Control of Dynamic Brake Through Heuristic Rule

In this paper, it is shown that the application of a dynamic brake or thyristorcontrolled braking resistor (TCBR) at the generator terminals enhances the power transfer limit over a transmission line greatly. Two types of dynamic brake configuration have been considered here: a 3-phase, bidirectional, fullwave, Y-connected, phase controlled conventional brake and a 3-phase, fullwave, thyristor-controlled rectifier bridge. A simple rule-based '' ON-OFF'' control law based on the local measurement of generator output power and its derivative is proposed in this paper. Detail digital simulation studies using the PSCAD/EMTDC package have been carried out. It was found that with the insertion of the dynamic brake circuit and its associated control, the system is able to recover following 3-line-to-ground faults even at very heavy power transfer levels, which is not possible otherwise.     

Effect of microstructure on non-linear behavior of ultrasound during low cycle fatigue of pearlitic steels

Influence of microstructural changes on the second harmonics of sinusoidal ultrasonic wave during low cycle fatigue (LCF) deformation in pearlitic steel was studied. Fatigue tests were interrupted and at every interruption, non-linear ultrasonic (NLU) parameter (β) was determined. Microstructures of cyclically deformed specimens at various cycles were examined by transmission electron microscopy (TEM). The variation of β with fatigue cycles was correlated with the microstructural changes and the results were explained through the variation in dislocation morphology and carbon content of the steel.     

Catalytic properties of dendron–OMS hybrids

The synthesis and catalytic testing of several dendron–ordered mesoporous silica hybrids are reported. These materials are active in both the nitroaldol (Henry) reaction and the transesterification of glyceryl tributyrate to afford methyl esters. In both reactions it is observed that dendrons terminated with primary amines are more catalytically active than samples containing dendrons terminated with secondary amines. On a mmol nitrogen per gram of silica basis, the first generation dendrons are the most active for both chemistries, and the SBA-15 samples display a higher activity than the MCM-41 samples. The pore-size effect observed is consistent with significant diffusion resistance in the MCM-41 samples. The activity trend observed in the SBA-15 materials is consistent with decreased cooperative effects between the amines and surface silanols as the dendrons become larger. Clear trends are observed indicating that higher generation dendrons are more selective to alcohol formation in the Henry reaction. The dendron catalysts are much more active and stable than simple amines attached to silica in the transesterification of triglycerides. Preliminary results shown indicate that these materials can also catalyze more demanding chemistries, an example of which is the Aldol condensation of 5-(hydroxymethyl)furfural and acetone. The results shown indicate that dendron–OMS hybrids can serve as effective solid base catalysts for a diverse range of chemistries.     

Analysis of thermoelastic response in a functionally graded spherically isotropic hollow sphere based on Green–Lindsay theory

This paper is concerned with the investigation of thermoelastic displacements and stresses in a functionally graded spherically isotropic hollow sphere due to prescribed temperature in the context of the linear theory of generalized thermoelasticity with two relaxation time parameters (Green and Lindsay theory). Both the surfaces of the body are free from radial stresses, and the inner surface is subjected to a time-dependent thermal shock whereas the outer one is maintained at constant temperature. The basic equations have been written in the form of a vector–matrix differential equation in the Laplace transform domain which is then solved by an eigenvalue approach. The numerical inversion of the transforms is carried out using a method of Bellman et al. The displacements and stresses are computed and presented graphically. It is found that the variation of the thermophysical properties of a material as well as the thickness of the body strongly influence the response to loading. A comparative study with the corresponding homogeneous material has also been made. The solution of the problem of a spherically isotropic infinite medium containing a spherical cavity has been derived theoretically by tending the outer radius to infinity, as a particular case.     

Shear strength response of reinforced pond ash

Reinforced pond ash is a composite material, which can be used as an alternative construction material in the field of geotechnical engineering. To study the shear strength response of reinforced pond ash, a series of unconsolidated undrained (UU) triaxial test has been conducted on both unreinforced and reinforced pond ash. In the present investigation the effects of confining pressure (σ₃), number of geotextile layers (N), and types of geotextiles on shear strength response of pond ash are studied. The results demonstrate that normal stress at failure (σ_1f) increases with increase in confining pressure. The rate of increase of normal stress at failure (σ_1f) is maximum for three layers of reinforcement, while the corresponding percentage increase in σ_1f is around (103%), when the number of geotextile layers increases from two layers to three layers of reinforcement. With increase in confining pressure the increment in normal stress at failure, Δσ increases and attains a peak value at a certain confining pressure (threshold value) after that Δσ becomes more or less constant. The threshold value of confining pressure depends on N, dry unit weight (γ_d) of pond ash, type of geotextile, and also type of pond ash.     

