2019 International Conference on Sustainable Energy Engineering and Application (ICSEEA)
Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) in unst... more Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) in unstable wind direction conditions, moderate, and intermittent wind sources, especially wind in an area of archipelago of Indonesia. To improve the VAWT performance, one of the influencing factors is blade design. The model of blade design will be affected by the output power. Therefore, the choice of blade design will be affected by the coefficient of power. The blade design was the airfoil of the type-H rotor of NACA 4212. Several empirical hypotheses obtained it through the practical experience subjected to use of the savonius blades. It will be shown in this study was to compare design a new type-H rotor VAWT blade using Computational Fluid Dynamic (CFD) software. The novel blade design was upper-curve H-blade of NACA 4212. It showed the result of the analytical analysis to be compared with the same upper-curve inverted blade, and with the upper-lower blade. The results of the performance comparison of numerical analysis, the upper-curve blade has a better power coefficient than the other types. Therefore, the upper-curve blade has the highest power output.
Measurements of a turbulent boundary-layer developing over systematically generated roughness are... more Measurements of a turbulent boundary-layer developing over systematically generated roughness are acquired for friction Reynolds numbers ranging between 3000 < Re τ < 6000. A set of near-Gaussian surfaces with matched amplitude parameters and specified effective slopes in streamwise and spanwise directions are synthesised using a roughness generation algorithm. Three cases are considered: (i) an isotropic surface with equal streamwise (ES x = 0.34) and spanwise effective slope (ES y = 0.34); (ii) an anisotropic spanwise elongated surface with ES x = 0.34 and ES y = 0.17, and (iii) an anisotropic streamwise elongated surface with ES x = 0.17 and ES y = 0.34. The surfaces are manufactured from square sheets of acetal copolymer using an in-house CNC router. Note that surface (iii) is obtained by simply rotating surface (ii) by 90 degrees. The principal interest here is to quantify the sensitivity of the Hama roughness function to systematic changes in surface anisotropy. To this end, hot-wire anemometry measurements are acquired at three different freestream velocities under zero-pressure gradient conditions for each surface. Relative to the isotropic case, an increase in the turbulence intensity is seen in the near-wall region for the anisotropic cases. As expected, decreasing ES x leads to a lower mean momentum deficit which confirms the findings of many previous experimental and numerical studies. However, results also suggest that ES y plays an important role. Even for the mildly anisotropic case considered here, the roughness function is seen to vary by up to 15% as ES y is reduced while ES x is held constant. In addition, regions of high streamwise dispersive velocity are seen to extend further into the flow field as ES y reduces. These observations suggest that existing models for drag prediction need to be modified to account for surface anisotropy.
Abstract Although the hull of a recently dry-docked large ship is expected to be relatively smoot... more Abstract Although the hull of a recently dry-docked large ship is expected to be relatively smooth, surface scanning and experimentation reveal that it can exhibit an “orange-peel” roughness pattern with an equivalent sand-grain roughness height = 0. 101 mm. Using the known value and integral boundary layer evolution, a recently cleaned and coated full-scale ship was predicted to experience a significant increase in the average coefficient of friction and total hydrodynamic resistance during operation. Here the report also discusses two recently reported empirical estimations that can estimate ks directly from measured surface topographical parameters, by-passing the need for experiments on replicated surfaces. The empirical estimations are found to have an accuracy of 4.5 − 5 percentage points in
Proceedings of the 22nd Australasian Fluid Mechanics Conference AFMC2020, 2020
Aims. The test-field method for computing turbulent transport coefficients from simulations of hy... more Aims. The test-field method for computing turbulent transport coefficients from simulations of hydromagnetic flows is extended to the regime with a magnetohydrodynamic (MHD) background. Methods. A generalized set of test equations is derived using both the induction equation and a modified momentum equation. By employing an additional set of auxiliary equations, we derive linear equations describing the response of the system to a set of prescribed test fields. Purely magnetic and MHD backgrounds are emulated by applying an electromotive force in the induction equation analogously to the ponderomotive force in the momentum equation. Both forces are chosen to have Roberts flow-like geometry. Results. Examples with an MHD background are studied where the previously used quasi-kinematic test-field method breaks down. In cases with homogeneous mean fields it is shown that the generalized test-field method produces the same results as the imposed-field method, where the field-aligned component of the actual electromotive force from the simulation is used. Furthermore, results for the turbulent diffusivity tensor are given, which are inaccessible to the imposed-field method. For MHD backgrounds, new mean-field effects are found that depend on the occurrence of cross-correlations between magnetic and velocity fluctuations. For strong imposed fields, α is found to be quenched proportional to the fourth power of the field strength, regardless of the type of background studied.
