• Journal of Hydrospace Technology
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• v.1 no.1
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• pp.29-40
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• 1995

This paper describes the procedure to predict steady and unsteady performances of a contrarotating propeller(CRP) by a mixed formulation of the boundary value problem(BVP) far the flow around a CRP. The blade BVP is treated by a classical vortex lattice method, whereas the hub BVP is solved by a potential-based panel method. Blades and trailing wakes are represented by a vortex and/or source lattice system, and hubs are represented by normal dipole and source distributions. Both forward and aft propellers are solved simultaneously, thus treating the interaction effect without iteration. The unsteady performance is computed directly in time domain. The new numerical procedure requires a large amount of storage and computing time, which is however no longer a limit in a modern computer system. Sample computations show that the steady performance compares very well with the experiments. The predicted unsteady behavior shows that the dominant harmonics of the total forces are multiples of not only the number of blades of the forward and aft propellers but also the product of both blade numbers. The magnitude of the latter harmonics, present also in uniform oncoming flow, may reach abort 50% of the mean torque for the aft propeller, which in turn may cause a serious vibration problem in the complicated contrarotating shafting system.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.252-256
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• 1999

In this research, the performance predictions of the submersible mixer were investigated. The variation of the performance characteristics by changing the impeller design parameters were discussed through the flow calculation results by using a commercial program, FLUENT. The performance of the submersible mixers is related to the velocity diffusion profiles downstream of the impeller and also the required input motor power to mix the fluid. In this study, the various design parameters such as the number of blade, the hub and tip diameters, the impeller blade profiles and revolution speed of the blades were taken for the fixed values. The blade sweep direction, the chord length distribution along with the radius of the blade and the inlet blade angle were changed to make different testing models. The flow calculation results show the effect of the changed design parameters on the performance of the submersible mixers and also give some helpful information for designing more efficient submersible mixers.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.14-26
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• 1989

This paper describes the method of statistical analysis and its programs for predicting the ship's powering performance. The equation for the wavemaking resistance coefficient is derived as the sectional area coefficients by using the wavemaking resistance theory and its regression coefficients are determined from the regression analysis of the model test results. The equations for the form factor, wake franction and thrust deduction fraction are derived by purely regression analysis of the principal dimensions, sectional area coefficients and model test results. The statistical analyses are performed using the various descriptive statistic and stepwise regression analysis techniques. The powering performance prognosis program is developed to cover the prediction of resistance coefficients, propulsive coefficients, propeller open-water efficiency and various scale effect corrections.

• Journal of Ship and Ocean Technology
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• v.9 no.1
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• pp.1-10
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• 2005

The procedures of model test and performance prediction for the CRP-POD propulsion ships, are studied. At the CRP-POD system, which are highly applicable to ultra large container carriers, RPM ratio of two propellers is not fixed, unlike conventional CRP system, and hence the power of each propeller must be predicted respectively. In this paper, a CRP-POD system is designed for 10,000 TEU class ultra large container carriers, and the characteristics of the CRP-POD system are experimentally studied. Finally, based on this study, the procedure of powering performance evaluation for CRP-POD propulsion ships is suggested. However, further studies on quantitative correction of the present procedure are required.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.52-68
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• 1991

A new propeller series is developed using the newly developed blade section(KH18 section) which behaves better cavitation characteristics and higher lift-drag ratio at wide range of angle-of-attack. The pitch and camber distributions are disigned in order to have the same radial and chordwise loading distribution with the selected circumferentially averaged wake input. Since the geometries of the series propeller, such as chord length, thickness, skew and rate distribations, are selected by regression of the recent full scale propeller geometric data, the performance prediction of a propeller at preliminary design stage can be mure realistic. Number of blades of the series propellers is 4 and the expanded blade area ratios are 0.3, 0.45, 0.6 and 0.75. Mean pitch ratios are selected as 0.5, 0.65, 0.8, 0.75 and 1.1 for each expanded area ratio. The new propeller series is composed of 20 propellers and is named as KD(KRISO-DAEWOO) propeller series. Propeller open water tests are performed at the experimental towing tank, and the cavitation observation tests and fluctuating pressure measurements are carried out at the cavitation tunnel of KRISO. $B_{P}-\delta$ curves, which can be used to select the optimum propeller diameter at the preliminary design stage, are derived from a regression analysis of the propeller often water test results. The KD-cavitation chart is derived from the cavitation observation test results by choosing the local maximum lift coefficient and the local cavitation number as parameters. The caviy extent of a propeller can be predicted more accurately by using the KD-cavitation chart at a preliminary design stage, since it is derived from the results of the cavitation observation tests in the selected ship's wake, whereas the existing cavitation charts, such as the Burrill's cavitation chart, are derived from the test results in uniform flow.

