bluuebunny/crossref_metadata_2025 huggingface dataset:
Cutting characteristics of ultrasonic surgical instruments
Authors: Parmar Dipesh , Mann Malveen , Walmsley A. Damien , Lea Simon C.
Published: March 2011

Objective: Ultrasonic surgical devices are becoming increasingly popular and work is required to understand the performance of the cutting tips. This experimental study looks to investigate the way in which ultrasonic bone cutting tools oscillate and how this oscillation is modified when contacted against bone surfaces with varying loads. The defects produced in instrumented bone surfaces were measured and related to the tip motion.

Methods: An ultrasonic cutting probe was scanned, unloaded, using a scanning laser vibrometer to determine its free oscillation pattern and amplitude. This probe tip was then contacted against bone under various loads to assess the modification in oscillation characteristics. Cuts were performed over a period of 10 s. The cut bone surfaces were assessed using laser profilometry to determine defect depths.

Results: The average vibration displacement amplitude at the probe tip, under load, was <12 μm in the longitudinal direction and was greatest for the cortical cutting mode. Elliptical probe motion was successfully mapped out under the range of loads tested. Defect depths of up to 0.36 mm were detected and were greatest when the tip was in contact with the bone with a load of 100 g.

Conclusions: This work showed that the nature of the surface being cut may significantly alter the mode shape and magnitude of the probe oscillation. The maximum depth of cut with minimum restraining of tip motion was achieved at 100 g contact load.

To cite this article:
 Parmar D, Mann M, Walmsley AD, Lea SC. Cutting characteristics of ultrasonic surgical instruments. Clin. Oral Impl. Res. xx, 2011; 000–000. doi: 10.1111/j.1600‐0501.2010.02121.x
Improved postural control after slackline training is accompanied by reduced H‐reflexes
Authors: Keller M. , Pfusterschmied J. , Buchecker M. , Müller E. , Taube W.
Published: March 2011

“Slacklining” represents a modern sports activity where people have to keep balance on a tightened ribbon. The first trials on the slackline result in uncontrollable lateral swing of the supporting leg. Training decreases those oscillations and therefore improves postural control. However, the underlying neural mechanisms are not known. Therefore, the present study aimed to highlight spinal adaptations going along with slackline training. Twenty‐four subjects were either assigned to a training or a control group and postural control was assessed before and after the 10 training sessions. Additionally, soleus Hoffmann (H)‐reflexes were elicited to evaluate changes in the excitability of the spinal reflex circuitry. Trained subjects were able to maintain balance on the slackline for at least 20 s (P<0.001) and reduced platform movements on the balance board (P<0.05). The H‐reflexes were significantly diminished (P<0.05) while no changes occurred in the background electromyography (bEMG). The control group showed no significant changes. From a functional point of view the reflex reduction may serve to suppress uncontrollable reflex mediated joint oscillations. As the bEMG remained unchanged, presynaptic rather than post‐synaptic mechanisms are speculated to be responsible for the changes in the Ia‐afferent transmission.
Respiratory infection risk in athletes: association with antigen‐stimulated IL‐10 production and salivary IgA secretion
Authors: Gleeson M. , Bishop N. , Oliveira M. , McCauley T. , Tauler P. , Muhamad A. S.
Published: March 2011

The purpose of this study was to examine factors influencing susceptibility to upper respiratory tract infections (URTI) in 18–35‐year‐old men and women engaged in endurance‐based physical activity during the winter months. Eighty individuals (46 males, 34 females) provided resting blood and saliva samples for determination of markers of systemic immunity. Weekly training and illness logs were kept for the following 4 months. Thirty subjects did not experience an URTI episode and 24 subjects experienced 3 or more weeks of URTI symptoms. These illness‐prone subjects had higher training loads and had ∼2.5‐fold higher interleukin (IL)‐4 and IL‐10 production by antigen‐stimulated whole blood culture than the illness‐free subjects. Illness‐prone subjects also had significantly lower saliva S‐IgA secretion rate and higher plasma IgM (but not IgA or IgG) concentration than the illness‐free subjects. There were no differences in circulating numbers of leukocyte subtypes or lymphocyte subsets between the illness‐prone and illness‐free subjects. The production of IL‐10 was positively correlated and the S‐IgA secretion rate was negatively correlated with the number of weeks with infection symptoms. It is concluded that high IL‐10 production in response to antigen challenge and low S‐IgA secretion are risk factors for development of URTI in physically active individuals.
Advancing oral medicine through informatics and information technology: a proposed framework and strategy
Authors: Schleyer T , Mattsson U , Ní Ríordáin R , Brailo V , Glick M , Zain RB , Jontell M
Published: March 2011

