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Safety is an important issue when manipulators operate in an environment where humans are present, such as the agriculture industry. An intrinsically safe mechanical system guarantees human safety when electronics or controls fail. However, industry also demands a certain operating velocity. A low inertia is the most important aspect to combine safety with a useful operating velocity, because this will limit the amount of kinetic or potential energy in the system and the required actuation forces. Low‐actuation forces limit the amount of static contact pressure between manipulator and human, a requirement for intrinsic safety. Low energy means that less contact force is required to put the manipulator to a stop in collision, an additional requirement. The goal of this paper is to find the maximum industrially applicable, manipulator mass for which intrinsic mechanical safety is guaranteed.

Observing existing and proposed manipulators in agriculture results in a required cycle time of 0.9 s, trajectory of 0.8 m and payload of 2 kg. Three important trade‐offs applying to the manipulator are identified. The first is between maximum velocity and acceleration, using cycle time and trajectory. The second is between maximum acceleration and mass, based on a measure for pain in contact pressure. The third is between maximum velocity and mass, using a collision model and the contact pressure during collision.

Combining all three trade‐offs results in an allowable arm effective inertia of 5.1 kg. Taking payload into account and converting to a realistic mass distribution results in a total mass of 9.3 kg. Compared to existing manipulators, both mass and payload are ambitious but realistic for the future development of an intrinsically safe manipulator.

Accuracy in positioning is not taken into account.

This paper combines safety criteria on maximum energy and maximum static pressure, while also taking industrial applicable operating velocity into account.

The purpose is to present a new approach for studying the phenomenon of traveling bubble cavitation.

A flow around a rigid, 2D hydrofoil (NACA‐0012) with a smooth surface is analyzed computationally. The Rayleigh‐Plesset equation is numerically integrated to simulate the growth and collapse of a cavitation bubble moving in a varying pressure field. The analysis is performed for both incompressible and compressible fluid cases. Considering the initial bubble radius as a uniformly distributed random variable, the probability density function of the maximum collapse pressure is determined.

The significance of the liquid compressibility during bubble collapse is illustrated. Furthermore, it is shown that the initial size of the bubble has a significant effect on the maximum pressure generated during the bubble collapse. The maximum local pressure developed during cavitation bubble collapse is of the order of 10⁴ atm.

A single bubble model that does not account for the effect of neighboring bubbles is used in this analysis. A spherical bubble is assumed.

A new approach has been developed to simulate traveling bubble cavitation by interfacing a CFD solver for simulating a flow with a program simulating the growth and collapse of the bubble. Probabilistic analysis of the local pressure due to bubble collapse has been performed.

THE compression‐ignition aircraft engine has arrived in practical form, but the question whether it has come to stay, or rather, whether it will completely displace the petrol engine in course of time, is one on which opinion is much divided. The object of this article is to explore the question from a theoretical point of view.

This study aims to propose a series of numerical and surrogate models to investigate the aerodynamic pressure inside cracks in high-speed railway tunnel linings and to predict the stress intensity factors (SIFs) at the crack tip.

A computational fluid dynamics (CFD) model is used to calculate the aerodynamic pressure exerted on two cracked surfaces. The simulation uses the viscous unsteady κ-ε turbulence model. Using this CFD model, the spatial and temporal distribution of aerodynamic pressure inside longitudinal, oblique and circumferential cracks are analyzed. The mechanism behind the pressure variation in tunnel lining cracks is revealed by the air density field. Furthermore, a response surface model (RSM) is proposed to predict the maximum SIF at the crack tip of circumferential cracks and analyze its influential parameters.

The initial compression wave amplifies and oscillates in cracks in tunnel linings, resulting from an increase in air density at the crack front. The maximum pressure in the circumferential crack is 2.27 and 1.76 times higher than that in the longitudinal and oblique cracks, respectively. The RSM accurately predicts the SIF at the crack tip of circumferential cracks. The SIF at the crack tip is most affected by variations in train velocities, followed by the depth and length of the cracks.

