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Optimal operation of a pyrolysis reactorJarullah, Aysar Talib, Hameed, S.A., Hameed, Z.A., Mujtaba, Iqbal M. January 2015 (has links)
No / In the present study, the problem of optimization of thermal cracker (pyrolysis) operation is discussed. The main objective in thermal cracker optimization is the estimation of the optimal flow rates of different feeds (such as, Gas-oil, Propane, Ethane and Debutanized natural gasoline) to the cracking furnace under the restriction on ethylene and propylene production. Thousands of combinations of feeds are possible. Hence the optimization needs an efficient strategy in searching for the global minimum. The optimization problem consists of maximizing the economic profit subject to a number of equality and inequality constraints. Modelling, simulation and optimal operation via optimization of the thermal cracking reactor has been carried out by gPROMS (general PROcess Modelling System) software. The optimization problem is posed as a Non-Linear Programming problem and using a Successive Quadratic Programming (SQP) method for solving constrained nonlinear optimization problem with high accuracy within gPROMS software. New results have been obtained for the control variables and optimal cost of the cracker in comparison with previous studies.
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Monitoring of pipeline using smart sensorsNugroho, Wibowo Harso, 1967- January 2001 (has links)
Abstract not available
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Prediction of low temperature cracking of asphalt concrete mixtures with thermal stress restrained specimen test resultsKanerva, Hannele K. 21 June 1993 (has links)
Low temperature cracking is attributed to tensile stresses induced in an
asphalt concrete pavement that develop when the pavement is subjected to a cold
temperature. Cracking results in poor ride quality and a reduction in service life of
the pavement. Low temperature cracking has been predicted by regression
equations, mechanistic approaches and by simulation measurements. The purpose of
the study reported herein is to (1) evaluate the Thermal Stress Restrained Specimen
Test (TSRST) as an accelerated performance test to simulate low temperature
cracking of asphalt concrete mixtures and (2) develop a deterministic and
probabilistic model to predict low temperature cracking with TSRST results.
Construction histories, cracking observations and temperature data were
collected for five test roads in Alaska, Pennsylvania and Finland. A full scale and
fully controlled low temperature cracking test program was conducted at the U.S.
Army Cold Regions Research and Engineering Laboratory (USACRREL).
Specimens were fabricated in the laboratory with original asphalt cements and
aggregates from the test roads. In addition, asphalt concrete pavement specimens
were cut from the test sections. The TSRST results obtained for these samples were
correlated with the field observations. Based on a statistical analysis of the data, the
TSRST fracture temperature is associated with the field cracking temperature and
crack frequency for the test roads where mixture properties dominated low
temperature cracking. It was concluded that the TSRST can be used to simulate low
temperature cracking of asphalt concrete mixtures.
A deterministic and a probabilistic model were developed to predict crack
spacing as a function of time using the TSRST results, pavement thickness and bulk
density, pavement restraint conditions and air temperature. The affect of aging on
pavement properties was incorporated in the models by predicting the field aging
with Long Term Oven Aging (LTOA) treatment in the laboratory. The calculation
of the crack spacing is based on the theory that the pavement slab cracks when the
pavement temperature reaches the cracking temperature of the mixture and the slab
is fully restrained. The deterministic model predicts crack spacing with time
whereas the probabilistic model predicts crack spacing and its variation with time
and yields the reliability of the design with regard to a minimum acceptable crack
spacing criterion defined by road authorities.
The models were verified by comparing the predicted crack spacings for the
five test roads to the observed crack spacings. The probabilistic model is
recommended for use in predicting the low temperature cracking of asphalt concrete
mixtures. / Graduation date: 1994
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Multiscale modeling of damage in multidirectional composite laminatesSingh, Chandra Veer 15 May 2009 (has links)
The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.
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Selection and performance evaluation of a test method to assess thermal cracking resistance of asphalt-aggregate mixturesJung, Duhwoe 30 July 1993 (has links)
Thermal distress in asphalt concrete pavements is a widespread problem around
the world. Thermal cracking can be divided into two modes of distress: low
temperature cracking and thermal fatigue cracking. Low temperature cracking results
from extremely cold temperatures; thermal fatigue cracking results from daily
temperature cycles.
Low temperature cracking is attributed to tensile stresses induced in the asphalt
concrete pavement as the temperature drops to an extremely low temperature. If the
pavement is cooled, tensile stresses develop as a result of the pavement's tendency to
contract. The friction between the pavement and the base layer resists the contraction.
If the tensile stress equals the strength of the mixture at that temperature, a micro-crack
develops at the surface of the pavement. Under repeated temperature cycles, the
crack penetrates the full depth and across the asphalt concrete layer.
