Physical Assemblies Research Articles

Physical and numerical investigation of a cemented granular assembly of steel spheres

AbstractIn this paper, steel spheres embedded in a cement matrix were studied using numerical and physical ISRM testing procedures. A challenge in discrete element simulations is to select appropriate micro‐mechanical models and parameters, to recover the observed macro‐mechanical behavior. An ideal experiment on cohesive granular assemblies constructed identical to numerical ones would validate these micro models for a set of measured micro‐parameters. The first part of the paper summarizes the previous studies in this area, outlines such experimental methodology and depicts the steps followed for the preparation and the testing of cemented granular assemblies together with the derivation of micro‐parameters. The second part discusses the results of numerical and physical ISRM standard tests including uniaxial and triaxial compression, Brazilian tensile and shear box tests. Physical samples were prepared using steel balls bonded with Portland cement, cured under controlled laboratory conditions and tested in compression, tension and shearing. Acoustic emissions were monitored in uniaxial tests to characterize the damage thresholds relative to volumetric strains. Numerical simulations were conducted with PFC 3D using micro‐mechanical parameters derived from physical testing. Parametric sensitivity studies were carried out to look into the dependency of macroscopic responses on the parameters. The results from both numerical and physical tests showed good correspondence in macroscopic behavior i.e. peak strength, stages of damage, mode of failures. However, the numerical simulations reflected a stiffer mechanical response than physical assemblies. Copyright © 2010 John Wiley & Sons, Ltd.

An Integrated Physical, Genetic and Cytogenetic Map of Brachypodium distachyon, a Model System for Grass Research

The pooid subfamily of grasses includes some of the most important crop, forage and turf species, such as wheat, barley and Lolium. Developing genomic resources, such as whole-genome physical maps, for analysing the large and complex genomes of these crops and for facilitating biological research in grasses is an important goal in plant biology. We describe a bacterial artificial chromosome (BAC)-based physical map of the wild pooid grass Brachypodium distachyon and integrate this with whole genome shotgun sequence (WGS) assemblies using BAC end sequences (BES). The resulting physical map contains 26 contigs spanning the 272 Mb genome. BES from the physical map were also used to integrate a genetic map. This provides an independent vaildation and confirmation of the published WGS assembly. Mapped BACs were used in Fluorescence In Situ Hybridisation (FISH) experiments to align the integrated physical map and sequence assemblies to chromosomes with high resolution. The physical, genetic and cytogenetic maps, integrated with whole genome shotgun sequence assemblies, enhance the accuracy and durability of this important genome sequence and will directly facilitate gene isolation.

The impact of poor assembly ergonomics on product quality: A cost–benefit analysis in car manufacturing

AbstractThe study aimed at analyzing the relationship between assembly ergonomics, assemblability (“ease of assembly”), and product quality and at quantifying these relationships in economic terms. This was in order to better to support the development of more ergonomic product and assembly solutions, particularly at early stages of the car development process. The assembly of 24,443 cars was studied for 8 weeks in an assembly plant and for another 16 weeks as factory‐complete vehicles. The results show increased risks for quality errors of 3.0 and 3.7 times and total action costs that were 8.7 times and 8.2 times higher for high and medium physical load assemblies compared to low physical load assemblies for 55 tasks assessed. © 2009 Wiley Periodicals, Inc.

An in situ calibration for hearing thresholds

Quantifying how the sound delivered to the ear canal relates to hearing threshold has historically relied on acoustic calibration in physical assemblies with an input impedance intended to match the human ear (e.g., a Zwislocki coupler). The variation in the input impedance of the human ear makes such a method of calibration questionable. It is preferable to calibrate the acoustic signal in each ear individually. By using a calibrated sound source and microphone, the acoustic input impedance of the ear can be determined, and the sound delivered to the ear calibrated in terms of either (i) the incident sound pressure wave or (ii) that portion of the incident sound pressure wave transmitted to the middle ear and cochlea. Hearing thresholds expressed in terms of these quantities are reported, these in situ calibrations not being confounded by ear canal standing waves. Either would serve as a suitable replacement for the current practice of hearing thresholds expressed in terms of sound pressure level calibrated in a 6cc or 2cc coupler.

Using genetic algorithms to characterize ferrofluid topographies in externally applied magnetic fields

Both ferrofluidics and genetic algorithms are relatively new fields. Due to complex physical interactions, ferrofluidic topographies and assemblies have only been solved using finite time step, Lattice Boltzmann, and finite-element methods in very simple magnetic field configurations. In this paper, we show that it is possible (and highly advantageous) to employ genetic algorithms to solve for the fluid topographies, which can be extended to include more complex magnetic fields.

On the Use of UML for Modeling Mechatronic Systems

This paper describes a modeling language that aims to provide a unified framework for representing control systems, namely, physical plants coupled with computer-based control devices. The proposed modeling methodology is based on the cardinal principle of object orientation, which allows describing both control software and physical components using the same basic concepts, particularly those of capsules, ports, and protocols. Furthermore, it is illustrated how the well-known object-oriented specification language unified modeling language can be adopted, provided an adequate formalization of its semantics, to describe structural and behavioral aspects of control systems, related to both logical and physical parts. Note to Practitioners-The development of an automated system within an industrial setting is a complex task, whose successful result depends on the joint efforts of a team of designers with different scientific backgrounds and specialized knowledge. In fact, an automated system is typically composed of a mechanical assembly, which must be precisely designed and manufactured, and a set of sensors and actuators (e.g., electrical drives, pneumatic systems, etc.), which are, on their turn, controlled most of the time by means of digital processors. Of course, both electrical parts and control algorithms (e.g., proportional, integral, and derivative (PID) regulators, logic and supervisory control, reference trajectories for mechanical motions, etc.) should be designed with the same care given to mechanical aspects. Moreover, it is undeniable that none of the various parts composing the automated system design specification can, on their own, allow engineers to understand the actual behavior of the whole system, especially without a common description language that is understandable for all of the designers. The present paper introduces a unified language which aims to support integrated design specifications of automated systems, including the dynamics of heterogeneous physical assemblies, the discrete-event behavior of distributed control software, and the specification of interface ports between the plant and the control system. With the proposed language, it is possible to obtain a complete picture of the automated system suitable for its simulation, documentation, and validation. The modeling language described in the paper supports the principles of object orientation. This choice moves in the direction of enhancing modularity and reusability properties of design specifications, which are aspects of great importance in the design practice. Moreover, the object-oriented approach to automated systems design proposed in the paper aims to introduce the concept of "design by extension" in the manufacturing industry. This means that the definition of specialization relationships between classes of components implies that those components should be designed in order to be substitutable with each other, especially from a dynamic point of view. This aspect will be the subject of further papers illustrating other practical insights on the use of object-oriented models for automated systems

Physical map-assisted whole-genome shotgun sequence assemblies.

We describe a targeted approach to improve the contiguity of whole-genome shotgun sequence (WGS) assemblies at run-time, using information from Bacterial Artificial Chromosome (BAC)-based physical maps. Clone sizes and overlaps derived from clone fingerprints are used for the calculation of length constraints between any two BAC neighbors sharing 40% of their size. These constraints are used to promote the linkage and guide the arrangement of sequence contigs within a sequence scaffold at the layout phase of WGS assemblies. This process is facilitated by FASSI, a stand-alone application that calculates BAC end and BAC overlap length constraints from clone fingerprint map contigs created by the FPC package. FASSI is designed to work with the assembly tool PCAP, but its output can be formatted to work with other WGS assembly algorithms able to use length constraints for individual clones. The FASSI method is simple to implement, potentially cost-effective, and has resulted in the increase of scaffold contiguity for both the Drosophila melanogaster and Cryptococcus gattii genomes when compared to a control assembly without map-derived constraints. A 6.5-fold coverage draft DNA sequence of the Pan troglodytes (chimpanzee) genome was assembled using map-derived constraints and resulted in a 26.1% increase in scaffold contiguity.

PSE: An Object-Oriented Representation for Modeling and Managing Part-of Relationships

Part-of relationships are needed to model structures of composite objects. Especially, composite objects, known as physical assemblies, are very popular in several applications. The existing object-oriented representations of physical assemblies and query languages based on them have several disadvantages. For example, they suppose that the user knows the structure of a physical assembly completely. This is not a realistic requirement in those cases where a physical assembly consists of a huge number of parts. Likewise the user has in them to control traversals of physical assemblies, i.e. they have a low degree of declarativity. Further, they do not support intensional and combined extensional-intensional queries which would be necessary in an advanced manipulation of physical assemblies. We develop the PSE (Part-of Structure Element) representation for removing the above disadvantages. The PSE representation is a set theoretical and constructor-oriented representation for physical assemblies and it can be used in the implementation based on both the object-oriented and deductive object-oriented database (DOOD) paradigms.

