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The present work is devoted to the numerical study of the stability of shallow jet. The effects of important parameters on the stability behavior for large scale shallow jets are considered and investigated. Connections between the stability theory and observed features reported in the literature are emphasized. The paper aims to discuss these issues.

A linear stability analysis of shallow jet incorporating the effects of bottom topography, bed friction and viscosity has been carried out by using the shallow water stability equation derived from the depth averaged shallow water equations in conjunction with both Chézy and Manning resistance formulae. Effects of the following main factors on the stability of shallow water jets are examined: Rossby number, bottom friction number, Reynolds number, topographic parameters, base velocity profile and resistance model. Special attention has been paid to the Coriolis effects on the jet stability by limiting the rotation number in the range of Ro∈[0, 1.0].

It is found that the Rossby number may either amplify or attenuate the growth of the flow instability depending on the values of the topographic parameters. There is a regime where the near cancellation of Coriolis effects due to other relevant parameters influences is responsible for enhancement of stability. The instability can be suppressed by the bottom friction when the bottom friction number is large enough. The amplification rate may become sensitive to the relatively small Reynolds number. The stability region using the Manning formula is larger than that using the Chézy formula. The combination of these effects may stabilize or destabilize the shallow jet flow. These results of the stability analysis are compared with those from the literature.

Results of linear stability analysis on shallow jets along roughness bottom bed are presented. Different from the previous studies, this paper includes the effects of bottom topography, Rossby number, Reynolds number, resistance formula and bed friction. It is found that the influence of Reynolds number on the stability of the jet is notable for relative small value. Therefore, it is important to experimental investigators that the viscosity should be considered with comparison to the results from inviscid assumption. In contrast with the classical analysis, the use of multi-parameters of the base velocity and topographic profile gives an extension to the jet stability analysis. To characterize the large scale motion, besides the bottom friction as proposed in the related literature, the Reynolds number Re, Rossby number Ro, the topographic parameters and parameters controlling base velocity profile may also be important to the stability analysis of shallow jet flows.

Granular lubrication is a new lubrication method and can be used in extreme working conditions; however, the obstacle of force transmission characteristics needs to be urgently solved to fully understand the mechanical and bearing mechanisms of granular lubrication.

A flat sliding friction cell is developed to study the force transmission behaviors of granules under shearing. Granular material, sliding velocity, granule size and granule humidity are considered in these experiments. The measured normal and shear force, which is transmitted from the bottom friction pair to the top friction pair via the granular lubrication medium, reveals the influence of these controlling parameters on the force transmission characteristics of granules.

Experimental results show that a low sliding velocity, a large granule size and a low granular humidity increase the measured normal force and shear force. Besides, a comparison experiment with other typical lubrication styles is also carried out. The force transmission under granular lubrication is mainly dependent on the force transmission path, which is closely related to the deconstruction and reconstruction of the force chains in the granule assembly.

These findings reveal the force transmission mechanism of granular lubrication and can also offer the helpful reference for the design of the new granular lubrication bearing.

The purpose of this paper is to propose a three‐dimensional thermal model for friction stir welding of AISI 1018 mild steel to predict the thermal cycle, temperature distribution, the effect of welding parameters on power required, heat generation and peak temperature during the friction stir welding process.

The mathematical expressions for heat generation during the friction stir welding process were derived. The simulations for various welding and rotational speeds were carried out on ANSYS software employing temperature and radius dependent moving heat source and applying the boundary conditions.

The predicted thermal cycle, torque required and temperatures were found to be in good agreement with the experimental results. The heat generation and peak temperatures were found to be directly proportional to rotational speed and inversely proportional to welding speed. The rate of increase in heat generation and peak temperature were found to be higher at lower rotational speeds and lower at higher rotational speeds. The heat generation during friction stir welding was found to be 71.4 per cent at shoulder, 23.1 per cent at pin side and 5.5 per cent at bottom of the pin.

A new temperature dependent slip factor has been used to determine the contribution of slipping and sticking on total heat generation. A temperature and radius dependent moving heat source has been employed.

To solve the problems caused by using precise molds for copper column positioning in the current column grid array package, this paper aims to optimize the proposed friction plunge micro-welding (FPMW) technology without mold assistance, to overcome the problems of low interfacial bonding strength, shrinkage cavities and flash defects caused by the low hold-tight force of solder on the copper column.

A pressurizing device installed under the drill chuck of the friction welding machine is designed, which is used to apply a static constraint to the solder ball obliquely downward to increase the hold-tight force of the peripheral solder on the copper column during welding and promote the friction metallurgical connection between them.

