EXPERIMENTAL STUDY hydrodynamic SEA WAVES WAY FOR DETERMINATION POWER LEG SUPPORT BRIDGE STRUCTURES AT SEA Sunda Strait

EXPERIMENTAL STUDY hydrodynamic SEA WAVES WAY FOR DETERMINATION POWER LEG SUPPORT BRIDGE STRUCTURES AT SEA Sunda Strait ABSTRACT In planning the structure of the foot buffer Sunda Strait Bridge in the sea there are important matters relating to the imposition of the environment that need attention. The accuracy in predicting operating expenses that occurred in the structure of the foot support bridge in the sea is strongly influenced by environmental conditions. Inaccuracy in predicting operating expenses, can cause structural design resulting buffer foot bridge in the sea is too strong (over design) or vice versa, which in turn will affect the strength and economic aspects. Assumed most of the structure of the foot buffer in marine type fixed bridge is under water, it can be said that the greatest dynamic loads caused by hydrodynamic forces to be dominated by the load due to wave force. Method of calculating wave force acting on an upright cylindrical structures immersed in water has been introduced by Morison, et al. (1950). According to Morison equation wave force consists of two components of force: inertia, in which there are inertia coefficient Cm; And the style in which there are drag drag coefficient Cd. The coefficient is very difficult to obtain from mathematical elaboration, and can only be obtained from the experimental results. For the purposes of the experiment will be conducted on the wave force measurement round cylinder models through experimental trials in the tank is equipped with a wave generator in the hydrodynamics laboratory BPPH UPT-BPP Technology in Surabaya. Data measurement results on cylindrical wave style further analyzed to obtain a non-dimensional coefficient of Cd and Cm coefficients. Data coefficient analysis results displayed in graphical form as a function of the angle of the cylinder and the function of the Reynolds number Re, to show the change in style of wave loading on the various dimensions of construction due to changes in the slope of the cylinder and cylinder construction. Keywords: style, wave, Cm, Cd, cylinder   INTRODUCTION 1 BACKGROUND. To achieve the purpose of producing structures supporting foot bridge in the sea that is safe, inexpensive and able to withstand the loads caused by the environmental burden during the period, several studies have been conducted in the laboratory and field. The study deals with the development of mathematical models, design rules, methods of planning and construction methods. Because of his complex environmental loading on the structure of the foot support bridge in the sea, among others, caused by the weight of the wind, waves, currents, ice (areas), earthquakes and the movement of the ocean floor, then to be able to analyze properly is a very difficult job. It required a simplification approaches and modeling the environmental load in order to assist in the loading calculations. In planning the structure of the foot support bridge on the sea there are important matters relating to the imposition of the environment that need attention. The accuracy in predicting operating expenses that occurred in the structure of the foot support bridge in the sea is strongly influenced by environmental conditions. Different environments will have different criteria for operating expenses as well. Inaccuracy in predicting operating expenses, can cause structural design resulting buffer foot bridge in the sea is too strong (over design) or vice versa, which in turn will affect the strength and economic aspects. Considering most of the structure of the foot buffer in marine type fixed bridge (jacket) is below the surface of the water, it can be assumed that the largest dynamic loads caused by hydrodynamic forces to be dominated by the brunt of a wave style. Method of calculating wave force acting on an upright cylindrical structures immersed in water has been introduced by Morison, et al. 1950 (1). The formulation is known as the "Morison Equation", which is a simplified formulation of the wave force acting on a cylinder. According to Morison equation wave force consists of two force components: inertial force (inertial force) in which there are inertia coefficient Cm, is the force resulting from acceleration wave particle motion, and drag force (drag force) in which there are drag coefficient Cd, a style arising from the movement of the particle wave velocity. The coefficient is very difficult to obtain from mathematical elaboration, and is usually obtained from the experimental results. Morison conduct experiments through the formulation of a wave-style cylinder upright on the tank experiments. Experiments conducted with wavy flow in the range of Reynolds numbers 0.22x104 105. Chakrabarti 1980 (5) repeated the experiments conducted experiments that have been done before (1976). With the same Re number (Re = 2x104 s / d 3x104), but the number of Kc with a wider variation (Kc = 0-85). Because of the limited range of Re numbers, the price coefficient Cd and Cm analysis results with the Morison equation are presented in graphical form only as a function of the number of Kc. The results of this study indicate that the coefficient of Cd and Cm in some places still spread from the average price, it is alleged among others, the movement of water particles berbedaan calculations with actual water movement and also mainly caused by not divariasikannya coefficients against Reynolds number Re. Dawson 1984 (6) conducted an experiment using cylinders upright in the waves with the Reynolds number Re <104. prices given coefficient Cd = 1.2 and Cm = 1.8 (constant). Dawson tried to compare the results of the calculation of the wave style with value Cd = 1.2 and Cm = 1.8 with the results of the study SARPKAYA (1976) for the frequency range of the parameter Re / Kc same. Apparently SARPKAYA results showed higher values up to 30% on local wave height H> 15 