Spatial Algorithms for Geometric Contact Detection in Multibody System Dynamics

In the present work, different algorithms for contact detection in multibody systems based on smooth contact modelling approaches are presented. Beginning with the simplest ones, some difficult interactions are subsequently introduced. In addition, a brief overview on the different kinds of contact/impact modelling is provided and an underlining of the advantages and the drawbacks of each of them is determined. Finally, some practical examples of each interaction are presented and analyzed and an outline of the issues arisen during the design process and how they have been solved in order to obtain stable and accurate results is given. The main goal of this paper is to provide a resource for the early-stage researchers in the field that serves as an introduction to the modelling of simple contact/impact events in the context of multibody system dynamics.

A Simple Contact Mechanics Model for Highly Strained Aqueous Surface Gels

Background Soft, biological, and bio-inspired materials are often compositionally heterogeneous and structurally anisotropic, and they frequently feature graded or layered organizations. This design complexity enables exceptional ranges in properties and performance yet complicates a fundamental understanding of the contact mechanics. Recent studies of soft gel layers have relied on Hertzian or Winkler foundation (“bed-of-springs”) models to characterize the mechanics but have found neither satisfactory. Objective The contact mechanics of soft gel layers are not yet fully understood. The aim of this work is to develop a simple contact mechanics model tailored for compositionally-graded materials with soft surface layers under high strains and deformations. Methods Concepts from polymer physics, fluid draining, and Winkler foundation mechanics are combined to develop a simple contact mechanics model which relates the applied normal force to the probe radius of curvature, elastic modulus, and thickness of soft surface layers subjected to high strains. Results This simple model was evaluated with two examples of graded surface gel layers spanning multiple length-scales, including commercially available contact lenses and stratified hydrogels. The model captures the nonlinear contact mechanics of highly strained soft aqueous gel layers more closely than either Hertz or Winkler foundation theory while simultaneously enabling a prediction for the thickness of the surface gel layer. Conclusion These results indicate that this simple model can adequately characterize the contact mechanics of highly strained soft aqueous gel layers.

Recruitment to Elective Cults: Network Structure and Ecology

During the first and second centuries of the Common Era the Christ cult spread from rural Palestine to the large cities of the Empire. This article draws insights from social network theory and from epidemiology, arguing that the Christ cult was not a simple contagion, spread by simple contact, but a ‘complex contagion’ that required persuasion, especially because adherence to the Christ cult entailed potential social costs and demanded high signalling costs.

Simple Contact Stiffness Model Validation for Tie Bolt Rotor Design With Butt Joints and Pilot Fits

Tie bolt rotors for centrifugal compressors comprise multiple shaft components that are held together by a single tie bolt. The axial connections of these rotors—including butt joints, Hirth couplings, and Curvic couplings—exhibit a contact stiffness effect, which tends to lower the shaft bending frequencies compared to geometrically identical monolithic shafts. If not accounted for in the design stage, shaft bending critical speed margins can be compromised after a rotor is built. A previous paper had investigated the effect of tie bolt force on the bending stiffness of stacked rotor assemblies with butt joint interfaces, both with and without pilot fits. This previous work derived an empirical contact stiffness model and developed a practical finite element modeling approach for simulating the axial contact surfaces, which was validated by predicting natural frequencies for several test rotor configurations. The present work built on these previous results by implementing the same contact stiffness modeling approach on a real tie bolt rotor system designed for a high pressure centrifugal compressor application. Each joint location included two axial contact faces, with contact pressures up to five times higher than previously modeled, and a locating pilot fit. The free-free natural frequencies for different amounts of tie bolt preload force were measured, and the frequencies exhibited the expected stiffening behavior with increasing preload. However, a discontinuity in the data trend indicated a step-change increase in the contact stiffness. It was shown that this was likely due to one or more of the contact faces becoming fully engaged only after sufficient tie bolt force was applied. Finally, a design calculation was presented that can be used to estimate whether contact stiffness effects may be ignored, which could simplify rotor analyses if adequate contact pressure is used.

