Добірка наукової літератури з теми "Narrow rigid tube"

The earlier constitutive model of Fang & Owens (Biorheology, vol. 43, 2006, p. 637) and Owens (J. Non-Newtonian Fluid Mech. vol. 140, 2006, p. 57) is extended in scope to include non-homogeneous flows of healthy human blood. Application is made to steady axisymmetric flow in rigid-walled tubes. The new model features stress-induced cell migration in narrow tubes and accurately predicts the Fåhraeus–Lindqvist effect whereby the apparent viscosity of healthy blood decreases as a function of tube diameter in sufficiently small vessels. That this is due to the development of a slippage layer of cell-depleted fluid near the vessel walls and a decrease in the tube haematocrit is demonstrated from the numerical results. Although clearly influential, the reduction in tube haematocrit observed in small-vessel blood flow (the so-called Fåhraeus effect) does not therefore entirely explain the Fåhraeus–Lindqvist effect.

When blood flows slowly in a narrow tube, red-cell aggregation results in formation of an approximately cylindrical “core” of red cells, which moves as a rigid body. The core is denser than the surrounding fluid, and sedimentation is observed in horizontal tubes. To model this, the Stokes flow of a fluid surrounding a long solid cylinder (the core) contained in a long hollow cylinder (the tube) is considered. The cylinder axes are parallel but not coincident. An exact analytic expression for the resistance coefficient for motion perpendicular to the axes is given. This coefficient increases rapidly with the ratio of core radius to tube radius, and core eccentricity. The predicted rate of sedimentation is comparable to that observed experimentally. The apparent viscosity of a two-phase medium consisting of a core of aggregated particles and surrounding pure fluid is calculated. For a core radius corresponding to experimental conditions, the apparent viscosity increases rapidly with increasing eccentricity of the core.

Secondary bending moment and geometric nonlinearity should be taken into account in pipe tower design. Taking the 110kV double-circuit narrow-base steel pipe tower as an example, the 110 kV double-circuit narrow-base steel pipe tower is compared and analyzed through the tower structure design software and the general finite element software ANSYS. The analysis results show that the narrow-base steel tube tower should adopt a rigid-truss structure model, and the influence of the secondary bending moment of the main material and the geometric nonlinearity should be considered. The secondary bending moment effect accounts for about 10-20% of the strength stress of the steel pipe main material. Through comparative analysis, a number of design points are summarized, which provides a certain practical guiding significance for the design and application of the double-circuit narrow-base steel pipe tower.

An analysis is presented of the mechanics of red blood cells flowing in very narrow tubes. Mammalian red cells are highly flexible, but their deformations satisfy two significant constraints. They must deform at constant volume, because the contents of the cell are incompressible, and also at nearly constant surface area, because the red cell membrane strongly resists dilation. Consequently, there exists a minimal tube diameter below which passage of intact cells is not possible. A cell in a tube with this diameter has its critical shape: a cylinder with hemispherical ends. Here, flow of red cells in tubes with near-minimal diameters is analysed using lubrication theory. When the tube diameter is slightly larger than the minimal value, the cell shape is close to its shape in the critical case. However, the rear end of the cell becomes flattened and then concave with a relatively small further increase in the diameter. The changes in cell shape and the resulting rheological parameters are analysed using matched asymptotic expansions for the high-velocity limit and using numerical solutions. Predictions of rheological parameters are also obtained using the assumption that the cell is effectively rigid with its critical shape, yielding very similar results. A rapid decrease in the apparent viscosity of red cell suspensions with increasing tube diameter is predicted over the range of diameters considered. The red cell velocity is found to exceed the mean bulk velocity by an amount that increases with increasing tube diameter.

