Aerospace

In the present work, we focus on spurious propagating disturbances (q-waves). To establish the existence of q-waves in computations, we compare properties of different numerical methods drawn from finite difference, finite volume and finite element methods. Existence and properties of q-waves are demonstrated with propagation of wave-packets following one-dimensional (1D) convection equation; skewed wave propagation and by solution of linearized rotating shallow water wave equation (LRSWE). Specific numerical experiments are performed with parameters that convert a wave-packet into a q-wave. We also show the case where q-waves are created additionally to physical disturbances those propagate downstream. Formation of q-waves are shown in the case of a discrete shielded vortex in the uniform flow and incompressible transitional flow past an aerofoil by solving the Navier-Stokes equation. In performing this exercise, we establish critical wavenumber range beyond which q-waves are created. Relevance of this information for DNS and LES is discussed. We have further discussed the case of spurious caustics in discrete computing.

This paper presents the results of experimental investigation of unsteady flows in a concentric circular annulus. The flow is generated by the controlled motion of a piston. A range of Reynolds number and boundary layer thickness is obtained by changing the piston velocity and piston displacement. Velocity profiles during deceleration of the flow are with reverse flow near the wall and are highly unstable due to their inflectional nature. The unstable flow ends in periodic vortices at walls of inner and outer pipes. Any arbitrary piston motion is expressed in terms of Fourier series and the generalized analytical solution is obtained for an arbitrary unsteady volume flow rate through the concentric pipe annulus. The velocity profiles for the experimental cases are obtained from the analytical solution. These mean velocity profiles are used for quasi-steady 3D linear stability analysis. The quasi-steady 3D linear stability analysis is used to explain the observed instability and tran...

The present study highlights the capability of a newly developed chimera grid methodolgy to analyze complex fluid flows. The developed chimera methodology incorporates high accuracy compact schemes on orthogonal body-fitted grids which guarantees Dispersion Relation Preservation and fourth-order Lagrange interpolation for minimization of interpolation error. Navier-Stokes equation formulated using streamfunction-vorticity variables is adopted for reasons of ac-curacy. Current analysis looks at a 2D incompressible flow past two-side-by-side cylinders at Reynolds number 100 and gap ratio 2.5. Computed results show excellent agreement with experiments and other computational results.

The Generation and propagation of the human voice is studied in two-dimensions using a full-body domain, using direct numerical simulation. The fluid/air in the vocal tract is modeled as a compressible and viscous fluid interacting with the non-linear, viscoelastic vocal folds (VF). The VF tissue material properties are multi-layered, with varying stiffness, and a finite-strain model is utilized and implemented in a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. The full-body domain includes the near VF region, the vocal tract, a simplified model of the soft palate and mouth, and extends out into the acoustic far-field. A new kind of inflow boundary condition based upon a quasi-one-dimensional formulation with constant sub-glottal volume velocity, which is linked to the VF movement, has been adopted. The sound pressure levels (SPL) measured are realistic and we analy...

Submitted for the DFD16 Meeting of The American Physical Society Direct numerical simulation of human phonation 1 SHAKTI SAURABH, DANIEL BODONY, University of Illinois at Urbana-Champaign-A direct numerical simulation study of the generation and propagation of the human voice in a full-body domain is conducted. A fully compressible fluid flow model, anatomically representative vocal tract geometry, finite deformation model for vocal fold (VF) motion and a fully coupled fluid-structure interaction model are employed. The dynamics of the multi-layered VF tissue with varying stiffness are solved using a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. A new inflow boundary condition, based upon a quasi-1D formulation with constant sub-glottal volume velocity, linked to the VF movement, has been adopted. Simulations for both child and adult phonation were performed. Acoustic characteristics obtained from these simulation are consistent with expected values. A sensitivity analysis based on VF stiffness variation is undertaken and sound pressure level/fundamental frequency trends are established. An evaluation of the data against the commonly-used quasi-1D equations suggest that the latter are not sufficient to model phonation. Phonation threshold pressures are measured for several VF stiffness variations and comparisons to clinical data are carried out.

