| 1. |
- Andrén, Peter
(författare)
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Development and results of the Swedish road deflection tester
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A project to construct a high-speed road deflection tester was initiated in the 1991. A mid-sized truck was used as a carrier for the first prototype. The results were promising and it was decided to build a full-size truck system. The new vehicle, based on a Scania R143 ML, was completed in 1997. The Road Deflection Tester (RDT) is equipped with two arrays of twenty noncontact laser sensors that collects transversal surface profiles at normal traffic speeds. One profile, placed between the wheel axles, constitutes an unloaded case. The other profile, just behind the rear axle of the vehicle, constitutes the loaded case. By subtracting the front cross profile from the corresponding rear one, the "deflection profile" is assessed. The deflection is assumed to vary with the stiffness of the road. In order to produce a large load on the rear wheels the engine was mounted in the back of the vehicle, slightly behind the rear axle. In testing mode the rear axle force is approximately 112 kN, and the front axle force is about 30 kN. An incremental wheel pulse transducer, two force transducers and two accelerometers, an optical speedometer and a gyroscope are also mounted on the RDT. The first test programme was carried out in 1998. Due to the careful choice of test sections, data from these sections still produce the best results. A smaller test programme was carried out in 2001, and a larger one in 2002 when the RDT was taken to England and France for demonstration. Promising results, both on an aggregated scale and for individual test sections, have been obtained. The RDT compares favourably with the Falling Weight Deflectometer. Short histories of road construction and road research give some historical and cultural background to the more recent developments. A more comprehensive history of rolling deflectographs presents all devices found in the literature from the start in the mid-fifties when the California Traveling Deflectograph and Lacroix Deflectograph were constructed, to the latest laser based High-Speed Deflectograph. Many references are given for further reading. The data acquisition hardware on the RDT system consist of sensors, signal converters, signal processing cards, an industrial computer for data communication, and an ordinary PC for operating the equipment and data storage. The software used to evaluate the data is written entirely in Matlab. Many levels of pre-processing make evaluation relatively fast, and the modularised design makes it easy to implement new evaluation algorithms in a clean and efficient way. A literature survey on the deformations of solids under static and moving load is presented in Appendix A. The static case started with Boussinesq in 1885, was much developed in the sixties, but since the eighties only a very limited amount of new results have been published. The moving load case, on the other hand, is still an field of active research and development.
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| 2. |
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| 3. |
- Ashwear, Nasseradeen, 1968-
(författare)
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Vibration Frequencies as Status Indicators for Tensegrity Structures
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Applications of vibration structural health monitoring (VHM) techniques are increasing rapidly. This is because of the advances in sensors and instrumentation during the last decades. VHM uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.The first part of the present work studies the improvement of current models for resonance frequency simulation of tensegrities by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness. From this, both local and global vibration modes are obtained. The resonance frequencies are seen as non-linearly dependent on the pre-stress level in the structure, thereby giving a basis for diagnosis of structural conditions from measured frequencies. The new aspects of tensegrity simulations are shown for simple, plane structures but the basic methods are easily used also for more complex structures.In the second part, the environmental temperature effects on vibration properties of tensegrity structures have been investigated, considering primarily seasonal temperature differences (uniform temperature differences). Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies made by temperature changes could be equivalent to the change made by damage (slacking). Different combinations of materials used and boundary conditions are also investigated. These are shown to have a significant impact on the pre-stress level and the natural frequencies of the tensegrity structures when the environment temperature is changed.
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| 4. |
- Dalilsafaei, Seif
(författare)
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Stiffness modification of tensegrity structures
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the concept of tensegrity structures was invented in the beginning of the twentieth century, the applications of these structures are limited, partially due to their low stiffness. The stiffness of tensegrities comes from topology, configuration, pre-stress and initial axial element stiffnesses. The first part of the present work is concerned with finding the magnitude of pre-stress. Its role in stiffness of tensegrity structures is to postpone the slackening of cables. A high pre-stress could result in instability of the structure due to buckling and yielding of compressive and tension elements, respectively. Tensegrity structures are subjected to various external loads such as self-weight, wind or snow loads which in turn could act in different directions and be of different magnitudes. Flexibility analysis is used to find the critical load combinations. The magnitude of pre-stress, in order to sustain large external loads, is obtained through flexibility figures, and flexibility ellipsoids are employed to ensure enough stiffness of the structure when disturbances are applied to a loaded structure. It has been seen that the most flexible direction is very much sensitive to the pre-stress magnitude and neither analytical methods nor flexibility ellipsoids are able to find the most flexible directions. The flexibility figures from a non-linear analysis are here utilized to find the weak directions. In the second part of the present work, a strategy is developed to compare tensegrity booms of triangular prism and Snelson types with a truss boom. It is found that tensegrity structures are less stiff than a truss boom when a transversal load is applied. An optimization approach is employed to find the placement of the actuators and their minimum length variations. The results show that the bending stiffness can be significantly improved, but still an active tensegrity boom is less stiff than a truss boom. Genetic algorithm shows high accuracy of searching non-structural space.
