103 research outputs found
Using reverberation chambers for em measurements
Get PDFReverberation chambers (RC) are being used for several decades. The main advantage is the high field strength which can be generated, with only modest power. In the last few years the use of RCs became much popular, for testing multi-path propagation for communication links, or testing the coupling of complex fields into transmission lines, as well as testing coupling into objects, and measuring the shielding effectiveness of materials. The costs for setting up a conventional RC, with rotating mode stirrers, is low compared to the cost of anechoic chambers. Existing chambers are making use of a paddle wheel to change the resonant modes in the chamber. A transportable reverberation chamber with varying angles between wall, floor and ceiling and with vibrating walls has been used for testing of many systems. Inside this Vibrating Intrinsic Reverberation Chamber(VIRC) a diffuse, statistically uniform electromagnetic field is created without the use of a mechanical, rotating, mode stirrer. This chamber results in a better homogeneity and increased field strength compared to conventional mode stirred reverberation chambers. The use of flexible material to build the VIRC is making a test facility at even lower cost possible. Furthermore such a VIRC can be built around a test object,and the test object is not to be moved to an anechoic chamber. This can reduce test costs for complex systems. The basic principles of RC and VIRC are explained, and several applications shown
Using reverberation chambers for em measurements
No full textReverberation chambers (RC) are being used for several decades. The main advantage is the high field strength which can be generated, with only modest power. In the last few years the use of RCs became much popular, for testing multi-path propagation for communication links, or testing the coupling of complex fields into transmission lines, as well as testing coupling into objects, and measuring the shielding effectiveness of materials. The costs for setting up a conventional RC, with rotating mode stirrers, is low compared to the cost of anechoic chambers. Existing chambers are making use of a paddle wheel to change the resonant modes in the chamber. A transportable reverberation chamber with varying angles between wall, floor and ceiling and with vibrating walls has been used for testing of many systems. Inside this Vibrating Intrinsic Reverberation Chamber(VIRC) a diffuse, statistically uniform electromagnetic field is created without the use of a mechanical, rotating, mode stirrer. This chamber results in a better homogeneity and increased field strength compared to conventional mode stirred reverberation chambers. The use of flexible material to build the VIRC is making a test facility at even lower cost possible. Furthermore such a VIRC can be built around a test object,and the test object is not to be moved to an anechoic chamber. This can reduce test costs for complex systems. The basic principles of RC and VIRC are explained, and several applications shown
FRANK : het ontwerp van een nieuw landmeetsysteem gebaseerd op panoramische beelden
No full textCivil Engineering and Geoscience
Plasticity under rough surface contact and friction
No full textThe ultimate objective of this work is to gain a better understanding of the plastic behavior of rough metal surfaces under contact loading. Attention in this thesis focuses on the study of single and multiple asperities with micrometer scale dimensions, a scale at which plasticity is known to be size dependent. The asperities have very simple geometries, either rectangular or sinusoidal and they are pressed into contact with a rigid platen. The analysis is performed using the discrete dislocation (DD) plasticity method, given its accuracy to describe microscale plasticity and its capability of predicting size effects. In DD, plasticity is modeled as the collective motions of discrete dislocations dislocations, which are modeled as line singularities in an otherwise isotropic linear elastic medium. The dislocation Burgers vector is the material length scale that allows to capture plasticity size effects. In Chapter 2, simulations are performed to investigate the flattening of a sinusoidal surface, for different dimensions and shape of the sinusoid. A size dependent response is found for asperities with the same amplitude-to-period (A/w) ratio. The smaller asperities are more difficult to deform plastically due to the limited dislocation density at the same strain. It is observed that the mean contact pressure can reach values up to about 40 times the yield pressure, thus significantly higher than what is predicted by the classical plasticity theory. This is mainly caused by the fact that the area of intimate contact is discontinuous and therefore the distribution of contact pressure is highly non homogeneous. Smaller contact regions are characterized by a very high stress concentration. The simulation results are rather insensitive to the contact conditions used, i.e. frictionless or sticking. When flattening periodic sinusoidal waves, it is not possible to assess a possible size dependence related to the spacing between asperities, since decreasing asperity spacing also reduces asperity size. Therefore in Chapter 3, simulations are performed for the flattening of an array of equally spaced sinusoidal asperities. This allows to investigate the effect of plastic interaction between neighboring asperities on the contact pressure. It is found that the mean contact pressure necessary to flatten closely spaced asperities is larger than that required to flatten widely separated asperities. The so-called asperity density effect is already present in purely elastic materials, and becomes more pronounced when plasticity is described by discrete dislocations. The origin of the asperity density effect is found to be a combination of plastic strain gradients, dislocation limited plasticity and interaction between plastic zones. In Chapter 4, simulations are performed to investigate the effect of flattening on the subsequent shearing behavior of