THE DISSOLUTION OR GROWTH OF A SPHERE

The problem of the dissolution or growth of an isolated, stationary, sphere in a large fluid body is analyzed. The motion of the boundary as well as the resulting motion in the liquid are properly taken into account. The governing equations are solved using a recently developed technique (Subramanian and Weinberg, 1981) which employs an asymptotic expansion in time. Results for the radius of the sphere as a function of time are calculated. The range of utility of the present solution is established by comparison with a numerical solution of the governing equations obtained by the method of finite differences.     

Dissolution of Multicomponent Bubbles

The behavior of an isolated, stationary, multicomponent gas bubble in a glassmelt containing several dissolved gases is considered. The relevant mass-transport equations are formulated and calculations are performed for the case of two diffusing gases using a quasi-stationary model and a numerical solution of the exact mass-transfer equations. The results obtained from these two approaches are compared. The factors which govern the dissolution or growth of a bubble are thermodynamic and kinetic in origin. The tendency of a bubble to grow or shrink at long times is controlled by departure from overall equilibrium, whereas the short-time bubble dynamics may be dominated by kinetic effects. As a result of the existence of these dual influences, maxima and/or minima occur in the functional dependence of the bubble radius on time.     

STRESS RELAXATION BEHAVIOR OF MICROWAVE-VACUUM-DRIED ALGINATE GELS

Swelling of alginate polymer matrix in water involves a build up of network pressure due to an elastic extension of the polymeric matrix. When this network pressure undergoes relaxation by means of dehydration, shrinkage may take place. Three different types of wet alginate gels were prepared and dried using microwave‐vacuum‐drying technique. Dried alginate gel solids had a porous structure. To understand the stress relaxation behavior of alginate gel‐based porous solid structures, uniaxial compressive relaxation studies were performed at selected strain rates, preloads and relaxation times Experimental relaxation curves were normalized and fitted to an empirical relationship, and relaxation behavior was explained. Stress relaxation data were also fitted to another empirical model. All three types of gels had similar elastic components. At lower strain rate, all samples had more resistance to elastic deformation. Stress relaxation information of the dried gel was related to its microstructure. Type 2 gel had more stiffness than type 1 and type 3 gels. The mechanism involved in stress relaxation was entanglement coupling of larger polymer chains in covalently cross‐linked alginate gels.     

Analytical simulation of rib-web forging

The friction calibration curves were generalized using ALPID simulations of ring compression tests and were used to establish the friction factor associated in the workpiece-tool interface. ALPID simulations were carried out for different rib-web sections. The metal flow characteristics were closely watched and load requirements for these processes were established. The distribution of effective strain and strain rate and stress were established.     

The influence of the environment and corrosion on the structural integrity of aircraft materials

Fatigue results of 1¹/₂ dog-bone jointed specimens manufactured from 7075-T6 aluminium alloy indicated that the application of corrosion preventative compounds (CPCs) at the faying surfaces slightly decreased the log mean fatigue life at 144 MPa, while the effect was not statistically significant at the higher stress level (210 MPa). The addition of the CPC also reduced fretting corrosion at the faying surfaces and shifted the fatigue initiation sites closer to the edge of fastener holes. Scatter in fatigue life was found to be associated with the location and size of the intermetallics at the initiation site. The presence of corrosion in the bores of the countersunk fastener holes reduced the fatigue life by up to one order of magnitude. Fatigue test results for dog-bone specimens manufactured from 7075-T651 and 2024-T351 aluminium alloys indicated that the presence of exfoliation corrosion reduced the fatigue life under dry conditions, with a greater reduction under humid conditions. The application of a CPC to the corroded region eliminated the influence humidity had on fatigue life.     

The interaction between corrosion management and structural integrity of aging aircraft

Aircraft joints feature prominently in aircraft structural degradation; fatigue cracking and corrosion damage are major issues, which can reduce joint strength and degrade service life. Protecting the structure against corrosion usually involves use of highly developed protective coatings – paints and sealants – and, increasingly, the application of corrosion inhibiting compounds (CICs) which retard corrosion principally by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact – in different ways – with joint structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to the extent to which application of CICs (or other lubricants) can cause a reduction in the fatigue life of mechanically fastened joints. The CICs are lubricants which will reduce the friction at the faying surface of the joint, and change the load transfer characteristics of the joint. This paper discusses results from a test program assessing the fatigue life and failure mode of simple riveted lap joints; the results show a distinct reduction in fatigue life for joints containing CICs, and the paper discusses the changes thought to be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, because areas such as sheet ends and fastener heads, where displacements are concentrated, may produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. This paper discusses the role of joint displacement in service as a factor contributing to degradation in aircraft coatings at joints, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes analyses of displacements in aircraft joints, to identify the levels of strain and to identify the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings.     

Study of PBL dynamics over northern plains in fixing stack height of a super thermal power station

The Planetary Boundary Layer plays an important role in air pollution meteorology and in fixing the Stack height of major air-polluting industries, including the super thermal power plants. In India a super thermal power plant is being set up at Yamunanagar (30·1° N, 77·33 ° E) and it has been studied using an acoustic sounder with a stack height of 220?m which would be the optimum height to keep the physical stack above surface based inversions for 80 per cent of the time and the elevated inversions for 50 per cent of time above. However, the hot plume rise would inject any pollutants above the surface based inversions for 95 per cent of the time     

OPTIMIZATION OF SPRAY DRYING CONDITIONS FOR PRODUCTION OF BIFIDUS MILK POWDER FROM COW MILK

Bifidus milk powder was prepared by supplementing cow's milk with predetermined level of additives to obtain slurry of desired concentration. The slurry was sterilized, cooled and inoculated with 24‐h‐old bulk culture of Bifidobacterium bifidum at 10% and incubated at 37C for 24 h, cooled and dried in SM Scientech Lab model spray dryer with predetermined spray drying conditions. The bifidus milk powder contains bifidobacteria counts from 1.88 × 10⁹ to 15.80 × 10⁹ cells/g dry weight and their percent survival was 4.17–35.11%. Maximum survival was obtained by using the following spray drying conditions: inlet temperature of 164.02C, slurry concentration of 25.62% total soluble solids and air pressure of 2.5 kg/cm². The high temperature and air pressure of spray drying markedly influenced the color and appearance of final product. The inlet temperature and air pressure showed a significant effect on survival of bifidobacteria in the final product.     

Pragmatic multi-stage simulated annealing for optimal placement of synchrophasor measurement units in smart power grids

Conventional power grids across the globe are reforming to smart power grids with cutting edge technologies in real time monitoring and control methods. Advanced real time monitoring is facilitated by incorporating synchrophasor measurement units such as phasor measurement units (PMUs) to the power grid monitoring system. Several physical and economic constraints limit the deployment of PMUs in smart power grids. This paper proposes a pragmatic multi-stage simulated annealing (PMSSA) methodology for finding the optimal locations in the smart power grid for installing PMUs in conjunction with existing conventional measurement units (CMUs) to achieve a complete observability of the grid. The proposed PMSSA is much faster than the conventional simulated annealing (SA) approach as it utilizes controlled uphill and downhill movements during various stages of optimization. Moreover, the method of integrating practical phasor measurement unit (PMU) placement conditions like PMU channel limits and redundant placement can be easily handled. The efficacy of the proposed methodology has been validated through simulation studies in IEEE standard bus systems and practical regional Indian power grids.