臺灣博碩士論文加值系統

本論文主要以數值模擬來探討局部沖刷於橋墩附近的流況變化及其物理機制，使用了兩個不同的現場案例，分別為后豐大橋的橋樑沖刷以及大甲溪實施固床工保護的間隙沖刷。數值模擬應用於此問題一直以來都是相當困難的課題，因此，於本論文中藉由商業軟體Flow-3D做分析及討論，其分析內容同時包含了定床跟動床兩種數值模型設置，並藉由實驗結果輔助之。於橋樑沖刷部分，定床的模擬中，分析第一根橋柱前的水深比較，其數值結果實驗結果相當吻合；於動床模擬中，在實驗設置裡加入了超音波儀器，從模擬結果可以清楚發現其存在位置會影響到底床的沖刷深度以及整個流場的變化，因此移除了該裝置之後，試著去探討在橋墩前所產生的跌水現象所引起的沖刷所帶來的影響。由模擬結果發現，有跌水沖刷的部分，主要沖刷位置會集中在橋柱前方形成一個沖刷坑，同時底床被掏刷過程中，橋柱迎水面會受到強勁的水流的流速衝擊，橋柱靠近底床部分最大，往上遞減。然而沒有跌水沖刷的部分，主要沖刷位置落在第一根橋柱周圍，其因素歸因於向下射流以及馬蹄型渦流。再者，固床工的間隙沖刷模擬，當底床設置為固床時，可以發現不論在何種大小流量下都會在第三階部分產生一個明顯的Z方向流速，並於固床工編原產生明顯的渦流。由於此間隙沖刷案例的模擬，其物理問題設置屬不連續體排列，因此在數值模擬過程中，不易觀察其確切的物理現象，因此，此部分的數值模擬尚待開發。

In this thesis, the flow field and physical mechanism of local scour problem around the bridge piers is mainly used by numerical simulation. Two different field cases are studied: they are the bridge scour effects surrounding the Hou-Feng Bridge and the gap scour effects about the stepped concrete block grade control structure in Ta-Jia river, respectively. It is an extremely difficult problem by using the numerical programming to solve these problems. Hence we seek the help from the commercial software, Flow-3D, to analyze the problem. The problem setting includes the rigid-bed and mobile-bed simulation and the laboratory experiments are aided in the meantime. The numerical results of the rigid-bed simulation are compared with the laboratory results in terms of the fluid depth in front of the first pier. The results from numerical studies and laboratory experiments match very well. In the mobile-bed simulation, the ultrasound device is added in the experiment and the scour depth and the variation of the whole flow field are interfered with the sensor. Hence after the ultrasound device is removed, the influence of the overfall flow in the bridge scour simulation can be clearly classified. The mainly scour hole is concentrated in front of the first pier in the numerical simulation with the overfall flow. In the meantime, the upstream of the first pier is borne by the current flow and the maximum flow velocity is measured close the bottom of the first pier. If the overfall flow is not considered in the simulation, the mainly scour hole is concentrated around the first pier. The reasons are attributed to the down flow and the horseshoe vortex. As for the rigid-bed simulation of the gap scour, the third step of the stepped concrete block grade control structure always existed the obvious velocity on the Z-axis and the strong vortex near the edge of the stepped concrete block grade control structure in the numerical simulation no matter how strength of the flow. In the gap scour simulation, it is difficult to observe the accurate physical phenomenon during the numerical simulation in light of its physical problem setting belongs to the discontinuous arrangement. Hence the applied numerical simulation still requires further development.

