[diss] Insinööritieteiden korkeakoulu / ENG

Permanent URI for this collection

https://aaltodoc.aalto.fi/handle/123456789/49

Browse

Now showing 1 - 20 of 694

The Judging of the Stability of Ships and the Determination of the Minimum Amount of Stability – Especially Considering the Vessels Navigating Finnish Waters
(Aalto University, 1939) Rahola, Jaakko; Sovelletun mekaniikan laitos; Department of Applied Mechanics; Insinööritieteiden korkeakoulu; School of Engineering
Aging of Iron-Based Martensites at Low Temperatures
(Helsinki University of Technology, 1992) Ullakko, Kari; Laboratory of Engineering Materials; Insinööritieteiden korkeakoulu; School of Engineering; Pietikäinen, Juha; Hänninen, Hannu
In the present work aging of iron-based martensites, defined as all the phenomena preceding the first stage of tempering, is studied using various methods. In some alloys aging was observed to start at very low temperatures, even near 4 K. Abnormally high or abnormally low tetragonality is observed in freshly formed martensite alloyed with Ni or Mn, respectively. The reason for high tetragonality obviously lies in the coherency at the interface between the martensite and the retained austenite. It is shown in the present work that the coherency is broken during aging in the temperature range of 100 - 200 K and it is accompanied by a decrease of tetragonality (first stage of aging). The new internal friction peak centered at 145 K corresponds to the movement of the coherent interface and the break of coherency. Some evidence for correlation between short range atomic ordering in austenite and the high tetragonality of the virgin martensite is given and a contribution of nontransformed ordered austenitic regions inside martensite plates to tetragonality is discussed. It is shown that the second stage of aging at temperatures about 200 - 270 K is controlled by the pinning of the dislocations by carbon atoms and the third stage (mainly above 250 K) by the clustering of carbon atoms in a solid solution. By means of Mössbauer spectroscopy, electrical resistivity and magnetic susceptibility measurements, a striking difference is shown between the redistribution of carbon and nitrogen atoms above 200 K. Evidence for the clustering of carbon and ordering of nitrogen is given and discussed. The dynamics of clustering was studied by means of small angle neutron scattering. Deformation of martensite at subambient temperatures reduced the tetragonality of martensite to cubic and changed the redistribution of carbon atoms. According to different measurements, practically no aging was observed below room temperature in the deformed martensite.
Requirements and information structures for building product data models
(VTT Technical Research Centre of Finland, 1995-12-08) Björk, Bo-Christer; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto
The term computer-integrated construction (CIC) is often used to describe a future type of construction process characterised by the extensive use of information technology. The key to successful CIC is the comprehensive integration of currently isolated computing applications in different phases of the construction process. Among the several types of data exchange standards needed to support such integration, the standards for structuring the information describing buildings (building product data models) are particularly important. No fully operational building product data models have as yet been formally standardised either on the national or international level, but the topic has been a subject of intensive research during the last few years. Building product data model proposals are usually defined using object-oriented information modelling techniques. The research which is presented in this summarising thesis was carried out primarily during the years 1988-92 at the Technical Research Centre of Finland. The report begins with a brief introduction to the general background of research concerning CIC and building product data models. Fundamental concepts of object orientation and product modelling are explained in a separate chapter. In order to position the author's research results, the "state of the art" in this research field is briefly reviewed. The research results are presented against the background of a kernel-aspect model framework, in line with current thinking among several leading researchers in this field. The results can loosely be classified into three distinctive groups: a number of requirements which building product data models should fulfil; specific information structures in building product data models; and the integration of product models with other types of information used in the construction process. The specific information structures which were studied include the abstraction hierarchies used in building product data models, the type object mechanism and information structures needed for modelling spaces and enclosing objects. The report ends with a discussion of the results, comparing them with the proposals and results of other researchers. Some directions for further research are also outlined.