The thermal stress restrained specimen test (TSRST) was identified as an
accelerated laboratory test to evaluate the thermal cracking resistance of asphalt concrete mixtures. The TSRST system developed at OSU includes a load system, data control/acquisition system and software, temperature control system, and specimen alignment stand. The overall system is controlled by a personal computer.
A TSRST is conducted by cooling an asphalt concrete specimen at a specified rate while monitoring the specimen at constant length. A typical thermally-induced stress curve is divided into two parts: relaxation and non-relaxation. The temperature at which the curve is divided into two parts is termed the transition temperature. The temperature at fracture is termed the fracture temperature and the maximum stress is the fracture strength.
An extensive number of TSRSTs over a wide range of conditions were performed to investigate the thermal cracking resistance of asphalt concrete mixtures. The TSRST results provided a very strong indication of low temperature cracking resistance for all mixtures considered. A ranking of mixtures for low temperature cracking resistance based on the TSRST fracture temperature was in excellent agreement with a ranking based on the physical properties of the asphalt cements.
It is highly recommended that the TSRST be used in mix evaluation to identify low temperature cracking resistance of asphalt concrete mixtures. The TSRST showed very promising results regarding the effect of all variables which are currently considered to affect the low temperature cracking of mixtures. The variables considered to have significant affect on the low temperature cracking resistance of mixtures in this study include asphalt type, aggregate type, degree of aging, cooling
rate, and stress relaxation. / Graduation date: 1994
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Multiscale modeling of damage in multidirectional composite laminatesSingh, Chandra Veer 15 May 2009 (has links)
The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.
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Tracking and detection of cracks using minimal path techniquesKaul, Vivek 27 August 2010 (has links)
The research in the thesis investigates the use of minimal path techniques to track and
detect cracks, modeled as curves, in critical infrastructure like pavements and bridges. We
developed a novel minimal path algorithm to detect curves with complex topology that may
have both closed cycles and open sections using an arbitrary point on the curve as the sole
input. Specically, we applied the novel algorithm to three problems: semi-automatic crack
detection, detection of continuous cracks for crack sealing applications and detection of crack
growth in structures like bridges. The current state of the art minimal path techniques only
work with prior knowledge of either both terminal points or one terminal point plus total
length of the curve. For curves with multiple branches, all terminal points need to be known.
Therefore, we developed a new algorithm that detects curves and relaxes the necessary user
input to one arbitrary point on the curve. The document presents the systematic development
of this algorithm in three stages. First, an algorithm that can detect open curves with
branches was formulated. Then this algorithm was modied to detect curves that also have
closed cycles. Finally, a robust curve detection algorithm was devised that can increase the
accuracy of curve detection. The algorithm was applied to crack images and the results of
crack detection were validated against the ground truth. In addition, the algorithm was also
used to detect features like catheter tube and optical nerves in medical images. The results
demonstrate that the algorithm is able to accurately detect objects that can be modeled as
open curves.
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Minimizing longitudinal pavement cracking due to subgrade shrinkageLuo, Rong, 1979- 28 August 2008 (has links)
The State of Texas has the most extensive network of surface-treated pavements in the nation. This network has suffered from the detrimental effects of expansive soils in the subgrade for decades. Longitudinal cracking on the Farm-to-Market (FM) network is one of the most prevalent pavement distresses caused by volumetric changes of expansive subgrades. Engineering practice has shown that geogrid reinforcement and lime treatment can effectively reduce the reflection of longitudinal cracking on the pavement over shrinking subgrade. However, little is known about the mechanism leading to the propagation of the shrinkage cracks to the surface of the pavement. The use of geogrid reinforcement and lime treatment is mostly based on empirical engineering experience and has not been addressed in depth. This dissertation research evaluates the stress field and constitutive models of the subgrade soil subjected to matric suction change. The non-uniform matric suction change in the subgrade is simulated by a thermal expansion model in a finite element program, ABAQUS, to determine the shrinkage stresses in the subgrade soil and pavement structure. Numerical solution by the finite element analysis shows that the most likely location of shrinkage crack initiation in the subgrade is close to the pavement shoulder and close to the interface of the base and subgrade. Linear elastic fracture mechanics theory is used to analyze the crack propagation in the pavement. Compared to the fracture toughness of the pavement materials, the stress concentration at the initial shrinkage crack tip is large enough to drive the crack to propagate further. When the shrinkage crack propagates through the whole pavement structure, a longitudinal crack develops at the pavement surface close to the pavement shoulder. Based on the analysis of shrinkage crack propagation, this dissertation investigates the mechanism of geogrid reinforcement and lime treatment. The geogrid can significantly reduce the stress concentration at the crack tip if the geogrid is placed at the bottom of the base. A geogrid with a higher stiffness further reduces the stress intensity factor at the upper tip of the shrinkage crack. The lime treatment can improve the mechanical properties of the expansive soil in several ways. The lime-treated soil has lower plasticity index, higher tensile strength and higher fracture toughness. The possible location of the shrinkage crack initiation is not in the lime-stabilized soil but in the untreated natural soil close to the bottom of the lime-treated layer, where tensile stresses exceed the tensile strength of the untreated soil. The shrinkage crack is less likely to develop through lime-treated soil, which has increased fracture toughness. The combination of geogrid reinforcement and lime treatment offers the most benefit for the control of dry-land longitudinal cracking. In a pavement with a lime-treated layer, the best place to install the geogrid is at the interface between the lime-stabilized layer and the untreated natural soil. If using a geogrid with high stiffness, the Mode I stress intensity factor may be reduced to a certain level that is lower than the fracture toughness of the pavement material.
