Deformation and Mechanical Properties of a Constant-Friction-Force Energy-Absorbing Bolt

The conventional bolts used in surrounding rock tunnels with large deformation often fail. As a solution to this problem, we developed an extensible bolt with energy-absorbing and constant-friction-force (EACF) characteristics. The EACF bolt mainly comprises a damping device, a hollow threaded bolt, a tightening nut, and a face plate. To reveal its working mechanism, the bolt was tested in terms of its friction, displacement, and energy absorption through a modified tensile test device in a laboratory. The static pull-out test results showed that the axial force-displacement curve of the bolt can be mainly divided into three stages: a conical extrusion stage, an elongation stage, and an elastic failure stage. The EACF bolts exhibited stable energy absorption behaviors when subjected to static loading. The maximum constant friction force could be adjusted by increasing the size and diameter of the straight section of the damping block, and the maximum elongation could be adjusted by increasing the length of the damping cylinder. When the properties of the bolt materials are kept constant, increasing the diameter of the damping block can help achieve a high constant resistance. The proposed EACF bolt has reliable deformation and energy-absorption properties, which ensure its stability when employed in tunnels under the combined action of support and surrounding rocks.

Drainage of an ice-dammed lake through a supraglacial stream: hydraulics and thermodynamics

The glacier-dammed Lac des Faverges, located on Glacier de la Plaine Morte (Swiss Alps), drained annually as a glacier lake outburst flood since 2011. In 2018, the lake volume reached more than 2 × 106 m3 and the resulting flood caused damages to the infrastructure downstream. In 2019, a supraglacial channel was dug to artificially initiate a surface lake drainage, thus limiting the lake water volume and the corresponding hazard. The peak in lake discharge was successfully reduced by over 90 % compared to 2018. We conducted extensive field measurements of the lake-channel system during the 48-days drainage event of 2019 to characterize its hydraulics and thermodynamics. The derived Darcy-Weisbach friction factor, which characterizes the water flow resistance in the channel, ranges from 0.17 to 0.48. This broad range emphasizes the factor’s variability, and questions the choice of a constant friction factor in glacio-hydrological models. For the Nusselt number, which relates the channel-wall melt to the water temperature, we show that the classic, empirical Dittus-Boelter equation with the standard coefficients is not adequately representing our measurements, and we propose a suitable pair of coefficients to fit our observations. This hints at the need to continue the research into how heat transfer at the ice/water interface is described in the context of glacial hydraulics.

Comment on “Improved pivot-slide model of the motion of a curling rock”

We point out three errors in a recent paper that is based on one of our two papers. Together our two papers describe a first-principles “pivot-slide model” of the motion of a curling rock. The most serious error is that the “improved pivot-slide model” (Mancini and de Schoulepnikoff. Can. J. Phys. 97(12), 1301 (2019) doi: 10.1139/cjp-2018-0356 ) is based on only our first paper, whereas the most important work in our model was described in our second paper, which those authors have overlooked. Another error is that the authors claim we use constant friction, whereas we actually use a velocity-dependent formulation of the ice friction coefficient. Thirdly, the authors use a time-dependent function for the ratio of pivoting time to sliding time, whereas in our second paper, we showed from first principles that this ratio does not depend on time.

