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2-D Physical Modeling to Measure the Effectiveness of Perforated Skirt Breakwater for Short-Period Waves Ajiwibowo, Harman
Journal of Engineering and Technological Sciences Vol 43, No 1 (2011)
Publisher : ITB Journal Publisher, LPPM ITB

The effectiveness of a breakwater can be measured by quantifying the transmission coefficient (KT). The smaller the coefficient, the better the performance of the breakwater. A physical modeling on the proposed breakwater was conducted to identify the coefficient of Perforated Skirt Breakwater (PSB). The PSB model was tested in 2-D wave flume at Ocean Wave Research Laboratory FTSL ITB, to obtain the effectiveness of PSB for short-period waves (prototype periods, Tp= 4 second and smaller). The scaling of PSB models applies the principle of Froude Similarity, where the Froude number in model equals to the Froude number in prototype (Frm=Frp). The flume is equipped with 5 resistance-type wave probes and 8-channel DAS (Data Acquisition System). Wave heights (H) and wave periods (T) data were observed both manually by visual observation and wave probes readings (processed later with method of âzero mean up-crossingâ technique). The incoming wave heights (Hi) and transmitted wave heights (Ht) were measured and processed to obtain the transmission coefficient (KT). The relationships between KT and non-dimensional variables (skirt draft / incident wave height, S/Hi) are analyzed and the calculated effectiveness of the PSB for varied environmental condition is obtained to be up to 70%.

Fractals and Nonlinearity of Ocean Waves Ajiwibowo, Harman
Jurnal Teknik Sipil Vol 10, No 3 (2003)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (122.711 KB)

Abstract. From observations using secondary field data and dimension calculations, ocean waves exhibit fractals. Fractals are also hypothesized to have a direct relation with the degree of the waves nonlinearity. We tooksecondary data of 40 time series of wave record taken from Grays Harbor Wave Refraction Experiment, Washington in 1999. The data are divided into two groups, one group being data taken from the water depth of 25 meters and second group being data taken from water depth of 12 meters. The selection of data is in such a way that the second group is the waves traveling from the first group. We use rescaled range analysis to calculate the fractal dimension of the waves and Goda nonlinearity parameter as a measure of the waves nonlinearity. From the results, we confirm that fractals are a function of waves nonlinearity.Abstrak. Dari data sekunder dan perhitungan dimensi, gelombang laut mempunyai karakteristik fraktal. Bentuk fractal dari gelombang laut diasumsikan mempunyai hubungan langsung dengan ketidaklinearan dari gelombang laut. Untuk pembuktian asumsi ini diambil data pengamatan 40 data seri waktu yang diambil dari eksperimen refraksi di Grays Harbor, Washington tahun 1999. Data ini dibagi menjadi 2 grup, grup pertama adalah data yang diambil di perairan dengan kedalaman 25 meter dan grup kedua diambil dari data yang diambil di perairan dengan kedalaman 12 meter. Pengambilan data di grup kedua adalah sedemikan rupa sehingga data ini adalah berasal dari gelombang yang berjalan dari data grup pertama. Setelah dilakukan perhitungan dimensi kurva dengan menggunakan Analisa Rescaled Range dan mengambil parameter Goda sebagai ukuran ketidaklinearan gelombang laut, didapati bahwa bentuk fraktal gelombang laut berhubungan langsung dengan ketidaklinearan gelombang.

Pemodelan Fisik 2-D untuk Mengukur Tingkat Efektivitas Perforated Skirt Breakwater pada Kategori Gelombang Panjang Wurjanto, Andojo; Ajiwibowo, Harman; Zamzami, Rahmat
Jurnal Teknik Sipil Vol 17, No 3 (2010)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1043.898 KB)

