bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Risk of Development of Substance Dependence for Barbiturates and Clobazam Prescribed as Antiepileptic Drugs: Results from a Questionnaire Study
Authors: Uhlmann Carmen , Fröscher Walter
Published: February 2009

There is no systematical research about the topic of dependence on antiepileptic drugs (AED) for patients with epilepsy, despite the fact that barbiturates and benzodiazepines comprise a potential risk of dependence. We hypothesize that there is no psychological substance dependence for patients with epilepsy, possibly because of their outcome expectations. The aim of the study was to examine these patients in terms of substance dependence. One hundred inpatients at the Lake Constance Epilepsy Center were asked about their experiences with AED in terms of dependence in a structured interview. We registered general statements about dependence of AED, markers for substance dependence, and outcome expectations. About 50% of the patients reported withdrawal symptoms and the development of tolerance, but less than 10% noticed loss of control and craving. Withdrawal symptoms and development of tolerance were significantly lower in a group of patients without barbiturates or clobazam versus patients with barbiturates or/and clobazam. There was no significant difference between these two groups in psychological criteria of dependence, that is, loss of control and craving. Outcome expectations of AED were clearly related to the efficacy against seizures, and only to a small amount to psychotropic effects. The study demonstrates that physiological variables of dependence are present more in patients with epilepsy with a permanent intake of barbiturates or clobazam, but psychological variables of dependence are rarely present in epileptic patients, with or without an intake of barbiturates and clobazam. These results confirm our hypothesis that substance dependence is not a major problem in benzodiazepines and barbiturates in patients with epilepsy. Outcome expectations seem to be related mainly to the anticonvulsant and not the psychotropic effect. This might be the reason for the absence of dependence.
Open‐Label Support for Duloxetine for the Treatment of Panic Disorder
Authors: Simon Naomi M. , Kaufman Rebecca E. , Hoge Elizabeth A. , Worthington John J. , Herlands Nannette N. , Owens Maryann E. , Pollack Mark H.
Published: February 2009

Panic disorder with or without agoraphobia is a common, often chronic and refractory anxiety disorder. Although a number of pharmacotherapies are now indicated for panic disorder, many patients do not respond to available interventions. We hypothesized that duloxetine, a serotonin‐norepinephrine reuptake inhibitor (SNRI) that has greater initial noradrenergic effects than venlafaxine, would have broad efficacy for individuals with panic disorder. Fifteen individuals with panic disorder with or without agoraphobia received 8 weeks of open label duloxetine flexibly dosed from 60 to 120 mg per day. Duloxetine treatment resulted in significant anxiolysis as measured by the primary outcome measure, the Panic Disorder Severity Scale (PDSS) (paired t(df) = 4.02(14), P= 0.0013), as well as measures of generalized anxiety, depression and quality of life (all P < 0.05). Although definitive conclusions are limited due to its small open‐label nature, this first prospective study provides preliminary support for the efficacy of duloxetine for panic disorder and suggests larger randomized controlled study is warranted.
Comparison of Direct and Indirect Tests for Small Intestinal Bacterial Overgrowth and Antibiotic‐Responsive Diarrhea in Dogs
Authors: German A.J. , Day M.J. , Ruaux C.G. , Steiner J.M. , Williams D.A. , Hall E.J.
Published: February 2009

Controversy exists over the diagnosis of idiopathic small intestinal bacterial overgrowth (SIBO) in dogs and some clinicians use the term antibiotic‐responsive diarrhea (ARD) in preference. However, whether such terms are interchangeable is not clear. To examine the relationship between duodenal bacterial numbers and a clinical response to antibiotics, SIBO and ARD were defined by nonoverlapping criteria. Quantitative duodenal juice bacteriology and indirect serum biochemical tests were used to assess small intestinal bacterial populations in 30 dogs with gastrointestinal disorders, including 9 with ARD. Serum total unconjugated bile acid (TUBA) concentrations were measured in all dogs, serum folate and cobalamin concentrations were measured in 29 of 30 dogs, and quantitative culture of duodenal juice was performed in 22 of 30 dogs. Serum TUBA concentrations also were measured in samples from 38 control dogs. Twenty of 22 affected (clinical) dogs in which quantitative bacteriology was performed were classified as having SIBO (>105colony‐forming units of total bacteria per milliliter of duodenal juice), but bacterial numbers did not differ significantly between dogs with ARD and dogs with other disorders. Increased folate (19/29), decreased cobalamin (16/ 29), or a combination (9/29) were common, but increased TUBA concentrations were documented in only 5 of 30 clinical dogs. Again, no significant differences were observed between dogs with ARD and those with other disorders, and a similar proportion (5/38) of controls had abnormally high TUBA concentrations. Finally, no significant differences were noted when duodenal bacteriology and TUBA concentrations were assessed before and during antibiotic therapy. These results question the utility of quantitative duodenal juice bacteriology and indirect biochemical marker tests for SIBO in the investigation of canine gastrointestinal disorders.
Congenital Hypothyroidism with Goiter in Toy Fox Terriers
Authors: Fyfe John C. , Kampschmidt Kit , Dang Van , Poteet Brian A. , He Qianchuan , Lowrie Charles , Graham Peter A. , Fetro Virginia M.
Published: February 2009

