The Experts below are selected from a list of 48 Experts worldwide ranked by ideXlab platform

Sofia Werner - One of the best experts on this subject based on the ideXlab platform.

  • Transitional Flow on Model Propellers and Their Influence on Relative Rotative Efficiency
    Journal of Marine Science and Engineering, 2019
    Co-Authors: Per Lindell, Sofia Werner
    Abstract:

    Unexpected low value of the Relative Rotative Efficiency ηR is sometimes noted when scaling the towing tank model-test result with the ITTC-78 method to obtain the propulsive Efficiency factors of propellers. The paper explains the causes of this phenomenon. The boundary layer state of three propellers was studied by a paint test and a RANS method. The paint tests showed that the propellers in behind conditions at low Reynolds number (Rn) are covered mainly with laminar flow, which is different from open water tests conducted at a high Rn. Apart from that a moderate difference in Rn between the open water and the self-propulsion test may lead to a low ηR value, the paper points out that flow separation in behind conditions could be another significant reason for the drop of ηR for some propellers. Therefore, two factors will lead to an unexpected decrease of ηR: (1) A slightly lower open water torque interpolated from an open water test carried out at a high Rn and (2) a slightly higher torque in a self-propulsion test due to laminar flow separation near the trailing edge. The phenomenon is caused by the Rn scaled effect and closely associated with design philosophy like the blade section profile, the chord length, and chordwise load distribution.

Per Lindell - One of the best experts on this subject based on the ideXlab platform.

  • Transitional Flow on Model Propellers and Their Influence on Relative Rotative Efficiency
    Journal of Marine Science and Engineering, 2019
    Co-Authors: Per Lindell, Sofia Werner
    Abstract:

    Unexpected low value of the Relative Rotative Efficiency ηR is sometimes noted when scaling the towing tank model-test result with the ITTC-78 method to obtain the propulsive Efficiency factors of propellers. The paper explains the causes of this phenomenon. The boundary layer state of three propellers was studied by a paint test and a RANS method. The paint tests showed that the propellers in behind conditions at low Reynolds number (Rn) are covered mainly with laminar flow, which is different from open water tests conducted at a high Rn. Apart from that a moderate difference in Rn between the open water and the self-propulsion test may lead to a low ηR value, the paper points out that flow separation in behind conditions could be another significant reason for the drop of ηR for some propellers. Therefore, two factors will lead to an unexpected decrease of ηR: (1) A slightly lower open water torque interpolated from an open water test carried out at a high Rn and (2) a slightly higher torque in a self-propulsion test due to laminar flow separation near the trailing edge. The phenomenon is caused by the Rn scaled effect and closely associated with design philosophy like the blade section profile, the chord length, and chordwise load distribution.

Amin Najafi - One of the best experts on this subject based on the ideXlab platform.

  • An experimental and CFD study on the effects of different pre-swirl ducts on propulsion performance of series 60 ship
    Ocean Engineering, 2019
    Co-Authors: Hashem Nowruzi, Amin Najafi
    Abstract:

    Abstract In the present paper, the effects of three different pre-swirl ducts on propulsion performance of a series 60 ship in comparison to the case with no duct are explored experimentally by self-propulsion test measurements and CFD analysis. To this accomplishment, Mewis duct, Becker twisted fins and unconventional half circular ducts are considered. For investigating the propulsion performance, thrust and torque coefficients, Efficiency components of the intended propulsion system, wake and pressure distributions are evaluated. Based on our tests, the highest thrust and torque coefficients are achieved at lower advance ratios for Becker twisted fins, while; Mewis ducts provided the highest value of thrust and torque coefficients at higher advance ratios. Maximum value for propeller behind hull Efficiency, Relative Rotative Efficiency and propulsive Efficiency are obtained with respect to unconventional half circular duct, Mewis duct, and the case with no pre-swirl duct. Based on the wake distribution analysis, local deformation on the upstream wake induced by pre-swirl ducts is detected. Moreover, it is found that the vortex shedding from trailing edges of the propeller blades has led to a defection on the downstream wake field.

Qi Pan - One of the best experts on this subject based on the ideXlab platform.

  • The influence of using a ducted propeller on motions and speed loss of a ship in waves
    'Norwegian University of Science and Technology (NTNU) Library', 2013
    Co-Authors: Qi Pan
    Abstract:

    Comparisons of experimental and numerical investigations into the effect of duct on motion variables and speed loss for a given ship model are presented. The purpose of these comparisons is to verify the advantage of using ducted propeller on sea keeping performance and added power or speed loss. Relevant damping theories concerning the lift characteristic of ducts are described as foundation for the numerical calculations of using an equivalent flat plate that represents the duct of ducted propeller in software of SHIPX. In SHIPX, a case ship of RR NVC Nor-lines 120m cargo vessel is defined and several plug-in are used to do simulations for bare ship (refers to vessel with open propeller) and ship with foil (represents vessel with ducted propeller). The duct‟s effect on RAOs for motion variables, added resistance and speed loss are evaluated respectively under 5 different wave conditions. A series of experiments on M3006 respectively with an open propeller and a ducted propeller are carried out in both calm water and 8 regular wave conditions in the large towing tank of MARINTEK center. Repetitions of tests under same wave conditions are used to make uncertainty analysis of measured variables. The effect of wave height and wave period affecting the duct‟s effect on motion variables and added resistance are discussed and compared with numerical results obtained from SHIPX. Additionally, by interpolation of propeller rotational speed given tow rope force at self-propulsion point, corresponding thrust and torque are obtained. Then the interpolated variables are used to calculate propulsive coefficients including thrust deduction, wake fraction and Relative Rotative Efficiency in both calm water and regular waves. The effect of wave height and wave period on propulsive coefficients are studied and compared for both open and ducted propeller. Furthermore, corrections are made for interpolation results to give more precise power prediction. The effect of propeller loading on wake fraction and propeller Efficiency varying with 5 different wave conditions are presented. Finally the duct‟s effect on added power is studied and compared with numerical results from SHIPX

Hamburg Univ. Inst. Fuer Schiffbau - One of the best experts on this subject based on the ideXlab platform.

  • Beitrag zur Abschaetzung von Widerstand und Propulsion von Ein- und Zweischraubenschiffen im Vorentwurf
    1997
    Co-Authors: Hollenbach K.u., Hamburg Univ. Inst. Fuer Schiffbau
    Abstract:

    With a view to improve reliability of the performance prognosis of modern merchant vessels in the preliminary design stage, model tank tests performed by the Vienna Ship Model Basin of the period from 1980 to 1995 have been analysed. The resistance test results are compared with the different statistical methods. The open water test results of stockpropellers are compared with the propeller efficiencies of the Wageninger B-screw series. For the model experiment results available a PC program for database-based ship trial prognosis has been developed. In addition to the database-based method a novel statistical method for estimating the ships resistance has been developed. This method is intended to enable estimating not only a mean resistance, but also the minimum resistance of good lines and the maximum resistance of poor lines. Furthermore formulas for estimating the wake factor, the thrust deduction factor and the Relative Rotative Efficiency for single and twin screw vessels are presented. The novel statistical method for resistance and propulsion factors has been tested with a control group of ship models which recently have been tested at the Hamburg Ship Model Basin (HSVA). (orig.)SIGLEAvailable from TIB Hannover: RA 489(588) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman