The global positioning system (GPS) is utilized for analysis of flows in the water environment. A float equipped with a GPS unit is designed to drift on the surface of the water. Its driving force is the fluid resistance exerted on a pair of rectangular plates. While it travels over the surface, the GPS unit evaluates its position every second, and spatiotemporal data that specify its motion are transmitted to be recorded. Results of experiments conducted to study unsteady flows generated in Kojima Lake are introduced

Numaguchi, Satoshi

Watanabe, Masaji

English

Okayama University Digital Information Repository

An Experimental Study of Unsteady Flows Generated in Kojima Lake

Okayama University Scientific Achievement Repository

Journal of the Faculty of Enviromental Science and Technology,Okayama UniversityVoLS, No. 1, pp.23·26, March 2003An Experimental Study of Unsteady Flows Generatedin Kojima LakeMasaji Watanabe1 and Satoshi Numaguchi2(Received November 30, 2002)The global positioning system (GPS) is utilized for analysis of flows in the water environment. Afloat equipped with a GPS unit is designed to drift on the surface of the water. Its driving force isthe fluid resistance exerted on a pair of rectangular plates. While it travels over the surface, theGPS unit evaluates its position every second, and spatiotemporal data that specify its motion aretransmitted to be recorded. Results of experiments conducted to study unsteady flows generatedin Kojima Lake are introduced.Key words: water environment, global positioning system1 INTRODUCTIONA GPS unit evaluates its position analyzing signalstransmitted from the GPS satellites. More accurateresults can be obtained with an additional feature toanalyze signals transmitted from a radiobeacon, whichis called the differential GPS. We conducted experi-ments to examine flows in the water environment witha float equipped with a differential GPS unit, whichwe call the GPS-float. The GPS-float is designed todrift on the surface of the water. The driving force ofthe GPS-float is the fluid resistance exerted on a pairof rectangular plates. Those plates are set crosswisein order to receive the fluid resistance as uniformlyas possible, and fixed to one end of a bar, while theother end is connected to a buoyant body of the GPS-float, and they are submerged in the water, while thebuoyant body stays on the surface. While the floattravels, the GPS unit evaluates its position once ev-ery fixed time interval, e.g. every second, analyzingsignals transmitted from the GPS satellites and a ra-diobeacon. Those spatiotemporal data concerning themotion of the GPS-float are transmitted with a wire-less modem, and they are in turn received with a re-ceiver to be recorded for an analysis. An illustrationof the GPS-float is given in Figure 1.In the following sections, we introduce some exper-imental results. Those experiments were conducted to1Department of Environmental and Mathematical Sciences,Faculty of Environmental Science and Technology, OkayamaUniversity.2The Graduate School of Natural Science and Technology(Mater's Course), Okayama University.~....~••-,. -._'.IIFigure 1: Illustration of the GPS-float; [1]: the GPSunit, [2]: the GPS antenna, [3]: the wireless modem.study unsteady flows generated in Kojima Lake. Ko-jima Lake is an artificial lake created by isolating apart of Kojima Bay with a bank. There are six gatesthat connect Kojima Lake and Kojima Bay. Thosegates are opened when it is necessary to discharge thewater in Kojima Lake to Kojima Bay in order to con-trol the water level of Kojima Lake, and such a dis-charge of the water generates an unsteady flow in Ko-jima Lake. We conducted experiments to study suchunsteady flows. In particular, we introduce results ob-tained in experiments conducted on May 23, 2002 andJune 25, 2002. Figures 2 and 3 show