Value Of Critical Depth Research Articles

Ultimate bearing capacity analysis and structural optimization of packer slip

The packer's slips indent the inner wall of the casing, leaving a series of marks between the teeth of the slips and the inner wall of the casing. Excessive bite depth can result in damage to the inner wall of the casing, potentially leading to failure. To minimize damage to the inner wall of the casing and improve the ultimate bearing capacity of the slip, a three-dimensional finite element analysis model of the slips is developed and validated through laboratory experiments. The optimization objective is to minimize casing damage and maximize bearing capacity. This paper examines the correlation between the residual collapse strength of the casing and the maximum depth of slips penetrating the inner wall. It determines the critical depth value by calculating the extrusion force endured by the inner wall of the casing as an optimization evaluation index. At the same time, the optimal structural parameters of the slips were determined through numerical simulation and orthogonal experiments. These parameters include a 90° dental angle, a 21° inner cone angle, a 219 mm outer diameter, and a 6.5 mm tooth pitch. The research results indicate that the equivalent stress of the improved slip has decreased by 8.66 %. The equivalent stress on the inner wall of the casing has been reduced by 9.34 %, and the maximum tooth mark depth of the casing has decreased by 30.48 %. Furthermore, the ultimate bearing capacity of the slip has increased by 2.24 times. Research has shown that the improved slip not only reduces damage to the inner wall of the casing and minimizes stress concentration on the slip, but also increases the ultimate bearing capacity of the slip. The research results can serve as a reference for the study and application of packers.

Study of the Performance of a Novel Radiator with Three Inlets and One Outlet Based on Topology Optimization.

In recent years, in order to obtain a radiator with strong heat exchange capacity, researchers have proposed a lot of heat exchangers to improve heat exchange capacity significantly. However, the cooling abilities of heat exchangers designed by traditional design methods is limited even if the geometric parameters are optimized at the same time. However, using topology optimization to design heat exchangers can overcome this design limitation. Furthermore, researchers have used topology optimization theory to designed one-to-one and many-to-many inlet and outlet heat exchangers because it can effectively increase the heat dissipation rate. In particular, it can further decrease the hot-spot temperature for many-to-many inlet and outlet heat exchangers. Therefore, this article proposes novel heat exchangers with three inlets and one outlet designed by topology optimization to decrease the fluid temperature at the outlet. Subsequently, the effect of the channel depth on the heat exchanger design is also studied. The results show that the type of exchanger varies with the channel depth, and there exists a critical depth value for obtaining the minimum substrate temperature difference. Then, the flow and heat transfer performance of the heat exchangers are numerically investigated. The numerical results show that the heat exchanger derived by topology optimization with the minimum temperature difference as the goal (Model-2) is the best design for flow and heat transfer performance compared to other heat sink designs, including the heat exchanger derived by topology optimization having the average temperature as the goal (Model-1) and conventional straight channels (Model-3). The temperature difference of Model-1 can be reduced by 37.5%, and that of Model-2 can be decreased by 62.5% compared to Model-3. Compared with Model-3, the thermal resistance of Model-1 can be reduced by 21.86%, while that of Model-2 can be decreased by 47.99%. At room temperature, we carried out the forced convention experimental test for Model-2 to measure its physical parameters (temperature, pressure drop) to verify the numerical results. The error of the average wall temperature between experimental results and simulation results is within 2.6 K, while that of the fluid temperature between the experimental and simulation results is within 1.4 K, and the maximum deviation of the measured Nu and simulated Nu was less than 5%. This indicated that the numerical results agreed well with the experimental results.