The hydrodynamic influence of deformable porous surface layers on the motion of a rigid sphere falling in a narrow cylindrical tube filled with a stationary Newtonian fluid is studied using lubrication theory. The porous layers on both the surface of the tube and the sphere are modelled as binary mixtures of solid and liquid components. The sphere is placed at an arbitrary position in the tube and is free to rotate. Effects of the clearance between the sphere and the tube, the eccentricity of the position of the sphere and the properties of the surface layers on the velocity and rotation of the sphere are studied. It is found that, when the lengthscale on which the velocity varies within the porous layer is much smaller than the clearance, the effects of the porous layer can be represented by an equivalent slip boundary condition, the slip velocity at the boundary being proportional to the local shear rate. The slip velocities have a strong influence on the motion of the sphere when the clearance is small. For a given clearance and slip parameters, both the falling and rotation velocities of the sphere increase with the sphere eccentricity. The shear stresses on the surfaces of both the tube and the sphere are greatly reduced when slip boundary conditions are applied, as is the pressure gradient in the region between the sphere and the tube wall. This work could have some relevance to the creeping motion of blood cells in the microcirculation where the glycocalyx, a polysaccharide-rich layer, covers the external surfaces of both endothelial and red blood cells.

The motion of a rigid ellipsoidal particle freely suspended in a Poiseuille flow of an incompressible Newtonian fluid through a narrow tube is studied numerically in the zero-Reynolds-number limit. It is assumed that the effect of inertia forces on the motion of the particle and the fluid can be neglected and that no forces or torques act on the particle. The Stokes equation is solved by a finite element method for various positions and orientations of the particle to yield the instantaneous velocity of the particle as well as the flow field around it, and the particle trajectories are determined for different initial configurations. A prolate spheroid is found to either tumble or oscillate in rotation, depending on the particle–tube size ratio, the axis ratio of the particle, and the initial conditions. A large oblate spheroid may approach asymptotically a steady, stable configuration, at which it is located close to the tube centreline, with its major axis slightly tilted from the undisturbed flow direction. The motion of non-axisymmetric ellipsoids is also illustrated and discussed with emphasis on the effect of the particle shape and size.

In the development of telemanipulated surgical robots, a class of continuum robots known as concentric tube robots has drawn particular interest for clinical applications in which space is a major limitation. One such application is transnasal surgery, which is used to access surgical sites in the sinuses and at the skull base. Current techniques for performing these procedures require surgeons to maneuver multiple rigid tools through the narrow confines of the nasal passages, leaving them with limited dexterity at the surgical site. In this article, we present a complete robotic system for transnasal surgery featuring concentric tube manipulators. It illustrates a bagging concept for sterility, and intraoperatively interchangeable instruments that work in conjunction with it, which were developed with operating room workflow compatibility in mind. The system also includes a new modular, portable surgeon console, a variable view-angle endoscope to facilitate surgical field visualization, and custom motor control electronics. Furthermore, we demonstrate elastic instability avoidance for the first time on a physical prototype in a geometrically accurate surgical scenario, which facilitates use of higher curvature tubes than could otherwise be used safely in this application. From a surgical application perspective, this article presents the first robotic approach to removing tumors growing behind the eyes in the orbital apex region, which has not been attempted previously with a surgical robot.

The main character distinguishing Minibiotus from Macrobiotus is the presence of peribuccal papulae instead of lamellae. However, most Minibiotus species also share a set of characters of the bucco-pharyngeal apparatus. This set is defined by ten morphological features (the first seven common to all species, the last three to most of them): antero-ventral mouth (1), teeth in oral cavity absent or strongly reduced (2), a rigid and narrow buccal tube (3), buccal tube wall thickened below the point of insertion of stylet supports (4), stylet supports inserted at considerable distance from the posterior end of the buccal tube (5), short ventral lamina (6), short macroplacoid row length (7), a double curvature of the buccal tube (8), first macroplacoid situated very close to the pharyngeal apophysis (9) and three almost rounded macroplacoids (10). We examined the original descriptions and/or the type material of several species belonging to the genus Macrobiotus that seemed to present this set of characters. It was concluded that several species should be transferred from Macrobiotus to Minibiotus. The following new combinations are proposed: Minibiotus subintermedius (Ramazzotti, 1962) comb. n., Minibiotus pustulatus (Ramazzotti, 1959) comb. n., Minibiotus julietae (de Barros, 1942) comb. n., Minibiotus marcusi (de Barros, 1942) comb. n., Minibiotus granatai (Pardi, 1941) comb. n., Minibiotus allani (Murray, 1913) comb. n., Minibiotus crassidens (Murray, 1907) comb. n. and Minibiotus acontistus (de Barros, 1942) comb. n.. As a result of these new combinations, the genera Minibiotus and Macrobiotus appear to be more homogeneous, but their monophyly has not yet been demonstrated. Further data are necessary to better analyze the systematic position of Macrobiotus lazzaroi Maucci, 1986, Macrobiotus spertii Ramazzotti, 1957 and Macrobiotus striatus Mihelčič, 1949.

