Initial clinical experience with the admiral oxygenator combined with separated suction.

The Admiral, a new microporous membrane oxygenator with a low surface area, decreased priming volume and two separate reservoirs, was tested in 30 adult patients. This study was undertaken to evaluate blood path resistance, gas exchange capabilities and blood trauma in clinical use, with and without shed blood separation. Patients were divided into 3 groups. Group 1 had valve surgery without separation of suction, Group 2 had coronary artery bypass grafting (CABG) with direct blood aspiration and Group 3 had coronary artery bypass grafting with shed blood separation. The suctioned, separated, cardiotomy blood in Group 3 was treated with an autotransfusion device at the end of bypass before being returned to the patient. Theoretical blood flow could be achieved in all cases without problem. The pressure drop through the oxygenator averaged 88 +/- 13 mmHg at 4 l/min and 109 +/- 12 mmHg at 5 l/min. O(2) transfer was 163 +/- 27 ml/min. Free plasma haemoglobin rose in all groups, but significantly less in group 3. Lactate dehydrogenase (LDH) rose significantly in Groups 1 and 2. Platelets decreased in all groups without significant differences. Clinical experience with this new oxygenator was safe, the reduced membrane surface did not impair gas exchange and blood trauma could be minimized easily by separating shed blood, using the second cardiotomy reservoir.

In vivo testing of a novel adjustable glaucoma drainage device.

PURPOSE: We report on the in vivo testing of a novel noninvasively adjustable glaucoma drainage device (AGDD), which features an adjustable outflow resistance, and assess the safety and efficiency of this implant. METHODS: Under general anesthesia, the AGDD was implanted on seven white New Zealand rabbits for a duration of 4 months under a scleral flap in a way analogous to the Ex-PRESS device and set in an operationally closed position. The IOP was measured on a regular basis on the operated and control eyes using a rebound tonometer. Once a month the AGDD was adjusted noninvasively from its fully closed to its fully open position and the resulting pressure drop was measured. The contralateral eye was not operated and served as control. After euthanization, the eyes were collected for histology evaluation. RESULTS: The mean preoperative IOP was 11.1 ± 2.4 mm Hg. The IOP was significantly lower for the operated eye (6.8 ± 2 mm Hg) compared to the nonoperated eye (13.1 ± 1.6 mm Hg) during the first 8 days after surgery. When opening the AGDD from its fully closed to fully open position, the IOP dropped significantly from 11.2 ± 2.9 to 4.8 ± 0.9 mm Hg (P < 0.05). CONCLUSIONS: Implanting the AGDD is a safe and uncomplicated surgical procedure. The fluidic resistance was noninvasively adjustable during the postoperative period with the AGDD between its fully closed and fully open positions.

New bench test for venous cannula performance assessment.

Cannula design is of prime importance for venous drainage during cardiopulmonary bypass (CPB). To evaluate cannulas intended for CPB, an in vitro circuit was set up with silicone tubing between the test cannula encased in a movable preload reservoir and another static reservoir. The pressure-drop (DeltaP) value (P-drainage - P-preload) was measured using Millar pressure transducers. Flow rate (Q) was measured using an ultrasound flowmeter. Data display and data recording were controlled using a LabView application, custom made particularly for our experiments. Our results demonstrated that DeltaP, Q, and cannula resistance (DeltaP/Q) values were significantly decreased when the cannula diameter was increased for Smart and Medtronic cannulas. Smartcanula showed 36% and 43% less resistance compared to Medtronic venous and Medtronic femoral cannulas, respectively. The cannula shape (straight- or curved-tips) did not affect the DLP cannula resistance. Out of five cannulas tested, the Smartcanula outperforms the other commercially available cannulas. The mean (DeltaP/Q) values were 3.3 +/- 0.08, 4.07 +/- 0.08, 5.58 +/- 0.10, 5.74 +/- 0.15, and 6.45 +/- 0.15 for Smart, Medtronic, Edwards, Sarns, and Gambro cannulas, respectively (two-way ANOVA, p < 0.0001). In conclusion, the present assay allows discrimination between different forms of cannula with high or low lumen resistance.