MODELING OF PIPELINE STRESS-STRAIN STATE IN COMPLICATED ENVIRONMENT

Purpose: The aim of this work is to study the stress-strain state of the pipeline affected by rill erosion. Design/methodology/approach: The pipeline modeling and the stress-strain analysis are carried out using the ANSYS finite element program which provides rather high accuracy of numerical experiments, and, as a consequence, achievement of results with high degree of confidence. The initial data for a series of numerical experiments are derived from actual conditions of the pipeline operation and interpreted for using them in the ANSYS program. Research findings: The numerical experiment includes several stages, namely: the develop-ment of the finite element model (FEM) of the pipeline affected by rill erosion; meshing pro-cess of the pipeline model; load application to the pipeline; and setting the boundary condi-tions. A series of numerical experiments is carried out in varying the depth of rill erosion re-sulting in the equivalent stress distribution (von Mieses stresses) over the pipeline FEM. The maximum and minimum values of the pipeline strains and von Mieses stresses are obtained. This stress distribution allows detecting the critical depth value for the rill erosion in the pipeline under study. A study of the stress-strain state is an important and urgent task, the solution of which determines a safe operation of the field pipeline. The stress-strain state caused by the internal and external pressure or tensile stresses affects the pipeline reliability. Evaluation of the pipeline properties is one of the preventive measures against accidental damage. Practical implications: The stress-strain state investigations are very important for ensuring a safe operation of the pipeline of interest. This is because the stress-strain state caused by the internal loads and external compressive or tensile stresses affects the pipeline reliability. Value: The estimation of the pipeline material properties assists in prevention of emergency situations.

Dual diagnostic method for fracture morphology of thermal coalbed methane reservoir

In most thermal coalbed methane production practices, the average single well production is low and the economic benefit is low. In order to improve the production of thermal coalbed methane, this paper presents a dual diagnosis method for fracture morphology of thermal coalbed methane reservoir to improve hydraulic fracturing effect. The study is carried out as follows: firstly, improved log-log curve method to adapt to coal seam fracturing construction, secondly, establish the inclined stress calculation model of coal seam to obtain the critical depth value, and finally, combine the improved log-log method and critical depth method to form a dual diagnosis approach. Take Baiyang River in Xinjiang as an example, obtain the traffic, rock mechanics and other parameters suitable for the Baiyang River block, the fracture morphology is verified by fracturing data. The experimental results show that the approach can diagnose fracture morphology accurately. <br><br><font color="red"><b> This article has been retracted. Link to the retraction <u><a href="http://dx.doi.org/10.2298/TSCI191209454E">10.2298/TSCI191209454E</a><u></b></font>

Study on gross streambank sediment erosion from the Godavari Khola, southeast Kathmandu Valley, Central Nepal

The fifth order Godavari Khola is flowing from the South to the North direction and is one of the major tributaries from the southern part of the Kathmandu Valley. As the urbanization is growing in the Kathmandu Valley the banks of the streams are being targeted for the housing and roads, therefore it is important to know the characteristic of the river behavior, nature of erosion and sediment production along its banks. This study accesses the stream bank erosion characteristics and sediment production by erosion along the Godavari Khola. It was conducted by surveying and accessing hydraulic parameters, Bank Erosion and Lateral Instability status, streambank recession rates and gross sediment erosion from the bank.
 The Godavari Khola has high bank erodibility and lateral instability as the hazard level of Bank Erosion and Lateral Instability (BELI) and width/depth ratio are quite high. Since the slope and the bankfull depth exceed the critical slope and critical depth values, respectively, the Godavari Khola is competent enough to mobilize its sediments. The apparent recession rate of the banks of the Godavari Khola is 0.66 m per year yielding 85 m3 volume of the displaced material which weighs 141 tonnes. The estimated bank erosion rate is in between 0.02 to 0.235 m/y and the gross erosion is estimated to be 320 tonnes per year. Similar to the other river of the Kathmandu Valley, the Godavari Khola is very disturbed by the anthropogenic activities. Riparian vegetation clearing and bad agricultural practice is one of the major causes for the high bank erosion and instability of the Godavari Khola.