Dear Editor: Time has proven that endoscopy is generally a safe and effective tool in the diagnosis and treatment of various conditions. It offers superior visualization with markedly decreased morbidity and mortality. In Otolaryngology, otoendoscopy has been gaining acceptance in providing improved otoscopic visualization and video recording of the tympanic membrane. We describe a technique of myringotomy and ventilation tube insertion under endoscopic visualization using a rigid Hopkins rod scope previously described by other authors based on their accepted clinical guidelines for myringotomy. 1,2 The use of rigid endoscopes provides visualization of the entire tympanic membrane with excellent resolution, better fidelity of color with a well-angled or side-to-side vision. The procedure is generally safe, convenient and can be performed in an out-patient setting. Correspondingly, the video recordings could improve disease documentation for baseline and post-myringotomy evaluation. They can also be a tool to enable better understanding for patients.3 Materials and Methods A total of seven (n=7) patients with symptomatic and non-resolving otitis media with effusion (OME) previously managed conservatively for 3-6 months from October 2009 to March 2010 were included in the study. The patients also had disabling otalgia with 4 of the subjects having more than 30 dB hearing loss. Subjects who had poor pain threshold, were deemed non-cooperative and those in the pediatric age group were excluded from the study. Informed consent with strict compliance to institutional ethical standards was signed by all patients. The procedures were all performed by the junior author at the E.N.T Diagnostic Unit of a private tertiary university hospital. Materials used for the procedure were the same as with conventional myringotomy (eg. aural speculum, Kley or sickle knife, Hartmann ear forceps and ventilation tube/s). The anesthetic used was an Eutectic Mixture of Local Anesthesia (EMLA®) cream 5 % (Astra-Zeneca, Sodertalje, Sweden) in a 1 cc tuberculin syringe, and 20-25% aqueous form of phenol solution. A 0 degree 4mm x 107.5mm rigid endoscope (KARL STORZ GmbH & Co. KG Mittelstr., Tuttlingen, Germany) was used. (Figure 1) First an otoendoscopy was performed and the clinical indications and risks for myringotomy were thoroughly discussed with each patient. EMLA® cream was applied to the ear canal and to the external surface of the tympanic membrane using a 1 cc tuberculin syringe. After 60 minutes, the external ear canal was cleared for complete visualization of the tympanic membrane. (Figure 2) The patient was then positioned seated on the examining chair with head tilted to the opposite side. Using a 0 degree 4mm x 107.5mm rigid endoscope, the posterior third of the external auditory canal and the tympanic membrane was visualized. The scope was held with the left hand only up to the anterior portion of the cartilaginous canal to avoid involuntary activation of the Xth cranial nerve and to allow further advancement of other instruments to the posterior canal. A shorter rigid otoendoscope (4mm x 45mm) or a smaller diameter pediatric rigid endoscope (2.7mm x 107.5mm) may be used if available. A Kley knife or myringotomy knife was dipped lightly in phenol solution and carefully advanced to the tympanic membrane for the preferred myringotomy stab incision. (Figure 3) Care was taken to avoid contact of the phenol and knife tip with the canal wall to avoid stimulating unnecessary movement, canal abrasion or dermal irritation from the phenol solution during the entire procedure. (Figure 3) The myringotomy incisions were made at the posterior-inferior tympanic membrane quadrant for ease of access and drainage. (Figure 4) Evacuation of middle ear fluid was performed using a 2 and 3 mm Frazer middle ear suction tip. The myringotomy incision was made large enough to admit the ventilation tube in four subjects with copious effusions. In these four, the tube was introduced and adjusted using a 1 mm x 8 cm (working length) Hartmann ear forceps. A 1.14 mm I.D. Armstrong beveled fluoroplastic grommet ventilation tube (Xomed, Jocksonville, FL) was used in 3 subjects while a Sheehy collar button tube without wire (Micromedics Inc, St. Paul, Minnesota,USA) was used in one. The choice of tube depended mainly on the authors’ preference, taking tube designs available for specific ear conditions into consideration. (Figure 4) All subjects were instructed to avoid vigorous activities for the first 48 hours post-myringotomy, with strict water precautions. Ofloxacin otic drops were then prescribed. Results