Abstrak. Efektifitas pemecah gelombang dapat diukur dengan mengukur koefisien transmisi (KT). Semakin kecil koefisien transmisi maka semakin efektif pemecah gelombang ini. Pengujian model fisik dilakukan untuk mengetahui nilai koefisien transmisi dari Perforated Skirt Breakwater (PSB). Model PSB diuji dalam saluran gelombang 2-D di Laboratorium Gelombang Teknik Kelautan FTSL ITB, untuk mengetahui keefektifannya terhadap kategori gelombang panjang (periode prototipe, Tp = 7 detik). Penskalaan untuk model PSB menggunakan prinsip Keserupaan Froude dimana bilangan Froude model setara dengan bilangan Froude prototipe (Frm=Frp). Saluran gelombang dilengkapi dengan 5 sensor gelombang tipe tahanan listrik dan 8 saluran DAS (Data Acquisition System). Data tinggi gelombang (H) dan periode gelombang (T) diamati secara manual melalui pengamatan visual dan diperoleh melalui rekaman sensor gelombang (yang selanjutnya diproses menggunakan metode âzero mean up-crossingâ). Tinggi gelombang datang di depan PSB (Hi) dan tinggi gelombang transmisi di belakang PSB (Ht) diukur dan diproses untuk mendapatkan koefisien transmisi (KT). Selanjutnya, hubungan antara KT dan bilangan tak-berdimensi, kedalaman sirip / tinggi gelombang datang (S/Hi) dianalisis dan nilai koefisien transmisi (KT) untuk berbagai kondisi lingkungan diperoleh. Abstract. The effectiveness of a breakwater can be measured by quantifying the transmission coefficient (KT). The smaller the coefficient, more effective the performance of the breakwater. A physical modeling on the proposed breakwater was conducted to identify the coefficient of Perforated Skirt Breakwater (PSB). The PSB model was tested in 2-D wave flume at Ocean Wave Research Laboratory FTSL ITB, to obtain the effectiveness of PSB for long-period waves (prototype periods, Tp= 7 second). The scaling of PSB models applies the principle of Froude Similarity, where the Froude number in the model equals to the Froude number in prototype (Frm=Frp). The wave flume is equipped with 5 resistance-type wave probes and 8-channels of DAS (Data Acquisition System). Wave heights (H) and wave periods (T) data were observed both manually by visual observation and from wave probes record (processed later with method of âzero mean up-crossingâ technique). The incomingÂ wave heights (Hi) and transmitted wave heights (Ht) - before and after PSB, respectively - were measured and processed to obtain the transmission coefficient (KT). The relationships between KT and non-dimensional variables (skirt draft / incident wave height, S/Hi) are analyzed and the calculated KT for varied environmental condition are obtained.

Analisis Hidrodinamika di Perairan Lemong, Kabupaten Lampung Barat, Provinsi Lampung Menggunakan Piranti Surface-Water Modeling System Wurjanto, Andojo; Ajiwibowo, Harman
Rekayasa Vol 13, No 2: August 2020
Publisher : Universitas Trunojoyo Madura

Pantai Lemong merupakan bagian dari Kawasan Pantai Pesisir Barat, Provinsi Lampung yang berpotensi terkena abrasi akibat gelombang dari Samudera Hindia. Rencana pengamanan pantai diperlukan untuk mencegah abrasi. Studi ini dilakukan untuk mengidentifikasi karakteristik pasang surut dan arus di perairan Lemong sebagai parameter untuk perencanaan pengaman pantai. Analisis pasang surut dan arus dilakukan dengan pemodelan numerik pada modul RMA2 dari perangkat lunak Surface-Water Modeling System (SMS). Data yang digunakan pada pemodelan adalah batimetri dan elevasi pasang surut setempat yang didapatkan dari hasil survei. Pemodelan dilakukan dengan metode online nesting dengan empat tingkat resolusi grid dengan resolusi tertinggi pada 1 x 1 km2 saat mendekat ke Perairan Pantai Lemong. Hasil pemodelan divalidasi dengan data lapangan berupa elevasi pasang surut pada dua titik di perairan dangkal dan tiga titik di perairan dalam. Hasil pemodelan menunjukkan bahwa tunggang pasang surut di wilayah Pantai Lemong mencapai 1,4 m dengan tipe mixed – dominan semi diurnal. Hasil pemodelan juga menunjukkan pola arus di Perairan Lemong yang memiliki arah dominan menuju Tenggara saat pasang dan menuju Barat Laut saat surut. Untuk pengembangan model berikutnya, disarankan agar menyertakan data kecepatan arus hasil survei lapangan dalam proses validasi sehingga kesesuaian hasil pemodelan dengan lapangan dapat lebih ditingkatkan.Hydrodynamic Analysis Using Surface-water Modeling System in Lemong Waters, West Lampung Regency, Lampung ProvinceLemong Beach is part of the western coast of Lampung Province which is prone to abrasion caused by the Indian Ocean waves. This study aims to identify the tidal and current characteristics in Lemong waters as a part of coastal protection planning. The tidal analysis is performed by using the RMA2 module from Surface-Water Modeling System (SMS). Data utilized in the model including bathymetry and local tidal elevations from field surveys. Modeling is conducted using an online nesting method utilizing four stages of grid resolution with 1 x 1 km2 as the highest used around the Lemong Beach Waters. The model is validated with the tidal elevations measured in two points in shallow water and three points in deep water areas. The modeling result shows that the tidal range of Lemong Beach Waters is approximately 1.4 meters as a mixed tide, dominantly in semi-diurnal. The model also shows that the current pattern in Lemong Beach Waters is dominantly moving towards southeast during flows and towards northwest during ebbs. Modeling can be further improved by including current speed from field measurement in the validation process.

