Wibowo, Yuni Ari (2016) Analisis Pengaruh Gaya Gelombang Non-Linier Orde-2 Terhadap Struktur Apung Tertambat Dengan Sistem External Turret Mooring. Masters thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Struktur apung tertambat pada gelombang acak akan menerima beban gelombang
orde-1 dan orde-2. Penelitian mengenai gaya gelombang orde-1 telah cukup banyak
dilakukan selama beberapa dekade, mengingat pentingnya gaya orde-1 terhadap struktur
apung. Penelitian ini difokuskan untuk mengkaji pengaruh gaya gelombang orde-2
terhadap sistem struktur tertambat external turret mooring dengan konfigurasi 6 tali
catenary. Tipe gaya gelombang yang bekerja divariasikan untuk menyelidiki pengaruhnya
terhadap respon struktur tertambat dan gaya tarik (tension) tali tambatnya. Simulasi
dilakukan dengan memodelkan kapal tanker ukuran Aframax 120.000 DWT dalam 3
kondisi pembebanan : sistem tertambat yang dikenai gaya gelombang orde-1, gaya
gelombang orde-2 dan kombinasi keduanya. Penelitian ini menggunakan pendekatan
domain frekuensi untuk menghitung perilaku hidrodinamis struktur terapung bebas.
Kemudian hasil tersebut digunakan untuk melakukan simulasi dalam domain waktu secara
simultan untuk mendapatkan perilaku gerak struktur tertambat dan tension tali tambatnya.
Respon struktur dan tension tali tambat dalam domain waktu kemudian ditinjau kembali
dalam domain frekuensi menggunakan metode fast fourier transform (FFT) untuk
menyelidiki karakteristiknya akibat tipe gaya gelombang yang bekerja.
Simulasi yang telah dilakukan menunjukkan bahwa meskipun intensitas gaya orde-
2 terbilang rendah, namun dapat menghasilkan respon surge dan tension tali tambat yang
cukup tinggi akibat adanya fenomena gerakan seret (drifting). Amplitudo respon surge
akibat gaya orde-1 dengan Hs mencapai 10m adalah sekitar 2m, sedangkan orde-2
menghasilkan sekitar 23m, sehingga rasio perbandingannya sekitar 1 : 11. Amplitudo
tension akibat orde-1 mencapai 7,5 ton dan akibat orde-2 sekitar 117,5 ton sehingga rasio
perbandingannya mencapai 1 : 15. Variasi kedalaman perairan juga diselidiki untuk
mengetahui pengaruhnya pada respon tertambat akibat gaya gelombang orde-2, yaitu pada
kedalaman 100, 300 dan 500m. Hasil yang didapatkan dari simulasi tersebut
mengindikasikan bahwa setiap penambahan kedalaman perairan sebesar 200 m dapat
meningkatkan respon surge akibat gaya orde-1 sebesar 5 – 9% atau sebesar 2 -5 meter dan
akibat orde-2 sebesar 9 – 19% atau sekitar 7 – 12 meter. Penambahan kedalaman perairan
juga meningkatkan tension tali tambat akibat orde-1 sebesar 60 - 65% atau sekitar 28 – 135
ton dan akibat orde-2 mencapai sekitar 75% atau sekitar 152 ton.
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Moored floating structures in random waves are subjected to large first order and
small low frequency second order wave forces. Due to the importance of the first order
wave force and motions they have been subject to investigation for several decades. This
study focuses to investigate the second order wave force effect towards floating structure
responses and mooring line tensions. A moored structure is configured as an external turret
system which is anchored by 6 catenary mooring lines. Variation in the type of wave forces
acts on Tanker model Aframax 120.000 DWT is investigated in order to predict the effect
of second order wave force. The simulations are performed in 3 loadcases : moored floating
structure subjected to first, second order wave forces and combination of both respectively.
In this study, modelling on the basis of the frequency-domain is adopted to compute the
hydrodymanic properties of freely floating structure and followed by simulation on the
basis of time-domain coupled dynamic analysis to observe the responses of moored floating
structure and tension of mooring lines. All responses and its tension re-observed in
frequency domain using the Fast Fourier Transform method in order to investigate its
characters.
The corresponding analysis reveals that the low frequency second order wave
force, even though relatively small in magnitude, could excite large both amplitude of surge
motion and tension of mooring lines. It may give rise to the amplitude of surge motion from
2m (first order) to 23m (second order) so the ratio of motion is 1 : 11. And for mooring line
tension, it rise from 7,5ton (first order) to 117,5ton (second order, so the ratio of tension is
1 : 15.Variation in the water depth is also investigated in order to calculate its effect towards
structure responses and mooring line tensions, namely 100m, 300m and 500m. The analysis
reveals that increasing water depth per 200m, it may give rise the surge response due to
first order wave force in 5 – 9% (2 – 5 meter) and 9 – 19% (7 – 12 meter) due to second
order wave force. Also it may give rise the mooring line tension due to first order wave
force in 60-65% (28 – 135 ton) and around 75% (152 ton) due to second order wave force.
| Item Type: | Thesis (Masters) |
|---|---|
| Additional Information: | RTKe 623.812 23 Wib a |
| Uncontrolled Keywords: | Gaya gelombang orde-2, external turret mooring, domain waktu simultan, respon gerak, tension tali tambat |
| Subjects: | Q Science > QA Mathematics > QA911 Fluid dynamics. Hydrodynamics |
| Divisions: | Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38101-(S2) Master Thesis |
| Depositing User: | Mr. Tondo Indra Nyata |
| Date Deposited: | 22 Aug 2017 04:14 |
| Last Modified: | 27 Dec 2018 08:40 |
| URI: | http://repository.its.ac.id/id/eprint/48708 |
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