Grinding of ceramics – sintered ceramics versus ceramic coatings

This paper reports the study of grinding characteristics of sintered alumina ceramic and plasma sprayed alumina coatings with respect to grinding forces, specific grinding energy, force ratio and surface integrity at high wheel speed and moderate downfeed. The ground surface of sintered ceramic showed some signatures of plastic deformation along with micro-brittle fracture whereas, in plasma sprayed ceramic coatings, micro-brittle fracture was the predominant mode of material removal under the same grinding condition. This is attributed to the comparable value of critical depth (dc) in ceramics and very low value of dc in ceramic coatings as compared to maximum uncut chip thickness. In sintered alumina, the specific tangential and normal forces are 0.10 and 0.30 N/mm respectively. On the other hand, the forces observed in plasma sprayed alumina coatings were low, and the maximum forces recorded were 0.05 and 0.23 N/mm respectively. SEM images of chips showed micro-brittle fracture as the predominant mode of material removal. Average surface roughness was found to be low in sintered alumina as compared to that in plasma sprayed coatings. Sintered ceramic was free from residual stress whereas in ceramic coatings, tensile residual stresses were observed.

Effects of shallow groundwater table and salinity on soil salt dynamics in the Keriya Oasis, Northwestern China

In this paper, the spatial and temporal variability of groundwater depth and groundwater salinity associated with agricultural activities and land cover and land use (LCLU) in the Keriya Oasis, Xinjiang Uyghur Autonomous Region of China, was investigated. A decision tree classification was developed for LCLU mapping by using Landsat 8 imagery. Radial basis function, Pearson’s correlation coefficient, Moran’s I statistics and geographically weighted regression were employed to identify the spatial and temporal relationship between topsoil salinity and LCLU types. The results showed that groundwater depth in about 75 % of the study area was less than 3.0 m. Groundwater salinity showed an increasing trend with decreasing groundwater depth. A relatively higher positive correlation (r = 0.87) was found between groundwater salinity and topsoil salinity. Topsoil salinity was exacerbated by agricultural activities at the upstream of seasonal rivers, causing severe soil salinization and soil degradation in the downstream. Both groundwater depth and soil salinity showed seasonal fluctuations with the shallowest groundwater level occurring in spring, while during summer and autumn, groundwater depth increased due to the extensive of agricultural water consumption and the regional evapotranspiration, which was followed by a winter recharge; non-saline groundwater region was 21 % of the research area in spring, which dropped to 1.1, 1.0 and 1.2 %, respectively, during the summer, autumn and winter. The results also demonstrated that shallow groundwater depth of 2.5 m is the critical depth value for soil salinization in the Keriya Oasis.

Inertia effects in textured hydrodynamic contacts

A flow analysis is carried out for a parallel textured slider to investigate the role of fluid inertia. Numerical simulations are performed for a laminar, two-dimensional, steady and isothermal flow. Stokes solutions are compared with Navier—Stokes solutions at the same Reynolds number. A range of texture depths is analysed. It is shown that there is an optimum value of texture depth that provides maximum load-carrying capacity. It is also shown that there is a critical depth value. Inertia has a negative effect on the load-carrying capacity for depths higher than the critical value, whereas it has a positive effect for lower depths. For a given texture depth, these effects are amplified as the Reynolds number increases. The global effect of inertia is positive when a realistic configuration of a parallel textured slider with a fore-region is considered.

Behaviour of crevice corrosion in iron

Crevice corrosion was investigated in iron exposed to a strong-buffered acetate solution (0.5 M CH 3COOH + 0.5 M NaC 2H 3O 2), pH = 4.66. The current and the potential gradient within the crevice were measured at crevice depth ( L) = 7.35, 8, 10, and 15 mm, for a crevice that was positioned facing the electrolyte in a downward position. A remarkable shift in potential (>1.2 V) in the active direction was measured inside the crevice cavity, when the potential at the outer surface was held at 800 mV(SCE). Experimentation showed that there is a critical depth value, above which little changes occur on the transition boundary between passive and active regions on the crevice wall, x pass, and below which x pass location shifts sharply towards the crevice bottom. Steeping of the potential gradient occurred with time indicating enhancement of crevice corrosion, which was seen by the gradual increase in the current. These findings were in close agreement with the IR voltage theory and related mathematical model predictions. Morphological examination showed an intergranular attack around the active/passive boundary ( x pass) on the crevice wall.