Hydrodynamic Model and Tidal Current Energy Potential in Lepar Strait, Indonesia Ajiwibowo, Harman; Pratama, Munawir Bintang
International Journal of Renewable Energy Development Vol 11, No 1 (2022): February 2022
Publisher : Center of Biomass & Renewable Energy, Diponegoro University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14710/ijred.2022.37028

Previous studies have shown the abundance of tidal energy resources in Indonesia. However, some sites have yet to be considered. The Lepar Strait, for example, is located between Bangka and Lepar Islands. This paper describes a field survey and numerical modelling conducted in the Lepar Strait. The modelling was performed using Delft3D, with the aim of determining potential sites for harvesting tidal current energy and estimate the generated power. In the modelling, the domain decomposition method was employed for model downscaling, allowing grid resolution reaching 130 x 130 m2, which is sufficient to represent the narrow gaps between tiny islands in the area of interest. The National Bathymetric (Batnas) from the Geospatial Information Agency (BIG) and the International Hydrographic Organization (IHO) tide constituents were applied for the bathymetry and tide elevation boundaries. The comparison between the surveyed and modelled data showed a good agreement. The RMSE and r for water level are > 0.95 and < 0.15, and the RMSE for velocity was <0.19. Furthermore, an energetic flow reaching 1.5 m/s was found at the Northern part of Lepar Strait, situated at the narrow gaps. The Gorlov Helical Turbine was selected in this study due to shallow water and low mean velocity. In the 2019 model, the power density and power output at the best potential sites were 2,436.94 kWh/m2 and 1,870.41 kWh, respectively. This number is higher than those previously found in Kelabat Bay. Nonetheless, it is still far below the currently promising project in Larantuka and Lombok Straits. Future research is recommended, to conduct a detailed field measurement campaign and assess the impact of energy extraction in more detail.

2-D Physical Modeling to Measure the Effectiveness of Perforated Skirt Breakwater for Short-Period Waves Harman Ajiwibowo
Journal of Engineering and Technological Sciences Vol. 43 No. 1 (2011)
Publisher : Institute for Research and Community Services, Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/itbj.eng.sci.2011.43.1.5

The effectiveness of a breakwater can be measured by quantifying the transmission coefficient (KT). The smaller the coefficient, the better the performance of the breakwater. A physical modeling on the proposed breakwater was conducted to identify the coefficient of Perforated Skirt Breakwater (PSB). The PSB model was tested in 2-D wave flume at Ocean Wave Research Laboratory FTSL ITB, to obtain the effectiveness of PSB for short-period waves (prototype periods, Tp= 4 second and smaller). The scaling of PSB models applies the principle of Froude Similarity, where the Froude number in model equals to the Froude number in prototype (Frm=Frp). The flume is equipped with 5 resistance-type wave probes and 8-channel DAS (Data Acquisition System). Wave heights (H) and wave periods (T) data were observed both manually by visual observation and wave probes readings (processed later with method of "zero mean up-crossing" technique). The incoming wave heights (Hi) and transmitted wave heights (Ht) were measured and processed to obtain the transmission coefficient (KT). The relationships between KT and non-dimensional variables (skirt draft / incident wave height, S/Hi) are analyzed and the calculated effectiveness of the PSB for varied environmental condition is obtained to be up to 70%.