JOURNAL OF SUSTAINABILITY SCIENCE AND MANAGEMENT, 2021
This is a study on the effect of hull roughness on ship resistance components (especially full vi... more This is a study on the effect of hull roughness on ship resistance components (especially full viscous resistance), which is tested using wind-tunnel experiments and Computational Fluid Dynamics (CFD) simulations. With the wind-tunnel experiment, a full viscous resistance analysis can be carried out to further explore changes in the friction and pressure resistance only without the wave resistance. In the experiments, the roughness model used sandpaper with an average roughness height (k a) = 162 µm, that then it was predicted equal with k s = 1475 µm. In the CFD simulations, the roughness parameter was represented by an equivalent sand grain roughness height (k s), and this was varied by several levels. The results indicated that there was a significant increase in ∆Ct (up to 73.7%) and ∆Cf (up to 106.96%), but only a slight increase in ∆Cp (up to 10.57%). The trend of the increase in resistance due to k s and Reynolds numbers were also discussed. The parameter k s were very influential on ∆Cf, but had only a slight effect on ∆Cp. With the significant results about the increase in ship resistance due to the roughness, both the friction and the pressure resistance component will lead to an increase in fuel consumption on a ship then it will increase levels of carbon emissions in the air.
The issue of global warming makes energy savings on ships compulsory. One of the biggest causes o... more The issue of global warming makes energy savings on ships compulsory. One of the biggest causes of energy waste is the increase in friction resistance due to the hull roughness that makes not hydraulically smooth. The process of cleaning and repainting the ship hull turned out to make a roughness that can provide a drag penalty. An investigation using a resolved Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) approached to assess the increase in ship resistance from a recently cleaned and painted ship hull roughness are reported. The rough surface was obtained through surface imprint during its annual dry-docking and digitized via a laser scanner. A roughness geometry that was obtained from the scanning was prepared for the CFD simulations. The results for two ships show that such surface would cause an increase in friction resistance of the full-scale ship by 33%-35%, which corresponds to an increase in the ship's total resistance by 7.5%-28%. The type of ship that is mostly affected by the roughness is a ship with a higher frictional resistance ratio (lower Froude Number) compared to residual resistances, where most of them are large ships.
IOP Conference Series: Earth and Environmental Science, 2019
This article will look into to the environmental and economic issues in the maritime sector that ... more This article will look into to the environmental and economic issues in the maritime sector that arise due to biofouling. For the shipping industry, biofouling is known to increase hull roughness that would lead to an increase in friction resistance and fuel consumption. Here we present a short review regarding ship-hull roughness due to biofouling and its associated increase in skin friction drag, and analysis of fuel consumption from an operating ship with two different anti-fouling coating. The data shows that a higher quality antifouling would result in a low biofouling attachment on the hull surface, resulting in a lower fuel consumption.
This paper describes initial experimental results from an ongoing investigation into the perturba... more This paper describes initial experimental results from an ongoing investigation into the perturbation of a zero pressure gradient turbulent boundary layer due to a very unusual surface roughness. A highly ordered and directional roughness pattern imposes a large-scale secondary flow onto the boundary layer. This causes a spanwise variation of the boundary layer thickness by a factor of up to 2 (for the strongest cases), in spite of the fact that the peak-to-trough roughness height is only £ ¢ ¤ ¦ ¥ § ¥ th of the boundary layer thickness. Initial results suggest that this unique surface roughness is acting as a vortex generator, producing large-scale arrays of counter-rotating streamwise vortices. These rough surfaces do not appear to obey Townsend's outer layer similarity approximation.