Oral Diseases (2011) 17 (Suppl. 1), 85–94

The implementation of information technology in healthcare is a significant focus for many nations around the world. However, information technology support for clinical care, research and education in oral medicine is currently poorly developed. This situation hampers our ability to transform oral medicine into a ‘learning healthcare discipline’ in which the divide between clinical practice and research is diminished and, ultimately, eliminated. This paper reviews the needs of and requirements for information technology support of oral medicine and proposes an agenda designed to meet those needs. For oral medicine, this agenda includes analyzing and reviewing current clinical and documentation practices, working toward progressively standardizing clinical data, and helping define requirements for oral medicine systems. IT professionals can contribute by conducting baseline studies about the use of electronic systems, helping develop controlled vocabularies and ontologies, and designing, implementing, and evaluating novel systems centered on the needs of clinicians, researchers and educators. Successfully advancing IT support for oral medicine will require close coordination and collaboration among oral medicine professionals, information technology professionals, system vendors, and funding agencies. If current barriers and obstacles are overcome, practice and research in oral medicine stand ready to derive significant benefits from the application of information technology.
Observations on hand‐mating behaviors, several physiological and hematological parameters in Turkish dairy goats
Authors: KONYALI Aynur , TÖLÜ Cemil , AYAĞ Bekir Sıtkı , AKBAĞ Hande Işıl
Published: March 2011

The aims of this study were to examine hand‐mating behavior of doe and buck and relationships of courtship behavior and physiological and hematological traits according to gestation results. Duration from beginning of observation until mating (M‐C), duration between two copulations (C‐C) and courtship behavioral index value of each sex (CBIVD; courtship behavioral index value of doe, CBIVB; courtship behavioral index value of buck) and mounting behavior of buck, were observed. Experience of doe was affected of CBIVD and CBIVB (P = 0.01 and P = 0.01, respectively). Bucks mounted significantly higher times on experienced does than on inexperienced ones (P = 0.00). On the other hand service number decreased with an increase in M‐C (P = 0.00). Elevated service number was observed with increased mounting frequency of buck (P = 0.03). There were strong correlations between CBIVD and CBIVB (r = 0.48, P = 0.00). Pregnancy was not influenced by vaginal pH value. Does, which gave multiple births, had higher vaginal pH (P = 0.05). Rectal temperature difference of doe had no influence on success of mating and birth type. On the other hand, birth type was affected by rectal temperature difference of buck. There was no significant difference of hematological parameters according to mating results. Hemoglobin, red blood cell count and mean corpuscular hemoglobin concentration values were higher in single births and mean cell volume value was lower in single births.
Effects of melanocortins on fetal development
Authors: Simamura Eriko , Shimada Hiroki , Shoji Hiroki , Otani Hiroki , Hatta Toshihisa
Published: March 2011

Melanocortins, adrenocorticotropic hormone (ACTH) and α‐, β‐, and γ‐melanocyte‐stimulating hormone (MSH) are produced in the placenta and secreted into embryos/fetuses. ACTH concentrations are higher in fetal plasma than in maternal plasma and peak at mid‐gestation in rats, whereas ACTH production starts in the anterior lobe of the fetal pituitary at later stages. Melanocortin receptors (MC1‐5R), receptors for ACTH and α‐, β‐ and γ‐MSH, are expressed in various adult organs. The specific function of these receptors has been well examined in the hypothalamic‐pituitary‐adrenocortical (HPA) axis and the HPA axis‐like network in the skin, and anti‐inflammatory effects for white blood cells have also been investigated. MC2R and/or MC5R are also expressed in the testis, lung, kidney, adrenal, liver, pancreas, brain and blood cells at different stages in mouse and rat embryos/fetuses. Melanocortins in embryos and fetuses promote maturation of the HPA axis and also contribute to the development of lung, testis, brain and blood cells. Recently, a unique ACTH function was revealed in fetuses: placental ACTH, which is secreted by the maternal leukemia inhibitory factor (LIF), and induces LIF secretion from fetal nucleated red blood cells. Finally, the maternal LIF‐placental ACTH‐fetal LIF signal relay regulates the LIF level and promotes neurogenesis in fetuses, which suggests that ACTH acts as a signal transducer or effector for fetal development in the maternal‐fetal signal pathway.
Effects of an Epiphytic Orchid on Arboreal Ant Community Structure in Panama
Authors: Yanoviak Stephen P. , Berghoff Stefanie M. , Linsenmair K. Eduard , Zotz Gerhard
Published: March 2011

Epiphytes are conspicuous structural elements of tropical forest canopies. Individual tree crowns in lowland forests may support more than 30 ant species, yet we know little about the effects of epiphytes on ant diversity. We examined the composition of arboreal ant communities onAnnona glabratrees and their interactions with the epiphytic orchidCaularthron bilamellatumin Panama. We surveyed the ants on 73 trees (45 withC. bilamellatumand 28 lacking epiphytes) and recorded their nest sites and behavioral dominance at baits. We found a total of 49 ant species (in 20 genera), ranging 1–9 species per tree. Trees withC. bilamellatumhad higher average (±SD) ant species richness (4.2±2.28) than trees without epiphytes (2.7±1.21). Hollow pseudobulbs (PBs) ofC. bilamellatumwere used as nest sites by 32 ant species, but only 43 percent of suitable PBs were occupied. Ant species richness increased with PB abundance in trees, but nest sites did not appear to be a limiting resource onA. glabra. We detected no close association between ants and the orchid. We conclude that higher ant species richness in the presence of the orchid is due to bottom‐up effects, especially the year‐round supply of extrafloral nectar. The structure of ant communities onA. glabrapartly reflects interference competition among behaviorally dominant species and stochastic factors, as observed in other forests.
Toxicity, inheritance and biochemistry of clofentezine resistance in Tetranychus urticae
Authors: Ay Recep , Ebru Kara Fatma
Published: March 2011

