Analysis of Factors Affecting the Rheological Properties of Muddy Flow and Their Measurement Method

Abnormal weather phenomena debris damage has recently been increasing worldwide. As primary rheological properties, the yield stress and plastic viscosity of muddy materials affect the flow distance and velocity. Therefore, in this study, direct and indirect measurement test methods for rheological properties and factors affecting the these properties were analyzed. Measurement methods utilize rheometers, shear creep, fall cones, inclined planes, direct shear, and ring shear, with each method having its respective advantages and disadvantages. Factors that affect rheological properties are water content, liquidity index, and the size of soil particles. This study enables determination of the best test and rheological properties suitable for the selected range and selected object.

Viscous gravity currents over flat inclined surfaces

Previous analyses of the flow of low-Reynolds-number, viscous gravity currents down inclined planes are investigated further and extended. Particular emphasis is on the motion of the fluid front and tail, which previous analyses treated somewhat cavalierly. We obtain reliable, approximate, analytic solutions in these regions, the accuracies of which are satisfactorily tested against our numerical evaluations. The solutions show that the flow has several time scales determined by the inclination angle, $\alpha$ . At short times, the influence of initial and boundary conditions is important and the flow is governed by both the pressure gradient and the direct action of gravity due to inclination. Later on, the areas where the boundary conditions are important shrink. This fact explains why previous solutions, being inaccurate near the front and the tail, described experimental data with high accuracy. At larger times, of the order of $\alpha ^{-5/2}$ , the influence of the pressure gradient may be neglected and the fluid profile converges to the square-root shape predicted in previous works. Important extensions of our approach are also outlined.

Further Analysis of the Passive Dynamics of the Compass Biped Walker and Control of Chaos via Two Trajectory Tracking Approaches

This work consists in analyzing and controlling the walk of the compass-type bipedal walker in order to stabilize its passive dynamic gait. The dynamic walking of the compass-gait walker is modeled by an impulsive hybrid nonlinear system. This impulsive hybrid nature is considered very complex as it can generate unwanted phenomena such as chaos and bifurcations. We show first by means of bifurcation diagrams and by varying the slope angle of the walking surface and also the length of the lower leg segment that the passive dynamic walking exhibits successive period-doubling bifurcations leading to chaos. Furthermore, in order to control chaos and hence obtain one-periodic walking behavior, we propose two control approaches based on tracking a desired trajectory. The first method consists in tracking the one-periodic passive dynamic walking generated by the compass model itself. The second control method lies in following a planned trajectory using the 4th-order Spline function. An optimization method is also achieved to design the parameters of the desired trajectory. Some features of the period-1 passive gait are used in the design of such Spline trajectory. Finally, we show some simulation results revealing the efficiency of the two proposed control methods in the control of the chaotic passive gait of the compass-gait walker. Moreover, we demonstrate the stabilization of the bipedal locomotion of the compass biped walker on different slopes: descending and ascending inclined planes and walking on a level ground. A comparison with the OGY-based control method is also performed to further show the superiority of these two control approaches.

Drop race: How electrostatic forces influence drop motion

Water drops sliding down inclined planes are an everyday phenomenon and are important in many technical applications. Previous understanding is that the motion is mainly dictated by viscous and capillary forces. Here we demonstrate that, in addition to these forces, drops on hydrophobic surfaces are affected by self-generated electrostatic forces. In a novel approach to determine forces on moving drops we imaged their trajectory when sliding down a tilted surface and apply the equation of motion. We found that drop motion on low-permittivity substrates is significantly influenced by electrostatic forces. Sliding drops deposit a negative charge on the surface, which interact with the positively charged drops. We derive an analytical model to describe the force and validate it by numerical computations. The results indicate how to describe and facilitate drop motion in applications, such as in microfluidics, water management on car surfaces, and the creation of sliding drop electrical generators.

Assessment of the Resolution of Nonplanar Flaws in Pressure Retaining Components in Terms of Stress Intensity Factors

When flaws are detected in pressure retaining components, assessments have to be done in order to demonstrate the fitness-for-service (FFS) of the component for continued operation. This FFS demonstration is performed in accordance with FFS Codes providing flaw assessment procedure and acceptance standards. The first step of the flaw assessment is the flaw characterization which aims at determining the flaw geometry to be used for the analyses. This key step is done according to flaw characterization rules provided in the FFS Codes and hence appears as essential for the rest of the assessment. According to the flaw characterization rules of ASME B&PV Code Section XI, a nonplanar flaw (i.e., oriented in two or more intersecting inclined planes, curvilinear geometry, or combinations of nonplanar geometry) shall be resolved into two planar flaws by projection of the flaw area into planes normal to the maximum principal stresses. This approach allows to simplify the flaw assessment but should remain conservative. Therefore, the conservatisms due to the simplified projection approach for nonplanar flaws are investigated in this paper. Current computational tools have been clearly improved so that the modelling of nonplanar flaws does not present any significant difficulty. In this frame, this paper compares the stress intensity factors of projected nonplanar flaws and the mixed mode stress intensity factor of actual nonplanar flaws. This is carried out for multiple flaw sizes, flaw shapes, flaw orientations and different load cases. The final scope is to quantify how the flaw projection into planes normal to the maximum principal stresses is conservative and how this conservatism could be improved, if need be.

Analysis of deformation characteristics of Asymmetric Gradient Extrusion in preparing ultra-fine grained bulk materials

A novel method to prepare ultra-fine grained bulk materials, which is named Asymmetric Gradient Extrusion (AGE), is proposed in this article. In AGE, the cross section of extrusion channel is rectangle and two inclined planes are stagger arranged along extrusion direction. To realize repeating extrusion, the thickness of workpiece is restricted to equal the width of channel’s outlet. The deformation characteristics of AGE was first theoretically analyzed by slip line field. Then, these results were verified and supplemented by finite element analysis. The results reveal that deformation characteristics of workpiece in channel is largely related to the two inclined planes. Two independent deformation zones (TIDZ) can be formed with increasing distance between the two inclined planes. In addition, the accumulated strain generated in the TIDZ is complementary in value. Furthermore, the shearing effects of workpiece subjected in one pass extrusion has been improved. A more uniform strain distribution and higher shearing effect can be generated in AGE, which make it as a very promising method to produce ultra-fine grained bulk materials.

Numerical study of dam-break fluid flow using volume of fluid (VOF) methods for different angles of inclined planes

In this paper, the effects of water on obstacles in dam-break flow for different angles of the inclined planes have been numerically examined. The presented computational data are compared with data from the experiment and computational simulation data of other authors. Good agreements between the obtained simulation results and measurement data demonstrate the satisfactory performance of the mathematical model and the numerical algorithm when reproducing a dam-break flow. Additionally, various problems were also considered: the effect of pressure distribution on the dam walls for different angles of the inclined plane. It was found that pressure distribution on the wall when the inclined angle [Formula: see text] = 15° was almost two times more than without inclination. To reduce the shock pressure value a new form of obstacle was used. With a new form of obstacle, the maximum pressure value on the dam wall decreased more than three times.

Metallic Microswimmers Driven up the Wall by Gravity

Experiments on autophoretic bimetallic nanorods propelling within a fuel of hydrogen peroxide show that tail-heavy swimmers preferentially orient upwards and ascend along inclined planes. We show that such gravitaxis is...