Quantification of Hydrodynamic Forces due to Torsional and Axial Vibrations in Ship Propellers

2013 ◽  
Author(s):  
B. P. M. van Esch ◽  
J. J. A. van Hooijdonk ◽  
N. W. H. Bulten
Keyword(s):  
Experimental Data ◽  
Open Water ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Water Condition ◽  
Reduced Frequency ◽  
Vibratory Motion ◽  
Trailing Vortices ◽  
Axial Vibrations ◽  
Oscillating Plate

CFD is used to compute the hydrodynamic coefficients for torsional and axial vibrations, for one type of the Wageningen B-series of ship propellers in open-water condition. It is shown that the wakes shed from the blades have an influence on the magnitude and the phase of the damping forces. The dependency on reduced frequency of the vibratory motion is explained. This phenomenon can be related to the lift deficiency of trailing vortices in the wake of an oscillating plate, as derived by Theodorsen and Von Kármán and Sears, and is frequently overlooked by more recent investigations. Results of the calculations are compared with theoretical and experimental data from literature.

Effects of Marine Growth on Hydrodynamic Coefficients of Rigid Tubular Cylinders

2014 ◽  
Vol 567 ◽  
pp. 247-252 ◽  
Author(s):  
A. M. Al-Yacouby ◽  
V. John Kurian ◽  
A.A. Sebastian ◽  
M.S. Liew ◽  
V.G. Idichandy
Keyword(s):  
Experimental Data ◽  
Water Depth ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Tank Model ◽  
Rigid Cylinder ◽  
Wave Heights ◽  
Wave Induced

In this paper the wave induced hydrodynamic forces and the corresponding hydrodynamic coefficients for a 42 mm diameter model pipe subjected to regular waves was investigated experimentally and the results were compared with the responses of a similar rigid cylinder fitted with marine growth. The main objective of this study was to quantify the effects of marine growth on the hydrodynamic forces experimentally and determine the associated hydrodynamic coefficients. The experimental data were generated from a set of wave tank model tests and the results were scaled up using a scale factor of 1:55. The thickness of marine growth applied on the model pipe was varied with respect to the water depth in the ratio of 3:2:1. Regular waves were generated with wave heights ranging from 0.02 m to 0. 2 m for modal period varying from 0.6 s to 3.25 s. The tests were conducted for Keulegan-Carpenter number ranging from 3.9 to 23.3. The findings of the experimental results revealed that increasing the thickness of the full scale prototype cylinder by 110 mm due to marine growth fittings, has increased the overall wave hydrodynamic forces by 16 to 90% depending on the wave heights and the wave frequencies at which the model was tested, proving that the drag coefficients have considerably increased.

The Impact of Inlet Distortion and Reduced Frequency on the Performance of Centrifugal Compressors

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
A. Grimaldi ◽  
V. Michelassi
Keyword(s):  
Experimental Data ◽  
Liquefied Natural Gas ◽  
Design Phase ◽  
Centrifugal Compressors ◽  
Axial Compressors ◽  
Inlet Distortion ◽  
Side Stream ◽  
Reduced Frequency ◽  
The Impact

This paper discusses the impact of inlet flow distortions on centrifugal compressors based upon a large experimental data base in which the performance of several impellers in a range of corrected flows and corrected speeds have been measured after been coupled with different inlet plenums technologies. The analysis extends to centrifugal compressor inlets including a side stream, typical of liquefied natural gas applications. The detailed measurements allow a thorough characterization of the flow field and associated performance. The results suggest that distortions can alter the head by as much as 3% and efficiency of around 1%. A theoretical analysis allowed to identify the design features that are responsible for this deviation. In particular, an extension of the so-called “reduced-frequency,” a coefficient routinely used in axial compressors and turbine aerodynamics to weigh the unsteadiness generated by upstream to downstream blade rows, allowed to determine a plenum-to-impeller reduced frequency that correlates very well with the measured performance. The theory behind the new coefficient is discussed together with the measurement details and validates the correlation that can be used in the design phase to determine the best compromise between the inlet plenum complexity and impact on the first stage.

