| 1. |
- Stensson, Sofia
(författare)
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Energy Efficiency in Shopping Malls : Some Aspects Based on a Case Study
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The building sector accounts for approximately 40 percent of our energy use. To reach existing environmental targets energy use will have to be reduced in all building types. At the European level, the main legislative instrument for improving the energy efficiency of the building stock is the Energy Performance of Buildings Directive (EPBD). The EPBD requires all member states to implement the directive in the building code and it also requires energy declarations to be performed at the building level.The first objective of this thesis is to describe energy use in shopping malls in Sweden and to suggest how this energy use can be reduced. The second objective is to determine whether current regulatory requirements are effective in promoting energy efficiency measures in Swedish shopping malls. Only limited background information was found from national energy statistics and scientific papers that deal specifically with energy use in shopping malls. The data available are difficult to analyse and compare due to inconsistencies in terminology regarding nomenclature and system boundaries. An improved terminology is presented in the thesis, with a distinction between organisationally and functionally divided energy, to facilitate future studies. Furthermore, when it comes to designing shopping malls and evaluating their energy use, correct input data are required. For calculations and simulations of energy demand in buildings, internal and external load patterns are important input data. The thesis provides occupancy, lighting and infiltration load data for shopping malls.Energy use in one shopping mall was investigated in detail and resulted in a validated calculation model for the prediction of energy use. To develop the calculation model an iterative empirical-theoretical methodology was used. It involved cross-checking measured data, assumptions related to operational and technical data, and model calculation results. The calculation model was then used for a more general analysis of energy efficiency measures and an evaluation of regulatory requirements. The thesis illustrates how the current building code and energy declarations are implemented in shopping malls today together with associated strengths and weaknesses.
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| 2. |
- Alfredsson, Svante
(författare)
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Constitutive Behaviour and Fracture of Adhesive Layers : Inverse Methods and Energetic Balance
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the automobile industry, current demands on reduced emissions with maintained or even increased crash worthiness, forces the industry to seek weight-reducing designs. The possibility to use lightweight materials is obviously attractive. At joints, these lightweight materials have to be connected to high-strength or low-cost materials. In this context adhesive joining can provide a flexible solution. The method adds little weight to the structure, it allows for material combinations that are not possible to weld, and it provides increased stiffness to the structure as compared to the conventional spot-welding procedure. Moreover, electrolytic isolation of the multi-material joints is achieved. In this thesis, experimental methods are developed to determine the complete stress-deformation relation for an adhesive layer loaded in shear. Generally, the stress distribution is non-uniform in the test geometries used. Evaluation of experiments is performed using an inverse method. The idea is to measure the energy release rate as a function of the crack tip deformation. The stress-deformation relation is obtained by a subsequent differentiation. The method is shown to be capable of capturing the complete stress-deformation relation under stable loading conditions. A method to accurately determine the energy release rate is needed for the inverse method to be successful. A closed form expression for the energy release rate of the end-notch flexure adhesive joint specimen (ENF) is derived in this thesis. An approximate formula containing measurable quantities is also given. It is shown that both the applied load and the crack tip deformation are needed to determine the instantaneous value of the energy release rate of the ENF-specimen. Experimental results show that the influence of the crack tip deformation can be substantial. An alternative specimen is also analysed theoretically. An initial theoretical study on mixed mode fracture of adhesive layers is also given in this thesis. A detailed comparison is made of the mode-mixity obtained using two different, frequently used mechanical models; the beam/adhesive layer model, and the continuum model, i.e. a model neglecting the presence of the adhesive layer. It is tempting to assume that the two methods would produce similar results for the case of a thin adhesive layer. However, this is only the case for geometries which are materially and geometrically symmetric with respect to the adhesive layer. For asymmetric joints, on the other hand, the two models are found to predict fundamentally different values of the mode-mixity. Moreover, the mode-mixity of the beam/adhesive layer model is found to depend highly on the relative stiffness of the adherends and the adhesive layer. This dependency is found to be quantified through two parameters.