Abstract  This study evaluates the toxicological and biochemical response of two‐spotted spider mites to clofentezine selection pressure. The mortality rate of Tetranychus urticae in adult females depends on increased clofentezine concentration and clofentezine was found to be effective against females. The resistance rate of the CUM strain selected 12 times once per generation with clofentezine was increased from 1.28‐ to 105.27‐fold. The interaction of some synergists with clofentezine was analyzed in the clofentezine‐resistant CLOF 12 strain. Synergists had no effect on clofentezine toxicity. The clofentezine‐resistant CLOF 12 strain showed resistance against chlorpyrifos, abamectin, propargite, fenpyroximate and amitraz. The modes of inheritance of resistance to clofentezine were found to be incompletely dominant and not sex‐linked. Esterase enzyme activity was detected both by gel electrophoresis and microplate reader methods, while glutathione S‐transferase (GST) and monooxygenase (P450) activity were detected only by the microplate reader method. During the selection period the esterase, the GST and the P450 enzymes activities were raised from 7.69, 7.09 and 0.003 3 to 18.40, 13.11 and 0.003 7 milli‐optical density/min/mg proteins, respectively. An increase was observed in the band intensity of esterases and esterase enzymes may play a role in clofentezine resistance in T. urticae.
Assessment of Managed Aquifer Recharge Potential Using Ensembles of Local Models
Authors: Smith Anthony J. , Pollock Daniel W.
Published: March 2011

A simple quantitative approach for assessing the artificial recharge potential of large regions using spatial ensembles of local models is proposed. The method extends existing qualitative approaches and enables rapid assessments within a programmable environment. Spatial discretization of a water resource region into continuous local domains allows simple local models to be applied independently in each domain using lumped parameters. The ensemble results can be analyzed directly or combined with other quantitative and thematic information and visualized as regional suitability maps. A case study considers the hydraulic potential for surface infiltration across a large water resource region using a published analytic model for basin recharge. The model solution was implemented within a geographic information system and evaluated independently in >21,000 local domains using lumped parameters derived from existing regional datasets. Computer execution times to run the whole ensemble and process the results were in the order of a few minutes. Relevant aspects of the case study results and general conclusions concerning the utility and limitations of the method are discussed.
RIPGIS‐NET: A GIS Tool for Riparian Groundwater Evapotranspiration in MODFLOW
Authors: Ajami Hoori , Maddock Thomas , Meixner Thomas , Hogan James F. , Guertin D. Phillip
Published: March 2011

RIPGIS‐NET, an Environmental System Research Institute (ESRI's) ArcGIS 9.2/9.3 custom application, was developed to derive parameters and visualize results of spatially explicit riparian groundwater evapotranspiration (ETg), evapotranspiration from saturated zone, in groundwater flow models for ecohydrology, riparian ecosystem management, and stream restoration. Specifically RIPGIS‐NET works with riparian evapotranspiration (RIP‐ET), a modeling package that works with the MODFLOW groundwater flow model. RIP‐ET improves ETg simulations by using a set of eco‐physiologically based ETg curves for plant functional subgroups (PFSGs), and separates ground evaporation and plant transpiration processes from the water table. The RIPGIS‐NET program was developed in Visual Basic 2005, .NET framework 2.0, and runs in ArcMap 9.2 and 9.3 applications. RIPGIS‐NET, a pre‐ and post‐processor for RIP‐ET, incorporates spatial variability of riparian vegetation and land surface elevation into ETg estimation in MODFLOW groundwater models. RIPGIS‐NET derives RIP‐ET input parameters including PFSG evapotranspiration curve parameters, fractional coverage areas of each PFSG in a MODFLOW cell, and average surface elevation per riparian vegetation polygon using a digital elevation model. RIPGIS‐NET also provides visualization tools for modelers to create head maps, depth to water table (DTWT) maps, and plot DTWT for a PFSG in a polygon in the Geographic Information System based on MODFLOW simulation results.
Automatic tumour volume delineation in respiratory‐gated PET images
Authors: Gubbi Jayavardhana , Kanakatte Aparna , Tomas Kron , Binns David , Srinivasan Bala , Mani Nallasamy , Palaniswami Marimuthu
Published: March 2011

Introduction: Positron emission tomography (PET) is a state‐of‐the‐art functional imaging technique used in the accurate detection of cancer. The main problem with the tumours present in the lungs is that they are non‐stationary during each respiratory cycle. Tumours in the lungs can get displaced up to 2.5 cm during respiration. Accurate detection of the tumour enables avoiding the addition of extra margin around the tumour that is usually used during radiotherapy treatment planning.

Methods: This paper presents a novel method to detect and track tumour in respiratory‐gated PET images. The approach followed to achieve this task is to automatically delineate the tumour from the first frame using support vector machines. The resulting volume and position information from the first frame is used in tracking its motion in the subsequent frames with the help of level set (LS) deformable model.

Results: An excellent accuracy of 97% is obtained using wavelets and support vector machines. The volume calculated as a result of the machine learning (ML) stage is used as a constraint for deformable models and the tumour is tracked in the remaining seven phases of the respiratory cycle. As a result, the complete information about tumour movement during each respiratory cycle is available in relatively short time.