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Failure resistance of high-cycle loaded welded joints / Daugiacikliškai apkrautų suvirintųjų jungčių atsparumas irimuiStonkus, Rimantas 23 February 2012 (has links)
The dissertation investigates the problems of welded joints resistance to fracture, affected by high-cycle load. The object of research is mechanical state of welded joints, formed in construction elements, in which the fracture process begins because of high-cycle load. Examination of fracture mechanism is important to ensure the design and running durability of large-size elements. Detailed analysis and interpretation allows to choose better calculation methodology for welded joints. The main aim of dissertation – to investigate the process of fracture in butted welded joints, which are loaded high-cyclically, to improve calculating methodology according to consistent patterns of crack formation, propagation, stop and complete fracture, defined by experimental analytical researches. The dissertation consists of an introduction, five chapters, summary of results, references and list of author’s publications on dissertation subject. The introduction reveals the investigated problem, the topicality of the issue, the object of research, describes the aim and tasks of the paper, research methodology, scientific novelty, the practical significance of the results examined in the paper and defended propositions. The introduction ends in presenting the author’s publications on dissertation subject and reports in conferences. The first chapter covers the literature review. It reviews the research works closely related to the dissertation topic and presents the topicality and problems... [to full text] / Disertacijoje nagrinėjamos suvirintųjų jungčių atsparumo irimui problemos, veikiant daugiacikliam apkrovimui. Tyrimo objektas yra suvirintųjų jungčių mechaninis būvis, susidarantis konstrukcijos elementuose, kuriuose dėl apkrovos daugiacikliškumo prasideda irimo procesas. Suirimo mechanizmo nagrinėjimas yra svarbus didelių gabaritų detalių projektiniam ir eksploataciniam ilgalaikiškumui užtikrinti. Detali analizė ir interpretacija leidžia parinkti tinkamesnę suvirintųjų jungčių skaičiavimo metodiką. Pagrindinis disertacijos tikslas – ištirti irimo procesus suvirintuose sandūriniuose sujungimuose, apkrautuose daugiacikliškai, patobulinti skaičiavimo metodiką pagal plyšio susidarymo, plitimo, sustojimo ir visiško suirimo dėsningumus, nustatytus eksperimentiniais analitiniais tyrimais.
Disertaciją sudaro įvadas, penki skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Įvade aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra. Pirmasis skyrius skirtas literatūros analizei. Jame apžvelgiami moksliniai darbai, glaudžiai susiję su disertacijos tematika, pateikiama daugiaciklio stiprumo suvirintuose komponentuose aktualijos... [toliau žr. visą tekstą]
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Susceptibility of creep aged material to stress relief cracking during repair weldingMoggee, Herman January 1998 (has links)
The repair welding of main steam pipelines, which involves the welding of new material onto
service-exposed material, are investigated. This paper investigates the literature and
experimental work surrounding this subject. The introduction provides a background to the
applicable welding technology. In section two the heat-affected zone is discussed with
emphasis on the residual stresses that develop in this zone. The mechanical properties of the
heat-affected zone are also investigated. This includes the tensile, toughness and hardness
properties as well as inspecting the relevant microstructures. The effect of post weld heat
treatment on these properties is also investigated. Section three investigates the
phenomenon of creep. Not only is this important due to the high temperatures at which these
pipelines operate, but creep is also associated with some failures of these weld during post
weld heat treatment. The creep properties of the heat-affected zone are investigated in detail
with the use of weld simulation. Sections four and five detail reasons for weld failure after
welding due to hydrogen and reheat cracking. Hydrogen cracking is investigated with the use
of slow strain rate tensile tests during cathodical charging the specimen with hydrogen. The
phenomenon of reheat cracking is investigated with the use of high temperature tensile tests
as well as a novel approach in which the stress relief of a welded joint is simulated while
measuring crack growth and stress relieved. / Dissertation (MEng)--University of Pretoria, 2014. / gm2014 / Materials Science and Metallurgical Engineering / Unrestricted
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