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| 3. |
- Amiryarahmadi, Nata
(författare)
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A Virtual Design Studio for Low-Frequency Sound from Walking in Lightweight Buildings
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years there has been a growing interest for building lightweight multistorey woodenresidential buildings in countries like Sweden with large and renewable forests. While positive aspectsof these buildings, such as sustainability, ease of construction and lightness, motivate building more inwood, poor acoustic performance is a risk which concerns the wooden-building industry.Low-frequency impact sound from walking of the neighbors upstairs is the main source of complaintsabout the acoustic performance of these buildings. The disturbance caused by walking sounds,transmitted through lightweight wooden floors, results in acoustic discomfort and impairs theperceived quality of the building; sometimes even when the building has fulfilled an acoustic classhigher than minimum requirement, according to the national standard on sound classification and itssingle number ratings. The standard methods for objective evaluation of impact sound insulation offloors cannot predict, at a satisfactory level, the walking sound annoyance that the inhabitants ofwooden buildings experience. This causes an uncertainty about the resulting perceived quality of thesebuildings, which greatly concerns the building manufacturers and demotivates them from choosinglightweight wooden elements over heavyweight building materials such as concrete. This uncertaintycan be overcome by evaluating the perceived acoustic quality of the building prior to its construction.One solution is to build test houses where the subjective acoustic performance of floor samples can beevaluated in advance to the building construction. However, building a test house is expensive;besides, for evaluating the effect of every design modification on the experienced acoustic comfort ofthe building, a real floor sample has to be built and installed in the house, which would be timeconsumingand costly. An alternative solution is to use virtual acoustic test facilities.In this thesis a virtual design studio for impact sound is developed. It is a tool that facilitates creatingand listening to the acoustic field generated by impact forces such as footsteps on lightweight floors. Italso provides the possibility to evaluate the acoustic performance of floor elements in an early designphase, and to investigate the correlation between design parameters and the perceived impact soundinsulation of the floor. The tool is demonstrated and a very first listening test shows that one can obtainresults which are in good agreement with the results in literature. Loudness, reverberation andthumping are shown to influence the annoyance. It is also shown that there is a difference in judgementof walking sounds by persons who have experience with lightweight floors at home and by those whodo not have that experience.
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| 4. |
- Anderberg, Staffan, 1981-
(författare)
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Methods for improving performance of process planning for CNC machining : an approach based on surveys and analytical models
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Process planning as an enabler of competiveness is often overlooked, but being one of the principal function in the product realisation flow it holds a key role by combining both product and production requirements into a production concept with respect to the current manufacturing system. As such the capability of process planning to a large extent dictates production cost, lead times, product quality etc. With the introduction of new demands on production, such as environmental impact and process capability, process planning must be able to manage these demands effectively. Accordingly, it is vital to study the effects that up-coming demands have on the act of process planning. The research methods employed in this work include surveys (questionnaires and interviews), industrial case studies and experiments to provide data for models developed. The main finding of this research is that there is a lack of quantified process planning performance knowledge in the industry, which leads to verification problems as to whether changes that are made render anticipated effects. Results of surveys also indicated a low level of digitalisation of product data and limited use of computer aids (CAM, feature-based CAM and PLM) in Swedish industry based on 144 companies' response. A concept to improve process planning performance through operation classification based on process capability indices (Cp/Cpk) was suggested. The role of process planning in designing cost efficient and energy efficient machining operations has been maintained throughout the thesis by showing how tool selection and machining parameters selection influences the possibilities to achieve these objectives. This work has also showed that no inherent contradictions appear to exist between achieving cost efficient and energy efficient machining operations. This thesis has contributed to an enhanced understanding of how process planning improvements can be achieved through a holistic perspective of the process planning function, where both technical and methodological aids are included. It is however essential to understand the current situation of the process planning organisation, its internal/external relations, level of digitalisation, competency level etc. before major changes of the process planning function are undertaken in order to be successful.
