Effects of heat release on the large-scale structure in turbulent mixing layers

1989 ◽  
Vol 199 ◽  
pp. 297-332 ◽  
Author(s):  
P. A. Mcmurtry ◽  
J. J. Riley ◽  
R. W. Metcalfe
Keyword(s):  
Heat Release ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Mixing Layer ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Mixing Layers ◽  
Turbulent Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

The effects of chemical heat release on the large-scale structure in a chemically reacting, turbulent mixing layer are investigated using direct numerical simulations. Three-dimensional, time-dependent simulations are performed for a binary, single-step chemical reaction occurring across a temporally developing turbulent mixing layer. It is found that moderate heat release slows the development of the large-scale structures and shifts their wavelengths to larger scales. The resulting entrainment of reactants is reduced, decreasing the overall chemical product formation rate. The simulation results are interpreted in terms of turbulence energetics, vorticity dynamics, and stability theory. The baroclinic torque and thermal expansion in the mixing layer produce changes in the flame vortex structure that result in more diffuse vortices than in the constant-density case, resulting in lower rotation rates of the large-scale structures. Previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers are shown to result from vorticity generation by baroclinic torques.

Large-scale structures in a forced turbulent mixing layer

1985 ◽  
Vol 150 ◽  
pp. 23-39 ◽  
Author(s):  
M. Gaster ◽  
E. Kit ◽  
I. Wygnanski
Keyword(s):  
Turbulent Mixing ◽  
Large Scale ◽  
Phase Distribution ◽  
Mixing Layer ◽  
Global Scale ◽  
Travelling Wave ◽  
Mean Flow ◽  
Turbulent Mixing Layer ◽  
Large Scale Structures ◽  
Scale Structures

The large-scale structures that occur in a forced turbulent mixing layer at moderately high Reynolds numbers have been modelled by linear inviscid stability theory incorporating first-order corrections for slow spatial variations of the mean flow. The perturbation stream function for a spatially growing time-periodic travelling wave has been numerically evaluated for the measured linearly diverging mean flow. In an accompanying experiment periodic oscillations were imposed on the turbulent mixing layer by the motion of a small flap at the trailing edge of the splitter plate that separated the two uniform streams of different velocity. The results of the numerical computations are compared with experimental measurements.When the comparison between experimental data and the computational model was made on a purely local basis, agreement in both the amplitude and phase distribution across the mixing layer was excellent. Comparisons on a global scale revealed, not unexpectedly, less good accuracy in predicting the overall amplification.

scholarly journals Large-Scale Structure in the Universe: Spatial Distribution and Peculiar Velocities

1987 ◽  
Vol 124 ◽  
pp. 335-348
Author(s):  
Neta A. Bahcall
Keyword(s):  
Dark Matter ◽  
Spatial Distribution ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Clusters Of Galaxies ◽  
Large Scale Structures ◽  
Peculiar Velocities ◽  
Scale Structures ◽  
The Universe

The evidence for the existence of very large scale structures, ∼ 100h−1Mpc in size, as derived from the spatial distribution of clusters of galaxies is summarized. Detection of a ∼ 2000 kms−1 elongation in the redshift direction in the distribution of the clusters is also described. Possible causes of the effect are peculiar velocities of clusters on scales of 10–100h−1Mpc and geometrical elongation of superclusters. If the effect is entirely due to the peculiar velocities of clusters, then superclusters have masses of order 1016.5M⊙ and may contain a larger amount of dark matter than previously anticipated.

Test Procedures and Simulation Model Calibration Strategies for Nonlinear Stiffness Behavior of Joints in Large-Scale Structures

2013 ◽  
Vol 554-557 ◽  
pp. 2400-2413
Author(s):  
Sebastian Hensel ◽  
Fred Jesche ◽  
Reimund Neugebauer ◽  
Reinhard Mauermann
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Tension Specimen ◽  
Joint Models ◽  
Joint Zone ◽  
Large Scale Structures ◽  
Scale Structures ◽  
Nonlinear Joint ◽  
Joint Behavior

State-of-art models for mechanical joints in large scale structures typically consider only the linear behavior of the joint zones with lower complex approaches, such as rigid or elastic beams or a merge of opposite sheet metal nodes. In the present study several feasible methods to model nonlinear joint behavior and the connection between sheets and joint are investigated and evaluated. A preferred combination based on nonlinear springs was chosen, which meets the requirements for application in large scale structure models: low computation time, mesh independence and availability in several FEM software packages. For the calibration of the joint zone models a 2-point-tension-specimen was used. Five different joint types and the two sheet material combinations aluminium/aluminium as well as steel/steel were investigated. With the calibrated models a more complex 5-point-tension-specimen was used to consider the local interoperation of the joints. Some deviations were determined especially for highly stressed joint zones. Hence an average function was defined to consider both, the local deformations in the joint zone and additionally the more global sheet deformations. Finally, the simplified joint models were used in a complex specimen model with 22 joints. The comparisons between experimentally and numerically determined results show a good accordance. The nonlinear joint behavior is captured very well. A method is presented, which uses 2-point-specimens to calibrate simplified joint models with nonlinear deformation characteristics. The efficient application in large scale structure models is possible due to simplicity, stability, low computation times and mesh independent implementation.