ENSURING CONTINUOUS HYSTERESIS OF SPROAD ACTION VALVE SAFETY VALVES

In the article principles of construction and design of spring valve units are considered, which allow to obtain a given dynamic quality to ensure constant hysteresis of spool safety valves of direct action. The analysis of efficiency of devices of correction of dynamic quality of spring valve units for ensuring their working capacity at variation of external operating factors by purposeful management of kinematic and force parameters of elastic-damping elements, and also the reasons influencing hysteresis It is noted that one of the reasons for the increase in hysteresis is damage to the rubber seals of the spool safety valves of direct action. Identifying the main causes of damage to rubber seals: constant friction of the edge of the radial holes of the spool on the seal ring; reverse the direction of the operating pressure; the pressure drop created by the axial hole of the spool when the valve is fully open. A spool spring valve with a mechanical spring having high throughput and low hysteresis is proposed. This characteristic was achieved through the use of high quality materials, which allowed to have a high throughput with minimal dimensions; optimization of geometrical characteristics of the flowing part of the valve; reducing the seal tension and, as a consequence, reducing the hysteresis. It is noted that the absence of contact of the radial holes of the spool with the rubber seal in the extreme off position protects the seal from plastic deformation during reverse flow. The prospect of further research in obtaining experimental dependences of the influence of spool speed, rubber stiffness, geometrical characteristics of the contact gap and pressure on the change of the valve hysteresis is revealed.

PROMISING AREAS OF TECHNOLOGY FOR THE RESTORATION OF MACHINE PARTS

With prolonged use of machines, wear of parts is accompanied by a decrease in performance indicators, causing a deterioration in the quality of products. The power take-off shaft experiences significant static and dynamic loads. The high wear rate of the power take-off shaft is due to constant friction with the clutch disc, gears, and bearing inner rings. The manufacture of a new power take-off shaft requires significant costs, so the development of new technological processes for repair and restoration is urgent. A promising direction of restoration technology in the organizational plan of deepening the method of group restoration technology is the creation of unified-group equipment for surface restoration. It has been established that most of the parts of remanufactured machines are rejected due to slight wear of the working surfaces, making up no more than 1% of the initial mass of parts. As experience and practice show, on the one hand, it is technically impossible to avoid the repair of agricultural machinery, and on the other, it is economically feasible. After all, most of the worn out parts have a high residual value: during their restoration, 20-30 times less metal and materials are consumed than in the manufacture of new ones. The following problems are considered: the choice of the technological process of restoration, the choice of technological equipment, tools. Restoration of details is a technically justified, economically justified measure. This allows repair shops to reduce downtime of faulty machines, improve the quality of maintenance and repair to positively affect the reliability of the use of machines. To restore the efficiency of worn parts requires 5-8 times less technological operations compared to the manufacture of new ones [1, 2]. Restoration of parts allows you to get a considerable economic effect, as much lower consumption of metal and auxiliary materials, and the cost of the restored part is 60-80% of the cost of new ones. Therefore, to make this recovery process effective, it is necessary to introduce new processing and recovery methods, as well as to improve existing equipment. The production of a new power take-off shaft requires significant costs, and the detection of new technological processes of repair and restoration is relevant.

Implementation of a Particle Resuspension Model in a CFD Code: Application to an Air Ingress Scenario in a Vacuum Toroidal Vessel

During a loss of vacuum accident (LOVA), dust particles that will be present in the future tokamak ITER are likely to be resuspended, inducing a risk for explosion and airborne contamination. Evaluating the particle resuspension/deposition and resulting airborne concentration in case of a LOVA is therefore a major issue and it can be investigated by using a CFD code. To this end, this article presents the implementation of a resuspension model in a CFD code (ANSYS CFX) and its application to an air ingress in a vacuum toroidal vessel with a volume comparable to ITER one. In the first part of the article, the Rock’n Roll model and its operational version with the Biasi’s correlation is presented. The second part of the article will be devoted to the implementation of the Rock’n’Roll model in ANSYS CFX for constant friction velocities and its adaptation to non-constant friction velocities. Finally, the paper presents the simulations obtained on the particle resuspension for an air ingress scenario in a large vacuum vessel. This case is particularly interesting and non-intuitive because as the initial pressure is reduced, the particle behavior is different from that at atmospheric pressure. Further, a competition between airflow forces and gravitational force occurs, due to the low pressure environment, potentially restricting the resuspension, and the pressure influence also has to be taken into account in the particle transport and deposition (Nerisson, 2011). Three particle diameters were studied allowing to show the evolution of the resuspension with this parameter and to calculate dust resuspension rates and airborne fractions during the air ingress.

