| 1. |
- Aalipour, Mojgan
(författare)
-
Human Factors Approach for Maintenance Improvement
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this research work is to explore and describe human factors affectingmaintenance execution. To achieve the purpose of this study, the influencing factors have been identified using a literature survey. They have been categorized into four main groups namely organizational, workplace, job and individual factors. The Analytical Hierarchy Process (AHP) method is employed on data questionnaires to rank the priority of the factors. The interrelationships between these factors have been recognized by theInterpretive Structural Modelling (ISM) model. In the present case studies, MICMAC1analysis technique is also implemented for identifying the driving, dependent, linkage and autonomous factors. The data was collected through a questionnaire survey involving the participation of 16 and 25 maintenance staff and 10 mining experts in Swedish and Iranian mines, respectively. Within the study, it has been identified that the temperature, work layout, tools design and tools availability are the most important factors in both mines related to these categories. However, the significant factors in the organizational and individual categories are different in the selected mines. The effect of workplace factors on the maintainability of mining equipment is discussed and thereafter a methodology for maintainability management in the design and operation phases is developed. In the thirdcase study HEART2 is applied to estimate the probability of human error occurring duringmaintenance execution in an Iranian cable company. This research supports maintenance management to gain knowledge of human factors that affect maintenance execution. Further, this understanding could be useful in the development of strategies to improve the execution of maintenance.Keywords: Human Factors, Maintenance Management, Human Reliability, HumanPerformance, AHP, ISM, MICMAC, HEART
|
|
| 2. |
|
|
| 3. |
- Abiri, Olufunminiyi
(författare)
-
Simplifications of non-local damage models
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ductile fracture presents challenges with respect to material modelling and numerical simulations of localization. The strain and damage localization may be unwanted as it indicates a failure in the process or, as in the case of machining and cutting, a wanted phenomenon to be controlled. The latter requires a higher accuracy regarding the modelling of the underlying coupled plastic and fracturing/damage behaviour of the material, metal in the current context as well as the robustness of the simulation procedure. The focus of this thesis is on efficient and reliable finite element solution of the localization problem through the non-local damage model. The non-local damage model extends the standard continuum mechanics theory by using non-local continuum theory in order to achieve mesh independent results when simulating fracture or shear localization. In this work, the non-local damage model and its various simplifications are evaluated in an in-house finite element code developed using Matlab™. The accuracy, robustness, efficiency and costs of the models are investigated and also compared to a general multi-length scale finite element formulation. A numerical study versus published data is used to demonstrate the validity of the model. The explicit non-local damage variant will be implemented in a commercial finite element code for use in machining simulation
|
|
| 4. |
- Aguilar, Wilson
(författare)
-
Study of the Synthesis of ZSM-5 from Inexpensive Raw Materials
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- ZSM-5 is an aluminosilicate with high silica ratio with suitable properties for catalysis, ion exchange, adsorption and membrane applications. ZSM-5 is usually produced industrially from concentrated systems in which there is formation of an amorphous gel phase. Typical syntheses of ZSM-5 require sources of silicon and aluminium, a mineralizer and an organic molecule as so-called templating agent. The silicon and aluminum sources widely used for the synthesis are pure reagent chemicals and in particular quaternary ammonium compounds like tetrapropyl ammonium hydroxides (TPA-OH), are employed as templating agents. Unfortunately, these compounds are rather expensive. Demand for inexpensive sources of aluminosilicates for the synthesis of ZSM-5 has increased during the last two decades. Natural raw materials such as kaolin clay and diatomaceous earth (diatomite) are two potential inexpensive sources of silica and alumina. Moreover, the molecule n-butylamine (NBA) has been reported as a low-cost templating agent to replace the quaternary ammonium compounds. The aim of this work was to show for the first time that leached metakaolinite or diatomite in combination with sodium hydroxide and n-butylamine could be used as inexpensive raw materials for the synthesis of ZSM-5 without using an additional source of silica. After synthesis optimization, both sources of aluminosilicate were found to behave differently during the course of synthesis and led to slightly different products. The chemical composition of the raw materials and the products were determined using inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). Crystallinity was examined by X-ray diffractometry (XRD), the morphology was studied by extreme-high-resolution scanning electron microscopy (XHR-SEM) and the specific surface area was estimated from nitrogen adsorption data by the BET method. The chemical composition of individual crystals was determined by energy dispersive spectrometry (EDS). Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and reduced the amount of impurities. The final ZSM-5 products had a SiO2/Al2O3 ratio in the range 20 – 40. The use of leached diatomite allowed reaching higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of mordenite were formed, which was related to the high calcium content of diatomite. Another considerable advantage of diatomite over kaolin is that diatomite does not require heat treatment at high temperature to convert the kaolin to reactive metakaolin. Further characterization of the system by XHR-SEM and EDS at low voltage was carried out in order to understand the nucleation and early growth of the ZSM-5 zeolite crystals. The observations with unprecedented detail strongly suggest that nucleation and the succeeding growth occurs on the gel surface. The growth rates in the various crystallographic directions already at an early stage are such that the shape of the growing crystals resembles that of the final crystals. However, as the early growth is interface mediated, the growth rate along the gel particles is high and the gel particles will become partially embedded inside the growing crystals at an early stage. The Si and Al nutrients are probably transported along the solid/liquid interface and possibly through the liquid in the form of nanoparticles detaching from the gel. The organic template was initially contained in the liquid. However, it remains unclear at which stage the template becomes incorporated in the solid material. EDS at low voltage was also used to gain compositional information about the sodium/calcium ion exchanged products and extraneous phases when kaolin and Bolivian montmorillonite clay were used for the synthesis of zeolite A by alkali fusion. In order to evaluate the cation exchange capacity (CEC) of the synthesized zeolite, ICP-SFMS and EDS were compared. The EDS method used in this work resulted in (Na,Ca)/Al ratios in equivalent moles very close to 1.0 as expected and was therefore found more reliable than ICP-SFMS to measure cation exchange capacity for zeolite A. To summarize, the present work shows that it was possible to synthesize well-crystallized ZSM-5 zeolite from inexpensive raw materials such as leached metakaolin or leached diatomite, sodium hydroxide and n-butyl amine. Furthermore, the crystallization mechanism evidenced in this system might be more general and also apply for other concentrated systems, e.g. those using TPA as structure-directing. Finally, this work displays that EDS at low voltage can provide valuable local compositional information in the field of zeolite synthesis.
|
|
| 5. |
- Ahmed, Hamzah
(författare)
-
Relationship Between Crystal Structure and Mechanical Properties in Cocrystals and Salts of Paracetamol
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oral tablets are convenient and widely administered drugdosage forms.The mechanical properties of a drug substance such as plasticity, ability to cohere into compacts and friction/adhesion are important in the development of a tablet formulation. Crystal engineering is an interesting and viabletool for improving or optimizing these technical properties of a drug substance.The creation of a lternative polymorphic forms, cocrystals, salts or hydrates of a drug substance can result in structural variations in the molecular packing of the crystals and, thereby, can alter the deformation behavior of the materials.Knowledge of the relationships between crystal modifications and the technical properties in multicomponent systems is limited, but represents a possibility to predict mechanical properties based on crystalstructure that facilitates engineering particles for the optimal processing performance. The overall objective of this thesis is thus to gain better understanding of the relationships between the crystal structure features and the mechanical properties of cocrystals and salts. Paracetamol form I, its cocrystals with oxalic acid and 4,4´-bipyridine, and its hydrochloride salt were selected as model systems in the study.The materials were scaled-up using rational crystallization methods and the physical purity was confirmed. The relevant properties of these powders were determined.Tablets were then made at applied pressures of50-250 MPa under controlled conditions.The tabletability and compactability of the powders were determined. The compression mechanics of the powders were the investigated according to a material classification protocol.Slip planes were identified by visually observing the crystal structures and based on the attachment energies calculated using different force fields in the materialsstudio.The tensile strengths of the powders increased with increasing pressure and the tabletability decreased in the order oxalic acid>paracetamol-hydrochloride salt≈paracetamol-oxalic acid>4,4´-bipyridine>paracetamol-4,4´-bipyridine.The tensile strength of the tablets decreased exponentially with increasing porosity,with some exceptions.Ingeneral, the cocrystals and the salt displayed intermediate compression