An Investigation of Screw Systems in the Finite Displacements of Bennett-Based 6R Linkages

1999 ◽  
Vol 122 (4) ◽  
pp. 426-430 ◽  
Author(s):  
Chintien Huang ◽  
Chi-Chih Sun
Keyword(s):  
Numerical Simulations ◽  
Second Order ◽  
Finite Displacement ◽  
Finite Displacements ◽  
Overconstrained Linkages

This paper investigates, via numerical simulations, the finite displacements of all the known Bennett-based 6R overconstrained linkages: Goldberg’s 6R, variant Goldberg 6R, Waldron’s hybrid 6R, and Wohlhart’s hybrid 6R linkages. An investigation of the finite displacements of nine distinct linkages reveals that every Bennett-based 6R linkage, except for the isomerization of Wohlhart’s hybrid linkage, inherits the linear properties of the Bennett mechanism. The relative finite displacement screws of some non-adjacent links of these linkages form screw systems of the second order. Thirty-one screw systems are reported in this paper. [S1050-0472(00)02204-2]

An Investigation of Screw Systems in the Finite Displacements of Bennett-Based 6R Linkages

1998 ◽  
Author(s):  
Chintien Huang ◽  
Chi-Chih Sun
Keyword(s):  
Numerical Simulations ◽  
Second Order ◽  
Finite Displacement ◽  
Finite Displacements ◽  
Overconstrained Linkages

Abstract This paper investigates, via numerical simulations, the finite displacements of all the known Bennett-based 6R overconstrained linkages: Goldberg’s linkages, variant Goldberg linkages, Waldron’s linkages, and Wohlhart’s linkages. An investigation of the finite displacements of nine distinct linkages reveals that every Bennett-based linkage, except for Wohlhart’s isomerization linkage, inherits the linear properties of the Bennett mechanism. The relative finite displacement screws of some non-adjacent links of these linkages form screw systems of the second order.

Linear Property of the Screw Surface of the Spatial RPRP Linkage

2005 ◽  
Vol 128 (3) ◽  
pp. 581-586 ◽  
Author(s):  
Chintien Huang ◽  
Han-Tsung Tu
Keyword(s):  
Vector Space ◽  
Ruled Surface ◽  
Second Order ◽  
Dimensional Vector ◽  
Dimensional Vector Space ◽  
Reference Position ◽  
Finite Displacements ◽  
Screw Surface ◽  
Intersection Operation ◽  
Linear Property

This paper investigates the screw surface of the RPRP linkage, an overconstrained linkage with mobility one. The screw surface is a ruled surface containing screws for displacing the coupler of the RPRP linkage from one reference position to all reachable positions. In this paper, two types of RPRP linkages, in folded and unfolded forms, are constructed by using hexahedrons in accordance with Delassus’ criteria. It is shown that the screw surfaces of both types of RPRP linkages can be represented by screw systems of the second order. These novel finite screw systems are obtained by intersecting two 3-systems corresponding to the finite displacements of the RP and PR dyads. The intersection of finite screw systems is conducted by employing the intersection operation of vector subspaces of the six-dimensional vector space.

scholarly journals Complex Motions in Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 346-346
Author(s):  
Vincent Icke
Keyword(s):  
Point Source ◽  
Numerical Simulations ◽  
Equatorial Plane ◽  
Planetary Nebulae ◽  
Second Order ◽  
Two Dimensional ◽  
Order Accuracy ◽  
Cylindrically Symmetric

I have made an extensive series of numerical simulations of aspherical PNs. This interacting-winds model consists of a point source of fast tenuous gas embedded in a flattened cloud of dense slow gas which is two-dimensional and cylindrically symmetric. I used a hydrocode specially designed to handle the extremely large gradients between the winds to second order accuracy. The outer shock shapes correspond very well to my analytic predictions. This shock may form cusps which compress the gas to form two rings on opposite sides of the equatorial plane.