The mechanism behind the variation of aerodynamic pressure in tunnel lining cracks is revealed. In addition, a reliable surrogate model is proposed to predict the mechanical response of the crack tip under aerodynamic pressures.

This paper aims to investigate the mechanism of spur gears running-in and to solve the lubrication problems of teeth running-in.

The elastohydrodynamic lubrication (EHL) model considering solid particles was established by applying multi-grid and multiple-grid integration methods to the numerical solution.

In the region where debris settle, transient pressure increases sharply, and a noticeable increase in the running-in load causes a remarkable increase in both the centre and maximum pressures and a slight increase in the minimum film thickness. Roughness wavelength makes a considerable difference to the minimum film thickness at double-to-single tooth transient. A considerable increase in rotation velocity can cause a remarkable reduction in both the centre and maximum pressures but an amazing increase in the minimum film thickness. The effects of roughness amplitude on the maximum pressure are considerably distinct.

Research on EHL of spur gears in the running-in process considering solid particles, surface roughness and time-variant effect is meaningful to practical gears running-in. Thermal effect can be included in the next study.

The analysis results can be applied to predict and improve lubrication performance of the meshing teeth.

The aim is to reduce gears’ manufacture and running-in costs and improve economic performance.

The EHL model that considers solid particles was established. The Reynolds equation was deduced taking the effects of solid particles into account. The EHL of spur gears running-in was investigated considering the time-variant effect, surface roughness, running-in load and rotation speed.

The aim of this paper is to study the effect of deterministic roughness and small elastic deformation of surface on flow rates, load capacity and coefficient of friction in Rayleigh step bearing under thin film lubrication.

Reynolds equation, pressure-density relationship, pressure-viscosity relationship and film thickness equation are discretized using finite difference method. Progressive mesh densification (PMD) method is applied to solve the related equations iteratively.

The nature and shape of roughness play a significant role in pressure generation. It has been observed that square roughness dominates the pressure generation for all values of minimum film thickness. Deformation more than 100 nm in bounding surfaces influences the film formation and pressure distribution greatly. Divergent shapes of film thickness in step zone causes a delay of pressure growth and reduces the load capacity with decreasing film thickness. The optimum value of film thickness ratio and step ratios have been found out for the maximum load capacity and minimum coefficient of friction, which are notably influenced by elastic deformation of the surface.

It is expected that these findings will help in analysing the performance parameters of a Rayleigh step bearing under thin film lubrication more accurately. It will also help the designers, researchers and manufacturers of bearings.

Most of the previous studies have been limited to sinusoidal roughness and thick film lubrication in Rayleigh step bearing. Effect of small surface deformation due to generated pressure in thin film lubrication is significant, as it influences the performance parameters of the bearing. Different wave forms such as triangular, sawtooth, sinusoidal and square formed during finishing operations behaves differently in pressure generation. The analysis of combined effect of roughness and small surface deformation has been performed under thin film lubrication for Rayleigh step bearing using PMD as improved methods for direct iterative approach.

This study aims to investigate the effects of single dent on the film thickness and pressure in elastohydrodynamically lubricated (EHL) point contacts by numerical analysis.

The governing equations of single dent were established and then the variations of the film thickness and pressure induced by the applied load, the entrainment velocity and the ball radius were investigated. Meanwhile, the film thickness and pressure under smooth and dented surfaces were compared with each other.

The dent enhances both the maximum pressure and the second pressure peak. The minimum film thickness arises before the dent under certain conditions. In the meantime, the pressure decreases at the inside of the dent and the film thickness is just the reverse. The entrainment velocity remarkably affects the overall film thickness, whereas the rest of the input parameters mainly decides the details of the film curve. All input parameters remarkably affect the overall pressure, especially the maximum pressure.

This work is helpful to understanding the effect of the single dent on the lubricating properties of EHL point contacts.

The purpose of this paper is to understand a flameproof distance necessary to avoid the flame harms to underground personnel which may have great significance to the safety of underground personnel and the disaster relief of gas explosions in coal mines.