There were a total of 7 patients, 3 males and 4 females, with age ranging from 25 to 65 years (mean=50). All of them tolerated the procedure well. Ventilation tubes were inserted in 4 subjects with copious middle ear effusions. All had minimal intra-operative (PAS 2-5) and post-operative pain (PAS 0-2). The procedures were done on an out-patient basis. Co-morbid conditions were likewise treated (Table 1). Six out of the seven subjects experienced immediate subjective relief of otalgia and hearing loss after myringotomy while one subject had persistent complaint of ear fullness. The main indication for the procedure was otitis media with effusion with significant hearing loss, otalgia and ear fullness non-responsive to 3 months conservative management. All patients had significant contributing factors for OME such as frequent infectious rhinitis or chronic persistent allergic rhinitis. Six of the 7 subjects had markedly improved hearing. Four subjects with a preoperative pure-tone evaluation of >30-40 dB hearing loss had pure-tone average improvement to 10-15 dB after subsequent hearing examinations. All subjects were evaluated post-operatively with otoendoscopy. One case was unresponsive and subsequently diagnosed with adhesive otitis media and advised to undergo myringoplasty. Discussion Endoscopic myringotomy under topical anesthesia is a generally safe and practical procedure. Its indications are the same with conventional myringotomy with or without ventilation tube insertion such as Otitis Media with Effusion persisting beyond 3 months with associated significant hearing loss, impending mastoiditis or intracranial complications, recurrent episodes of acute otitis media (> 3 episodes in 6 months or > 4 episodes in 12 months), chronic tympanic membrane or pars flaccida, barotrauma, autophony (hearing body sounds; eg. breathing) due to patulous or widely open eustachean tube, craniofacial anomalies predisposing to middle ear dysfunction (e.g. cleft palate), and middle ear dysfunction due to head and neck radiation and skull base surgery.4 Endoscopic visualization of the tympanic membrane enables better patient understanding of their ear conditions. Such has been the basis for the procedure along with the use of 5% EMLA® to decrease the pain and discomfort of patients undergoing out-patient myringotomy procedures.5 Phenol on the other hand aids in faster creation of tympanic membrane incision and decreases post-operative bleeding through its tissue vaporizing chemical cauterization effect with negligible toxicity if given in minute amount.6 Furthermore for post-operative cases of middle ear surgeries, it can be used for surveillance and middle ear cleaning. This can improve post-operative follow-up and possibly decrease the need for second look surgery.7 Generally, endoscopic myringotomy provides a complete and enhanced visualization of the tympanic membrane and some middle ear structures that only appear as silhouettes with conventional otoscopy. Rigid endoscopes may have less illumination and magnification compared to an operating microscope traditionally used in myringotomy procedures but it can provide an angled or “off line-of-site” visualization of the tympanic membrane and canal wall advantageous in trans-canal visualization of the tympanic membrane. Just like the conventional out-patient myringotomy, endoscopic myringotomy under topical anesthesia is less costly than performing the procedure under general anesthesia or through sedation requiring a more controlled clinical setting. Smaller diameter and shorter endoscopes may be more feasible for diagnostic otoendoscopy, but a rigid 4 mm endoscope is more widely available in most local clinics. The major disadvantage of this procedure is the instrumentation in very young or uncooperative patients with a narrow external auditory canal. One-handed instrumentation and lens fogging may also be encountered but can be reduced with familiarity with the procedure. The indications for endoscopic myringotomy as with those for traditional myringotomy remain suggestions and do not represent the standard of care. Clinicians can modify them when medically necessary as treatment options should always be individualized to meet each patient’s need. Failure to improve hearing may suggest another middle ear condition that necessitates further evaluation. Some cases may need myringotomy tube replacement while surgery is reserved for failed tympanic membrane healing. Lastly, like any other surgical technique and instrumentation, the major key to a successful endoscopic myringotomy is still good patient selection.