Congenital hypothyroidism with goiter was observed to segregate as a simple autosomal recessive trait in Toy Fox Terriers (TFTs). Neonatal affected pups exhibited inactivity, abnormal hair coat, stenotic ear canals, and delayed eye opening. Palpable ventrolateral cervical swellings were evident by 1 week of age. Serum thyroid hormone and thyroid‐stimulating hormone concentrations were low and high, respectively. Histologic examination of the cervical masses disclosed cuboidal to columnar follicular epithelial cell hyperplasia with widely varying follicular size, shape, and amount of colloid. Oral thyroid hormone replacement therapy restored near‐normal growth and development. At 8 weeks of age, radioiodine uptake and perchlorate discharge testing indicated an iodine organification defect. Biochemical analysis of thyroid tissue from affected dogs demonstrated enzymatic iodine oxidation deficiency and lack of sodium dodecyl sulfate–resistant thyroglobulin dimers, suggesting thyroid peroxidase deficiency. A nonsense mutation in the thyroid peroxidase gene of affected dogs was discovered and demonstrated to segregate with the disease. A DNA‐based carrier test was developed and currently is used by TFT breeders to prevent this disorder.
Arterial Thromboembolism in Cats: Acute Crisis in 127 Cases (1992–2001) and Long‐Term Management with Low‐Dose Aspirin in 24 Cases
Authors: Smith Stephanie A. , Tobias Anthony H. , Jacob Kristin A. , Fine Deborah M. , Grumbles Pamela L.
Published: February 2009

Records of 127 cats with arterial thromboembolism (ATE) were reviewed. Abyssinian, Birman, Ragdoll, and male cats were overrepresented. Tachypnea (91%), hypothermia (66%), and absent limb motor function (66%) were common. Of 90 cats with diagnostics performed, underlying diseases were hyperthyroidism (12), cardiomyopathy (dilated [8], unclassified [33], hypertrophic obstructive [5], hypertrophic [19]), neoplasia (6), other (4), and none (3). Common abnormalities were left atrial enlargement (93%), congestive heart failure (CHF, 44%), and arrhythmias (44%). Of cats without CHF, 89% were tachypneic. Common biochemical abnormalities were hyperglycemia, azotemia, and abnormally high serum concentrations of muscle enzymes. Of 87 cats treated for acute limb ATE, 39 (45%) survived to be discharged. Significant differences were found between survivors and non‐survivors for temperature(P <.00001), heart rate(P= .038), serum phosphorus concentration(P= .024), motor function(P =.008), and number of limbs affected(P= .001). No significant difference was found between survivors and nonsurvivors when compared by age, respiratory rate, other biochemical analytes, or concurrent CHF. A logistic regression model based on rectal temperature predicted a 50% probability of survival at 98.9oF (37.2oC). Median survival time (MST) for discharged cats was 117 days. Eleven cats had ATE recurrences, and 5 cats developed limb problems. Cats with CHF (MST: 77 days) had significantly shorter survival than cats without CHF (MST: 223 days;P= .016). No significant difference was found in survival or recurrence rate between cats receiving high‐dose aspirin (>40 mg/cat q72h) and cats receiving low‐dose aspirin (5 mg/cat q72h). Adverse effects were less frequent and milder for the lower dosage.
Regurgitant Fraction Measured by Using the Proximal Isovelocity Surface Area Method in Dogs with Chronic Myxomatous Mitral Valve Disease
Authors: Kittleson Mark D. , Brown William A.
Published: February 2009

Previous studies have demonstrated that regurgitant fraction can be measured by using the proximal isovelocity surface area (PISA) method. For this study, we utilized this Doppler echocardiographic method to estimate the magnitude of mitral regurgitation in dogs with myxomatous mitral valve disease. Seventeen older, small dogs with chronic mitral regurgitation and no to mild myocardial failure were studied. A blinded observer judged the clinical severity of mitral regurgitation to be mild, moderate, or severe by using echocardiographic assessment of left heart size. The regurgitant fraction was calculated by using the PISA method and spectral Doppler echocardiography. The regurgitant fraction was compared to the clinical assessment of severity for each dog and to calculations of left atrial size. Five dogs had clinically mild mitral regurgitation. Four of these dogs had a regurgitant fraction between 22 and 41%, whereas 1 had a regurgitant fraction of 73%. The 3 dogs with clinical evidence of moderate mitral regurgitation had a regurgitant fraction of 46–65%. All 9 dogs with clinically severe mitral regurgitation had a regurgitant fraction greater than 75% (78–88%). The regurgitant fraction was statistically different between each group (P< .001). A good but curvilinear relationship was found between left atrial size and regurgitant fraction (r2= 0.72). In this study, dogs with clinically severe mitral regurgitation consistently had hemodynamically severe regurgitation (regurgitant fraction > 75%), whereas dogs with clinically mild to moderate disease had lesser degrees of regurgitation. Good correlation was found between regurgitant fraction and left atrial size. We conclude that the major determinant of left atrial size and disease severity in dogs with mitrial regurgitation is the degree of mitral regurgitation.
Spontaneous Feline Hypertension: Clinical and Echocardiographic Abnormalities, and Survival Rate
Authors: Chetboul Valerie , Lefebvre Hervé P. , Pinhas Carine , Clerc Bernard , Boussouf Maya , Pouchelon Jean‐Louis
Published: February 2009