Statistical analysis of vehicle time headways
(Helsinki University of Technology, 1996-05-31) Luttinen, R. Tapio; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto; Laboratory of Transportation Engineering; Liikennetekniikan laboratorio
The properties of vehicle time headways are fundamental in many traffic engineering applications, such as capacity and level of service studies on highways, unsignalized intersections, and roundabouts. The operation of modern vehicle-actuated traffic signals is based on the measurement of time headways in the arriving traffic flow. In addition, the vehicle generation in traffic flow simulation is usually based on some theoretical vehicle time headway model. The statistical analysis of vehicle time headways has been inadequate in three important aspects: 1) There has been no standard procedure to collect headway data and to describe their statistical properties. 2) The goodness-of-fit tests have been either powerless or infeasible. 3) Test results from multi-sample data have not been combined properly. A four-stage identification process is suggested to describe the headway data and to compare it with theoretical distributions. The process includes the estimation of the probability density function, the hazard function, the coefficient of variation, and the squared skewness and the kurtosis. The four-stage identification process effectively describes those properties of the distribution that are most helpful in selecting a theoretical headway model. One of the major problems in the headway studies has been the method for goodness-of-fit tests. The two most commonly used tests are the chi-square test and the nonparametric Kolmogorov-Smirnov test. The chi-square test is not very powerful. The nonparametric Kolmogorov-Smirnov test should be applied only, when the parameters of the distribution are known. If the parameters are estimated from the data, as in typical headway studies, the nonparametric Kolmogorov-Smirnov test gives too conservative results. These problems are addressed by parametric goodness-of-fit tests based on Monte Carlo methods. Another great problem has been the lack of theoretical foundation in dealing with multi-sample data. The headway data usually consist of several samples, and the null hypothesis is tested against each of them. Two methods are presented to strengthen the evidence of multi-sample tests: 1) The combined probability method gives a single significance probability based on several independent tests. 2) The moving probability method is used to describe the variation of combined probabilities against traffic volume. These methods were applied to time headway data from Finnish two-lane two-way roads. The independence of consecutive headways was tested using autocorrelation analysis, runs tests and goodness-of-fit tests for the geometric bunch size distribution. The results indicate that the renewal hypothesis should not be accepted in all traffic situations. This conclusion is partly supported by a further analysis of previous studies. Five theoretical distributions were tested for goodness of fit: the negative exponential distribution, the shifted exponential distribution, the gamma distribution, the lognormal distribution and the semi-Poisson distribution. None of these passed the tests. In the parameter estimation the maximum likelihood method was preferred. For distributions having a location (threshold) parameter, a modified maximum likelihood method was shown to give good estimates. The proposed procedures give a scientific foundation to identify and estimate statistical models for vehicle time headways, and to test the goodness of fit. It is shown that the statistical methods in the analysis of vehicle headways should be thoroughly revised following the guidelines presented here.
Implementation of technical change as organizational problem-solving process : management and user activities
(VTT Technical Research Centre of Finland, 1998-03-20) Hyötyläinen, Raimo; Department of Mechanical Engineering; Konetekniikan osasto
During the last two decades the growing innovation and management research has paid attention to the aspects of technical change. However, there are differing assumptions about the nature of the process of change. According to the innovation design dilemma two categories of innovation related to technical change have been identified, technical and organizational innovation. It has been become evident that there is a growing need to unite these two types of innovation into a common approach. The focus of the study is the planning and implementation process of technical change in the user organization. The aim is to find out what kinds of planning and implementation models, methods and organizational forms can further innovative and organizational problem-solving activity in the implementation process of technical systems, which is contributing to the success of this process. The study is based on long term and intensive development and research activity concerning the implementation process of three Flexible Manufacturing Systems in two companies. The FMS-study began in 1985 and was completed in 1992. Through the developmental approach based on experimental development research, the study was able to specify in great detail the progress of the implementation process in the cases. Attention was paid to social activity of the implementation process. The issue is how and by whom new techno-organizational solutions are finally brought about and carried out inside the user organization. New training, planning, organization and development methods were introduced and experimented with in the intensive cases, which created a rich and real picture of development potentials of the organization. The analysis of the case study results showed that the implementation process of technical change consisted of a series of problem-solving and development steps taken by the user organization and its actors. This was a controversial, complex and long process in which the management, planners, support persons and users with different interests and ways of acting designed and constructed, mainly in a step by step way, the concrete technical and organizational characteristics of the "activity system". This was performed by solving planned and unanticipated problems that emerged during the definition of the innovation problem and goal setting, planning phase, implementation phase and operation phase. The system model of the implementation process of technical change was created based on the analysis and evaluation of the case study results. The model presents in great detail the connections and relations between the results of the implementation process in the cases and the management's and users' ways of acting with their many dependencies and interactions. According to the system model of the implementation process, the most important factors from the point of view of the success or failure of the results are the following elements: viewpoint on the nature of change; design concept; and organizational patterns. The relations of these elements are described by the development model of the implementation process of technical change. The development model is further specified and presented as a solution to the innovation design dilemma. The case study results proved that the organizational patterns carried the most central role in explaining the results of the implementation process. They determined the quality of the problem-solving process in the planning process, implementation phase and "normal" operation phase through which the results were gained. In the cases, the roles of support persons and users, the users' way of working, actions of the management, co-operation patterns and the use of systematic methods were the factors which contributed mostly to successful results. In the study, three planning and implementation models (techno-centric model, user-centered model, and lean production model) were chosen as the organizational patterns by which the organizational practices of the cases were studied. Comparative analysis of the activities of the management and users showed that the ways of acting in the cases were characterized mainly by the "techno-centric" and "user-centered" models. However, some features could be seen as practices in accordance with the "lean production" model. The case studies demonstrated that the adoption of new kinds of planning and implementation practices was a controversial process. The planning and implementation process can be seen to form an "experimental field" where the difficulties, set-backs and good results experienced may act as a ground for learning and seeking new planning practices, implementation models and management approaches.
