Prejeto/Received: 11. 2. 2005 Izvirni znanstveni članek – Original scientific paper Sprejeto/Accepted: 18. 12. 2006 LABORATORIJSKA UPORABA SLEDILA ZA MERJENJE DINAMIKE PREMEŠ ČANJA PLAVIN V TURBULENTNIH TOKOVIH LABORATORY APPLICATION OF A SATELLITE FOR MEASURING DYNAMICS OF SEDIMENT TRANSPORT IN TURBULENT FLOWS Matjaž MIKOŠ, Mojca SPAZZAPAN Za sodobne študije premeš čanja re čnih sedimentov smo razvili in testirali novo instrumentizirano umetno sledilo (satelit), imenovano prodnik vohun (SPY), kjer kratica v angleš čini pomeni “dinamiko posameznih delcev”. Ta nova vrsta sledila ima vgrajena tipala v umetni intrumentizirani kroglasti prodnik premera 99 mm in mase 994,6 g. Sledilo se lahko uporablja za prepoznavanje in merjenje razli čnih kinemati čnih in dinami čnih elementov (predvsem tr čnih in trenjskih sil) v času gibanja po re čnem dnu ali v času mirovanja na re čnem dnu. Satelit je bil testiran v laboratorijskih pogojih v žlebu s tremi razli čnimi vrstami dna žleba (dno iz nevezanih prodnikov, jekleno dno, dno iz betonskih ploš č z vgrajenimi prodniki) in razli čnim naklonom dna žleba med 0,025 in 0,055. Glavni merjeni dinami čni parametri so bile amplitude tr čnih in trenjskih sil ter čas med posameznimi kontakti sledila. Dobljeni rezultati za brezdimenzijske strižne napetosti od 0,05 do 0,12 so pokazali na uporabno vrednost satelita v laboratorijskih pogojih za raziskovanje premeš čanja posameznih sedimentnih delcev v turbulentnih tokovih. Klju čne besede: premeš čanje plavin, re čna hidravlika, merilni instrumenti, sledila, laboratorijski poskusi, pospeškometri We have developed and tested a new instrumented artificial satellite for advanced sediment transport studies, called SPY-Cobble, where the acronym SPY stands for “Single Particle dYnamics”. This new type of tracers with internal sensors is an artificial, instrumented spherical cobble of 99 mm in diameter and has a mass of 0.9946 kg. It may be used for detection and measurements of different elements of kinematics and dynamics (especially contact forces due to impact and friction) when moving as bed load or resting on the bed surface. The satellite was tested under controlled laboratory conditions in a flume using three different flume bed materials (loose sediment bed made of cobble and boulder clasts, steel bed, flume bed made of concrete plates with cast pebble clasts) and different flume slopes between 0.025 and 0.055. The main measured dynamic parameters were the amplitudes of impact and friction forces and the time between contacts of the tracer. The obtained results for non-dimensional shear stress between 0.05 and 0.12 have shown the applicability of the satellite within the laboratory environment for transport studies on single sediment particle movement in turbulent flows. Key words: sediment transport, fluvial hydraulics, measuring instruments, tracers, laboratory experiments, accelerometers 1. UVOD Merilno napravo, razvito za spremljanje dinamike premeš čanja grobih plavin, smo poimenovali prodnik vohun. Razvoj in testiranje prodnika vohuna sta opisana drugje (Spazzapan et al., 2004). Do današnje oblike je prototip prešel skozi ve č razvojnih obdobij. V sedanji obliki je 1. INTRODUCTION The measuring device developed for following dynamics of coarse sediment transport was called the SPY-Cobble. The development and testing of the satellite are described elsewhere (Spazzapan et al., 2004). Up to its present form, the prototype has undergone several phases of development. At Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 40 sledilo sestavljeno iz kroglaste kovinske konstrukcije, oble čene v epoksidno zaš čitno plast, dveh elektronskih tiskanin, ki sta nameš čeni vzporedno v njegovem središ ču, zamenljivega vira energije (9 V baterija), vgrajenega v eni polovici kovinske kroglaste konstrukcije, in 3 enoosnih pospeškometrov, pritrjenih na kovinsko konstrukcijo na drugi strani (slika 1). Prodnik vohun je v taki izvedbi 99 mm velika krogla z maso 994,6 g. Metoda in izvedba naprave je v Sloveniji patentirana (Mikoš et al., 2001), oboje je tudi v svetovnih razmerah patentibilno. present, the satellite consists of a spherical metal construction coated by epoxy resin, two built-in electronic boards, which are mounted horizontally in its centre, a replaceable power source, which is a standard 9V battery, built-in on one side of the metal construction, and three one-axis accelerometers attached to the metal construction on the other side (see Figure 1). The SPY-Cobble in this composition is 99 mm in diameter and has a mass of 994.6 g. The method and the apparatus are patented in Slovenia (Mikoš et al., 2001) and are patentable worldwide. Slika 1. Prodnik vohun in njegovi sestavni deli. Zaprta medeninasta krogla brez epoksidne zaš čitne plasti (zgoraj) in elektronski tiskanini in vir napajanja (desno). Figure 1. SPY-Cobble and its parts. The closed brass sphere with no epoxy coating (on top) and the two electronic boards and a battery (on right). 2. REZULTATI MERITEV Merilno napravo z dodanim pasivnim radijskim oddajnikom bi lahko uporabljali tudi v naravnem re čnem okolju. Vendar smo jo tako, kot je, uporabili samo v laboratorijskih pogojih. Najprej smo testirali njeno uporabnost na zraku in pod vodo v laboratorijskem žlebu na Fakulteti za gradbeništvo in geodezijo Univerze v Ljubljani. Ti rezultati so prikazani drugje (Mikoš et al., 2000). Nato smo sistemati čno opravili dva niza laboratorijskih meritev v nagibnem laboratorijskem žlebu na Svobodni univerzi v Berlinu (Freie Universität Berlin). 