79 research outputs found
Relating Robotic- and Ultrasound-Based Techniques for Characterizing the Effects of Changes in Muscle Properties Following Stroke
No full textBackground: Following a stroke, muscle tissue is prone to atrophy, decreased fascicle length, loss of sarcomeres, and a possible enhancement of collagenous extracellular matrix. Decreased fascicle length associated with a loss of sarcomeres, and a possible enhancement of collagenous extracellular matrix are thought to result in an increase in passive stiffness and therefore contribute to movement dysfunction. Valid and reliable in-vivo, non-invasive, and cost-effective assessment of muscle stiffness eludes conventional rehabilitation practice. Ultrasound-based shear wave elastography is a new measurement technique; capable of measuring muscle elasticity however evidence for criterion validity is lacking for paretic muscle in individuals with stroke. Thus our aim was to (1) to investigate the concurrent/criterion validity of shear wave elastography, for estimating the passive stiffness of biceps, with an established robotic perturbation metric for quantifying joint stiffness in individuals with severe chronic stroke and (2) confirm that both metrics were capable of detecting a difference between paretic and non-paretic arms. Methods: Passive elbow stiffness during extension was quantified using a robotic device that administered a controlled elbow joint extension perturbation. Passive biceps elasticity was quantified using a conventional ultrasoundbased shear wave elastography. Stiffness values were extracted at 7 elbow joint positions in the paretic and non-paretic arms of 10 stroke patients. Sophisticated post-processing of muscle EMG was administered to confirm muscle quiescence during all measurements. Results: There was a significant correlation between passive biceps elasticity and joint stiffness during elbow extension with a strengthening relationship approaching end range extension. Both metrics identified increased passive stiffness with elbow extension joint stiffness 2.26 times greater and biceps stiffness 1.19 times greater on the paretic side. Conclusion: Shear wave elastography appears to be a valid and viable tool for the estimation of muscle stiffness in individuals with severe chronic stroke. The ability to quantify muscle elasticity will expand the depth and breadth of the clinician’s evaluation and offer a new target for therapeutic intervention.Mechanical, Maritime and Materials EngineeringBiomedical Engineerin
Catalytic oxidation of soot: Potential for reduction of diesel particulate emissions
No full textApplied Science
De hydroformylering van propeen
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
Onderzoek van 2-dimensionale stromingen m.b.v. het hele-Shaw spleetmodel en een regensimulator
No full textTengevolge van de regenval heeft de waterstand de neiging omhoog te komen. Andere factoren van watertoevoer zijn o.a. kwel, irrigatiewater, doorspoelwater, sneeuwval. Zij zijn t.o.v. de regen in kwantitatief opzicht minder belangrijk en worden verder verwaarloosd. De gevallen neerslag moet op lange termijn meer afgevoerd worden om een constant polderpeil te waarborgen. Dit afvoeren geschiedt in diepe polders (b.v. droogmakerijen) altijd door de gemalen. Als het polderpeil (= grondwaterstand) hoger ligt dan het ontvangende water (boezem, rivier of zee) is het mogelijk om op natuurlijke wijze (= d.m.v. zwaartekracht) te lozen. In dit verslag wordt in het midden gelaten hoe het water geloosd wordt. Er wordt echter wel vanuit gegaan dat afvoer zodanig is dat er een constant slootwaterpeil gehandhaafd blijft. De regen, die op het maaiveld valt, zakt vertikaal tussen de korrels door naar beneden tot het grondwater, dat daardoor zal stijgen boven het constante slootpeil. Tengevolge van dit niveauverschil ontstaat er een grondwaterstroming naar de sloot. De korrelstructuur heeft een remmende invloed op deze stroming en destemeer naarmate de doorlatendheid van de grond kleiner is en/of de af te leggen afstand voor een waterdeeltje groter is. In evenwichtstoestand bij constante neerslag ontstaat er zodoende een constant niveauverschil tussen grond- en slootwater en deze is groter naarmate de afstand tot de sloot groter en/of de doorlatendheid kleiner is.Hydraulic EngineeringCivil Engineering and Geoscience
De industriële zuivering van caprolactam
No full textDocument(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science
Critical Flow Calculations of Compressible Non-Ideal Fluids Based on an EOS
No full textThis thesis comprises the results of a graduation project which has been executed at the Laboratory of Applied Thermodynamics and Phase Equilibria, faculty of Chemical Engineering and Materials Science, Delft University of Technology (DUT). It is a part of a research project being carried out by Dr. L.Z. Boshkov and prof. J. de Swaan Arons; the project is financially sponsored by the Royal Dutch Shell Company. The aim of the research project is to present a systematic approach to the modelling and sizing of safety relief valves. Pressure or safety relief valves are routinely placed on chemical reactors and pressure vessels handling gases or liquids to protect the equipment against pressure build-up. Because the modelling still causes non-trivial tasks for chemical engineers, the research project was started to structurize the problems. In this work the results will be discussed with respect to t the critical flow of both one- and two-phase flow of non-ideal fluids through PRV 's at given stagnation states using an EOS. The results in this thesis are calculated for the non-ideal RK-fluid, however, the derived theories are presented as general as possible which makes extension to other EOS possible. The results in this thesis are calculated for the non-ideal RK-fluid, however, the derived