Through a roadway with a length of 100 m and a cross-section area of 80 mm×80 mm, the flame propagation of premixed methane-air deflagrations were simulated by using AutoReaGas software for various fuel concentrations (7, 8, 9.5, 11, and 14 percent), fuel volumes (0.0128, 0.0384, 0.064, and 0.0896 m3), initial temperatures (248, 268, 288, 308, and 328 K), and initial pressures (20, 60, 101.3, 150, and 200 kPa).

The maximum combustion rate for each point follows a changing trend of increasing and decreasing with the distance increasing from the ignition source, and it increases with the fuel volume increasing or the initial pressure increasing, and decreases with the initial temperature increasing. However, increasing the initial temperature increases the flame arrival time for each point. The flameproof distance follows a changing trend of increasing and decreasing with the fuel concentration increasing, and it linearly increases with the fuel volume increasing or the initial temperature increasing. However, the flameproof distances are all 17 m for various initial pressures.

Increasing initial temperature increases flame arrival time for each test point. Flameproof distance increases and then decreases with fuel concentration increasing. Increasing fuel volume or initial temperature linearly increases flameproof distance. Initial pressure has little impact on the flameproof distance.

The purpose of this paper is to understand the lubricating properties of the tripod sliding universal joint (TSUJ) in order to overcome its premature failures caused by the poor lubricating regime.

A simplified geometrical model is derived from the main mating surfaces redesigned, and then the effects of the applied load and reduced elastic modulus, as well as the lubricant viscosity on the pressure and film thickness, are theoretically studied by using multi‐level methods.

The obtained results show that increasing applied load increases the overall pressure distribution and decreases the overall film thickness. Higher viscosity results in a thicker oil film and a remarkable second pressure peak even exceeding the central pressure. High‐reduced elastic modulus increases the overall pressure but hardly influences on the film thickness.

Numerical analysis on the lubricating properties of TSUJ has been carried out on the basis of the simplified geometrical model. However, there are other factors affecting the lubricating performance such as temperature and surface roughness and so on. Besides, the corresponding experimental investigation should be conducted in the succeeding work.

This work is a new application of elastohydrodynamic lubrication in practical viewpoint and provide a new direction in designing futuristic tripod universal joints. Thus, the results are of great value for its design and application.

Analyses were performed during the conceptual design stage of a 20in. threaded connector for deep water J‐pipe lay, as part of a research project developed by Tecnomare and partly funded by the EEC. The joint consists of two parts, namely a pin and a box, provided with cylindrical threads. It was essential for the joint design to be fully leak‐proof for both internal and external pressure and this requirement had to be satisfied also under the maximum bending moment allowable for the sealine. Sealing was accomplished on a cone surface by screwing the pin into the box until yield was reached. The FEM analysis was carried out primarily to check that the pin and box remain pressed to one another over the sealing surface in every design condition with adequate pressure to prevent leakage. For this purpose, the analysis was a powerful design technique, as it gave an easy understanding of the structural behaviour and provided proper stiffness by making the joint either larger or thinner wherever required. The main characteristic of this work is that FEM analysis has been utilized as a design method rather than as a check. The analysis was performed by means of ADINA (Automatic Dynamic Incremental Non‐linear Analysis) program. Contact pressure between sealing surfaces, as achieved during the joint screwing phase, was modelled through thermal elongation. Pressure loads and external forces were superimposed through a step‐by‐step procedure, by accounting for the elastoplastic behaviour all around the sealing surface. In order to verify the behaviour of the mechanical joint, six prototypes have been fabricated and tested under the design loads of the lay phase and the operative life. The results of the tests confirmed the correct design and the results of non‐linear finite element analysis. The most important performances of the joint can be summarized as follows: (1) the make‐up phase is rapid and easy: no problems of frictional pick‐up took place; (2) no leakage happened during the internal pressure tests: the pressure of 300atm (1.5 times the design internal pressure) was maintained for 12h; (3) the load conditions of the second series of tests were: 200atm of internal pressure and the maximum allowable bending moment relevant to the pipe: after 2h no leakage happened. This paper describes the model used for the analysis, discusses its implications and the most important results achieved in comparison with the tests of the experimental phase.