2. MEASUREMENT RESULTS The device with an added passive radio transmitter could be used also in the natural river environment. But we have used the device such as it is under laboratory conditions only. Firstly, it has been tested in air and under water in a laboratory flume at the Faculty of Civil and Geodetic Engineering in Ljubljana. Results of these measurements are presented elsewhere (Mikoš et al., 2000). Secondly, we have systematically conducted two sets of measurements in a tilting laboratory flume at the Free University in Berlin. Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 41 2.1 PRVI NIZ LABORATORIJSKIH POSKUSOV Prvi niz sistemati čnih laboratorijskih poskusov smo opravili v 10 m dolgem in 0,81 m širokem nagibnem laboratorijskem žlebu na Svobodni univerzi v Berlinu. Dno žleba je bilo prekrito z gibljivimi naravnimi prodniki s srednjim zrnom d m = 86 mm in d 90 = 93 mm (prodniki so bili sicer v intervalu od 20 do 120 mm). Opravili smo 9 poskusov, kjer je vsak poskus obsegal vsaj 10 posameznih meritev. Med vsako meritvijo smo merili razli čne parametre toka, prikazane v preglednici 1. Premer prodnika vohuna je bil D = 0,099 m, gostota je bila 1957,7 kg/m 3 in relativna gostota z ozirom na vodo je bila s = 1,9577. Srednjo preto čno hitrost v žlebu smo merili z robustnim elektromagnetnim merilcem pretoka (Nautilus, merilno obmo čje 0–2,5 m/s), meritev smo povpre čili na 5 s. Merili smo tudi povpre čno globino toka ter s pomo čjo povpre čne hitrosti toka ocenili dejanski pretok vode v žlebu. Na osnovi ena čb stalnega enakomernega toka smo izra čunali razli čne koli čnike (k St in c) kakor tudi Froudovo število Fr, ki je pokazalo, da je bil tok tako v mirnem kot tudi v dero čem režimu. Na za četku vsake posamezne meritve smo prodnik vohun položili v vodni tok na zgornjem koncu žleba. Tok je prodnik odnesel preko hrapavega dna žleba do konca v nekaj 10 s. Izbrana je bila dolžina meritve 10 s (zaradi relativno po časnega prenosa podatkov iz prodnika v ra čunalnik). Razvili smo postopek za analizo izmerjenega signala, pri čemer smo upoštevali samo izmerjene pospeške, ve čje od 0,05 g. Vsak tak kratek niz pospeškov smo imenovali dogodek. Minimalni in maksimalni časovni razmik med posameznimi dogodki je bil pri analizi nastavljen na 25 ms in 2 s. Spodnja meja 25 ms pomeni, da so bili izmerjeni pospeški, ve čji od 0,05 g, ki so si sledili v zaporedju krajšem od 25 ms, prepoznani kot en dogodek. Prepoznani dogodki v izmerjenem signalu so bili sešteti za vsako posamezno meritev in vsak poskus (preglednica 1). 2.1 FIRST SET OF LABORATORY TESTS We systematically conducted the first set of laboratory tests in a 10-m long and 0.81-m wide tilting laboratory flume at the Free University in Berlin. Its bottom was covered with movable natural clasts with the arithmetic mean d m = 86 mm and d 90 = 93 mm, respectively (clasts were in the range between 20 mm and 120 mm). We performed 9 tests each comprising at least 10 separate runs. During each run, various flow parameters were measured, as presented in Table 1. The diameter of the SPY-Cobble was D = 0.099 m, density was 1957.7 kg/m 3 , and relative density to water was s = 1.9577. The mean water velocity was measured by a robust electromagnetic flow sensor (Nautilus, measuring range from 0 m/s to 2.5 m/s), averaging over 5 seconds. The water depth was gauged, and using mean flow velocities the actual water discharge was determined. On the basis of equations for steady uniform flow, different coefficients (k St and c) were calculated as well as the Froude number Fr, which shows that the flow was sub- as well as supercritical. At the beginning of each run, the SPY-Cobble was introduced into the upper end of the flume and was transported by the flow over the rough bed for several tens of second. The measurement during each run was set to be 10 seconds long (due to the relatively slow data transfer from the device to a computer). An algorithm was developed for processing of the measured signal, taking into account only the measured accelerations larger than 0.05 g. Each such short set of accelerations was then called an event. The minimal and maximal time span between events was for the analysis set to be 25 ms and 2 s, respectively. The lower limit of 25 ms means that the measured accelerations larger than 0.05 g in a sequence shorter than 0.25 ms were recognised as one event. Recognised events in the measured signal were counted for each run and test (see Table 1). Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 42 Preglednica 1. Pregled prvega niza laboratorijskih poskusov v nagibnem žlebu. Merjeni parametri toka: S – nagib dna, h – preto čna globina, v – srednja preto čna hitrost; ra čunani parametri toka: Q – pretok, Fr – Froudovo število, k St – Stricklerjev koeficient, c – Chezyjev parameter, θ = (S h) / ((s – 1) D) – brezdimenzijska strižna napetost (Shieldsov parameter); analizirani parametri: F – srednja maksimalna sila, t – srednji časovni zamik. Table 1. On overview of the first set of laboratory tests in the tilting flume. Measured flow parameters: S – bottom slope, h – water depth, v – mean flow velocity; calculated flow parameters: Q – water discharge, Fr – Froude number, k St – Strickler’s coefficient, c – Chezy parameter, θ = (S h) / ((s – 1) D) – non-dimensional shear stress (Shields parameter); analysed parameters: F – mean peak force, t – mean time lag. meritve – Measured ra čun – Calculated analiza – Analysed poskus Test meritev Runs [-] dogodki Events [-] S [-] h [cm] v [m/s] Q [l/s] Fr [-] k St [m 1/3 /s] c [-] θ [-] F [N] t [s] 1 11 545 0.035 19.0 1.37211 1.0122.16 5.360.070 17.13 0.183 2 11 571 0.040 18.5 1.39208 1.0521.25 5.190.078 16.93 0.191 3 11 522 0.045 18.0 1.43208 1.1621.15 5.070.085 23.03 0.187 4 11 512 0.055 17.0 1.47202 1.3020.43 4.850.099 26.22 0.187 5 11 451 0.025 26.0 1.38291 0.7521.43 5.460.069 14.68 0.172 6 10 383 0.030 25.0 1.44292 0.8520.95 5.310.079 20.84 0.217 7 10 470 0.035 24.0 1.50292 0.9620.76 5.230.089 22.38 0.196 8 11 374 0.040 23.0 1.55289 1.0620.65 5.160.097 29.40 0.249 9 11 385 0.045 22.0 1.58282 1.1620.44 5.070.104 29.06 0.244 Nato so bili dogodki pretvorjeni v tr čne oziroma trenjske sile. Primer izmerjenega signala in prepoznanih maksimalnih vrednosti sil je prikazan za izbrano meritev na sliki 2. Časovni razmik med posameznimi vrhovi sil je bil imenovan časovni zamik med dogodki. Razmerje med merjenimi maksimalnimi silami in njihovimi pripadajo čimi časovnimi zamiki je za izbrano meritev prikazano na sliki 3. Zatem smo opravili statisti čno analizo izmerjenih maksimalnih sil in njihovih časovnih zamikov v odvisnosti od razli čnih merjenih parametrov toka iz preglednice 1. Maksimalne sile so najbolj linearno vzajemno soodvisne od brezdimenzijskih strižnih napetosti θ (Shieldsov parameter). Sliki 4 in 5 prikazujeta statisti čne parametre maksimalnih sil in časovnih zamikov za vse poskuse v odvisnosti od brezdimenzijske strižne napetosti θ. Nadalje smo dolo čili srednjo maksimalno silo za vsak poskus v odvisnosti od pripadajo če srednje hitrosti toka (slika 6) in brezdimenzijske strižne napetosti θ (slika 7). The recognised events were then converted into impact forces or friction forces. An example of a measured signal and recognised peak forces is given for one run in Figure 2. The time span between peaks was called the time lag between events. The relationship between measured peak forces and their time lags is shown for one run in Figure 3. After that, a statistical analysis was performed of measured peak forces and their respective time lags as a function of diverse measured flow parameters, as presented in Table 1. For the maximal peak forces, the best linear correlation was found to be given by non-dimensional shear stresses θ (Shields parameter). The statistical parameters of peak forces and time lags for all tests as a function of the non-dimensional shear stress θ are shown in Figures 4 and 5. Furthermore, mean peak force for each test was determined and is shown in Figure 6 as a function of the corresponding water flow velocity, and in Figure 7 as a function of non- dimensional shear stress θ. Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 43 Slika 3. Razmerje med maksimalnimi silami F [N] in pripadajo čimi časovnimi zamiki za dogodke meritve št. 9, poskus 4. Ta meritev je imela 47 prepoznanih dogodkov. Figure 3. A relationship between peak forces F [N] and their time lags for events of run No. 9, test No. 4. There were 47 detected events for this run. Slika 4. Vse maksimalne sile F [N] v odvisnosti od pripadajo čih časovnih zamikov [s]. Ta niz meritev je obsegal skupaj 4213 prepoznanih dogodkov. Črne (temne) oznake prikazujejo srednje vrednosti maksimalnih sil za poskuse E1–E4 (skupaj 2150 prepoznanih dogodkov) in rde če (svetle) oznake za poskuse E5–E9 (skupaj 2063 prepoznanih dogodkov). Figure 4. All peak forces F [N] as a function of their respective time lags [s]. There were 4213 events altogether for this set of tests. Black (dark) symbols represent mean peak forces of tests E1–E4 (2150 detected events) and red (light) symbols those of tests E5–E9 (2063 detected events). časovni zamiki [s] – Time lags [s] F [N] F [N] časovni zamiki [s] – Time lags [s] Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 44 Slika 5. Statisti čna analiza maksimalnih sil F [N] in časovnih zamikov [s] med njimi v odvisnosti od brezdimenzijske strižne napetosti θ [-]. Krožci 'o' predstavljajo srednje vrednosti ter trikotniki “ ∇” in “ ∆” predstavljajo srednje vrednosti ± 1 standardno odstopanje. Črne (temne) oznake prikazujejo srednje vrednosti maksimalnih sil za poskuse E1–E4 in rde če (svetle) oznake za poskuse E5–E9. Figure 5. Statistical analyses of peak forces F [N] and time lags [s] between them, as a function of non-dimensional shear stress θ [-]. Circles 'o' represent mean values and triangles “ ∇” and “ ∆” represent mean values ± one standard deviation. Black (dark) symbols represent mean peak forces of tests E1–E4 and red (light) symbols those of tests E5–E9. Slika 6. Srednja maksimalna sila F [N] za vsak poskus prvega niza poskusov v nagibnem žlebu v odvisnosti od preto čne hitrosti vode [m/s]. Figure 6. Mean peak force F [N] for each experiment of the first set of tests in the tilting flume as a function of water flow velocity [m/s]. F [N] hitrost [m/s] – Velocity [m/s] θ [-] θ [-] F [N] časovni zamiki [s] – Time