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Quasi-morphisms via Local Action Data and Quasi-isometries

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Algebra Colloquium 2016年第1期23卷 111-116页

作者： gabi Ben-Simon Department of Mathematics ORT Braude College P.O. Box 78 Karmiel 2161002 Israel

In this work we first present a principle which says that quasi-morphisms can be obtained via local data of group action on certain appropriate spaces. In a rough manner the principle says that instead of starting with a given group and trying to build or study its space of quasi-morphisms, we should start with a space with a certain structure, in such a way that groups acting on this space and respecting this structure will automatically carry quasi-morphisms, where these are supposed to be better understood. This principle plays an important role in the second result of this paper, which is a universal embedding of the projective space of the linear space of quasi-morphisms of any given countable group, into the space of quasi-isometries of a certain universal metric space.

关键词： quasi-rnorphisms discrete groups quasi-isometries

Numerical Noise Prediction in Fluid Machinery

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Journal of Thermal Science 2005年第3期14卷 230-235,248页

作者： Iris PANTLE Franco MAGAGNATO Martin gabi Department of Fluid Machinery University of Karlsruhe D-76128 Karlsruhe Department of Fluid Machinery University of Karlsruhe D-76128 Karlsruhe Department of Fluid Machinery University of Karlsruhe D-76128 Karlsruhe

Numerical methods successively became important in the design and optimization of fluid machinery. However, as noise emission is considered, one can hardly find standardized prediction methods combining flow and acoustical optimization. Several numerical field methods for sound calculations have been developed. Due to the complexity of the considered flow, approaches must be chosen to avoid exhaustive computing. In this contribution the noise of a simple propeller is investigated. The configurations of the calculations comply with an existing experimental setup chosen for evaluation. The used in-house CFD solver SPARC contains an acoustic module based on Ffowcs Williams-Hawkings Acoustic Analogy. From the flow results of the time dependent Large Eddy Simulation the time dependent acoustic sources are extracted and given to the acoustic module where relevant sound pressure levels are calculated. The difficulties, which arise while proceeding from open to closed rotors and from gas to liquid are discussed.

关键词： numerical noise prediction fluid machinery computational aero-acoustics large eddy simulation

Empirical Model for the Quantitative Prediction of Losses of Radial Fans based on CFD Calculations

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Journal of Thermal Science 2013年第4期22卷 304-310页

作者： Heiko Ratter Saban Caglar Martin gabi Institute of Fluid Machinery Karlsruhe Institute of Technology Kaiserstrasse 1276131 Karlsruhe Germany

In a classical layout process of a fan the quantity of losses is estimated as a sum and expressed in the overall efficiency rote However the characteristic of the pressure rise, the losses and the efficiency rate beside the design point is not known. Against this background a numerical model was developed to calculate quantitative values of occurring losses at radial fan impellers at an early stage in the design process. It allows to estimate the pressure rise and efficiency rate of a given fan geometry at and beside the design point. The physics of losses are described in literature, but obtaining quantitative values is still a challenge. As common in hydraulic theory the losses are calculated with analytic formulas supported by coefficients and efficiency rates, which have to be determined empirically. This paper shows the method how to determine the coefficients for a given radial fan. Therefore a representative radial fan with backward curved blades was designed in reference to classical design guidelines. Performance measuring was done conform to ISO 5801. The flow was calculated at 8 different operation points using CFD methods. The RANS equations are solved by using the SST-k-omega turbulence model. The flow do- main consists of one blade section including inlet channel and outflow chamber. Spatial discretization is done by a block-structured mesh of approx. 1.8 million cells. Performance data show a very good agreement between measurement and calculation.

关键词： loss model radial fan CFD RANS

LINC complex independent perinuclear actin organization and cell migration

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BIOCELL 2022年第4期46卷 931-935页

作者： ANDREA FRACCHIA gabi GERLITZ Department of Molecular Biology Faculty of Life Sciences and Ariel Center for Applied Cancer ResearchAriel UniversityAriel40700Israel Department of Bone Marrow Transplantation and Cancer Immunotherapy Hadassah Medical OrganizationJerusalem91120Israel

The link of the metazoan nucleus to the actin cytoskeleton is highly important for actin polymerization and migration of multiple cell types as well as for mechanotransduction and even affects the cellular *** mechanisms of organization of actin filaments next to the nuclear envelope have been *** these mechanisms the most studied one is the Linker of nucleoskeleton and cytoskeleton(LINC)complex-dependent perinuclear actin ***,recently additional mechanisms have been identified:an Actin-related protein-2/3(Arp2/3)-dependent perinuclear actin polymerization during migration of dendritic cells and a perinuclear actin rim that is formed in response to external force application or migration *** parallel,there are also reports on cancer cells that migrate in a LINC complex independent manner and on cancers with reduced expression of the LINC complex ***,suggesting that LINC complex independent migration may be associated with tumour formation.

