Jiji, K S; Jayadas, N H; Babu, C A(Cochin University Of Science And Technology, May , 2015)
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Abstract:
Salient pole brushless alternators coupled to IC engines are
extensively used as stand-by power supply units for meeting in-
dustrial power demands. Design of such generators demands high
power to weight ratio, high e ciency and low cost per KVA out-
put. Moreover, the performance characteristics of such machines
like voltage regulation and short circuit ratio (SCR) are critical
when these machines are put into parallel operation and alterna-
tors for critical applications like defence and aerospace demand
very low harmonic content in the output voltage. While designing
such alternators, accurate prediction of machine characteristics,
including total harmonic distortion (THD) is essential to mini-
mize development cost and time.
Total harmonic distortion in the output voltage of alternators
should be as low as possible especially when powering very sophis-
ticated and critical applications. The output voltage waveform
of a practical AC generator is replica of the space distribution of
the
ux density in the air gap and several factors such as shape
of the rotor pole face, core saturation, slotting and style of coil
disposition make the realization of a sinusoidal air gap
ux wave
impossible. These
ux harmonics introduce undesirable e ects on
the alternator performance like high neutral current due to triplen
harmonics, voltage distortion, noise, vibration, excessive heating
and also extra losses resulting in poor e ciency, which in turn
necessitate de-rating of the machine especially when connected
to non-linear loads. As an important control unit of brushless
alternator, the excitation system and its dynamic performance
has a direct impact on alternator's stability and reliability.
The thesis explores design and implementation of an excitation
i
system utilizing third harmonic
ux in the air gap of brushless al-
ternators, using an additional auxiliary winding, wound for 1=3rd
pole pitch, embedded into the stator slots and electrically iso-
lated from the main winding. In the third harmonic excitation
system, the combined e ect of two auxiliary windings, one with
2=3rd pitch and another third harmonic winding with 1=3rd pitch,
are used to ensure good voltage regulation without an electronic
automatic voltage regulator (AVR) and also reduces the total
harmonic content in the output voltage, cost e ectively.
The design of the third harmonic winding by analytic methods
demands accurate calculation of third harmonic
ux density in
the air gap of the machine. However, precise estimation of the
amplitude of third harmonic
ux in the air gap of a machine by
conventional design procedures is di cult due to complex geome-
try of the machine and non-linear characteristics of the magnetic
materials. As such, prediction of the eld parameters by conven-
tional design methods is unreliable and hence virtual prototyping
of the machine is done to enable accurate design of the third har-
monic excitation system.
In the design and development cycle of electrical machines, it is
recognized that the use of analytical and experimental methods
followed by expensive and in
exible prototyping is time consum-
ing and no longer cost e ective. Due to advancements in com-
putational capabilities over recent years, nite element method
(FEM) based virtual prototyping has become an attractive al-
ternative to well established semi-analytical and empirical design
methods as well as to the still popular trial and error approach
followed by the costly and time consuming prototyping. Hence,
by virtually prototyping the alternator using FEM, the important
performance characteristics of the machine are predicted.
Design of third harmonic excitation system is done with the help
of results obtained from virtual prototype of the machine. Third
harmonic excitation (THE) system is implemented in a 45 KVA
ii
experimental machine and experiments are conducted to validate
the simulation results. Simulation and experimental results show
that by utilizing third harmonic
ux in the air gap of the ma-
chine for excitation purposes during loaded conditions, triplen
harmonic content in the output phase voltage is signi cantly re-
duced. The prototype machine with third harmonic excitation
system designed and developed based on FEM analysis proved
to be economical due to its simplicity and has the added advan-
tage of reduced harmonics in the output phase voltage.
Paulose,M M; Narayanan Nampoothiri,V N; Sreejith,P S(School of Engineering, May , 2006)
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Abstract:
The study aims to the hydrodynamic characteristics of swirling fluidized bed, using large particles (Geldart D-type) selected from locally available agricultural produce (coffee beans and black pepper). The important variables considered in the present study include percentage area of opening, angle of air injection and the percentage useful area of the distributor. A total of seven distributors have been designed and fabricated for a bed column of 300 mm, namely single row vane type distributors (15˚ and 20˚ vane angle), inclined hole type distributors (15˚ and 20˚ vane angle) and perforated plate distributors. The useful area of distributor of single row vane type, three now vane-type and inclined hole-type distributors are respectively 64%,91% and 94%. The hydrodynamic parameters considered in the present study include distributor pressure drop, air velocity, minimum fluidizing velocity, bed pressure drop, bed height and the bed behaviour.