lags [s] Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 45 Slika 7. Srednja maksimalna sila F [N] za vsak poskus prvega niza poskusov v nagibnem žlebu v odvisnosti od brezdimenzijske strižne napetosti θ [-]. Figure 7. Mean peak force F [N] for each experiment of the first set of tests in the tilting flume as a function of non-dimensional shear stress θ [-]. Slika 8. Zna čilni signal treh merjenih pospeškov v nagibnem žlebu pri 1 % padcu dna. Figure 8. Typical signal of three measured accelerations in the tilting flume at 1 % slope. F [N] θ [-] čas [s] – Time [s] Nivoji pretvorbe – Levels of conversion Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 46 Vsi prikazani rezultati na slikah 3 do 7 so bili izmerjeni z uporabo prodnika vohuna z enim enoosnim pospeškometrom. Dobljeni rezultati so bili ocenjeni kot realisti čen prikaz dogajanja v laboratorijskem žlebu in torej dovolj dobri, da nadaljujemo z razvojem sledila. Tako smo vanj vgradili še dva enakovredna enoosna pospeškometra. Vsi nadaljnji rezultati so bili dobljeni s tako opremljenim prodnikom. Slika 8 prikazuje zna čilen signal izmerjenih pospeškov za izbrano meritev pri 1 % nagiba dna žleba, hitrosti toka 1,09 m/s in globini toka 16 cm. Nato smo razvili programsko orodje za avtomatsko prepoznavanje maksimalnih vrednosti lo čenih dogodkov, to je trkov v izmerjenem signalu pospeškov. Pri tej avtomatski analizi smo uporabili vektorsko vsoto pospeškov, da bi v signalu dolo čili okno, v katerem se je pojavil dogodek. Za analizo dolžine in usmeritve vektorja tr čne ali trenjske sile smo nato uporabili posamezne komponente, torej izvirni signal in ne njihovo vektorsko vsoto. 2.2 DRUGI NIZ LABORATORIJSKIH POSKUSOV Drugi sistemati čni niz laboratorijskih poskusov smo opravili v istem 10 m dolgem in 0,81 m širokem nagibnem laboratorijskem žlebu na Svobodni univerzi v Berlinu. Njegovo dno je bilo za prvi del tega niza meritev (del A) pokrito z gibljivimi naravnimi prodniki s srednjim premerom d m = 86 mm in d 90 = 93 mm (prodniki so bili veliki od 20 do 120 mm). Te razmere so ponovile razmere iz prvega niza laboratorijskih meritev. V delu A smo izvedli 6 poskusov (A1 do A6), vsak poskus je bil sestavljen iz treh posameznih meritev. V času posamezne meritve je bilo gibljivo dno laboratorijskega žleba prakti čno stabilno in vodni tok je erodiral le nekaj prodnikov (do nekaj 10 kilogramov). Izmerjena prodonosnost je bila manjša od 3 kg/s. Ta vrednost se zdi visoka, vendar se je prodnik vohun le izjemoma zaletel v drugi prodnik v gibanju in njegovo gibanje v žlebu je bilo prakti čno neodvisno od prodonosnosti. Za drugi del tega niza meritev (del B) smo iz žleba odstranili naravne prodnike in izvedli 7 poskusov (B1 do B7, vsaki č 1 meritev) na All the results shown on Figures 3 to 7 were obtained by the SPY-Cobble with only one built-in one-axis accelerometer sensor. The obtained results were evaluated as a realistic expression of circumstances in the laboratory flume and as such to be good enough to proceed with the cobble development. Therefore, two identical sensors were added to it. All following results were obtained using the SPY-Cobble with three sensors. The typical signal of measured accelerations for one run with 1 % of the flume bottom slope, the water velocity of 1.09 m/s and the water depth of 16 cm is shown on Figure 8. We then developed a software system that automatically recognises the maximum values of separated events, namely hits in the signals of acceleration. When we automatically detect the windows of the vector sum in which the hits are present, we go back to its components, which are our true acceleration signal and which determine the force vector length and direction. 2.2 SECOND SET OF LABORATORY TESTS In the same tilting laboratory flume at the Free University in Berlin (10-m long and 0.81- m wide), we systematically conducted the second set of laboratory tests. Its bottom was for the first part of the test (part A) covered with freely moving natural clasts with the arithmetic mean d m = 86 mm and d 90 = 93 mm, respectively (clasts were in the range between 20 mm and 120 mm). This situation reassembles the situation in the first set of test. In part A, we performed 6 tests (A1 through A6) comprised of 3 runs each. During each run the movable bed of the flume was practically stable and only some clasts (up to few tens of kilograms) were eroded. The measured sediment transport rates were lower than 3 kg/s. This value might seem to be high, but the SPY-Cobble was rarely hit by a moving clast and its movement was practically undisturbed by sediment transport. For the second part of the test (Part B), we have taken out the natural clasts and performed 7 tests (B1 through B7, 1 run each) Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 47 jeklenem dnu brez prodnikov. Za tretji del tega niza poskusov (del C) smo dno laboratorijskega žleba prekrili z betonskimi ploš čami, v katerih so bili vliti naravni prodniki (slika 9) – negibljivo dno. Izvedli smo 10 poskusov (C1 do C10, vsaki č 5 meritev). Med vsako meritvijo smo merili razli čne parametre toka in iz njih izra čunali druge relevantne parametre, prikazane v preglednici 2. on the steel bottom, with no clasts present in the flume at all. For the third part of the test (Part C), the bottom was covered by concrete