a rectangular asperity protruding from a large single crystal. The shearing is applied after the pillar is flattened to different depths. In large asperities, i.e. a couple of square micrometers, the dislocations generated during flattening promote early plasticity upon shearing, i.e the contact shear stress is reduced, when plastic deformation takes place upon flattening. However, flattening smaller asperities to the same displacement, instead, does not affect subsequent plastic shearing. Despite there are many dislocations in the asperities, they are closely packed on a few active slip planes and therefore have smaller mobility. The simulations are also performed for on multiple asperities to investigate the effect of spacing on their shearing behavior. It is found that closely spaced asperities are easier to plastically shear than isolated asperities. This effect is mainly triggered by the fact that shearing closely spaced asperities in the elastic regime gives rise to a wide region in the subasperity where the shear stress is large and therefore facilitates dislocation nucleation. This effect fades when asperities are very protruding, and plasticity mainly occurs inside of the asperities. In Chapter 5, simulations are performed to investigate the static frictional behavior of a metal asperity on a large single crystal, in contact with a rigid platen. The focus of this chapter is on understanding the relative importance of plasticity and contact sliding in a single asperity at a scale where plasticity is size dependent. Sliding of a contact point is taken to occur when the shear traction exceeds the normal traction at that point times a friction coefficient. Plasticity initiates through the nucleation of dislocations from Frank-Read sources in the metal and is modeled as the collective motion of edge dislocation. Results show that at large contact pressures and friction coefficients, plasticity controls the frictional behavior of a single asperity. When self-similar asperities of different size are flattened to the same depth while loaded tangentially, there is no trace of a size effect in their frictional behavior. However, when they are submitted to the same contact pressure smaller asperities slide while larger asperities deform plastically.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
Gait Variability and Kinematic Alterations in People with Diabetes Mellitus and Peripheral Neuropathy
No full textBackground: People with diabetes and peripheral neuropathy have been reported to show alterations in lower limb joint function compared to healthy non-diabetic people. Specifically the maximum angular movement available at certain joints can be reduced during static, non-weight bearing tasks. Limited joint range of motion has the potential to compromise balance and stability thereby increasing the risk of falling. It is unclear whether a reduction in the extent of movement available at the joints is reflected by a reduction in the amount of angular movement actually utilised during a functional task such as stair negotiation. The aim of this study was to determine if people with diabetes show reduced dynamic range of motion at the ankle, knee and hip joints during stair ascent and descent in comparison to controls. Falls risk during stair negotiation was calculated by measuring the degree of variability in dynamic joint range of motion. Methods: Data were generated from three groups: subjects with diabetes and peripheral neuropathy (DPN), diabetes without peripheral neuropathy (DM), and healthy controls (Ctl). The study was conducted in a gait laboratory using motion capture and related 3D software for analysis. Joint range of motion for the ankle, knee, and hip were captured during level walking, stair ascent, and descent. A seven step, bespoke staircase was fabricated for this purpose. Analysis of Variance (ANOVA) and Newman-Keuls tests were used to analyse the data. Results: Significantly reduced ankle range of motion, in the sagittal plane, was observed in the DPN group during stair ascent when compared to the controls. For stair descent, the DPN group demonstrated a significant increase in knee and hip ROM in the frontal plane, and also hip ROM in the transverse plane. No significant differences between the groups were identified for joint variability. Conclusions: People with DPN demonstrate alterations in dynamic range of motion at the lower limb joints during stair ascent and descent. The degree of angular movement utilised for both stair tasks was decreased at the ankle joint and this has the potential to undermine balance and stability. In contrast, angular movement at the knee and hip joints was increased in the frontal and transverse planes. This may compensate for impaired balance and stability by increasing the base of support to maintain balance and assist in foot clearance and placement. The specific combination of increased angular movement at the knee and hip may represent a compensatory stair gait strategy in response to reduced angular movement at the ankle joint
Adapting an in-cylinder process model to a 2-stroke Bolnes engine and preparations for ammonia-diesel operation
No full textTo achieve the emission goals set out by the International Maritime Organization in 2018. Low or zerocarbon fuels will have to be used. Ammonia is considered to be a possible candidate since it doesn’t contain carbon. This thesis will attempt to study two methods that characterize the closed-cylinder process of an internal combustion engine; the Seiliger approach and Wiebe function. Two things are the main focus of this thesis. Namely, the application of these methods and how this process will be different for ammonia-diesel combustion compared to diesel combustion. The application will be done for a two-stroke compression ignition engine. The operating conditions that are considered are four load points 20%, 40%, 60%, and 100% at a constant engine speed. The application of this method means building an anti-causal and causal simulation model using Matlab Simulink. Both models simulate what happens in one cylinder during the closed-cylinder process, require the engine parameters