The present study is concerning bottom boundary layer beneath solitary wave over smooth beds condition. A new generation system was proposed to generate an oscillatory motion similar to solitary wave in a closed conduit water tunnel using a mechanical system. This generation system facilitates easy measurement of periodical oscillatory motion to replace solitary wave motion with a sufficient tranquil period. The velocities were measured by using a Laser Doppler Veloci-meter (LDV) at 17 to 22 points in the vertical direction. The experiments were accomplished with different velocities under single and periodical oscillatory motion conditions and validations have been done in some various terms of experiment relevant to solitary wave boundary layer. A good agreement is achieved in validation of free stream velocity and also both single and periodical oscillatory motion measurements methods. Furthermore, validation of velocity distribution in time variation obtains a critical Reynolds number which has a good agreement with the finding of previous researchers.
Beberapa penyebab utama terjadinya genangan banjir di Kota Pasuruan adalah kemiringan dasar sungai di bagian hilir yang relatif datar, sedimentasi di muara sungai sehingga menghambat aliran sungai menuju laut, serta erosi dan pengangkutan sedimen di sungai yang tidak terkendali. Genangan banjir terjadi pada lahan pertanian, pemukiman, kawasan indsutri, serta pada ruas Jembatan Jalan Nasional. Studi ini bertujuan untuk memperoleh pemodelan genangan banjir di Sungai Welang sehingga selanjutnya dapat dijadikan referensi tambahan pada rencana pengembangan di Sungai Welang. Analisa hidrologi dilakukan untuk memperoleh debit banjir rancangan kala ulang 25 tahun dengan Hidrograf Satuan Sintetik Nakayasu yaitu sebesar 620,27 m 3 /det. Pemodelan hidraulik kondisi eksisting dilakukan dengan menggunakan analisa aliran 2D HEC-RAS menggunakan simulasi unsteady flow. Diperoleh luas genangan yang disebabkan oleh debit banjir rancangan kala ulang 25 tahun adalah sebesar 438,262 ha. Sementara pemodelan pengendalian banjir direncanakan dengan debit banjir kala ulang 25 tahun yaitu berupa tanggul dan normalisasi dilakukan dengan fitur channel modification pada RAS-Mapper.
Wilayah Sungai Jatiroto yang terletak di perbatasan Kabupaten Lumajang dan Kabupaten Jember sering diterjang banjir ketika musim penghujan tiba. Tahun 2022 kejadian banjir menerjang wilayah bagian hilir Sungai Jatiroto dengan ketinggian air rata-rata 30-50 cm. Adanya pengaruh backwater dari Sungai Bondoyudo di bagian hilir dan kiriman debit dari anak sungai membuat kapasitas penampang Sungai Jatiroto tidak dapat menampung debit air yang masuk. Tujuan dari pemodelan aliran ini untuk mengetahui titik ruas sungai yang terjadi limpasan sehingga dapat dijadikan rekomendasi rencana pencegahan dan mitigasi bencana banjir. Kalibrasi pemodelan aliran untuk menentukan n Manning menggunakan debit pengamatan di bendung dan data historis banjir pada tanggal 23 Desember 2018. Hasil dari simulasi aliran menggunakan HEC-RAS 5.0.7 didapatkan nilai n Manning sebesar 0,025 dan 0,023. Debit banjir rencana yang digunakan untuk analisis pemodelan kondisi eksisting yaitu Q2th sebesar 373,10 m3/det. Dari hasil simulasi aliran kondisi eksisting Q2th bahwasanya di beberapa ruas sungai terjadi luapan air terutama ruas bagian hilir.
This paper reports on continues an experimental investigation of characterizing transition to turbulence for solitary wave boundary layer in a smooth bed condition. A series of experiments have been carried out by means of a closed conduit solitary wave generation system over the Reynolds number (Re) range 5.64 x 105 – 7.34 x 105. Additionally, the instantaneous velocities were measured by using a Laser Doppler Veloci-meter (LDV) over 50 wave numbers and at 17 to 22 points in the vertical direction. The turbulence intermittency has been analyzed based on experimental data. Moreover, momentum method has been employed for calculating bottom shear stress for all cases. And then, the turbulence intensity is plotted to give clearly description how turbulence generated in the various values of Re. The phase difference and wave friction factor obtained from the present experiment has an excellent agreement with the result of previous studies. Inconsistency critical Reynolds number (Recr) can be found in solitary wave case in terms of phase difference and wave friction factor, this observable fact is difference with sinusoidal wave case which has consistency in Recr.
A wave flume is commonly used in solitary wave boundary layer research. However, it is hard to reproduce near-bed hydrodynamic and sediment transport phenomena at a realistic scale. Latterly, an oscillating water tunnel has been utilized to examine turbulent solitary wave boundary layer (Sumer et al. 2010). Both of experimental facilities actually have main difficulty to achieve reliable ensemble average. In this study, a new generation system for solitary wave boundary layer which enables to do measurement under single and periodical motion is proposed. As a result, single and periodical measurements confirm a good agreement. It is concluded that the new generation system is able to investigate solitary wave boundary layer and applicable for sediment transport experiment by facilitating ensemble averaging. 1 M. Eng. 2
The Manning equation is commonly used in assessing the bed stress and also in modeling the wave propagation and run up. Nevertheless, this method might lead to an inaccurate estimation of the bed stress. In the present study, we will discuss the application of wave boundary layer in wave modeling. The free stream velocity at several cross sections is obtained from numerical simulation of solitary wave run up on a sloping beach. The wave propagation is calculated using the depth averaged equation with conventional Manning approach. The 1D vertical k-ω model will be used to assess the bed stress in wave propagation and run up. The velocity will be used as an input for the 1D model at the corresponding cross section. .
1.Fredsøe Deigaard, 1992Deigaard, 1998 M. Eng. M. Eng.
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