Resolving Turbulent Wakes

2003 ◽  
Vol 125 (5) ◽  
pp. 823-834 ◽  
Author(s):  
Stephen A. Jordan
Keyword(s):  
Fourth Order ◽  
Incompressible Flows ◽  
Spectral Characteristics ◽  
The Body ◽  
Scale Model ◽  
Inertial Subrange ◽  
Spectral Energy ◽  
Turbulent Statistics ◽  
Convective Derivative ◽  
Fifth Order

Resolving the turbulent statistics of bluff-body wakes is a challenging task. Frequently, the streamwise grid point spacing approaching the vortex exit boundary is sacrificed to gain near full resolution of the turbulent scales neighboring the body surface. This choice favors the solution strategies of direct numerical and large-eddy simulations (DNS and LES) that house spectral-like resolving characteristics with inherent dissipation. Herein, two differencing stencils are tested for approximating four forms of the convective derivative in the DNS and LES formulations for incompressible flows. The wake spectral characteristics and conventional parameters are computed for Reynolds numbers Re=200 (laminar wake) and Re=3900. These tests demonstrated reliable stability and spectral-like accuracy of compact fifth-order upwinding for the advective derivative and fourth-order cell-centered Pade´ (with fourth-order upwinding interpolation) for the Arakawa form of the convective derivative. Specifically, observations of the DNS computations suggest that best results of the wake properties are acquired when the inertial subrange of the spectral energy is fully resolved at the grid-scale level. The LES solutions degraded dramatically only when the fifth-order upwind stencil resolved the spanwise periodic turbulence. Although the dynamic subgrid-scale model showed strong participation on the instantaneous level, its spectral contributions were negligible regardless of the chosen grid-scale scheme.

scholarly journals An Unstructured Finite Volume Method for Incompressible Flows With Complex Immersed Boundaries

2009 ◽  
Author(s):  
Lin Sun ◽  
Sanjay R. Mathur ◽  
Jayathi Y. Murthy
Keyword(s):  
Finite Volume Method ◽  
Finite Volume ◽  
Incompressible Flows ◽  
Simple Algorithm ◽  
Flow Region ◽  
Solid Material ◽  
The Body ◽  
Immersed Boundary ◽  
Material Points ◽  
Volume Method

A numerical method is developed for solving the 3D, unsteady, incompressible flows with immersed moving solids of arbitrary geometrical complexity. A co-located (non-staggered) finite volume method is employed to solve the Navier-Stokes governing equations for flow region using arbitrary convex polyhedral meshes. The solid region is represented by a set of material points with known position and velocity. Faces in the flow region located in the immediate vicinity of the solid body are marked as immersed boundary (IB) faces. At every instant in time, the influence of the body on the flow is accounted for by reconstructing implicitly the velocity the IB faces from a stencil of fluid cells and solid material points. Specific numerical issues related to the non-staggered formulation are addressed, including the specification of face mass fluxes, and corrections to the continuity equation to ensure overall mass balance. Incorporation of this immersed boundary technique within the framework of the SIMPLE algorithm is described. Canonical test cases of laminar flow around stationary and moving spheres and cylinders are used to verify the implementation. Mesh convergence tests are carried out. The simulation results are shown to agree well with experiments for the case of micro-cantilevers vibrating in a viscous fluid.

scholarly journals The Arab Formation in central Abu Dhabi: 3-D reservoir architecture and static and dynamic modeling

GeoArabia ◽  
2003 ◽  
Vol 8 (1) ◽  
pp. 47-86 ◽  
Author(s):  
Jürgen Grötsch ◽  
Omar Suwaina ◽  
Ghiath Ajlani ◽  
Ahmed Taher ◽  
Reyad El-Khassawneh ◽  
...  
Keyword(s):  
Dynamic Modeling ◽  
Fourth Order ◽  
High Energy ◽  
Development Planning ◽  
Abu Dhabi ◽  
Small Scale ◽  
Reservoir Properties ◽  
Depositional Facies ◽  
Well Completion ◽  
Fifth Order

ABSTRACT A 3-D geological model of the Kimmeridgian-Tithonian Manifa, Hith, Arab, and Upper Diyab formations in the area of the onshore Central Abu Dhabi Ridge was based on a newly established sequence stratigraphic, sedimentologic, and diagenetic model. It was part of an inter-disciplinary study of the large sour-gas reserves in Abu Dhabi that are mainly hosted by the Arab Formation. The model was used for dynamic evaluations and recommendations for further appraisal and development planning in the studied field. Fourth-order aggradational and progradational cycles are composed of small-scale fifth-order shallowing-upward cycles, mostly capped by anhydrite within the Arab-ABC. The study area is characterized by a shoreline progradation of the Arab Formation toward the east-northeast marked by high-energy oolitic/bioclastic grainstones of the Upper Arab-D and the Asab Oolite. The Arab-ABC, Hith, and Manifa pinch out toward the northeast. The strongly bioturbated Lower Arab-D is an intrashelf basinal carbonate ramp deposit, largely time-equivalent to the Arab-ABC. The deposition of the Manifa Formation over the Arab Formation was a major back-stepping event of the shallow-water platform before the onset of renewed progradation in the Early Cretaceous. Well productivity in the Arab-ABC is controlled mainly by thin, permeable dolomitic streaks in the fifth-order cycles at the base of the fourth-order cycles. This has major implications for reservoir management, well completion and stimulation, and development planning. Good reservoir properties have been preserved in the early diagenetic dolomitic streaks. In contrast, the reservoir properties of the Upper Arab-D oolitic/bioclastic grainstones deteriorate with depth due to burial diagenesis. A rock-type scheme was established because complex diagenetic overprinting prevented the depositional facies from being directly related to petrophysical properties. Special core analysis and the attribution of saturation functions to static and dynamic models were made on a cell-by-cell basis using the scheme and honoring the 3-D depositional facies and property model. The results demonstrated the importance of integrating sedimentological analysis and diagenesis with rock typing and static and dynamic modeling so as to enhance the predictive capabilities of subsurface models.