摘要 ................................................................................................................................ I
Abstract .......................................................................................................................... II
Content .......................................................................................................................... III
Figure lists ....................................................................................................................... V
Table lists ....................................................................................................................... XI
Chapter 1 Introduction ................................................................................................... 1
1.1 Descriptions of the damage near Hou-Feng Bridge .......................................... 2
1.2 Review of previous investigations ..................................................................... 5
1.3 The gap scour at stepped concrete block grade control structure ...................... 7
1.4 Flow 3D ............................................................................................................. 9
1.5 Structure of this thesis ..................................................................................... 11
Chapter 2 Basic theory for local scour and the experimental setting ................... 13
2.1 The classification of erosion type .................................................................... 13
2.2 Physical behavior of the flow over the local scour region .............................. 19
2.3 Laboratory experiments ..................................................................................... 21
2.3.1 Transform field scale to laboratory scale ............................................. 22
2.3.2 Laboratory experimental setting and equipments ................................. 23
2.4 Procedure of laboratory experiments ............................................................... 26
2.4.1 Experiment 1: rigid bed ........................................................................ 27
2.4.2 Experiment 2: gravel and clear water ................................................... 29
Chapter 3 Numerical experiments ............................................................................... 31
IV
3.1 Procedure of numerical setting by Flow-3D ................................................... 32
3.2 Numerical simulation 1: rigid bed case ......................................................... 34
3.3 Use the small domain to simulate all the mobile bed cases ............................. 38
3.4 Experiment 2: mobile bed with ultrasound device .......................................... 41
3.5 Experiment 3: mobile bed case ........................................................................ 45
3.6 Experiment 4: remove the first river bed in mobile bed case .......................... 46
Chapter 4 Results and discussions ............................................................................. 48
4.1 Rigid-bed case ................................................................................................... 48
4.2 Critical Shields number ................................................................................... 58
4.3 Mobile bed simulation with ultrasound device ............................................... 63
4.4 Mobile bed case ............................................................................................... 71
4.5 Remove the first river bed in mobile bed case .................................................. 84
Chapter 5 Experimental setting of gap scour and discussions ................................ 93
5.1 Field site investigation ..................................................................................... 93
5.2 Experimental setting .......................................................................................... 96
5.3 Scour of “all-gaps-opened” conditions ............................................................ 99
5.4 Numerical setting for gap scour ...................................................................... 102
5.4.1 Numerical simulation 1: the scour depth is fixed in the geometry ....... 103
5.4.2 Numerical simulation 2: gap scour at a steeped concrete block grade
control structure ........................................................................................................... 107
5.5 Results and discussions ................................................................................... 111
5.5.1 The gap scour with the given scour depth .......................................... 112
5.5.2 The gap scour with the mobile bed condition ...................................... 117
Chapter 6 Conclusion and recommendation ............................................................ 119
6.1 Conclusion ............................................................................................................... 119
6.2 Recommendation ..................................................................................................... 121
Reference ...................................................................................................................... 122

References
[1] H.N. Hsieh, “Acoustical scour monitoring applied to scale model of HouFeng
Bridge”, master''s thesis in Department of Civil Engineering College of
Engineering, NTU, 2010.
[2] Rouse, H. “Discharge characteristics of the free overfall.” Civil Engineering (N.Y.),
1936.
[3] Beltaos, S. “Oblique impingement of plane turbulent jets”, J. Hydr. Div., pp.
1177-1192,1976.
[4] Beltaos, S., and N. Rajaratnum. “Plane turbulent impinging jets”. J. Hydr. Res.,
1973.
[5] Robinson, K. M. “Predicting stress and pressure at an overfall”, Res, 11:29-59,
1992.
[6] Fogle, A. W., J. C. McBurnie, B. J. Barfield, and K. M. Robinson. “Modeling free
jet trajectory at an overfall and resulting shear stress distribution in the plunge
pool”, Trans. ASAE, 36(5): 1309-1318. 1993.
[7] Stein, O. R., P. Y. Julien, and C. V. Alonso. “Mechanics of jet scour downstream
of a headcut”. J. Hydr. Res., 31:6, 723-738, 1993.
[8] Jia, Y., T. Kitamura, and S. S. Y. Wang. “Simulation of scour process in plunging
pool of loose bed material”. ASCE J. Hydraulic Eng, 127(3): 219–229, 2001.
[9] G. J. Hanson, K. M. Robinson and K. R. Cook. “Scour below an overfall: part II.
prediction”, Trans. ASAE, Vol. 45(4): 957–964, 2002
[10] Chabert, J. and EngeldInger, P., “Etude des Affouillements Authur des Piles des
Ponts”, Laboratoire National d''Hydraulique, 1956.
[11] Laursen, E. M., “Scour at Bridge Crossings”, Trans. A.S.C.E., Voil. 127, Pt. 1, pp.
123
166-180, 1962.
[12] Jain, S. C. and Fischer, E. E., “Scour around bridge piers at high Froude numbers”,
Report Number F.H.W.A.-R.D.-79-104, Federal Highway Administration,
Washington D.C, 1979.
[13] Chee, R. K. W., “Live-Bed Scour at bridge sites”, M.E. Thesis, Auckland
University, Auckland, New Zealand, 1982.
[14] Ettema, R., “Scour at bridge piers”, Ph.D. Thesis, Auckland University, Auckland,
New Zealand. Report No. 124, 1980.
