scholarly journals Development of a wave-current numerical model using Stokes 2nd Order Theory

2019 ◽  
Vol 2 (1 (Nov)) ◽  
pp. 1-14
Author(s):  
Catherine Lloyd ◽  
Tim O'Doherty ◽  
Allan Mason-Jones
Keyword(s):  
Numerical Model ◽  
Experimental Testing ◽  
Order Theory ◽  
Multiphase Model ◽  
Flow Conditions ◽  
Regular Waves ◽  
Ansys Cfx ◽  
Testing Facility ◽  
Uniform Current ◽  
Current Characteristics

The optimisation of a Numerical Wave Tank is proposed to accurately model the sub surface conditions generated by regular waves superimposed on a uniform current velocity. ANSYS CFX 18.0 was used to develop a homogenous multiphase model with volume fractions to define the different phase regions. By applying CFX Expression Language at the inlet of the model, Stokes 2nd Order Theory was used to define the upstream wave and current characteristics. Horizontal and vertical velocity components, as well as surface elevation of the numerical model were compared against theoretical and experimental wave data for 3 different wave characteristics in 2 different water depths. The comparison highlighted the numerical homogeneity between the theoretical and experimental data. Therefore, this study has shown that the modelling procedure used can accurately replicate experimental testing facility flow conditions, providing a potential substitute to experimental flume or tank testing.

Numerical Simulations of Regular Waves in a Hydrodynamic Laboratory Basin

2012 ◽  
Author(s):  
Monica Campos Silva ◽  
Marcelo de Araújo Vitola ◽  
Waldir Terra Pinto ◽  
Carlos Antônio Levi
Keyword(s):  
Numerical Model ◽  
Practical Importance ◽  
Numerical Algorithms ◽  
Physical Modelling ◽  
Wave Theory ◽  
Offshore Structures ◽  
Stokes Wave ◽  
Regular Waves ◽  
Ansys Cfx ◽  
Commercial Code

Hydrodynamic behavior of offshore floating structures is of fundamental practical importance to engineers and designers. Physical modelling of offshore structures in hydrodynamic laboratory is a common practice in this field. Due to the increasing in the computer power and the development of the numerical algorithms, the use of the numerical wave tanks (NWT) have become a complementary tool to the model tests. The knowledge of the drawbacks of numerical model is an important issue for engineers and researchers, especially in the models whose governing equations do not have exact solution. This work presents the application of numerical model to simulate the generation and propagation of regular waves in the LabOcean Basin (LabOceano/ COPPE/UFRJ) using the commercial code Ansys-CFX. A cross-section of the offshore basin have been used. Waves have been generated by flap type wavemaker. Period wave in the range from 1.75 to 3.00 seconds have been simulated. For all tests, the analytical wave steepness is smaller than 0.017. Numerical results have been compared with Stokes wave theory and experimental data obtained in the offshore basin. Both the behavior of the free surface and the reflection coefficient have been evaluated. Good agreement was found for the wave profile, mean wave height and mean wave period. Divergences between numerical and experimental results were found evaluating the reflection parameters.

scholarly journals FLOATING BREAKWATER RESPONSE TO WAVE ACTION

1988 ◽  
Vol 1 (21) ◽  
pp. 162 ◽  
Author(s):  
Michael Isaacson ◽  
Ronald Byres
Keyword(s):  
Numerical Model ◽  
Experimental Testing ◽  
Diffraction Theory ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Floating Breakwater ◽  
Mooring Forces ◽  
Wave Drift Forces ◽  
Floating Breakwaters ◽  
Incident Waves

The present paper describes a study carried out to investigate floating breakwater behavior in waves. Components of the study include a field survey of floating breakwaters in British Columbia, Canada, the development of a numerical model of breakwater behavior and the experimental testing of a particular breakwater design. The numerical model has been developed to provide breakwater motions, transmission coefficients and mooring forces. The model combines linear diffraction theory for obliquely incident waves, a mooring analysis, the inclusion of viscous damping coefficients obtained from experimental or field data, and the inclusion of drag and wave drift forces for use in the static analysis of the moorings. The experiments were carried out with normally incident regular waves of different heights and periods. Preliminary results indicate that the numerical model should prove to be a useful tool in floating breakwater design.