plates with cast natural clasts (Figure 9) – fixed bed – and 10 tests were performed (C1 through C10, 5 runs each). During each run, various flow parameters were measured and calculated, as presented in Table 2. Preglednica 2. Pregled drugega niza laboratorijskih meritev v nagibnem žlebu (za razlago parametrov glej preglednico 1). Table 2. On overview of the second set of laboratory tests in the tilting flume (for definition of parameters see Table 1). meritev – Measured ra čun – Calculated analiza – Analysed poskus Test meritve Runs [–] dogodki Events [–] S [-] h [cm] v [m/s] Q [l/s] Fr [-] k St [m 1/3 /s] c [-] θ [-] F [N] t [s] A1 3 183 0.035 24.5 1.452880.8819.80 5.00 0.090 52.920.16 A2 3 154 0.040 23.5 1.482820.9519.43 4.87 0.099 35.280.16 A3 3 144 0.045 23.0 1.502801.0018.84 4.71 0.109 37.000.18 A4 2 86 0.050 22.5 1.512751.0318.25 4.55 0.119 43.220.18 A5 3 140 0.055 22.0 1.552761.1118.14 4.50 0.128 40.890.17 A6 3 121 0.0625 21.0 1.642791.3118.05 4.57 0.138 42.570.18 B1 1 121 0.020 13.5 2.322544.0662.34 14.26 0.028 8.84 0.11 B2 1 62 0.025 13.0 2.372504.4058.41 13.27 0.034 10.430.06 B3 1 59 0.030 13.0 2.412544.5554.22 12.32 0.041 9.02 0.06 B4 1 56 0.035 12.5 2.442474.8652.17 11.78 0.046 8.63 0.07 B5 1 55 0.040 12.0 2.502435.3151.38 11.52 0.051 9.55 0.07 B6 1 48 0.045 12.0 2.552485.5249.41 11.08 0.057 9.96 0.08 B7 1 52 0.050 12.0 2.582515.6547.43 10.63 0.063 9.81 0.07 C1 5 701 0.005 18.5 0.831240.3836.15 8.71 0.010 12.860.09 C2 5 318 0.010 16.0 1.091410.7636.98 8.70 0.017 32.270.17 C3 5 181 0.015 14.0 1.371551.3741.49 9.55 0.022 49.100.20 C4 5 146 0.020 13.0 1.511591.8641.61 9.45 0.027 59.050.21 C5 5 142 0.025 13.0 1.601692.0139.43 8.96 0.034 55.010.19 C6 5 147 0.030 12.0 1.661612.3439.39 8.83 0.038 62.520.19 C7 5 117 0.035 11.0 1.711522.7139.81 8.80 0.041 69.550.20 C8 5 143 0.040 11.0 1.771582.9038.55 8.52 0.046 56.940.17 C9 5 120 0.045 10.0 1.811473.3439.60 8.61 0.047 62.470.16 C10 5 117 0.050 10.0 1.861513.5338.61 8.40 0.053 72.540.18 Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 48 Slika 9. Pogled na dno laboratorijskega žleba za del C drugega niza laboratorijskih meritev. Dno je bilo prekrito z betonskimi ploš čami z vlitimi naravnimi prodniki (število prodnikov na m 2 je bilo v povpre čju 35, minimalni premer d min = 4 cm, srednji premer d m = 7 cm in maksimalni premer d max = 10 cm). Smer toka v 0,81 m širokem žlebu je bila z leve na desno. Figure 9. A view of the flume bottom for part C of the second set of laboratory tests. The bottom was covered by concrete plates with fixed (cast) natural clasts (number of clasts per m 2 was 35 on average, minimum diameter d min = 4 cm, mean diameter d m = 7 cm, and maximum diameter d max = 10 cm). The flow direction in the 0.81 m wide flume is from left to right. Merjeni pospeški vsake meritve se lahko prikažejo v obliki zvo čnega zapisa. Vsak dogodek lahko slišimo in tako dobimo precej jasen vtis o dogajanju. Vse zvo čne zapise smo ustvarili iz originalnih meritev pospeškov s pomo čjo funkcij “sound.m” in “soundsc.m” v programskem okolju Matlab ® . Sliki 10 in 11 prikazujeta rezultate analize merjenih pospeškov, in sicer lo čeno za posamezne dele A, B in C tega niza laboratorijskih poskusov. Slika 10 prikazuje odvisnost maksimalnih sil in njihovih časovnih zamikov. Slika 11 prikazuje statisti čno analizo maksimalnih sil v odvisnosti od brezdimenzijske strižne napetosti θ. Nadalje je bila dolo čena srednja maksimalna sila za vsak poskus, in sicer v odvisnosti od hitrosti toka (slika 12) oziroma v odvisnosti od brezdimenzijske strižne napetosti θ (slika 13). 3. RAZPRAVA Opravljena raziskava je potrdila, da je prodnik vohun dovolj robusten in popolnoma uporaben za meritve dinamike posameznih sedimentnih delcev v turbulentnem toku. Kljub temu ga je treba obravnavati kot uporaben prototip. Glavna omejitev pri njegovi uporabi je laboratorijsko okolje, v katerem ga lahko uspešno uporabimo, saj bi za uporabo v naravnem okolju najprej morali dodati npr. pasivni radijski oddajnik, da bi lahko napravo po meritvah znova našli. Measured accelerations during each run can also be presented in a form of a sound file. In this case each event can be heard and quite a realistic impression can be achieved only by listening to a sound file. All sound files have been converted from original acceleration measurements using MATLAB ® functions “sound.m” and “soundsc.m”. The results of the analyses of measured accelerations are presented in Figures 10 and 11, separately for each part of the tests (A, B, and C). Figure 10 presents the dependence of peak forces and their respective time lags. Figure 11 presents statistical analyses of peak forces as a function of the non-dimensional shear stress θ. Furthermore, mean peak force for each test was determined and it is shown in Figure 12 as a function of the corresponding water flow velocity, and in Figure 13 as a function of non-dimensional shear stress θ. 3. DISCUSSION The SPY-Cobble has proved to be robust enough and fully functional by means of measurements of single coarse particle dynamics in turbulent flows. Still, it should be considered as a functional prototype. The major limitation in its use is the laboratory environment, where it can be used sucessfully and usefully, because modifications would be needed for its recovering in a natural environment, such as adding a passive radio transmitter. Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 49 Slika 10. Prikaz maksimalnih sil F [N] v odvisnosti od časovnih zamikov [s], posebej za vse tri dele drugega niza laboratorijskih poskusov v nagibnem laboratorijskem žlebu (del A – gibljivi naravni prodniki, del B – jekleno dno, del C – vliti naravni prodniki). Za del A je bilo prepoznanih 828 trkov, za del B je bilo trkov 453 in za del C 2132 trkov. Figure 10. All peak forces F [N] as a function of their respective time lags [s], given separately for all three parts of the second set of tests in a tilting flume (A – movable natural clasts, B – steel bottom, and C – fixed natural clasts). For part A, there were 828, for part B 453, and for part C 2132 detected peaks. časovni zamiki [s] – Time lags [s] časovni zamiki [s] – Time lags [s] časovni zamiki [s] – Time lags [s] del A – Part A del B – Part B del C – Part C F [N] F [N] F [N] Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 50 Slika 11. Statisti čna analiza maksimalnih sil F [N] in časovnih zamikov [s] med trki v odvisnosti od brezdimenzijske strižne napetosti θ za vse tri dele drugega niza poskusov v nagibnem laboratorijskem žlebu (del A – gibljivi naravni prodniki, del B – jekleno dno, del C – vliti naravni prodniki). Krožci 'o' ozna čujejo srednje vrednosti parametrov, trikotniki “ ∇” in “ ∆” pa srednjo vrednost ± ena standardna deviacija. Figure 11. Statistical analyses of peak forces F [N] and time lags [s] between them, as a function of non-dimensional shear stress θ given separately for all three parts of the second set of tests in a tilting flume (A – movable natural clasts, B – steel bottom, and C – fixed natural clasts). Circles 'o' represent mean values and triangles “ ∇” and “∆” represent mean values ± one standard deviation. del A – Part A del B – Part B del C – Part C F [N] F [N] F [N] časovni zamiki [s] – Time lags [s] časovni zamiki [s] – Time lags [s] časovni zamiki [s] – Time lags [s] θ [-] θ [-] θ [-] θ [-] θ [-] θ [-] Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 51 Slika 12. Srednja maksimalna sila F m [N] za vsak poskus treh delov (A, B in C) drugega niza laboratorijskih poskusov v nagibnem žlebu v odvisnosti od preto čne hitrosti vode [m/s]. Figure 12. Mean peak force F m [N] for each run of three parts (A, B, and C) of the second set of tests in the tilting flume as a function of water flow velocity [m/s]. Slika 13. Srednja maksimalna sila F m [N] za vsak poskus vseh treh delov (A, B in C) drugega niza laboratorijskih poskusov v nagibnem žlebu v odvisnosti od brezdimenzijske strižne napetosti θ [-]. Figure 13. Mean peak force F m [N] for each run of three parts (A, B, and C) of the second set of tests in the tilting flume as a function of non-dimensional shear stress θ [-]. hitrost [m/s] – Velocity [m/s] F m [N] F m [N] θ [-] A B C A B C Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 52 Druge lastnosti prototipa, kot so hitrost vzor čevanja, razpoložljivi prostor pomnilnika ali hitrost prenosa podatkov, lahko dosežemo s spremembo dolo čenih elektronskih delov. Vendar obstaja možnost, da tovrstne spremembe negativno vplivajo na minimalno porabo energije, kot jo ima merilna naprava sedaj. Dva niza opravljenih laboratorijskih poskusov v nagibnem laboratorijskem žlebu ob razli čnih hidravli čnih pogojih sta pokazala, da lahko prodnik vohun uspešno meri kontaktne sile in natan čno poda čase teh kontaktov med gibanjem posameznega sedimentnega delca (sliki 10 in 11). Opravljene meritve s prodnikom vohunom lahko opišemo kot meritve gibanja posameznega sedimentnega delca v čisti vodi in ob nepomi čnem dnu. Če je bila v posameznem primeru prisotna šibka prodonosnost, jo lahko zanemarimo, saj prakti čno ni imela omembe vrednega vpliva na dinamiko gibanja prodnika vohuna. To seveda ne bi ve č držalo v primeru popolnoma gibljivega dna in visoke prodosnosti. Take soodvisnosti ob omenjenih hidravli čnih razmerah je treba s prodnikom vohunom še raziskati. Opravljene laboratorijske meritve so podprle veljavnost kvadratnega zakona trka, ki dolo ča, da je maksimalna tr čna sila odvisna od druge potence tr čne hitrosti. Res je, da nismo neposredno merili hitrosti prodnika vohuna, toda slika 12 potrjuje veljavnost omenjenega zakona. Za del A ta zakon ne velja popolnoma, saj so bili prodniki v laboratorijskem žlebu gibljivi. Tako se ob kontaktih med njimi in prodnikom vohunom niso pojavili le centri čni trki. To je še toliko bolj veljavno za meritve v delu B, kjer je bilo dno žleba sestavljeno iz jeklenih ploš č. Pri takih razmerah so bile izmerjene visoke hitrosti toka zaradi majhne hrapavosti ostenja (slika 12). Prodnik vohun je v glavnem drsel ali se kotalil po dnu žleba in le deloma udarjal ob dno. To je poglavitni vzrok, da je odvisnost srednje maksimalne sile od hitrosti toka v tem primeru konstantna in ne kvadratna. Tudi maksimalne sile so nekoliko nizke, saj je prodnik vohun v glavnem drsel in se kotalil in ni udarjal ob jekleno dno. Hidravli čne razmere v delu C nato znova popolnoma potrjujejo veljavnost kvadratnega zakona trkov (slika 12). Dno žleba je bilo Other features such as sampling speed, space available for storage and speed of download could be improved by changes of certain electronic parts, although these changes might negatively