in. Chakrabarti, Tam, and Wolbert 1975 (7) conduct tests on cylinders tilted to the direction of movement of the wave. Style wave equation calculated by Morison. For the velocity and acceleration of particles in the wave equation used speed and acceleration components normal to the cylinder axis, ignoring tangential component. Based on these assumptions Morison equation formulation in any orientation cylinder can generate coefficients Cd and Cm which have the same price for both horizontal and vertical cylinders. Furthermore, the cylinder with a slope of 45 deg. to the direction of movement of the wave, the wave style horizontal and vertical direction will have the same price. Tests carried out in the range of numbers Kc = mT / D = 0 - 17:50 for the orientation of the cylinder upright, horizontal cylinder perpendicular to the wave direction, tilted cylinder 15 and 30 degrees to the horizontal plane perpendicular to the wave, and horizontal cylinders parallel to the direction of the wave. Shigemura 1980 (8) carry out tests on cylinders tilted in two different areas: (A) Cylinder tilted in the vertical plane parallel to the direction of the waves; (B) slant cylinder in a vertical plane parallel to the wave crests. Tests conducted with cylinder angle of each field (A and B) 0, ± 10, ± 20, ± 30 degrees to the vertical axis. The results of the analysis of the (A) the time-independent conditions displayed in graphic form the relationship between the coefficient of Cd and Cm as a function of rmsKc (rmsKc = U2.T / D, where U = the average speed of the cylinder normal direction) for various slope angles of testing . It appears that almost all of its value Cd and Cm in the range of values for Cd and Cm upright cylinder. Results of analysis for the field (B) shows that the coefficient of variation of Cd and Cm have the same value with the variation coefficient obtained from experiments in the field of A for various tilt cylinders. SARPKAYA, Raines, and Trytten 1982 (9) to conduct research on the flow of the cylinder tilted sinusoidal oscillations with the main objective to verify the use of "independence principle" experimentally. tilt toward the direction of the wave is 45, 60, and 90 degrees in the horizontal position to the direction of flow. The test results are displayed in graphical form coefficients Cd and Cm changes for different tilt angles as a function of the price of Kc. That relationship did not prove that the independence principle fully applicable to the cylinder. Inferred from observations also flow around the cylinder, the flow around and behind cylinders with cylinders tilted upright different characteristics. Cotter and Chakrabarti 1984 (10) analyzed the coefficient of Cd and Cm of the local wave force measurements in the test section. Experiments conducted on the cylinder with the angle of 0, 30, 45 degrees to the vertical, and the range of numbers Kc = 1-39 and Re = 1500-91000. Cd and Cm values are shown as average prices and COV (coefficient of variation) as a function of the number of Kc at different tilt angles tested cylinder. From the results of this study concluded that the independence principle can be applied when the normal component of velocity and acceleration used in the Morison equation. Ferrante et al. 1981 (11) conducted a study on the use of Morison equation on cylinders tilted especially in determining the speed and acceleration of particles in predicting wave loading. Some assumptions are applied respectively on two platforms with different sizes to determine differences in the calculation of the total force in the style of the actual total. Of these studies concluded that the assumptions apply only normal component of velocity and acceleration that causes the wave force on the cylinder side, will produce intermediate wave-style prices. Heideman and SARPKAYA 1985 (12) conducted a study to determine the hydrodynamic coefficients of price changes on a cylinder because of changes in the speed and acceleration of particles under the influence of a vertical cylinder around it, in a steady stream and oscillation. The test results are depicted in graphic form the relationship between hydrodynamic coefficients with numbers Re (steady flow) and the relationship between the number of hydrodynamic coefficients Kc (oscillatory flow). It appears that (in steady flow) rates the closest Cd Cd priced single cylinder is a cylinder is S = 5D. Li and Xu, 1989 (13) Horizontal cylinder experiment with loading waves combined with currents. Tests performed on the number Kc = (Um + Uc). T / D = 2.9 - 42 and number Re = 3080-21780. Price coefficients Cd and Cm analysis results displayed as a function of the number Kc and velocity ratio Uc / Um. When coefficients are compared with test results from Iwagaki upright cylinder (1985), the price coefficient on horizontal cylinders in some places show greater price than the vertical cylinder. The magnitude of the coefficient of Cd and Cm can not be separated from the influence of the flow behavior around the structure. Where the characteristics of the flow, among others depending on the speed and acceleration of water particles, the diameter of the cylinder, tilt cylinder, wave parameters, surface roughness, density of water, the level of turbulence flow, and others. From the fact mentioned above, the use of "independence principle" or "sine-cosine law" can not simply be applied to any cylinder oriented, because the flow around cylindrical structures for various orentasi will have different characteristics. The difference in the slope of the cylinder will cause a different load, the value of the coefficient of Cd and Cm are different also. Cylindrical structures with arbitrary orentasi until now has not been widely studied, and have not reached agreement among the designers of the coefficient Cd and Cm especially at critical transition areas and wastelands (104 $(function(){$("#butToggle").click(function(){$('#dvt').toggle(1000);});});

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