as input, and produce the same results. The anti-causal model processes the pressure as a function of the crank angle to determine the combustion reaction rate. The causal model simulates the combustion reaction rate using a Wiebe function to determine the pressure. The Wiebe function is determined based on the reaction coordinate produced by the anti-causal model. By using the Wiebe function, the causal model produces smoother results than the anti-causal model. The Seiliger parameters are determined by using a Newton-Rhapson solver with the maximum pressure, maximum temperature, indicated work, and heat input as equivalence criteria. The results produced by this thesis generally show that the constructed method can produce accurate results. However, this accuracy is correlated to the operating conditions of the engine. As for the changes necessary for ammonia-diesel combustion. These changes have been provided on a conceptual level, with conceptual meaning in terms of equations and assumptions. These changes have not been implemented into a computer model that has been verified and validated. The fundamental difference for the constructed method according to this thesis is the fact that the combustion parameters; start and end of combustion for the two fuels have to be incorporated in the combustion model used for the anti-causal and causal model. This change has to be made, along with assumptions that the injected fuel evaporates and combusts almost simultaneously. This assumption is considered to be highly questionable for ammonia.Marine Technolog
Steel quantity and cost comparison of modular construction options for sea-transported pipe racks
No full textThis thesis is aimed at finding the most cost effective way of executing Modular Execution Strategy (MES) for building pipe racks of a project that an engineering company Fluor B.V. is currently executing in Kuwait. A pipe rack is a steel structure which is constructed to efficiently place and support multiple levels of pipelines for industrial plants such as refinery plants, chemical plants or power plants.The Modular Execution Strategy aims at relocating parts of fabrication and assembly activities of a pipe rack construction to potentially low cost locations at which the conditions for fabrication and assembly activities are more favorable. The pre-assembled pipe racks will be transported to the onshore installation site by a vessel, which results in sea-transport design requirements (due to vessel motions) in addition to the in-place design. Three options of different configuration for MES were considered. The first option is to transport only upper parts of the pipe racks without their bottom columns and assemble the bottom columns at the installation site. The second option is to transport the complete pipe racks including bottom columns which are stiffened by temporary bracings. The last option is to transport complete pipe racks with strengthened columns having a larger profile dimensions.In order to consider various sizes of pipe racks, 27-representative configurations of pipe racks of the project were selected. These pipe racks were designed to withstand in-place loadings and sea-transport loadings with a quasi-static analysis method. The in-place loadings are weight of pipe lines and wind force. The sea-transport loadings are forces due to motions of a vessel and critical sea-transport loadings come from roll + heave and pitch + heave. Quantities of steel for each option were found after completion of the design. Subsequently, the quantities were translated into steel work cost which includes procurement, fabrication, assembly and installation costs of steel work.As a conclusion, it was found that considering the quantities and costs of steel work for the project, option 1 (transport the pipe racks without columns) is the most cost effective solution. If pinned supports are used at the vessel deck, which are more favorable for the company, it was calculated that option 1 requires, on average, 15% and 30% less cost than option 2 and option 3 respectively. For clamped supported conditions, option 1 still requires 15% less cost than both option 2 and option 3.Furthermore, it was demonstrated by performing a resonance check and a dynamic analysis for a tall two-dimensional frame, that a quasi-static analysis method could be used to assess the sea-transport loadings. It was found that there is very low possibility of resonance and only low dynamic amplification. In this thesis, the focus has been on differences in the structural configurations. Other aspects, some of which may be difficult to express in cost terms such as logistical difficulty, safety/risk, and project schedule, were not taken into account. Therefore, in order to verify the attractiveness of each option in more detail, it is suggested to also make a complete assessment of those mentioned aspects.<br/
Population Aging in Canada: Software for Exploring the Implications for the Labour Force and the Productive Capacity of the Economy
Get PDFThis report has two purposes: (1) to introduce a new version of the MEDS (Models of the Economic Demographic System) software; and (2) to apply it in a series of illustrative projections. The software is designed to illustrate the medium- to longer-term responses of the Canadian population and economy to a wide range of factors on either the demographic side, such as changes in rates of fertility, migration, and mortality, or the economic side, such as changes in the rate of technical progress or the educational attainment of young people or of new immigrants. "Standard" projections are provided, together with nineteen alternative projections. (For some illustrative projections, see http://socserv.mcmaster.ca/qsep.) The range of projections indicates the breadth of applications for which MEDS has been designed. It serves also to provide some quantitative measures of the likely demographic and economic consequences of population aging, and indicates the scope for evaluating policy initiatives by means of simulation.macroeconomic projections, economic-demographic system
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