characteristics as compared to the reference substances.The elastic recovery of the cocrystal and salt forms of paracetamol was not markedly different from that of paracetamol.It was found that slip plane prediction based on the attachment energies was not reliable. While it was possible to explain the improved tableting properties of powders based on the crystal features (i.e. the presence of slip planes and flat layers), no clear relationship was found with yield pressure. This may be attributed to possible brittle material characteristics and the surface energies of the crystals,which need to be further studied.Thus, cocrystallization and salt formation introduced structural features that were responsible for changes in the compaction and compression properties of drug substances. In future work, we intend to extend these studies to provide a clear picture of structure-mechanical property relationships in organic molecular crystals over multiple length scales;molecules to crystals to bulk powder.Key words Crystal engineering, solid forms, cocrystals, salts, tableting, crystal structure, mechanical properties, compression analysis
|
|
| 6. |
- Aittamaa, Simon
(författare)
-
Programming embedded real-time systems : implementation techniques for concurrent reactive objects
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An embedded system is a computer system that is a part of a larger device with hardware and mechanical parts. Such a system often has limited resources (such as processing power, memory, and power) and it typically has to meet hard real-time requirements. Today, as the area of application of embedded systems is constantly increasing, resulting in higher demands on system performance and a growing complexity of embedded software, there is a clear trend towards multi-core and multi-processor systems. Such systems are inherently concurrent, but programming concurrent systems using the traditional abstractions (i.e., explicit threads of execution) has been shown to be both difficult and error-prone. The natural solution is to raise the abstraction level and make concurrency implicit, in order to aid the programmer in the task of writing correct code. However, when we raise the abstraction level, there is always an inherent cost. In this thesis we consider one possible concurrency model, the concurrent reactive object approach that offers implicit concurrency at the object level. This model has been implemented in the programming language Timber, which primarily targets development of real-time systems. It is also implemented in TinyTimber, a subset of the C language closely matching Timber’s execution model. We quantify various costs of a TinyTimber implementation of the model (such as context switching and message passing overheads) on a number of hardware platforms and compare them to the costs of the more common thread-based approach. We then demonstrate how some of these costs can be mitigated using stack resource policy. On a separate track, we present a feasibility test for garbage collection in a reactive real-time system with automatic memory management, which is a necessary component for verification of correctness of a real-time system implemented in Timber
|
|
| 7. |
- Akhmetkaliyeva, Raya
(författare)
-
Coercive estimates for the solutions of some singular differential equations and their applications
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate thesis deals with the study of existence and uniqueness together with coercive estimates for solutions of certain differential equations. The thesis consists of four papers (papers A, B, C and D) and an introduction, which put these papers into a more general frame and which also serves as an overview of this interesting field of mathematics. In the text below the functions r(x), q(x), m(x) etc. are functions on (-∞,+∞), which are different but well defined in each paper. In paper A we study the separation and approximation properties for the differential operator ly=-y″+r(x)y′+q(x)y in the Hilbert space L2 :=L2(R), R=(-∞,+∞), as well as the existence problem for a second order nonlinear differential equation in L2 . Paper B deals with the study of separation and approximation properties for the differential operator ly=-y″+r(x)y′+s(x)‾y′ in the Hilbert spaceL2:=L2(R), R=(-∞,+∞), (here ¯y is the complex conjugate of y). A coercive estimate for the solution of the second order differential equation ly =f is obtained and its applications to spectral problems for the corresponding differential operatorlis demonstrated. Some sufficient conditions for the existence of the solutions of a class of nonlinear second order differential equations on the real axis are obtained. In paper C we study questions of the existence and uniqueness of solutions of the third order differential equation (L+λE)y:=-m(x)(m(x)y′)″+[q(x)+ir(x)+λ]y=f(x), (0.1) and conditions, which provide the following estimate: ||m(x)(m(x)y′)″||pp+||(q(x)+ir(x)+λ)y||pp≤ c||f(x)||pp for a solution y of (0.1). Paper D is devoted to the study of the existence and uniqueness for the solutions of the following more general third order differential equation with unbounded coefficients: -μ1(x)(μ2(x)(μ1(x)y′)′)′+(q(x)+ir(x)+λ)y=f(x). Some new existence and uniqueness results are proved and some normestimates of the solutions are given.
|
|
| 8. |
- Al-Douri, Yamur K.
