Design of the Deployable Mechanisms Based on the Cardanic Motion of Planar Four-Bar Linkage

2014 ◽  
Author(s):  
Win-Bin Shieh
Keyword(s):  
Boundary Conditions ◽  
Planar Model ◽  
Building Unit ◽  
The Past ◽  
Straight Line ◽  
Systematic Methodology ◽  
Deployable Mechanism ◽  
Four Bar Linkage

A deployable mechanism is a mechanism that is designed to be repeatedly expanded and contracted without failure. Most deployable mechanisms are over-constrained mechanisms with a mobility of one. Although many deployable mechanisms had been proposed and employed in application in the past decades, few generalized methodologies for the synthesis of both planar and spatial deployable mechanisms are available. In this paper, a systematic methodology, based on the Cardanic motion of planar linkage, for the synthesis of both the spatial and planar deployable mechanisms is presented. By using the characteristics that some of the coupler points of Cardanic linkages are able to move along a straight line, a building unit mechanism that utilizes such a linkage can be extended or retracted as desired. Once the boundary conditions of the building unit mechanisms are obtained, design of an entire deployable mechanism, planar or spatial, can be fulfilled. After the design is achieved, motion of the synthesized mechanism is simulated in Pro/Engineer, and the prototype of a planar model is manufactured for the justification of this method.

Approximations and boundary conditions for continuous-time threshold autoregressive processes

1994 ◽  
Vol 31 (4) ◽  
pp. 1103-1109 ◽  
Author(s):  
Rob J. Hyndman
Keyword(s):  
Time Series ◽  
Boundary Conditions ◽  
Continuous Time ◽  
Linear Time ◽  
Autoregressive Processes ◽  
Threshold Autoregressive ◽  
The Past ◽  
Time Threshold ◽  
Non Linear ◽  
The Way

Continuous-time threshold autoregressive (CTAR) processes have been developed in the past few years for modelling non-linear time series observed at irregular intervals. Several approximating processes are given here which are useful for simulation and inference. Each of the approximating processes implicitly defines conditions on the thresholds, thus providing greater understanding of the way in which boundary conditions arise.

scholarly journals The effect of surface plastic hardening technology, residual stresses and boundary conditions on the buckling of a beam

2020 ◽  
pp. 87-98
Author(s):  
V P Radchenko ◽  
O S Afanaseva ◽  
V E Glebov
Keyword(s):  
Residual Stresses ◽  
Boundary Conditions ◽  
Hardened Layer ◽  
Surface Plastic ◽  
Straight Line ◽  
Calculated Profile ◽  
Inhomogeneous Temperature ◽  
Inhomogeneous Temperature Field ◽  
Plastic Hardening ◽  
Initial Strains

The complex influence of the surface plastic hardening technology, residual stresses, and boundary conditions on the bending of a hardened beam of EP742 alloy was performed. A phenomenological method of restoring the fields of residual stress and plastic deformations performed by its experimental verification in the particular case of ultrasonic hardening is given. The correspondence of the calculated and experimental data for the residual stresses is observed. For assess the influence of the formed residual stresses on convex cylinders, the calculation methods are used for initial strains based on using analogies between the initial (residual) plastic strains and temperature strains in an inhomogeneous temperature field. This allowed us to reduce the consideration of the problem to the problem of thermoelasticity, which was further solved by numerical methods. The effect of four types of boundary conditions for fixing the ends of the beams (rigid fastening and articulation of the ends and ribs in various combinations, cantilever) on the shape and size of the bending of the beam 10×10×100 mm after ultrasonic hardening is studied in detail. It was found that the minimum deflection is observed with a hard seal of both ends of the beam. The effect of the thickness of the beam, which varied from 2 to 10 mm, on their buckling under the same distribution of residual stresses in the hardened layer was studied, and the nonlinear nature of the increase in the deflection boom with decreasing thickness for all types of boundary conditions was established. It is shown that under all boundary conditions, the curvature along the length of the beam practically does not change, therefore it can be considered constant. The consequence of this is the preservation of the hypothesis of flat sections after the hardening procedure, which is confirmed by the calculated profile of the beam section in plane symmetry, close to a straight line. The influence of the anisotropy of surface plastic hardening on the buckling of the beam was found to be significant, which can serve as the basis for choosing the optimal hardening procedure. The performed parametric analysis of the task is presented in the form of graphical and tabular information on the results of the calculations.

