Full Navier-Stokes Model Research Articles

An Engineering Approach to Improve Performance Predictions for Wind Turbine Applications: Comparison with Full Navier-Stokes Model and Experimental Measurements

An Engineering Approach to Improve Performance Predictions for Wind Turbine Applications: Comparison with Full Navier-Stokes Model and Experimental Measurements

Proprioceptive feedback amplification restores effective locomotion in a neuromechanical model of lampreys with spinal injuries

Spinal injuries in many vertebrates can result in partial or complete loss of locomotor ability. While mammals often experience permanent loss, some nonmammals, such as lampreys, can regain swimming function, though the exact mechanism is not well understood. One hypothesis is that amplified proprioceptive (body-sensing) feedback can allow an injured lamprey to regain functional swimming even if the descending signal is lost. This study employs a multiscale, integrative, computational model of an anguilliform swimmer fully coupled to a viscous, incompressible fluid and examines the effects of amplified feedback on swimming behavior. This represents a model that analyzes spinal injury recovery by combining a closed-loop neuromechanical model with sensory feedback coupled to a full Navier-Stokes model. Our results show that in some cases, feedback amplification below a spinal lesion is sufficient to partially or entirely restore effective swimming behavior.

Validation and inter-comparison of models for landslide tsunami generation

The Mapping and Modeling Subcommittee of the US National Tsunami Hazard Mitigation Program convened a workshop in January 2017 to evaluate the present state of numerical models for the simulation of tsunamis generated by submarine or subaerial landslides. A range of benchmark tests were provided to participants, with three tests emphasized: (i) a laboratory submarine solid slide in a 2D horizontal tank, (ii) a laboratory submarine granular slide in a 1D flume, and (iii) a field case based on submarine slides which occurred in Port Valdez, AK during the 1964 Alaska earthquake. Nine landslide tsunami models configured with 21 different combinations of physical options were benchmarked, including: (1) hydrostatic models with no frequency dispersion, which include the nonlinear shallow equation models traditionally used for modeling coseismic tsunamis; (2) Boussinesq or one-layer weakly dispersive models; (3) Multi-layer or non-hydrostatic (i.e., dispersive) models; and (4) Full Navier–Stokes models. Model/data comparison indicates that the inclusion of frequency dispersion in model formulations is critical to obtaining physically reasonable results for the test cases considered. Because the importance of dispersive effects is unknown a priori for any given simulated event, the central recommendation from this work is that a model with at minimum a leading-order representation of frequency dispersion effects be used whenever possible for landslide tsunami simulations.

A critical analysis of transport models for refueling of MOF-5 based hydrogen adsorption system

This work presents a critical analysis of 2D model of refueling a hydrogen storage tank containing MOF-5 adsorbent under cryogenic and room temperature conditions. Three isotherm models, viz. Unilan, modified Dubinin–Astakhov DA and Tóth, were fitted with experimental data of hydrogen adsorption from the literature, and their effect on refueling of adsorbent bed is analyzed. The choice of isotherm has the greatest impact on predicting refueling behavior, for both flow-through and end-flow (i.e., batch) systems. A comparison between the ideal gas assumption and virial equation of state indicates that the former reasonably captures the overall behavior at lower computational cost. Analysis of the role of momentum balance, solved as full Navier–Stokes model and with Darcy’s approximation, indicates same hydrogen uptake in the adsorbent bed and only a minor difference in the predicted velocity profiles. Finally, effect of temperature-dependent physical properties of gas, adsorbent and walls is analyzed.

The role of curvature feedback in the energetics and dynamics of lamprey swimming: A closed-loop model

Like other animals, lampreys have a central pattern generator (CPG) circuit that activates muscles for locomotion and also adjusts the activity to respond to sensory inputs from the environment. Such a feedback system is crucial for responding appropriately to unexpected perturbations, but it is also active during normal unperturbed steady swimming and influences the baseline swimming pattern. In this study, we investigate different functional forms of body curvature-based sensory feedback and evaluate their effects on steady swimming energetics and kinematics, since little is known experimentally about the functional form of curvature feedback. The distributed CPG is modeled as chains of coupled oscillators. Pairs of phase oscillators represent the left and right sides of segments along the lamprey body. These activate muscles that flex the body and move the lamprey through a fluid environment, which is simulated using a full Navier-Stokes model. The emergent curvature of the body then serves as an input to the CPG oscillators, closing the loop. We consider two forms of feedback, each consistent with experimental results on lamprey proprioceptive sensory receptors. The first, referred to as directional feedback, excites or inhibits the oscillators on the same side, depending on the sign of a chosen gain parameter, and has the opposite effect on oscillators on the opposite side. We find that directional feedback does not affect beat frequency, but does change the duration of muscle activity. The second feedback model, referred to as magnitude feedback, provides a symmetric excitatory or inhibitory effect to oscillators on both sides. This model tends to increase beat frequency and reduces the energetic cost to the lamprey when the gain is high and positive. With both types of feedback, the body curvature has a similar magnitude. Thus, these results indicate that the same magnitude of curvature-based feedback on the CPG with different functional forms can cause distinct differences in swimming performance.

