Predictive Simulation of Underwater Implosion: Coupling Multi-Material Compressible Fluids With Cracking Structures

2014 ◽  
Author(s):  
Kevin G. Wang ◽  
Patrick Lea ◽  
Alex Main ◽  
Owen McGarity ◽  
Charbel Farhat
Keyword(s):  
Structural Dynamics ◽  
High Speed ◽  
Three Dimensional ◽  
Computational Approach ◽  
Quantitative Prediction ◽  
Potential Threat ◽  
Two Phase ◽  
Riemann Solvers ◽  
Adjacent Structures ◽  
Highly Nonlinear

The implosive collapse of a gas-filled underwater structure can lead to strong pressure pulses and high-speed fragments that form a potential threat to adjacent structures. In this work, a high-fidelity, fluid-structure coupled computational approach is developed to simulate such an event. It allows quantitative prediction of the dynamics of acoustic and shock waves in water and the initiation and propagation of cracks in the structure. This computational approach features an extended finite element method (XFEM) for the highly-nonlinear structural dynamics characterized by large plastic deformation and fracture. It also features a finite volume method with exact two-phase Riemann solvers (FIVER) for the solution of the multi-material flow problem arising from the contact of gas and water after the structure fractures. The Eulerian computational fluid dynamics (CFD) solver and the Lagrangian computational structural dynamics (CSD) solver are coupled by means of an embedded boundary method of second-order accuracy in space. The capabilities and performance of this computational approach are explored and discussed in the full-scale simulations of a laboratory implosion experiment with hydrostatic loading and a three-dimensional manufactured implosion problem with explosion loading.

Development and Validation of a Three-Dimensional Multiphase Flow CFD Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

2012 ◽  
Author(s):  
Stephan Uhkoetter ◽  
Stefan aus der Wiesche ◽  
Michael Kursch ◽  
Christian Beck
Keyword(s):  
Experimental Data ◽  
Multiphase Flow ◽  
Gas Turbines ◽  
High Speed ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Journal Bearings ◽  
Heavy Duty ◽  
Present Contribution ◽  
Two Phase

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach including cavitation and air entrainment for high-speed turbo-machinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty type gas turbine journal bearings.

Age-Related Differences in Throwing Techniques Used by the Catcher in Baseball

1994 ◽  
Vol 6 (3) ◽  
pp. 225-235 ◽  
Author(s):  
Shinji Sakurai ◽  
Bruce Elliott ◽  
J. Robert Grove
Keyword(s):  
High Speed ◽  
High Performance ◽  
Age Groups ◽  
Three Dimensional ◽  
Transformation Method ◽  
High Speed Photography ◽  
Two Phase ◽  
Ball Speed ◽  
Age Related ◽  
Release Speed

Three-dimensional (3-D) high speed photography was used to record the overarm throwing actions of five open-age, four 18-year-old, six 16-year- old, and six 14-year-old high-performance baseball catchers. The direct linear transformation method was used for 3-D space reconstruction from 2-D images of the catchers throwing from home plate to second base recorded using two phase-locked cameras operating at a nominal rate of 200 Hz. Selected physical capacity measures were also recorded and correlated with ball release speed. In general, anthropometric and strength measures significantly increased through the 14-year-old to open-age classifications, while a range of correlation coefficients from .50 to .84 was recorded between these physical capacities and ball speed at release. While many aspects of the kinematic data at release were similar, the key factors of release angle and release speed varied for the different age groups.

Gradient-Augmented Level Set Two-Phase Flow Method With Pretreated Reinitialization for Three-Dimensional Violent Sloshing

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Jianjian Xin ◽  
Fulong Shi ◽  
Qiu Jin ◽  
Lin Ma
Keyword(s):  
Free Surface ◽  
Level Set ◽  
Two Phase Flow ◽  
Three Dimensional ◽  
Surface Shape ◽  
Phase Flow ◽  
Two Phase ◽  
Correction Technique ◽  
Highly Nonlinear ◽  
Violent Sloshing

Abstract A three-dimensional (3D) gradient-augmented level set (GALS) two-phase flow model with a pretreated reinitialization procedure is developed to simulate violent sloshing in a cuboid tank. Based on a two-dimensional (2D) GALS method, 3D Hermite, and 3D Lagrange polynomial schemes are derived to interpolate the level set function and the velocity field at arbitrary positions over a cell, respectively. A reinitialization procedure is performed on a 3D narrow band to treat the strongly distorted interface and improve computational efficiency. In addition, an identification-correction technique is proposed and incorporated into the reinitialization procedure to treat the tiny droplet which can distort the free surface shape, even lead to computation failure. To validate the accuracy of the present GALS method and the effectiveness of the proposed identification-correction technique, a 3D velocity advection case is first simulated. The present method is validated to have better mass conservation property than the classical level set and original GALS methods. Also, distorted and thin interfaces are well captured on all grid resolutions by the present GALS method. Then, sloshing under coupled surge and sway excitation, sloshing under rotational excitation are simulated. Good agreements are obtained when the present wave and pressure results are compared with the experimental and numerical results. In addition, the highly nonlinear free surface is observed, and the relationship between the excitation frequency and the impulsive pressure is investigated.