International Journal of Heat and Fluid Flow, 2013
The effect of converging-diverging riblet-type surface roughness (riblets arranged in a 'herringb... more The effect of converging-diverging riblet-type surface roughness (riblets arranged in a 'herringbone' pattern) are investigated experimentally in a zero pressure gradient turbulent boundary layer. For this initial parametric investigation three different parameters of the surface roughness are analysed in detail; the converging-diverging riblet yaw angle a, the streamwise fetch or development length over the rough surface F x and the viscous-scaled riblet height h +. It is observed that this highly directional surface roughness pattern induces a large-scale spanwise periodicity onto the boundary layer, resulting in a pronounced spanwise modification of the boundary layer thickness. Hot-wire measurements reveal that above the diverging region, the local mean velocity increases while the turbulent intensity decreases, resulting in a thinner overall boundary layer thickness in these locations. The opposite situation occurs over the converging region, where the local mean velocity is decreased and the turbulent intensity increases, producing a locally thicker boundary layer. Increasing the converging-diverging angle or the viscous-scaled riblet height results in stronger spanwise perturbations. For the strongest convergent-divergent angle, the spanwise variation of the boundary layer thickness between the diverging and converging region is almost a factor of two. Such a large variation is remarkable considering that the riblet height is only 1% of the unperturbed boundary layer thickness. Increasing the fetch seems to cause the perturbations to grow further from the surface, while the overall strength of the induced high and low speed regions remain relatively unaltered. Further analysis of the pre-multiplied energy spectra suggests that the surface roughness has modified or redistributed the largest scale energetic structures.
A field was discovered in 1972 with current ten drilled wells with different reservoir characteri... more A field was discovered in 1972 with current ten drilled wells with different reservoir characteristics throughout the structure. The A reservoir is an irregular carbonate buildup of Peutu limestone oriented north-northwest. The thickness of this unit varies from 45 meters (147.6 ft) in A-8 to 458 meters (1,502.2 ft) and in A-7A with a gas column of 120 meters (393.6 ft). The A field is 2 to 3 kilometers wide by 9 kilometers long and covers area about 20 square kilometers. The reservoir in A Field is Peutu limestone beside the Tampur Dolomite below. Thin section analysis and investigation of drill cuttings indicate that Peutu formation contains 37 carbonate lithofacies. For modeling purposes, these facies are grouped into 5 reservoir facies (rock types) based on combination of depositional facies and diagenetic unit. The tampur is modeled as dolostone facies with some dispersed shale streaks. Combination of Seismic interpretation and general tectonic history indicate that the reservo...
2019 International Conference on Sustainable Energy Engineering and Application (ICSEEA)
Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) in unst... more Vertical Axis Wind Turbine (VAWT) has advantages over Horizontal Axis Wind Turbine (HAWT) in unstable wind direction conditions, moderate, and intermittent wind sources, especially wind in an area of archipelago of Indonesia. To improve the VAWT performance, one of the influencing factors is blade design. The model of blade design will be affected by the output power. Therefore, the choice of blade design will be affected by the coefficient of power. The blade design was the airfoil of the type-H rotor of NACA 4212. Several empirical hypotheses obtained it through the practical experience subjected to use of the savonius blades. It will be shown in this study was to compare design a new type-H rotor VAWT blade using Computational Fluid Dynamic (CFD) software. The novel blade design was upper-curve H-blade of NACA 4212. It showed the result of the analytical analysis to be compared with the same upper-curve inverted blade, and with the upper-lower blade. The results of the performance comparison of numerical analysis, the upper-curve blade has a better power coefficient than the other types. Therefore, the upper-curve blade has the highest power output.
Measurements of a turbulent boundary-layer developing over systematically generated roughness are... more Measurements of a turbulent boundary-layer developing over systematically generated roughness are acquired for friction Reynolds numbers ranging between 3000 < Re τ < 6000. A set of near-Gaussian surfaces with matched amplitude parameters and specified effective slopes in streamwise and spanwise directions are synthesised using a roughness generation algorithm. Three cases are considered: (i) an isotropic surface with equal streamwise (ES x = 0.34) and spanwise effective slope (ES y = 0.34); (ii) an anisotropic spanwise elongated surface with ES x = 0.34 and ES y = 0.17, and (iii) an anisotropic streamwise elongated surface with ES x = 0.17 and ES y = 0.34. The surfaces are manufactured from square sheets of acetal copolymer using an in-house CNC router. Note that surface (iii) is obtained by simply rotating surface (ii) by 90 degrees. The principal interest here is to quantify the sensitivity of the Hama roughness function to systematic changes in surface anisotropy. To this end, hot-wire anemometry measurements are acquired at three different freestream velocities under zero-pressure gradient conditions for each surface. Relative to the isotropic case, an increase in the turbulence intensity is seen in the near-wall region for the anisotropic cases. As expected, decreasing ES x leads to a lower mean momentum deficit which confirms the findings of many previous experimental and numerical studies. However, results also suggest that ES y plays an important role. Even for the mildly anisotropic case considered here, the roughness function is seen to vary by up to 15% as ES y is reduced while ES x is held constant. In addition, regions of high streamwise dispersive velocity are seen to extend further into the flow field as ES y reduces. These observations suggest that existing models for drag prediction need to be modified to account for surface anisotropy.
