Vibrations of guyed masts

Imperial Users onl

Development of a methodology for pseudo-rigid-body models of compliant segments with inserts, and experimental validation

Compliant mechanisms have shown a great deal of potential in the last few decades in providing better solutions to design problems with numerous benefits; however, their use has been limited due to current challenges in the material selection. With ever increasing focus on the applications of compliant mechanisms, it is necessary to find alternatives to the existing materials and methods of prototyping. The purpose of this work is to develop a methodology for pseudo-rigid-body models of compliant segments with compliant inserts, comprised of a resilient material placed between the layers of a softer material, to alleviate any creep and strength issues associated with the softer material. The pseudo-rigid-body models (PRBMs) for such beams subjected to various boundary conditions are presented and validated by means of analytical and experimental methods. Pseudo-rigid-body models are used to devise simple methods of large deflection analysis, and help expedite the compliant mechanism design process. A method to improve the accuracy of the PRBM of a fixed-free beam by evaluating more accurate values of the stiffness coefficient is also presented --Abstract, Page iii

Performance investigation of a document retrieval system on a voice-data integrated token ring local area network

Lately, the interest in integration of voice and data on local computer networks has been on the rise. Subsequently, much research has been devoted to exploring various techniques that are implementable using the existing standards. This research has focused on the design issues in implementing a document retrieval system on a token ring network. The presence of voice and data traffic on the network complicates the protocol design further. The performance requirements of these traffic types are different. Voice creates stream traffic on a network, where as data traffic is bursty. Voice packets need to be delivered within a limited time interval, whereas the data emphasizes on error-free delivery. The necessity and the technological feasibility with off-the-shelf components has prompted this study. A possible solution is discussed in this dissertation;During the course of this research, due to the time consuming nature of simulation experiments, a need for efficient simulation techniques was felt. Thus, as a byproduct of the initial goal of protocol design, an approximate version of the regenerative simulation was developed and is discussed here in detail;Lastly, modeling difficulties encountered in forming an analytical model are listed and a performance analysis of the subsystems of interest is given

INFO 2009 Coursework 2 - Go Green - Group 7 - Green ICT

A Website on GREEN ICT by the Go Green Group as a part of the resource set made for the Info2009 2011-12 coursewor

Design of a Meta-assembler

Electrical Engineerin

Development, characterization and applications of magnetorheological fluid based "smart" materials on the macro-to-micro scale

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2007.Includes bibliographical references (p. 193-208).Magnetorheological fluids belong to the class of field-responsive fluids that undergo large, reversible and fast changes in their rheological properties when acted upon by an external magnetic field. 'Smart' or controllable composite materials have been obtained by doping polymers, foams, fabrics etc. with these field-responsive fluids. The resulting composite materials have potential applications in numerous fields ranging from adaptive energy absorption, automotive crash protection to microfluidic valves, mixers and separation devices. A series of stable magnetorheological (MR) fluids have been systematically characterized under steady shearing, creep and large amplitude oscillatory shear (LAOS) flow conditions. A rheometer fixture for applying nearly uniform magnetic fields up to 0.4 T has been fabricated to measure both steady-state and transient changes in the fluid properties under applied fields. Stable MR fluids with a markedly improved dynamic response (yield stress as a function of magnetic field) compared to commercial fluids have been formulated by increasing the constituent particle size and by stabilizing the system against sedimentation. A new "soft-glassy rheology" model has been used to model the fluid response time and visco-elasto-plastic response under creep conditions and oscillatory loadings.(cont.) The experiments and model show that the evolution of chain structure and plastic collapse in these suspensions exhibits a universal scaling with the dimensionless stress s = [sigma]/[sigma]y. Structure evolution, pattern formation and dynamics of MR fluid flow in microchannel geometries has been analyzed using high-speed digital video microscopy. In order to elucidate the mechanisms that control MR structure formation, experiments have been performed while varying the magnetic field, particle size, channel geometry, concentration and fluid composition. Excellent qualitative agreement has been obtained with Brownian Dynamics simulations and useful scalings based on interplay of magnetostatic & viscous forces have been extracted to understand the field-dependent fluid response on the macro & micro scale. Novel MR elastomeric materials and microparticles have been synthesized by doping photo-curable or thermo-curable polymers with field-responsive fluids. A high-throughput micromolding technique for synthesis of controllable particles of anisotropic shapes and sizes has been developed. Flexible and permanent chain-like structures have also been synthesized using amidation chemistry. Potential microfluidic applications such as field-responsive valves, mixers and separation devices using these 'smart' materials have also been investigated.by Suraj Sharadchandra Deshmukh.Ph.D