Second-order velocity structure functions in direct numerical simulations of turbulence with Rλ up to 2250

2020 ◽  
Vol 5 (10) ◽  
Author(s):  
Takashi Ishihara ◽  
Yukio Kaneda ◽  
Koji Morishita ◽  
Mitsuo Yokokawa ◽  
Atsuya Uno
Keyword(s):  
Numerical Simulations ◽  
Velocity Structure ◽  
Structure Functions ◽  
Second Order ◽  
Direct Numerical Simulations

scholarly journals A semi-implicit, second-order-accurate numerical model for multiphase underexpanded volcanic jets

2013 ◽  
Vol 6 (6) ◽  
pp. 1905-1924 ◽  
Author(s):  
S. Carcano ◽  
L. Bonaventura ◽  
T. Esposti Ongaro ◽  
A. Neri
Keyword(s):  
Relaxation Time ◽  
Numerical Model ◽  
Numerical Simulations ◽  
Solid Phase ◽  
Maximum Velocity ◽  
Second Order ◽  
Three Dimensions ◽  
Lagrangian Model ◽  
Coarse Particles ◽  
Nonequilibrium Effects

Abstract. An improved version of the PDAC (Pyroclastic Dispersal Analysis Code, Esposti Ongaro et al., 2007) numerical model for the simulation of multiphase volcanic flows is presented and validated for the simulation of multiphase volcanic jets in supersonic regimes. The present version of PDAC includes second-order time- and space discretizations and fully multidimensional advection discretizations in order to reduce numerical diffusion and enhance the accuracy of the original model. The model is tested on the problem of jet decompression in both two and three dimensions. For homogeneous jets, numerical results are consistent with experimental results at the laboratory scale (Lewis and Carlson, 1964). For nonequilibrium gas–particle jets, we consider monodisperse and bidisperse mixtures, and we quantify nonequilibrium effects in terms of the ratio between the particle relaxation time and a characteristic jet timescale. For coarse particles and low particle load, numerical simulations well reproduce laboratory experiments and numerical simulations carried out with an Eulerian–Lagrangian model (Sommerfeld, 1993). At the volcanic scale, we consider steady-state conditions associated with the development of Vulcanian and sub-Plinian eruptions. For the finest particles produced in these regimes, we demonstrate that the solid phase is in mechanical and thermal equilibrium with the gas phase and that the jet decompression structure is well described by a pseudogas model (Ogden et al., 2008). Coarse particles, on the other hand, display significant nonequilibrium effects, which associated with their larger relaxation time. Deviations from the equilibrium regime, with maximum velocity and temperature differences on the order of 150 m s−1 and 80 K across shock waves, occur especially during the rapid acceleration phases, and are able to modify substantially the jet dynamics with respect to the homogeneous case.

scholarly journals Nonsphericity of the Moon and Near Sun-Synchronous Polar Lunar Orbits

2009 ◽  
Vol 2009 ◽  
pp. 1-24 ◽  
Author(s):  
Jean Paulo dos Santos Carvalho ◽  
Rodolpho Vilhena de Moraes ◽  
Antônio Fernando Bertachini de Almeida Prado
Keyword(s):  
Numerical Simulations ◽  
Artificial Satellite ◽  
Nonuniform Distribution ◽  
Second Order ◽  
The Moon ◽  
Disturbing Potential ◽  
Short Period ◽  
Coupling Terms ◽  
Lunar Artificial Satellite ◽  
Hori Method

Herein, we consider the problem of a lunar artificial satellite perturbed by the nonuniform distribution of mass of the Moon taking into account the oblateness (J2) and the equatorial ellipticity (sectorial termC22). Using Lie-Hori method up to the second order short-period terms of the Hamiltonian are eliminated. A study is done for the critical inclination in first and second order of the disturbing potential. Coupling terms due to the nonuniform distribution of mass of the Moon are analyzed. Numerical simulations are presented with the disturbing potential of first and second order is. It an approach for the behavior of the longitude of the ascending node of a near Sun-synchronous polar lunar orbit is presented.