Systemic hypertension was diagnosed in 58 of 188 untreated cats referred for evaluation of suspected hypertension‐associated ocular, neurologic, cardiorespiratory, and urinary disease, or diseases frequently associated with hypertension (hyperthyroidism and chronic renal failure). Hypertensive cats were significantly older than normotensive subjects (13.0 ± 3.5 years versus 9.6 ± 5.0 years;P <.01), and had a greater prevalence of retinal lesions (48 versus 3%;P <.001), gallop rhythm (16 versus 0%;P <.001), and polyuria‐polydipsia (53 versus 29%;P <.01). Blood pressure was significantly higher(P <.001) in cats with retinopathies (262 ± 34 mm Hg) than in other hypertensive animals (221 ± 34 mm Hg). Hypertensive cats had a thicker interventricular septum (5.8 ± 1.7 versus 3.7 ± 0.64 mm;P <.001) and left ventricular free wall (6.2 ± 1.6 versus 4.1 ± 0.51 mm;P <.001) and a reduced diastolic left ventricular internal diameter (13.5 ± 3.2 versus 15.8 ± 0.72 mm;P <.001) than control cats. Left ventricular geometry was abnormal in 33 of 39 hypertensive subjects. No significant difference was found in age or blood pressure at the initial visit between cats that died or survived over a 9‐month period after initial diagnosis of hypertension. Mean survival times were not significantly different between hypertensive cats with normal and abnormal left ventricular patterns. Further prospective studies are needed to clearly identify the factors involved in survival time in hypertensive cats.
Gastrointestinal Leiomyosarcoma in 14 Dogs
Authors: Cohen Michele , Post Gerald S. , Wright James C.
Published: February 2009

A retrospective review over a 5‐year period was performed to identify clinical characteristic features and survival in 14 dogs with intestinal leiomyosarcoma after surgery. Anemia, hypoglycemia, polyuria, and polydipsia were identified as common clinical signs in these dogs. Dogs that survived the immediate postoperative period had a median survival of 21.3 months, (range 0.1–72.5 months). The 1‐ and 2‐year survival rates were 75 and 66%, respectively. Dogs with intestinal leiomyosarcoma that survive the immediate postoperative period can experience long‐term survival after surgical excision. Furthermore, dogs with histologically documented metastasis at the time of surgery also appear to have a long survival, with a mean survival of 21.7 months (range 4.2–41.5 months).
Power Consumption and Temperature Considerations in Disk Drives
Authors: Schreck Erhard , Ferber Joerg
Published: February 2009

This work studies the contributions of various drive components to the overall drive temperature and temperature gradients within a drive. Data is presented from a variety of 3.5 inch disk drives under varying operating conditions. The average drive case temperature is a result of individual contributors like electronics components on the PCB, spindle motor and actuator. Each of these components dissipate power depending on their main function, the drive operation and in some cases depending on the current drive temperature. Due to the large variety of drive designs this work concentrates on the characteristics of different components in terms of individual temperatures and time constants rather than detailed analysis of one specific disk drive.
A New Universal Approach for Slider Optimization
Authors: Hanke Andreas V. , Talke Frank E.
Published: February 2009

A new method for the optimization of slider bearings in magnetic recording disk drives is described. The new approach subdivides the chosen design area of the slider to be optimized in a number of small rectangular subregions. Each subregion is allowed to be at one of two height levels, one level corresponding to the air bearing surface and the other to the intermediate level between recess level and air bearing level. The pressure distribution over the slider and the flying height of the slider are calculated for all possible combinations of height levels of the subregions and the solution is determined that minimizes a chosen objective function. After determining an optimum solution with an initial coarse subdivision, a refinement of the solution is obtained by further subdivision of the individual subregions, and repeating the evaluation of the objective function to determine the optimum solution. The subregion approach does not require an a priory knowledge of a good initial design and results in novel air bearing contours.
Effect of Air Content on Cavitation Inception as Investigated by Depressurizing Still Water
Authors: Tanibayashi Hidetake , Matsuura Yoshinori , Inoue Kimihito , Ogura Kenji
Published: February 2009

It has been recognized that air content in water affects inception of cavitation and its development. Number of nuclei in the water which are considered to trigger cavitation, however, has been found to be almost independent of air content, as far as the nuclei are counted by a coulter counter. In this study, the mechanisms of cavitation inception are investigated with emphasis on the role of air content in water. As a result, it is shown that nuclei in water increase with air content when the water is supersaturated with air by depressurization. This was proved by experiments both in atmospheric and reduced pressure conditions. From this study the effect of air content on cavitation may be interpreted as follows: free air bubbles are formed when the water is supersaturated by depressurization and they become nuclei which induce cavitation inception.
Approximating Annular Duct Flow in ER/MR Dampers Using a Rectangular Duct
Authors: Yoo Jin-Hyeong , Wereley Norman M.
Published: February 2009