Energy-Based Prediction of the Displacement of DCFP Bearings

Isolation systems are currently being widely applied for earthquake resistance. During the design stage for such systems, the displacement response and input energy of the isolation layer are two of the main concerns. The prediction of these values is also of vital importance during the early stages of the structural design. In this study, the simple prediction method of double concave friction pendulum (DCFP) bearings is proposed, which can relate the response displacement of the isolation layer to the ground velocity through energy transfer with sufficient accuracy. Two friction models (the precise and simplified model) and a constant friction coefficient of double concave friction pendulum (DCFP) bearings are comprehensively validated by full-scale sinusoidal dynamic tests under various conditions. In addition, a response analysis, based on previous studies, was conducted using the friction models under selected unidirectional earthquake excitations, and the accuracy of using the simplified model in the response analysis was verified. Based on the response analysis data, this article verifies and optimizes the proposed prediction method by parameterizing the characteristics of earthquakes and combining the energy balance in order to gain a deeper understanding of the design of the isolation systems.

Topology Optimization of Acetabular Cup by Finite Element Simulation

Hip replacements typically consist of a four-part piece. Our research will focus primarily on the acetabular component. Several different types of materials can be used when creating a hip replacement implant ranging from plastic to titanium. Different materials are used to accommodate for allergic reactions or circumventing potential health risks. Aside from the material, the size of the components plays a factor in terms of durability; a larger diameter head might avoid dislodgement though it could increase wear and tear on the stems through constant friction. A patient’s force applied to the hip replacement is usually measured through a number of physical assessments. Finite element analysis (FEA), a computer-based method of data observation, allows for us to accurately simulate hip forces and their impact on the hip replacements. Through this, it becomes easier to predict and calculate the performance of specific designs. Generative systems can also be used to support performance analysis and optimization through assessing a multitude of cases, many of which apply in real-world scenarios. By applying both systems, we designed and modeled an acetabular cup that when measured decreased the mass from 129 grams initially down to 52 grams, a 60% decrease in total mass. Furthermore, the design we created lessened the trauma on the piece through distributing force across the entirety of the piece rather than specific segments only. This shows an increased durability and life expectancy when compared to usual acetabular cups.

A constant friction coefficient model for concave friction bearings

This paper develops a constant friction coefficient model that best represents a velocity-dependent friction model for predicting structural response of buildings isolated with concave friction bearings. To achieve this goal, the effect of friction model on structural response of three hypothetical isolated buildings with different number of stories subjected to different earthquake scenarios was numerically investigated. The structural numerical models of the isolated buildings were developed in OpenSees with superstructure is represented by a shear frame model and isolation system using single friction pendulum bearings is modeled by a 3-D friction pendulum bearing element which accepts different friction models. The numerical models were subjected to 30 pairs of ground motions, representing service earthquake level, design basic earthquake level and maximum considered earthquake level at a strong seismic activity area in the world. The investigation reveals that friction coefficient models significantly affect the structural response and there is no constant friction coefficient model that simultaneously best predicts isolation system response and superstructure response. The constant friction coefficient that best predicts isolation system response produces a large error on prediction of superstructure response and vice versa. Based on the numerical results, a constant friction coefficient model for different criteria was developed. Keywords: friction coefficient model; friction bearing; isolation system; earthquake response; time-history analysis.

Immund Poses: funk, photography, gender performativity and dance in the construction of the contemporary photographic portrait

As a phenomenon, funk is wider than its specificities as a musical genre. The cultural space it occupies highlights issues related to the body, gender, race and social classes as sociopolitical aspects in constant friction with elite culture and the media, which absorb it and attempt to sanitize it. If something needs to be sanitized through the erasure of social and racial traits of funk singers and dancers, it is because this condition is seen as abject - immund. This article makes use of the concept of immund to analyze the black and LGBT body within the funk universe by examining the portraits of six young men in light of theoretical reflections derived from the fields of dance, performance art and politics.