theories are presented as general as possible which makes extension to other EOS possible. When concerning the one-phase flow calculations for the RK-fluid, one can conclude that the obtained results are equivalent to published results [Leung & Epstein, 1988]. In contrast to the latter published results, in this work an analytical maximization criterium is applied which provides more insight into the process equation which has to be used. Another important conclusion is that in this thesis the thermodynamic limits of one-phase critical flow are described and calculated. Both the spinodal and the saturation curve are indicated in the presented diagrams. The approach has been used to develop a new kind of phase diagrams: the critical flow phase diagrams (CFPD). This CFPD can be applied as an engineering tool in PRV design studies. With respect to the two-phase critical flow calculations, the well-known HEM have been worked out for non-ideal fluids using an EOS for the first time. Again an analytical maximization criterium has been applied to obtain the results. The results in this work are in a preliminary stage but one can conclude that they are in qualitatively correspondence with published data. On the face on it, the developed model can relatively easy be extended to critical flow processes which start in the one-phase region but have a maximum in mass flux in the two-phase region, and to processes concerning binary mixtures or even multi-component systems. When these extensions are succeeded, for the first time a general theory will have been derived that covers the entire range of initial vessel temperatures and pressures.Applied SciencesChemical Technology and Materials ScienceApplied Thermodynamics and Phase Equilibri
Compliant Full Film Lubricated Bearings: Concept Design & Development
No full textFull film lubricated bearings are machine components that excel in their ability to carry high loads with very little friction. Their main archetypes, passive hydrodynamic and active hydrostatic bearings, are used in a wide variety of applications, ranging from hydraulic pumps to high precision machine benches. They are most commonly lubricated using oil-based lubricants and have been a staple in improving machine performance for many decades. The continuous search for higher performing and more sustainable designs has given ample opportunity to revisit these machine components, and to investigate their possible implementation into machines and fields that so far have not been able to make use of their superior performance characteristics. This lack of increased implementation is often due to fundamental limitations of these components. Both the performance of hydrostatic and hydrodynamic bearings is directly coupled to their need for a thin lubricant film to provide stiffness and load capacity. For hydrostatic bearings in particular, this requirement can more accurately be defined as the need for the bearing surfaces to remain parallel to its counter-surface, separated by a thin film of lubricant in the order of 100 micrometer. Not only the performance, but also ecological constraints have been more dominant in recent years. The conventional use of oil-based lubricants has given researchers the motivation to look for cleaner and more sustainable lubricants. The engineering community keeps on moving forward to a higher performing and more sustainable future.This thesis investigates one fundamental design direction to obtain higher performance and increase the implementation field of full film bearings. By implementing compliant design, or the use of elastic elements, several facets of in particular hydrostatic bearing limitations are investigated. Two fundamental limitations are dominant throughout this dissertation: the design for changing counter surfaces and the design for multiple operating conditions. Several principles are introduced that improve the use of hydrostatic bearings for non-constant counter surfaces. These principles are the use of functionally graded materials to minimize the pre-loading effect the hydrostatic pressure has on the elastic bearing support, distributed whiffletree support-systems to increase bearing deformability, and the introduction of a compliant water-filled universal joint with superior stiffness characteristics compared to the state of the art. The universal joint makes use of the principle of closed-form pressure balancing, which is pressurizing an enclosed body of fluid to obtain low rotation stiffness while maintaining high support stiffness. All these principles are described through design models and are further investigated with the use of finite element models.The second dominant subject that is investigated in this dissertation is developing hydrostatic bearings that function for multiple operating conditions with the use of compliant elements. This principle, defined in this work as passive shape shifting, gives hydrostatic bearings more flexibility when it comes to designing for more discrete load cases, such as the one that can be found in hydraulic pumps. Besides describing this concept design principle with finite element models, a step towards real life application is also made in a scaled case study. By combining the previously mentioned compliant universal joint and a hydrostatic bearing using the principle of passive shape shifting, a contact-mechanics free alternative for axial piston pumps is proposed. This mechanism is designed for a scaled case study and validated through experimental work and finite element modelling. This thesis, which is conceptual in nature, combines these different design directions and therefor shows design directions that broaden the field of use for full film lubricated bearings by using elastic elements.Mechatronic Systems Desig