scholarly journals Bubble Dynamics in a Narrow Gap Flow under the Influence of Pressure Gradient and Shear Flow

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 208
Author(s):  
Peter Reinke ◽  
Jan Ahlrichs ◽  
Tom Beckmann ◽  
Marcus Schmidt
Keyword(s):  
Shear Flow ◽  
Pressure Gradient ◽  
High Speed ◽  
Bubble Dynamics ◽  
Three Dimensional ◽  
High Speed Imaging ◽  
Two Phase ◽  
Bubble Generation ◽  
Gap Flow ◽  
The Impact

The volume-of-flow method combined with the Rayleigh–Plesset equation is well established for the computation of cavitation, i.e., the generation and transportation of vapor bubbles inside a liquid flow resulting in cloud, sheet or streamline cavitation. There are, however, limitations, if this method is applied to a restricted flow between two adjacent walls and the bubbles’ size is of the same magnitude as that of the clearance between the walls. This work presents experimental and numerical results of the bubble generation and its transportation in a Couette-type flow under the influence of shear and a strong pressure gradient which are typical for journal bearings or hydraulic seals. Under the impact of variations of the film thickness, the VoF method produces reliable results if bubble diameters are less than half the clearance between the walls. For larger bubbles, the wall contact becomes significant and the bubbles adopt an elliptical shape forced by the shear flow and under the influence of a strong pressure gradient. Moreover, transient changes in the pressure result in transient cavitation, which is captured by high-speed imaging providing material to evaluate transient, three-dimensional computations of a two-phase flow.

Dynamic Reduced Electrothermal Model for Integrated Power Electronics Modules (IPEM)

2004 ◽  
Vol 126 (4) ◽  
pp. 477-490 ◽  
Author(s):  
M. Herna´ndez-Mora ◽  
J. E. Gonza´lez ◽  
M. Ve´lez-Reyes ◽  
J. M. Ortiz-Rodrı´guez ◽  
Y. Pang ◽  
...  
Keyword(s):  
Power Electronics ◽  
Thermal Model ◽  
High Speed ◽  
Three Dimensional ◽  
Thermal Response ◽  
Software Tool ◽  
Computational Time ◽  
Highly Nonlinear ◽  
Numerical Formulation ◽  
Good Agreement

Background: This paper presents a reduced mathematical model using a practical numerical formulation of the thermal behavior of an integrated power electronics module (IPEM). This model is based on the expanded lumped thermal capacitance method (LTCM), in which the number of variables involved in the analysis of heat transfer is reduced only to time. Method of Approach: By applying the LTCM, a simple, nonspatial, but highly nonlinear model is obtained for the case of the IPEM Generation II. Steady and transient results of the model are validated against results from a three-dimensional, transient thermal analysis software tool, FLOTHERM™ 3.1. The electrothermal coupling was obtained by implementing the reduced-order thermal model into the SABER™ circuit simulator. Two experimental setups, for low- and high-speed thermal responses, were developed and used to calibrate the reduced model with actual data. Results: The comparison of the LTCM model implemented in a Generation II IPEM with FLOTHERM 3.1 results compared very favorably in terms of accuracy and efficiency, reducing the computational time significantly. Additional validations of the reduced thermal model were made using experiment data for the low-speed thermal response at different constant powers, and good agreement was demonstrated in all cases. A comparison between SABER™ simulations, which incorporated the proposed LTCM, and the fast thermal experimental response results is also presented to validate the dynamic electrothermal model response, and excellent agreement was found for this case. Conclusions: The good agreement found for all three cases presented, the three-dimensional, transient numerical formulation, and the low- and high-speed experimental data indicates that reduced electrothermal models are an excellent alterative for design methodologies of new generations of IPEMs.

Three-Dimensional Two-Phase Flow Simulations of Water Braking Phenomena for High-Speed Test Track Sled

2021 ◽  
Author(s):  
Jose Terrazas ◽  
Arturo Rodriguez ◽  
Vinod Kumar ◽  
Richard Adansi ◽  
V. M. Krushnarao Kotteda
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Initial Boundary ◽  
Phase Flow ◽  
Momentum Exchange ◽  
Two Phase ◽  
Test Track ◽  
Speed Test ◽  
Liquid Phases ◽  
Multi Phase Flow

Abstract Specializing in high-speed testing, Holloman High-Speed Test Track (HHSTT) uses a process called ‘water braking’ as a method to bring vehicles at the test track to a stop. This method takes advantage of the higher density of water, compared to air, to increase braking capability through momentum exchange. By studying water braking using Computational Fluid Dynamics (CFD), forces acting on track vehicles can be approximated and prepared for prior to actual test. In this study, focus will be made on the brake component of the track sled that is responsible for interacting with the water for braking. By discretizing a volume space around our brake, we accelerate water and air to relatively simulate the brake engaging. The model is a multi-phase flow that uses the governing equations of gas and liquid phases with the finite volume method, to perform 3D simulations. By adjusting the inflow velocity of air and water, it is possible to simulate HHSTT sled tests at various operational speeds. In the development of the 3D predictive model, convergence issues associated with the numerical mesh, initial/boundary conditions, and compressibility of the fluids were encountered. Once resolved, the effect of inflow velocities of water and air on the braking of the sled are studied.

