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The optimal leg compliance to reject disturbances in bipedal running was determined. An optimization study was performed, in which the potential energy in the leg of a model with a flat foot was optimized. The optimal disturbance rejection behavior improves w.r.t. foot length up to a factor 3 w.r.t. zero foot length.

Architecture plays an important role in defining the identity of a certain place. It tells about the people's activity, history, politics, finances, culture, industry, ideas and dreams. Amsterdam West nowadays is experienced by most people as a lifeless, anonymous and unsafe area. A reason for this can be found in the big scale repetitive building style of the postwar reconstruction. Analyses of this area reveal an unclear relation between building and activity of its habitants. The architecture offers little possibility for display of economical activity and has little possibility to transform according to this activity. For creating a more lively and livable city part, the project seeks to create an interaction between habitants and buildings, attributing to an own identity. Chosen strategy is a bottom up approach in connecting and creating urban frontrooms. The term 'frontroom' refers to a place used for display and exchange with the outside world, found in housing typology. This strategy is translated in three interventions in a strip in the heart of Osdorp: flats, market square and event hall. The design of the event hall shows how these interventions work as an instrument for people to use. Technical solutions, like the multi-layered facade containing sliding doors made of translucent plastic and moveable wooden louvers, provide a changeable outer and inner appearance of the event space. Architecture functions as the framework able to adapt and transform along with the activity of people.

Short-wave irregularities in the wheel-rail interface are at the basis of track and vehicle damage and deterioration. On the short term, they result into high dynamic train-track interaction forces and a high energy input into the system that must be dissipated in the different system components or "levels", leading on its turn to progressive deterioration on the long term. Furthermore, the short-wave defects grow into longer defects in the track geometry, due to the fact that the train is a travelling multi-body mass-spring system. The lifetime of the track and its components can be extended by adjusting the "path" of the dissipated power spectrum through the system and adjusting component and system properties with respect to their hysteretic behaviour. Instead of life-time extension, such measures may also aim at an extension of maintenance intervals, which is important to optimise the availability of e.g. high-speed lines. The present study investigates two particular types of short defects in detail: rail welds and wheel flats. In longitudinal direction and on a global scale, the contact between a rolling wheel and a rail can be distinguished into continuous single-point contact and transient double-point contact. The contact type that occurs depends on the actual geometry of the wheel-rail interface in the running direction. The first contact type leads to a dynamic amplification of the static axle load, whereas the second leads to wheel-rail impact. Especially the latter contact type is detrimental to the rail system and should be prevented as much as possible or detected at an early stage. The introduction of rail welds instead of the traditionally bolted connections reduced the dynamic forces at rail joints globally with a factor three. However, welds remain potential damage initiators due to the local geometrical and metallurgical discontinuity. Investigations show an approximately linear relationship between the extreme value of the dynamic wheel-rail contact force at a weld, the maximum absolute rail inclination and the train speed. The geometry of rail welds is traditionally assessed with the principle of vertical tolerances. A new assessment method for rail welds is proposed, with norm values for the allowable inclination depending on the line section train speed. This method is based on a relatively strong correlation between discretised maximum rail geometry inclinations (first derivatives) and extreme dynamic wheel-rail contact forces, relative to the poor correlation between tolerances and extreme forces. The method aims at a reduction and uniformisation of dynamic contact forces at rail welds, in order to avoid deterioration. Wheel flats are commonly assessed on the basis of their length and/or depth, or automatically detected by wheel impact load detectors in the track. This study has shown that the minimum circumferential wheel tread curvature is the critical parameter that governs the dynamic wheel-rail interaction in the presence of wheel flats. It determines which contact type occurs for a given flat geometry: continuous single-point contact, in the subcritical speed regime, or transient double-point contact, in the transcritical speed regime. It furthermore determines the magnitude of the contact force in the subcritical regime. Both speed regimes are shown to exhibit essentially different features with respect to the dynamic wheel-rail interaction: the track stiffness governs the interaction for low train speeds and long flats, whereas for high speeds and/or short flats the inertial properties of the wheel and the rail govern the interaction. The force-speed relationship is non-linear in the first regime, whereas linearity is a good approximation in the second regime.