Living tradition or panda's cage? : an analysis of the urban conservation in Kyoto : case study: 35 Yamahako neighbourhoods
(Helsinki University of Technology, 1999-08-21) Salastie, Riitta "Ri"; Department of Architecture; Arkkitehtiosasto; History of Architecture; Arkkitehtuurin historia
The focus of the research is the city centre of Kyoto and there, the group of thirty-five hoko neighbourhoods known for the organisation of the Gion Festival. At the present moment the wooden town heritage in the area is threatened in a number of ways. Such threats are both the threatening effects of town planning as well as the lack of appropriate urban conservation policies. Focusing on a few, selected landmarks and areas has led to the compartmentalising of the city and to the failure of municipal authorities to identify culturally dependent and place-oriented value-categories. In the process the heritage evaluation methods in use have played more than a minor role. The methodological approach taken in the thesis aims to an approach where the dwelling patterns and cultural patterns are identified as an inseparable entity. Such an approach is especially important in Kyoto where traditional townhouses were never just residential spaces but had important production and cultural functions as well. Cultural values are analysed through the tradition of the Screen Festival. The wooden townhouse context plays an important role as the scenic stage of the festival. The interpretation of the Japanese context and its implications for urban conservation work are an essential part of the research. The inter-relationship between the urban dwelling and the street and the importance of place are defined as major cultural values to be focused on. The heritage argumentation methods are seen as an important tool how to enhance cultural values and continuous use. On-site recording is used as an important evaluation tool. The author measured for the thesis approximately one hundred wooden facades of traditional townhouses in the survey area. Furthermore, as a member of the Kyoto University research team the author participated in an extensive field research during the Gion Festival in three following years, where all screen displays and their urban settings were documented including more than 160 antique screens. The conclusions of the thesis suggest that the wooden town heritage cannot be assessed through selected (expert) values alone, but also other values and meanings must be taken into consideration. The wooden town heritage is appreciated, not only because of its visual and historical characteristics but also because of its capacity to hold cultural values and ways of life. Individual interpretations and cultural readings add to the significance of place. The traditional display patterns are identified as key cultural values that should be an essential part of heritage assessment work. The conclusions of the research do not apply only to Kyoto but are closely related to the urban conservation problems of wooden towns in general. Because of the fragility of the wooden town tradition and the authenticity problems involved, the methodological approach should be paid special attention. The wooden town heritage cannot be evaluated using same criteria as towns built in stone or brick. Changes and alterations must be tolerated if any of the wooden town heritage is to be preserved. Social values, cultural practices and individual interpretations should be added as an important element in the evaluation practices of heritage.
Simulation of the flow past a long-range artillery projectile
(Helsinki University of Technology, 2000-06-02) Kaurinkoski, Petri; Department of Mechanical Engineering; Konetekniikan osasto; Laboratory of Aerodynamics; Aerodynamiikan laboratorio
In this work, an eddy breakup model for chemical reactions is implemented to an existing multi-block Navier-Stokes solver, which is then used to solve the flow past a supersonic long-range base-bleed projectile. The new scheme is validated by simulating an axisymmetric bluff-body stabilized flame, which has been measured in a wind tunnel and simulated numerically by other work groups. Comparison of the numerical results for the projectile shows the importance of the chemistry modelling for accurate numerical predictions. The final combustion of the fuel-rich propellant simulated in this work makes a dramatic difference in the predicted aerodynamic drag of the projectile. The drag reduction due to base bleed is more than doubled when the chemical reactions are accounted for, and the drag prediction based on the simulations including chemical reactions is excellent.
Fire safety design of composite slim floor structures
(Helsinki University of Technology, 2000-12-07) Ma, Zhongcheng; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto; Laboratory of Steel Structures; Teräsrakennetekniikan laboratorio
A structural fire safety design method for composite steel-concrete slim floor structures was developed, including the characterization of fully-developed compartment fire curves and the equivalent fire exposure, temperature analysis of the composite structures, and the structural response analysis of composite slim floor structures subjected to fire. Special interest was given to the structural responses of the slim floor beam both as an isolated member and a part of the frame structure. The mechanical interaction behind the global deformation response of the frame was emphasized. Although the analyzed objects concentrated on composite slim floor structures, the according fire safety design method and the explored structural response mechanism in fire are equally applicable to other types of building structures.