Conclusions: The combination of the LS and ML approach accurately delineated the tumour volume from all frames, thereby providing a scope of using PET images towards planning an accurate and effective radiotherapy treatment for lung cancer.
Remarks on the taxonomy and nomenclature of the Stipa tianschanica complex (Poaceae), on the base of a new record for the flora of Tajikistan (central Asia)
Authors: Nobis Marcin
Published: March 2011

The taxonomic position and distribution of Stipa tianschanica Roshev, a species new to the flora of Tajikistan (central Asia), are discussed. Its morphological characters are compared with other members of the S. tianschanica complex and information on their taxonomy and distribution are presented. The distinguishing features of S. tianschanica subsp. tianschanica, S. tianschanica subsp. gobica (Roshev.) D. F. Cui and S. klemenzii Roshev. are presented in a table, together with photographs of their lemma surfaces and a list of their synonyms. Analysis of the morphological characters of the taxa provides new information on their variability and a new combination, S. tianschanica subsp. gobica var. pubescens (Hanelt & Davažamc) M. Nobis comb. nov., is proposed. A key to the taxa of Stipa sect. Smirnovia Tzvel. occurring in Tajikistan (especially in the area of Pamirs), a description of S. tianschanica subsp. tianschanica and illustrations of the most important diagnostic characters of the taxon are included.
Maranta rugosa sp. nov. (Marantaceae) from central Brazil
Authors: Marcelo Alvarenga Braga João , Vieira Silvana
Published: March 2011

Maranta is a neotropical genus usually found in moist and shaded habitats in pluvial to semideciduous forests and Cerrado, with diversity center in central Brazil. A new species from Mato Grosso, M. rugosa J. M. A. Braga & S. Vieira, is described and illustrated. The new species is somewhat similar to M. parvifolia Petersen with which it is compared.
A benefit analysis of screening for invasive species – base‐rate uncertainty and the value of information
Authors: Sahlin Ullrika , Rydén Tobias , Nyberg Cecilia D. , Smith Henrik G.
Published: March 2011

1.. Implementation of the full spectra of screening tools to prevent the introduction of invasive species results in a need to evaluate the cost‐efficiency of gathering the information needed to screen for these species.

2.. We show how the Bayesian value of information approach can be used to derive the benefit of a screening model based on species traits, which in combination with the base rate of invasiveness, i.e. the proportion of invasive species among those introduced and established, predicts species‐specific invasiveness.

3.. A pre‐posterior Bayesian analysis demonstrated that the benefit of the screening model of invasiveness depends on both the accuracy in predictions and the uncertainty in the base rate of invasiveness. However, even though increasing model accuracy always generates higher model benefit, acknowledging or neglecting the uncertainty in the base rate of invasiveness does not. This means that uncertainty in the base rate is important to consider in the cost‐benefit analysis of the screening model.

4.. As an example, we derived the benefit of basing decisions on a screening model trained for a data set on species traits of invasive and non‐invasive marine macroalgae introduced into Europe. The benefit ranged from 0·6% to 19% of the loss of introducing an invasive species, where the actual value can be estimated if we know the monetary values of impacts from introducing invasive and not introducing non‐invasive species.

5.. Cost‐benefit analyses of screening models for invasive species is one means to reach efficient management of the risks of non‐indigenous species. Value of information is a useful tool for benefit analysis of predictive models with respect to decision‐making, which goes beyond the investigations of model accuracy. Here, we use value of information analysis to evaluate which sources of uncertainty that is most worth while to reduce and how to set the cost of gathering further species‐specific information which will improve the accuracy of a screening.
Mechanical Characterization of a Viscoelastic Disc for Lumbar Total Disc Replacement
Authors: Benzel Edward C. , Lieberman Isador H. , Ross E. Raymond , Linovitz Raymond J. , Kuras James , Zimmers Kari
Published: March 2011

A viscoelastic artificial disc may more closely replicate normal stiffness characteristics of the healthy human disc compared with first-generation total disc replacement (TDR) devices, which do not utilize viscoelastic materials and are based on a ball and socket design that does not allow loading compliance. Mechanical testing was performed to characterize the durability and range of motion (ROM) of an investigational viscoelastic TDR (VTDR) device for the lumbar spine, the Freedom® Lumbar Disc. ROM data were compared with data reported for the human lumbar disc in the clinical literature. Flexibility and stiffness of the VTDR in compression, rotation, and flexion/extension were within the parameters associated with the normal human lumbar disc. The device constrained motion to physiologic ranges and replicated normal stress/strain dynamics. No mechanical or functional failures occurred within the loads and ROM experienced by the human disc. Fatigue testing of the worst case VTDR device size demonstrated a fatigue life of 50 years of simulated walking and 240 years of simulated significant bends in both flexion/extension and lateral bending coupled with axial rotation, with no functional failures. These results indicate that the VTDR evaluated in this mechanical study is durable and has the ability to replicate the stiffness and mechanics of the natural, healthy human lumbar disc.
Two-Degree-of-Freedom Flow-Induced Vibrations of a Circular Cylinder With a High Moment of Inertia Ratio
Authors: Kheirkhah Sina , Yarusevych Serhiy
Published: March 2011