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| 5. |
- Andersson, Tobias
(författare)
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Mechanical Behaviour of Adhesive Layers : Methods to Extract Peel and Mixed Mode Properties
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mechanical Behaviour of Adhesive Layers Methods to Extract Peel and Mixed Mode Properties TOBIAS ANDERSSON Department of Applied Mechanics Chalmers University of Technology ABSTRACT This thesis is concerned with methods to extract material properties of thin adhesive layers loaded in peel and in mixed mode. The first part of the thesis is devoted to an experimental method to determine the complete stress-elongation relation (or cohesive law) for an adhesive layer loaded in peel using the DCB-specimen. The method is based on the concept of equilibrium of the energetic forces acting on the specimen. Two sources of energetic forces are identified: the start of the adhesive layer and the positions of the two acting loads. By use of the concept of equilibrium of energetic forces, it is possible to measure the energy release rate of the adhesive layer instantaneously during an experiment. The complete stress-elongation relation is found to be the derivative of the energy release rate with respect to the elongation of the adhesive layer at its start. By this procedure, an effective property of the adhesive layer is measured. The validity of the approach is investigated by experiments where the adherends deform 1) elastically and 2) plastically. It is found that a unique stress-elongation is obtained when the adherends deform elastically. The same relation cannot be used to predict the experiments where the adherends deform plastically indicating that the approach has limited applicability. The second part of the thesis is concerned with the development of a mesomechanical finite element model of a thin adhesive layer loaded in mixed mode. The model is calibrated to previously performed experiments. In these, the adhesive layer is loaded in monotonically increasing peel or shear. An in situ SEM-study is also performed and used to guide the modelling and calibration. The purpose of the mesomechanical finite element model is to facilitate the development of constitutive laws for adhesive layers. The modelling is based on Xu and Needleman’s method where all continuum finite-elements are surrounded by interface elements that allow for the development of micro cracks. Thus, this enables the modelling of the entire process of degradation and fracture of the adhesive layer. A genetic algorithm is developed for the calibration. The simulations are shown to be in reasonably good agreement with the experiments. Keywords: adhesive layer, stress-elongation relation, J-integral, energetic force, experimental method, RVE, interface elements, genetic algorithm
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| 6. |
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| 7. |
- Bengtsson, Magnus, 1973
(författare)
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Quality-Driven Production of Aggregates in Crushing Plants
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aggregate quality is of great importance, and in this context it is essential to understand how various process parameters influence the product quality characteristics. Thus, there is a need for aggregate producers to improve their process knowledge.Research has led to an improved understanding of how different process parameters affect the outcomes of specific comminution processes. In aggregate production, breakage models are one example of such a research result. These models have been refined over the years. The breakage models that have been presented to date can accurately predict the size distribution of aggregates. On the other hand, they cannot normally predict any other material characteristics such as shape and strength. This thesis outlines the research to date, which has focused on a frequently discussed quality parameter, namely the shape of the product. Knowledge of various methodologies is required to measure this parameter. A novel method for measuring the shape of fine aggregates is presented. The rheology test, the methodology of which was originally based on a New Zealand standard, can be correlated with other data to measure particle shape in accordance with the F-aspect method. The correlation between these methods is very good, and since the rheology test is easy to use, it is suitable for a quarry or a basic test facility.The cone crusher is the most commonly used tertiary stage crusher today. One of its great advantages is that it produces a relatively low amount of fines. However, it only produces acceptable particle shapes for certain fraction sizes. The vertical shaft impact crusher (VSI) creates particles of a very satisfactory shape across all fractions, including fine aggregate, as confirmed by studies using the aforementioned rheology test.This thesis presents two models for predicting shape in crushed aggregate from a cone crusher. The first model is empirical, and my conclusion is that there are four dominating parameters affecting shape: the average feed size, the closed side setting (CSS), throw and eccentric speed. To further investigate how compressive breakage affects particle shape, an inter-particle breakage model is introduced. This model simulates a specific crushing stage inside the crusher. Simulation results show that the outcome from a crushing event can be predicted with good accuracy. A VSI model for describing particle size and shape is presented in this work. It is proposed that the dominating breakage mechanism in a VSI equipped with a rock box is of abrasive character. Abrasive breakage can appropriately shape all particle sizes, assuming the crusher is operated at a proper velocity.The empirical cone crusher model and the VSI models are combined in a mathematical simulation in order to determine how a crushing plant should be operated to maximise both yield and aggregate quality. The results show that there exists a set of rules to determine the crusher and screen settings that will achieve the best performance in terms of product yield and quality requirements.
