One of the components of the Indonesia Tsunami Early Warning System (InaTEWS) is a surface buoy. The surface buoy is exposed to dynamic and random loadings while operating at sea, particularly due to waves. Because of the cyclic nature of the wave load, this may result in a fatigue damage of the keel structure, which connects the mooringline with the buoy hull. The operating location of the buoy is off the Java South Coast at the coordinate (10.3998 S, 108.3417 E). To determine the stress transfer function, model tests were performed, measuring the buoy motions and the stress at the mooring line. A spectral fatigue analysis method is applied for the purpose of estimating the fatigue life of the keel structure. Utilizing the model-test results, the S-N curve obtained in a previous study and the wave data at the buoy location, it is found that the fatigue life of the keel structure is approximately 11 years
ABSTRAKPaper ini secara ringkas menjelaskan desain dan analisis struktur unit dasar laut (OBU) sebagai pasangan pelampung (buoy) permukaan untuk mendeteksi dini kejadian tsunami. Pekerjaan kerekayasaan ini seperti juga konstruksi laut lainnya yang didasarkan pada bidang teknik perkapalan. Langkah pertama yang dilakukan adalah pembuatan konsep desain OBU kemudian perhitungan stabilitas dilakukan, dan langkah terakhir adalah perhitungan kekuatan struktur untuk kasus beban hidrostatik dan beban impak pada saat OBU mendarat di dasar laut yang berkedalaman sekitar 2000m
Waste steel from used ship propeller shafts is reused for the keel structures of InaTEWS buoys. Because of the application of waste material, fatigue life assessment is critical. The purpose of this study is to assess the mechanical and fatigue properties of the waste material and to estimate the fatigue life of the keel structure as a result of sea wave loading. Material tests, fatigue tests and model tests were performed to obtain the parameters required for the estimation of the fatigue life, together with application of the spectral analysis method, including the effects of spectral band width. Chemical and tensile tests identified the material as low-carbon steel, with mechanical properties comparable to AISI 1035 steel. The fatigue tests resulted in an S-N curve (NS m = K) with m = 7.7 and K = 3.2×10 24 , showing a lower fatigue strength than AISI 1035 steel. The observed reduction in fatigue strength is ascribed to the previous use of the shaft. The calculated fatigue life based on the experimental S-N curve and the observed in-situ wave data is approximately 9.5 years, with a safety factor of 5.
Indonesia as a country that often experiences tsunami disasters needs to have an early warning system against tsunami disasters. This system can use various existing technologies, one of which is the tsunami buoy system. The new tsunami buoy system does not use the natural mooring system but uses the wave glider system. This paper discusses the structural strength of the surface floater of wave glider using Eva Foam and Fiberglass material for skin and Alluminium material for frame and kell. The surface floater using 16 pieces for frame and 1 piece for keel. Enviromental loads is use in this paper like hydrodynamics load and weight load. The results from this paper is material from Eva Foam has a maximum principle stress is 12693 Pa and shear stress is 6114.6 Pa. For material from Fiberglass has maximum principle stress is 11.875 Pa and shear stress is 6076.3 Pa. Safety factor (SF) from maximum principle stress and shear stress for Eva Foams is up to 6x and SF for maximum principle and shear stress for Fiberglass is up to 26x. Conclusions for this paper is the desain for surface floater of wave glider it can be operated in the sea with draugh 0.18 m.
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