PEMODELAN FISIK 3-D PADA FLOATING – TYPE BREAKWATER Harman Ajiwibowo
Jurnal Ilmu dan Teknologi Kelautan Tropis Vol. 10 No. 1 (2018): Jurnal Ilmu dan Teknologi Kelautan Tropis
Publisher : Department of Marine Science and Technology, Faculty of Fisheries and Marine Science, IPB University

BP Tangguh memiliki fasilitas pelabuhan di Teluk Bintuni, Papua Barat dengan kedalaman perairan 6 m hingga 9 m. Pada kasus ini direncanakan suatu breakwater terapung untuk melindungi aktivitas dan fasilitas pelabuhan. Pengujian model fisik 3-D dilakukan di kolam gelombang untuk menentukan efektivitas terhadap kondisi lingkungan perairan Teluk Bintuni dengan mengukur koefisien transmisi (KT). Kolam gelombang dilengkapi dengan piston pembangkit gelombang monokromatik, 4 wave gauge dan DAS (Data Acquisition System) 8 kanal. Data tinggi (H) dan periode gelombang (T) diperoleh dari rekaman sensor gelombang dan divalidasi dengan pengamatan pada peilschaal. Tinggi gelombang datang di depan breakwater (Hi) dan tinggi gelombang transmisi di belakang breakwater (Ht) diukur dan diproses untuk mendapatkan KT. Selanjutnya, hubungan antara KT dan bilangan tak berdimensi lainnya dianalisis. Hasil dari model fisik ini adalah breakwater terapung yang diajukan efektif untuk gelombang pendek dan menengah, dan tidak efektif untuk gelombang panjang. Selain itu, konfigurasi breakwater pada satu sisi bagian utara saja (konfigurasi 1) dipilih karena perbandingan dengan konfigurasi breakwater di dua sisi (utara dan barat, konfigurasi 2) dihasilkan gelombang transmisi yang tidak jauh berbeda. Bahkan konfigurasi 2 (breakwater di dua sisi) menghasilkan gelombang berdiri pada kolam pelabuhan dengan tinggi lebih dari tinggi gelombang datang. Pada gelombang pendek, breakwater terapung menghasilkan koefisien transmisi sebesar 0,5 hingga 0,7. Koefisien transmisi mengecil apabila gelombang datang dengan periode yang lebih kecil lagi.

Modelling Tidal Flow Hydrodynamics of Sunda Strait, Indonesia Munawir Bintang Pratama; Vengatesan Venugopal; Harman Ajiwibowo; Juventus Welly Ginting; Franto Novico
ILMU KELAUTAN: Indonesian Journal of Marine Sciences Vol 25, No 4 (2020): Ilmu Kelautan
Publisher : Marine Science Department Diponegoro University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.14710/ik.ijms.25.4.165-172

In the past years, Indonesian people put more attention to Sunda Strait located between Java and Sumatra Islands, one of the busiest straits occupied with residential, recreational, fisheries, transportation, industrial and mining activities. Previous works on numerical modelling of tidal flow hydrodynamics of the Sunda Strait have resulted in good agreement against field data; however, the calibration of the models used was not described in detail. This paper presents the process of setting up the model, extensive calibration, validation and prediction of tidal currents for the Sunda Strait. A two-dimensional tidal-driven model is constructed using Delft3D, an open-source developed by Deltares. Four different bathymetry datasets, four different boundary condition configurations, and various bed roughness values are used, and their suitability in predicting tidal water level and current are investigated. It is found that changing the bathymetry and boundary conditions improve the model validation significantly. GEBCO_2019 bathymetry dataset outperforms the Batnas, even though it has a coarser resolution. For boundary conditions, the combination of water level and current velocity results in a better validation compares to using water level or current velocity only. However, the bed roughness shows an insignificant influence in predicting tidal conditions. The averaged current velocity is lower at the Southern than the Northern side of the strait due to a larger cross-section, consequence of deeper water. High tidal currents of magnitude around 2 m.s-1 are seen at the bottleneck of the strait.

Fractals and Nonlinearity of Ocean Waves Harman Ajiwibowo
Jurnal Teknik Sipil Vol 10 No 3 (2003)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/jts.2003.10.3.2