Local and distortional buckling of perforated steel wall studs
(Helsinki University of Technology, 2000-12-08) Kesti, Jyrki; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto; Laboratory of Steel Structures; Teräsrakennetekniikan laboratorio
The local and distortional buckling behaviour of flange and web-stiffened compression members was investigated. In particular, the behaviour of web-perforated sections was investigated both numerically and experimentally. Perforation reduces the perpendicular flexural stiffness of the web and thus particularly reduces the distortional buckling strength of the section. The main task of the research was to develop a design method for estimating the compression capacity of a perforated steel wall-stud under centric loading. The influence of the gypsum sheathing on the distortional buckling strength is also taken into account. It was shown that the method given in Eurocode 3 is quite rough and sometimes gives inaccurate results for estimating the elastic distortional buckling stress of both C-sections and intermediate stiffened plates. In the case of C-sections, the method developed by Lau and Hancock and the method developed by Schafer and Peköz correlate better with the results defined numerically. The Finite Strip Method (FSM) and Generalized Beam Theory (GBT) provided particularly good tools with which to analyze local and distortional buckling modes. It was also shown that interaction between different distortional buckling modes should be taken into account when analysing sections having both web and flange stiffeners. Distortional buckling stress of the web-perforated C-section with or without web stiffeners can be determined by replacing the perforated web part with an equivalent plain plate corresponding to the same perpendicular bending stiffness. Distortional buckling stress may be determined by some numerical method such as FSM or GBT. For the web-perforated C-section, an analytical method for the distortional buckling is also presented. Gypsum sheathing connections give rotational restraint to the wall–stud, thus improving distortional buckling strength. Some practical guidelines are given for calculating the rotational restraint. Buckling analysis showed that relatively small restraint may double the distortional buckling stress of the web-perforated section. Buckling analysis and experimental research showed that screw pitch also has a considerable effect on the distortional buckling stress. Using restraint values given by the connection tests, the predicted values for the gypsum board braced columns are in good accordance with the test results. In practical design, utilizing the gypsum board in the determination of the distortional buckling stress requires that the sheathing retains its capacity and stiffness for the expected service life of the structure. Furthermore, the connection characteristics should be carefully examined. Based on the results of the experimental and theoretical studies, design proposals were made for the design of compressed web-perforated steel wall studs. Some practical guidelines were also given for taking into account the gypsum sheathing. These design proposals are also valid for solid steel wall studs, especially for slender sections, which are sensitive to distortional buckling.
Behaviour of a semi-continuous beam-column connection for composite slim floors
(Helsinki University of Technology, 2000-12-11) Malaska, Mikko; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto; Laboratory of Steel Structures; Teräsrakennetekniikan laboratorio
The flooring system with its connections to the supporting column significantly influences the technical quality and performance of the steel-concrete composite design and the overall economic viability of the construction. Expectations of technical and economic flexibility and cost-effectiveness that alternative feasible solutions may offer motivate research and development in this field. This study focuses on the behaviour of beam-column connections in a building frame consisting of slim floor beams. The principal purpose was to gain a better understanding of the engineering features of semi-continuous composite joints and to apply this knowledge in the design of structures frequently used in Finland. A new advanced structural design connecting a slim floor beam to a tubular steel column section filled with concrete was designed using an application of the semi-continuous concept. The design was implemented and the construction tested in a thorough empirical study. Experimental work included two tests on bare steel connections and four tests on composite connections with full-scale specimens. The two tests on the bare steel connections demonstrated the joint behaviour during the erection and concreting work of the floor. Four specimens of composite connections were then tested in order to learn the influence of the slab characteristics on the connection behaviour in terms of the amount of reinforcement used in the slab, the shear-to-moment ratio, and the concrete strength. A mathematical model for predicting the moment-rotation characteristics of the joint response was formulated based on the geometrical and mechanical joint properties and findings from the empirical study. In the model formulation the basic mechanism of force transfer within the components of a composite connection was applied. Derived from the model and validated by the experimental results simple and robust methods that can be used by the designers are proposed.
Developments in turbulence modelling with Reynolds-averaged Navier-Stokes equations
(Helsinki University of Technology, 2001-04-27) Rautaheimo, Patrik; Department of Mechanical Engineering; Konetekniikan osasto; Laboratory of Applied Thermodynamics; Sovelletun termodynamiikan laboratorio
The performance of different low-Reynolds number turbulence models applied to various flows is described. The emphasis is put on Chien's k – ε model, an explicit algebraic Reynolds-stress model by Speziale et al., and a full Reynolds-stress closure. The Reynolds-stress closure of this work has been developed by the author by combining different existing models. Accurate numerical methods are developed to couple the momentum equations and the low-Reynolds number Reynolds-stress equations. Two methods are introduced and these vary depending on how much the source terms are taken into account implicitly. The production of turbulence can be used to couple the inviscid part of the momentum equations and the Reynolds-stress equations in the approximate Riemann solution. As demanding problems are computed, it has been essential to parallelize the computer code. This has been performed via a message passing package. The code shows an excellent parallel performance even in the most complex topologies simulated. In this thesis, validations are presented for ten different fluid dynamic problems. The test cases vary from a simple channel flow to complicated flows in rotating machinery. In the validations it is found that the Reynolds-stress closure generally performs better than the two-equation models in complex flows. Especially streamline curvature is better captured by the Reynolds-stress closure. For the skin friction, the present Reynolds-stress closure does not give satisfactory results, and thus, some further development is needed. For simpler situations the two-equation models give comparable or even better results than the more complex models.