scholarly journals Time Scale for Scour Beneath Pipelines Due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Current

2021 ◽  
Vol 9 (2) ◽  
pp. 114
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Time Scale ◽  
Current Flow ◽  
Irregular Waves ◽  
Wave Crest ◽  
Random Wave ◽  
Random Waves ◽  
Flow Conditions ◽  
Regular Waves ◽  
Nonlinear Random Waves ◽  
2D And 3D

This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.

scholarly journals NUMERICAL PREDICTIONS AND MECHANICAL TESTING OF BRAIDED COMPOSITE STRUCTURES UTILISING DIGITAL IMAGE CORRELATION

2016 ◽  
Vol 7 ◽  
pp. 43
Author(s):  
Emil Pitz ◽  
Matei-Constantin Miron ◽  
Imre Kállai ◽  
Zoltán Major
Keyword(s):  
Numerical Model ◽  
Digital Image Correlation ◽  
Digital Image ◽  
Composite Structures ◽  
Experimental Testing ◽  
Single Layer ◽  
Failure Criteria ◽  
Image Correlation ◽  
Braided Composites ◽  
Numerical Predictions

The current paper is describing the implementation of a multiscale numerical model for prediction of stiffness and strength in braided composites. The model is validated by experimental testing of single-layer braided tubes under torsional loading utilising digital image correlation (DIC). For the numerical model the entire braided structure is modelled at yarn detail level, taking into account the yarn behaviour as well as individual yarn-to-yarn interactions by using cohesive contact definitions. By means of Hashin’s failure criteria and cohesive contact damage, failure of the yarns and failure of the yarn-to-yarn interface is being accounted for. Thereby the material failure behaviour can be predicted. For validation of the model, torsion tests of biaxially braided single-layer composite tubes were performed. The strain distribution at the specimen surface was studied using the DIC system ARAMIS in 3D mode.

scholarly journals Verification and Validation of a Methodology to Numerically Generate Waves Using Transient Discrete Data as Prescribed Velocity Boundary Condition

2021 ◽  
Vol 9 (8) ◽  
pp. 896
Author(s):  
Rafael P. Maciel ◽  
Cristiano Fragassa ◽  
Bianca N. Machado ◽  
Luiz A. O. Rocha ◽  
Elizaldo D. dos Santos ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Numerical Analysis ◽  
Laboratory Experiment ◽  
Ocean Waves ◽  
Discrete Data ◽  
Multiphase Model ◽  
Computational Domain ◽  
Regular Waves ◽  
Ansys Fluent ◽  
Wave Channel

This work presents a two-dimensional numerical analysis of a wave channel and a oscillating water column (OWC) device. The main goal is to validate a methodology which uses transient velocity data as a means to impose velocity boundary condition for the generation of numerical waves. To achieve this, a numerical wave channel was simulated using regular waves with the same parameters as those used in a laboratory experiment. First, these waves were imposed as prescribed velocity boundary condition and compared with the analytical solution; then, the OWC device was inserted into the computational domain, aiming to validate this methodology. For the numerical analysis, computational fluid dynamics ANSYS Fluent software was employed, and to tackle with water–air interaction, the nonlinear multiphase model volume of fluid (VOF) was applied. Although the results obtained through the use of discrete data as velocity boundary condition presented a little disparity; in general, they showed a good agreement with laboratory experiment results. Since many studies use regular waves, there is a lack of analysis with ocean waves realistic data; thus, the proposed methodology stands out for its capacity of using realistic sea state data in numerical simulations regarding wave energy converters (WECs).

scholarly journals Surge Limit Prediction for Automotive Air-Charged Systems

2019 ◽  
Vol 4 (4) ◽  
pp. 34
Author(s):  
Johannes Bühler ◽  
Sebastian Leichtfuß ◽  
Heinz-Peter Schiffer ◽  
Thomas Lischer ◽  
Simon Raabe
Keyword(s):  
Development Process ◽  
Experimental Testing ◽  
Piping System ◽  
Economic Perspective ◽  
Flow Conditions ◽  
Strong Variation ◽  
Piston Engine ◽  
Hot Gas ◽  
Compressor Surge ◽  
Compressor Aerodynamics