Main objectives and new aspects of combination treatment of hypertension

AIM: To review the various pharmacological approaches currently proposed for the treatment of hypertension. RESULTS: With the evolution of pharmacological treatment of hypertension, various classes of agent (diuretics, beta-blockers, angiotensin converting enzyme inhibitors, calcium antagonists and alpha 1-blockers) have become available for the initiation of antihypertensive therapy. As monotherapy, each type of agent will normalize blood pressure in about half of all hypertensive patients. Replacing one drug with another that acts through a different mechanism improves the probability of controlling blood pressure. Another way to increase the number of responders is to increase the dose; however, this often results in more side effects. A preferable way of improving efficacy is to combine low doses of drugs that have different impacts on the cardiovascular system, thus opposing the compensatory responses that tend to limit the blood pressure drop. CONCLUSION: Low-dose drug combinations are generally well tolerated and the treatment of hypertension can be simplified by using fixed-dose combinations. These combinations have the potential to become a valuable alternative in the initiation of antihypertensive therapy.

Prevention of Caval Collapse During Venous Drainage for CPB.

A new plastic self-expanding Smartcanula (Smartcanula LLC, Lausanne, Switzerland) is designed for central insertion and prevention of caval collapse. The objective of our work is to assess the influence of the new design on atrial chatter. Caval collapse over the entire caval axis, right atrial, hepatic, renal vein, and iliac vein is realized in drainage tubes with holes at 5 cm distance intervals. Smartcanulas with various lengths (26 cm [= right atrial], 34 cm [= hepatic], 43 cm [= renal], and 53 cm [= iliac]) versus two-stage cannulas are compared. Pressure drop (ΔP) is measured using Millar pressure-transducers. Flow rate (Q) is measured using an ultrasonic flow meter. Cannula resistance is defined as the ΔP/Q ratio. Data display and recording are controlled using LabView virtual instruments. At an 88 cm height differential, Q values are 8.69 and 6.8 l/min, and ΔP/Q ratios are 0.63 and 1.28 for the 26-cm Smartcanula and the reference cannula, respectively. The 34-cm Smartcanula showed 8.89 l/min and 0.6 ΔP/Q ratio vs. 7.59 l/min and 0.9 for the control cannula (P < 0.05). The 43-cm and 53-cm Smartcanulas showed Q values of 9.04 and 8.81 l/min, respectively, and ΔP/Q2 ratio of 0.6. The Smartcanula outperforms the two-stage cannula, and direct cannula insertion without guide wire is effective.

A novel technique using echocardiography to evaluate venous cannula performance perioperatively in CPB cardiac surgery.

OBJECTIVE: Transthoracic echocardiography (TTE) has been used clinically to disobstruct venous drainage cannula and to optimise placement of venous cannulae in the vena cava but it has never been used to evaluate performance capabilities. Also, little progress has been made in venous cannula design in order to optimise venous return to the heart lung machine. We designed a self-expandable Smartcanula (SC) and analysed its performance capability using echocardiography. METHODS: An epicardial echocardiography probe was placed over the SC or control cannula (CTRL) and a Doppler image was obtained. Mean (V(m)) and maximum (V(max)) velocities, flow and diameter were obtained. Also, pressure drop (DeltaP(CPB)) was obtained between the central venous pressure and inlet to venous reservoir. LDH and Free Hb were also compared in 30 patients. Comparison was made between the two groups using the student's t-test with statistical significance established when p<0.05. RESULTS: Age for the SC and CC groups were 61.6+/-17.6 years and 64.6+/-13.1 years, respectively. Weight was 70.3+/-11.6 kg and 72.8+/-14.4 kg, respectively. BSA was 1.80+/-0.2 m(2) and 1.82+/-0.2 m(2), respectively. CPB times were 114+/-53 min and 108+/-44 min, respectively. Cross-clamp time was 59+/-15 min and 76+/-29 min, respectively (p=NS). Free-Hb was 568+/-142 U/l versus 549+/-271 U/l post-CPB for the SC and CC, respectively (p=NS). LDH was 335+/-73 mg/l versus 354+/-116 mg/l for the SC and CC, respectively (p=NS). V(m) was 89+/-10 cm/s (SC) versus 63+/-3 cm/s (CC), V(max) was 139+/-23 cm/s (SC) versus 93+/-11 cm/s (CC) (both p<0.01). DeltaP(CPB) was 30+/-10 mmHg (SC) versus 43+/-13 mmHg (CC) (p<0.05). A Bland-Altman test showed good agreement between the two devices used concerning flow rate calculations between CPB and TTE (bias 300 ml+/-700 ml standard deviation). CONCLUSIONS: This novel Smartcanula design, due to its self-expanding principle, provides superior flow characteristics compared to classic two stage venous cannula used for adult CPB surgery. No detrimental effects were observed concerning blood damage. Echocardiography was effective in analysing venous cannula performance and velocity patterns.