(författare)
-
Information assurance for maintenance of railway track
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Railway traffic is steadily increasing, having a negative impact on maintenance and resulting in decreased track availability, comfort, and safety. Swedish railway track maintenance mostly focuses on the actual track condition via a nationwide condition-based maintenance (CBM) strategy. For maintenance to be conducted in an appropriate way, data on the actual track condition must be accurate; furthermore, those data need to be converted into accurate information for maintenance decisions. An information assurance (IA) framework has the potential to deal with the system risks from a technical perspective. The framework is a guideline that can be implemented within CBM to understand both condition monitoring data behaviour and the information processing used to reach maintenance decisions.This research investigates ways of an information assurance (IA) framework can be implemented in the following CBM steps: data collecting, data processing and making maintenance decisions on Swedish railway. The framework can be used to understand data behaviour, information processing and the communication between information layers for decisions at organisation, infrastructure and data/information levels. The research uses both qualitative and quantitative methods to investigate critical information data, parameters, and problems and to suggest which areas need improvement. Quantitative analysis of the Swedish track geometry database reveals specific information about the behaviour of the railway data and their processing to make maintenance decisions.A case study shows how certain sections of a railway track are monitored and evaluates maintenance practices on those sections. The study finds several different types of measurements are taken using several different measurement systems. It is difficult to integrate these data for proper processing. In addition, there are problems of incomplete or irregular data; this affects the derivation of information and the use of models to understand track irregularities.Given the problems of data processing and subsequent decision making, the study suggests implementing an IA framework with CBM. The study checks the achievement of three IA principles in the existing data: authenticity, integrity and availability. The results show data have problems of authenticity and integrity, something also mentioned by the stakeholders in interviews. In particular years and on certain track sections, CM data are more than 5 percent incomplete, significantly affecting analysis. Incomplete track measurement data reach as high as 63 percent for the parameters of standard deviation (STD), longitudinal level and STD cooperation. Inaccurate measured values for alignment long wavelength within certain speed limits reach as high as 71 percent. These indicators are important for calculating track quality but are either incomplete or incorrect, negatively affecting the calculation of the Q-value and estimations of the track quality. This, in turn, negatively affects the maintenance decisions. Using information assurance will increase the system performance by permitting stakeholders to make accurate decisions.The suggested information assurance framework can discover technical problems but it needs to be improved using technologies, techniques and services to ensure complete and accurate data are available to be processed for maintenance decisions.
|
|
| 9. |
- Al-Gburi, Majid
(författare)
-
Restraint in structures with young concrete : Tools and estimations for practical use
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks. Restraint represents one of the main sources of thermal and shrinkage stresses at early age concrete. Paper I, deals with both the compensation plane method, CPM, and local restraint method, LRM, as alternative methods studying crack risks for early age concrete. It is shown that CPM can be used both for cooling and heating, but basic LRM cannot be applied to heating. This paper presents an improved equivalent restraint method, ERM, which easily can be applied both for usage of heating and cooling for general structures. Restraint curves are given for two different infrastructures, one founded on frictional materials and another on rock. Such curves might be directly applied in design using LRM and ERM.In Paper II, existing restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the wall for the typical structure wall-on-slab. It has been proven that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, it is shown that the results from the neural network can be represented by a series of basic weight and response functions. Thus, the results can easily be made available to any engineer without use of complicated software.Paper III, discusses the influence of five casting sequences for the typical structure slab-on-ground. The aim is to map restraints from adjacent structures for a number of possible casting sequences, and to identify the sequence with the lowest restraint. The paper covers both continuous and jumped casting sequences, which include one, two and three contact edges. The result shows that the best casting sequence is the continuous technique with one contact edge.
|
|
| 10. |
- Al-Jabban, Wathiq
(författare)
-
Soil Modification By Adding Small Amounts of Soil Stabilizers : Impact of Portland Cement and the Industrial By-Product Petrit T
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis presents results of laboratory experiments regarding the effectiveness of adding small amounts of binders in order to modify and improve the mechanical performance of low organic clayey silt soil. Two types of binders have been used i.e. cement and an industrial by-product named Petrit T. The study covered both the immediate and longterm effects on the soil material. Binder content was added by soil dry weight, Petrit T at 2, 4 and 7% and cement at 1, 2, 4 and 7%. An experimental program has been carried out, including tests of consistency limits, unconfined compressive strength, density, solidification, grain size distribution (by laser particle size analyzer) and pH. The tests were conducted on the treated soil with varying binder contents and after different curing periods, i.e. after 7, 14, 28, 60 and 90 days. Results show that cement is more effective in improving the physical and engineering properties than Petrit T. Plasticity index decreases after treatment and leads to an immediate increase in workability. This is found directly after treatment and it increases with time. Soil density increased, whilst water content decreased, with increasing binder content and curing time. Particle size distribution of soil is changed toward the granular side by the reduction of the particles in clay size fraction and increasing silt size particles after 28 days of treatment. Both binder types resulted in an immediate effect on the soil pH value. This value increased to 12.3 after adding 7% of the binder and then it gradually decreased as curing time increased. The cement treated soil exhibits a more brittle failure behavior than the soil treated with Petrit T. In this case a more ductile behavior was observed. The findings confirmed that adding small binder contents of cement and by-product Petrit T significantly improved the physical and mechanical properties of soil, which can contribute to reduce the environmental threats and costs that are associated with using high binder contents in various construction projects.
|
|
