静電的および電磁的加速環境下における高エネルギーイオン生成メカニズム

Tohoku University博士（工学）要約のみthesi

Sensorless fault diagnosis of centrifugal pumps

Analysis of electrical signatures has been in use for some time to assess the condition of induction motors. In most applications, induction motors are used to drive dynamic loads, such as pumps, fans, and blowers, by means of belts, couplers and gear-boxes. Failure of either the electric motors or the driven loads is associated with operational disruptions. The large costs associated with the resulting idle equipment and personnel can often be avoided if the degradation is detected in its early stages, prior to reaching catastrophic failure conditions. Hence the need arises for cost- effective schemes to assess not only the condition of the motor but also of the driven load. This work presents an experimentally demonstrated sensorless approach for model- based detection of three different classes of faults that frequently occur in centrifugal pumps. A fault isolation scheme is also developed to distinguish between motor re- lated and pump related faults. The proposed approach is sensorless, in the sense that no mechanical sensors are required on either the pump or the motor driving the pump. Rather, fault detection and isolation is carried out using only the line voltages and phase currents of the electric motor driving the pump, as measured through standard potential transformers (PT's) and current transformers (CT's) found in industrial switchgear. The developed fault detection and isolation scheme is insensitive to electric power supply variations. Furthermore, it does not require a priori knowledge of a motor or pump model or any detailed motor or pump design parameters; a model of the system is adaptively estimated on-line. The developed algorithms have been tested on three types of staged pump faults using data collected from a centrifugal pump connected to a 3, 3 hp induction motor. Results from these experiments indicate that the proposed model-based detection scheme effectively detects all staged faults with fault detection times comparable to those obtained from vibration analysis. In addition to the staged fault experiments, extended healthy operation reveals no false alarms by the proposed detection algorithm. The proposed fault isolation method successfully classifies faults in the motor and the pump without any mis-classification

An improved contact detection algorithm for DEM modeling of polydisperse systems: Application to coal-ash mixture fluidization

Discrete element modelling (DEM) are becoming increasingly common for modelling of particulate flows such as avalanches and landslides and in many “solids-only” unit operations like grinding and milling, as well as in numerous gas-solid applications such as pneumatic conveying, fluidized beds and circulating fluidized beds (1). In such simulations, realistic size distributions have not been taken into account in the past. In real operations, sizes of dispersed entities can vary over several orders in magnitude. This issue is particularly pronounced when one is trying to simulate polydisperse systems, such as coal-ash mixtures, wherein a single coal particle may be (in general) surrounded by many much smaller ash particles, even when the overall mass fraction of the ash may be only a few percent. Figure 1 shows the idea schematically. One of the main reasons for this challenge is the DEM calculations required contact detection in the dispersed objects. When the sizes of these objects vary to a great degree, the contact detection poses a computational bottleneck. Amongst others, notably Perkins and Williams have proposed “Double Ended Spatial Sorting” (DESS) for contact detection which is insensitive to variation in particle sizes (2). It had been shown in their contribution in that DESS has a complexity of N log(N), where N is the number of entities being simulated. Please click Additional Files below to see the full abstract