scholarly journals The Unavoidable Metaphor of Memorial Architecture: The Boundaries and Event-Space of Chernobyl Reactor No. 4

2021 ◽  
Author(s):  
◽  
Christopher Ian van der Veen
Keyword(s):  
Boundary Conditions ◽  
Functional Capacity ◽  
Event Space ◽  
The Past ◽  
External Influences ◽  
Built Form ◽  
Actual Event ◽  
Chernobyl Reactor

<p>In the design of memorial architecture, there is encountered an overuse of literal metaphor in order to translate difficult concepts into the built form. These metaphors are explored in contemporary examples of memorial and hybrid-memorial typologies. Within Chernobyl, there is a set of criteria that enable these metaphorical interpretations to operate on a more complex level, and allow the act of memorialising a truer response. The unique conditions contained within the reactor allow for a reinterpretation of architectural process, which is already realised by the existing Sarcophagus - a reactive memorial itself, designed to entomb the burnt core and its radioactive properties. As such, the reactor and its attached site can no longer be re-used in any functional capacity; the proposed memorial embraces these criteria, exploiting phenomenological thought in order to locate a set of boundary conditions. This creates an event-space -  that being the location of inhabitable architecture within the reactor. Event-space exists between the boundaries established, which is a conceptual entity that is able exist in reality, and enable flashes of the past events to surface, which are interpreted by the memorial inhabitants. The memorial uses this event-space, within the sites absence of function, to locate the actual event of the disaster in the past. This fragile undertaking is achieved by placing greater responsibility on architecture to mediate the design of memorial, and remove external influences that halt this process.</p>

scholarly journals Trends in Stratospheric Ozone: Lessons Learned from a 3D Chemical Transport Model

2006 ◽  
Vol 63 (3) ◽  
pp. 1028-1041 ◽  
Author(s):  
Richard S. Stolarski ◽  
Anne R. Douglass ◽  
Stephen Steenrod ◽  
Steven Pawson
Keyword(s):  
Time Series ◽  
Solar Cycle ◽  
Ultraviolet Radiation ◽  
Boundary Conditions ◽  
Interannual Variability ◽  
Transport Model ◽  
Stratospheric Ozone ◽  
Chemical Transport ◽  
Chemical Transport Model ◽  
The Past

Abstract Stratospheric ozone is affected by external factors such as chlorofluorcarbons (CFCs), volcanoes, and the 11-yr solar cycle variation of ultraviolet radiation. Dynamical variability due to the quasi-biennial oscillation and other factors also contribute to stratospheric ozone variability. A research focus during the past two decades has been to quantify the downward trend in ozone due to the increase in industrially produced CFCs. During the coming decades research will focus on detection and attribution of the expected recovery of ozone as the CFCs are slowly removed from the atmosphere. A chemical transport model (CTM) has been used to simulate stratospheric composition for the past 30 yr and the next 20 yr using 50 yr of winds and temperatures from a general circulation model (GCM). The simulation includes the solar cycle in ultraviolet radiation, a representation of aerosol surface areas based on observations including volcanic perturbations from El Chichon in 1982 and Pinatubo in 1991, and time-dependent mixing ratio boundary conditions for CFCs, halons, and other source gases such as N2O and CH4. A second CTM simulation was carried out for identical solar flux and boundary conditions but with constant “background” aerosol conditions. The GCM integration included an online ozonelike tracer with specified production and loss that was used to evaluate the effects of interannual variability in dynamics. Statistical time series analysis was applied to both observed and simulated ozone to examine the capability of the analyses for the determination of trends in ozone due to CFCs and to separate these trends from the solar cycle and volcanic effects in the atmosphere. The results point out several difficulties associated with the interpretation of time series analyses of atmospheric ozone data. In particular, it is shown that lengthening the dataset reduces the uncertainty in derived trend due to interannual dynamic variability. It is further shown that interannual variability can make it difficult to accurately assess the impact of a volcanic eruption, such as Pinatubo, on ozone. Such uncertainties make it difficult to obtain an early proof of ozone recovery in response to decreasing chlorine.

scholarly journals Optimal synthesis of a four-bar linkage by method of controlled deviation

2004 ◽  
Vol 31 (3-4) ◽  
pp. 265-280 ◽  
Author(s):  
Radovan Bulatovic ◽  
Stevan Djordjevic
Keyword(s):  
Objective Function ◽  
Optimal Synthesis ◽  
Straight Line ◽  
Individual Comparison ◽  
Four Bar Linkage ◽  
The Given ◽  
Initial Selection ◽  
Selection Of ◽  
Process Calculation ◽  
Made In