In general, ER/MR dampers have a cylindrical cross-section, for reasons of simplicity of design and maximum strength of the damper. Usually the ER/MR effect is activated by applying field across an annular valve. However, for simplicity of the analysis and design, a rectangular duct flow model is usually adopted. This paper compares analytical solutions of the rectangular and annular duct model under the assumption of uniform field across the valve gap. To compare errors between annular and rectangular duct models, a formulation for the error in the case of Bingham plastic material will be derived for flow mode dampers. This paper focuses on the errors of shear stress, velocity profile and equivalent viscous damping coefficient arising from the approximation of an annular duct as a rectangular duct. The impact of the small gap assumption, that is, the valve gap, d, is much smaller than the annular radius, R1, is thoroughly investigated. We conclude that the approximate rectangular duct model can accurately describe the annular valve behavior as long as d/R1 ≪ 1.
Vortex Identification in Turbulent Flows: Isotropic, Sphere Wake
Authors: Chakraborty P. , Balachandar S. , Adrian R. J.
Published: February 2009

Vortices, the regions of swirling coherent motion of fluid, are of fundamental importance in understanding the dynamics of turbulent flows. Recent advances in computational and experimental resources have resulted in massive volumes of highly resolved flow field data. Identification of coherent vortex structures from these space-time discretized flow dataset is the key issue of vortex identification. We consider identification schemes based on pointwise analysis of the velocity gradient tensor. A new measure of the local spatial coherence in a vortex is introduced. Different criteria are compared for two classes of turbulent flows: isotropic and sphere wake. Remarkably similar vortex structures are observed using the Q, λ2 and swirling strength criterion. An explanation based on swirling strength and the proposed local coherence measure is offered for this observation.
An Alternate Formed Suction Inlet Design for Large Vertical Turbine Pumps
Authors: Werth David E. , Cheek Daniel E.
Published: February 2009

Formed suction inlets are often used under, or in place of, bell intakes for large pumps when adverse approach flow conditions are present. The present research study is aimed at developing a new design of a formed suction inlet (FSI) based on pump bell diameter to increase the efficiency and usefulness of this type of pump intake. It is also intended that this research supplement existing information regarding FSI’s, which will encourage the development of standard design criteria.
Novel Low Reynolds Number Mixers for Microfluidic Applications
Authors: Vanka S. P. , Winkler C. M. , Coffman J. , Linderman E. , Mahjub S. , Young B.
Published: February 2009

We present two new designs of compact mixers that can provide good mixing at low Reynolds numbers encountered in many microfluidic devices. The new designs benefit from curvature induced cross-stream vortices to enhance mixing of two co-flowing streams of fluids arranged side by side. One of the designs is a spiral of rectangular cross-section, while the other is a series of concentric circular channels arranged as a labyrinth. Both utilize the formation of sustained secondary flows to enhance mixing between two streams. Currently, the devices are fabricated in aluminum using standard machining techniques. However, they can be reduced further in size using standard microfabrication techniques. Mixing experiments were conducted in these channels at a Reynolds number of 6.8 using two sucrose solutions, one of which was laced with Rhodamine 6G dye. Compared to a experiment in an equivalent straight channel, a significant enhancement in the mixing of the two streams, as indicated by the intensity of the second fluid’s color, was observed. The present designs provide a compact and easy-to-fabricate alternative to various other concepts proposed in literature.
Active Control of Flow Separation Using Supersonic Microjets
Authors: Kumar Vikas , Alvi Farrukh
Published: February 2009

The separation of boundary layers in engine inlets and ducts, such as in ‘S’ ducts, can significantly compromise the performance of aircraft propulsion systems. For example, in engine inlets, the separation of the incoming boundary layer can result in reduced pressure recovery and unsteady loading on the engine fan blades. This can lead to fatigue and failure of components and may also result in aerodynamic stall on the compressor blades (Wygnanski 1996). The study presented herein focuses primarily on observations of the flow over an adverse pressure gradient where supersonic microjets are used to control flow separation. The geometry used for this study is a simple, diverging ‘Stratford’ ramp equipped with arrays of 400μm supersonic microjets. By activating these microjets, we were able to eliminate the separated flow with minimal mass flux less than 1.5% of the flow rate based on the boundary layer thickness.
The Effect of Upstream Flow Conditions to Laminar Mixing in a Miniature Combustion Chamber
Authors: Woodfield Peter L. , Tatsumi Kazuya , Nakabe Kazuyoshi , Suzuki Kenjiro
Published: February 2009