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| 8. |
- Biel, Anders
(författare)
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Mechanical behaviour of adhesive layers : experimental methods, cohesive laws, and fracture mechanics
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Adhesive joining is today viewed as one of the key technologies to achieve decreased emissions in the automobile industry. To decrease weight, optimal material selection often results in different materials for different parts. This leads to the necessity to join mixed material. Here, the use of adhesives is the most promising joining technology. For a rational design process, good models for strength analysis of adhesively joined structures are essential. With cohesive modelling, fracture of the adhesive layer is modelled with a stress-deformation law. This law - often denoted a cohesive law - gives the traction exerted on the adherends due to the deformation of the adhesive layer. This thesis is concerned with experimental methods to measure cohesive properties of engineering adhesives and standardized methods to measure the fracture energy of adhesives. A new method to measure cohesive laws is developed. With this method, the cohesive law of an epoxy adhesive is measured in shear. In peel loading, with elastically deforming adherends, the cohesive law is shown to be independent of the geometry of the specimen. If the adherends deform plastically the fracture energy increases. Experiments are performed in order to determine the temperature dependence of the cohesive layer for an epoxy adhesive. It is shown that the peak stress is strongly dependent on the temperature while the fracture energy shows only small temperature dependence. Experiments are also performed to study the influence of strain rate in peel and shear loading. The experiments show that the peak stress increases with an increasing strain rate and that the fracture energy increase in peel loading and decreases in shear with increasing strain rate. A new method to experimentally determine the relation between damage and plasticity in the adhesive during the fracture process is developed. For the present adhesive, it is shown that only minor plasticity occurs during the fracture process in peel loading. For peel, several commonly used methods to evaluate the fracture energy using the double cantilever beam specimen are critically studied. For some methods the error in evaluated fracture energy is larger than 40 %. It is shown that the evaluated fracture energy is more dependent on the choice of method than on the cohesive properties of the adhesive layer.
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| 9. |
- Borgström, Karin Margaretha, 1956-
(författare)
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Determination of the thermal conductivity of the insulation in district heating mains : Field measurements
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns the development of a measurement method for determination in the field of the thermal conductivity of the insulation in buried district heating mains. The thermal conductivity of the insulation is calculated from the measured value of the radial heat flow through the heating main, the measured temperature difference across the insulation, and the dimensions of the heating main. The heat flow has been measured with a heat flux sensor which was fitted to the surface of the casing. The temperature has been measured with copper/constantan thermocouples. It is a necessary condition for the method used in the project for determination of the thermal conductivity of the heating main insulation that the heating main is uncovered and is not in contact with the surrounding soil over a distance of about 1.5 m and that the measurements are made directly on the heating main. In this way, no account need be taken of the material surrounding the heating main, nor of the effect of this material on the measurements. No interference is needed with the heating main which would affect the distribution of the district heating water, and the heating main can remain in operation during measurements. Shielding insulation consisting of preformed insulation sections which were placed over the casing of the heating main and covered the heat flux sensor and some of the casing. The function of this insulation was to shield the heat flux sensor from external thermal disturbances. In the field measurements, a copper guard plate of 0.5 mm thickness, the temperature of which could be adjusted, was also placed over the shielding insulation in order to maintain the temperature on the heat flux sensor as constant as possible. When temperature and heat flow are measured, the instruments used will be affected by conditions which prevail at the time of measurement. It is therefore very important to analyse the sources of error which may arise in the measuring situation at hand. The effect of these factors on the measured values has been studied by ' laboratory measurements ' theoretical calculations ' field measurements On the basis of the resulting values of heat flows and temperatures obtained in field measurements on plastic heating mains which were operating under normal conditions, the thermal conductivity of the insulation of the main has been estimated. The method has been tested on plastic heating mains with directly foamed insulation, since this is the most common type of heating main both in the existing district heating network and in new construction. The measuring method can also be used on other circular heating mains.
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| 10. |
- Cabanettes, Frédéric, 1982-
(författare)
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Cam Roller Contact : Surfaces and Tribology
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The automotive industry and the design of engines are strongly ruled by performance and legislation demands. In the valve train, mechanical components such as camshafts and rollers are defined by specifications including more and more constraints concerning their ability to face wear thus prolonging lifetime.The aim of the thesis is to develop tools facilitating the choice between different manufacturing processes for wear optimization purposes of cam and roller components for IC engine valve trains. Tools are both experimental and theoretical.For the experimental part, statistical and relocated studies of wear have been performed. It is shown that measuring the very same surface before and after experiments is preferable to understand wear mechanisms of cams and rollers. A set of analysis tools for describing changes between unworn and relocated worn surfaces is developed. As results, it is found that the predominant mechanism of wear for cams and rollers is a flattening of asperities: surfaces are pressed and plastic deformations occur.In parallel, simulations have been developed to explain theoretically the wear observed. Micro and macro simulations are developed to predict the ability of a given manufacturing process to resist wear. For the microscopic simulation, a rough contact model including elasto-plastic behavior of materials is used and shows good correlations with experiments. Concerning the macroscopic simulation, a model including form deviations due to manufacturing is developed and computes oil film thicknesses and deformations. The different parameters computed by both simulations are indicators of the wear performance of different surfaces. It is shown that such simulation can rank different manufacturing processes in terms of ability to face wear.
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