Submitted for the DFD15 Meeting of The American Physical Society Study of human phonation in a full-body domain 1 SHAKTI SAURABH, DANIEL BODONY, Univ of Illinois-Urbana-The generation and propagation of the human voice is studied in two-dimensions using a full-body domain, using direct numerical simulation. The fluid/air in the vocal tract is modeled as a compressible and viscous fluid interacting with the non-linear, viscoelastic vocal folds (VF). The VF tissue material properties are multi-layered, with varying stiffness, and a finite-strain model is utilized and implemented in a quadratic finite element code. The fluid-solid domains are coupled through a boundary-fitted interface and utilize a Poisson equation-based mesh deformation method. The fullbody domain includes the near VF region, the vocal tract, a simplified model of the soft palate and mouth, and extends out into the acoustic far-field. A new kind of inflow boundary condition based upon a quasi-one-dimensional formulation with constant sub-glottal volume velocity, which is linked to the VF movement, has been adopted. The sound pressure levels (SPL) measured are realistic and we analyze their connection to the VF dynamics and glottal and vocal tract geometries.

In this paper, a newly proposed machining method named "surface defect machining" (SDM) was explored for machining of nanocrystalline beta silicon carbide (3C-SiC) at 300 K using MD simulation. The results were compared with isothermal high temperature machining at 1200 K under the same machining parameters, emulating ductile mode micro laser assisted machining (l-LAM) and with conventional cutting at 300 K. In the SDM simulation, surface defects were generated on the top of the (010) surface of the 3C-SiC work piece prior to cutting, and the workpiece was then cut along the h100i direction using a single point diamond cutting tool at a cutting speed of 10 m/s. Cutting forces, subsurface deformation layer depth, temperature in the shear zone, shear plane angle and friction coefficient were used to characterize the response of the workpiece. Simulation results showed that SDM provides a unique advantage of decreased shear plane angle which eases the shearing action. This in turn causes an increased value of average coefficient of friction in contrast to the isothermal cutting (carried at 1200 K) and normal cutting (carried at 300 K). The increase of friction coefficient, however, was found to aid the cutting action of the tool due to an intermittent dropping in the cutting forces, lowering stresses on the cutting tool and reduced operational temperature. Analysis shows that the introduction of surface defects prior to conventional machining can be a viable choice for machining a wide range of ceramics, hard steels and composites compared to hot machining.

This paper develops product representations as component networks that evolve from sharing of interfaces with other components in a product and links them to the external world of sourcing. The paper formally defines and develops two measures of component modularity by linking Graph Theory and Product Architecture principles. The first measure, degree modularity, is related to the strength of design dependencies with adjacent components. The second measure, bridge modularity, is related to the criticality of components. These two component modularity measures are calculated and interpreted by studying the actual product architecture of two products -a small machinery product and an automobile subsystem. A sourcing framework is suggested, treating product obsolescence as a moderating variable in the effect of modularity on sourcing. The paper concludes with a discussion of how component modularity measures can help managers to take better decisions in the arena of sourcing -both at an operational level and at the strategic level. Directions for future work are discussed.

In this paper, we explore how firms can manage their sourcing better by developing relationships not only with their suppliers but also with their suppliers' suppliers. We detail an empirical case study explaining how the firm developed relationships with its suppliers and raw material suppliers via a collaborative center, the sourcing hub. We then analytically model the scenarios encountered in our empirical work, and examine two facets of upstream sourcing under uncertain demand scenarios: (a) firms can supply raw material directly to their suppliers, and this may be beneficial for the firm and its suppliers, (2) firms can bring their suppliers together at the sourcing hub, and the resulting cooperation between suppliers is beneficial for the suppliers and the raw material suppliers. Overall, our work explores the market and economic conditions under which active management of upstream sourcing can add value to supply chains.

3C-SiC (the only polytype of SiC that resides in a diamond cubic lattice structure) is a relatively new material that exhibits most of the desirable engineering properties required for advanced electronic applications. The anisotropy exhibited by 3C-SiC during its nanometric cutting is significant, and the potential for its exploitation has yet to be fully investigated. This paper aims to understand the influence of crystal anisotropy of 3C-SiC on its cutting behaviour. A molecular dynamics simulation model was developed to simulate the nanometric cutting of single-crystal 3C-SiC in nine distinct combinations of crystal orientations and cutting directions, i.e. (1 1 1) −1 1 0 , (1 1 1) −2 1 1 , (1 1 0) −1 1 0 , (1 1 0) 0 0 1 , (1 1 0) 1 1 −2 , (0 0 1) −1 1 0 , (0 0 1) 1 0 0 , (1 1 −2) 1 −1 0 and (1 −2 0) 2 1 0 .