A three-dimensional unstructured finite-volume method is used to investigate laminar flow characteristics of a miniature chamber with a possible application to micro gas turbine combustor design. The chamber is cylindrical in shape and 20mm in diameter with the fuel stream entering via a single jet in the center of one end of the can. Oxidizer jets are generated by a circular baffle plate having six holes surrounding the fuel jet. Attention is given to the effect of the inlet conditions on the flow structure and mixing pattern inside the chamber. Computations are carried out with the calculation domain inlet being positioned at two different locations; (1) at the immediate entrance to the combustion chamber (2) one combustor diameter upstream of the baffle plate. Numerous inlet conditions are considered including ‘top-hat’, fully-developed, swirling, an annular backward facing step and some asymmetrically skewed profiles. The baffle plate is shown to have a significant smoothing effect on the inlet conditions for a Reynolds number of 100.
Flow in Vortex Chamber Oscillation Device
Authors: Nakashima Masahiro , Nozaki Tsutomu , Tabata Takahide
Published: February 2009

This paper describes about the vortex chamber oscillation device. The flow mechanism of the fluidics is applied in this device. The water jet issuing from this device oscillates by itself. By using the circular device having the diameter of 48mm and various elliptic devices with the major axis from 52mm to 60mm, the swinging flow has been observed by the high-speed camera. Next, the high-speed camera also has captured the flow feature inside of the vortex chamber oscillation devices. The image obtained from the high-speed camera has been processed by the PIV-method. The results of the image processing have been presented as the velocity vector diagrams and vorticity contour map. And the angle of sprinkled water has been also measured by means of the frame overlapping method. By using these results, the effects of the geometrical configuration of the vortex chamber on the oscillating phenomena have been investigated.
Using the Particle Level Set Method and a Second Order Accurate Pressure Boundary Condition for Free Surface Flows
Authors: Enright Doug , Nguyen Duc , Gibou Frederic , Fedkiw Ron
Published: February 2009

In this paper, we present an enhanced resolution capturing method for topologically complex two and three dimensional incompressible free surface flows. The method is based upon the level set method of Osher and Sethian to represent the interface combined with two recent advances in the treatment of the interface, a second order accurate discretization of the Dirichlet pressure boundary condition at the free surface (2002, J. Comput. Phys.176, 205) and the use of massless marker particles to enhance the resolution of the interface through the use of the particle level set method (2002, J. Comput. Phys., 183, 83). Use of these methods allow for the accurate movement of the interface while at the same time preserving the mass of the liquid, even on coarse computational grids. Also, these methods complement the level set method in its ability to handle changes in interface topology in a robust manner. Surface tension effects can be easily included in our method. The method is presented in three spatial dimensions, with numerical examples in both two and three spatial dimensions.
Effects of Swirling Flows on Pneumatic Transport of Solids in Pipes (Keynote)
Authors: Tomita Yuji
Published: February 2009

By applying swirling air flow, particles can be transported with smaller air velocity as compared to the conventional flow without swirl in both horizontal and vertical flows. The total pressure drop along the pipeline is generally larger than that of the flow without swirl, but becomes small and even smaller than that of conventional one when the air velocity decreases. Thus, the swirling flow is effective in low velocity pneumatic transport of suspension mode. By using weak swirl as compared to the previous one, also decreases the particle breakage when the air velocity is low. A numerical simulation shows that the kinetic energy of particles at the wall collision becomes smaller than that in flow without swirl when the breakage is decreased.
Mixing of Carbon Dioxide Gas and Air by a Pulsating Jet With a Reversed Flow
Authors: Muramatsu Akinori , Era Yoshinobu
Published: February 2009

We consider pulsating jets as one method for the rapid mixing of two different gases. Pulsed carbon dioxide gas was issued from a round nozzle into still air. The intensity of the pulsation was set at the value which produced an oscillatory reversed flow in the nozzle exit. Spatial and temporal changes of concentration and velocity were investigated in the mixing region. The mixing of the gases is dramatically enhanced near the nozzle exit. Neither the concentration nor the velocity monotonically decays in the streamwise direction, because the ambient air is drawn periodically by the reversed flow. The direction of the velocity changes periodically at the boundary, which is the position where the mean concentration becomes the minimal value. The lump of any concentration is torn off because of the direction change in the velocity. There is also a phase difference between concentration and velocity.
Droplet-Laden Homogeneous Turbulent Flow Over Unheated and Heated Cylinders
Authors: Presser Cary , Papadopoulos George , Widmann John F.
Published: February 2009

The dispersal of high boiling point liquid fire suppression agents around solid obstacles is investigated to obtain a better understanding of the physical processes of droplet transport in cluttered spaces. To this end, the present experimental investigation examines the flow field dynamics of grid-generated homogeneous turbulent flow over obstacles, and spray transport in such flow fields. Transport of both water droplets and aerosol particles was characterized upstream and downstream of a cylinder using particle image velocimetry (PIV). Data were obtained for the cylinder at ambient temperature and after being heated to 423 K to estimate the effects of the hot cylinder surface on droplet transport. The results indicate that smaller droplets are entrained into the recirculation region behind the cylinder while the larger droplets impact the cylinder surface, accumulate and drip off, or are transported around the surface. The flow over the heated cylinder indicates the formation of a vapor layer on the downstream side of the cylinder in the shear region between the recirculation zone and free stream. Thus, vaporization of smaller droplets near the heated cylinder surface suggests an increased probability of vapor, and reduced probability of droplet entrainment into cylinder wake region.
Simulation of the Water Hammer in a Hydro Power Plant Caused by Draft Tube Surge
Authors: Ruprecht Albert , Helmrich Thomas
Published: February 2009