photographs ofthe GPS-float in the experiments on May 23, 2002 and2324 J. Fac. Environ. Sci. and Tech .. Okayama Univ. 8 (1) 2003Figure 2: The experiment conducted in Kojima Lakeon May 23, 2002.Figure 4: Kojima Lake and its vicin.ity; [1]: SasagaseRiver, [2]: Kurashiki River, [3]: the gates.500 -EXPERIMENTAL AREA4000 r3500 -5000 -2500 -I 2000 ->-1sao -1000 -Figure 3: The experiment conducted in Kojima Lakeon June 25, 2002.o L-2000 -1500 -1000 -500 0 500 1000 1500 2000X (m)June 25, 2002, respectively.Figure 5: An area where the experiments were con-ducted.2 EXPERIMENTS USING THE GPS-FLOATSeto Inland Sea separates Shikoku Island from themain island of Japan. Okayama prefecture lies in themain island and faces Seto Inland Sea. We conductedexperiments using the GPS-float to study unsteadyflows generated in Kojima Lake in Okayama prefec-ture. Kojima Lake is an artificial lake created by iso-lating a part of Kojima Bay which connects with SetoInland Sea. There are two rivers that serve as the pri-mary water source for Kojima Lake: Sasagase Riverand Kurashiki River. An illustration of Kojima Lakeand its vicinity is given in Figure 4. There are six gatesthat connect Kojima Lake and Kojima Bay. Each ofthose gates is 24 m wide. They are opened when thedischarge of the water from Kojima Lake to KojimaBay is necessary in order to control the water level ofKojima Lake. Such a discharge generates an unsteadyflow in Kojima Lake. We introduce results of experi-ments conducted to study such unsteady flows on May23, 2002, and June 25, 2002. Those results are givenin terms of the trajectories of the GPS-fioat, and theylie in the box shown in Figure 5.On May 23, 2002, the gates were opened approxi-mately from 4:10 am to 6:50 am GMT. The dischargeof the water through the gates generated an unsteadyflow in Kojima Lake, and we conducted an experi-ment to study the unsteady flow. Figure 6 shows thetemporal change of the water level of Kojima Lakefrom 4:00 am to 7:00 am GMT on May 23, 2002. Italso shows the temporal changes of the tide level ofKojima Bay, the water levels of Kurashiki River andSasagase River. Those water levels are in accordancewith a local standard (Awabiura Point). The gatesM. WATANABE et al. I An Experimental Study of Unsteady Flows Generated in Kojima Lake 25.,200 400 600 800 1000 1200X(m]J13~O~52~OJ8'I IGPS-FLOAT EXPERIMENT (MAY 23, 2002)I3800 r3800 -3400 -3200 -I>-3000 -2800 -2600 -2400 L-2008:001.3WATER lEVElS (MAY 23, 2002)1.' r-----.----,---,---,------,---'-----r------,----,0.2 '--_--'-_-----L__~_---'-_--..__-'--_----"--_---'~~ .~ 5~ 5~O 6~ 6:~ 7~O 7~TIME [aMTI1.10.81.20 .•0.30.80.50.'0.7Figure 6: The temporal changes in the water levelsof Kojima Lake, Kurashiki River, Sasagase River, andthe tide level of Kojima Bay on May 23, 2002.Figure 7: The trajectory of the GPS-float obtained inthe experiment on May 23, 2002.were opened when the tide level of Kojima Bay becameas low as the water level of Kojima Lake, and theywere closed when they became almost equal. Whilethe gates were open, the water level of Kojima Lakelowered approximately by 0.25 m while the tide levelof Kojima Bay also lowered approximately by 0.23 m.We conducted an experiment using the GPS-float tostudy the unsteady flow generated by the dischargeof the water. Figures 7 shows the trajectory of theGPS-float, which shows its movement from 4:7:00 to6:43:14 GMT. Time elapsed (minute) after the gateswere opened is also indicated. The GPS float trav-eled an approximate distance of 934.0967 m, and itsaverage velocity was approximately 0.0997 m/s.We conducted an experiment also on June 25,2002,when the gates were opened approximately from 5:00am to 7:40 am GMT. Figure 8 shows the temporalchanges of the water levels of Kojima Lake, KurashikiRiver, Sasagase River, the tide level of Kojima Bayfrom 5:00 am to 8:00 am GMT on June 25, 2002.While the