Two degree-of-freedom vortex-induced vibrations of a moderate mass and high moment of inertia ratio pivoted cylinder were investigated experimentally. The experiments were performed at a constant Reynolds number of 2100 for a range of reduced velocities from 3.4 to 11.25. The results show that, in addition to the reduced velocity, the transverse damping ratio has a significant effect on the amplitudes of response. The cylinder tip is observed to trace orbital trajectories, which is shown to be attributed to the frequencies of oscillations in both directions locking onto the natural frequency in the synchronization region. The results indicate that a phase angle between the streamwise and transverse oscillations governs the direction and orientation of the orbiting motion. Flow visualization results show that, at a given reduced velocity and transverse damping ratio, near-wake development changes along the cylinder span. The observed shedding patterns are shown to differ from those expected at the corresponding experimental parameters for one-degree-of-freedom uniform amplitude cylinder vibrations.
The Effect of In-Line Oscillation on the Forces of a Cylinder Vibrating in a Steady Flow
Authors: Peppa Sofia , Kaiktsis Lambros , Triantafyllou George
Published: March 2011

In this paper we present a computational study of the forces acting on a circular cylinder vibrating both transversely and in-line to a uniform stream. The in-line vibration frequency is equal to twice the transverse frequency. The cylinder thus follows a figure-eight trajectory, emulating the trajectory of a free vortex-induced vibration. We consider three values of transverse oscillation frequency, in the regime of the natural frequency of the Ka´rma´n street, for a Reynolds number of 400. We find that the fluid forces are greatly influenced by the direction in which the figure-eight is traversed. We also find that the spectrum of the lift force is characterized by the strong presence of odd-numbered higher harmonics. Moreover, depending on the combination of oscillation amplitude and frequency, the lift force exhibits aperiodic time dependence.
Hydroelastic Stability of a Flexible Panel: Eigen-Analysis and Time-Domain Response
Authors: Tan Ben H. , Lucey Anthony D. , Pitman Mark W.
Published: March 2011

A state-space model, based upon computational modeling, is used to investigate the hydroelastic stability of a finite flexible panel interacting with a uniform flow. A merit of this approach is that it allows the fluid-structure system eigenmodes to be found readily when structural inhomogeneity is included or a source of external excitation is present. The system studied herein is two-dimensional although the concepts presented can be readily extended to three dimensions. Two problems are considered. In the first, we solve the initial-value, boundary-value, problem to show how the system response evolves from a source of localized excitation. This problem is deceptively complex and has evidenced some very unusual behaviour as demonstrated by theoretical studies based on the assumption of an infinitely long flexible panel. Our contribution herein is to formulate and illustrate the use of a hybrid of theoretical and computational models that includes the effects of finiteness. In the second problem we solve the boundary-value problem to determine the long-time response and investigate the effects of adding localized structural inhomogeneity on the linear stability of a flexible panel. It is well known that a simple flexible plate first loses its stability to divergence that is replaced by modal-coalescence flutter at higher speeds. Our contribution is to show how the introduction of localized structural inhomogeneity can be used to modify the divergence-onset and flutter-onset critical flow speeds.
The Role of Axial Flow in Near Wake on the Cross-Flow Vibration of the Inclined Cable of Cable-Stayed Bridges
Authors: Matsumoto Masaru
Published: March 2011

Nowadays, the violent wind-induced vibration, including “rain-wind induced vibration” and “dry-galloping”, of stay-cables of cable-stayed bridges has become the most serious issue for bridge design. Up-to-date, the major factors for excitation of inclined cables have been clarified to be, for “rain-wind” induced vibration, the formation of “water-rivulet” on the particular position of upper cable surface, and, for “dry galloping”, the “axial flow” which flows in the near wake along cable-axis, and the effect of drag-force associated with Reynolds number, separately. However, the details of the effect of “axial flow” remain unsolved. Thus, this study aims to clarify the effect of axial flow in near wake on the aero-elastic vibration of inclined cables basing on various experiments. The mean velocity of axial flow was almost 60% of approaching wind velocity. Furthermore, the aerodynamic effect of the “axial flow” on cross-flow vibration of inclined cables is discussed in relation to the mitigation of Karman vortex shedding in near wake. Since the role of axial flow seems to be similar to the splitter plate installed in wake from the point of mitigation of Karman vortex shedding, to clarify the cross-flow response in relation to the mitigation of Karman vortex, the perforated ratio of the splitter plate was variously changed, then the similarity of effect of axial flow and the one of splitter plate was verified comparing their unsteady lift force-characteristics. In summary, it is shown that the axial flow on aerodynamic cross-flow vibration might excite like galloping similarly with the splitter plate by mitigation of Karman vortex.
Impulsive Plunging Wave Breaking Downstream of a Bump in a Shallow Water Flume
Authors: Koo Bonguk , Wang Zhaoyuan , Yang Jianming , Kang Donghoon , Stern Frederick
Published: March 2011