scholarly journals Numerical Simulations of Extragalactic Jets in an Inhomogeneous Environment

1996 ◽  
Vol 175 ◽  
pp. 467-468
Author(s):  
Steve Higgins ◽  
TIM O'BRIEN ◽  
James Dunlop
Keyword(s):  
Numerical Simulations ◽  
Three Dimensional ◽  
Second Order ◽  
Godunov Method ◽  
Radio Sources ◽  
Cartesian Coordinates ◽  
Extragalactic Radio Sources ◽  
Extragalactic Jets ◽  
Hydrodynamic Code

We have simulated the passage of an extragalactic jet through a medium containing an ensemble of cool, dense clouds. The hydrodynamic code uses the second-order Godunov method of Falle (Falle 1991, van Leer 1979) in three-dimensional, cartesian coordinates. We have estimated the synchrotron emissivity and used this to produce synthetic radio maps. The results are reminiscent of structures seen in many extragalactic radio sources.

On the Line Geometry of Finite Screw Systems and Point Displacements

2006 ◽  
Author(s):  
Chintien Huang ◽  
Bahram Ravani
Keyword(s):  
Line Geometry ◽  
Novel Treatment ◽  
Finite Displacement ◽  
Finite Displacements ◽  
The One ◽  
Definition Of ◽  
New Framework

This paper unveils line-geometric foundations of finite displacement screw systems, with an emphasis on incompletely specified displacement of points. Linear line complexes are basic entities used in this research. Bisecting linear line complexes arising from finite displacements are proved to be subject to a reciprocal condition if a new definition of pitch of finite screws is defined. This definition was the one used to formulate finite screw systems. The relations among intersections of linear line complexes, screw systems, and varieties of lines are established in order to investigate finite screw systems. A novel treatment of point displacements allows us to visualize finite screw systems when they are formed by intersecting linear line complexes. This paper provides geometric insights into finite displacement screws and presents a new framework for the unification of finite and infinitesimal kinematics.

scholarly journals On the prediction of equilibrium states in homogeneous turbulence

1989 ◽  
Vol 209 ◽  
pp. 591-615 ◽  
Author(s):  
Charles G. Speziale ◽  
Nessan Mac Giolla Mhuiris
Keyword(s):  
Kinetic Energy ◽  
Numerical Simulations ◽  
Turbulent Kinetic Energy ◽  
Time Evolution ◽  
Dissipation Rate ◽  
Flow Instability ◽  
Turbulence Models ◽  
Second Order ◽  
Equilibrium States ◽  
Unstable Flow

A comparison of several commonly used turbulence models (including the K–ε model and three second-order closures) is made for the test problem of homogeneous turbulent shear flow in a rotating frame. The time evolution of the turbulent kinetic energy and dissipation rate is calculated for these models and comparisons are made with previously published experiments and numerical simulations. Particular emphasis is placed on examining the ability of each model to predict equilibrium states accurately for a range of the parameter Ω/S (the ratio of the rotation rate to the shear rate). It is found that none of the commonly used second-order closure models yield substantially improved predictions for the time evolution of the turbulent kinetic energy and dissipation rate over the somewhat defective results obtained from the simpler K–ε model for the unstable flow regime. There is also a problem with the equilibrium states predicted by the various models. For example, the K–ε model erroneously yields equilibrium states that are independent of Ω/S while the Launder, Reece & Rodi model and the Shih-Lumley model predict a flow relaminarization when Ω/S > 0.39 - a result that is contrary to numerical simulations and linear spectral analyses, which indicate flow instability for at least the range 0 [les ] Ω/S [les ] 0.5. The physical implications of the results obtained from the various turbulence models considered herein are discussed in detail along with proposals to remedy the deficiencies based on a dynamical systems approach.

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