Abstract Although the hull of a recently dry-docked large ship is expected to be relatively smoot... more Abstract Although the hull of a recently dry-docked large ship is expected to be relatively smooth, surface scanning and experimentation reveal that it can exhibit an “orange-peel” roughness pattern with an equivalent sand-grain roughness height = 0. 101 mm. Using the known value and integral boundary layer evolution, a recently cleaned and coated full-scale ship was predicted to experience a significant increase in the average coefficient of friction and total hydrodynamic resistance during operation. Here the report also discusses two recently reported empirical estimations that can estimate ks directly from measured surface topographical parameters, by-passing the need for experiments on replicated surfaces. The empirical estimations are found to have an accuracy of 4.5 − 5 percentage points in
Proceedings of the 22nd Australasian Fluid Mechanics Conference AFMC2020, 2020
Aims. The test-field method for computing turbulent transport coefficients from simulations of hy... more Aims. The test-field method for computing turbulent transport coefficients from simulations of hydromagnetic flows is extended to the regime with a magnetohydrodynamic (MHD) background. Methods. A generalized set of test equations is derived using both the induction equation and a modified momentum equation. By employing an additional set of auxiliary equations, we derive linear equations describing the response of the system to a set of prescribed test fields. Purely magnetic and MHD backgrounds are emulated by applying an electromotive force in the induction equation analogously to the ponderomotive force in the momentum equation. Both forces are chosen to have Roberts flow-like geometry. Results. Examples with an MHD background are studied where the previously used quasi-kinematic test-field method breaks down. In cases with homogeneous mean fields it is shown that the generalized test-field method produces the same results as the imposed-field method, where the field-aligned component of the actual electromotive force from the simulation is used. Furthermore, results for the turbulent diffusivity tensor are given, which are inaccessible to the imposed-field method. For MHD backgrounds, new mean-field effects are found that depend on the occurrence of cross-correlations between magnetic and velocity fluctuations. For strong imposed fields, α is found to be quenched proportional to the fourth power of the field strength, regardless of the type of background studied.
JOURNAL OF SUSTAINABILITY SCIENCE AND MANAGEMENT, 2021
This is a study on the effect of hull roughness on ship resistance components (especially full vi... more This is a study on the effect of hull roughness on ship resistance components (especially full viscous resistance), which is tested using wind-tunnel experiments and Computational Fluid Dynamics (CFD) simulations. With the wind-tunnel experiment, a full viscous resistance analysis can be carried out to further explore changes in the friction and pressure resistance only without the wave resistance. In the experiments, the roughness model used sandpaper with an average roughness height (k a) = 162 µm, that then it was predicted equal with k s = 1475 µm. In the CFD simulations, the roughness parameter was represented by an equivalent sand grain roughness height (k s), and this was varied by several levels. The results indicated that there was a significant increase in ∆Ct (up to 73.7%) and ∆Cf (up to 106.96%), but only a slight increase in ∆Cp (up to 10.57%). The trend of the increase in resistance due to k s and Reynolds numbers were also discussed. The parameter k s were very influential on ∆Cf, but had only a slight effect on ∆Cp. With the significant results about the increase in ship resistance due to the roughness, both the friction and the pressure resistance component will lead to an increase in fuel consumption on a ship then it will increase levels of carbon emissions in the air.
The issue of global warming makes energy savings on ships compulsory. One of the biggest causes o... more The issue of global warming makes energy savings on ships compulsory. One of the biggest causes of energy waste is the increase in friction resistance due to the hull roughness that makes not hydraulically smooth. The process of cleaning and repainting the ship hull turned out to make a roughness that can provide a drag penalty. An investigation using a resolved Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) approached to assess the increase in ship resistance from a recently cleaned and painted ship hull roughness are reported. The rough surface was obtained through surface imprint during its annual dry-docking and digitized via a laser scanner. A roughness geometry that was obtained from the scanning was prepared for the CFD simulations. The results for two ships show that such surface would cause an increase in friction resistance of the full-scale ship by 33%-35%, which corresponds to an increase in the ship's total resistance by 7.5%-28%. The type of ship that is mostly affected by the roughness is a ship with a higher frictional resistance ratio (lower Froude Number) compared to residual resistances, where most of them are large ships.