Quality characteristics of fine aggregates and controlling their effects on concrete
(Helsinki University of Technology, 2001-05-11) Järvenpää, Hanna; Department of Materials Science and Rock Engineering; Materiaali- ja kalliotekniikan osasto; Laboratory of Mechanical Process Engineering and Recycling; Mekaanisen prosessi- ja kierrätystekniikan laboratorio
For the aggregate producer, the concrete aggregates are end products, while, for the concrete manufacturer, the aggregates are raw materials to be used for mix designs and successful concrete production. The aim of this study was to identify which fine aggregate characteristics are important, and additionally to relate the extent of the effect that the aggregate has on the concrete as compared against the effect of the changes in mix design. The testing programme contained six different mix designs in which 21 fine aggregate products were studied in 215 castings. The mix designs consisted of two cement amounts (300 or 350 kg/m3) corresponding to low and high paste volumes, with three admixture possibilities: no admixture, superplasticizer or air-entraining agent. The results of the experiments show that the effect of the fine aggregate characteristics on the flow value was greater than the effect of the cement amount. Furthermore, the entrained and entrapped air amounts correlated strongly with the flow value of the concrete. The compressive strength for the same mix design differed according to the fine aggregate characteristics, and the difference ranged between 8.4...18.8 MPa on the six mix designs. The superplasticizer enhanced the quality differences of the aggregate products. The effect of the porosity of the fine aggregate on the drying shrinkage exceeded twice the effect of the mix design changes, i.e. amount of paste and/or the admixtures. A program for predicting the interaction between the fine aggregate and concrete was developed. The Bayesian method was used for statistical processing, and non-parametric non-linear Gaussian process models were applied for the interaction models. The program includes four concrete properties; flow value, air %, bleeding and compressive strength. The most important fine aggregate characteristics in the models are: shape and particle porosity related semi-coarse fraction parameters (flow value and air %), flakiness and Los Angeles value of the semi-coarse fraction (compressive strength) and particle porosity of the semi-coarse and surface area of the fines fractions (bleeding). As an example of the model predictions, six different fine aggregate combinations were modelled; two gravel products representing past and future gravel types and four crushed rock products representing different strength qualities and shape characteristics.
Frequence-domain approach for calculating wind-induced vibration and aeroelastic stability characteristics of long-span bridges
(Helsinki University of Technology, 2001-09-21) Kiviluoma, Risto; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto
The frequency-domain approach is applied to the aerodynamic and aeroelastic analysis of long-span bridges. Numerical models are deduced for the simultaneous buffeting and flutter analysis and for the vortex and signature turbulence induced response calculation. The goal, considered to be achieved, is to develop numerical models capable to reliable parametric studies of detailed three-dimensional structural models of bridges. For the models, semi-empirical approach based on aerodynamic data obtained through section model tests in a wind tunnel, is employed. The data consists of the steady aerodynamic coefficients and flutter derivatives of a deck segment to be used in the buffeting and flutter analysis. A complemental data is suggested to be extracted for the vortex and signature turbulence induced response calculation. The simultaneous analysis model for buffeting and flutter uses theoretically complete coupled-mode approach in which most of the unintentional simplifications of earlier models are removed. It has merits for the non-iterative calculation of flutter characteristics and feasibility to efficient computer implementation. The vortex-induced response calculation is based on the band-limited white-noise excitation model while the signature-turbulence model employs approach typical in simplified buffeting analysis of bridge girders. The vortex-induced vibration calculation model facilitates imperfect spanwise correlation and turbulence reduction effects through mutually simple mathematical formulation. To obtain aerodynamic input parameters for the verification study, wind tunnel tests for the spring supported section model are carried out in a smooth flow. The Instrumental variable method is formulated for acceleration signals and used on evaluating flutter derivatives through coupled-motion experiments. To verify the numerical models, the calculated responses of the Raippaluoto and Kärkinen Bridges, two cable-stayed bridges in Finland involving double I-girder steel-concrete composite deck, are compared with the on-site measurements. Here, the responses and the wind turbulence data are measured on three occasions during storm and strong winds in 1999-2000.
Thermal fatigue of austenitic and duplex stainless steels
(Helsinki University of Technology, 2001-11-23) Virkkunen, Iikka; Department of Mechanical Engineering; Konetekniikan osasto
Thermal fatigue behavior of AISI 304L, AISI 316, AISI 321, and AISI 347 austenitic stainless steels as well as 3RE60 and ACX-100 duplex stainless steels was studied. Test samples were subjected to cyclic thermal transients in the temperature range 20 - 600°C. The resulting thermal strains were analyzed with measurements and numerical calculations. The evolution of thermal fatigue damage was monitored with periodic residual stress measurements and replica-assisted microscopy. The elastic strains of the ferrite phase in duplex stainless steels were studied using Barkhausen noise. Finally, destructive analyses including fractographic scanning electron microscopy (SEM) studies and transmission electron microscopy (TEM) analyses were performed. The surface residual stresses changed markedly during the first load cycles. In the austenitic stainless steels yielding during the rapid cooling resulted in compressive residual stresses from -200 MPa (20 - 300°C temperature cycle) to -600 MPa (20 - 600°C temperature cycle). After 10 cycles the residual stresses stabilized and then started to relax due to crack formation. Cracks were seen to initiate from persistent slip bands (PSBs) and in 3RE60 from MnS inclusions. In duplex stainless steels the phase boundaries retarded crack growth markedly. In the austenitic stainless steels, the fracture surfaces of thermal fatigue cracks showed extensive striation formation, i.e. they were similar to mechanical fatigue. The dislocation density was lower than expected based on mechanical fatigue data. Dislocation tangles and occasional cell tendency was observed. In duplex stainless steels the plastic deformation concentrated to the austenite phase. The obtained thermal fatigue data were compared with mechanical fatigue data from literature and with the ASME design curve. The ASME design curve was found to give safe design life, although the remaining safety factor on strain is decreased to 1.5. The total strain (elastic+plastic) caused by thermal loading was solved with linear-elastic FE-analysis. Thermal fatigue crack growth was predicted successively using total strain solution of an uncracked component and a strainbased growth model: da / dN = C7 Δε tot m7 a, where C7=1.6 and m7=1.3 for the studied austenitic stainless steels. The model is applicable to small fatigue cracks (0.05 - 4 mm) growing in varying temperature and strain fields and is temperature-independent in the studied range.