It has been observed that, in general, the distributor pressure drop decreases with an increase in the percentage area of opening, Further, and increase in the area of opening above 17% will not considerably reduce the distributor pressure drop. In the present study, for the distributor with an area of opening 17%, and corresponding to the maximum measured superficial velocity of 4.33 m/s, the distributor pressure drop obtained was 55.25mm of water. The study on the bed behavior revealed that, in a swirling fluidized bed, once swirl motion starts, the bed pressure drop increases with superficial velocity in the outer region and it decreases in the inner region. This means that, with higher superficial velocity, the air might get by-passed through the inner boundary of the bed (around the cone). So, depending on the process for which the bed is used, the maximum superficial velocity is to be limited to have an optimum bed performance.
Bindu, C S; Dr. Beena, K S(Cochin University of Science and Technology, January 16, 2012)
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Abstract:
The increase in traffic growth and maintenance expenditures demands the urgent need for building better, long-lasting, and more efficient roads preventing or minimizing bituminous pavement distresses. Many of the principal distresses in pavements initiate or increase in severity due to the presence of water. In Kerala highways, where traditional dense graded mixtures are used for the surface courses, major distress is due to moisture induced damages. The Stone Matrix Asphalt (SMA) mixtures provide a durable surface course. Proven field performance of test track at Delhi recommends Stone Matrix Asphalt as a right choice to sustain severe climatic
and heavy traffic conditions. But the concept of SMA in India is not so popularized and its application is very limited mainly due to the lack of proper specifications.
This research is an attempt to study the influence of additives on the
characteristics of SMA mixtures and to propose an ideal surface course for the pavements. The additives used for this investigation are coir, sisal, banana fibres (natural fibres), waste plastics (waste material) and polypropylene (polymer). A preliminary investigation is conducted to characterize the materials used in this study. Marshall test is conducted for optimizing the SMA mixtures (Control mixture-without additives and Stabilized mixtures with additives). Indirect tensile strength tests, compression strength tests, triaxial strength tests and drain down sensitivity tests are conducted to study the engineering properties of stabilized mixtures. The comparison of the performance of all stabilized mixtures with the control mixture and among themselves are carried out. A statistical analysis (SPSS package Ver.16) is performed to establish the findings of this study
Description:
School of Engineering, Cochin
University of Science and Technology
Josephkunju,Paul C; Dr.Sreejith,P S(Cochin University of Science & Technology, September , 2008)
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Abstract:
The thesis presented here unveils an experimental study of the hydrodynamic
characteristics of swirling fluidized bed viz. pressure drop across the distributor and the
bed, minimum fluidizing velocity, bed behaviour and angle of air injection. In swirling
fluidized bed the air is admitted to the bed at an angle 'Ѳ' to the horizontal. The vertical
component of the velocity v sin Ѳ causes fluidization and the horizontal component
v cos Ѳ contributes to swirl motion of the bed material.The study was conducted using spherical particles having sizes 3.2 mm, 5.5 mm & 7.4
mm as the bed materials. Each of these particles was made from high density
polyethylene, nylon and acetal having relative densities of 0.93, 1.05 and 1.47
respectively.The experiments were conducted using conidour type distributors having four rows of
slits. Altogether four distributors having angles of air injection (Φ)- 0°, 5°, 10° & 15°
were designed and fabricated for the study. The total number of slits in each distributor
was 144. The area of opening was 6220 mm2 making the percentage area of opening to
9.17. But the percentage useful area of opening of the distributor was 96.The experiments on the variation of distributor pressure drop with superficial velocity
revealed that the distributor pressure drop decreases with angle of air injection.
Investigations related to bed hydrodynamics were conducted using 2.5 kg of bed
material. The bed pressure drop measurements were made along the radial direction of
the distributor at distances of 60 mm, 90 mm, 120 mm & 150 mm from the centre of
the distributor. It was noticed that after attaining minimum fluidizing velocity, the bed pressure drop increases along the radial direction of the distributor. But at a radial
distance of 90 mm from the distributor centre, after attaining minimum fluidizing
velocity the bed pressure drop remains almost constant. It was also observed that the
bed pressure drop varies inversely with particle size as well as particle density.An attempt was made to determine the effect of various parameters on minimum
fluidizing velocity. It was noticed that the minimum fluidizing velocity varies directly
with angle of air injection (Φ), particle size and particle density.The study on the bed behaviour showed that the superficial velocity required for
initiating various bed phenomena (such as swirl motion and separation of particles from
the cone at the centre) increase with increase in particle size as well as particle density.