• The KSFM Journal of Fluid Machinery
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• v.3 no.2 s.7
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• pp.31-35
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• 2000

In this research, the performance predictions of the submersible mixer were investigated. The variation of the performance characteristics by changing the impeller design parameters were discussed through the flow calculation results by using a commercial program, FLUENT. The performance of the submersible mixers is related to the velocity diffusion profiles downstream of the impeller and also the required input motor power to mix the fluid. In this study, the various design parameters such as the number of blade, the hub and tip diameters, the impeller blade profiles and revolution speed of the blades were taken for the fixed values. The blade sweep direction, the chord length distribution along with the radius of the blade and the inlet blade angle were changed to make different testing models. The flow calculation results show the effect of the changed design parameters on the performance of the submersible mixers and also give some helpful information for designing more efficient submersible mixers.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.7
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• pp.527-534
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• 2018

The endurance of the multi-copter is one of the important variables that determine the mission performance. Therefore, accurate endurance should be defined as essential for performing effective missions. In this paper, we present the results of the study on the flight performance of the aircraft, especially the hovering of the drone(multi-copter). Unlike conventional aircraft, which consider aerodynamic performance by the fuselage, the multi-copter is mostly determined by the propulsion system. Therefore, the research method classifies the various parts constituting the drone system into functions, analyzes the performance of the unit parts and obtains the experimental data by sorting out the specifications and functions at the component level and mathematical formulation, The results of this study are as follows. In addition, the 5kg class quad copter was used to predict and verify the voltage change with endurance through analysis of in situ flight. By predicting endurance under various conditions, it can help design/build the right Multi-copter for mission.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.1
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• pp.110-116
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• 2016

In this study an attempt has been made to study the hydrodynamic performance of pumpjet propulsor. Numerical investigation based on the Reynolds Averaged NaviereStokes (RANS) computational fluid dynamics (CFD) method has been carried out. The structured grid and SST ${\kappa}-{\omega}$ turbulence model have been applied. The numerical simulations of open water performance of marine propeller E779A are carried out with different advance ratios to verify the numerical simulation method. Results show that the thrust and the torque are in good agreements with experimental data. The grid independent inspection is applied to verify accuracy of numerical simulation grid. The numerical predictions of hydrodynamic performance of pumpjet propulsor are carried out with different advance ratios. Results indicate that the rotor provides the main thrust of propulsor and the balance performance of propulsor is generally satisfactory. Additionally, the curve of propulsor efficiency is in good agreement with experimental data. Furthermore, the pressure distributions around rotor and stator blades are reasonable. Beyond that, the existence of tip clearance accounts for the appearance of tip vortex that leads to a further loss in efficiency and a probability of cavitation phenomenon.

• Journal of Aerospace System Engineering
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• v.12 no.6
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• pp.23-31
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• 2018

In the present work, the thrust and torque of multicopter propellers in hovering are predicted based on BET method. The geometry information of the propellers is obtained using a three dimensional scanner and the airfoil section is extracted using CATIA. EDISON CFD is adopted to calculate the drag and lift of airfoil at a given geometry and flow conditions and then thrust is calculated with respect to a given RPMs based on BET. Two simulations with laminar and turbulent flows are considered. The predicted value is compared with the performance data from the Product Company and results from JavaProp software, which is used in the design and prediction of propellers. In the case of a 9-inch propeller, the thrust from the product company is corresponding to the results between the laminar and turbulent flow conditions. In the 16-inch case, the predicted thrust at turbulent flow conditions conformed well with reference one. The predicted torque shows a big difference with the reference data.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.24-34
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• 2021

This paper predicts the speed-power-rpm relationship in regular head waves using various indirect methods: load variation, direct powering, resistance and thrust identity, torque and revolution, thrust and revolution, and Taylor expansion methods. The subject ship is KVLCC2. The wave conditions are the regular head waves of λ/LPP = 0.6 and 1.0 with three wave steepness ratios at three ship speeds of 13.5, 14.5 and 15.5 knots (design speed). In the case of λ/LPP = 0.6 at design speed, two more wave steepness ratios have been taken into consideration. The indirect methods have been evaluated through comparing the speed-power-rpm relationships with those obtained from the resistance and self-propulsion tests in calm water and in waves. The load variation method has been applied to predict propulsive performances in waves, and to derive overload factors (ITTC, 2018). The overload factors have been applied to obtain propulsive efficiency and propeller revolution. The thrust and revolution method (ITTC, 2014) has been modified.