THE EXPERIMENTAL VERIFICATION OF NUMERICAL MODELS OF PLUNGING BREAKERS

Results of a WAVE-FOLLOWER EXPERIMENT are presented, in which a moving current meter entrained in the crest of a steep Stokes wave and a moving high-speed film camera follows the wave with its non-linear phase velocity. Measurements of wave particle velocities are then obtained both in non-breaking steep wave crests, and in breaking waves. The breaking waves in deep water conditions are obtained by the application of a non-linear sweep frequency modulation technique, and the Stokes wave becomes unstable due to interaction of 13 wave components focused into one single point in space and time, KJELDSEN 1982. The result of this interaction is a large freak wave, breaking as a plunging breaker in deep water. Measured crest particle velocities obtained with the current meter exceeded the phase velocity of this wave with 36 %. Digitalisation of the high-speed film showed that particle velocities at the very tip of the plunging jet obtained the value 2.65 times the linear phase velocity. These results are then compared with predictions obtained from numerical simulations by LONGUET-HIGGINS & COKELET 1976 and VINJE & BREVIG 1980.

Download Full-text

Kinematics in a Diffracted Wave Field: Particle Image Velocimetry (PIV) and Numerical Models

24th International Conference on Offshore Mechanics and Arctic Engineering: Volume 3 ◽

10.1115/omae2005-67176 ◽

2005 ◽

Cited By ~ 1

Author(s):

Trygve Kristiansen ◽

Rolf Baarholm ◽

Geir J. Ro̸rtveit ◽

Ernst W. Hansen ◽

Carl Trygve Stansberg

Keyword(s):

Potential Theory ◽

High Speed ◽

Numerical Models ◽

Vertical Cylinder ◽

Industrial Applications ◽

Second Order ◽

Surface Elevation ◽

High Speed Camera ◽

Non Linear ◽

Theoretical Results

As the use of CFD in industrial applications increases, so does the need for verification and validation of the theoretical/numerical results. This paper focuses on tools for validation and in particular, on the use of Particle Imaging Velocimetry (PIV) as such a tool. Diffraction of regular waves due to a single, fixed vertical cylinder is investigated. Theoretical results of wave run-up and wave kinematics are compared to measurements from model tests. Theoretical results are obtained by second order potential theory and by fully non-linear CFD computations. The second order potential theory frequency-domain results are computed by the industry standard code WAMIT, while the fully nonlinear time-domain simulations are performed by the commercial CFD code Flow-3D. Measurements are obtained by means of wave probes, PIV and snapshots taken with a high-speed camera. The experiments are made with the model in place as well as without the model, for validation of the incident flow field. For the identification of non-linear effects, the steepness of the waves is varied. The surface elevation is measured by means of the wave probes, while the PIV equipment measures the kinematics. High quality photos taken by the high-speed camera give a detailed overview of the surface elevation for inspection. In addition to focusing on validation tools, the paper also addresses some critical aspects associated with the CFD computations, such as the modeling of boundary conditions. The work is based partly upon results from the WaveLand JIP, Phase 2.

Download Full-text

Additively Manufactured Parts Made of a Polymer Material Used for the Experimental Verification of a Component of a High-Speed Machine with an Optimised Geometry—Preliminary Research

Polymers ◽

10.3390/polym13010137 ◽

2020 ◽

Vol 13 (1) ◽

pp. 137

Author(s):

Artur Andrearczyk ◽

Bartlomiej Konieczny ◽

Jerzy Sokołowski

Keyword(s):

Polymer Material ◽

High Speed ◽

Numerical Models ◽

Flow Analysis ◽

Experimental Tests ◽

Strength Analysis ◽

Compressor Wheel ◽

Operational Characteristics ◽

3D Printed ◽

Novel Method

This paper describes a novel method for the experimental validation of numerically optimised turbomachinery components. In the field of additive manufacturing, numerical models still need to be improved, especially with the experimental data. The paper presents the operational characteristics of a compressor wheel, measured during experimental research. The validation process included conducting a computational flow analysis and experimental tests of two compressor wheels: The aluminium wheel and the 3D printed wheel (made of a polymer material). The chosen manufacturing technology and the results obtained made it possible to determine the speed range in which the operation of the tested machine is stable. In addition, dynamic destructive tests were performed on the polymer disc and their results were compared with the results of the strength analysis. The tests were carried out at high rotational speeds (up to 120,000 rpm). The results of the research described above have proven the utility of this technology in the research and development of high-speed turbomachines operating at speeds up to 90,000 rpm. The research results obtained show that the technology used is suitable for multi-variant optimization of the tested machine part. This work has also contributed to the further development of numerical models.