Modeling the flow around and the hydrodynamic drag on net meshes using REEF3D

2021 ◽  
pp. 1-21
Author(s):  
Gang Wang ◽  
Tobias Martin ◽  
Liuyi Huang ◽  
Hans Bihs
Keyword(s):  
Open Source ◽  
Empirical Formula ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Drag ◽  
Hydrodynamic Coefficients ◽  
Flume Experiments ◽  
Simulation Accuracy ◽  
Flow Interactions ◽  
Fluid Properties ◽  
Good Agreement

Abstract The hydrodynamics and flow around net meshes has recently drawn more and more attention because it is closely related to the expected forces on aquaculture. In terms of modelling the hydrodynamic forces on nets, Morison or screen force models are ordinarily. However, they mainly rely on empirical, experimental or cylindrical hydrodynamic coefficients, neglecting the flow interactions between adjacent net twines. In this study, the open-source hydrodynamic toolbox REEF3D is adopted to analyze the flow around net meshes and investigate the hydrodynamic drag on the structure. The simulation accuracy is in good agreement with flume experiments and previous research. The results demonstrate that 2 × 2 or 3 × 3 mesh cases are more reliable for studying the flow around net meshes including the flow interactions around adjacent twines. It is further shown that controlling the solidity of the net through changing net bar diameters has different effects on the flow around meshes than controlling it by the twine length. This paper presents a first step in the aim to derive a new empirical formula for the drag coefficients depending on the solidity and fluid properties which is more appropriate for to the physics involved in offshore conditions.

Numerical and Experimental Investigation of the Reynolds Number and Reduced Frequency Effects on Low-Pressure Turbine Airfoils

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
M. Bolinches-Gisbert ◽  
David Cadrecha Robles ◽  
Roque Corral ◽  
Fernando Gisbert
Keyword(s):  
Experimental Data ◽  
Numerical Data ◽  
Low Pressure ◽  
Reconstruction Method ◽  
Low Speed ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Aerodynamic Properties ◽  
Numerical Solver ◽  
Turbine Airfoils

Abstract This article compares experimental and numerical data for a low-speed high-lift low pressure turbine (LPT) cascade under unsteady flow conditions. Three Reynolds numbers representative of LPTs have been tested, namely, 5 × 104, 105, and 2 × 105; at two reduced frequencies, fr = 0.5 and 1, also representative of LPTs. The experimental data were obtained at the low-speed linear cascade wind tunnel at the Polytechnic University of Madrid using hot wire, Laser Doppler Velocimetry (LDV), and pressure tappings. The numerical solver employs a sixth-order compact scheme based on the flux reconstruction method for spatial discretization and a fourth-order Runge–Kutta method to march in time. The longest case ran 550 h on 40 GPUs to reach a statistically periodic state. Pressure coefficients around the profile, boundary layer profiles and exit cross section distributions of velocity, pressure loss defect, shear Reynolds stress, and angle are compared against high-quality experimental data. Cascade loss and exit angle have also been compared against the experimental data. Very good agreement between experimental and numerical data is seen. The results demonstrate the suitability of the present methodology to predict the aerodynamic properties of unsteady flows around LPT linear cascades accurately.