scholarly journals Kinetics of atomic force microscope probe interaction with inhomogeneous polymer surface in fast nano-indentation regime

2021 ◽  
pp. 21-29
Author(s):  
I. A. Morozov ◽  
Keyword(s):  
Mechanical Properties ◽  
Atomic Force Microscopy ◽  
High Speed ◽  
Polymer Surface ◽  
Three Dimensional ◽  
Material Surface ◽  
Two Phase ◽  
Experimental Conditions ◽  
Force Microscopy ◽  
Atomic Force

Atomic force microscopy (AFM) is a powerful tool for studying the structural and physical-mechanical properties of surfaces. The AFM experiment consists in detecting the interaction be-tween the probe and the material. The probe is an elastic cantilever fixed horizontally at one end; a tip is located at the free end of the cantilever. The interaction of the tip with the surface causes de-flection of the cantilever, which is interpreted depending on the experimental conditions. High-speed indentation atomic force microscopy methods allow obtaining maps of three-dimensional re-lief and physical-mechanical properties of the material in high resolution at micro- and nanoscale levels. In this case, the probe is rapidly pressed on the material and the interaction is recorded at each point of the surface of the studied area. The user sets the speed at which the probe approaches the material surface. This value is assumed to be constant and is called the indentation rate. How-ever, this is not true: the tip speed at the loose end of the cantilever depends in general on many factors. As an example of investigation of polyurethane surface (heterogeneous two-phase poly-mer) it is shown that the probe-material interaction speed nonlinearly depends on the surface area, indentation depth and direction, nominal speed of experiment, cantilever properties. This affects the measurement of relief topography, stiffness, Van der Waals forces and adhesion between the probe and the material. Thus, for a correct quantitative interpretation of the results, the interaction speed of the tip with the material must be taken into account; this statement is especially important when working with soft polymers. The presented methods can be useful in the study of a wide class of soft heterogeneous materials.

Unsteady Numerical and Experimental Study of Cavitation in Axial Pump

2014 ◽  
Vol 4 (1) ◽  
pp. 55-68
Author(s):  
Mohamed Adel ◽  
Nabil H. Mostafa
Keyword(s):  
Numerical Simulation ◽  
Void Growth ◽  
High Speed ◽  
Volume Fraction ◽  
Numerical Study ◽  
Three Dimensional ◽  
Axial Flow ◽  
Two Phase ◽  
Impeller Blade ◽  
Axial Pump

This paper presents an experimental and three-dimensional numerical study of unsteady, turbulent, void growth and cavitation simulation inside the passage of the axial flow pump. In this study a 3D Navier-Stokes code was used (CFDRC, 2008) to model the two-phase flow field around a four blades axial pump. The governing equations are discretized on a structured grid using an upwind difference scheme. The numerical simulation used the standard K-e turbulence model to account for the turbulence effect. The numerical simulation of void growth and cavitation in an axial pump was studied under unsteady calculating. Pressure distribution and vapor volume fraction were completed versus time at different condition. The computational code has been validated by comparing the predicated numerical results with the experiment. The predicted of cavitation growth and distribution on the impeller blade also agreed with that visualized of high speed camera.

scholarly journals A new twist on gyroscopic sensing: body rotations lead to torsion in flapping, flexing insect wings

2015 ◽  
Vol 12 (104) ◽  
pp. 20141088 ◽  
Author(s):  
A. L. Eberle ◽  
B. H. Dickerson ◽  
P. G. Reinhall ◽  
T. L. Daniel
Keyword(s):  
Structural Dynamics ◽  
High Speed ◽  
Three Dimensional ◽  
Dynamic Mode ◽  
Normal Strain ◽  
Wingbeat Frequency ◽  
Insect Wing ◽  
Insect Wings ◽  
Gyroscopic Forces ◽  
Wing Tip

Insects perform fast rotational manoeuvres during flight. While two insect orders use flapping halteres (specialized organs evolved from wings) to detect body dynamics, it is unknown how other insects detect rotational motions. Like halteres, insect wings experience gyroscopic forces when they are flapped and rotated and recent evidence suggests that wings might indeed mediate reflexes to body rotations. But, can gyroscopic forces be detected using only changes in the structural dynamics of a flapping, flexing insect wing? We built computational and robotic models to rotate a flapping wing about an axis orthogonal to flapping. We recorded high-speed video of the model wing, which had a flexural stiffness similar to the wing of the Manduca sexta hawkmoth, while flapping it at the wingbeat frequency of Manduca (25 Hz). We compared the three-dimensional structural dynamics of the wing with and without a 3 Hz, 10° rotation about the yaw axis. Our computational model revealed that body rotation induces a new dynamic mode: torsion. We verified our result by measuring wing tip displacement, shear strain and normal strain of the robotic wing. The strains we observed could stimulate an insect's mechanoreceptors and trigger reflexive responses to body rotations.

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