IOP Conference Series: Earth and Environmental Science, 2019
This article will look into to the environmental and economic issues in the maritime sector that ... more This article will look into to the environmental and economic issues in the maritime sector that arise due to biofouling. For the shipping industry, biofouling is known to increase hull roughness that would lead to an increase in friction resistance and fuel consumption. Here we present a short review regarding ship-hull roughness due to biofouling and its associated increase in skin friction drag, and analysis of fuel consumption from an operating ship with two different anti-fouling coating. The data shows that a higher quality antifouling would result in a low biofouling attachment on the hull surface, resulting in a lower fuel consumption.
This paper describes initial experimental results from an ongoing investigation into the perturba... more This paper describes initial experimental results from an ongoing investigation into the perturbation of a zero pressure gradient turbulent boundary layer due to a very unusual surface roughness. A highly ordered and directional roughness pattern imposes a large-scale secondary flow onto the boundary layer. This causes a spanwise variation of the boundary layer thickness by a factor of up to 2 (for the strongest cases), in spite of the fact that the peak-to-trough roughness height is only £ ¢ ¤ ¦ ¥ § ¥ th of the boundary layer thickness. Initial results suggest that this unique surface roughness is acting as a vortex generator, producing large-scale arrays of counter-rotating streamwise vortices. These rough surfaces do not appear to obey Townsend's outer layer similarity approximation.
International Journal of Heat and Fluid Flow, 2013
The effect of converging-diverging riblet-type surface roughness (riblets arranged in a 'herringb... more The effect of converging-diverging riblet-type surface roughness (riblets arranged in a 'herringbone' pattern) are investigated experimentally in a zero pressure gradient turbulent boundary layer. For this initial parametric investigation three different parameters of the surface roughness are analysed in detail; the converging-diverging riblet yaw angle a, the streamwise fetch or development length over the rough surface F x and the viscous-scaled riblet height h +. It is observed that this highly directional surface roughness pattern induces a large-scale spanwise periodicity onto the boundary layer, resulting in a pronounced spanwise modification of the boundary layer thickness. Hot-wire measurements reveal that above the diverging region, the local mean velocity increases while the turbulent intensity decreases, resulting in a thinner overall boundary layer thickness in these locations. The opposite situation occurs over the converging region, where the local mean velocity is decreased and the turbulent intensity increases, producing a locally thicker boundary layer. Increasing the converging-diverging angle or the viscous-scaled riblet height results in stronger spanwise perturbations. For the strongest convergent-divergent angle, the spanwise variation of the boundary layer thickness between the diverging and converging region is almost a factor of two. Such a large variation is remarkable considering that the riblet height is only 1% of the unperturbed boundary layer thickness. Increasing the fetch seems to cause the perturbations to grow further from the surface, while the overall strength of the induced high and low speed regions remain relatively unaltered. Further analysis of the pre-multiplied energy spectra suggests that the surface roughness has modified or redistributed the largest scale energetic structures.
A field was discovered in 1972 with current ten drilled wells with different reservoir characteri... more A field was discovered in 1972 with current ten drilled wells with different reservoir characteristics throughout the structure. The A reservoir is an irregular carbonate buildup of Peutu limestone oriented north-northwest. The thickness of this unit varies from 45 meters (147.6 ft) in A-8 to 458 meters (1,502.2 ft) and in A-7A with a gas column of 120 meters (393.6 ft). The A field is 2 to 3 kilometers wide by 9 kilometers long and covers area about 20 square kilometers. The reservoir in A Field is Peutu limestone beside the Tampur Dolomite below. Thin section analysis and investigation of drill cuttings indicate that Peutu formation contains 37 carbonate lithofacies. For modeling purposes, these facies are grouped into 5 reservoir facies (rock types) based on combination of depositional facies and diagenetic unit. The tampur is modeled as dolostone facies with some dispersed shale streaks. Combination of Seismic interpretation and general tectonic history indicate that the reservo...
Uploads
Papers by Bagus Nugroho