Effect of lubricant on the wear of prosthetic joint materials
(Helsinki University of Technology, 2001-11-28) Ahlroos, Tiina; Department of Mechanical Engineering; Konetekniikan osasto; Laboratory of Machine Design; Koneensuunnitteluopin laboratorio
The wear of ultra-high molecular weight polyethylene (UHMWPE) in prosthetic hip and knee joints is a significant clinical problem. The wear particles cause inflammatory tissue reactions which may lead to osteolysis and loosening of the implant fixation. The effect of lubricant on the wear of polyethylene was studied with a reciprocating pin-on-flat (RPF) apparatus, uniaxial (HUT-2) and three-axis (HUT-3) hip joint simulators, circularly translating pin-on-disk (CTPOD) device, biaxial rocking motion (BRM-1 and BRM-2) hip wear simulators, and a three-axis ball-on-flat (BOF) knee wear simulator. The aim was to produce wear similar to that known to occur clinically. To accomplish this, the basic criteria for the lubricant were: 1) no polyethylene transfer layer should form on the metal counterface, 2) the bearing surface of the polyethylene should become burnished, 3) the wear particle size should be of the order of 1 μm, and 4) the wear factor should be of the order of 1 x 10-6 mm3/Nm. The lubricants studied were human prosthetic joint fluid, bovine and calf serum, bovine albumin and gamma-globulin, soybean lecithin, dipalmitoylphosphatidylcholine (DPPC), soy protein, and distilled water. The counterfaces of polyethylene were CoCr, stainless steel, alumina, and diamondlike carbon (DLC). All the criteria were met by bovine and calf serum, albumin and gamma-globulin. Hence, albumin and gamma-globulin proved to be the crucial fractions of serum and synovial fluid with respect to producing clinically relevant wear of polyethylene. In conclusion, realistic wear was produced when the direction of sliding constantly changed relative to the polyethylene specimen, and a protein-based lubricant was used.
Fly ash mixtures as flexible structural materials for low-volume roads
(Helsinki University of Technology, 2001-12-07) Lahtinen, Pentti; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto
Extensive research and several studies have been carried out on the recycling of industrial by-products in soil construction in Finland in the 1990's. The research and studies have been made mainly in the laboratory of SCC Viatek Ltd SGT in cooperation with the public research institutes. The main beneficiaries have been the industry, the national road administration and the municipalities. The Doctoral Thesis focuses on the versatile usage opportunities of the fly ashes (FA) from the combustion of coal and biofuel like peat and wood and their mixtures with certain other industrial by-products in soil construction. The main objective of this thesis is to show the conditions and premises on which the NRC (New Recycled Construction) -materials are at least as viable or even more viable than the natural stone materials in the applications for low-volume roads. The research and studies have succeeded in the development of new materials and structure applications for low-volume roads, proper equipment and work methods to manufacture the NRC-structures and proper test methods for the quality assurance of the materials. The new FA-based construction materials include; a) materials based on FA, fibre-ashes, gypsum-ashes and slag-ashes for NRC-solid structures; b) binder admixtures based on FA for the stabilisation of old road structure courses; c) binder admixtures based on FA for the mass-column stabilisation of soft soil. It has been shown that FA from biofuel that have been studied relatively little so far may have even better geotechnical properties than the FA from coal. Additionally it has been possible to attain a versatile array of materials by mixing the FA with fibre sludge (outcome: fibre-ashes), process gypsum (outcome: gypsum-ashes) or stainless steel slag (outcome: slag-ashes). The properties of the different mixtures can be regulated by changing the proportion of different components. Thus, it has been possible to find proper materials for low-volume roads that require high heat insulation, deformation durability and bearing capacity. The studies on the test methods have been focused on the methods and criteria to optimise the properties and to assess the long-term durability of the NRC-materials. It has been possible to show that the most important methods to assess the long-term durability are the tests for frost susceptibility and the freeze-thaw durability. It is not possible to judge the long-term durability of NRC-materials with the mere stress-strain tests. Also the environmental impact of the NRC-materials has been studied both in the laboratory by leaching tests and in the full-scale test structures with samples of soil and groundwater. The studies include also the use of a mathematical dynamic transportation model to predict the distribution of molybdenum from the coal ash structures to the environment surrounding the structures. The environmental studies indicate that there is no environmental risk involved in the use of FA-based materials in soil construction, assuming that the materials are used in a proper way. NRC-technology will make the sustainable road construction possible. The durable NRC-structures will be economically viable alternatives to the conventional stone structures. Additionally it will be possible to save even 24 % of the non-renewable gravel and other natural resources, and there will be less need to use land for deposits or for stone intake at sensitive groundwater areas.