The results show that the application of static constraint during welding can increase the compactness of the solder near the friction interface and effectively inhibit occurrences of flash, shrinkage cavities and crystal defects such as vacancies. Therefore, compared with the unconstrained (UC) FPMW, the average strength of the statically constrained (SC) FPMW joints and aged SC-FPMW joints can be increased by 51.1% and 122.6%, and the problem of the excessive growth of the interfacial connection layer in the UC-FPMW joints during aging can be effectively avoided.

The application of static constraint effectively inhibits the occurrence of defects such as shrinkage cavities, vacancies and flash in FPMW joints, and the welding quality is significantly improved.

The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which resembles the laser heating process, for researchers and graduate students working in the laser processing area, which can help them to improve the understanding of the laser machining process.

A numerical scheme employing the control volume approach is introduced to model the flow and heating situations. The effect of jet velocity on the heat transfer rates and skin friction around the cylindrical cavity subjected to the jet impingement was investigated.

Increasing jet velocity at nozzle exit enhances the heat transfer rates from the cavity wall and modifies the skin friction at cavity wall, which is more pronounced as the cavity depth increases to 1 mm.

The effects of nozzle cone angle on the flow structure and heat transfer characteristics were not examined, which perhaps limits the general usefulness of the findings.

Very useful information are provided for the laser gas assisted processing, which has a practical importance in machining industry.

This paper provides original information for the effects of the gas jet velocity on the cooling rates of the laser produced cavity.

Coastal sections suffering from erosion generally show the common symptom of a lack of available sand to allow the build up of the natural coastal barrier. Soft methods of coastal protection, including beach nourishment, profile nourishment, feeder berms, compensation‐dredging, aim to tackle the problem at its source, i.e. by supplying sand to the system. When thoroughly designed, these methods are considered the best technical/economical and appropriate solutions.

Since the introduction of two‐piece cans in 1962, manufacture of aluminium beverage cans has been a large and growing section of the packaging industry. There are two methods used for making two piece cans, namely:

This paper aims to estimate the bearing capacity of a surface strip and circular footings lying on layered sand using numerical limit analysis.

Lower and upper bound limit analysis, as well as finite elements and second-order conic programming (SOCP), are used in this analysis. The yield criterion of Mohr-Coulomb is used to model soil behavior. Using this technique, stringent lower and upper bounds on ultimate bearing capacity can be achieved by assuming an associated flow law.

The obtained results indicate that the exact collapse load is typically being bracketed to within 6% about a mean of both the bounds. The obtained results are compared with the existing literature wherever applicable.

To the best of the authors’ knowledge, no study has used lower and upper bound limit analysis, as well as finite elements and SOCP, to estimate the bearing capacity of a surface strip and circular footings lying on layered sand.

This paper aims to provide a theoretical principle for the stability control of robot climbing stairs, autonomously based on human–robot interaction. Through this research, tracked mobile robots with human-robot interaction will be extensively used in rescue in disaster, exploration on planetary, fighting in battle, and searching for survivors in collapsed buildings.

This paper introduces the tracked mobile robot, based on human–robot interaction, and its six moving postures. The dynamic process of climbing stairs is analyzed, and the dynamic model of the robot is proposed. The dynamic stability criterion is derived when the tracked mobile robot contacts the stairs steps in one, two and more points. A further conduction of simulation on the relationship of the traction force and bearing force vs the velocity and acceleration in the three cases was carried out.

This paper explains that the tracked mobile robot, based on human–robot interaction, can stably climb stairs so long as the velocity and acceleration satisfy the dynamic stability criterion as noted above. In addition, the experiment tests the correctness of dynamic stability analysis when the tracked mobile robot contacts the stair steps in one, two or more points.

This paper provides the mechanical structure and working principle of the tracked mobile robot based on human–robot interaction and proposes an identification method of dynamic stability criterion when the robot contacts the stairs steps in one, two and more points.

This paper aims to summarize the influence law of hybrid deposited and micro-rolling (HDMR) technology on the shaping strain and residual stress. And the rolling parameters combination was further optimized to guide the actual production.

This paper proposed a three-dimensional coupled thermo-mechanical model of the HDMR process. The validated model is used to investigate the influences of rolling parameters on stress and plastic strain (the distance between the energy source and roller [D_e–r], the rolling compression [c_r] and the friction coefficient [f_r]). The orthogonal optimization of three factors and three levels was carried out. The influence of rolling parameters on the plastic strain and residual stress is analyzed.

The simulation results show that HDMR technology can effectively increase the shaping strain of the weld bead and reduce the residual tensile stress on the weld bead surface. Furthermore, the influence of rolling parameters on stress and strain is obtained by orthogonal analysis, and the corresponding optimal combination is proposed. Also, the rolling temperature significantly affects the residual stress, and the rolling reduction has a substantial effect on the plastic deformation.

Owing to the choice of research methods, this paper failed to study microstructure evolution.

This paper provides a reference principle for the optimal selection of rolling parameters in HDMR.