In order to validate existing models of sedimentation in active sedimentary environments, detailed stratigraphic information is indispensable. Near-surface geophysical methods provide a means to acquire high-resolution images of the stratigraphic succession in the shallow subsurface. Land-based and marine methods have been tested in the Verdronken Land van Saeftinge. This intertidal flat area is cut by numerous tidal gullies, and high tidal amplitudes enable the application of different techniques at various water levels. Data acquisition focused on the upper 10 - 20 m of the active sediment bodies. Applied techniques include high-resolution seismic acquisition, geo-electrical methods (DC resistivity), electromagnetic techniques, CPT, and manual drilling. In general the acoustic methods allowed more reliable and detailed interpretation of the sedimentary structures than the electric/electromagnetic methods. The latter suffered from the effect of tidal action and salt-water intrusion, and their application on land proved very strenuous. CPT and shallow cores provided valuable ground-truth information. The results clearly indicate that no single technique can provide all the answers. Only an integrated use of (complementary) methods will allow getting a better grip on the sedimentary architecture and preservation potential in active estuarine sedimentary environments.

This dissertation qualitatively investigates the morphodynamic response of a large inlet system to IPCC projected relative sea level rise (RSLR). Adopted numerical approach (Delft3D) used a highly schematised model domain analogous to the Ameland inlet in the Dutch Wadden Sea. Predicted inlet evolution indicated the typical channel/shoal pattern of the Ameland inlet and an agreement with the empirical-equilibrium relations. RSLR enhances the existing flood-dominance of the system leading to erosion on the ebb-tidal delta and accretion in the basin. Tidal flat evolution was quite stable applying low RSLR whereas the system indicated turning into a lagoon under high RSLR. Nourishment application hardly enabled the RSLR induced sediment demand of tidal flat evolution.

Post-Exodus or the involuntary prisoners of Architecture, is a project about corrupt well intended top-down pretentions. A project about when utopia becomes dystopia. About when the built environment becomes out of tune with experienced and desired reality. Accumulating to the point of large scale vacancy and crisis. The focus of the project will be the case of the Kleiburg flat, the last untouched piece of Bijlmer ideology. The project was done in the graduation lab 'Design as Politics' with the underlying theme 'In the Ghetto', in which a personal view on the definition of a ghetto was encouraged. In this project the ghetto is described as an urban area that resonates with negative associations, as a segregated area often associated with the social-economic-weaker section. Due to the unpopularity of the urban area, real-estate values drop, investors and project-developers stay away. Conditions deteriorate. For those who want to leave the ghetto but can not afford to do so, the ghetto becomes an urban prison. The title of the project plays with the idea of architecture's ability to manifest dreams and desires. As the exodus took place and people moved towards the better, they left behind the old. The exodus was for those who could afford to leave; those unable to escape the undesired urban conditions where left behind. Post-Exodus focuses on these deprived areas, on these places of undesired architecture. It searches how to become a desired place once again, even when the means are limited. The research investigates a South-American Prison situated in Bolivia, in the capital city of La Paz. In the old city center, on the old colonial spanish grid the prison of San Pedro stands. Hidden behind the stucco walls, upon passing the guarded gate, a unexpected vivid community is revealed; the self-regulating inmate population of San Pedro. The prison was inspired by the panopticon model (Pentonville, London) of Jeremy Bentham. Built around the nineteen hundreds, this ideological prison model proved to be one of unrealistic utopia. The penitentiary system could not live up to the build expectations. The conditions of the inmate population deteriorated inside the prison walls. Without a welfare state or governmental subsidies the prisoners where appointed to their own ability to take matters into their own hands. Escape was not an option, the solution had to come from within... The do-it-yourself attitude of the prisoners resulted in an unique bottom-up transformation of the old prison model. Over time the prisoners slowly adapted the building to fit their basic needs, constantly fighting for their rights and defending every square inch. They held no nostalgia of the past, adapting to the new reality of their needs, adapting the build environment at best to survive. Over time San Pedro Prison developed its own logic, a mini-society with its own micro-economy, micro-policies, democratic elections, a prison real-estate market, cafes, restaurants, fitness area, sauna's, pool halls, tv corners, shops, dentist, churches, ceremony square, football competitions, tourism, workplaces, jobs and even more.. The San Pedro Prison inspires to look in a different way at the