Dynamic Aspects of Sprays for Absorption Applications

Spray columns show potential for absorption applications such as CO2 capture because of the low gas phase pressure drop and resistivity to the corrosive action of amine solvents such as Monoethanolamine (MEA) due to the lack of internal hardware. Spray absorption data in terms of mass transfer coefficients is needed for robust design, whereas dropsize data and interfacial area data are required to improve the current understanding of spray absorption. The aim of this study was to measure spray absorption rates, drop size, and surface area for the CO2-MEA system in a laboratory spray column. In specific, the study was conducted to elucidate the effect of increasing MEA concentration on spray absorption of CO2. Further, the interfacial area inside the Spray column was ascertained by absorbing CO2 in a low normality Sodium hydroxide (NaOH) solution as a measure of the spray efficiency. Absorption rates for the CO2-MEA system were found to decrease with increasing inlet loading on one hand, and increase with L/G ratio, and MEA concentration on the other. Dropsize measurements were found to be practically independent of the inlet loading. A new methodology to compute planar area from dropsize measurements was developed. The computed planar surface areas were found to be comparable for the two MEA concentrations tested. Free MEA content was thus found to dominate the spray absorption process. Increasing MEA concentration for spray absorption of CO2 may be a feasible option. Interfacial area measurements inside the spray column were found to be strongly dependent on the contactor height. The interfacial area in sprays was found comparable to packed columns at low gas-liquid contact heights. Data for both the CO2-MEA and CO2-NaOH system, points to a large degree of mass transfer in the region in the immediate vicinity of the nozzle tip. Short contact spray columns for absorption applications are thus recommended.Chemical Engineerin

Smart fluids for advanced automotive applications

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003.Includes bibliographical references (p. 122-129).Energy management is of vital concern in the automotive industry and many components need to satisfy stringent 'impact-safe' requirements. These energy absorption requirements conflict with the design demands for more compliant, thinner materials leading to a conflict of stiffness problem. A 'novel' energy absorbing material that adapts to environmental conditions and user specifications has been conceptualized, designed, modeled and tested in the present work. This adaptive energy absorbing material consists of an elastomeric foam impregnated with a field-responsive fluid such as a magnetorheological fluid or a shear-thickening fluid. Stable and inexpensive magnetorheological (MR) fluids based on carbonyl iron powder have been synthesized in the laboratory. The rheological properties, including the field dependent yield-stress, of the fluid have been measured at magnetic fields varying from 0.0 to 0.4 Tesla using a custom-built fixture for the AR 2000/ 1000N rheometers. Steady shear rheological experiments and transient creep tests have also been performed on a shear-thickening fluid consisting of 56% w/w corn-starch in water. The large, reversible changes in the rheological behavior of field-responsive fluids have been utilized for controlling the stress-strain behavior and energy absorption characteristics of cellular solids. The mechanical properties of 'dry' and field-responsive fluid-impregnated cellular solids have been determined using Texture Analyzer modified with a custom-built attachment. Foams impregnated with MR fluids have shown a tremendous improvement in the energy-absorption capacity. The energy absorbed per unit volume at moderate magnetic fields (B ~/~ 0.2 T) has been found to increase by 30 to 50 times as compared to the energy absorbed at zero-field. A 'two-layer' scaling model has been proposed to explain the increase in the foam plateau stress based on an assumption that the MR fluid forms a secondary layer on the solid edges of the foam and determines the composite elastic modulus. Experiments have been carried out to determine the effect of control parameters such as the magnetic field, volume fraction of the fluid impregnating the foam and the strain rate on the mechanical behavior of the composite. The magnetic field has been varied from 0.0 to 0.2 T, the volume fraction from 0% to 60% and the strain rate from 0.02 to 2.0 s-1. All the experimental data has been found to collapse onto a single master curve using appropriate shift factors based on the proposed theoretical model. Impact testing using a 'drop-ball' test apparatus, built in-house, has been performed for a scaled down headrest model. Designs for an adaptive headrest and various automotive components have also been described in detail. The present work has thus presented a 'novel' class of conformable field-responsive fluid based composites that can be used for rapidly switching energy absorbing applications.by Suraj Sharadchandra Deshmukh.S.M

Geospatial approach for assessment of groundwater quality

The increasing population, erratic distribution of rainfall, and their rising demand for water in domestic and irrigation are fulfilled by groundwater resources. Due to overexploitation, there is the deterioration of groundwater quality, and hence to evaluate the groundwater quality, a study was undertaken to understand the water suitability for drinking as well as for irrigation purposes. For this study, five villages, namely Kumulur, Tachankurunchi, Pudurutamanur, Pandaravadai and Poovalur, were selected from Trichy District, Tamil Nadu, India, with an aerial extent of 45.1 km2. For the water quality assessment, samples were drawn from 53 locations from the sources like open wells, bore wells and hand pumps, etc. Parameters of pH, EC, TDS, Anions—CO3-2, CO3 2−, HCO3−, Cl−, SO42-, Cations—Ca2+, Mg2+, B3+, Na+ and potassium (K+) were estimated using the standard analytical procedure in three different seasons, viz., S-I (September 2019), S-II (December 2019) and S-III (March 2020). The WQI was computed for drinking water quality and found that 25% of samples in S-I, 80% samples in S-II and 83% samples in S-III were above the permissible limit for drinking purposes. Indices like Sodium Percentage, Sodium Adsorption Ratio, Permeability Index, Kelly’s Ratio, Magnesium Hazard Ratio, Potential Salinity, USSL Diagram, Wilcox Plot, Piper Diagram and Gibbs plot were evaluated for examining irrigation water quality. The results revealed that in 90% of the area, the water is suitable for irrigation purposes and a few locations (10%) wherein the salt content of water is relatively higher than the entire study area.</p