Compressor surge has been investigated and predicted since the early days of turbomachinery research. Experimental testing of turbomachinery applications is still needed to determine whether stable compressor operation is possible in the expected application regime. Measuring compressor maps and operating ranges on hot gas test stands is common. The test benches are designed and optimized to ensure ideal inflow and outflow conditions as well as low measurement uncertainty. Compressor maps are used to match turbocharger and application. However, a shift in surge limit, caused by the piping system or application, can only be adequately addressed with full engine tests. Ideal measurements use the corresponding piston engine in the charged-air system. This can only take place in the development process, when surge detection is unfavorable from an economic perspective. The surge model for turbochargers presented here is an extension of the Greitzer’s surge model, which considers the effect of inlet throttling. Application components, such as air filters, pipe elbows and flow straighteners, reduce pressure in front of the compressor and flow conditions might differ from those in laboratory testing. Experimental results gathered from the hot gas test stand at TU Darmstadt indicate strong variation in surge limit, influenced by inlet throttling. An extension to the surge model is developed to explain the observed phenomena. The model was validated using extensive experimental variations and matches the experienced surge limit shift. Additional measurements with a piston engine downstream of the turbocharger demonstrated the validity of the surge model. The results also show that surge is a system-dependent phenomenon, influenced by compressor aerodynamics and boundary conditions.

On Demand Thermal Protection (ODTP): A New Approach for Designing Garments Exposed to Flash Flame Incidents

2012 ◽  
Author(s):  
Eduardo Mendoza ◽  
Jean-pierre Cooper ◽  
John W. Evangelista ◽  
Margaret Auerbach ◽  
Özer Arnas
Keyword(s):  
Heat Transfer ◽  
Numerical Model ◽  
Heat Equation ◽  
Thermal Protection ◽  
Experimental Testing ◽  
Sudden Change ◽  
Muscle Layer ◽  
The Body ◽  
On Demand ◽  
Combined Convection

Soldiers, first responders and other high risk occupations such as power line technicians are routinely exposed to dangerous situations where severe burn injuries are possible. Standard flame resistant (FR) fabrics provide minimal burn protection when exposed to a flash flame incident. As a result, improvement in thermal protection is desperately needed and remains an ongoing subject of research and development. A simplified one dimensional physical model composed of a muscle layer, skin/fat layer, air gap(s) and fabric layer(s) is used to model heat transfer entering the body covered by a garment that is exposed to a flash flame. Heat transfer within the skin and muscle layers is modeled by combined conduction, metabolic heat generation and blood perfusion by a recently developed modification to the heat equation termed the bio-heat equation. Boundary conditions include a fixed temperature (core body temperature) at the inside of the muscle layer and combined convection and radiation from the flame on the outside of the fabric. The heat equation is solved by discretizing the domain in one dimension and using a finite volume approach to derive the finite difference equations. This model is an initial step to be used to provide an assessment of common FR garments with respect to both comfort in ambient conditions and protection during a flash flame. It also provides for parametric analysis to determine ideal thermo-physical properties, fabric thicknesses and layering for better protection during flash flame incidents. Estimates for time to burn injury from the numerical model is presented with experimental results using live mannequin flame tests (ASTMF-1930), standard vertical flame tests (ISO-17492) and a non-standard flame test with combined convection and radiation heat fluxes up to 85 kW/m2. The main effort of this study revolves around an initial working design for a dynamic garment termed On Demand Thermal Protection (ODTP). The primary focus of the design is the development of a thermistor circuit embedded in a protective garment to act as an electric sensor for rapidly deploying the necessary thermal protection that is needed as predicted by the numerical model instantaneously in the event of a flash flame incident. An initial prototype is being developed with a focus on designing the thermistor circuit to mechanically actuate protective components in a flash-flame environment. Concepts include rapidly releasing a pressurized flame retardant fluid through vinyl tubing sewn into a garment and deploying a protective barrier around the face and neck when the thermistor circuit detects a sudden change in heat transfer. A summary of the prototype along with experimental testing to date compared to the theoretical predictions from the model described above is presented.