Dog: A Friendly Pathway to Zoonoses

Canis lupus familaris (Dog); a companion animal or even considered man’s best friend is believed to have been living in harmony with humans since thousands of years. Recent discovery in Chauvet cave in France: foot print of 8-year-old boy alongside the paw print is believed to have been dated back to Paleolithic period. Reports even suggest that pet owners are less prone to high cholesterol and high blood pressure than the non-pet owners. However, dogs are also the major reservoir of various zoonotic infections. Several bacterial, viral or protozoal diseases that occur in human are transmitted from the dogs. Such diseases are known as zoonotic diseases. These diseases can be transmitted by simple contact with the infected dogs or by infected urine or feces, saliva or aerosols. Viral infections such as rabies and noro virus, bacterial infection such as pasteurellosis, salmonellosis, campylobacteriosis, leptospirosis and Methicillin-Resistant Staphylococcus aureus (MRSA) infections and protozoal infections like ancylostomiasis, toxocariasis and Dipylidium caninum infection are the most common zoonotic infections. This paper focuses on these diseases including information on signs and symptoms, mode of transmission and prevention of these diseases. As much as these infections are concerned, knowledge boosting of the pet owners regarding zoonotic disease along with proper hygiene and good sanitation practices could considerably decline the rate of zoonoses transmission and consequences.

Correction: Yamamuro et al. Power Generation in Slope-Type Thin-Film Thermoelectric Generators by the Simple Contact of a Heat Source. Coatings 2019, 9, 63

In the original version of article [...]

Can Rust Spread Through Temporary Contact?

Background: Despite the process of rusting being well known, it was uncertain whether rust was contagious or not through temporary contact that is, involving no permanent bonding. Objective: The study investigated whether rust could be transmitted through temporary contact using controls. Methods: Eight rusted steel wool rolls, each less than 3.50 g were staggeringly arranged in groups of four onto two non-rusted steel plates, each measuring 400 x 200 mm, with control cells in between. After 10 days, rust stains formed on the plates and the rolls were removed. The conspicuous stains were monitored every month by means of manual tracing. After six monthly observations, the first month tracings were superimposed onto each respective plate. Results: Although intrinsic rust had formed on the control and experimental cells, the original stains remained constant in shape and size. Conclusion: Rust is probably not transmitted to other metals by simple contact

Simple Contact Stiffness Model Validation for Tie Bolt Rotor Design With Butt Joints and Pilot Fits

Tie bolt rotors for centrifugal compressors comprise multiple shaft components that are held together by a single tie bolt. The axial connections of these rotors — including butt joints, Hirth couplings, and Curvic couplings — exhibit a contact stiffness effect, which tends to lower the shaft bending frequencies compared to geometrically identical monolithic shafts. If not accounted for in the design stage, shaft bending critical speed margins can be compromised after a rotor is built. A previous paper had investigated the effect of tie bolt force on the bending stiffness of stacked rotor assemblies with butt joint interfaces, both with and without pilot fits. This previous work derived an empirical contact stiffness model and developed a practical finite element modeling approach for simulating the axial contact surfaces, which was validated by predicting natural frequencies for several test rotor configurations. The present work built on these previous results by implementing the same contact stiffness modeling approach on a real tie bolt rotor system designed for a high pressure centrifugal compressor application. Each joint location included two axial contact faces, with contact pressures up to five times higher than previously modeled, and a locating pilot fit. The free-free natural frequencies for different amounts of tie bolt preload force were measured, and the frequencies exhibited the expected stiffening behavior with increasing preload. However, a discontinuity in the data trend indicated a step-change increase in the contact stiffness. It was shown that this was likely due to one or more of the contact faces becoming fully engaged only after sufficient tie bolt force was applied. Finally, a design calculation was presented that can be used to estimate whether contact stiffness effects may be ignored, which could simplify rotor analyses if adequate contact pressure is used.