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| 5. |
- Dijkstra, Erik J.
(författare)
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Constrained Optimization for Prediction of Posture
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ability to stand still in one place is important in a variety of activities of daily living. For persons with motion disorders, orthopaedic treatment, which changes geometric or biomechanical properties, can improve the individual'sposture and walking ability. Decisions on such treatment require insight in how posture and walking ability are aected, however, despite expectations based on experience, it is never a-priori known how a patient will react to a treatment. As this is very challenging to observe by the naked eye, engineering tools are increasingly employed to support clinical diagnostics and treatment planning. The development of predictive simulations allows for the evaluation of the eect of changed biomechanical parameters on the human biological system behavior and could become a valuable tool in future clinical decision making. In the first paper, we evaluated the use of the Zero Moment Point as a computationally inexpensive tool to obtain the ground reaction forces (GRFs) for normal human gait. The method was applied on ten healthy subjects walking in a motion analysis laboratory and predicted GRFs are evaluated against the simultaneously measured force plate data. Apart from the antero-posterior forces, GRFs are well-predicted and errors fall within the error ranges from other published methods. The computationally inexpensive method evaluated in this study can reasonably well predict the GRFs for normal human gait without using prior knowledge of common gait kinetics. The second manuscript addresses the complications in the creation and analysis of a posture prediction framework. The fmincon optimization function in MATLAB was used in conjunction with a musculoskeletal model in OpenSim. One clear local minimum was found in the form of a symmetric standing posture but perturbation analyses revealed the presence of many other postural congurations, each representing its own unique local minimum in the feasible parameter space. For human postural stance, this can translate to there being many different ways of standing without actually noticing a difference in the efforts required for these poses.
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| 6. |
- Engelhardt, Ilka. A. D., 1986-
(författare)
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Plasma and Dust at Saturn's Icy Moon Enceladus and Comet 67P/Churyumov-Gerasimenko
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Saturn’s moon Enceladus and comet 67P/Churyumov-Gerasimenko both are examples of icy solar system objects from which gas and dust flow into space. At both bodies, the gas becomes partly ionized and the dust grains get charged. Both bodies have been visited by spacecraft carrying similar Langmuir probe instruments for observing the plasma and the charged dust. The conditions at Enceladus and the comet turn out to be different, so we emphasize different aspects of their plasma environments. At Enceladus, we concentrate on the characteristic plasma regions and charged dust. At the comet, we investigate cold electrons.At Enceladus, internal frictional heating leads to gas escaping from cracks in the ice in the south pole region. This causes a plume of gas, which becomes partially ionized, and dust, becoming charged. We have investigated the plasma and charged nanodust in this region by the use of the Langmuir Probe (LP) of the Radio and Plasma Wave Science (RPWS) instrument on Cassini. The dust charge density can be calculated from the quasineutrality condition, the difference between ion and electron density measurements from LP. We found support for this method by comparing to measurements of larger dust grains by the RPWS electric antennas. We use the LP method to find that the plasma and dust environment of Enceladus can be divided into at least three regions. In addition to the well known plume, these are the plume edge and the trail region.At the comet, heat from the Sun sublimates ice to gas dragging dust along as it flows out into space. When gas molecules are hit by ionizing radiation we get a plasma. Models predict that the electron temperature just after ionization is around 10 eV, but that this collisions with the neutral gas should cool the electrons to below 0.1 eV. The Langmuir Probe instrument LAP has previously been used to show that the warm component exists at the comet. We present the first measurements of the cold component, co-existing with the warm component. We find that that the cold plasma often is observed as brief pulses in the LAP data, which we interpret as filamentation of the cold plasma.
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| 7. |
- Enström, Johanna
(författare)
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A Systems View of Advancements in Biomass Supply Chains
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Forest fuel is an important source of energy with potential for increased use in the Nordic countries. Profitable forest operations are dependent on logistics as the forest is a natural resource with varying conditions over widespread areas. In comparison to saw log and pulp wood supply, forest fuel supply has to face challenges like low product value, seasonality and irregularity of customer demand, low bulk density and the need to process the biomass prior to delivery. In order to utilize both the economic potential and societal benefits from replacing fossil-based fuels with renewable forest fuels these challenges must be managed. This requires efficient long distance transports, with changes of transport mode typically required.This thesis examines preconditions necessary for logistic planning to achieve cost and energy efficient long distance transports within supply chains for forest fuel. The thesis has an explorative approach, including both qualitative and quantitative techniques. Paper I provides a review of the development within forestry logistics in Sweden and Finland since the beginning of the century, with focus on transports, terminal usage and storage related aspects. Paper II uses qualitative interviews to deepen the understanding of a specific forest fuel supply chain by focusing on communications and relations between the actors. Paper III is a study of the influence of a terminal before maritime transport of wood chips using simulation. Paper I shows that forestry logistics faces challenges, primarily related to increased variations in field conditions caused by climate change. The importance of terminal storage for the supply of forest products will likely increase as an effect. Also the entrepreneurs interviewed in Paper II stressed the benefits of terminals in the supply chain, e.g. enhanced planning opportunities and a more even workflow over the year. Paper III puts cost for extra terminal handling in relation to storage costs in a port and demonstrates the importance of including variation in logistic planning. The terminal flows were not profitable in the case of a small port. In order to make a well-founded decision gains in other parts of the supply chain must also be considered, even when they are harder to quantify. This deserves attention in future research.