The Aerodynamic Analysis of a Rotating Wind Turbine by Viscous-Coupled 3D Panel Method

In addition to the many typical failure mechanisms that afflict wind turbines, units in Taiwan are also susceptible to catastrophic failure from typhoon-induced extreme loads. A key component of the strategy to prevent such failures is a fast, accurate aerodynamic analysis tool through which a fuller understanding of aerodynamic loads acting on the units may be derived. To this end, a viscous-coupled 3D panel method is herewith proposed, which introduces a novel approach to simulating the severe flow separation so prevalent around wind turbine rotors. The validity of the current method’s results was assessed by code-to-code comparison with RANS data for a commercial 2 MW wind turbine rotor. Along the outboard and inboard regions of the rotor, pressure distributions predicted by the current method showed excellent agreement with the RANS data, while pressure data along the midspan region were slightly more conservative. The power curve predicted by the current method was also more conservative than that predicted by the RANS solver, but correlated very well with that provided by the turbine manufacturer. Taking into account the high degree of comparability with the more sophisticated RANS solver, the excellent agreement with the official data, and the considerably reduced computational expense, the author believes the proposed method could be a powerful standalone tool for the design and analysis of wind turbine blades, or could be applied to the emerging field of wind farm layout design by providing accurate body force input to actuator line rotors within full Navier-Stokes models of multi-unit wind farms.

A hybrid method for modelling two dimensional non-breaking and breaking waves

This is the first paper to present a hybrid method coupling an Improved Meshless Local Petrov Galerkin method with Rankine source solution (IMLPG_R) based on the Navier–Stokes (NS) equations, with a finite element method (FEM) based on the fully nonlinear potential flow theory (FNPT) in order to efficiently simulate the violent waves and their interaction with marine structures. The two models are strongly coupled in space and time domains using a moving overlapping zone, wherein the information from both the solvers is exchanged. In the time domain, the Runge–Kutta 2nd order method is nested with a predictor–corrector scheme. In the space domain, numerical techniques including ‘Feeding Particles’ and two-layer particle interpolation with relaxation coefficients are introduced to achieve the robust coupling of the two models. The properties and behaviours of the new hybrid model are tested by modelling a regular wave, solitary wave and Cnoidal wave including breaking and overtopping. It is validated by comparing the results of the method with analytical solutions, results from other methods and experimental data. The paper demonstrates that the method can produce satisfactory results but uses much less computational time compared with a method based on the full NS model.

Numerical modeling of drag for flow through vegetated domains and porous structures

In this paper, we study flow through vegetated wetlands using high resolution computational models to describe the flow. The goal is to describe drag characteristics of this flow at the large scales as a function of Reynolds number. This work is of importance to scientists and engineers dealing with wetland health and restoration, inland flooding due to tropical storms and hurricanes, and river lining projects. The existence of vegetation affects the flow resistance, which is a major factor in determining velocity and water level distribution in wetlands.For low Reynolds numbers, wetlands behave similarly to porous media, where it is well-known that Stokes flow at the micro-scale can be upscaled through homogenization to Darcy’s Law at the macro-scale. As Reynolds number increases moderately, small-scale drag effects can be captured by adding a quadratic and/or cubic term to the Darcy equation; the so-called Darcy–Forchheimer model. For higher Reynolds numbers, Stokes equation is no longer a valid approximation, and full Navier–Stokes models must be used. We utilize large eddy simulation (LES) to study vegetative drag at high Reynolds numbers. The numerical simulations in this paper are performed using the Proteus Toolkit, which is under development by Kees and Farthing at ERDC.

Comparison and Validation of Plug and Boundary Layer Flow Models of Monolithic Reactors: Catalytic Partial Oxidation of Methane on Rh Coated Monoliths

Catalytic partial oxidation of methane in short residence time rhodium coated monolithic reactors offers an attractive route for syngas production. The plug flow and boundary layer flow approximations are considered as computationally efficient substitutes for the full Navier-Stokes model of the reactor while including detailed heterogeneous and homogeneous chemistry. The one dimensional plug flow model has trivial computational demands but only a limited range of application. The boundary layer model provides an excellent, computationally manageable substitute for the full Navier-Stokes model over a wide range of operating conditions. Using the 38-step elementary surface reaction mechanism of Deutschmann et al. (2001a) and the full GRI 3.0 mechanism for gas phase oxidation of methane, the boundary layer model can predict the experimental data of Hickman et al. (1993a) and Horn et al. (2007) with high accuracy. Sensitivity analyses with the boundary layer model delineate the complex surface phenomena responsible for the sharp transitions in reactor performance observed experimentally on increasing the feed methane to oxygen ratio. The detrimental influence of gas phase reactions on increasing the pressure to industrial levels (>20 bars) is also clearly demonstrated.