Dynamic Stability Response of Piggyback Pipelines

2010 ◽  
Author(s):  
Hammam Zeitoun ◽  
Masˇa Brankovic´ ◽  
Knut To̸rnes ◽  
Simon Wong ◽  
Eve Hollingsworth ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Dynamic Response ◽  
Dynamic Stability ◽  
Large Diameter ◽  
Hydrodynamic Forces ◽  
Model Testing ◽  
Equivalent Diameter ◽  
Pipeline System ◽  
Hydrodynamic Coefficients ◽  
Hydrodynamic Loads

One of the main aspects of subsea pipeline design is ensuring pipeline stability on the seabed under the action of hydrodynamic loads. Hydrodynamic loads acting on Piggyback Pipeline Systems have traditionally been determined by pipeline engineers using an ‘equivalent pipeline diameter’ approach. The approach is simple and assumes that hydrodynamic loads on the Piggyback Pipeline System are equal to the loads on a single pipeline with diameter equal to the projected height of the piggyback bundle (the sum of the large diameter pipeline, small diameter pipeline and gap between the pipelines) [1]. Hydrodynamic coefficients for single pipelines are used in combination with the ‘equivalent diameter pipe’ to determine the hydrodynamic loads on the Piggyback Pipeline System. In order to assess more accurately the dynamic response of a Piggyback Pipeline System, an extensive set of physical model tests has been performed to measure hydrodynamic forces on a Piggyback Pipeline System in combined waves and currents conditions, and to determine in-line and lift force coefficients which can be used in a dynamic stability analysis to generate the hydrodynamic forces on the pipeline [2]. This paper describes the implementation of the model testing results in finite elements dynamic stability analysis and presents a case study where the dynamic response of a Piggyback Pipeline System was assessed using both the conventional ‘equivalent diameter approach’ and the hydrodynamic coefficients determined using model testing. The responses predicted using both approaches were compared and key findings presented in the paper, in terms of adequacy of the equivalent diameter approach, and effect of piggyback gap (separation between the main line and the secondary line) on the response.

Coupling of Heave and Roll for High-Speed Planing Hulls

2014 ◽  
Author(s):  
Carolyn Q. Judge
Keyword(s):  
High Speed ◽  
Hydrodynamic Forces ◽  
Hydrodynamic Coefficients ◽  
Lift Forces ◽  
Surface Changes

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. The dynamic lift forces acting on the bottom of a planing hull dominate the hydrodynamics and these lift forces are known to depend on speed and wetted surface. As a planing boat rolls the wetted surface changes, which affects the dynamic lift. A series of tests using a wooden prismatic planing hull model with a constant deadrise of 20 degrees were done at static heel and heave positions as well as oscillating heave conditions. This paper presents the results from these experiments, primarily looking at the hydrodynamic coefficients in heave as a function of heel angle and exploring the coupling between these motions for a prismatic high-speed planing hull.

scholarly journals Power Boat Operators' Visual Behavior Patterns

1977 ◽  
Vol 21 (3) ◽  
pp. 179-183 ◽  
Author(s):  
Susanne M. Gatchell
Keyword(s):  
Open Water ◽  
Corneal Reflection ◽  
Limited Access ◽  
Water Condition ◽  
Different Types ◽  
Processing Information ◽  
Visual Reference ◽  
Movement System ◽  
The Right ◽  
Speed Accuracy

Power boat operators' visual characteristics were recorded with a corneal reflection eye movement system in order to determine their foveal fixations. Data were collected while three (3) subjects performed three (3) different types of navigation tasks at three (3) velocities in two (2) boating environments. Results indicate that boaters scanned a significantly larger area to the right of the vessel during a limited access water condition than during an open water condition. More fixations to the right of the boat during a limited access water condition may be related to the fact that their cockpit station is on this side of the vessel. A significant velocity-navigation task interaction was observed for the duration parameters. It has been speculated that this effect was due to a speed/accuracy trade-off. During a channel task with increased velocities, the durations increased. McDowell (1975) related similar increases in automobile drivers' durations to processing information more accurately. The decrease in durations, which the boaters exhibited during compass and visual reference tasks, may be related to an increased information processing rate.

