scholarly journals Development of a Semi-analytical Dynamic Thrust Force Model

2021 ◽  
Author(s):  
Marin Akter ◽  
Mohammad Abdul Alim ◽  
Md Manjurul Hussain ◽  
Kazi Shamsunnahar Mita ◽  
Anisul Haque ◽  
...  
Keyword(s):  
Water Mass ◽  
Stokes Equations ◽  
Thrust Force ◽  
Variational Iteration Method ◽  
Navier Stokes ◽  
Force Model ◽  
Dynamic Force ◽  
Navier Stokes Equations ◽  
Cyclone Sidr ◽  
Saint Venant Equations

Abstract A moving water mass generates force which is exerted on its moving path. Cyclone generated storm surge or earthquake generated tsunami are specific examples of moving water mass the generates force along the coasts. In addition to human lives, these moving water masses cause severe damages to the coastal infrastructure due to tremendous force exerted on these structures. To assess the damage on these infrastructures, an essential parameter is the resultant force exerted on these structures. To evaluate the damages, there is hardly any quantitative method available to compute this force. In this paper we have developed a semi-analytical model, named as Dynamic Force Model (DFM), by using Variational Iteration Method to compute this force. As governing equations, we have used the Saint Venant equations which are basically 1D shallow water equations derived from the Navier-Stokes equations. The verified, calibrated and validated DFM is applied in Bangladesh coastal zone to compute dynamic thrust force due to tropical cyclone SIDR.

A Note on Rotor Instability Caused by Liquid Motions

1991 ◽  
Vol 58 (3) ◽  
pp. 804-811 ◽  
Author(s):  
O. Holm-Christensen ◽  
K. Tra¨ger
Keyword(s):  
Degrees Of Freedom ◽  
Stokes Equations ◽  
Theoretical Data ◽  
Newtonian Liquid ◽  
Navier Stokes ◽  
Stability Conditions ◽  
Dynamic Force ◽  
Navier Stokes Equations ◽  
The Stability ◽  
Rotor Axis

The stability conditions of a hollow rotor partially filled with a Newtonian liquid are investigated. The rotor is considered here to be a rigid body, supported by springs and dampers, and exposed to an external dynamic force in the shape of actions of the encountered liquid. The system has two degrees-of-freedom, defined by deflection in two mutually orthogonal fixed directions perpendicular to the rotor axis. The fluid motions are described by Navier-Stokes equations and comparison is made between the inviscid and viscous case in connection with their predictions of the stability conditions. Experiments are performed with two different rigidity ratios and results are found to be in agreement with theoretical data.

scholarly journals Numerical Modelling of the Interaction of Moving Fish Nets and Fluid

2020 ◽  
Author(s):  
Tobias Martin ◽  
Gang Wang ◽  
Hans Bihs
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Force Model ◽  
Lumped Mass ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Lumped Mass Method ◽  
Proposed Model ◽  
Significant Difference ◽  
Dynamic Equilibria

Abstract The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.

Numerical analysis on effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller

2019 ◽  
Vol 234 (2) ◽  
pp. 490-501
Author(s):  
Mohammad Bakhtiari ◽  
Hassan Ghassemi
Keyword(s):  
Numerical Method ◽  
Stokes Equations ◽  
Thrust Force ◽  
Circular Disk ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Thrust Coefficient ◽  
Navier Stokes Equations ◽  
Blade Number ◽  
Marine Propulsion

Marine cycloidal propeller, as a special type of marine propulsion system, is used for ships that require high maneuverability, such as tugs and ferries. In a marine cycloidal propeller, the thrust force is generated by rotation of a circular disk with a number of lifting blades fitted on the periphery of the disk, so that the propeller axis of rotation is perpendicular to the direction of thrust force. Each blade pitches about its own axis, and the thrust magnitude and direction can be adjusted by controlling the pitching angle of the blades. Therefore, the propulsion and maneuvering units are combined together and no separate rudder is needed to maneuver the ship. Two configurations of marine cycloidal propeller have been studied and developed based on propeller pitch: low-pitch propeller (designed for advance coefficient less than one, means λ < 1) and high-pitch propeller (designed for λ > 1). Low-pitch marine cycloidal propellers are used in applications with low-speed maneuvering requirements, such as tugboats and minesweepers. In this study, the effects of blade number on hydrodynamic performance of low-pitch marine cycloidal propeller with pure cycloidal motion of the blades are investigated. The turbulent flow around marine cycloidal propeller is solved using a 2.5D numerical method based on unsteady Reynolds-averaged Navier–Stokes equations with shear-stress transport k–ω turbulent model. The presented numerical method was validated against experimental data and showed good agreement. The results showed that the thrust coefficient of marine cycloidal propeller generally decreases by increasing the blade number, whereas the torque coefficient increases. Consequently, the hydrodynamic efficiency of marine cycloidal propeller drops as the blade number increases.