It was also observed that the particle size and particle density directly influence the
superficial velocity required for various regimes of bed behaviour such as linear
variation of bed pressure drop, constant bed pressure drop and sudden increase or
decrease in bed pressure drop.Experiments were also performed to study the effect of angle of air injection (Φ). It was
noticed that the bed pressure drop decreases with angle of air injection. It was also
noticed that the angle of air injection directly influence the superficial velocity required
for initiating various bed phenomena as well as the various regimes of bed behaviour.
Description:
Division of Mechanical Engineering,
Cochin University of Science and Technology
Biju Augustine, P; Dr.Bhasi, M; Dr.Madhu, G(Cochin University Of Science And Technology, May 6, 2013)
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Abstract:
Production Planning and Control (PPC) systems have grown and changed
because of the developments in planning tools and models as well as the use of
computers and information systems in this area. Though so much is available in
research journals, practice of PPC is lagging behind and does not use much from
published research. The practices of PPC in SMEs lag behind because of many reasons, which need to be explored This research work deals with the effect of identified variables such as forecasting, planning and control methods adopted, demographics of the key person, standardization practices followed, effect of training, learning and IT usage on firm performance. A model and framework has been developed based on literature. Empirical testing of the model has been done after collecting data using a questionnaire schedule administered among the selected respondents from Small and Medium Enterprises (SMEs) in India. Final data included 382 responses. Hypotheses linking SME performance with the use of forecasting, planning and controlling were formed and tested. Exploratory factor analysis was used for data reduction and for identifying the factor structure. High and low performing firms were classified using a Logistic Regression model. A confirmatory factor analysis was used to study the structural relationship between firm performance and dependent variables.
Description:
School Of Engineering
Cochin University Of Science And Technology
Biju Augustine; Dr Bhasi, M; Dr Madhu, G(Cochin University of Science and Technology, May 6, 2013)
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Abstract:
Production Planning and Control (PPC) systems have grown and changed
because of the developments in planning tools and models as well as the use of
computers and information systems in this area. Though so much is available in
research journals, practice of PPC is lagging behind and does not use much from
published research. The practices of PPC in SMEs lag behind because of many reasons,
which need to be explored.
This research work deals with the effect of identified variables such as
forecasting, planning and control methods adopted, demographics of the key person,
standardization practices followed, effect of training, learning and IT usage on firm
performance. A model and framework has been developed based on literature.
Empirical testing of the model has been done after collecting data using a
questionnaire schedule administered among the selected respondents from Small and
Medium Enterprises (SMEs) in India. Final data included 382 responses. Hypotheses
linking SME performance with the use of forecasting, planning and controlling were
formed and tested. Exploratory factor analysis was used for data reduction and for
identifying the factor structure. High and low performing firms were classified using a
Logistic Regression model. A confirmatory factor analysis was used to study the
structural relationship between firm performance and dependent variables.
Bindhu, B K; Dr.Madhu, G(Cochin University of Science And Technology, December 21, 2013)
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Abstract:
Effective solids-liquid separation is the basic concept of any
wastewater treatment system. Biological treatment methods involve
microorganisms for the treatment of wastewater. Conventional activated
sludge process (ASP) poses the problem of poor settleability and hence
require a large footprint. Biogranulation is an effective biotechnological
process which can overcome the drawbacks of conventional ASP to a great
extent. Aerobic granulation represents an innovative cell immobilization
strategy in biological wastewater treatment. Aerobic granules are selfimmobilized
microbial aggregates that are cultivated in sequencing batch
reactors (SBRs). Aerobic granules have several advantages over
conventional activated sludge flocs such as a dense and compact microbial
structure, good settleability and high biomass retention.
For cells in a culture to aggregate, a number of conditions have to be
satisfied. Hence aerobic granulation is affected by many operating
parameters. The organic loading rate (OLR) helps to enrich different
bacterial species and to influence the size and settling ability of granules.
Hence, OLR was argued as an influencing parameter by helping to enrich
different bacterial species and to influence the size and settling ability of
granules. Hydrodynamic shear force, caused by aeration and measured as
superficial upflow air velocity (SUAV), has a strong influence and hence it
is used to control the granulation process. Settling time (ST) and volume
exchange ratio (VER) are also two key influencing factors, which can be
considered as selection pressures responsible for aerobic granulation based
on the concept of minimal settling velocity. Hence, these four parameters -
OLR, SUAV, ST and VER- were selected as major influencing parametersfor the present study. Influence of these four parameters on aerobic
granulation was investigated in this work
Description:
Division of Safety and Fire Engineering
School of Engineering
Cochin University of Science and Technology