Brittle–ductile transition in the diamond cutting of glasses with the aid of ultrasonic vibration

High efficiency mirror surface machining of brittle materials such as glasses and ceramics has become more important as these materials have become used more widely in optical and electronic devices. In this work, the ultrasonic vibration diamond cutting of glasses was performed in order to investigate the effect of tool vibration on the brittle–ductile transition mechanism. The effect of cutting speed on the critical depth of cut was studied by groove cutting experiments. The value of critical depth of cut has been found to vary with the ratio of vibration speed to cutting speed. The characteristics of the surface generated in the ductile mode have been examined and the measures for minimizing the influence of tool vibration on surface finish are suggested. The reason for the increase in the critical depth of cut is discussed based on the analysis of the ultrasonic vibration cutting process and the measured data of cutting force.

FLOW MEASUREMENTS WITH TRAPEZOIDAL FREE OVERFALL

ABSTRACT A quasi-theoretical end-depth-discharge (EDD) relationship for free overfall in trapezoidal channels for negative, zero and mild bed slopes is presented in this paper. The theoretical procedure applied to compute the discharge over a weir is applied to free overfall to get EDD relationship. The shape of pressure distribution at brink is assumed a quadratic parabola. The pressure distribution factors, obtained by Rajaratnam and Muralidhar, are used, herein. The resulting equation can easily be used to compute end depth for given value of critical depth or discharge. But the equation is difficult to solve for critical depth or discharge for given value of end depth because critical depth appeared implicitly in the equation. Therefore, a closed form equation for dimensionless discharge is proposed, which contains minimal error and is simple to use. The available experimental data are used to verify the proposed EDD relationship. The calculated discharges, using the proposed EDD relationship, show excellent agreement with the experimental values.

ALBEDO AND DEPTH OF MELT PONDS ON SEA-ICE

For a 1-month period during the spring–summer season, over 500 in situ measurements of the albedo, depth and selected properties of melt ponds were made at four sea-ice sites in the Canadian Arctic Archipelago. There are three aims of the investigation: to examine the variation in spectral reflectance of melt ponds in relation primarily to clouds, pond depth, and ice type; to compute and assess with reliability, and for the first time, the statistical properties of pond depth; and to derive pond albedo parameterizations for implementation in sea-ice model simulations. It was found that pond reflectance curves vary significantly with cloud cover, pond depth, and ice type. A simple univariate statistical analysis showed that surface ice morphology controls pond depth. Application of the Kruskal–Wallis test evidenced that differences between first-year ice, multi-year ice, and landfast ice-pond-depth distributions are statistically significant. Lastly, calibrated non-linear regression functions show that visible and near-infrared pond albedos decrease exponentially with depth until some critical depth value is exceeded. The relationship is weakest in the visible spectrum, particularly under cloudy sky conditions.

Agricultural criteria for subsurface drainage: A systems analysis

The effects of subsurface drainage on agriculture are analysed in relation to drain discharge, control of the watertable and salt evacuation. The drain discharge depends mainly on external factors (the water balance), whereas the level of the watertable can be influenced by the design of the drainage system. Agricultural drainage criteria must therefore be sought in the required degree of watertable control, given a certain water balance. To this end, relationships between watertable depth and crop production or production factors need to be determined, and critical depth values need to be derived. As the watertable fluctuates, a suitable indicator has to be found for it from the depth-duration-frequency relationship. The variable that gives the highest degree of statistical explanation is the most suitable. It can be a long-term, average depth, or an extreme, short-term, shallow depth. The corresponding agricultural drainage criteria are called long-term and short-term criteria. The first are associated with steady-state drain-spacing equations, the second with either steady-state or unstead-state equations, depending on the ratio of storage to recharge or discharge.