Lateral instability in normal viscous fingers

We study a low-amplitude, long-wavelength lateral instability of the Saffman-Taylor finger by means of a phase-field model. We observe such an instability in two situations in which small dynamic perturbations are overimposed to a constant pressure drop. We first study the case in which the perturbation consists of a single oscillatory mode and then a case in which the perturbation consists of temporal noise. In both cases the instability undergoes a process of selection.

Relevance of dynamic wetting in viscous fingering patterns

We demonstrate that wetting effects at moving contact lines have a strong impact in viscous fingering patterns. Experiments in a rotating Hele-Shaw (HS) cell, dry or prewetted, show consistent morphological differences. When the wetting fluid invades a dry region, contact angle dynamics yield a kinetic contribution to the interface pressure drop that scales with capillary number as Ca2¿3 but is significantly larger than the Park-Homsy kinetic correction. Numerical results are in very good agreement with experiments and show that standard HS equations work best for prewetted cells.

Evidence for a sodium-induced activation of central neurogenic mechanisms in one-kidney, one-clip renal hypertensive rats

The mechanisms sustaining high blood pressure in conscious one-kidney, one-clip Goldblatt rats were evaluated with the use of SK&F 64139, a phenylethanolamine N-methyltransferase inhibitor capable of crossing the blood-brain barrier and of captopril, an angiotensin converting enzyme inhibitor. The rats were studied 3 weeks after left renal artery clipping and contralateral nephrectomy. During the developmental phase of hypertension, two groups of rats were maintained on a regular salt (RNa) intake, whereas two other groups were given a low salt (LNa) diet. On the day of the experiment, the base-line mean blood pressure measured in the LNa rats (177.4 +/- 5.2 mm Hg, mean +/- S.E., n = 15) was similar to that measured in the RNa rats (178.7 +/- 5.4 mm Hg, n = 16). SK&F 64139 (12.5 mg p.o.) induced a significantly more pronounced (P less than .001) blood pressure decrease in the RNa rats (-25.6 +/- 3.6 mm Hg, n = 8) than in the LNa rats (-4.3 +/- 3.3 mm Hg, n = 7) during a 90-min observation period. On the other hand, captopril (10 mg p.o.) normalized blood pressure in LNa rats (n = 8), but produced only a 13.4 mm Hg blood pressure drop in RNa rats (n = 8). RNa rats treated with SK&F 64139 were found to have decreased phenylethanolamine N-methyltransferase activity by an average 80% in selected brain stem nuclei when compared with nontreated rats. No significant difference in plasma catecholamine levels was found between the RNa and LNa rats. These results suggest that, in this experimental model of hypertension, the sodium ion might increase the model of hypertension, the sodium ion might increase the vasoconstrictor contribution of the sympathetic system via a centrally mediated neurogenic mechanism while at the same time it decreases the renin-dependency of the high blood pressure.

A new concept of integrated cardiopulmonary bypass circuit.