The effect of dissolved ozone on the corrosion behaviour of some stainless steels
(Helsinki University of Technology, 2001-12-14) Pehkonen, Antero; Department of Materials Science and Rock Engineering; Materiaali- ja kalliotekniikan osasto; Laboratory of Corrosion and Material Chemistry; Korroosion ja materiaalikemian laboratorio
The corrosion behaviour of some stainless steels and pure metals has been investigated in solutions with dissolved ozone. The pH of the test solution was 1, 2, 3 and neutral (adjusted by H2SO4). 2.3 and 23 g/l Na2SO4 was added to increase the conductivity in anodic and cathodic polarisation measurements. The temperature of the test solution was 20, 50 and 75 °C. Test materials were four different stainless steels: ferritic stainless steel Polarit 815 and austenitic stainless steels Polarit 720, Polarit 752 and Ralloy 654MO. Also Armco iron, pure Mo, Ni and Cr were tested. The general electrochemical behaviour of stainless steels and pure metals was studied with potentiodynamic cyclic polarisation experiments at scanning rates 1, 10 and 100 mV/min and pitting behaviour at 10 mV/min. Potentiostatic experiments were also used. Immersion tests were also carried out mainly to produce test samples for surface examination but also to measure the weight losses. The structure and thickness of the oxidized surfaces were examined and analysed using optical microscope, SEM, GDOS, ESCA and X-ray diffractometer methods. Dissolved ozone increases the redox-potential of test solutions to about +1200 mV vs. SCE and the corrosion potential of stainless steel to the transpassive region, below the oxygen evolution potential. The current densities of stainless steels in this region increase as the amount of alloying elements increases. On the other hand, dissolved ozone increases current densities only slightly compared to oxygen bubbled solution. Higher ozone concentration obtained under high pressure has no effect on the corrosion behaviour of stainless steels. The corrosion of stainless steels is general but peeling of oxide layers was also observed. Shallow corrosion damages are formed in immersion. In cyclic polarisation experiments pits are formed in Ralloy 654MO. The pits formed are similar to those formed by chloride induced pitting. As the pH of the solution is decreased, the current density of higher alloyed steels increases at higher pH than lower alloyed steels. Dissolved ozone increases the thickness of the oxide layers greatly. In oxygen bubbled solution at pH 3 the thickness of the layers is a few nanometers and in ozonated solution 60 - 260 nm. The compositions of these oxide layers has been found to vary greatly. Cr concentration is negligible in the oxide layers especially for Ralloy 654MO and P752. Molybdenum concentrates in the outer layer, even more so with lower alloyed steels. Iron and alloying elements have oxidised to their highest valencies. The main components in the oxide layers are iron oxides and on the surfaces also MoO6 occurs.
Fuzzy traffic signal control : principles and applications
(Helsinki University of Technology, 2002-01-31) Niittymäki, Jarkko; Department of Civil and Environmental Engineering; Rakennus- ja ympäristötekniikan osasto; Laboratory of Transportation Engineering; Liikennelaboratorio; Pursula, Matti, Prof.
The FUSICO (Fuzzy Signal Control)-research project was started in 1996 at the Helsinki University of Technology. The main goals of the project are theoretical analysis of fuzzy traffic signal control, generalized fuzzy rules using linguistic variables, validation of fuzzy control principles, calibration of membership functions, and development of a fuzzy adaptive signal controller. This thesis discusses four hypotheses for fuzzy traffic signal control. They are I) generality of fuzzy control, II) competitiveness of fuzzy control III) multilevelity, -dimensionality and -objectiveness and IV) realisticity in real traffic signal control. The control principles and rules for the fuzzy control are modeled based on the actions of an experienced policeman represented by knowledge of an experienced signal control planner. According to the results the control parameters of fuzzy traffic signal control can be divided into three different groups: traffic volume, capacity, and level of service parameters. The fuzzy control algorithm of isolated traffic signal control can be derived based on these parameters. The fuzzy inference is perhaps the most important part of fuzzy control, but also the methods of fuzzification and defuzzification have to be introduced. Some artificial methods, like genetic algorithms and neural networks, have been tested without any benefits in comparison with the empirical membership functions. The fuzzy similarity method, which is based on Lukasiewicz's logic, has been introduced as a potential defuzzification method. In the development phase, the testing of fuzzy control has been done by simulation. Several different control strategies have been tested in different isolated control environments. The results of signalized pedestrian crossing indicated that the fuzzy control provides pedestrian friendly control keeping vehicle delay smaller than the conventional control. Based on the experiences of the Pappis-Mamdani control algorithm, a new control algorithm for two-phase vehicle control was developed. According to the statistical tests, the application area of fuzzy control is wide. The results of multi-phase control indicated that the traditional extension principle still is a better traffic signal control mode in the area of very low traffic volumes. However, an application area of fuzzy control is available. The experiences of fuzzy public tranport priorities and fuzzy control on major arterials have been promising. The multilevel (traffic situation, phase selection and extension inference) fuzzy control makes adaptivity possible. This also means that the number of control programs can be smaller than in the traditional VA-control. The most significant difference between traditional and fuzzy control methods is that the extension principle in VA-control looks at only the green signal groups, but the fuzzy control analyzes also the queues behind the red signal groups. This multi-dimensionality, the opposite input-parameters and the free rule-base development enable the multi-objective control. Finally, the fuzzy control methods have been tested in several real intersections. The proposed controller consists of traffic and control models, and it is justified that this kind of on-line simulation or simulation based traffic control is a working method. According to the statistical tests of before-and-after studies, the fuzzy control has proven to be a potential control method in real isolated traffic signal control.
