The Detection, Genesis, and Modeling of Turbulence Intermittency in the Stable Atmospheric Surface Layer

Intermittent transitions between turbulent and non-turbulent states are ubiquitous in the stable atmospheric surface layer (ASL). Data from two field experiments in Utqiagvik, Alaska, and from direct numerical simulations are used to probe these state transitions so as to (i) identify statistical metrics for the detection of intermittency, (ii) probe the physical origin of turbulent bursts, and (iii) quantify intermittency effects on overall fluxes and their representation in closure models. The analyses reveal three turbulence regimes, two of which correspond to weakly turbulent periods accompanied by intermittent behavior (regime 1: intermittent, regime 2: transitional), while the third is associated with a fully turbulent flow. Based on time series of the turbulence kinetic energy (TKE), two non-dimensional parameters are proposed to diagnostically categorize the ASL state into these regimes; the first characterizes the weakest turbulence state, while the second describes the range of turbulence variability. The origins of intermittent turbulence activity are then investigated based on the TKE budget over the identified bursts. While the quantitative results depend on the height, the analyses indicate that these bursts are predominantly advected by the mean flow, produced locally by mechanical shear, or lofted from lower levels by turbulent ejections. Finally, a new flux model is proposed using the vertical velocity variance in combination with different mixing length scales. The model provides improved representation (correlation coefficients with observations of 0.61 for momentum and 0.94 for sensible heat) compared to Monin–Obukhov similarity (correlation coefficients of 0.0047 for momentum and 0.49 for sensible heat), thus opening new pathways for improved parametrizations in coarse atmospheric models.

Effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the contact zone with a cylindrical surface

This paper aims to determine the effect of the sector radius of a workpiece-deforming tool on the stress-strain state in the center of elastoplastic deformation and residual stresses in the hardened zone of the surface layer of cylindrical workpieces. A mathematical model of local loading was constructed using the finite element method and AN-SYS software. This model was used to determine the values of temporary and residual stresses and deformations, as well as the depth of plastic zone, depending on the sector radius of the working tool. The simulation results showed that, under the same loading of a cylindrical surface, working tools with different sector radii create different maximum tempo-rary and residual stresses. An assessment of the stress state was carried out for situations when the surface layer of a product is treated by workpiece-deforming tools with a different shape of the working edge. It was shown that, compared to a flat tool, a decrease in the radius of the working sector from 125 to 25 mm leads to an increase in the maximum temporary and residual stresses by 1.2–1.5 times, while the plastic zone depth increases by 1.5–2.4 times. The use of a working tool with a flat surface for hardening a cylindrical workpiece ensures minimal temporary residual stresses, com-pared to those produced by a working tool with a curved surface. A decrease in the radius of the working sector leads to an increase in temporary residual stresses by 2–7%. The plastic zone depth ranges from 1.65 to 2.55 mm when chang-ing the sector radius of the working tool.

Perbandingan Tebal Perkerasan Menggunakan Nilai CBR Laboratorium dan CBR Lapangan (DCP) (JLS Jarit-Puger)

CBR (California Bearing Ratio) data is used to find out the level of subgrade density, so that a safe pavement thickness can be planned. The calculation of the CBR (California Bearing Ratio) can be done by testing CBR laboratory and DCP. CBR results have a high effect on the surface layer, so that the layer becomes thinner. This condition, if converted to the working price, will be more affordable and efficient. Therefore, this study aims to compare the results of laboratory CBR and Field Cbr (Dcp) to the thickness of flexible pavements in the Development of Trans South-South Java Road Project (TRSS) Lot 8 Jarit - Puger. The method used is Bina Marga Pd T-01-2002-B. Secondary data obtained by weigh bridges and service providers, namely PT. Brantas Abipraya (Persero). Field CBR value using DCP tool is 25.19% while Laboratory CBR value is 21.616%. The results of pavement thickness using Field CBR values ​​for UR 10 years are D1 7.5 cm, D2 10cm, for UR 20 years D1 10 cm, D2 11 cm, for UR 30 years D1 11 cm, D2 12 cm, and for UR 40 years obtained D1 13 cm, D2 14 cm. The greater the CBR value, the thinner the pavement thickness.

The Effect of Combined Processing on Residual Stresses in the Surface Layer of Power Plant Parts

The purpose of this research was to analyze the change in residual stresses in the surface layer of steel samples taking into account the technological heredity effect on the value and sign of residual stresses. An installation of combined processing was developed. Combined processing consists of sequentially performing electromechanical processing and diamond smoothing. All areas of the samples were studied—after machining (i.e., in the initial state), after electromechanical processing, and after diamond smoothing. The research shows that the sign and value of residual stresses are significantly affected by the combined processing modes. The main parameters of the surface layer are formed at the final stage of the combined processing–diamond smoothing. This paper gives recommendations on the use of combined processing for power plant parts.

Electromechanical Surfacing Technique

The paper considers an electromechanical surfacing technique of parts’ work surfaces. It was found out that depending on strain temperature, rate and degree there were special type structures formed on a surface layer with a phase change (a bright layer), i.e. a hot deformed structure with and without recrystallization and a cold deformed structure. Depending on the original structure and hardening conditions, during surfacing of parts a thickness of this area may achieve 0.3 mm max. Impact of steel electromechanical treatment on the structure and the surface layer was found out. Depending on properties of surfaces being treated it is possible to use plate-like and roller-type tools for electromechanical hardening. It was shown that roller- type tools possessed enhanced durability and enlarged areas of surfaces being treated, though ensured poorer finish of surfaces being treated.

Features of the Grinding Technology with the Use of Nanomodified Coolant

The results of the analysis of the possibility of constructing a system for ensuring the quality of mechanical engineering parts by nanomodification of the surface layer are presented. The implementation is considered on the example of grinding technologies with nanomodified lubricating coolant. Mathematical models describing the process of creating conditions for nanomodification of the surface layer and algorithms for practical implementation are presented.