Влияние адгезии на трение качения и скольжения: эксперимент

Normal and tangential contact between a cylindrical steel indenter (wheel) and an elastomer with high adhesive properties is investigated. In the case of indentation in the normal direction, a computer simulation of the process of indentation and detachment was carried out, which shows good coincidence with an experiment. For the rolling friction mode, when analyzing the measured dependences of the tangential component of the contact force on the wheel displacement, the adhesive component of the friction force was determined. The situation of sliding friction, in which the rotation of the wheel was impossible, is considered. In the presence of adhesion, the sliding friction force is proportional to the contact area. In the absence of adhesion (the elastomer is covered with a chalk dust), a stick-slip friction mode is realized. The frequency and amplitude of stick-slip transitions depend on the indentation depth of the indenter into the elastomer.

Design of cylindrical steel liquid tanks with stepped walls using One-foot method

Cylindrical steel tanks are used in most countries to store bulk volumes of both solid and liquid products such as water, oil, gasoline and grain. Such steel tanks are prone to buckling when subjected to external pressure either due to vacuum or due to wind. These types of shell structures are generally controlled by elastic buckling failure because of the thin wall thickness. Cylindrical shells are commonly constructed with stepwise variable wall thickness due to economic reasons. The thickness of the tank shell wall is designed to increase from top to bottom because the stress resultants on the tank wall gradually increase towards the base of the tank. For open-top tanks, a primary stiffening ring is required at or near the top to maintain roundness under all loads. Stress resultants in a primary stiffening ring were previously identified by the Author for uniform wall thick tanks. In this new study, the applicability of this hand calculation method in stepped wall tanks has been investigated. Pursuant to this goal, a specified tank shell was designed considering One-foot method. Then, the stepped wall tank was transformed into an equivalent 1-course tank for hand calculation. Using the previously developed hand calculation method by Author, a test for the in-plane bending moment in the ring was conducted to achieve an acceptable value for stepped wall tanks. The analysis results show that the previously proposed method for uniform wall thick tanks may also be used for stepped wall tanks considering an equivalent thickness. On the other hand, using Linear Buckling Analysis (LBA), the buckling mode was obtained for two different stepped wall tanks in the study.

TREATING WASTE SLUDGE FROM WATER-PURIFICATION PLANTS WITH THE GEOPOLYMERIZATION METHOD

Treatment of the sludge from water-purification plants is becoming more and more urgent due to the inability to increase its storage area. To avoid CO2 emissions, the use of non-Portland cement binders is recommended. The application of geopolymerization of waste sludge (WS) from water-purification plants is a novel solution. Curing conditions including high temperature, pressure or microwaves enhance the formation of geopolymer bonds. This paper presents the results of a research on the treatment of the WS of the Thu Duc water-purification plant (Vietnam) with the geopolymerization method. Solid phases were prepared by mixing the WS and fly ash (FA). The FA proportions of the solid phases were (10, 40, 70) w/%. The alkali-activated solution (AAS) was a mixture of a 40 w/% NaOH 6M solution and 60 w/% water glass (WG: Na2O.nSiO2 with n = 1.75 and volumetric density r = 1.40 kg/L). The geopolymer materials were mixtures containing an 80 w/% solid phase and a 20 w/% liquid phase of the AAS. Geopolymer samples were formed in a cylindrical steel mold with a diameter of 10 mm at a high pressure. The samples were cured in a 112 W microwave oven for 30 s or in a dryer at 110 °C for 24 h. The compressive strength and volumetric density of both sample groups were determined and compared to each other. The formation of geopolymer bonds was investigated using XRD, FTIR and SEM.

EFFECT OF MOISTURE ON NITROGEN DIOXIDE FORMATION IN LAMINAR FLAME OF NATURAL GAS

The paper contains the results of experimental studies of the effect of moisture on nitrogen dioxide formation and on oxidation of NO to NO2 in laminar premixed flame of natural gas. The water vapor is shown to be the third very influential participant, along with fuel and oxidizer, in the combustion process. Injection of moisture into the combustion zone has an effect due to the insertion of additional quantities of HO2- and OH– radicals into the process, which contributes to the intensification of the oxidation of NO to NO2. Introduction of the concept of the “excess moisture ratio” in the combustion process is proposed. The studies were executed at the laboratory installation in conditions of formation of the V-shaped laminar flame of natural gas behind a transverse cylindrical steel stabilizer, with determining the concentrations of flue gas components.

