OR-SAGA: Over-relaxed stochastic average gradient mapping algorithms for finite sum minimization

In heat flow determinations, it is customary to treat the surface temperature variation as a finite sum of Fourier components. The medium is assumed to be homogeneous or horizontally stratified with each layer having a constant conductivity and diffusivity. This allows the effect of each periodic component to be calculated analytically. We extend this formulation to include cases where thermal conductivities in some layers of a stratified medium may vary linearly with depth as have been found in the sediments of some continental lakes. The application of this formalism to temperature measurements in Lake Greifensee and Lac Leman shows that even with excellent records of bottom temperature variations over several years, failure to take into account the conductivity variation leads to errors as high as 20% in heat flow density values, depending on the depth interval used. The combined effects of lack of detailed knowledge of conductivity structure and the use of too short and (or) inaccurate records of bottom temperature variations, leading to very significant errors, are also discussed, with particular reference to the problems arising from a lack of recognition of the existence of nonannual terms in the bottom temperature variation and the use of probes that do not penetrate the sediments deeply enough.

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A Numerical Study of Fluid Structure Interaction of a Flexible Submerged Cylinder Mounted on an Experimental Rig

Volume 7: Ocean Engineering ◽

10.1115/omae2015-42219 ◽

2015 ◽

Author(s):

Erkan Cakir ◽

Ayhan Akinturk ◽

Alejandro Allievi

Keyword(s):

Numerical Study ◽

Coupled Analysis ◽

Mapping Algorithms ◽

Automatic Mapping ◽

Structural Responses ◽

Submerged Cylinder ◽

Physics Model ◽

System Coupling ◽

Force Data ◽

Experimental Rig

The aim of the study is to investigate VIV effects, not only on a test cylinder but also on the experimental rig being towed under water at a prescribed depth and operating speeds. For this purpose, a numerical Multi-Physics model was created using one way coupled analysis simultaneously between the Mechanical and Fluent solvers of ANSYS software package. A system coupling was developed in order to communicate force data alternately between the solvers with the help of automatic mapping algorithms within millesimal time periods of a second. Numerical investigation into the dynamic characteristics of pressure and velocity fields for turbulent viscous fluid flow along with structural responses of the system, stressed the significance of time and space scales for convergence and accuracy of our Finite Volume (FV) CFD calculations.

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