An Experimental and Numerical Investigation of Multiphase Flow Splitting at an Impacting T-Junction Between a Single Flowline And Two Risers
No full textIn 2011, Royal Dutch Shell plc (Shell) took the final investment decision to develop the Prelude gas field using the world’s first Floating Liquefied Natural Gas (FLNG) facility. FLNG poses some new technical challenges. For example, as the vessel is moored to the seabed, it is subject to movements induced by waves, winds and tides. Therefore, flexible instead of rigid risers are used to bring the gas from the seabed to the surface. However, these risers are limited in diameter. For Prelude each flowline is connected to a single riser. In new future projects it might be beneficial to have a single (larger diameter) subsea flowline at the sea floor which is split into two or more flexible risers. This flow split is complicated as gas wells produce a multiphase mixture of gas, hydrocarbon condensates and/or water. There thus is a need to understand how the different phases will distribute over the multiple risers, and how this will influence the whole operation. In previous lab experiments [1], a horizontal symmetric impacting T-junction was used to divide the multiphase mixture from the horizontal flowline into two vertical risers. It was found that at low gas flow rates, for which the flow regime in the risers is hydrodynamic slug flow, non-symmetric distributions in the phase split are the rule rather than the exception. These maldistributions exhibit transient behaviour, and exhibit hysteresis. However, in gas production from dry fields with low Liquid to Gas Ratios (LGR), the gas flow rates generally are higher and the flow regime in the vertical risers is annular flow. In this flow pattern, liquids flow in the upward direction and no liquid buildup occurs at the riser base. As annular flow is more stable in time, it is expected that for these conditions the phase splits are evenly distributed over the two risers and no transient behaviour is present. The main aim of the present study was to verify the hypothesis that if the gas flow rate is sufficiently high to sustain annular flow in both risers the phases will distribute evenly. Thereto experiments were performed in the Severe Slugging Loop (SSL) at the Shell Technology Centre Amsterdam. The loop consists of a 100 [m] horizontal flowline connected via an impacting T-junction to two 1.25 [in] diameter vertical risers of 16.8 [m] height. The facility is operated with an air-water mixture at atmospheric pressure and ambient temperature. As the SSL is not equipped with flow meters to measure the phase flow in the risers, a new method is developed to identify maldistribution in the phase split. In two phase flow in a vertical riser, the flow rates in the pipe are not uniquely determined by the pressure drop. However, in the current dual riser experiments the total flow rate in the setup is known. It is found that, with the use of single riser benchmark data and visual inspection, one can distinguish between an equal and an unequal phase split. Experiments are performed to test the stability of the phase split, and the effect of hysteresis for various gas and liquid flow rate combinations. It is observed that five different states exist for the flow split in the single flowline dual riser geometry. Out of these, only two are stable, which occur on opposite sides of a certain gas flow rate transition point. This point is identified as the minimum in the pressure gradient curve for a single vertical riser. This minimum can be linked to the transition from churn flow to annular flow. In addition to the experiments, a computational model is proposed to predict the phase split. In this model, the Shell Flow Correlations (SFC) for multiphase pipe flow are used to propagate the boundary conditions of the system from the riser tops to the corresponding outlets of the splitter at the base of the risers. Next, all possible phase splits which satisfy the extended Bernoulli equation and the conservation of momentum in the splitter are identified. The model conserves mass implicitly. The extended Bernoulli equation is implemented as the Advanced Double Stream Model (ADSM) [2], the control volume approach is used for the conservation of momentum. All three sub-models assume 1D steady state fully developed flow in the different parts of the geometry. By imposing different back pressures on the risers, for a constant gas and liquid flow, the model can generate phase split curves. These are compared to experimental data available in the literature and experimental results by Van de Gronden. It is found that the write-up of the derivations in the original ADSM paper [2] contains typos or errors. Therefore we have derived new relations, but they do not exhibit the same behaviour as the modelling results presented in the paper. From the comparison with the experimental results, it is concluded that the proposed computational model, which assumes 1D steady state fully developed flow, predicts a much too symmetric phase split. The modelling effort has not yet resulted in a reliable for the phase split prediction model.Applied Science
A Type Synthesis Approach to Compliant Shell Mechanisms
No full textMechanical, Maritime and Materials EngineeringPrecision and Microsystems Engineerin
Critical flow models of one-and two-phase compressible fluids
No full textIn this essay the description of the critical flow of one- and two-phase (one component) mixtures through different types of flow ducts will be discussed. The essay is an introduction into a graduation project, at the Delft University of Technology, aiming to describe the flow phenomena and modelling of venting processes through pressure relief valves…Applied SciencesChemical Technology and Material ScienceApplied Thermodynamics and Phase Equilibri
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