scholarly journals Linearization of symmetrical and asymmetrical two-way Doherty amplifier

2012 ◽  
Vol 25 (2) ◽  
pp. 161-170 ◽  
Author(s):  
Aleksandar Atanaskovic ◽  
Natasa Males-Ilic ◽  
Bratislav Milovanovic
Keyword(s):  
Fourth Order ◽  
Linearization Technique ◽  
The Third ◽  
Simulation Process ◽  
Input And Output ◽  
Carrier Cell ◽  
Fifth Order ◽  
Doherty Amplifier

The linearization effects on two-way Doherty amplifiers are presented in this paper. Symmetrical Doherty amplifier with the additional circuit for linearization has been realized and measurements of the linearization influence on the third- and fifth-order intermodulation products have been carried out. Asymmetrical Doherty amplifier has been designed and effects of the applied linearization technique have been considered through the simulation process. The linearization approach uses the fundamental signals? second harmonics and fourth-order nonlinear signals that are extracted at the output of the peaking cell, adjusted in amplitude and phase and injected at the input and output of the carrier cell in Doherty amplifier.

Measurements of Mean Velocity and Turbulent Statistics in a Centrifugal Blood Pump

2002 ◽  
Author(s):  
Steven W. Day ◽  
James C. McDaniel ◽  
Phillip P. Lemire ◽  
Houston G. Wood
Keyword(s):  
Blood Flow ◽  
Left Ventricle ◽  
Heart Transplantation ◽  
Mechanical Design ◽  
Left Ventricular ◽  
The Body ◽  
Western World ◽  
Mean Velocity ◽  
Centrifugal Blood Pump ◽  
Turbulent Statistics

An estimated 150,000 patients in the Western World require heart transplantation every year, while only 4,000 (2.5%) of them actually receive a donor heart [1]. This lack of available donors for heart transplantation has led to a large effort since the 1960s to develop an artificial mechanical heart as an alternative to heart transplant. Most end stage cardiac failures result from cardiac disease or tissue damage of the left ventricle. After this failure, the ventricle is not strong enough to deliver an adequate supply of oxygen to critical organs. A left ventricular assist device (LVAD) is a mechanical pump that does not replace the native heart, but rather works in concert with it. An LVAD can effectively relieve some strain from a native heart, which has been weakened by disease or damage, and increase blood flow supplied to the body to maintain normal physiologic function. The inlet to the LVAD is attached to the native left ventricle, and the output of the assist pump rejoins the output of the native heart at the aorta, as shown in Figure 1. Blood flow from both the aortic valve and the assist pump combine and flow through the body. The clinical effectiveness of LVADs has been demonstrated; however, all of the currently available pumps have a limited life because of either the damage that they cause to blood or their limited mechanical design life.

The Hand as a Homunculus – A Perspective from Hand Acupuncture Therapy

2020 ◽  
Vol 25 (02) ◽  
pp. 251-255
Author(s):  
Du Hyun Ro ◽  
Hyun Sik Gong
Keyword(s):  
Acupuncture Therapy ◽  
Alternative Medicine ◽  
Human Body ◽  
Scientific Evidence ◽  
The Body ◽  
Scale Model ◽  
Human Being ◽  
Scientific Fields

Homunculus is a term used to refer to any representation of a miniature human being. In scientific fields, the word homunculus has been used to refer to any scale model of the human body that represents physiological, psychological, or other human functions. The hand is thought as a homunculus of the body in Hand Acupuncture Therapy, a type of alternative medicine in Korea. Hand acupuncture therapists believe stimulating the hand can improve bodily health. Although there is a need for scientific evidence regarding this concept, those that perform hand acupuncture seem to recognize the importance of hand in our body.

scholarly journals Diagonally Implicit Runge–Kutta Type Method for Directly Solving Special Fourth-Order Ordinary Differential Equations with Ill-Posed Problem of a Beam on Elastic Foundation