The plunging wave-breaking process for impulsive flow over a bump in a shallow water flume is described using complementary experiments and simulations, which is relevant to ship hydrodynamics since it includes effect of wave-body interactions and wave breaking direction is opposite to the mean flow. Phase averaged measurements (relative to the time at which the maximum wave height is reached just before the first plunge) are conducted, including the overall flume flow and 2D PIV center-plane velocities and turbulence inside the plunging breaking wave and bottom pressures under the breaking wave. A total number of 226 individual plunging wave-breaking tests were conducted, which all followed a similar time line consisting of startup, steep wave formation, plunging wave, and chaotic wave breaking swept downstream time phases. The plunging wave breaking process consists of four repeated plunging events each with three [jet impact (plunge), oblique splash and vertical jet] sub-events, which were identified first using complementary CFD. Video images with red dye display the plunging wave breaking events and sub-events. The first and second plunges take longer than the last two plunges. Oblique splashes and vertical jets account for more time than plunging. The wave profile at maximum height, first plunge, bump and wave breaking vortex and entrapped air bubble trajectories, entrapped air bubble diameters, kinetic, potential, and total energy, and bottom pressures are analyzed. The simulations on four different grids qualitatively predict all four time phases, all four plunging events and their sub-events, and bottom pressure but with reduced velocity magnitudes and larger post-breaking water elevations. The medium grid results are presented and the fine grid simulations are in progress. Similarities and differences are discussed with the previous deep water or sloping beaches experimental and computational studies.
Simulation of Two-Phase Flow Past a Vertical Surface-Piercing Circular Cylinder
Authors: Stern Frederick , Yang Jianming , Suh Jungsoo , Koo Bonguk
Published: March 2011

Large-eddy simulation of the flow past a surface-piercing circular cylinder is performed to investigate the effects of Reynolds and Froude numbers using a high fidelity orthogonal curvilinear grid solver. The present study extends and supports the conclusions of the precursory work for medium Reynolds and Froude numbers. Organized periodic vortex shedding is observed in deep flow. At the interface, the organized periodic vortex shedding is attenuated and replaced by small-scale vortices. The streamwise vorticity and outward transverse velocity generated at the edge of the separated region cause the weakened vortex shedding at the interface. The main source of the streamwise vorticity and the outward transverse velocity at the interface is the lateral gradient of the difference between the vertical and transverse Reynolds normal stresses.
Fluidelastic Instability and Periodic Fluid Forces in a Normal Triangular Tube Bundle Subjected to Air-Water Flow
Authors: Ricciardi G. , Pettigrew M. J. , Mureithi N. W.
Published: March 2011

Two-phase flow in power plant steam generators can induce tube vibrations, which may cause fretting-wear and even fatigue cracks. It is therefore important to understand the relevant two-phase flow-induced vibration mechanisms. Fluidelastic instabilities in cross-flow are known to cause the most severe vibration response in the U-bend region of steam generators. This paper presents test results of the vibration of a normal triangular tube bundle subjected to air-water cross-flow. The test section presents 31 flexible tubes. The pitch-to-diameter ratio of the bundle is 1.5, and the tube diameter is 38 mm. Tubes were flexible in the lift direction. Seven tubes were instrumented with strain gauges to measure their displacements. A broad range of void fractions (from 10% to 90%) and fluid velocities (up to 13 m/s) were tested. Fluidelastic instabilities were observed for void fractions between 10% and 60%. Periodic fluid forces were also observed. The results are compared with those obtained with the rotated triangular tube bundle, showing that the normal triangular configuration is more stable than the rotated triangular configuration.
Aeroelastic Response to Gust Using CFD Techniques
Authors: Liauzun Ce´dric
Published: March 2011

A numerical method to predict the aeroelastic response of an aircraft to a gust is assessed. It is based on the use of CFD techniques to compute accurately the aerodynamic fields. Gust models are then implemented as a field of grid deformation speed, that depends on both space and time. The numerical method has been first validated for a 2D Naca12 airfoil embedded in an inviscid flow and submitted to a sharp edged gust, by comparisons with results presented by Zaide et al. It has afterwards been validated in the case of a 3D wing submitted to a harmonic gust in the subsonic domain by comparisons with computations using the Doublet Lattice Method. After the validation step, the method has been used first to investigate the influence of the aerodynamic nonlinearities that occurs in the transonic domain, and at last to compute the aeroelastic responses of wings to gust excitations.
On the Feasibility of Modeling Two-Phase Flow-Induced Fluidelastic Instability in Tube Bundles
Authors: Mureithi Njuki W.
Published: March 2011

In the 80’s a number of theoretical models were developed to model fluidelastic instability, primarily for single phase flows. The models ranged from purely analytical models to semi-empirical models requiring considerable experimental data as input. While these models were very successful in uncovering the nature of fluidelastic instability and the underlying mechanisms in single phase flow, this work seemed to stop short of getting to the next step of practical application to two-phase flows. During the same period, Connors formula became ‘entrenched’ in industry to the extent that the formula now forms part of the design norms against fluidelastic instability. In an ongoing research program the quasi-steady model has been chosen as a possible candidate for modeling fluidelastic instability in two-phase flows. This paper discusses the challenges associated with accurate modeling of fluidelastic instability in two phase flows using this and other models. The unsteady model is shown to have limitations when it comes to measuring accurately the necessary unsteady fluid force coefficients. A comparison of the stability analysis results with experimental measurements shows that the quasi-steady model can give a reasonable estimate of the instability velocity as well as the inter-tube dynamics. Finally, the remaining challenges, before the quasi-steady model and possibly other models can be fully implemented for prototypical conditions are discussed. In particular the need for more work to understand the flow itself is highlighted.
The Effect of Flow Pulsations on the Streamwise Vibration of a Cantilevered Rigid Cylinder
Authors: Konstantinidis Efstathios , Giagopoulos Dimitris , Sherwood Joseph , Balabani Stavroula
Published: March 2011

