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Arbitrary Direction (arbitrary + direction)

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Engineering60%

Selected Abstracts

Response to three-component seismic motion of arbitrary direction

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
Julio J. Hernández
Abstract This paper presents a response spectrum analysis procedure for the calculation of the maximum structural response to three translational seismic components that may act at any inclination relative to the reference axes of the structure. The formula GCQC3, a generalization of the known CQC3-rule, incorporates the correlation between the seismic components along the axes of the structure and the intensity disparities between them. Contrary to the CQC3-rule where a principal seismic component must be vertical, in the GCQC3-rule all components can have any direction. Besides, the GCQC3-rule is applicable if we impose restrictions to the maximum inclination and/or intensity of a principal seismic component; in this case two components may be quasi-horizontal and the third may be quasi-vertical. This paper demonstrates that the critical responses of the structure, defined as the maximum and minimum responses considering all possible directions of incidence of one seismic component, are given by the square root of the maximum and minimum eigenvalues of the response matrix R, of order 3×3, defined in this paper; the elements of R are established on the basis of the modal responses used in the well-known CQC-rule. The critical responses to the three principal seismic components with arbitrary directions in space are easily calculated by combining the eigenvalues of R and the intensities of those components. The ratio rmax/rSRSS between the maximum response and the SRSS response, the latter being the most unfavourable response to the principal seismic components acting along the axes of the structure, is bounded between 1 and ,(3,a2/(,a2 + ,b2 + ,c2)), where ,a,,b,,c are the relative intensities of the three seismic components with identical spectral shape. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Morphological study of Czochralski-grown lanthanide orthovanadate single crystals and implications on the mechanism of bulk spiral formation

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2010
Hengjiang Cong
Single crystals of monoclinic Nd:LaVO4 with dimensions up to Ř28 × 21,mm have been grown from the near-stoichiometric melt by the Czochralski method, making use of various seed orientations that are perpendicular to the (010), (10), (001) and (00) crystal planes. A sample was also prepared with the seed orientation in an arbitrary direction relative to the crystal. The anisotropic properties of the crystal are manifested in the growth morphology of the as-grown crystals, where different degrees of bulk spiral growth were observed. It was also found that employing the (001) or (00) seed faces severely suppressed the bulk spiral growth, and thus high quality and large-scale Nd:LaVO4 crystals were obtained. The constituent segregation coefficients and high-temperature stability, including the melting point, were determined and evaluated. Based on the attachment energy model of Hartman,Perdok theory, morphology predictions were made for monoclinic LaVO4 and tetragonal YVO4 orthovanadate single crystals. Correlating with the as-grown morphology of both crystals developed along different seed orientations, a theoretical explanation is provided for the influences of seed crystals on bulk spiral formation, crystal quality and utilization ratio. It suggests that breaking the axial symmetry of the ideal atomic level interface between crystal and melt plays a crucial triggering role in bulk spiral formation in the Czochralski growth of lanthanide orthovanadate single crystals. Selecting a proper seed orientation that yields such a highly axially symmetric surface structure consisting of a series of large-area facets with similar growth velocities can greatly reduce bulk spiral formation and thus is preferable in the Czochralski growth of large-sized low-symmetry oxide crystals. [source]

Design and Control of a Four-Wheeled Omnidirectional Mobile Robot with Steerable Omnidirectional Wheels

JOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 4 2004
Jae-Bok Song
Omnidirectional mobile robots are capable of arbitrary motion in an arbitrary direction without changing the direction of wheels, because they can perform 3 degree-of-freedom (DOF) motion on a two-dimensional plane. In this research, a new class of omnidirectional mobile robot is proposed. Since it has synchronously steerable omnidirectional wheels, it is called an omnidirectional mobile robot with steerable omnidirectional wheels (OMR-SOW). It has 3 DOFs in motion and one DOF in steering. One steering DOF can function as a continuously variable transmission (CVT). CVT of the OMR-SOW increases the range of velocity ratio from the wheel velocities to robot velocity, which may improve performance of the mobile robot. The OMR-SOW with four omnidirectional wheels has been developed in this research. Kinematics and dynamics of this robot will be analyzed in detail. Various tests have been conducted to demonstrate the validity and feasibility of the proposed mechanism and control algorithm. © 2004 Wiley Periodicals, Inc. [source]