A method to improve the productivity of legged manipulators performing on-site manufacturing tasks on large-scale structures

2020 ◽  
pp. 095440622094745
Author(s):  
Yuan Hu ◽  
Weizhong Guo ◽  
Hao Chen ◽  
Xiaolong Jing
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Parallel Robot ◽  
Scale Structure ◽  
Legged Robots ◽  
End Effector ◽  
Large Scale Structures ◽  
Structure Simulation ◽  
Scale Structures ◽  
Simulation Results

Legged manipulators that combine legged robots with manipulators have emerged as a new solution to large-scale structure on-site manufacturing tasks. However, the productivity of legged manipulators is strongly affected by the positioning and repositioning process. This paper aims to improve the productivity of legged manipulators by reducing the required positioning and repositioning times. By treating a legged manipulator that attaches all feet to the ground as a virtual parallel robot, the workspace of the on-board manipulator can be enlarged while the end-effector maintains the motion precision. By choosing working positions that enable a legged manipulator to cover more processing regions with the enlarged workspace at a time, the required positioning and repositioning times can be reduced. The proposed method is implemented through a variant of a genetic algorithm to find the minimum set of working positions that enable a hexapod manipulator to accomplish welding tasks on a large-scale structure. Simulation results show that the required working positions of the hexapod manipulator are reduced significantly and thus higher productivity can be obtained. The flowchart to implement the proposed method is expected to improve the productivity of other kinds of legged manipulators that perform on-site manufacturing tasks.

FORMATION OF LARGE SCALE STRUCTURES OF THE UNIVERSE ON THE CONNECTION MACHINE-2.

1993 ◽  
Vol 04 (01) ◽  
pp. 197-205 ◽  
Author(s):  
JEAN-MICHEL ALIMI ◽  
HANS SCHOLL
Keyword(s):  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Large Scale Structures ◽  
Preliminary Results ◽  
Connection Machine ◽  
Scale Structures ◽  
The Universe

We have developped two new N-body codes on Connection Machine 2. We present preliminary results concerning the formation of large scale structure of the Universe.

scholarly journals Explosive Origins of Large-Scale Structures

1988 ◽  
Vol 130 ◽  
pp. 321-329
Author(s):  
Jeremiah P. Ostriker
Keyword(s):  
Galaxy Formation ◽  
Large Scale ◽  
Cosmic Strings ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Energy Output ◽  
Galaxy Groups ◽  
Large Scale Structures ◽  
The Galaxy ◽  
Scale Structures

Large scale structures up to 5h−1 mpc, the galaxy-galaxy correlation length and the size of typical galaxy groups and clusters, can be produced quite naturally from explosions originating in young galaxies (Ostriker and Cowie, 1981: “OC”) or quasars (Ikeuchi, 1981: “I”) with energy output of 1061 ergs. But very large-scale structure in the 25 mpc −50 mpc range possibly indicated by cluster-cluster correlations (Bahcall, 1987a), can only be produced by much more energetic events of 1065 ergs which are far beyond the output of any objects currently known. This follows simply from the dimensional arguments which give R = c(Eσ/t2)0.2 implicit in the classic Seldov-Taylor solution and cosmological analogs (cf Ostriker, 1986). Thus very large scale structure can only be produced by explosions if many small ones can coalesce suitably at early epochs (OC) or single giant events are produced by exotic objects such as superconducting cosmic strings (Ostriker, Thompson and Witten 1986: “OTW”). If however these large events do occur, then many specific properties of very large-scale structures will be produced quite naturally (cf Bahcall, 1987b, Weinberg, Ostriker and Dekel, 1987 “WOD”). Before discussing these points, it is appropriate to say a few words on the importance of hydrodynamics in general and explosions in particular, since the latter will certainly be a consequence of galaxy formation even if they are not the primary cause.

scholarly journals Decoupling local mechanics from large-scale structure in modular metamaterials

2017 ◽  
Vol 114 (14) ◽  
pp. 3590-3595 ◽  
Author(s):  
Nan Yang ◽  
Jesse L. Silverberg
Keyword(s):  
Mechanical Properties ◽  
Large Scale ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Design Parameters ◽  
Mechanical Function ◽  
Large Scale Structures ◽  
Mechanical Metamaterials ◽  
Wide Range ◽  
Scale Structures

A defining feature of mechanical metamaterials is that their properties are determined by the organization of internal structure instead of the raw fabrication materials. This shift of attention to engineering internal degrees of freedom has coaxed relatively simple materials into exhibiting a wide range of remarkable mechanical properties. For practical applications to be realized, however, this nascent understanding of metamaterial design must be translated into a capacity for engineering large-scale structures with prescribed mechanical functionality. Thus, the challenge is to systematically map desired functionality of large-scale structures backward into a design scheme while using finite parameter domains. Such “inverse design” is often complicated by the deep coupling between large-scale structure and local mechanical function, which limits the available design space. Here, we introduce a design strategy for constructing 1D, 2D, and 3D mechanical metamaterials inspired by modular origami and kirigami. Our approach is to assemble a number of modules into a voxelized large-scale structure, where the module’s design has a greater number of mechanical design parameters than the number of constraints imposed by bulk assembly. This inequality allows each voxel in the bulk structure to be uniquely assigned mechanical properties independent from its ability to connect and deform with its neighbors. In studying specific examples of large-scale metamaterial structures we show that a decoupling of global structure from local mechanical function allows for a variety of mechanically and topologically complex designs.

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