OBJECTIVE: Standard cardiopulmonary bypass (CPB) circuits with their large surface area and volume contribute to postoperative systemic inflammatory reaction and hemodilution. In order to minimize these problems a new approach has been developed resulting in a single disposable, compact arterio-venous loop, which has integral kinetic-assist pumping, oxygenating, air removal, and gross filtration capabilities (CardioVention Inc., Santa Clara, CA, USA). The impact of this system on gas exchange capacity, blood elements and hemolysis is compared to that of a conventional circuit in a model of prolonged perfusion. METHODS: Twelve calves (mean body weight: 72.2+/-3.7 kg) were placed on cardiopulmonary bypass for 6 h with a flow of 5 l/min, and randomly assigned to the CardioVention system (n=6) or a standard CPB circuit (n=6). A standard battery of blood samples was taken before bypass and throughout bypass. Analysis of variance was used for comparison. RESULTS: The hematocrit remained stable throughout the experiment in the CardioVention group, whereas it dropped in the standard group in the early phase of perfusion. When normalized for prebypass values, both profiles differed significantly (P<0.01). Both O2 and CO2 transfers were significantly improved in the CardioVention group (P=0.04 and P<0.001, respectively). There was a slightly higher pressure drop in the CardioVention group but no single value exceeded 112 mmHg. No hemolysis could be detected in either group with all free plasma Hb values below 15 mg/l. Thrombocyte count, when corrected by hematocrit and normalized by prebypass values, exhibited an increased drop in the standard group (P=0.03). CONCLUSION: The CardioVention system with its concept of limited priming volume and exposed foreign surface area, improves gas exchange probably because of the absence of detectable hemodilution, and appears to limit the decrease in the thrombocyte count which may be ascribed to the reduced surface. Despite the volume and surface constraints, no hemolysis could be detected throughout the 6 h full-flow perfusion period.