Transfer Functions for Helical Springs

1969 ◽  
Vol 91 (4) ◽  
pp. 1011-1016 ◽  
Author(s):  
B. L. Johnson ◽  
E. E. Stewart
Keyword(s):  
Experimental Data ◽  
Experimental Investigation ◽  
Steady State ◽  
Transfer Functions ◽  
Helical Springs ◽  
Response Characteristics ◽  
Transmitted Force ◽  
Vibratory Motion ◽  
Frequency Response Characteristics ◽  
Displacement Force

This study reports the results of an analytical and experimental investigation of helical springs subjected to vibratory motion. Transfer functions are presented for both displacement and transmitted force as outputs with force as the input. Steady-state sinusoidal Magnitude Ratio (displacement—force) and Transmittance Ratio (force—force) are plotted along with substantiating experimental data. It is shown that an actual spring displays frequency response characteristics over most of the frequency spectrum that would render its function useless in many cases.

Hydrodynamic Analysis of Macroalgae Local Model Using Computational Fluid Dynamics

2020 ◽  
Author(s):  
Ming Chen ◽  
Solomon C. Yim ◽  
Daniel Cox ◽  
Zhaoqing Yang ◽  
Thomas Mumford
Keyword(s):  
Fluid Dynamics ◽  
Experimental Data ◽  
Computational Fluid Dynamics ◽  
Current Model ◽  
Global Scale ◽  
Local Scale ◽  
Constant Current ◽  
Scale Model ◽  
Effective Diameter ◽  
Hydrodynamic Coefficients

Abstract In this article, a local scale, fully nonlinear coupled fluid-structural interaction (FSI) sugar kelp model has been developed using a computational fluid dynamics (CFD) method. In this model, to be consistent with available experimental data, the sugar kelp is approximated as elongated rectangles with smoothed isosceles triangles at the ends and a single kelp model with one end fixed in a channel with constant current model is developed. Several different current speeds are simulated, and the resulting drag forces and calculated drag coefficients are validated by comparison with experimental data from the literature. In a previous study, a global scale model was developed using a computational structural dynamics (CSD) method to simulate macroalgae farming system and guide the system configuration design. In the global scale model, the hydrodynamic forces are calculated using Morison’s equation and the kinematics and dynamics of the sugar kelp are simplified and the group of kelps attached to the long line is modeled as a slender structure with the same length and an effective diameter such that the volumes are consistent with the real physical system. This simplified model matches the weight and buoyancy but adjusting the hydrodynamic properties when the general hydrodynamic coefficients are employed. Therefore, optimal hydrodynamic coefficients used in global scale model were determined to obtain the hydrodynamic force more accurately. The validated local scale model is then be applied to determine the hydrodynamic coefficients of the simplified sugar kelp model for global dynamic analysis.

Squeeze Film Damping Models Compared With Tests on Microsystems

2006 ◽  
Author(s):  
Hartono (Anton) Sumali ◽  
David S. Epp
Keyword(s):  
Experimental Data ◽  
Damping Ratio ◽  
Laser Doppler Vibrometer ◽  
Squeeze Film ◽  
Parallel Plates ◽  
Squeeze Film Damping ◽  
Wide Range ◽  
Oscillation Frequencies ◽  
Oscillating Plate ◽  
The Continuum

This paper compares three models for computing forces caused by gas film squeezed between parallel plates. The models are used to calculate damping forces on an oscillating plate at different oscillation frequencies. The damping forces are then used to calculate nondimensional damping ratios. The damping ratios are used in making comparisons among the models and with experimental data. The experiment used an oscillating MEMS plate suspended by folded springs. The substrate (base) was shaken with a piezoelectric transducer. The plate vibrated as a result, especially at the resonant frequency. The velocities of the suspended plate and of the substrate were measured with a laser Doppler vibrometer and a microscope. Experimental modal analysis gave the damping ratio. To achieve a wide range of squeeze numbers, the experiment was repeated under several different pressures. The measurement was also repeated on an array of plates. Experimental data indicate that, for atmospheric and higher pressures, squeeze-film damping forces can be modeled accurately with a very simple model. For lower pressures in the continuum regime, a more complete model by Veijola (2004) predicts the damping ratio very well.

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