Download Full-text

A Practical Numerical Approach to Characterizing Non-Linear Shrinkage and Optimizing Dimensional Deviation of Injection-Molded Small Module Plastic Gears

Polymers ◽

10.3390/polym13132092 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2092

Author(s):

Xiansong He ◽

Wangqing Wu

Keyword(s):

Injection Molding ◽

High Speed ◽

Numerical Approach ◽

Linear Shrinkage ◽

Influential Factor ◽

Dimensional Deviation ◽

Non Linear ◽

Injection Molded ◽

Plastic Gears ◽

Circle Diameter

This paper was aimed at finding out the solution to the problem of insufficient dimensional accuracy caused by non-linear shrinkage deformation during injection molding of small module plastic gears. A practical numerical approach was proposed to characterize the non-linear shrinkage and optimize the dimensional deviation of the small module plastic gears. Specifically, Moldflow analysis was applied to visually simulate the shrinkage process of small module plastic gears during injection molding. A 3D shrinkage gear model was obtained and exported to compare with the designed gear model. After analyzing the non-linear shrinkage characteristics, the dimensional deviation of the addendum circle diameter and root circle diameter was investigated by orthogonal experiments. In the end, a high-speed cooling concept for the mold plate and the gear cavity was proposed to optimize the dimensional deviation. It was confirmed that the cooling rate is the most influential factor on the non-linear shrinkage of the injection-molded small module plastic gears. The dimensional deviation of the addendum circle diameter and the root circle diameter can be reduced by 22.79% and 22.99% with the proposed high-speed cooling concept, respectively.

Download Full-text

Development and Validation of Quasi-Eulerian Mean Three-Dimensional Equations of Motion Using the Generalized Lagrangian Mean Method

Journal of Marine Science and Engineering ◽

10.3390/jmse9010076 ◽

2021 ◽

Vol 9 (1) ◽

pp. 76

Author(s):

Duoc Nguyen ◽

Niels Jacobsen ◽

Dano Roelvink

Keyword(s):

Surface Waves ◽

Deep Water ◽

Surf Zone ◽

Equations Of Motion ◽

Three Dimensional ◽

Breaking Waves ◽

Successful Implementation ◽

Random Waves ◽

Mean Motion ◽

Generalized Lagrangian

This study aims at developing a new set of equations of mean motion in the presence of surface waves, which is practically applicable from deep water to the coastal zone, estuaries, and outflow areas. The generalized Lagrangian mean (GLM) method is employed to derive a set of quasi-Eulerian mean three-dimensional equations of motion, where effects of the waves are included through source terms. The obtained equations are expressed to the second-order of wave amplitude. Whereas the classical Eulerian-mean equations of motion are only applicable below the wave trough, the new equations are valid until the mean water surface even in the presence of finite-amplitude surface waves. A two-dimensional numerical model (2DV model) is developed to validate the new set of equations of motion. The 2DV model passes the test of steady monochromatic waves propagating over a slope without dissipation (adiabatic condition). This is a primary test for equations of mean motion with a known analytical solution. In addition to this, experimental data for the interaction between random waves and a mean current in both non-breaking and breaking waves are employed to validate the 2DV model. As shown by this successful implementation and validation, the implementation of these equations in any 3D model code is straightforward and may be expected to provide consistent results from deep water to the surf zone, under both weak and strong ambient currents.

Download Full-text

An Improved Lagrangian-Inverse Method for Evaluating the Dynamic Constitutive Parameters of Concrete

Materials ◽

10.3390/ma13081871 ◽

2020 ◽

Vol 13 (8) ◽

pp. 1871

Author(s):

Xinlu Yu ◽

Yingqian Fu ◽

Xinlong Dong ◽

Fenghua Zhou ◽

Jianguo Ning

Keyword(s):

High Speed ◽

Inverse Method ◽

Image Correlation ◽

Analysis Method ◽

Stress Strain ◽

Optical Techniques ◽

Element Simulation ◽

Non Linear ◽

Constitutive Parameters ◽

Inverse Analysis Method

The dynamic constitutive behaviors of concrete-like materials are of vital importance for structure designing under impact loading conditions. This study proposes a new method to evaluate the constitutive behaviors of ordinary concrete at high strain rates. The proposed method combines the Lagrangian-inverse analysis method with optical techniques (ultra-high-speed camera and digital image correlation techniques). The proposed method is validated against finite-element simulation. Spalling tests were conducted on concretes where optical techniques were employed to obtain the high-frequency spatial and temporal displacement data. We then obtained stress–strain curves of concrete by applying the proposed method on the results of spalling tests. The results show non-linear constitutive behaviors in these stress–strain curves. These non-linear constitutive behaviors can be possibly explained by local heterogeneity of concrete. The proposed method provides an alternative mean to access the dynamic constitutive behaviors which can help future structure designing of concrete-like materials.