Micromechanics of oxides - From complex scales to single crystals

Protective oxide scales shield high temperature materials from corrosion, thus ensuring safety and long material life under adverse operating conditions. Cracking and spallation of such scales can lead to fatigue crack initiation and expose the material to further oxidation. It is therefore imperative to measure the fracture properties of oxides so that they can be incorporated in the life estimation models of high temperature materials. Existing models require inputs on oxide properties such as fracture strain and elastic modulus. The established measurement methods are mainly applied for thick (several microns) scales, but for many materials such as superalloys the oxides are thinner (< 1 \ub5m), and the results would be affected by the influence of substrate and residual stresses. Focused ion beam machining (FIB) enables the preparation of micro sized specimens in the size range of these scales. \ua0In this work, a modified microcantilever geometry with partially removed substrate is proposed for testing of oxide scales. Room temperature microcantilever bending of thermally grown superalloy oxide (complex oxide with an upper layer of spinel and lower layer of Cr2O3) revealed the presence of plasticity, which is attributed to the deformation of the upper cubic spinel layer and low defect density of the volume being probed. Due to difficulties in isolating Cr2O3 from the complex oxide layer, dedicated oxidation exposures are performed on pure chromium to generate Cr2O3 which is tested using the same cantilever geometry at room temperature and 600 \ub0C. Results show lower fracture strain at 600 \ub0C in comparison to room temperature and presence of cleavage type of transgranular fracture in both cases, pointing to a need for studying cleavage fracture of Cr2O3. This was analysed using microcantilever bending of single crystal Cr2O3 to identify the preferential cleavage planes. Finally, fracture toughness was also measured through microcantilever bending and micropillar splitting. \ua0Thus, it is shown that micromechanical testing is an effective tool for measuring fracture properties of oxide scales. The fracture study of Cr2O3 scales show that it is a complex process in which the crystallographic texture also plays a role. Surface energy and fracture toughness criterion was unable to explain the fracture behaviour of single crystal Cr2O3 observed from experiments. Such a comprehensive analysis can contribute towards the development of reliable models for oxidation assisted failure

KNOWLEDGE OF FARMERS TOWARDS PRIVATIZATION OF AGRICULTURAL EXTENSION SERVICES IN GANJAM DISTRICT OF ODISHA

A vast country like India cannot afford to ignore ever increasing role of PAES carried out by many individuals and agencies like Agricultural consultants, group of progressive farmers, mass media like newspapers, TV, agricultural magazines, non-government organizations, private sector banks etc. Today the challenge is not the same. Finding better market for surplus produced decides Indian agriculture. Limited rescores in extension compel to look for the support of other extension system, thus opened thinking on private extension. The present extension system has ultimatum for reshaping and strengthening the structural design for the delivery of agricultural technology and services as needed by the farming community. The study was conducted in Ganjam District of Odisha purposively for investigating socio-economic status and the association of independent variables with farmers’ knowledge towards Privatization of Agricultural Extension Services. Descriptive research design was used for the present study. A total of 120 respondents were selected purposively as a sample for the present investigation. The data was collected by using pre-tested schedule and analyzed using appropriate statistical tools. Karl Pearson’s Co-efficient of Correlation test was applied to find out the association between farmers knowledge with independent variables. The major findings of the study were the socio-economic status of the respondents was found to be of medium level, the knowledge of the respondents towards PAES had significant association with the Age, Annual income, Education, Land holding Mass Media Exposure, Extension contact, Risk orientation, and scientific orientation. From the study, it is clear that PAES has become essential in our country to increase the competitiveness in the world and give justice to our farmers. At the same time, it requires great caution about problems and constraints emerged in PAES. Keeping this points stated above the present study was undertaken in Ganjam district of Odisha with the following objectives: « To determine the socio-economic status of the respondents. « To ascertain the association between independent variables and knowledge of farmers towards Privatization of Agricultural Extension Service (PAES). View Article DOI: 10.47856/ijaast.2021.v08i7.00

A REVIEW ON THE MATERIALS USED FOR BEARING AND FAILURE BEHAVIOR

This paper highlights the metallic, polymeric and ceramic materials used to manufacture the bearings, the kind of failures experienced with those materials and their causes. The failure mechanism of bearings and influence of various elements on their properties are reviewed. It is identified from the study that the failure is mainly provoked by initiating the surface micro crack/flake and then subsequently propagating them to failure. Materials influencing wear resistance to control the material removal rate without much compromising the fracture toughness are discussed. The advanced composite materials used in bearings are also discussed. A review on nano composites is also done to turn out the research on bearing materials towards nano composites. The evolution of MMC, nano composites is investigated to come to a conclusion on stimulating a research work to make a better material for bearings at room temperature and cryogenic temperature. A suitable polymer material is suggested for carrying out the research at cryogenic temperature for low temperature application of bearings