Algorithms ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 10 ◽  
Author(s):  
Nizam Ghawadri ◽  
Norazak Senu ◽  
Firas Adel Fawzi ◽  
Fudziah Ismail ◽  
Zarina Ibrahim
Keyword(s):  
Differential Equations ◽  
Ordinary Differential Equations ◽  
Elastic Foundation ◽  
Fourth Order ◽  
Sixth Order ◽  
Test Problems ◽  
Type Method ◽  
Ill Posed ◽  
Runge Kutta ◽  
Fifth Order

In this study, fifth-order and sixth-order diagonally implicit Runge–Kutta type (DIRKT) techniques for solving fourth-order ordinary differential equations (ODEs) are derived which are denoted as DIRKT5 and DIRKT6, respectively. The first method has three and the another one has four identical nonzero diagonal elements. A set of test problems are applied to validate the methods and numerical results showed that the proposed methods are more efficient in terms of accuracy and number of function evaluations compared to the existing implicit Runge–Kutta (RK) methods.

THREE‐DIMENSIONAL INDUCED POLARIZATION AND ELECTROMAGNETIC MODELING

Geophysics ◽  
1975 ◽  
Vol 40 (2) ◽  
pp. 309-324 ◽  
Author(s):  
Gerald W. Hohmann
Keyword(s):  
Integral Equation ◽  
Green's Functions ◽  
Green’S Functions ◽  
Three Dimensional ◽  
Induced Polarization ◽  
The Body ◽  
Scale Model ◽  
Two Dimensional ◽  
Electromagnetic Modeling ◽  
The Earth

The induced polarization (IP) and electromagnetic (EM) responses of a three‐dimensional body in the earth can be calculated using an integral equation solution. The problem is formulated by replacing the body by a volume of polarization or scattering current. The integral equation is reduced to a matrix equation, which is solved numerically for the electric field in the body. Then the electric and magnetic fields outside the inhomogeneity can be found by integrating the appropriate dyadic Green’s functions over the scattering current. Because half‐space Green’s functions are used, it is only necessary to solve for scattering currents in the body—not throughout the earth. Numerical results for a number of practical cases show, for example, that for moderate conductivity contrasts the dipole‐dipole IP response of a body five units in strike length approximates that of a two‐dimensional body. Moving an IP line off the center of a body produces an effect similar to that of increasing the depth. IP response varies significantly with conductivity contrast; the peak response occurs at higher contrasts for two‐dimensional bodies than for bodies of limited length. Very conductive bodies can produce negative IP response due to EM induction. An electrically polarizable body produces a small magnetic field, so that it is possible to measure IP with a sensitive magnetometer. Calculations show that horizontal loop EM response is enhanced when the background resistivity in the earth is reduced, thus confirming scale model results.

scholarly journals Semi Implicit Hybrid Methods with Higher Order Dispersion for Solving Oscillatory Problems

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
S. Z. Ahmad ◽  
F. Ismail ◽  
N. Senu ◽  
M. Suleiman
Keyword(s):  
Fourth Order ◽  
Absolute Stability ◽  
Hybrid Methods ◽  
Order Method ◽  
The Third ◽  
Dispersion Order ◽  
Runge Kutta ◽  
Fifth Order ◽  
Higher Order Dispersion ◽  
Order Dispersion

We constructed three two-step semi-implicit hybrid methods (SIHMs) for solving oscillatory second order ordinary differential equations (ODEs). The first two methods are three-stage fourth-order and three-stage fifth-order with dispersion order six and zero dissipation. The third is a four-stage fifth-order method with dispersion order eight and dissipation order five. Numerical results show that SIHMs are more accurate as compared to the existing hybrid methods, Runge-Kutta Nyström (RKN) and Runge-Kutta (RK) methods of the same order and Diagonally Implicit Runge-Kutta Nyström (DIRKN) method of the same stage. The intervals of absolute stability or periodicity of SIHM for ODE are also presented.

Localized and Distributed Energy in Wave–Current Flow

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Santosh Kumar Singh ◽  
Anatoliy Khait ◽  
Pankaj Kumar Raushan ◽  
Koustuv Debnath
Keyword(s):  
Velocity Field ◽  
Current Flow ◽  
Spectral Characteristics ◽  
Maximum Energy ◽  
Spectral Energy ◽  
Distributed Energy ◽  
Hilbert Huang Transform ◽  
Mode Function ◽  
Intrinsic Mean ◽  
The Imf

Abstract Evaluation of localized and distributed in time spectral energy in wave–current coexisting environment is investigated in this study. In order to understand the inherent characteristics of the flow under consideration, the Hilbert-Huang transform (HHT) is introduced to determine the instantaneous frequency corresponding to the maximum energy carrying by the velocity field. This frequency is associated with the timescale of the most energetic velocity fluctuations. The intrinsic mean frequency of the intrinsic mode function (IMF) is reduced with the increase in the IMF number. It was shown that the maximum energy is concentrated close to the center of the IMF series. The spectral characteristics obtained by the HHT are carefully compared with those obtained by more conventional Fourier and wavelet transform (FFT and WT, respectively). Addition of the surface wave component to the velocity field of the current-only case leads to the extension of the frequency range containing the dominant portion of the energy.

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