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| 8. |
- Eriksson, Anders
(författare)
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A discrete-event simulation approach to improve efficiency in stump fuel supply chains
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Current concerns about climate change and fossil fuel dependency have intensified interest in renewable energy and increased demand for sustainable alternatives. Softwood tree stumps could be a very interesting renewable fuel assortment. The stump-root system constitutes about 25% of stem volume. In Sweden, stump fuel extraction is not a well-established practice and large resources are currently left in the forest after final felling. The stump fuel supply chain is both challenging and complex due to distance between resource and end-user, bulkiness of the material, initially high moisture and ash content, and number of sub-processes involved. Optimisation of logistics issues within the stump fuel supply chain is crucial to ensure low delivery cost. Carefully planned stump fuel systems can reduce the supply costs and help deliver the fuel at a competitive price. In this thesis, various systems for stump transport and comminution were evaluated, particularly regarding resource use efficiency and cutting of unnecessary costs. Various factors associated with different aspects such as harvest site characteristics, fuel quality, biomass losses and machine performance were also evaluated in terms of their impact on fuel cost. A discrete-event simulation approach was applied. Models for all machines and activities included, from forest to end-user, were developed and programmed using the ExtendSim simulation language. The simulation results showed large variations in system performance and system cost. The cost of different transport and comminution alternatives differed by approximately a factor of two, irrespective of transport distance. The most cost-effective option proved to be crushing stumps on the ground and using a self-loading truck for wood fuel transport. Minimising idle machine capacity was identified as a key factor in achieving a cost-effective system. Moreover, well-planned stump storage was shown to reduce the delivery cost significantly. The most influential parameter for fuel cost was machine productivity. Enabling machines to operate efficiently throughout the whole supply chain is crucial for system economics and can be decisive for stump fuel feasibility.
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| 9. |
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| 10. |
- Eriksson, Anders
(författare)
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Cathodic Arc Synthesis of Ti-Si-C-N Thin Films from Ternary Cathodes
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cathodic arc deposition is a powerful technique for thin film synthesis, associated with explosive phase transformations resulting in an energetic and highly ionized plasma. This Thesis presents film growth through arc deposition from compound cathodes of Ti3SiC2, providing source material for plasma and films rich in Si and C. The interest for the resulting Ti-Si-C-N films is inspired by the two ternaries Ti-Si-N and Ti-C-N, both successfully applied as corrosion and wear resistant films, with a potential for synergistic effects in the quarternary system.When using a rotating substrate fixture setup, which is common in high capacity commercial deposition systems, the repeated passage though the plasma zone results in growth layers in the films. This effect has been observed in several coating systems, in deposition of various materials, but has not been explained in detail. The here investigated layers are characterized by a compositional modulation in Si and Ti content, which is attributed primarily to preferential resputtering in segments of rotation when the plasma has high incidence angle towards the substrate normal. For depositions in a non-reactive environment, the films consist of primarily understoichiometric TiCx, Ti, and silicide phases, and display a modest hardness (20-30 GPa) slightly improved by a decreasing layer thickness. Hence, the side effects of artificial layering from substrate rotation in deposition systems should be recognized.Adding N2 to the deposition process results in reactive growth of nitride material, formed in a wide range of compositions, and thereby enabling investigation of films in little explored parts of the Ti-Si-C-N system. The structure and properties of such films, comprising up to 12 at% Si and 16 at% C, is highly dependent on the supply of N2 during deposition. Superhard (45-50 GPa) cubic-phase (Ti,Si)(C,N) films with a nanocrystalline feathered structure is formed at N-content of 25-30 at%. At higher N2 deposition pressure, C and Si segregate to column and grain boundaries and the cubic phase assumes a more pronounced nitride character. This transformation is accompanied by substantially reduced film hardness to 20 GPa. Ti-Si-C-N films thus display a rich variety of structures with favorable mechanical properties, but in the regime of high Si and C content, the amount of N must be carefully controlled to avoid undesirable formation of weak grain boundary phases based on Si, C and N.
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