ANALYSIS OF EMBANKMENT SLOPE STEEPNESS AND STABILITY

This paper describes the stability calculations of the most common road embankments slopes and their results using the modified Bishop method. By searching for the smallest possible effective angle of internal friction of the different slope steepness embankments, the possible different bases of the embankment, the weight of the embankment soil, the load caused by transport and the location of load application (shoulder) were evaluated. Analyzing the obtained calculation results, it was determined that at a slope of 1:2 (26.57°) steepness, to ensure slope stability, the calculated effective internal friction angle of the embankment soil should be φʹd ≥ 28.5°, and at a slope of 1:1.75 (29.74°) steepness – φʹd ≥ 29.8°. When the slope is 2:3 (33.69°) steepness, the stability of the slope cannot be guaranteed.

Early On-Set Prediction Of Vortex-Ring State Of Quadrotors

The OpenFOAM CFD package was used to initially investigate the aerodynamic effects of vortex-ring state of a quadrotor, then to study various quadrotor flight maneuvers to minimize the thrust loses of vortex-ring state and followed by possible detection methods for a drone entering vortex-ring state. Vortex-ring state is characteristic of a decrease in the effective angle of attack of incoming airflow due to a rotor descending into its downwash. This causes significant loses in the thrust of the rotor, which typically leads to severe flight upsets for rotorcraft. A quadrotor was studied at varying descent velocities to investigate wake roll-up at the rotor tips and the subsequent effects on rotor thrust and power. The quadrotor was then subjected to non-vertical descent angles to investigate thrust loss mitigation approaches due to vortex-ring state. A method of detecting the on-set of vortex-ring state is proposed using various differential pressure measurements on the quadrotor. It has been shown that by monitoring the pressure difference between the top of the quadrotor body and the bottom of one of the quadrotor legs, a pressure drop can be seen just prior to the on-set of vortex-ring state. This pressure drop was shown to occur during descending flight regimes and may prove to be an effective pre-vortex-ring state warning system.

Early On-Set Prediction Of Vortex-Ring State Of Quadrotors

The OpenFOAM CFD package was used to initially investigate the aerodynamic effects of vortex-ring state of a quadrotor, then to study various quadrotor flight maneuvers to minimize the thrust loses of vortex-ring state and followed by possible detection methods for a drone entering vortex-ring state. Vortex-ring state is characteristic of a decrease in the effective angle of attack of incoming airflow due to a rotor descending into its downwash. This causes significant loses in the thrust of the rotor, which typically leads to severe flight upsets for rotorcraft. A quadrotor was studied at varying descent velocities to investigate wake roll-up at the rotor tips and the subsequent effects on rotor thrust and power. The quadrotor was then subjected to non-vertical descent angles to investigate thrust loss mitigation approaches due to vortex-ring state. A method of detecting the on-set of vortex-ring state is proposed using various differential pressure measurements on the quadrotor. It has been shown that by monitoring the pressure difference between the top of the quadrotor body and the bottom of one of the quadrotor legs, a pressure drop can be seen just prior to the on-set of vortex-ring state. This pressure drop was shown to occur during descending flight regimes and may prove to be an effective pre-vortex-ring state warning system.

Numerical Simulation of Flow over Bionic Airfoil

In this study, the aerodynamic performance of bionic airfoil was numerically studied by CFD method. The bionic airfoil was represented by the combination of airfoil and a small trailing edge flap. A variety of configurations were calculated to study the effect of flap parameters, such as the flap angle, position, and shape, on the bionic airfoil aerodynamic characteristics based on two layouts which were that (1) there was a tiny gap between the airfoil and the flap and (2) there was no gap between the two. The results showed that the flap angle and position had significant effects on the aerodynamic performance of the airfoil with the two layouts. Compared with the clean airfoil, the maximum lift coefficients of the first layout and the second layout could be increased by 10.9% and 7.9%, respectively. And the effective angle of attack (AoA) range for improving the lift-to-drag ratio could reach 7°. The flap shape also affected the airfoil aerodynamic characteristics, and the flap with the sinusoid curve shape showed ideal performance.

Analysis of the Control Effect and Parameter Optimisation of Urban Surface Deformation in Underground Coal Mining with Solid Backfilling

To solve the problems of surface deformation and destruction of buildings caused by urban mining and realise the coordinated development of mining cities, the solid backfilling method was used to extract coal resources beneath the buildings of Tangshan. Based on surface deformation monitoring data of the continuously operating reference station (CORS) system for the past 5 years, the surface deformation process caused by solid backfilling was analysed. The final results revealed a maximum surface subsidence of 66 mm in the T zone coal area and 31 mm in the F zone area. Furthermore, the surface control effects of the caving method and the solid backfilling method were compared and analysed, and it was shown that solid backfilling could meet the surface building setup requirements. Moreover, based on the probability integral method, the effects on surface deformation due to the surface length of the F zone, compression ratio, and coal pillar width were analysed, and the effects on the prediction results due to the subsidence factor, tangent of the major effective angle, and offset distance of the inflection point were studied. The results showed that the compression ratio is the main factor controlling the surface deformation and that it should be kept above 80% for solid backfilling of urban mines. The subsidence factor should be 0.82, and the tangent of the major effective angle should be 2.15 when the surface subsidence of solid backfilling is to be predicted. This paper provides a technical reference for the realisation of urban mining with solid backfilling.

Comparative analysis of marine diesel engines by ultimate efficiency increase under direct air flow control

The paper presents a comparative analysis of the operational parameters and parameters of marine diesel engines obtained as a result of computational and theoretical studies with direct control of air flow using an adjustable turbocharger nozzle to ensure the maximum allowable efficiency of diesel engines. The objects under study are: two-stroke marine diesel engine, operating on the screw characteristics; marine four-stroke diesel working on the screw characteristics; marine four-stroke diesel working on the load characteristics. As a result of the rotation of the blades of the adjustable nozzle in the direction of reducing the angle of their installation the diesel engine efficiency increases. However, the maximum pressure of the cycle also increases, the pressure drop decreases during purging the cylinders, the effective angle of gas exit from the turbine nozzle decreases, and the compressor's surge stability margin changes. There has been studied the design potential of diesel engines for the maximum increase in their efficiency, which made it possible to accept the stable operation of the compressor in all the studied modes. In the course of the research, boundary values were found for the maximum pressure of the diesel cycle, the pressure drop for purging the cylinders and the effective angle of flow exit from the nozzle apparatus, beyond which the specified parameters did not go beyond all the studied modes of operation of diesels. Taking into account the limitations of the greatest potential for improving efficiency in the equity modes of loads has a four-stroke diesel engine, operating on the screw characteristics, the smallest capacity is the same petrol, but working on the load characteristics.