Suspended Objects Research Articles

Development of a Simulation Model for Solid Objects Suspended in a Fluctuating Fluid

We introduce a new scheme for the future application of Real-coded Lattice Gas (RLG) to the numerical simulation of suspended solid objects in a fluctuating fluid environment. The reproduction of Brownian motion for a single solid object is verified through the Gaussian distribution of its displacements. The effectiveness of the solid–solid interaction model is also confirmed in an N-body simulation.

On preshaped reference inputs to reduce swing of suspended objects transported with robot manipulators

One of the application areas of robot manipulators is pick-and-place operations where some objects may not be grasped by robot manipulators due to the task constraints. Such objects, for example those simply suspended, need to be carried by a hook or a similar device attached to the manipulator endpoint. This paper presents the results and implications of a study into preshaped reference inputs to reduce the swing of suspended objects at the end of a desired trajectory. Two reference input preshaping methods are considered; (i) superimposing a ramp function onto another function, and (ii) convolving a sequence of impulses with a desired reference input to generate a shaped input. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while superimposing a ramp function onto another function such as a cycloid does not increase the transportation time while reducing the swing, whereas the latter, convolving a sequence of impulses with a cycloid, increases the transportation time. In addition to this, the robustness of the first method to the uncertainties in the natural frequency of the suspended object is better than that of the second method. The simulation and experimental results prove that by properly preshaping the reference input of a robot manipulator, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

Hearing shape.

In 4 experiments, participants listened to suspended occluded objects set into vibration by a pendular hammer. In Experiment 1, participants provided analogue measures of the heights and widths of 3 rectangular steel plates equal in area and weight. The same report method and rectangular dimensions were used in Experiment 2 with 3 plates each of steel, wood, and Plexiglas. Heights and widths were distinguished and perceived in similar proportions to the actual dimensions regardless of material composition. In Experiments 3 and 4, participants successfully identified circular, triangular, and rectangular plates of a single material (Experiment 3) and of 3 different materials (Experiment 4). Discussion focuses on the dependency of perceived dimensions on the physical properties and linear dimensions of the plates and the acoustic structure determined by the solutions to the 2-dimensional wave equation.

Swing-free transportation of suspended objects with robot manipulators

This paper addresses the swing-free transport of simply suspended objects which cannot be grasped by robot manipulators, and therefore, must be carried by a hook or a similar device attached to the manipulator endpoint. Two methods are presented to stop the suspended object in a swing-free state at the end of a move/gross motion; (1) limiting transportation time, thus stopping the manipulator at the instant when the object completes one or more full cycle(s), and (2) adjusting traveling time of each section of a three-piece continuous trajectory provided that a given transportation time is unchanged. A hydraulically actuated robot manipulator carrying a compound pendulum was employed as an experimental system to test the methods. Simulation and experimental results are presented to demonstrate the feasibility of both methods. It is concluded that while limiting transportation time is not a preferred way to eliminate swing at the end of the move as it depends on the period of oscillation of the suspended object, the latter is a more practical and applicable method and is valid for moves of any length. The results reveal that by properly planning the acceleration of the transporting device, a robot manipulator or a similar device such as a crane, a swing-free stop is obtainable. The proposed approaches are simple and easy to implement.

Electromagnetic suspension: new results using neural networks

Due to nonlinear magnet characteristics, controllers for magnetically suspended vehicles are usually designed by using linear small perturbation models. This assumption of linearity poses serious constraints on the operating range (allowable airgap) of the suspended objects. A brief account of using neural network (NN) concepts in the formulation of the nonlinear airgap-force characteristics of an experimental electromagnetic suspension system is presented. The main advantage of using the NN is the designer's ability to identify the magnet-force characterstics through experimental data (learning). >

A numerical method for suspension flow

Peskin's (J. Comput. Phys.25, 220, 1977) immersed boundary technique is modified to give a new numerical method for studying a fluid with suspended elastic particles. As before, the presence of the suspended particles is transmitted to the fluid through a force density term in the fluid equations. As a result, one set of equations holds in the entire computational domain, eliminating the need to apply boundary conditions on the surface of suspended objects. The new method computes the force density by discretizing the stress-strain constitutive equations for an elastic solid on a grid, using data provided by clusters of Lagrangian points. This approach clearly specifies the material properties of the suspended objects. A simple data structure for the Lagrangian points makes it easy to model suspended solids with arbitrary shape and size. The method is validated by comparing numerical results for elastic vibrations and particle settling in viscous fluids, with theory and analysis. The capability of the method to do a wide range of problems is illustrated by qualitative results for lubrication and cavity flow problems.

レガ族の知恵の紐

Among the Lega, who occupy a vast forest area in the eastern part of Zaïre, we sometimes find a cord suspended in the meeting house of a village. On that cord (mutánga in Lega), such trifle things as a leaf, a charcoal, teeth of a dog, a feather of a cock, miniatures of an ax, a stick, etc. are fastened. We may take them for mere rubbish, but in reality each of them corresponds to a proverb. For example, teeth of a dog are tied to that cord to show the proverb saying “the teeth of a dog shine, but they eat dirty things”. Indeed, a man can not be judged by externals; an amiable person may be black-hearted.The author, during his stay in Hombo-Otobora area in North and South Kivu Regions in 1989, had opportunities to study this visual way of showing proverbs. The population among whom he made research is called Balega-Bakano. They are said to be of Bahavu origin, seem to speek a genuine Lega, though many of them are bilingual with Tembo.Analysing the mutánga which an informant made for the author, a total of 48 proverbs are described in this paper. Of the suspended objects, about 70% are natural and the rest are manufactured.In analysis, we realize how carefully the Lega observe the things, natural or artificial, around them. They see into the nature of a thing, and express it in a proverb by alluding to human affaires.The Lega can be characterized as a “proverb people”, who assert that one can not speak without knowledge of the proverb. In that point, mutánga which “strings proverbs”, should be an essence of the Lega spiritual world.

Wideband monopulse sonar performance: cylindrical target simulation using an acoustic scattering center model

A time-domain simulation that lends itself to the study of complex ocean environments, including complex seafloor shapes and suspended objects, has been developed. This simulation is used to study the response of a monopulse sonar to the presence of rigid cylinders near the seafloor. An acoustic-scattering-center model is developed to represent the cylinders, and several examples are presented and discussed.

Swing-free transport of suspended objects: a general treatment

It is shown that there is a family of control strategies that result in swing-free movement of objects suspended from a movable point (e.g. a bridge crane). While it is possible to control the swing with acceleration periods of arbitrary length, it is necessary in that case to know the period of the suspended object, which requires knowledge of the location of the object's center of mass. In a practical application of this result, the best strategy is to build a sensing system into the bridge and crane hook that allows the crane to recognize when the hook is directly below its support point. The control strategy is then to accelerate for one full period, which is recognized when the hook returns to the point directly below its support point. If the bridge continues to move at this velocity, the suspended object will not swing. To stop in a swing-free state, the crane begins to decelerate at the same rate as it accelerated, starting at a distance from its goal equal to the distance traveled while accelerating.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>