affect the minimal power consumption, which the device has at the present. Two sets of measurements in the tilting flume under different hydraulic conditions have proved that the SPY-Cobble can successfully measure contact forces and give precise times of contacts during single particle transport (Figures 10 and 11). The measurements conducted using SPY-Cobble can be defined as single particle transport in clear water and stable bed. When there was weak sediment transport in some runs, we could neglect it because it had practically no significant influence on the dynamics of the SPY-Cobble. This would not be true in case of fully movable bed and high sediment transport rates. This interrelations under such hydraulic conditions are still to be investigated using the SPY-Cobble. The conducted laboratory measurements have supported the validity of quadratic impact law. It is true that we did directly measure the tracer velocity, but Figure 12 supports the validity of the quadratic impact law. For part A, this law is not fully correct, because clasts in the flume were movable and during the impacts or contact events between them and the tracer, centric impacts were not the only type of collisions. This is even more true for the runs in part B, where the flume bottom was made of steel plates. Under such conditions very high water flow velocities were measured due to low roughness of the flume (Figure 12). The SPY-Cobble was mainly sliding, partially rolling, and practically had little impact with the flume bottom. That is why in this case the functional dependence of the mean detected peak forces on the water flow velocity is constant rather than quadratic. Also peak forces are rather low, because the tracer was mainly sliding and rolling and not impacting the steel plates. But hydraulic conditions in part C gave a full validity of the quadratic impact law (Figure 12). The flume bottom was covered by fixed natural clasts, cast in concrete plates (Figure 9). Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 53 prekrito z betonskimi ploš čami, v katerih so bili vliti (negibljivi) naravni prodniki (slika 9). Mnogo manj je možno ugotoviti o časovnih zamikih med posameznimi trki oziroma tr čnimi dogodki (slika 11). Kljub temu je očitno, da so časovni zamiki v primeru kotaljenja ali drsenja (del B) v povpre čju mnogo manjši kakor v primeru prevladujo čega poskakovanja (del A in C). Ta o čitna razlika med delom B in deloma A in C se lahko sliši, če pozorno prisluhnemo izmerjenim zvo čnim zapisom meritev pospeškov. Analiza merjenih maksimalnih sil (slika 13) in časovnih zamikov (slika 11) bo v prihodnje usmerjena v oblikovanje ustrezne slu čajne porazdelitve teh dveh parametrov. Tak pristop bo pomagal izdelati generator sinteti čnih časovnih zaporedij kontaktov in pripadajo čih maksimalnih sil, ki bi kar najbolj ustrezale naravnim dogodkom pri premeš čanju sedimentov. Glavni namen bo poiskati soodvisnost med hidravli čnimi parametri (hitrost toka, globina toka, strižna napetost), sedimentološkimi parametri (velikost delca, gostota delca) in parametri slu čajne porazdelitvene funkcije. 4. ZAKLJU ČKI Na osnovi opravljene raziskave lahko zaklju čimo, da obstaja o čitna potreba po nadaljnjem razvoju obstoje čih vrst sledil kakor tudi po razvoju novih vrst sledil z uporabo novih tehnologij. Če so magnetna in radijska sledila dovolj dobra za sledenje njihovemu gibanju v času poplavnega vala z namenom dolo čiti obdobja gibanja in mirovanja ter njihovo razporeditev, potem je nujen nov tip sledila, če želimo pridobiti nov vpogled v dinamiko premeš čanja plavin. Novorazviti instrumentizirani prodnik vohun je primer bolj kompleksnega sledila, ki je bil zaradi svoje proizvodne cene (nekaj tiso č €) testiran le v laboratorijskih razmerah. Ker podobnih sledil v svetu še ni, tudi ni na voljo meritev, ki bi jih lahko vzeli za primerjavo. Ocena uporabnosti je bila zato izvedena s pomo čjo teorije trkov in kvadratnega zakona trka. Raziskava je pokazala, da je prodnik vohun uporabno raziskovalno orodje, ki daje Much less can be stated about the time lags between individual impacts or contact events (Figure 11). Nevertheless, it is obvious that under rolling and sliding, as in part B, these lag times are much lower on average than in the case of saltating movements, as prevailing in parts A and C. These clear differences between part B on one hand and parts A and C on the other, can also be heard, namely by carefully listening to the sound files from these measurements. A further analysis of the measured peak forces (Figure 13) and time lags (Figure 11) will go into creating an appropriate stochastic distribution of these two parameters. This will help to establish a generator of synthetic time series of contacts and corresponding peak forces, which should be able to match natural sediment transport events as closely as possible. The main task will be to find the correlation between hydraulic parameters (water flow velocity, water depth, shear stresses), sedimentological parameters (particle size and density), and parameters of stochastic probability distribution function. 