[15] Y.M. Chiew And B.W. Melville, “Local scour around bridge piers”, J.Hydr. Res.,
Vol.25, No.1, pp15-26, 1987.
[16] Flow-3D user manual version 9.4, 2009.
[17] Melville, B. W., and Coleman, S. E. “Bridge scour”. Water Resources Publications,
Colorado, USA, 550pp, 2000.
[18] Laursen, E. M., “Analysis of relief bridge scour”, J. Hydr. Div., Vol. 89, No. 3, pp.
93-118, 1963.
[19] Melville, B. W. and Chiew, Y. M., “Time scale for local scour at bridge piers,” J.
Hydr. Engrg., ASCE, Vol.125, No.1, pp. 59~65, 1999.
[20] Shen, H. W., Schneider, V. R., and Karaki, S. S, “Mechanics of local scour”. U.S.
Department of Commerce, National Bureau of Standards, Institute for Applied
Technology, Washington, D.C, 1966.
[21] Maza, J. A,‘‘Socavacion en cauces naturales.’’ A. J. Miguel Rodriguez, translator,
Rep. No. 114, School of Engineering, University of Auckland, Auckland, New
Zealand, 1968.
[22] Ettema, R, ‘‘Scour at bridge piers.’’ Rep. No. 216, School of Engrg., University of
Auckland, Auckland, New Zealand, 1980.
124
[23] Chiew, Y. M, ‘‘Local scour at bridge piers.’’ Rep. No. 355, Dept. of Civ. Engrg.,
University of Auckland, Auckland, New Zealand, 1984.
[24] Raudkivi, A. J. and Ettema, R., “Clear-water acour at cylindrical piers”, J. Hydr.
Engrg., ASCE, Vol.109, No.3, p.338-349, 1983
[25] Raudkivi, A. J., Ettema, R., “Effect of sediment gradation on clear water scour”, J.
Hydr. Div. ASCE, Vol.103, No.NY10, p.1209-1213, 1977
[26] Guo, J., Hunter Rouse and Shields diagram, Proc 1th IAHR-APD Congress,
Singapore, Vol. 2, 1069-1098, 2002.
[27] Kleinhans, M.G., Sort out sand & gravel: sediment transport and deposition in
sand-gravel bed rivers, Ph.D. Thesis, Universitaat Utrecht 2002.
[28] Soulsby, R., Dynamics of Marine Sands, Ch 9: Bedload transport, Thomas Telford
Publications, London, 1997.
[29] Mastbergen, D.R. and J.H. Von den Berg, Breaching in fine sands and the
generation of sustained turbidity currents in submarine canyons, Sedimentology
[30] Raudkivi, A.J. and Ettema, R.,"Stability of armour layers in rivers." J. Hydr. Div.,
pp. 1047-1057, 1982.
[31] Raudkivi, A.J. and Ettema, R., "Scour at cylindrical bridge piers in armored beds."
J. Hydr. Engrg. vol. 111, no. 4, 1985.
[32] Worman, A., "Riprap protection without filter layers." J. Hydr. Engrg. pp.
1615-1630, 1989.
[33] Worman, A., "Incipient motion during static armoring." J. Hydr. Engrg. pp.
496-501, 1992.
[34] Sumer, B.M., Cokgor, S. and Fredsoe, J., "Suction removal of sediment from
between armor blocks." J. Hydr. Engrg. pp. 293-30, 2001.
125
[35] Tsorng, S.J., Yang, Z.S., and Lai, J.S., "Measurements of flow field between
blocks in various geometries." 18th Conference of Hydraulic Engineering,
PingTung, Taiwan, H-11., 2009.
[36] Lagasse P.F., Byars M.S., Zevenbergen L.W. and Clopper, P. E., "Bridge Scour
and Stream Instability Countermeasures." Federal Highway Administration, 1997.
[37] Wu, C.S., "Design of stepped concrete block grade control structure", Master
Thesis, Hydraulics & Ocean Engineering, NCKU, Tainan, Taiwan., 2004.
[38] Guo, Y.H. and Chang, Y.Z., "Failure mechanisms of flexible grade control and
protections. "Hydraulics. (16): 201-210, 2006.
[39] Chang, C.C., " Experimental study on the reciprocal effect of overfall flow scour
and bridge scour", Master Thesis, Hydraulics & Ocean Engineering, NCKU,
Tainan, Taiwan., 2002.