The effect of pulsations superimposed on a mean incident flow on the streamwise vibration of an elastically-supported cantilevered rigid cylinder with two coupled translational and rotational degrees of freedom was investigated experimentally. The pulsation frequency was varied between 7.8–19.2 Hz corresponding to 1.2–3.0 times the vortex shedding frequency from a fixed cylinder in steady flow whereas the amplitude of the pulsations and the incident-flow mean velocity were held constant, the latter corresponding to a Reynolds number of 2160. The results show that there are two excitation regions in which the amplitude of vibration increases up to 400% compared to that in steady flow at the same Reynolds number. As the pulsation frequency is further increased in each range, the amplitude of the vibrations drops almost linearly down to a level near that without flow pulsations although the frequency of vibration remains locked-on at the imposed pulsation frequency in all cases.
Development of Flexible Liquid Damper
Authors: Kawabata Shinichi , Bunkhlong Weerachai , Nakamura Tomomichi
Published: March 2011

The “Flexible Liquid Damper” (FLD) is a new concept of a vibration control device. The damper is composed of only two parts, a flexible ball and liquid filling in the flexible ball. The damper design is simple, but the mechanism underlying its significant damping capacity has not been clarified. Two kinds of tests are conducted to investigate the characteristics of the damper in this study. One is the sinusoidal sweep test, while the other is the free decay test. First, several parameters of the damper are investigated, such as its size, material and the properties of the liquid itself. As a result, it is found that the case of around 50% volume is the most effective rather than the case where the ball is 100% filled with liquid. Moreover, other conditions have some effect, such as the wall thickness of the ball, and the liquid viscosity. Both the free vibration and the sinusoidal sweep tests show its great damping capacity. The damping effect obtained in free vibration tests is higher than that by the sinusoidal sweep tests. In some test cases, two dominant peaks are observed; the peaks only appear in the case of some combinations of the damper parameters. An attempt is made to analyze the damping mechanism using the general-purpose computational tool “ANSYS”, by creating an analytical model of the damper to simulate the test results. From the numerical results, it is found that the vibration control mechanism of this damper is mainly similar to the mechanism of the dynamic vibration absorber. However, the numerical results also show that the damper is not a simple dynamic vibration absorber and may include some other energy dissipation or energy transfer mechanism.
The Low Reynolds Number Limit of Vortex and Wake-Induced Vibrations
Authors: E´tienne Ste´phane , Pelletier Dominique
Published: March 2011

Vortex and wake induced vibrations (VIV/WIV) of a circular cylinder at low values of the Reynolds number (Re) are simulated by means of a fully coupled fluid-structure interaction numerical model based on the finite element method. It is shown that VIV/WIV could occur far below the first Hopf bifurcation (Re <47). The main objective of this study is to determine the limiting Reynolds-Reduced velocity (Ur) curve that separates the non-vibrational area from the possible vibrations occurrence area. We assume that by taking a zero mass cylinder and zero structural damping we will obtain the low limit of vibrations in terms of Re and Ur. It is shown in particular that transverse vibrations could occur for reduced velocities larger than 40 and not below 3.5.
Vortex-Induced In-Line Vibration and Random Vibration of a Circular Cylinder Under Various Inflow Conditions
Authors: Nishihara Takashi , Eguchi Yuzuru
Published: March 2011

The flow-induced vibrations (FIV) of cylindrical structures subjected to a cross flow have been investigated in a number of studies owing to their practical importance. The results of these studies have been compiled into guidelines for the evaluation of FIV of cylindrical structures. However, the applicability of the guidelines to cases with upstream structures and with an oblique inflow has not been fully examined. In this paper, we describe the response characteristics of vortex-induced in-line vibration and random vibration of a circular cylinder under various inflow conditions. Water tunnel tests were conducted on a circular cylinder in a cross flow at three yaw angles of 0, 30 and 45 degrees to clarify the effects of the yaw angle on vortex-induced in-line vibration and random vibration. The vibration amplitudes of a circular cylinder downstream of another circular cylinder of five times larger diameter were also measured to investigate the effects of inflow turbulence generated by an upstream cylinder. The tests were conducted for two different relative locations of the upstream cylinder in the same reduced-velocity range as that of the single-cylinder tests. The response amplitudes and onset flow velocities obtained by the tests were compared with values predicted using the cosine law and the guidelines to verify the evaluation methods in the guidelines.
Flow-Induced Wave Generated on a Thin Film Under Shear Loading
Authors: Kudou Gaku , Watanabe Masahiro , Hara Kensuke
Published: March 2011