Response to three-component seismic motion of arbitrary direction

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
Julio J. Hernández
Abstract This paper presents a response spectrum analysis procedure for the calculation of the maximum structural response to three translational seismic components that may act at any inclination relative to the reference axes of the structure. The formula GCQC3, a generalization of the known CQC3-rule, incorporates the correlation between the seismic components along the axes of the structure and the intensity disparities between them. Contrary to the CQC3-rule where a principal seismic component must be vertical, in the GCQC3-rule all components can have any direction. Besides, the GCQC3-rule is applicable if we impose restrictions to the maximum inclination and/or intensity of a principal seismic component; in this case two components may be quasi-horizontal and the third may be quasi-vertical. This paper demonstrates that the critical responses of the structure, defined as the maximum and minimum responses considering all possible directions of incidence of one seismic component, are given by the square root of the maximum and minimum eigenvalues of the response matrix R, of order 3×3, defined in this paper; the elements of R are established on the basis of the modal responses used in the well-known CQC-rule. The critical responses to the three principal seismic components with arbitrary directions in space are easily calculated by combining the eigenvalues of R and the intensities of those components. The ratio rmax/rSRSS between the maximum response and the SRSS response, the latter being the most unfavourable response to the principal seismic components acting along the axes of the structure, is bounded between 1 and ,(3,a2/(,a2 + ,b2 + ,c2)), where ,a,,b,,c are the relative intensities of the three seismic components with identical spectral shape. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Scaling turbulent atmospheric stratification.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 631 2008
III: Space, time stratification of passive scalars from lidar data
Abstract In this third and final part of the series, we concentrate on the temporal behaviour of atmospheric passive scalars. We first recall that,although the full (x, y, z, t) turbulent processes respect an anisotropic scale invariance,that due to advection,the generator will generally not be a diagonal matrix. This implies that the scaling of (1-D) temporal series will generally involve three exponents in real space: 1/3, 1/2, 3/5, for spectra ,, = 5/3, 2, 11/5, with the first and last corresponding to domination by advection (horizontal and vertical respectively), and the second to pure temporal development (no advection). We survey the literature and find that almost all the empirical ,, values are indeed in the range 5/3 to 2. We then use meteorological analyses to argue that, although pure temporal development is unlikely to be dominant for time-scales less than the eddy turnover time of the largest structures (about 2 weeks), an intermittent vertical velocity could quite easily explain the occasionally observed ,, , 2 spectra. We then use state-of-the-art vertically pointing lidar data of backscatter ratios from both aerosols and cirrus clouds yielding several (z, t) vertical space,time cross-sections with resolution of 3.75 m in the vertical, 0.5,30 s in time and spanning 3,4 orders of magnitude in temporal scale. We first test the predictions of the anisotropic, multifractal extension of the Corrsin-Obukhov law in the vertical and in time, separately finding that the cirrus and aerosol backscatters both followed the theoretical (anisotropic) scalings accurately; three of the six cases show dominance by the horizontal wind, the others by the vertical wind. In order to test the theory in arbitrary directions in this (z, t) space, and in order to get more complete information about the underlying physical scale, we develop and apply a new Anisotropic Scaling Analysis Technique (ASAT) which is based on a nonlinear space,time coordinate transformation. This transforms the original differential scaling into standard self-similar scaling; there remains only a ,trivial' anisotropy. This method is used in real space on 2-D structure functions. It is applied to both the new (z, t) data as well as the (x, z) data discussed in part II. Using ASAT, we verify the theory to within about 10% over more than three orders of magnitude of space,time scales in arbitrary directions in (x, z) and (z, t) spaces. By considering the high- (and low-) order structure functions, we verify the theory for both weak and strong structures; as predicted, their average anisotropies are apparently the same. Putting together the results for (x, z) and (z, t), and assuming that there is no overall stratification in the horizontal (x, y) plane, we find that the overall (x, y, z, t) space is found to have an effective ,elliptical dimension' characterizing the overall space,time stratification equal to Deff, st = 3.21 ± 0.05. Copyright © 2008 Royal Meteorological Society [source]