PEMODELAN ALIRAN UNSTEADY FLOW 1D UNTUK ANALISIS ROUTING BANJIR DI FLUME DENGAN METODE KARAKTERISTIK

GURAWAN DJATI WIBOWO, Dr. Ir. Istiarto, M.Eng.

2014 | Tesis | S2 Teknik Sipil

Model numerik routing banjir bertujuan untuk memprediksi kelakuan penjalaran gelombang banjir unsteady flow di lapangan. Pemahaman tentang teknik numerik yang diaplikasikan ke dalam komputasi hidrolik sangat menunjang untuk memajukan sistem peringatan banjir serta pengendalian banjir di Indonesia. Penelitian ini berusaha memodelkan aliran unsteady 1D dengan salah satu metode numerik, yaitu metode karakteristik. Model simulasi ini akan di aplikasikan pada kasus perambatan gelombang banjir di flume. Pemodelan aliran 1 D mennsimulasikan penjalaran gelombang banjir di flume, dengan panjang flume 9.0m, kekasaran manning = 0.01 m1/3.s, lebar flume 40 cm, So =0.0001 dan syarat batas hulu merupakan banjir yang telah disetting penulis serta syarat batas hilir merupakan aliran kritis (terjunan). Hasil penelitian ini menunjukkan bahwa untuk tahapan waktu ( t = 0.25 s) kondisi hasil hitungan routing banjir tidak stabil, dengan bilangan Courant (Cr) berkisar 0.9902 s/d 1.6865. Sementara pada hasil routing pada  t = 0.22 s,  t = 0.20 s,  t = 0.18 s juga menunjukkan ketidakstabilan numerik. Secara umum terjadi osilasi debit routing maupun kedalaman air routing terutama pada pias 10, 15, 20 dan pias 30. Hasil routing dengan  t = 0.14 s menunjukkan kestabilan numerik dengan tidak terjadi goncangan hitungan di sepanjang pias (pias 1 s/d pias 45). Perbedaan puncak banjir antara running program computer dengan  t = 0.16s dengan  t = 0.14s terbesar sebesar 1.30% (pada pias 5) dan terkecil -0.10% di pias 10. Kata kunci : metode karakteristik, routing banjir, kestabilan numerik

Flood routing numerical model aims to predict the flood wave propagation behavior in unsteady flow field. Understanding of numerical techniques applied to the hydraulic computation is very supportive to advance flood warning systems and flood control in Indonesia. This study attempted to model the unsteady flow with one of the 1D numerical method, the method of characteristics. The simulation model will be applied in case of a flood wave propagation in the flume. 1 D flow modeling to simulate flood wave propagation in the flume, the flume length 9.0m, manning coefficient = 0:01 m1/3.s, flume width of 40 cm, So = 0.0001 and the upper boundary condition is a flood that has be set as well as the author of the downstream boundary condition is critical flow (waterfall). The results of this study indicate that for stage time (t = 0:25 s) flood routing results of a calculation condition is unstable, with the Courant number (Cr) ranging from 0.9902 s / d 1.6865. While the routing results in t= 0:22 s, t= 0.20 s, t = 0:18s also showed numerical instability. In general, discharge oscillation occurs routing routing and water depth, especially on cross section 10, 15, 20 and 30. The result running model hydraulic with t = 0:14 s shows that all of cross section is stable (cross section 1 s/d 46)..The difference between the flood peak with computer program running t = 0.16s to 0.14s t largest of 1,30% (on cross section 5) and the smallest on the cross section 10 of -0.10% . Keywords: method of characteristics, flood routing, numerical stability

Kata Kunci : metode karakteristik, routing banjir, kestabilan numerik; method of characteristics, flood routing, numerical stability