NUMERICAL SIMULATION OF FLOW AND SEDIMENT TRANSPORT ALONG A CHANNEL WITH UNDERWATER SILL

NURUL AZIZAH, Prof. Ir. Radianta Triatmadja, Ph. D; Prof. Dr. Ir. Bambang Agus Kironoto

2016 | Tesis | S2 Teknik Sipil

Struktur pencegah sedimentasi seperti underwater sill (UWS) dapat digunakan untuk membelikkan aliran sedimen, dan mencegahnya untuk masuk ke dalam kolam pelabuhan atau saluran navigasi. Dalam penelitian ini, digunakan model kuasi 3D-numerik yang disebut model multi-layered untuk mensimulasikan aliran dan transport sedimen yang dipengaruhi oleh underwater sill. Model ini terdiri dari dua model utama yaitu model hidrodinamik yang berdasarkan atas metode karakteristik dan model sedimen tersuspensi yang didasarkan pada metode partikel-tracking. Sebuah saluran lurus dengan UWS diletakakan ditengah antara batas hulu dan hilir. Ketinggian UWS serta parameter sedimen yang disajikan dalan angka Rouse divariasikan untuk mengamati efektivitas struktur tersebut terhadap sedimentasi. Pengaruh UWS pada pola aliran dan sedimentasi, distribusi vertikal konsentrasi sedimen tersuspensi, dan efektivitas struktur underwater sill dalam mengontrol aliran dan mengurangi sedimentasi dianalisis. Simulasi numerik menunjukkan bahwa UWS secara signifikan mengubah pola aliran dan transport sedimen. Kemampuan UWS dalam membelokkan arus dan sedimen meningkat seiring dengan peningkatan ketinggian UWS. Adanya bangunan memberikan kontribusi dalam mengurangi transpor sedimen yang menyebabkan masalah pendangkalan di kolam pelabuhan. Jumlah pengurangan endapan ini disebabkan oleh UWS dengan ketinggian terkecil (huws = 1/7 h) yaitu 45% untuk sedimen dengan angka Rouse 1,8, 15% untuk sedimen dengan angka Rouse 1,2, dan hanya 1% untuk sedimen dengan angka Rouse 0,8. Reduksi pendangkalan meningkat seiring dengan meningkatnya ketinggian UWS.

Sediment prevention structures such as underwater sill (UWS) may be used to divert the sediment movement, and prevent it to enter the port basin or navigation channel. In this study, a quasi 3D-numerical model called multi-layered model is utilize in other to simulate the current and suspended sediment that are affected by underwater sill. The model consisted of two main. There are the hydrodynamic model that was based on characteristic method and suspended sediment model that was based on particle tracking method. A straight channel with an UWS approximately a half way between upstream and downstream boundaries was simulated. The height of the UWS as well as the sediment parameter which is presented as the rouse number were varied to observe the effectiveness of such structure against sedimentation. The influence of UWS on current and sedimentation pattern, vertical distribution of suspended sediment concentration, and the implication of effectiveness of underwater sill structures to control the flow and reduce sedimentation were analyzed. The numerical simulations indicated that the UWS significantly altered the current and sediment transport pattern. The capability of UWS in deflecting the current and sediment increase along with the increment of UWS height. It presence contributes in reducing the sediment transport that cause siltation problem in port basin. The amount of siltation�s reduction provide by UWS with the smallest height (huws = 1/7 h) was 45% for sediment with rouse number of 1.8, 15 % for sediment with rouse number of 1.2, and only 1 % for sediment with rouse number of 0.8. The siltation�s reduction is increase as the increasing of UWS height.

Kata Kunci : Sediment transport, Underwater sill (UWS), Method of Characteristics, Particle tracking method, Numerical Simulation.