Pore-scale modeling of two-phase flow instabilities in porous media

Les problèmes d'écoulements multiphasiques en média poreux sont d'un grand intérêt pour de nombreuses applications scientifiques et techniques ; comme la séquestration de C02, l'extraction de pétrole et la dépollution des aquifères. La complexité intrinsèque des systèmes multiphasiques et l'hétérogénéité des formations géologiques sur des échelles multiples représentent un challenge majeur pour comprendre et modéliser les déplacements immiscibles dans les milieux poreux. Les descriptions à l'échelle supérieure basées sur la généralisation de l'équation de Darcy sont largement utilisées, mais ces méthodes sont sujettes à limitations pour les écoulements présentant de l'hystérèse. Les avancées récentes en terme de performances computationnelles et le développement de méthodes précises pour caractériser l'espace interstitiel ainsi que la distribution des phases ont favorisé l'utilisation de modèles qui permettent une résolution fine à l'échelle du pore. Ces modèles offrent un aperçu des caractéristiques de l'écoulement qui ne peuvent pas être facilement observées en laboratoire et peuvent être utilisé pour expliquer la différence entre les processus physiques et les modèles à l'échelle macroscopique existants. L'objet premier de la thèse se porte sur la simulation numérique directe : les équations de Navier-Stokes sont résolues dans l'espace interstitiel et la méthode du volume de fluide (VOF) est employée pour suivre l'évolution de l'interface. Dans VOF, la distribution des phases est décrite par une fonction fluide pour l'ensemble du domaine et des conditions aux bords particulières permettent la prise en compte des propriétés de mouillage du milieu poreux. Dans la première partie de la thèse, nous simulons le drainage dans une cellule Hele-Shaw 2D avec des obstacles cylindriques. Nous montrons que l'approche proposée est applicable même pour des ratios de densité et de viscosité très importants et permet de modéliser la transition entre déplacement stable et digitation visqueuse. Nous intéressons ensuite à l'interprétation de la pression capillaire à l'échelle macroscopique. Nous montrons que les techniques basées sur la moyenne spatiale de la pression présentent plusieurs limitations et sont imprécises en présence d'effets visqueux et de piégeage. Au contraire, une définition basée sur l'énergie permet de séparer les contributions capillaires des effets visqueux. La seconde partie de la thèse est consacrée à l'investigation des effets d'inertie associés aux reconfigurations irréversibles du ménisque causé par l'interface des instabilités. Comme prototype pour ces phénomènes, nous étudions d'abord la dynamique d'un ménisque dans un pore angulaire. Nous montrons que, dans un réseau de pores cubiques, les sauts et reconfigurations sont si fréquents que les effets d'inertie mènent à différentes configurations des fluides. A cause de la non-linéarité du problème, la distribution des fluides influence le travail des forces de pression, qui, à son tour, provoque une chute de pression dans la loi de Darcy. Cela suggère que ces phénomènes devraient être pris en compte lorsque que l'on décrit l'écoulement multiphasique en média poreux à l'échelle macroscopique. La dernière partie de la thèse s'attache à démontrer la validité de notre approche par une comparaison avec des expériences en laboratoire : un drainage instable dans un milieu poreux quasi 2D (une cellule Hele-Shaw avec des obstacles cylindriques). Plusieurs simulations sont tournées sous différentes conditions aux bords et en utilisant différents modèles (modèle intégré 2D et modèle 3D) afin de comparer certaines quantités macroscopiques avec les observations au laboratoire correspondantes. Malgré le challenge de modéliser des déplacements instables, où, par définition, de petites perturbations peuvent grandir sans fin, notre approche numérique apporte de résultats satisfaisants pour tous les cas étudiés. - Problems involving multiphase flow in porous media are of great interest in many scientific and engineering applications including Carbon Capture and Storage, oil recovery and groundwater remediation. The intrinsic complexity of multiphase systems and the multi scale heterogeneity of geological formations represent the major challenges to understand and model immiscible displacement in porous media. Upscaled descriptions based on generalization of Darcy's law are widely used, but they are subject to several limitations for flow that exhibit hysteric and history- dependent behaviors. Recent advances in high performance computing and the development of accurate methods to characterize pore space and phase distribution have fostered the use of models that allow sub-pore resolution. These models provide an insight on flow characteristics that cannot be easily achieved by laboratory experiments and can be used to explain the gap between physical processes and existing macro-scale models. We focus on direct numerical simulations: we solve the Navier-Stokes equations for mass and momentum conservation in the pore space and employ the Volume Of Fluid (VOF) method to track the evolution of the interface. In the VOF the distribution of the phases is described by a fluid function (whole-domain formulation) and special boundary conditions account for the wetting properties of the porous medium. In the first part of this thesis we simulate drainage in a 2-D Hele-Shaw cell filled with cylindrical obstacles. We show that the proposed approach can handle very large density and viscosity ratios and it is able to model the transition from stable displacement to viscous fingering. We then focus on the interpretation of the macroscopic capillary pressure showing that pressure average techniques are subject to several limitations and they are not accurate in presence of viscous effects and trapping. On the contrary an energy-based definition allows separating viscous and capillary contributions. In the second part of the thesis we investigate inertia effects associated with abrupt and irreversible reconfigurations of the menisci caused by interface instabilities. As a prototype of these phenomena we first consider the dynamics of a meniscus in an angular pore. We show that in a network of cubic pores, jumps and reconfigurations are so frequent that inertia effects lead to different fluid configurations. Due to the non-linearity of the problem, the distribution of the fluids influences the work done by pressure forces, which is in turn related to the pressure drop in Darcy's law. This suggests that these phenomena should be taken into account when upscaling multiphase flow in porous media. The last part of the thesis is devoted to proving the accuracy of the numerical approach by validation with experiments of unstable primary drainage in a quasi-2D porous medium (i.e., Hele-Shaw cell filled with cylindrical obstacles). We perform simulations under different boundary conditions and using different models (2-D integrated and full 3-D) and we compare several macroscopic quantities with the corresponding experiment. Despite the intrinsic challenges of modeling unstable displacement, where by definition small perturbations can grow without bounds, the numerical method gives satisfactory results for all the cases studied.