This paper deals with an experimental study of flow-induced wave generated on a thin film under shear loading. The experiment is carried out to investigate the deformed shape of the thin film with various values of shear loading, and the wave propagation due to the interaction of the deformed shape of the thin film with the fluid flow in the narrow passage. As a result, it is clarified that the flow-induced wave occurs to the thin film caused by interaction of the corrugated shape of the corrugation due to the shear loading with the fluid flow in the narrow passage. Moreover, it is clarified that the traveling direction of the flow-induced wave is determined by the corrugated shape of the corrugation and fluid flow direction. The flow-induced wave propagates diagonally, almost across the fluid flow direction.
Experimental and Numerical Investigation of Flow Induced Vibration of Steam Control Valve
Authors: Yonezawa Koichi , Ogi Kanako , Takino Tomofumi , Tsujimoto Yoshinobu , Endo Takahide , Tezuka Kenichi , Morita Ryo , Inada Fumio
Published: March 2011

Control valves of the main steam flow for power plants are operated under wide range of valve openings and pressure ratios. In the present paper, experimental and numerical investigations are described in order to clarify mechanisms of the valve head vibration. Experiments are conducted with two types of the valve head support. One is a flexible support and the other one is with an exciter. Results show that valve head vibrations with large amplitude appear with the flexibly supported valve head under certain range of valve openings and the pressure ratio. With the valve head exciter, dynamic fluid forces are measured. Results show that the added damping force becomes negative around the condition where the valve head oscillation is observed with flexible support. Numerical analyses are carried out in order to observe the flow field. In the simulations, forced vibrations of valve head are assumed. Results show that the pressure distribution on the valve head surface changes depending on the excitation frequencies, and as a result, the negative damping force occurs.
Towards a Model of Vibration for a Cantilevered Mixing Rotor
Authors: Kippers Noel , Holloway Gordon , Gerber Andrew
Published: March 2011

This paper presents an analytic model for a mixing shaft with a standard 45° pitched-blade impeller (PBI) in a baffled mixing vessel. The vibrations and orbits are influenced by a combination of structural and hydrodynamic forces which are sensitive to geometric parameters, fluid properties and rotational speed. Results are included for three water-glycerol mixtures with viscosities of 50 cP, 100 cP and 500 cP and rotational speeds up to 1.3 time the natural frequency of the shaft with both tensile and compressive axial thrust loads resulting from the pitched blades. Experimental results for the expected mean squared vibration response, power spectral densities (PSD) and orbit statistics are presented. A model is presented that explains a number of trends that were experimental observed including asymmetry of the shaft’s vibration amplitude with rotation direction.
Wind Tunnel Studies on the Galloping of Lightly-Iced Transmission Lines
Authors: Fleming Patrick H. , Popplewell Neil
Published: March 2011

The aerodynamics involved in the galloping of lightly-iced transmission lines were studied in a series of wind tunnel experiments. A representative section of a lightly-iced conductor produced in an outdoor freezing rain simulator was used throughout. In the first set of experiments aerodynamic loads were measured on a static model at different wind speeds and angles of attack. These experiments showed that the well-established den Hartog criterion does not predict an instability at wind speeds associated with transmission line galloping. A second set of experiments examined the effects of different steady rotational motions on the aerodynamic loads. Automated controls were used to rotationally oscillate the model in a repeatable manner at various angles of attack and rotational amplitudes as well as frequencies. The drag remained consistent with quasi-steady values, while the lift was affected by the rotational motion. This rotation-induced lift was enhanced by ice surface irregularities, but further studies were needed to fully assess its importance.
Hyperchaotic Behaviour of Shells Subjected to Flow and External Force
Authors: Amabili Marco , Karagiozis Kostas , Pai¨doussis Michael P.
Published: March 2011

This study treats the nonlinear behaviour of cylindrical shells subjected to internal fluid flow and to an external periodic transverse point force. The shell is supported at both ends by axial and rotational springs capable of simulating boundary conditions ranging from clamped to simple supports. This complex boundary condition configuration is preferred in our analysis in order to be able to compare theoretical findings with water-tunnel experiments available in the literature. The external concentrated point force is applied at mid-length of the immersed shell structure acting in the radial direction and the excitation frequency values lie within the spectral neighbourhood of one of the shell’s lowest frequencies for different flow velocities. The structural model is based on the full nonlinear Donnell shell equations of motion including the effect of the in-plane inertia and accounting for geometric imperfections. The fluid is assumed to be incompressible and inviscid and the flow isentropic and irrotational; it is modelled using potential flow theory with the addition of unsteady viscous terms obtained from the time-averaged Navier-Stokes equations. The coupled system is discretized using a solution expansion based on trigonometric functions satisfying the shell boundary conditions exactly. Numerical results show the nonlinear response at different flow velocities for (i) a fixed excitation amplitude and variable excitation frequency, and (ii) fixed excitation frequency varying the excitation amplitude. Bifurcation diagrams of Poincare´ maps obtained from direct time integration are presented, as well as the maximum Lyapunov exponent, in order to classify the system dynamics. In particular, periodic, quasi-periodic, sub-harmonic and chaotic responses have been detected. The full spectrum of the Lyapunov exponents and the Lyapunov dimension have been calculated for the chaotic response; they reveal the occurrence of large-dimension hyperchaos.