Nanomechanical response of a silicon specimen coated with a sp 3 crystalline carbon coating (1.8 nm thickness) was investigated using MD simulation. A sharp conical rigid tip was impacted at the speed of 50 m/s up to a depth of $ 80% of the coating thickness. Unlike pure silicon specimen, no metallic phase transformation was observed i.e. a thin coating was able to resist Si-I to Si-II metallic phase transformation signifying that the coating could alter the stress distribution and thereby the contact tribology of the substrate. The stress state of the system, radial distribution function and the loaddisplacement curve were all aligned with above observations. 1 Crown

This paper presents novel advances in the deformation behaviour of polycrystalline and single crystal silicon using molecular dynamics (MD) simulation and validation of the same via nanoindentation experiments. In order to unravel the mechanism of deformation, four simulations were performed: indentation of a polycrystalline silicon substrate with a (i) Berkovich pyramidal and a (ii) spherical (arc) indenter, and (iii and iv) indentation of a single crystal silicon substrate with these two indenters. The simulation results reveal that high pressure phase transformation (HPPT) in silicon (Si-I to Si-II phase transformation) occurred in all cases; however, its extent and the manner in which it occurred differed significantly between polycrystalline silicon and single crystal silicon, and was the main driver of differences in the nanoindentation deformation behaviour between these two types of silicon. Interestingly, in polycrystalline silicon, the HPPT was observed to occur more preferentially along the grain boundaries than across the grain boundaries. An automated dislocation extraction algorithm (DXA) revealed no dislocations in the deformation zone, suggesting that HPPT is the primary mechanism in inducing plasticity in silicon.

We compare the leadership evaluations of 1,748 global leaders by superiors, peers, and subordinates in ten national clusters to see whether global leadership styles differ between cultures, in answer to the question: Do global leaders in the East display different leadership behavioral patterns from their counterparts in the West? Our study uses data collected via the Global Executive Leadership Inventory (GELI; , which measures global leadership behavior across twelve dimensions, to derive insight into whether ratings of global leaders differ on the basis of their cultural origins. The 360-degree feedback data in GELI allow us to evaluate global leadership behaviors from multiple perspectives: that of the leaders themselves, as well as their superiors, peers, and subordinates. Using multilevel modeling analysis of self-ratings and observer ratings, we find that while global leaders across the world display similar patterns of leadership behavior, there are significant differences in some leadership dimensions that can be attributed to the leaders" cultural origins.

This review aims to summarize state-of-the-art knowledge on silicon manufacturing using an ultra precision manufacturing process known as single point diamond machining. After highlighting the many contributions that molecular dynamics (MD) simulation has made in aiding the study of silicon manufacturing, this review provides critical insight into some of the analytical theories concerning high pressure phase transformation mechanisms underlying the so called brittle-ductile transition. This review is aimed at providing a particular focus on understanding of the process rather than the process parameters (i.e. rather than suggesting an optimum mix of machining variables, the importance of each machining variable namely, maximum undeformed chip thickness, cutting edge radius, cutting tool rake and clearance angle, crystal structure of the material, anisotropy of the material and tool wear, all of which are essential for efficient silicon manufacturing is highlighted).

For centuries, scratch testing has been used to characterize the hardness of materials, yet a quantitative measure of hardness through scratch testing is not known. In this paper, a new measure “cutting hardness” is proposed as a novel indicator for evaluation of hardness of the material from orthogonal scratch testing. The new measure is applied to nanocrystalline silicon and iron, along with their carbon alloys via molecular dynamics (MD) simulation. It is shown that various simulation based studies concerning material removal can be easily validated by using the cutting hardness measure without recourse to a tailor made experiment.

In this paper, a newly proposed machining method named "surface defect machining" (SDM) was explored for machining of nanocrystalline beta silicon carbide (3C-SiC) at 300 K using MD simulation. The results were compared with isothermal high temperature machining at 1200 K under the same machining parameters, emulating ductile mode micro laser assisted machining (l-LAM) and with conventional cutting at 300 K. In the SDM simulation, surface defects were generated on the top of the (010) surface of the 3C-SiC work piece prior to cutting, and the workpiece was then cut along the h100i direction using a single point diamond cutting tool at a cutting speed of 10 m/s. Cutting forces, subsurface deformation layer depth, temperature in the shear zone, shear plane angle and friction coefficient were used to characterize the response of the workpiece. Simulation results showed that SDM provides a unique advantage of decreased shear plane angle which eases the shearing action. This in turn causes an increased value of average coefficient of friction in contrast to the isothermal cutting (carried at 1200 K) and normal cutting (carried at 300 K). The increase of friction coefficient, however, was found to aid the cutting action of the tool due to an intermittent dropping in the cutting forces, lowering stresses on the cutting tool and reduced operational temperature. Analysis shows that the introduction of surface defects prior to conventional machining can be a viable choice for machining a wide range of ceramics, hard steels and composites compared to hot machining.