The system oscillations of a water power plant caused by the draft tube flow in part load are investigated. A coupled simulation of a one-dimensional water hammer analysis and a three-dimensional flow calculation of the draft tube vortex rope is applied. With this approach the excitations of the oscillations, frequencies and amplitudes, have not to be estimated but are obtained from the simulation. This allows an accurate prediction of the system oscillations caused by draft tube surge.
Transient Analyses for Great Falls Hydro Plant
Authors: Schohl Gerald A.
Published: February 2009

Transient analyses provide estimates of maximum pressure in the Great Falls Unit 1 penstock following load rejection. Additional transient analyses, along with hydrodynamic force and moment coefficients, provide estimates of unsteady loads on the Unit 1 emergency butterfly valve during closure. Position varying force and moment coefficients for a butterfly valve were determined by CFD modeling. A new method for representing turbine and pump-turbine characteristics that involves a slight modification to the standard Suter representation permits linear interpolation between the discrete curves representing data at different wicket gate openings.
Concept Water Hammer
Authors: Sharp Bruce B.
Published: February 2009

Why Concept Water Hammer? We have a range of hydraulic concepts but as a poor cousin of hydrology it is often regarded as an exercise in Bernoulli and little else. Water hammer seldom gets suitable treatment which is neglectful, since in physical structures dynamic loads are not regarded lightly as most building codes will show. Expert systems for water hammer are proliferating and are indeed powerful. They tend to be machines which are activated by the press of a button and where the driver’s features are not visible, intrinsic rather than transparent. It would seem essential to have simple analytical techniques or some clear guidelines to provide a way of developing an overview, even approximate, which lends confidence to the sophisticated solution. There is a need, yet to be satisfied, to specify the dynamic limits of low pressures beside the maximum allowable over pressure for pipe plate thickness. There is a need, yet to be satisfied, to integrate dynamic (water hammer) analysis with the design of an optimum pipe size for a pumping associated system (see Sharp [1]) There is a need, to give priority to management of systems which are at risk due to water hammer, not now, but in years hence, when custom dictates that capacities increase and indeed gravity systems become pumping systems. In truth, optimum (least cost) systems often result when pumping is integrated rather than via a simple gravity flow system. In the same way as an earthquake vulnerability triggers the design approach in a structural analysis problem, so should Concept water hammer, where there is the possibility of air intrusion or 2 phase flow, demanding stringent guidelines for analysis. Is it good management to allow significant air ingress through anti-vacuum valves when the consequences of purging or restart have not been evaluated? When there are competitive water supply authorities having common or associated flow systems, Concept Water Hammer will need to show the degree of liability of one authority to another in the management of their distinct but associated systems. When a mechanical device with specification regarding water hammer is freely available Concept Water Hammer will emphasise the fact that such devices have characteristics that are not unique because they become defined as they are incorporated in a system, that is they are system specific. Examples of valve use and pumping with optimum rules and the limits of accuracy that can be obtained will be discussed. Uncertainties can be assisted by sensitivity analyses in forming a background for Concept Water Hammer.
Experimental and Numerical Mixing Studies Inside a Reactor Pressure Vessel
Authors: Ho¨hne T. , Kliem S. , Prasser H.-M. , Rohde U.
Published: February 2009

The work was aimed at the experimental investigation and numerical simulation of coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR). For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been designed. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors and velocity measurements by LDA technique. The CFD calculations were carried out with the CFD-code CFX-4. For the design of the facility, calculations were performed to analyze the scaling of the model. It was found, that the scaling of 1:5 to the prototype meets both: physical and economical demands. Flow measurements and the corresponding CFD calculations in the ROCOM downcomer under steady state conditions showed a Re number independency at nominal flow rates. The flow field is dominated by recirculation areas below the inlet nozzles. Transient flow measurements with high performance LDA-technique showed in agreement with CFX-4 results, that in the case of the start up of a pump after a laminar stage large vortices dominate the flow. In the case of stationary mixing, the maximum value of the averaged mixing scalar at the core inlet was found in the sector below the inlet nozzle, where the tracer was injected. At the start-up case of one pump due to a strong impulse driven flow at the inlet nozzle the horizontal part of the flow dominates in the downcomer. The injection is distributed into two main jets, the maximum of the tracer concentration at the core inlet appears at the opposite part of the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-4 was validated and can be used in reactor safety analysis. Due to the good agreement between measured results and the corresponding CFD-calculation efficient modules for the coupling of thermal hydraulic computer codes with three-dimensional neutron-kinetic models using the results of this work can be developed. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment.
Turbulence Modeling for the Axially Rotating Pipe From the Viewpoint of Analytical Closures
Authors: Rubinstein Robert , Zhou Ye
Published: February 2009