4. CONCLUSIONS Based on the research, we can conclude that there is an obvious need to further develop the existing types of sediment tracers, as well as to develop new types of tracers, using more advanced technologies. If magnetic and radio tracers are good enough to follow a tracer during a flood to determine moving and resting periods and their distribution, then a new type of a tracer is needed if more insight into the dynamics of sediment transport is expected. A new instrumented tracer SPY-Cobble is an example of a more sophisticated tracer, which, because of its costs (several thousand €), has only been tested in the laboratory environment. Because there are no similar tracers developed in the world, there are also no measurements that could be taken for comparison pourposes. Assessment of its usefulness was therefore done on the basis of impact theory and the quadratic impact law. The tracer has proven to be a valuable Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 54 naslednje neprekinjene vrednosti parametrov premeš čanja grobih sedimentih delcev: - to čne čase kontaktov z okoliškimi trdimi telesi (pesek, prod, groblja, skale, samice); - vršne intenzitete dinami čnih trenjskih ali tr čnih sil, ki delujejo na sledilo v času teh kontaktov; - srednjo hitrost sledila in - na čin gibanja med posameznimi kontakti (kotaljenje, drsenje, poskakovanje). Za dolo čitev dejanske poti sledila bi morali v prodnik vgraditi dodatni enoosni sensor. Opisani podatki omogo čajo raziskovalcu oblikovati bolj dodelan model premeš čanja grobih sedimentnih delcev, npr. na osnovi Lagrangeovega pristopa in z uporabo statisti čnih in slu čajno porazdeljenih parametrov. Možen je razvoj modela premeš čanja z uporabo mehanike kontakta in lastnosti materialov, ki bi se kombinirali z merjenimi vrednostmi pomembnih parametrov, kot so koeficient odboja “e” ali trajanje trka “t”. Za bolj kompleksne modele premeš čanja, kot je to bilo nakazano zgoraj, je treba prodnik vohun razviti v novo fazo. Če bi ga želeli uporabiti kot uporabno raziskovalno orodje v dolinskih prodonosnih rekah in ne le v strmih hudournikih, je treba predvsem zmanjšati njegovo velikost. ZAHVALA Sledilo je bilo razvito v okviru evropskega projekta EROSLOPE II “Dynamics of Sediments and Water in Alpine Catchments – Processes and Prediction” (projekt ENV4- CT96-0247). Avtorja se zahvaljujeta za finan čno pomo č Evropske komisije in Ministrstva za znanost in tehnologijo Republike Slovenije, ki sta projekt sofinancirala. research tool, which gives the following continuously defined parameters of transport of coarse sediment particles: - precise times of contacts with surrounding bodies (sand, gravel, pebbles, cobbles, boulders); - peak intensities of dynamic friction or impact forces acting upon the tracer during these contacts; - mean tracer velocity, and - way of movement between contacts (rolling, sliding, or saltating). For the determination of the pathway of the tracer, an additional one-axis accelerometer should be built into it. These data enable a researcher to design a more profound model of coarse sediment transport, e.g. based on the Lagrangian approach and statistically or stochastically distributed parameters. One could even develop a transport model using contact mechanics and material properties, combining them with the measured values of important parameters such as restitution coefficient “e” or duration of impacts “t”. For more sophisticated transport models, one should further develop the SPY-Cobble. Especially, one should reduce its size, in order to use it as a relevant research tool not only in steep torrents, but also in gravel-bed rivers. ACKNOWLEDGEMENT The satellite was developed within the framework of the European project EROSLOPE II “Dynamics of Sediments and Water in Alpine Catchments – Processes and Prediction” (project ENV4-CT96-0247). The financial support of the European Commission and of the Ministry of Science and Technology of the Republic of Slovenia is greatly acknowledged. Mikoš, M., Spazzapan, M.: Laboratorijska uporaba sledila za meritve dinamike premeš čanja plavin v turbulentnih tokovih – Laboratory Application of a Satellite for Measuring Dynamics of Sediment Transport in Turbulent Flows © Acta hydrotechnica 23/38 (2005), 39–55, Ljubljana 55 VIRI – REFERENCES Mikoš, M., Četina, M., Krzyk, M., Spazzapan-Escorza, M. (2000). EROSLOPE II – Hydraulics in steep mountain streams – final report. University of Ljubljana, Faculty of Civil and Geodetic Engineering, 60 p. Mikoš, M., Petrov či č, J., Spazzapan, M. (2001). Postopek in naprava za merjenje elementov dinamike gibanja in sil, ki delujejo na posamezne delce v naravnem okolju (A Method and an Apparatus for Measuring of Movement Dynamics Elements and Forces Acting Upon Single Particles in Natural Environment). Patent No.: P-9900222. Ljubljana: Urad RS za intelektualno lastnino, 10 p. (in Slovenian). Spazzapan, M., Petrov či č, J., Mikoš, M. (2004). Novo sledilo za merjenje dinamike premeš čanja plavin v turbulentnih tokovih – A New Satellite for Monitoring Dynamics of Sediment Transport in Turbulent Flows. Acta hydrotechnica 22, 135–148. Naslova avtorjev – Authors’ addresses izr. prof. dr. Matjaž Mikoš Fakulteta za gradbeništvo in geodezijo – Faculty of Civil and Geodetic Engineering Univerza v Ljubljani – University of Ljubljana Jamova c. 2, SI-1000 Ljubljana E-mail: mmikos@fgg.uni-lj.si mag. Mojca Spazzapan IBM Slovenia Trg republike 3, SI-1000 Ljubljana E-mail: mojca.spazzapan@si.ibm.com