This paper considers optimal synthesis of a four-bar linkage by method of controlled deviations. The advantage of this approximate method is that it allows control of motion of the coupler in the four-bar linkage so that the path of the coupler is in the prescribed environment around the given path on the segment observed. The Hooke-Jeeves?s optimization algorithm has been used in the optimization process. Calculation expressions are not used as the method of direct searching, i.e. individual comparison of the calculated value of the objective function is made in each iteration and the moving is done in the direction of decreasing the value of the objective function. This algorithm does not depend on the initial selection of the projected variables. All this is illustrated on an example of synthesis of a four-bar linkage whose coupler point traces a straight line, i.e. passes through sixteen prescribed points lying on one straight line. .

The Analysis of an Elastic Four-Bar Linkage on a Vibrating Foundation Using a Variational Method

1980 ◽  
Vol 102 (2) ◽  
pp. 320-328 ◽  
Author(s):  
B. S. Thompson
Keyword(s):  
Variational Method ◽  
Boundary Conditions ◽  
Equations Of Motion ◽  
Stress Strain ◽  
Variational Theorem ◽  
Vibrating Foundation ◽  
Four Bar Linkage

A variational method is employed to derive the equations of motion and the associated boundary conditions for a flexible crank-rocker linkage sited on a foundation which vibrates perpendicular to the plane of the mechanism. The links oscillate in axial, flexural and torsional modes, and the equations governing this behavior are systematically constructed using a variational theorem by permitting independent variations of the stress, strain, displacement and velocity parameters.

Synthesis of a Large Oscillation Four-Bar Mechanism

1997 ◽  
Author(s):  
Gloria K. Starns ◽  
Donald R. Flugrad
Keyword(s):  
Reduced Gradient Method ◽  
Large Oscillation ◽  
Oscillation Mechanism ◽  
Straight Line ◽  
Transmission Angle ◽  
Reduced Gradient ◽  
Generalized Reduced Gradient ◽  
Angular Oscillations ◽  
Four Bar Linkage ◽  
Effective Transmission

Abstract This paper demonstrates procedures implemented for the synthesis of a four-bar mechanism that produces large angular oscillations of the output member while maintaining effective transmission angles. The mechanisms are modeled as being driven by a force applied at the coupler link. Additionally this force’s line of action is constrained to occur along an approximate straight line. This research was conducted out of the need for a device that is capable of retraction of the horizontal tool bar housed on the back of a tractor. The tool bars accommodate the implements required to accomplish the numerous tasks of the farmer, i.e. row markers, sprayer arms, planters, etc. Upon retraction of the tool bar so that it is parallel to ground, the appropriate tools are lowered to their working position. As the length of these bars increases, a savings of time and increased productivity is realized. Kurt Hain makes the following observation regarding large oscillation mechanisms in [1]: “It would be very difficult to solve this problem with one four-bar linkage, because it is difficult to design a four-bar linkage having such a large oscillation of a crank without running into problems of poor transmission angle characteristics; it might be possible to use linkages in combinations with gears, but this would make the mechanism more expensive, less efficient, and probably noisier.” In this study simulated annealing, a genetic algorithm and the generalized reduced gradient method are used to produce mechanisms with large angular oscillations of the output member and transmission angles that vary by as little as 20° from 90°. A comparative analysis of each of the optimization procedures is presented with observations regarding the efficacy of each method in the solution of the large oscillation mechanism.

Equations for Four-Bar Line-Envelopes

1981 ◽  
Vol 103 (4) ◽  
pp. 743-749 ◽  
Author(s):  
K. H. Hunt ◽  
E. F. Fichter
Keyword(s):  
The Other ◽  
Straight Line ◽  
Sliding Joint ◽  
Line Equation ◽  
Four Bar Linkage ◽  
Sliding Joints

A line-equation (in tangential coordinates) is derived for the envelope of a general straight line attached to the coupler of a planar hinged four-bar linkage. Since a line can be identified with an axis of relative translation parallel to a sliding joint, the study of how lines move in a mechanism has practical potential. Nevertheless the emphasis here is on the geometry of the line-envelopes, and some envelopes are plotted both as samples of what can be obtained and to exemplify some of the properties which they possess. Towards the end of the paper all the other forms of planar four-bar linkage, namely those in which one or two sliding joints replace hinges, are examined, and their envelope-equations are presented.

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