A single-point model eddy viscosity model of rotation effects on the turbulent flow in an axially rotating pipe is developed based on two-point closure theories. Rotation is known to impede energy transfer in turbulence; this fact is reflected in the present model through a reduced eddy viscosity, leading to laminarization of the mean velocity profile and return to a laminar friction law in the rapid rotation limit. This model is compared with other proposals including linear redistribution effects through the rapid pressure-strain correlation, Richardson number modification of the eddy viscosity in a model of non-rotating turbulence, and the reduction of turbulence through the suppression of near-wall production mechanisms.
PANS Turbulence Model for Seamless Transition Between RANS and LES: Fixed-Point Analysis and Preliminary Results
Authors: Girimaji Sharath S. , Srinivasan Ravi , Jeong Euhwan
Published: February 2009

Partially-averaged Navier-Stokes (PANS) approach has been recently developed as a possible bridging model between Reynolds-averaged Navier-Stokes (RANS) method and large-eddy simulations (LES). The resolution control parameters in PANS are the fractions of unresolved kinetic energy (fk) and unresolved dissipation (fε). We investigate the fixed-point behavior of PANS and present some preliminary results obtained using this model. By comparing the fixed-point behavior of PANS and URANS (unsteady Reynolds-averaged Navier-Stokes) methods, the possible advantage of the former over the latter is explained. Initial results from two-dimensional simulations of flow past square results are also presented.
RANS-Based VLES of Thermal and Magnetic Convection at Extreme Conditions
Authors: Hanjalic´ K. , Kenjeresˇ S.
Published: February 2009

For thermal and magnetic convection at very high Rayleigh and Hartman numbers, which are inaccessible to the conventional large eddy simulation (LES), we propose a time-dependent Reynolds-average-Navier-Stokes (T-RANS) approach in which the large-scale deterministic motion is fully resolved by time and space solution, whereas the unresolved stochastic motion is modelled by a “subscale” model for which an one-point RANS closure is used. The resolved and modelled contribution to the turbulence moments are of the same order of magnitude and in near-wall regions the modelled heat transport becomes dominant, emphasizing the role of the subscale model. This VLES approach, with an algebraic stress/flux subscale model, verified earlier in comparison with direct numerical simulation (DNS) and experiments in classic Rayleigh-Be´nrad convection, is now expanded to simulate Rayleigh-Be´nard (R-B) convection at very high Ra numbers — at present up to O(1016) — and to magnetic convection in strong uniform magnetic fields. The simulations reproduce the convective cell structure and its reorganization caused by an increase in Ra number and effects of the magnetic field. The T-RANS simulations of classic R-B indicate expected thinning of both the thermal and hydraulic wall boundary layer with an increase in the Ra number and an increase in the exponent of the Nu ∝ Ran correlation in accord with recent experimental findings and Kraichnan asymptotic theory.
Advances in Rapid Distortion Theory: From Rotating Shear Flows to the Baroclinic Instability
Authors: Cambon Claude , Salhi Aziz
Published: February 2009

The essentials of Rapid Distortion Theory (RDT) are recalled for homogeneous turbulence subjected to rotational mean flows, including its linkage to stability analysis. The latter ‘linkage’ is of particular importance from our viewpoint, since it also attracted the attention of Charles Speziale, resulting in at least two papers (Speziale et al., 1996; Salhi et al., 1997) with particular emphasis on rotating flows. New analytical solutions and related RDT results are presented for shear flows possibly including buoyancy forces, with system rotation or mean density stratification. Finally, combining shear, rotation and stratification, RDT is shown to be pertinent to revisiting the baroclinic instability. This instability results from the tilting of mean isopycnal surfaces under combined effects of vertical shear and system rotation, in a vertically (stably) stratified medium rotating around the vertical direction. In conclusion, the challenge of reproducing RDT dynamics in single-point closure models is briefly discussed, from the viewpoint of structure-based modeling (Cambon et al., 1992; Kassinos et al., 2000).
Preconditioned High-Resolution Scheme for Gravitational Flows With Condensation
Authors: Yamamoto Satoru , Niiyama Daisuke , Shin Byeong-Rog
Published: February 2009

A numerical method for simulating gravitational flows in atmospheric conditions is presented. This is based on the preconditioning method, Roe’s Riemann solver, the 4th-order compact MUSCL extrapolation, and the LU-SGS scheme. The fundamental equations for governing condensate flows with homogeneous and heterogeneous nucleations are transformed to the preconditioned equations. Natural convections with and without condensation at 1g and 0g around a circular cylinder are numerically investigated.
Prediction of Inlet Distortion Induced Axial Compressor Flow Field Instability in Mid-Air Refueling
Authors: Liu Ningyu , Ng Eddie Yin-Kwee , Lim Hong Ngiap , Tan Tock Lip
Published: February 2009