Implementation and evaluation of air flow and heat transfer routines for building simulation tools
(VTT Technical Research Centre of Finland, 2002-08-23) Tuomaala, Pekka; Department of Mechanical Engineering; Konetekniikan osasto
Environmental, epidemiological and economical reasons increase the pressure to design, construct and maintain better buildings in the future. Therefore, a new assembly of simulation routines for predicting both ventilation and heat transfer processes of buildings were studied. The work was limited to implementation and evaluation of new air flow and heat transfer routines for building simulation tools. Development of simulation tool user-interfaces, post-processors and component database have all been excluded. The simulation routines were implemented in a new building simulation tool BUS++, which was based on discretisation and solution of mass, momentum, and heat balance equations. Ventilation fans, external wind and thermal buoyancy were included as driving forces for air infiltration and ventilation process. Two completely new routines were developed and implemented to obtain more reliable estimations of dynamic and multi-mode heat transfer covering thermal convection, conduction, and radiation. The first new routine focused on defining a rational thermal calculation network, and the second one concentrated on simulation of thermal radiation in a room. Finally, a rigorous set of tests were conducted to validate the air flow and heat transfer routines implemented in BUS++. The test set included commonly utilised analytical verifications and inter-model comparisons as well as completely new empirical validation test cases. The new rational gridding method reduced simulation times by 44 % to 86 % in a typical slab test case with a cyclic excitation, and the new routine for thermal radiation was up to ten times faster than the conventional matrix radiosity method. In addition, the simulation and validation data showed good agreement, especially for the analytical verifications and inter-model comparisons with typical differences less than 2 %. Despite these promising results, more research work is needed to further develop the simulation routines. In the future, special attention ought to be paid to simulation tool user-interfaces to facilitate full utilisation of the simulation tool by a wide range of users.
Influence of kinetic energy sources and internal obstructions on room air conditioning strategy, efficiency of ventilation and room velocity conditions
(Helsinki University of Technology, 2002-08-30) Hagström, Kim; Department of Mechanical Engineering; Konetekniikan osasto; Laboratory of Heating, Ventilating and Air Conditioning; LVI-tekniikan laboratorio
There is a variety of different methods consulting engineers use to design room system, room air diffusion, such as assumption of perfect mixing, design methods employing the empirical relations determined through research, air jet theory and computational fluid dynamics (CFD) codes. The most common design methods based on air jet theory allows only for the prediction of extreme values of air velocities and air temperatures in the occupied zone. However, the results of most analytical and experimental studies has been received from tests in empty rooms and do not reflect the influence of the obstructions or other kinetic energy sources on the room conditions, air distribution and ventilation efficiency. The objectives of the study have been to investigate the influence of different factors on the room air conditions, airflow pattern and efficiency of ventilation and to utilize the collected information to improve current design practices. Scale models and full scale experiments and computational fluid dynamics simulations were conducted in order to study the influence of an occupied zone obstruction level, air distribution method, air change rate, heat and contaminant source plus non-uniformity on the room system performance and the efficiency of ventilation. A new room air conditioning strategy classification was developed. In classification the zonal strategy is introduced to separate room flow situations that cannot be explained by mixing strategy. It is suggested the room air conditioning strategy should be used as a target for design of the room air conditioning system. A simple method for the calculation of the room average velocity conditions was developed. The method is based on the kinetic energy balance of the room space, thus taking into account both air jets and heat sources. Following the presented design algorithm, a designer can estimate the average velocity level within a ventilated room and furthermore utilize it for evaluation of comfort conditions. The calculation method developed is reasonably accurate in mixed conditions, but additional development is needed to take into account zone effects. The room obstructions do not influence on room contaminant distribution within the studied ranges and air distribution methods. The room heat sources are important factors for contaminant removal effectiveness and contaminant uniformity inside the occupied zone with zonal air distribution methods. There exists non-uniformity of the contaminant concentrations within the occupied zone that should not be neglected when designing room air distribution. The non-uniform distribution of heat and contaminant sources within the ventilated space can have a remarkable influence on the contaminant removal effectiveness and especially on the contaminant distribution within the occupied zone. A straightforward comparisons between the measurement data and CFD simulation results is difficult because the comfort oriented, omni-directional air speed measurements are not directly comparable with the air velocity computed with the turbulence models. The use of an artificial, modified velocity method gives especially in low speed areas better correspondence between the measured and calculated speeds.

Browse

Browsing [diss] Insinööritieteiden korkeakoulu / ENG by Issue Date

Results Per Page

Sort Options