built environment we inhabit. It inspires to think in a different way about our attitude towards buildings. It inspires to think in a different way about architecture. It inspires to see how in the worst conceivable conditions, the prisoners of San Pedro where able to transform their built environment into a more favorable condition, to suit their lives and needs better. Transformation as a continues process, attuning to the ever changing times. Kleiburg is dead, it's ideology faded in the face of reality. Time has changed, Kleiburg stood still. If Kleiburg is not to parish in irrelevance it must once more become a part of our dreams and desires. Emergent societal trends and changes must then form the basis of its transformation. In times of financial crisis, unpredictability and uncertainty the means are limited. The answers must not be sought in the top-down financial power of big project developers but in the power of the ordinary people; the power of the people dwelling and working in and around Kleiburg. The design investigates a bottom-up approach, a do-it-yourself attitude, a gradual growth towards a new future. To clarify such a development a scenario was written in which the existing local social and urban fabric where extrapolated into the Kleiburg building. The initial conditions are dictated by the structural possibilities of the Kleiburg flat itself. The installation of the 'Gate' marks the presence of an underlying democratic process. Spatial hierarchy determines the relationship of space and influence of individuals/collectives on the built environment. In a set of projects possibilities are designed, each design telling a different story, each story exploring a new theme, each theme adding to a bigger scale. By the time we look back at all the different designs we will witness the emergence of museum. A Bottom-Up-Museum symbolizing the deconstruction of the prestigious 'starchitect' object, reconstructed by ordinary people.

In general electric field forces have the distinctive property of being able to mediate forces to virtually any material in a fully non-invasive and contact-free fashion. Based on this property, electrostatic levitation holds great promise for the semiconductor, solar panel, and flat-panel display industry since the handling of (semi)conducting and dielectric materials in a contact-free manner can bring many advantages and solve long-standing contamination and particulate control problems. These problems arise from the direct mechanical contact through which dielectric and semiconductor materials are commonly handled by process equipment in these industrial areas. Direct mechanical contact can cause chemical and particulate contamination of the handled material. Furthermore, it can result in electrostatic charging through tribo-electric effects, which raises the electrostatic potential of the handled material causing air-borne particles to be attracted to it. Ultimately, chemical and particulate contamination can critically affect performance, reliability, and product yield of the manufactured devices. Electrostatic levitation offers the inherent capability to avoid these contamination problems. In addition to enhancing contamination control, electrostatic levitation can provide uniformly distributed suspension forces. This is an advantage in the handling of very large and thin glass substrates used in the manufacture of flat panel displays as it leads to minimal mechanical deformation of the substrates. This thesis presents a comprehensive and in-depth study on the use of electrostatic fields for the contact-free suspension of (semi)conducting and dielectric materials. The electrostatic levitation devices that have been developed are specifically geared toward novel applications in the semiconductor and flat-panel display industry. Closed-loop feedback control is necessary to stabilize the position and attitude of the levitated object. In order to stably levitate an object, only three degrees of freedom are required to be actively controlled, i.e. the vertical motion and the angular motions represented by the pitch and roll angles. The lateral and longitudinal movements are passively stabilized by restrictive forces originating from the fringing fields existing between the outer edges of the stator electrodes and the suspended object. A generic voltage-controlled electrostatic levitator for the contact-free suspension of conducting disks or panels was developed first. Its main building blocks consist of a feedback controller, high-voltage dc amplifiers, displacement sensors, and a stator electrode structure. Simple guidelines based on the assumption of uniform electric fields are established for the design of suitable stator electrode patterns and applied voltage distributions, which guarantee electric potentials on disks/panels close to zero volts. Squeeze film air damping plays a major role since it may impact the dynamic behavior of the levitator significantly. The reason for this lies in the fact that the forces arising from squeeze film damping can approach values that are of the same order of magnitude as the electrostatic suspension forces. We also investigated both theoretically and experimentally the restrictive lateral forces produced by the fringing fields. These forces are weaker than the levitation forces. In line with the theoretical model, the measurements show that the lateral force can be increased by applying higher stator voltage magnitudes or by decreasing the air gap separation. Based on these observations, the stator design was improved by adding a ring of peripheral sector electrodes having the primary function of generating the fringing fields. Levitation experiments have been conducted in an atmospheric environment, demonstrating the successful suspension of a 4-inch silicon wafer, having a mass of 9.4 g, at a nominal gap separation of 300 µm utilizing centralized PID feedback control. At constant ring electrode voltages of ±1.2 kV, a lateral stiffness value of 0.84 N/m was produced by the improved stator produced, which corresponds to an increase of a factor of 5.5 relative to the conventional stator. A major and growing industrial area of potential application of electrostatic levitation constitutes liquid crystal display (LCD) manufacturing. Glass substrates are basic and essential components in LCDs. They belong to the class of lossy dielectrics. Their charge relaxation times may complicate the task of levitating them stably. A stator electrode suitable for the levitation of lossy dielectrics consists of a regular planar array of parallel bar electrodes to which voltages of differing polarities are alternatingly applied. We develop a general analytical model of the levitation field and force on a lossy dielectric plate produced by this stator electrode. This model takes into account the influence of the atmospheric humidity on the electrostatic charging dynamics. The levitation force dynamics are studied by evaluating the transient response of the field under a step in the applied voltages. In this context, the rate of electric charge build up on the plate is characterized by the suspension initiation time (TSI), which is defined as the time elapsed between applying step voltages to the stator electrodes and start of lift-off of the dielectric plate from its initial position. TSI is theoretically predicted for 0.7 mm thick soda-lime glass substrates, typically used in the manufacturing of liquid crystal displays (LCDs), as a function of electrode geometry, air gap separation, ambient humidity, and step voltage magnitudes. The predicted results are shown to be in good agreement with previously published experimental data. Position measurement based on capacitive sensing technology has been investigated as well since it can lead to an improved level of levitator cleanliness. This stems from the fact that the sensing electrodes can be integrated into the stator electrodes rendering compact, planar structures. A charge-discharge capacitive displacement sensor with improved stray capacitance immunization capabilities was developed. In addition a simple and cost-effective capacitive sensor using the oscillation principle was designed and realized. Both sensors have been calibrated for different target materials, i.e. silicon, aluminum, and soda-lime and quartz glass. Measurements demonstrate a good linear behavior for both sensors. The final part of this thesis deals with cost-effective and compact electrostatic levitator designs. These designs are characterized by small footprints to ensure cleanliness and scalable to many degrees of freedom multi-electrode levitators without incurring excessive and prohibitive economic costs. The first designed levitator is driven by a relay based switching controller. Its key properties are that it is devoid of high-voltage dc amplifiers and a maximum number of only two high-voltage power supplies, capable of delivering constant dc voltages, are required. This number is entirely independent of the number of individually controlled stator electrodes. The inherent switching nature of the system imposes limit cycle oscillations on the levitated object. It is due to the squeeze-film air damping that these oscillations can be significantly suppressed, in particular at small gap separations down to 100 µm or lower. Successful levitation has been achieved for 4-inch silicon wafers, 100×100 mm quartz glass substrates, and a highly flexible aluminum sheet measuring 280×280 mm, respectively. Experiments with the silicon wafer and glass substrates at reference air gap separations down to 100 µm or lower demonstrate limit cycle amplitudes below 1 µm. The second levitator is based on hysteresis control and represents a fundamental improvement on the first levitator in that it enables incorporating active damping in the system through derivative control. This fact opens up the possibility of operating the levitator in vacuum without degradation in performance as demonstrated by simulations. Overall, the proposed levitator retains largely the advantages of the relay control driven levitator. A 4-inch silicon wafer was levitated successfully at a reference gap separation of 200 µm exhibiting a good transient and steady-state suspension performance. The measured switching period was 1.5 ms and the amplitude of the voltage ripple was 10 V. The stability of the limit cycles in both levitators has been analyzed using the describing function method and Filippov’s theory. The first method follows an approximate approach while the second method offers a more precise avenue of tackling the stability analysis coupled with the key capability of analyzing multi-DOF systems.