The propagation of strong distortion at inlet of an axial compressor is investigated by applying the critical distortion line and the integral method. The practical applications, such as flaming of leakage fuel during mid-air refueling process, are implemented to show the details of the numerical methodology used in analysis of the axial flow compressor behavior and the propagation of inlet distortion. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion is further described by a compressor critical performance and its critical characteristic. The simulated results present a useful physical insight to the significant effects of inlet parameters on the distortion extension, velocity, and compressor characteristics. The distortion level, the size of distortion area, and the incidence angle at compressor inlet, and the rotor blade speed are found to be the major parameters affecting the mass flow rate of engine.
A Study in the Impeller-Volute Interactions of a Double-Suction Centrifugal Pump
Authors: Chung Kyung-Nam , Park Pyun-Gu , Kim Jin-Young
Published: February 2009

In this study, unsteady flow field of an industrial double-suction centrifugal pump has been solved to obtain the interaction between impeller and volute casing. Quasi-steady and unsteady methods have been used. A block-structured grid is employed to represent the complicated pump geometry. The velocity field and the pressure fields of the pump are analyzed for the rated point and off-design points. Magnitude of the interaction is evaluated numerically.
LES Analysis of a Rocket Turbopump Inducer in Non-Cavitating and Cavitating Flows
Authors: Yamanishi Nobuhiro , Kato Chisachi , Matsumoto Yoichiro
Published: February 2009

A large eddy simulation (LES) of a rocket turbopump inducer in non-cavitating and cavitating flows is presented. The computation takes full account of the interaction between the rotating inducer and the stationary casing by using a multi-frame-of-reference dynamic overset grid approach. A streamline-upwind finite element formulation with second-order accuracy both in time and space is used to discretize the governing equation. It is implemented in parallel by a domain-decomposition-programming model. The evolution of cavitation is represented by the source/sink of vapor phase in the incompressible liquid flow. The pressure-velocity coupling is based on the fractional-step method for incompressible fluid flows, in which the compressibility is taken into account through the low Mach number assumption. The internal flow of an inducer is simulated and compared with water tunnel experiments at the design (φ = 0.078) and off-design conditions (φ = 0.05 and 0.09) in non-cavitating flows. The overall head-flow characteristics of computed results show good agreement with experiments. Such results show that the applied LES code can be used as a design tool for rocket turbopump inducers.
Reconsideration of the Fan Scaling Laws: Part II — Applications
Authors: Sardar Asad M. , George William K.
Published: February 2009

The entire approach to the scaling of fan performance was reconsidered in Part I from first principles using the Navier-Stokes equations appropriate to rotating and swirling (incompressible) flows. Generalized fan scaling laws (GFSL) were derived, consistent with the fact that both Strouhal and Reynolds number must be maintained constant for full dynamical similarity to be possible. As a consequence, dynamic similarity is only possible if ΩD2/ν = const. (in addition to U/ΩD = constant, or equivalently, Q/ΩD3 = constant). This can be contrasted with the classical fan laws (CFSL) which for the same flow rate coefficient would imply that Q/ΩD3 = const. The differences in fan scaling laws between GFSL and CFSL lead to very different fan pressure and fan power scaling criteria. For example, using the GFSL, the pressure coefficient (or Euler number), similarity between the model and prototype fan results in ΔPm/ΔPp = 1/(Lm/Lp)2 (for constant kinematic viscosity), whereas the CFSL pressure scaling criteria lead to ΔPm/ΔPp = (Ωm/Ωp)2 (Lm/Lp)2. Clearly these are very different scaling results and affect the scaling of all the relevant fan performance parameters. In this paper, several applications will be described of experimental programs which utilized these GFSL to design dynamically similar scale models of automotive fans, and these designs are contrasted with what might have been done had the classical laws been used. Three of the facilities were built, and each allowed detailed flow measurements, which would not otherwise have been possible. In addition, the implications and advantages of making tests in a high-pressure facility are explored. Some suggestions will also be made as to how the generalized scaling laws can be applied in design practice.
Index of Quality for Large Eddy Simulations
Authors: Celik Ismail B. , Cehreli Zeynep N. , Yavuz Ibrahim
Published: February 2009

In the light of rapidly increasing applications of large-eddy-simulations (LES) it is deemed necessary to impose some quality assessment measures for such studies. The validation of LES is difficult because of the fact that both the sub-grid scale (sgs) model contribution and numerical discretization errors are functions of the grid resolution. In this study various index of quality measures, here and after referred to as LES_IQ, are proposed and applied to some case studies. The recommended LES_IQ is based on the concept of Richardson’s extrapolation. It is postulated that in practical applications of LES numerical dissipation will always be a significant part of the overall dissipation and it must be accounted for in any assessment of the quality of LES results. It is further suggested that an LES_IQ of 75% to 85% can be considered adequate for most engineering applications that typically occur at high Reynolds numbers; LES-IQ greater than 90% can be classified as DNS.
Similarity Formulations for Turbulent Boundary Layers at High Reynolds Numbers
Authors: Kunkel Gary J. , Marusic Ivan
Published: February 2009

Data obtained from the high Reynolds number atmospheric boundary layer are used to analyze existing mean-flow and turbulence intensity similarity formulations. From the results of this analysis a new streamwise turbulence intensity formulation is proposed that is suggested to be applicable across the entire smooth-wall high Reynolds number turbulent boundary layer. The new formulation is also shown to be consistent with the mixed-flow scaling suggested by other studies.