gates were open, the water level of KojimaLake lowered approximately by 0.72 m while the tidelevel of Kojima Bay also lowered approximately by 0.7m. The GPS float traveled an approximate distanceof 821.8722 m, and its average velocity was approxi-mately 0.1895 m/s. Figures 9 shows the trajectory ofthe GPS-float, which shows its movement from 6:11:55to 7:24:14 GMT.studied by analyzing the equation governing the dy-namics of the flow (Watanabe 1999, 2000 (1), (2),2002(1), (2), Watanabe, et al. 2001). Since the drivingforce of the GPS-float is the fluid resistance exertedon a pair of rectangular plates, one can simulate itsmotion by solving its momentum equation providedthe fluid resistance is specified, and, the fluid resis-tance can be determined by solving equations thatgovern the dynamics of the flow (Watanabe 1999, 2000(2), 2002 (1), (2), Watanabe, et al. 2001). Thus ex-perimental results obtained using the GPS-float canbe introduced into numerical studies to examine theircorrespondence with numerical results.ACKNOWLEDGMENTSWe would like to thank people in the Kojima Bay Cen-tral Administration Office, the Section of Land Im-provement in the Kojima Bay Area for sharing dataconcerning the water level of the Kojima Lake andthe tide level of the Kojima Bay. We would also liketo thank people in the Machining Center, the Facultyof Engineering, Okayama University for building theGPS-float, and those students in the Faculty of Envi-ronmental Science and Technology who kindly helpedus with the GPS-float experiment.REFERENCES3 CONCLUSIONThe GPS-float is designed to study flows in the wa-ter environment experimentally (Watanabe 1999, 2000(2), 2002 (1), (2), Watanabe, et al. 2001). On theother hand, the flows in the water environment can beWatanabe, M. (1999): A numerical simulation oflake flow and a GPS-float experiment, The Sec-ond International Symposium on Water Envi-ronment, Okayama University, Journal of theFaculty of Environmental Science and Technol-ogy, Okayama University (Special Edition), pp.111-116.26 J. Fac. Environ. Sci. and Tech., Okayama Univ. 8 (1) 2003WATER LEVELS (JUNE 25, 2002)1.' ,------,-------,---r-----r----,-'--'""'::";;;;:-;-:-:;;::-----,1.31.21.10.•0.'0.70.'0.'0..0.'0.2."" ."" ."" 5:30 6:00 6:30TIME fGUT)7:00 7:30 8:00Figure 9: The trajectory of the GPS-Hoat obtained inthe experiment on June 25, 2002.Figure 8: The temporal changes in the water levelsof Kojima Lake, Kurashiki River, Sasagase River, andthe tide level of Kojima BayWatanabe, M. (2000) (1): A numerical analysis ofunsteady How in Kojima Lake, Journal of theFaculty of Environmental Science and Technol-ogy, Okayama University 5(1), pp. 31-34.Watanabe, M. (2000) (2): On analysis of unsteadyHows in lakes and marshes and its experiments, Lectures supported by Kogakukai, Science andEngineering Reports of Tohokugakuin University,34(2), pp. 49-53.(in Japanese)Watanabe, M. and Kunisada, S. (2001): An exper-imental evaluation of lake How simulation, Jour-nal of the Faculty of Environmental Science andTechnology, Okayama University 6(1), pp. 11-15.Watanabe, M. (2002) (1): A numerical analysis andan experimental study of unsteady How in Ko-jima Lake, Journal of the Faculty of Environ-mental Science and Technology, Okayama Uni-versity 7(1), pp. 39-44.Watanabe, M. (2002) (2): Utilization of the globalpositioning system for analyses of Hows in wa-ter environments, The 6TH World Multiconfer-ence on Systemics, Cybernetics and Informatics,PROCEEDINGS Volume V, Computer Science1(2002),172-176.3800 r3800 -3'00 -3200 -I>3000 -2800 -2800 -2.00 L-200GPS-FLOAT EXPERIMENT (JUNE 25, 2002),J200 'DO 600 800 tODD 1200X(m)

An Experimental Study of Unsteady Flows Generated in Kojima Lake

Abstract

Similar works

Full text

Available Versions

Okayama University Digital Information Repository

Okayama University Scientific Achievement Repository