Abstract. From observations using secondary field data and dimension calculations, ocean waves exhibit fractals. Fractals are also hypothesized to have a direct relation with the degree of the waves nonlinearity. We tooksecondary data of 40 time series of wave record taken from Grays Harbor Wave Refraction Experiment, Washington in 1999. The data are divided into two groups, one group being data taken from the water depth of 25 meters and second group being data taken from water depth of 12 meters. The selection of data is in such a way that the second group is the waves traveling from the first group. We use rescaled range analysis to calculate the fractal dimension of the waves and Goda nonlinearity parameter as a measure of the waves nonlinearity. From the results, we confirm that fractals are a function of waves nonlinearity.Abstrak. Dari data sekunder dan perhitungan dimensi, gelombang laut mempunyai karakteristik fraktal. Bentuk fractal dari gelombang laut diasumsikan mempunyai hubungan langsung dengan ketidaklinearan dari gelombang laut. Untuk pembuktian asumsi ini diambil data pengamatan 40 data seri waktu yang diambil dari eksperimen refraksi di Grays Harbor, Washington tahun 1999. Data ini dibagi menjadi 2 grup, grup pertama adalah data yang diambil di perairan dengan kedalaman 25 meter dan grup kedua diambil dari data yang diambil di perairan dengan kedalaman 12 meter. Pengambilan data di grup kedua adalah sedemikan rupa sehingga data ini adalah berasal dari gelombang yang berjalan dari data grup pertama. Setelah dilakukan perhitungan dimensi kurva dengan menggunakan Analisa Rescaled Range dan mengambil parameter Goda sebagai ukuran ketidaklinearan gelombang laut, didapati bahwa bentuk fraktal gelombang laut berhubungan langsung dengan ketidaklinearan gelombang.

Pemodelan Fisik 2-D untuk Mengukur Tingkat Efektivitas Perforated Skirt Breakwater pada Kategori Gelombang Panjang Andojo Wurjanto; Harman Ajiwibowo; Rahmat Zamzami
Jurnal Teknik Sipil Vol 17 No 3 (2010)
Publisher : Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/jts.2010.17.3.7

Abstrak. Efektifitas pemecah gelombang dapat diukur dengan mengukur koefisien transmisi (KT). Semakin kecil koefisien transmisi maka semakin efektif pemecah gelombang ini. Pengujian model fisik dilakukan untuk mengetahui nilai koefisien transmisi dari Perforated Skirt Breakwater (PSB). Model PSB diuji dalam saluran gelombang 2-D di Laboratorium Gelombang Teknik Kelautan FTSL ITB, untuk mengetahui keefektifannya terhadap kategori gelombang panjang (periode prototipe, Tp = 7 detik). Penskalaan untuk model PSB menggunakan prinsip Keserupaan Froude dimana bilangan Froude model setara dengan bilangan Froude prototipe (Frm=Frp). Saluran gelombang dilengkapi dengan 5 sensor gelombang tipe tahanan listrik dan 8 saluran DAS (Data Acquisition System). Data tinggi gelombang (H) dan periode gelombang (T) diamati secara manual melalui pengamatan visual dan diperoleh melalui rekaman sensor gelombang (yang selanjutnya diproses menggunakan metode "zero mean up-crossing"). Tinggi gelombang datang di depan PSB (Hi) dan tinggi gelombang transmisi di belakang PSB (Ht) diukur dan diproses untuk mendapatkan koefisien transmisi (KT). Selanjutnya, hubungan antara KT dan bilangan tak-berdimensi, kedalaman sirip / tinggi gelombang datang (S/Hi) dianalisis dan nilai koefisien transmisi (KT) untuk berbagai kondisi lingkungan diperoleh. Abstract. The effectiveness of a breakwater can be measured by quantifying the transmission coefficient (KT). The smaller the coefficient, more effective the performance of the breakwater. A physical modeling on the proposed breakwater was conducted to identify the coefficient of Perforated Skirt Breakwater (PSB). The PSB model was tested in 2-D wave flume at Ocean Wave Research Laboratory FTSL ITB, to obtain the effectiveness of PSB for long-period waves (prototype periods, Tp= 7 second). The scaling of PSB models applies the principle of Froude Similarity, where the Froude number in the model equals to the Froude number in prototype (Frm=Frp). The wave flume is equipped with 5 resistance-type wave probes and 8-channels of DAS (Data Acquisition System). Wave heights (H) and wave periods (T) data were observed both manually by visual observation and from wave probes record (processed later with method of "zero mean up-crossing" technique). The incoming wave heights (Hi) and transmitted wave heights (Ht) - before and after PSB, respectively - were measured and processed to obtain the transmission coefficient (KT). The relationships between KT and non-dimensional variables (skirt draft / incident wave height, S/Hi) are analyzed and the calculated KT for varied environmental condition are obtained.

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