Aging Behavior of Lithium Titanate Battery under High-Rate Discharging Cycle

The high-rate discharging performance of a lithium titanate battery is one of its main properties. In conditions that require ultra-high-rate discharging, a lithium titanate battery can be discharged continuously at a current of 50 C (50 times of its maximum capacity) or higher. In this paper, we take cylindrical steel shell lithium titanate cells as the research object and perform aging cycles at 66 C on these cells. The ultra-high-rate discharging cycles cause a rapid high-power capacity fading while the available capacity at normal current rate is not affected. The capacity at 66 C decreases to 80% of initial value in 10 cycles. This paper also analyzes the aging process of a lithium titanate battery at high-rate discharging with incremental capacity (IC) analysis, and presents the aging behavior of lithium titanate battery qualitatively, which is inconsistent with existing research. We attribute the aging mechanism of ultra-high-rate discharging cycles to the decrease of ionic mobility and increase of polarization resistance. Mechanical damage is observed in the CT scan of an aged cell, which we presume to be the result of rapid strain of cathode material.

Reduction in the Electromagnetic Interference Generated by AC Overhead Power Lines on Buried Metallic Pipelines with Screening Conductors

This paper presents a numerical study on the reduction in the voltage and current induced on a 13.5 km buried metallic pipeline by an overhead power line. The mitigation effectiveness of different configurations and cross-section shapes of screening conductors is computed by means of a methodology that combines a 2D Finite Element Analysis with circuital analysis. A 35.72% reduction of the maximum induced voltage is obtained when 4 cylindrical steel screening conductors with 8 mm radius are buried 0.25m below the soil surface, along the pipeline path. The maximum induced pipeline current is reduced by 26.98%. A parametric study is also performed, to assess the influence of the per-unit-length admittance to earth of the screening conductors on the mitigation efficacy. The results show that screening conductors may help in reducing the inductive coupling between overhead power lines and buried metallic pipelines, and that the assumption of perfectly insulated screening conductors leads to an underestimation of the produced mitigation effect.

Piezo-based flexural vibration suppression for an annular rotor via rotating-frame H2 control optimization

Elastic vibration can arise in annular and thin-walled rotor structures, impacting on operating performance and the risk of failure. Feedback control to reduce flexural vibration can be realized using lightweight actuators and sensors embedded in the rotor structure. To design optimal controllers, rotating-frame models of both the structural dynamics and sources of excitation are required. This paper describes a solution to this problem for the case of an annular rotor equipped with piezo patch actuators and sensors. To account for space-fixed external excitation sources, a forcing function is considered involving specified spatial and frequency domain distributions. A model-based [Formula: see text] synthesis is used to compute optimal control solutions. These are tested experimentally on a thin-walled cylindrical steel rotor for cases with narrowband and broadband excitation sources, applied from the fixed frame. The results show that frequency-splitting within the rotating-frame dynamics plays a key role in predicting and controlling resonance. The effectiveness of the optimal control methodology in reducing circumferential vibration of the annular rotor is also confirmed.

A New Approach for Cylindrical Steel Structure Deformation Monitoring by Dense Point Clouds

As fundamental load-bearing parts, the cylindrical steel structures of transmission towers relate to the stability of the main structures in terms of topological relation and performance. Therefore, the periodic monitoring of a cylindrical steel structure is necessary to maintain the safety and stability of existing structures in energy transmission. Most studies on deformation analysis are still focused on the process of identifying discrepancies in the state of a structure by observing it at different times, yet relative deformation analysis based on the data acquired in single time has not been investigated effectively. In this study, the piecewise cylinder fitting method is presented to fit the point clouds collected at a single time to compute the relative inclination of a cylindrical steel structure. The standard deviation is adopted as a measure to evaluate the degree of structure deformation. Meanwhile, the inclination rate of each section is compared with the conventional method on the basis of the piecewise cylinder fitting parameters. The validity and accuracy of the algorithm are verified by real transmission tower point cloud data. Experimental results show that the piecewise cylinder fitting algorithm proposed in this research can meet the accuracy requirements of cylindrical steel structure deformation analysis and has high application value in the field of structure deformation monitoring.