Impingement jet cooling of end windings in a high-speed electric machine

The rotational speed of high-speed electric machines is over 15 000 rpm. These machines are compact in size when compared to the power rate. As a consequence, the heat fluxes are at a high level and the adequacy of cooling becomes an important design criterion. In the high-speed machines, the air gap between the stator and rotor is a narrow flow channel. The cooling air is produced with a fan and the flow is then directed to the air gap. The flow in the gap does not provide sufficient cooling for the stator end windings, and therefore additional cooling is required. This study investigates the heat transfer and flow fields around the coil end windings when cooling jets are used. As a result, an innovative and new assembly is introduced for the cooling jets, with the benefits of a reduced amount of hot spots, a lower pressure drop, and hence a lower power need for the cooling fan. The gained information can also be applied to improve the cooling of electric machines through geometry modifications. The objective of the research is to determine the locations of the hot spots and to find out induced pressure losses with different jet alternatives. Several possibilities to arrange the extra cooling are considered. In the suggested approach cooling is provided by using a row of air jets. The air jets have three main tasks: to cool the coils effectively by direct impingement jets, to increase and cool down the flow that enters the coil end space through the air gap, and to ensure the correct distribution of the flow by forming an air curtain with additional jets. One important aim of this study is the arrangement of cooling jets in such manner that hot spots can be avoided to wide extent. This enables higher power density in high-speed motors. This cooling system can also be applied to the ordinary electric machines when efficient cooling is needed. The numerical calculations have been performed using a commercial Computational Fluid Dynamics software. Two geometries have been generated: cylindrical for the studied machine and Cartesian for the experimental model. The main parameters include the positions, arrangements and number of jets, the jet diameters, and the jet velocities. The investigated cases have been tested with two widely used turbulence models and using a computational grid of over 500 000 cells. The experimental tests have been made by using a simplified model for the end winding space with cooling jets. In the experiments, an emphasis has been given to flow visualisation. The computational analysis shows good agreement with the experimental results. Modelling of the cooling jet arrangement enables also a better understanding of the complex system of heat transfer at end winding space.

Fluid flow and dispersion predictions in porous media by utilizing advanced numerical methods

Diplomityön tavoitteena oli tarkastella numeerisen virtauslaskennan avulla virtaukseen liittyviä ilmiöitä ja kaasun dispersiota. Diplomityön sisältö on jaettu viiteen osaan; johdantoon, teoriaan, katsaukseen virtauksen mallinnukseen huokoisessa materiaalissa liittyviin tutkimusselvityksiin, numeeriseen mallinnukseen sekä tulosten esittämiseen ja johtopäätöksiin. Diplomityön alussa kiinnitettiin huomiota erilaisiin kokeellisiin, numeerisiin ja teoreettisiin mallinnusmenetelmiin, joilla voidaan mallintaa virtausta huokoisessa materiaalissa. Kirjallisuusosassa tehtiin katsaus aikaisemmin julkaistuihin puoliempiirisiin ja empiirisiin tutkimusselvityksiin, jotka liittyvät huokoisen materiaalin aiheuttamaan painehäviöön. Numeerisessa virtauslaskenta osassa rakennettiin ja esitettiin huokoista materiaalia kuvaavat numeeriset mallit käyttäen kaupallista FLUENT -ohjelmistoa. Työn lopussa arvioitiin teorian, numeerisen virtauslaskennan ja kokeellisten tutkimusselvitysten tuloksia. Kolmiulotteisen huokoisen materiaalinnumeerisessa mallinnuksesta saadut tulokset vaikuttivat lupaavilta. Näiden tulosten perusteella tehtiin suosituksia ajatellen tulevaa virtauksen mallinnusta huokoisessa materiaalissa. Osa tässä diplomityössä esitetyistä tuloksista tullaan esittämään 55. Kanadan Kemiantekniikan konferenssissa Torontossa 1619 Lokakuussa 2005. ASME :n kansainvälisessä tekniikan alan julkaisussa. Työ on hyväksytty esitettäväksi esitettäväksi laskennallisen virtausmekaniikan (CFD) aihealueessa 'Peruskäsitteet'. Lisäksi työn yksityiskohtaiset tulokset tullaan lähettämään myös CES:n julkaisuun.