Advanced query language for manipulating complex entities

Complex entities are one of the most popular ways to model relationships among data. Especially complex entities, known as physical assemblies, are popular in several applications. Typically, complex entities consist of several parts organized at many nested levels. Contemporary query languages intended for manipulating complex entities support only extensional queries. Likewise, the user has to master the structures of complex entities completely, which is impossible if a physical assembly consists of a huge number of parts. Further, query languages do not support the manipulation of documents related to parts of physical assemblies. In this paper we introduce a novel, declarative and powerful query language, in which the above deficiencies have been eliminated. Our query language supports text information retrieval related to parts and it contains intensional and combined extensional–intensional query features. These features support making queries of new types. In the paper we give several sample queries, which demonstrate the usefulness of these query types. In addition, we show that conventional extensional queries can be formulated intuitively and compactly in our query language. Among other things this is due to our query primitives allowing removal of the explicit specification of navigation from the user.

Modeling Nonspherical Particles Using Multisphere Discrete Elements

In this paper axisymmetrical particles are modeled as multisphere discrete elements using a method in which particles are represented by overlapping spheres, fixed rigidly with respect to a local coordinate system. Contact detection is sphere-based and the resultant forces are transformed to the particle centroid to calculate the particle motion using standard discrete element method conventions. The multisphere method was used to model discharge of ellipse-shaped particles through an orifice in a flat-bottomed hopper and the simulations compared with physical experiments at the same scale. There was good agreement between the flow behavior of the simulated and physical particle assemblies for all orifice sizes. The rate of discharge and the vertical velocity profiles in the region of converging flow determined for the simulated and physical flows were in close agreement for flow from the larger orifices. A similar relationship between frequency of arch formation, particle mean diameter, and orifice diameter as for spheres was observed.

Bridge over troubled water: the apparent discrepancy between simulated and experimental non-ambient water structure

Recent neutron diffraction experiments, which exploit hydrogen isotope substitution techniques to extract the HH, OH and OO site - site radial distribution functions for water, indicate that as the temperature of water is raised above the critical point, the hydrogen-bonding network, as measured by the height of the first peak in the OH distribution function, collapses. Several computer simulations, however, dispute the accuracy of the experimentally determined distribution functions: they show that the measured data cannot be obtained from any physical arrangement of water molecules. By applying additional constraints on the small-radius behaviour of the radial distribution functions, and by repeating some of the experiments under different experimental conditions, the accuracy of the extracted radial distribution functions has now been improved. The new distribution functions, while not qualitatively different from what has already been published, satisfy the fundamental objection to the previous results, namely they can be simulated with physical assemblies of water molecules. These simulated distributions of molecules indicate a weak degree of hydrogen bonding in water at 673 K which is greatly reduced compared to that in the hydrogen-bond network of ambient water. The analysis is supported by a new computer simulation of water structure using an `empirical' water interaction potential, which contains none of the long-range features of traditional charge models, such as SPC/E. This short-range potential is able to reproduce most features of the experimental data to good accuracy, even under supercritical conditions.

The number of configurations in an assembly and cooperative phenomena

We consider an ideal problem of adsorption of single and double particles upon a solid surface which has its sites of accommodation regularly arranged, and by comparing the equilibrium properties obtained by Bethe's method with the ordinary statistical formulae, we obtain approximate expressions for:(1) g(N, n, X), the number of ways of arranging n particles upon N sites of a lattice so that the number of neighbouring sites occupied by the particles is X.(2) g2(N, n, X), the number of ways of arranging n double particles upon N sites so that each of the double particles takes up two adjacent sites and the number of neighbouring sites occupied by two different particles is X.Both these expressions are found to agree with the exact values when the N sites lie on a straight line. When we use the first expression to construct the configurational partition functions of certain physical assemblies and expand them in powers of 1/kT, they are found to agree with the corresponding rigorous expressions as far as (1/kT)3, which is the highest power which we can find rigorously at present. With the help of the first expression, formal equations for superlattice formation in an alloy with the composition 1: 1 and equations for the separation into phases of regular liquids are given. Lastly we show that atoms and molecules in a regular liquid may dissociate or recombine suddenly accompanied by a latent heat. This is a new cooperative phenomenon, which may bear some resemblance to the melting process between the solid and liquid states.