Higher Order Wave-Current Elevations in Deep Water

2011 ◽  
Author(s):  
Anne Katrine Bratland ◽  
Ragnvald Bo̸rresen ◽  
Per Ivar Barth Berntsen
Keyword(s):  
Deep Water ◽  
Higher Order ◽  
Irregular Waves ◽  
Ocean Current ◽  
Regular Waves ◽  
Third Order ◽  
Uniform Current ◽  
Current Interaction ◽  
The Waves ◽  
Wave Elevations

Wave-current interaction refers to the interaction between surface gravity waves and ocean current flow. This interaction implies an exchange of energy, i.e. both the waves and the current are affected. The present paper describes the calculation of wave elevations in higher order unidirectional, irregular waves with a uniform current in deep water. Results for regular waves are compared with those obtained for Stokes second and third order waves with uniform current according to the method described by Fenton [1]. The results for higher order wave elevations in irregular waves have been compared with waves and current generated in a model test basin and reasonable agreement has been found.

scholarly journals Effect of Rotor Spacing and Duct Diffusion Angle on the Aerodynamic Performances of a Counter-Rotating Ducted Fan in Hover Mode

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1338
Author(s):  
Woo-Yul Kim ◽  
Santhosh Senguttuvan ◽  
Sung-Min Kim
Keyword(s):  
Steady State ◽  
Numerical Model ◽  
Figure Of Merit ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Flow Conditions ◽  
Thrust Coefficient ◽  
Ducted Fan ◽  
Aerodynamic Performances ◽  
Rotor Model

The aerodynamic performance of a counter-rotating ducted fan in hover mode is numerically analyzed for different rotor spacings and duct diffusion angles. The design of the counter-rotating fan is inspired by a custom-designed single rotor ducted fan used in a previous study. The numerical model to predict the aerodynamic performance of the counter-rotating ducted fan is developed by adopting the frozen rotor approach for steady-state incompressible flow conditions. The relative angle between the front and the rear rotor is examined due to the usage of the frozen rotor model. The results show that the variation of thrust for the different relative angles is extremely low. The aerodynamic performances are evaluated by comparing the thrust, thrust coefficient, power coefficient, and figure of merit (FOM). The thrust, thrust coefficient, and FOM slightly increase with increasing rotor spacing up to 200 mm, regardless of the duct diffusion angle, and reduce on further increase in the rotor spacing. The duct diffusion angle of 0° generates about 9% higher thrust and increases the FOM by 6.7%, compared with the 6° duct diffusion angle. The duct diffusion angle is highly effective in improving the thrust and FOM of the counter-rotating ducted fan, rather than the rotor spacing.

Fine sediment retention in storage chambers: an assessment of time-dependent effects

2002 ◽  
Vol 45 (7) ◽  
pp. 123-131 ◽  
Author(s):  
V.R. Stovin ◽  
J.P. Grimm ◽  
A.J. Saul
Keyword(s):  
Fine Sediment ◽  
Multiphase Model ◽  
Storm Events ◽  
Dimensional Model ◽  
Flow Conditions ◽  
Sediment Retention ◽  
Fine Sediments ◽  
Storage Chamber ◽  
Flow Hydraulics ◽  
The Uk

The optimisation of the design of a storage chamber is generally based upon some measure of the chamber's sedimentation efficiency. In the UK, chambers that minimise the deposition of fine sediments are preferred. Previous laboratory and CFD-based studies to measure efficiency have focused on steady flow conditions. However, both the flow hydraulics within a storage chamber and the pollutant loading in the incoming sewage vary markedly during storm events. This paper outlines a CFD-based approach for determining “overall” chamber efficiency. The approach employs an unsteady volume-of-fluid multiphase model and stochastic particle tracking. Preliminary results from a simplified two-dimensional model are presented.

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