A viscous blade body force model for computational fluid dynamics–based throughflow analysis of axial compressors

2021 ◽  
pp. 095441002199955
Author(s):  
Jian Li ◽  
Jinfang Teng ◽  
Mingmin Zhu ◽  
Xiaoqing Qiang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Stokes Equations ◽  
Skin Friction Coefficient ◽  
Navier Stokes ◽  
Force Model ◽  
Navier Stokes Equations ◽  
Design Speed ◽  
Airfoil Cascade ◽  
Throughflow Model

In recent years, the computational fluid dynamics (CFD) techniques have attracted enormous interest in the throughflow calculations, and one of the major concerns in the CFD-based throughflow method is the modeling of blade forces. In this article, a viscous blade force model in the CFD-based throughflow program was proposed to account for the loss generation. The throughflow code is based on the axisymmetric Navier–Stokes equations. The inviscid blade force is determined by calculating a pressure difference between the pressure and suction surfaces, and the viscous blade force is related to the local kinetic energy through a skin friction coefficient. The viscous blade force model was validated by a linear controlled diffusion airfoil cascade, and the results showed that it can correctly introduce the loss into the CFD-based throughflow model. Then, the code was applied to calculate the transonic NASA rotor 67, and the calculated results were in good agreement with the measured results, which showed that the calculated shock losses reduce the dependence of the throughflow calculation on the empirical correlation. Last, the 3.5-stage compressor P&W3S1 at 85%, 100%, and 105% of the design speed was performed to demonstrate the reliability of the viscous blade force model in a multistage environment. The results showed that the CFD-based throughflow method can easily predict the spanwise mixing due to the inclusion of the turbulence model, and predicted results were in acceptable agreement with the experimental results. In a word, the proposed viscous blade force model and CFD-based throughflow model can achieve the throughflow analysis with an acceptable level of accuracy and a little time-consuming.

Numerical Modelling of the Interaction of Moving Fish Nets and Fluid

2021 ◽  
pp. 1-10
Author(s):  
Tobias Martin ◽  
Gang Wang ◽  
Hans Bihs
Keyword(s):  
Stokes Equations ◽  
Navier Stokes ◽  
Force Model ◽  
Lumped Mass ◽  
Navier Stokes Equations ◽  
Linear System Of Equations ◽  
Lumped Mass Method ◽  
Proposed Model ◽  
Significant Difference ◽  
Dynamic Equilibria

Abstract The significant difference in length scales between the flow around a moving fish net and the flow around each twine of the net prevents the resolution of the complete structure within a discrete fluid domain. In this paper, this issue is overcome by calculating the net and fluid dynamics separately and incorporate their interaction implicitly. The forces on the net are approximated using a screen force model, and the motion of the net is computed with a lumped mass method. Here, a linear system of equations is derived from the dynamic equilibria and kinematic relations. The net model is coupled to the CFD solver REEF3D which solves the incompressible Navier-Stokes equations using high-order finite differences in space and time. Several numerical calculations are provided, and the comparison of loads and velocity reduction with available measurements indicates the good performance of the proposed model.

scholarly journals Bore Pressure on Horizontal and Vertical Surfaces

2019 ◽  
Author(s):  
Jiaqi Liu ◽  
Masoud Hayatdavoodi ◽  
R. Cengiz Ertekin
Keyword(s):  
Laboratory Experiments ◽  
Stokes Equations ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Numerical Techniques ◽  
Governing Equations ◽  
Navier Stokes Equations ◽  
Theoretical Approaches ◽  
Inclined Surfaces ◽  
Saint Venant Equations

Abstract Bores generated by dam-break and initial mound of water and their propagation over horizontal and inclined surfaces are studied by use of theoretical approaches. Calculations are carried out in two and three dimensions and particular attention is given to the bore impact on horizontal and vertical surfaces. Downstream of the initial mound of water may be wet or dry. Discussion is provided on the influence of the downstream water on the bore behaviour and impact. Three methods are used in this study, namely the Reynolds-Averaged Navier-Stokes equations (RANS), the Green-Naghdi (GN) equations and Saint Venant equations (SV). The governing equations subject to appropriate boundary conditions are solved with various numerical techniques. Results of these models are compared with each other, and with laboratory experiments when available. Discussion is given on the limitations and applicability of these models to study the bore generation, propagation and pressure on horizontal and vertical surfaces. It is found that the GN equations compare well with the RANS equations, while the SV equations have substantially simplified the solution.

Effects of stator splitter blades on aerodynamic performance of a single-stage transonic axial compressor

2020 ◽  
Vol 14 (4) ◽  
pp. 7369-7378
Author(s):  
Ky-Quang Pham ◽  
Xuan-Truong Le ◽  
Cong-Truong Dinh
Keyword(s):  
Stokes Equations ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Aerodynamic Performance ◽  
Numerical Results ◽  
Single Stage ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Operating Stability ◽  
Length Coverage

Splitter blades located between stator blades in a single-stage axial compressor were proposed and investigated in this work to find their effects on aerodynamic performance and operating stability. Aerodynamic performance of the compressor was evaluated using three-dimensional Reynolds-averaged Navier-Stokes equations using the k-e turbulence model with a scalable wall function. The numerical results for the typical performance parameters without stator splitter blades were validated in comparison with experimental data. The numerical results of a parametric study using four geometric parameters (chord length, coverage angle, height and position) of the stator splitter blades showed that the operational stability of the single-stage axial compressor enhances remarkably using the stator splitter blades. The splitters were effective in suppressing flow separation in the stator domain of the compressor at near-stall condition which affects considerably the aerodynamic performance of the compressor.

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