Characterizing the impact of minor cannula design modification.

OBJECTIVE: Bench evaluation of the hydrodynamic behavior of venous cannulas is a valuable technique for the analysis of their performance during cardiopulmonary bypass (CPB). The aim of this study was to investigate the effect of the internal diameter of the extracorporeal connecting tube of venous cannulas on flow rate (Q), pressure drop (delta P), and cannula resistance (delta P/Q²) values, using a computer assisted test bench.¦METHODS: An in vitro circuit was set up with silicone tubing between the test cannula encased in a movable reservoir, and a static reservoir. The delta P, defined as the difference between the drainage pressure and the preload pressure, was measured using high-fidelity Millar pressure transducers. Q was measured using an ultrasonic flowmeter. Data display and data recording were controlled using virtual instruments in a stepwise fashion.¦RESULTS: The 27 F smartcanula® with a 9 mm connecting tube diameter showed 17% less resistance compared to that with an 8 mm connecting tube diameter. Q values were 7.22±0.1 and 7.81±0.04 L/min for cannulas with 8 mm and 9 mm connecting tube diameters, respectively. The delta P/Q² ratio values were 72% lower for the Medtronic cannula with a 9 mm connecting tube diameter compared to that with an 8 mm connecting tube diameter. Q values for the Medtronic cannula were 3.94±0.23 and 6.58±0.04 L/min with 8 mm and 9 mm connecting tube diameters, respectively. The 27 F smartcanula® showed 13% more flow rate compared to the 28 F Medtronic cannula using the unpaired Student t-test (p<0.0001).¦CONCLUSIONS: Our results demonstrated that Q was increased but delta P and delta P/Q² values were significantly decreased when the connecting tube diameter was increased for venous cannulas. The connecting tube diameter significantly affected the resistance to liquid flow through the cannula. Smartcanulas® outperform Medtronic cannulas.

Hydraulisen kuristinmallin ja liikealustan ohjauksen kehittäminen reaaliaikasimulointiin

Diplomityön ensimmäisessä vaiheessa tutkittiin hydraulisen kuristimen ominaisuuksia ja esiteltiin numeerisesti tehokas kuristinmalli käyttäenpolynomifunktiota virtauksen laminaarisen ja transitioalueen kuvaukseen. Puoliempiirisen mallin paremmuus tulee esille siinä, että kuristimen geometriatietoja ei tarvita laskettaessa virtausta paine-eron perusteella. Reaaliaikasimuloinnissa esiintyy kompromisseja tarkkuuden ja laskentanopeuden välillä. Tätä asiaa tutkittiin kahden virtausalueen kuristinmallilla. Transition paine-eron ja integrointiaika-askelen valinnan vaikutus tarkkuuteen ja laskentanopeuteen tutkittiin. Toisessa vaiheessa tutkittiin mahdollisimman hyvän liiketuntuman tuottamista liikealustalla ohjaussignaalia kehittämällä. Liikealustan liikeradan rajallisuudesta johtuen ohjauksessa on perinteisesti käytetty washout-suodatusta, joka erottelee simuloitavan järjestelmän kiihtyvyyssignaalista vain nopeatkiihtyvyydet. Tässä työssä tutkittiin hitaiden kiihtyvyyksien ottamista mukaan liikealustan ohjaukseen liikealustan liikeradan puitteissa. Tämä toteutettiin kuvaamalla hitaat kiihtyvyydet kallistamalla liikealustaa, jolloin käyttäjään kohdistuva voima saatiin kuvattua gravitaatiota hyväksi käyttäen.