关键词： Cell migration Actin Lamins Nuclear envelope Cancer

Flow Field and Performance of Cross Flow Fans——Experimental and Theoretical Investigations

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Journal of Thermal Science 2003年第3期12卷 234-238页

作者： Martin gabi Simon Dornstetter Toni Klemm Institute of Fluid Machinery University of Karlsruhe (TH) D-76128 Karlsruhe GermanyRobert Bosch GmbH D-71701 Schwieberdingen GermanyInstitute of Fluid Machinery University of Karlsruhe (TH) D-76128 Karlsruhe Germany

Due to the construction and the operating principle the prediction of performance of Cross Flow Fans (CFF) is difficult and the knowledge about the internal flow regime is limited. To investigate the impact of geometrical parameters on the performance of CFF, experimental investigations, using Particle Imaging Velocimetry (PIV), and CFD calculations were carried out. Some results of PIV measurements and CFD calculations are presented, which give an impression of the internal flow and confirm the numerical calculations.

关键词： fans cross-flow fans computational fluid dynamics particle imaging velocimetry

Calculation of the VKI turbine blade with LES and DES

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Journal of Thermal Science 2007年第4期16卷 321-327页

作者： F.Magagnato B.Pritz M.gabi FSM University of KarlsruheGermany

The prediction of the laminar to turbulent transition is essential in the calculation of turbine blades, compressor blades or airfoils of airplanes since a non negligible part of the flow field is laminar or transitional. In this paper we compare the prediction capability of the Detached Eddy Simulation （DES） with the Large Eddy Simulation （LES） using the high-pass filtered （HPF） Smagorinsky model （Stolz et al.[1]） when applied to the calculation of transitional flows on turbine blades. Detailed measurements from Canepa et al.[2] of the well known VKI-turbine blade served to compare our results with the experiments. The calculations have been made on a fraction of the blade （10%） using non-reflective boundary conditions of Freund at the inlet and outlet plane extended to internal flows by Magagnato et al.[3] in combination with the Synthetic Eddy Method （SEM） proposed by Jarrin et al.[4]. The SEM has also been extended by Pritz et al.[5] for compressible flows. It has been repeatedly shown that hybrid approaches can satisfactorily predict flows of engineering relevance. In this work we wanted to investigate if they can also be used successfully in this difficult test case.

关键词： Turbine blade LES DES transition

Investigations on the Flow Field in an Unshrouded Pump Impeller Geometry

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Journal of Thermal Science 2012年第2期21卷 136-144页

作者： Sten Sieber Friedrich Frhlig Saban Caglar Martin gabi Fchgebiet Strmungsmaschinen Karlsruhe Institute of Technology Germany

Transient CFD simulations are performed to investigate the flow behaviour inside an unshrouded pump using the SAS method. Two blade designs are compared at two different tip clearances and the results are validated by measurements. The detected vortex structure is visualized by the normalized helicity, further discussed regarding its development and behaviour and finally implicated to the efficiency of the two different blade designs.

关键词： unshrouded pump tip clearance helicity

Prediction of the Resonance Characteristics of Combustion Chambers on the Basis of Large-Eddy Simulation

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Journal of Thermal Science 2005年第2期14卷 156-161页

作者： Franco MAGAGNATO Balázs PRITZ Horst BCHNER Martin gabi Department of Fluid Machinery University of Karlsruhe GermanyDepartment of Fluid Machinery University of KarlsruheGermanyEngler-Bunte-Institute/Division for Combustion Technology University of KarlsruheGermanyDepartment of Fluid Machinery University of KarlsruheGermany

In the last few years intensive experimental investigations were performed at the University of Karlsruhe to develop an analytical model for the Helmholtz resonator-type combustion system. In the present work the resonance characteristics of a Helmholtz resonator-type combustion chamber were investigated using large-eddy simulations (LES), to understand better the flow effects in the chamber and to localize the dissipation. In this paper the results of the LES are presented, which show good agreement with the experiments. The comparison of the LES study with the experiments sheds light on the significant role of the wall roughness in the exhaust gas pipe.

关键词： compressible large-eddy simulation combustion instabilities oscillating flow damping ratio.

A Novel Approach to Predict the Stability Limits of Combustion Chambers with Large Eddy Simulation

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Journal of Thermal Science 2010年第3期19卷 261-265页

作者： B.Pritz F.Magagnato M.gabi Department of Fluid Machinery University of Karlsruhe Kaiserstr.1276131 KarlsruheGermany

Lean premixed combustion,which allows for reducing the production of thermal NOx,is prone to combustion *** is an extensive research to develop a reduced physical model,which allows-without time-consuming measurements-to calculate the resonance characteristics of a combustion system consisting of Helmholtz resonator type components (burner plenum,combustion chamber).For the formulation of this model numerical investigations by means of compressible Large Eddy Simulation (LES) were carried *** these investigations the flow in the combustion chamber is isotherm,non-reacting and excited with a sinusoidal mass flow *** a combustion chamber as a single resonator subsequently a coupled system of a burner plenum and a combustion chamber were *** this paper the results of additional investigations of the single resonator are *** flow in the combustion chamber was investigated without excitation at the *** was detected,that the mass flow rate at the outlet cross section is pulsating once the flow in the chamber is *** fast Fourier transform of the signal showed that the dominant mode is at the resonance frequency of the combustion *** result sheds light on a very important source of self-excited combustion *** the LES can provide not only the damping ratio for the analytical model but the eigenfrequency of the resonator also.

关键词： compressible large-eddy simulation combustion instabilities oscillating flow damping ratio