Download Full-text

Influence of Attached Masses on Impact Forces and Running Style in Heel-Toe Running

International Journal of Sport Biomechanics ◽

10.1123/ijsb.3.3.264 ◽

1987 ◽

Vol 3 (3) ◽

pp. 264-275 ◽

Cited By ~ 3

Author(s):

Alexander Bahlsen ◽

Benno M. Nigg

Keyword(s):

Body Mass ◽

High Speed ◽

Impact Force ◽

Force Plate ◽

The Body ◽

Additional Mass ◽

Impact Forces ◽

Running Shoes ◽

High Speed Film ◽

Vertical Impact

Impact forces analysis in heel-toe running is often used to examine the reduction of impact forces for different running shoes and/or running techniques. Body mass is reported to be a dominant predictor of vertical impact force peaks. However, it is not evident whether this finding is only true for the real body mass or whether it is also true for additional masses attached to the body (e.g., running with additional weight or heavy shoes). The purpose of this study was to determine the effect of additional mass on vertical impact force peaks and running style. Nineteen subjects (9 males, 10 females) with a mean mass of 74.2 kg/56.2 kg (SD = 10.0 kg and 6.0 kg) volunteered to participate in this study. Additional masses were attached to the shoe (.05 and .1 kg), the tibia (.2, .4, .6 kg), and the hip (5.9 and 10.7 kg). Force plate measurements and high-speed film data were analyzed. In this study the vertical impact force peaks, Fzi, were not affected by additional masses, the vertical active force peaks, Fza, were only affected by additional masses greater than 6 kg, and the movement was only different in the knee angle at touchdown, ϵ0, for additional masses greater than .6 kg. The results of this study did not support findings reported earlier in the literature that body mass is a dominant predictor of external vertical impact force peaks.

Download Full-text

22—THE DESIGN AND DYNAMICS OF NON-LINEAR CAMS FOR USE IN HIGH-SPEED WEFT-KNITTING MACHINES PART IV: THE DESIGN AND PERFORMANCE OF NON-LINEAR CAMS APPLIED TO A WEFT-KNITTING MACHINE

Journal of the Textile Institute ◽

10.1080/00405007808631439 ◽

1978 ◽

Vol 69 (6) ◽

pp. 180-186 ◽

Cited By ~ 6

Author(s):

J. J. F. Knapton ◽

T. W.-Y. Lau

Keyword(s):

High Speed ◽

Non Linear ◽

And Performance

Download Full-text

Investigating particle phase velocity in a 3D spouted bed by a novel fiber high speed photography method

10.1063/1.4816878 ◽

2013 ◽

Author(s):

Long Qian ◽

Yong Lu ◽

Wenqi Zhong ◽

Xi Chen ◽

Bing Ren ◽

...

Keyword(s):

Phase Velocity ◽

High Speed ◽

High Speed Photography ◽

Particle Phase ◽

Spouted Bed ◽

Photography Method

Download Full-text

Comparison of Two Numerical Algorithms for Computing the Effects of Mistuning of Fan Flutter

Volume 7B: Structures and Dynamics ◽

10.1115/gt2016-57324 ◽

2016 ◽

Cited By ~ 2

Author(s):

L. Salles ◽

M. Vahdati

Keyword(s):

Numerical Models ◽

Three Dimensional ◽

Numerical Algorithms ◽

Mode Shapes ◽

Minimal Amount ◽

Aeroelastic System ◽

Cpu Time ◽

Influence Coefficients ◽

Non Linear ◽

The Time Domain

The aim of this paper is to study the effects of mistuning on fan flutter and to compare the prediction of two numerical models of different fidelity. The high fidelity model used here is a three-dimensional, whole assembly, time-accurate, viscous, finite-volume compressible flow solver. The Code used for this purpose is AU3D, written in Imperial College and validated for flutter computations over many years. To the best knowledge of authors, this is the first time such computations have been attempted. This is due to the fact that, such non-linear aeroelastic computations with mistuning require large amount of CPU time and cannot be performed routinely and consequently, faster (low fidelity) models are required for this task. Therefore, the second model used here is the aeroelastic fundamental mistuning model (FMM) and it based on an eigenvalue analysis of the linearized modal aeroelastic system with the aerodynamic matrix calculated from the aerodynamic influence coefficients. The influence coefficients required for this algorithm are obtained from the time domain non-linear Code by shaking one blade in the datum (tuned) frequency and mode. Once the influence coefficients have been obtained, the computations of aero damping require minimal amount of CPU time and many different mistuning patterns can be studied. The objectives of this work are to: 1. Compare the results between the two models and establish the capabilities/limitations of aeroelastic FMM, 2. Check if the introduction of mistuning would bring the experimental and computed flutter boundaries closer, 3. Establish a relationship between mistuning and damping. A rig wide-chord fan blade, typical of modern civil designs, was used as the benchmark geometry for this study. All the flutter analyses carried out in this paper are with frequency mistuning, but the possible consequences of mistuned mode shapes are briefly discussed at the end of this paper. Only the first family of modes (1F, first flap) is considered in this work. For the frequency mistuning analysis, the 1F frequency is varied around the annulus but the 1F mode shapes remain the same for all the blades. For the mode shape mistuning computations, an FE analysis of the whole assembly different mass blades is performed. The results of this work clearly show the importance of mistuning on flutter. It also demonstrates that when using rig test data for aeroelastic validation of CFD codes, the amount mistuning present must be known. Finally, it should be noted that the aim of this paper is the study of mistuning and not steady/unsteady validation of a CFD code and therefore minimal aerodynamic data are presented.

Download Full-text