Study of Damage and Fracture Toughness Due to Influence of Creep and Fatigue of Commercially Pure Copper by Monotonic and Cyclic Indentation

Fracture toughness is the ability of a component containing a flow to resist fracture. In the current study, the Ball indentation (BI) test technique, which is well acknowledged as an alternative approach to evaluate mechanical properties of materials due to its semi-nondestructive, fast, and high accurate qualities is used to estimate damage and the fracture toughness for copper samples subjected to varying levels of creep and fatigue. The indentation fracture toughness shows the degradation of Cu samples when they are subjected to different creep conditions. Axial fatigue cycling increases the strength at the mid-gauge section compared to other regions of the samples due to initial strain hardening. The advancement of indentation depth with indentation fatigue cycles experiences transient stage, i.e., jump in indentation depth has been observed, which may be an indication of failure and followed by a steady state with almost constant depth propagation with indentation cycles.     

Effect of silica doping on the densification and grain growth in zinc oxide

The ability of silica (SiO₂) in controlling the densification and grain growth behavior of nano crystalline zinc oxide (ZnO) has been systematically studied. It has been observed that SiO₂ acts as a sintering inhibitor in the ZnO–SiO₂ system up to 4 wt.% limiting value beyond which densification behavior of the system remains almost unchanged, especially above 1100 °C. The addition of SiO₂ to ZnO retards grain growth which in turn results a finer ultimate grain size as compared to the undoped ZnO. However, stabilization in grain size occurs at ≥4 wt.% SiO₂ addition. It has been observed that SiO₂ incorporation changes the grain growth mechanism up to 4 wt.% addition, beyond which no remarkable changes was noticed. The grain growth (n) shows distinctly different slopes as a function of sintering time for the SiO₂ doped ZnO systems than undoped ZnO. The different slopes tend to indicate that different diffusion mechanisms and probably the formation of a secondary phase (Zn–Si–O) at the grain boundary control the densification and grain growth. The thermal expansion coefficient of the system has been found to decrease substantially beyond 4 wt.% SiO₂ addition to ZnO.     

Estimation of crack opening area for leak before break analysis of nuclear reactor system

The crack opening area has been estimated by various models for leak before break analysis of nuclear reactor systems. A number of linear elastic fracture mechanics models have been employed. A model has been derived based on Forman et al. [Forman, R.G., Hickman, J.C., Shivakumar, V., 1985. Stress intensity factors for circumferential through cracks in hollow cylinders subjected to combined tension and bending loads. Eng. Frac. Mech. 21, 563-571] model for stress intensity factors. The linear elastic fracture models entail the use of plasticity corrections. The convergence behaviour of the iterative implementation for plasticity correction has been studied. An elasto-plastic fracture mechanics model has also been adopted for comparative study undertaken here. The range of applicability of the models has been reviewed.     

Unveiling the self-assembly behavior of copolymers of AAc and DMAPMA in situ to form smart hydrogels displaying nanogels-within-macrogel hierarchical morphology

Stimulus responsive hydrogels are being considered as one of the most crucial biomaterials of current generation. A new technique has been established for developing hydrogels based on Acrylic acid (AAc) and N-[3-(Dimethylamino)propyl]-methacrylamide (DMAPMA), and relevant mechanism has been delineated. Aqueous redox copolymerization of different molar ratios of AAc and DMAPMA at 41 ± 1 °C, leading to the formation of interlocked nanogels of ∼300 nm diameter, which acted as the building blocks of a series of superabsorbent hydrogels having robust, honey-comb type three-dimensional architecture. Monomer composition, monomer feed ratio and water content in feed has been found to be important factors in the development of the stable poly(AAc-co-DMAPMA) hydrogel membranes (PADMAs) without any active crosslinking agent. At the cues of pH change from 7.0 to 3.5, pulsatile swelling-deswelling behavior varied, ranging from ∼5900% to ∼60% (mass) respectively, underlining smart hydrogel characteristics needed for specific biomedical applications. Elastic modulus of the gels, equilibrated at pH 7.0, is recorded to be >15 kPa under uniaxial compression. Underlying mechanism of the formation of such robust three-dimensional structures in poly(AAc-co-DMAPMA) hydrogel membranes, and the origin of hierarchical ‘nano-to-macro’ scale morphological features has been proposed.