Акустичне моделювання слухових функцій людини потребує створення математичної моделі сприйняття звуку зовнішнім відділом слухової системи, яка є невід’ємною частиною слухового апарату. На сьогоднішній день акустичне моделювання зовнішнього вуха не розглядалося, оскільки увага приділялася тільки проходженню звуку через зовнішній слуховий канал, а роль вушної раковини у сприйнятті звуку вважалася несуттєвою. Зв’язок роботи з науковими програмами, планами, темами Робота виконується на замовлення виробничого об’єднання «Фонтек–С» з ціллю впровадження у подальші розробки звукових сигналізаційних пристроїв. Мета і задачі дослідження. Розробити математичну модель зовнішнього вуха у вигляді поєднання приймального рупора з вузькою трубою із жорсткими стінками. Для досягнення мети необхідно виконати наступні завдання: - розробити математичну модель зовнішнього вуха; - виконати огляд строгих та наближених підходів до розрахунків звукового поля в рупорах різних форм; - розрахувати елементи математичної моделі; - дослідити роботу математичної моделі; - виконати аналіз отриманих результатів;
Acoustic modeling of auditory functions of a person requires the creation of a mathematical model for the perception of sound by the external department of the auditory system, which is an integral part of the auditory apparatus. Today, the acoustic modeling of the external ear has not been considered, since attention was paid only to the passage of sound through the external auditory canal, and the role of the ear bowl in the perception of sound was considered insignificant. Relationship of work with scientific programs, plans, themes The work is carried out on request of the production association "Fontec-C" for the purpose of further development of sound signaling devices. The purpose and tasks of the study. Develop a mathematical model of the external ear in the form of a combination of a horn with a narrow tube with rigid walls. To achieve the goal, you must accomplish the following tasks: - develop a mathematical model of the external ear; - to perform a review of strict and close approaches to the calculation of the sound field in the horns of various forms; - calculate the elements of the mathematical model; - to study the work of mathematical model; - to analyze the results obtained;
Акустическое моделирование слуховых функций человека требует создания математической модели восприятия звука внешним отделом слуховой системы, которая является неотъемлемой частью слухового аппарата. на сегодняшний день акустическое моделирование наружного уха не рассматривался, поскольку внимание уделялось только прохождению звука через внешний слуховой канал, а роль ушной раковины в восприятии звука считалась несущественной. Связь работы с научными программами, планами, темами Работа выполняется по заказу производственного объединения «Фонтек-С» с целью внедрения в дальнейшие разработки звуковых сигнализационных устройств. Цель и задачи исследования. Разработать математическую модель внешнего уши в виде сочетания приемного рупора с узкой трубой с жесткими стенками. Для достижения цели необходимо выполнить следующие задачи: - разработать математическую модель внешнего уха; - выполнить обзор строгих и приближенных подходов к расчетов звукового поля в рупор различных форм; - рассчитать элементы математической модели; - исследовать работу математической модели; - выполнить анализ полученных результатов;

A multibody transportation system that moves with fluid inside a small-diameter tube has been studied by a lot of researchers. It is expected to be developed for future engineering applications such as a micro machine that transports medicines to a certain part of a body. This paper deals with the flow characteristics around a single rigid body and transient motion of the body when a body is influenced by pressure force from upstream. The model considered a body smaller than a diameter of a tube so that the force on the body can be numerically and analytically estimated as viscous friction force. It was assumed that the flow is axisymmetric, laminar and taken to be Newtonian and incompressible. It was obtained that the axial component of the fluid velocity decreases and pressure increases near the body like stagnation flow. Moreover, the pressure rapidly increases behind the body and decreases in front of the body with increasing diameter of the body.

A multibody system that moves with fluid inside a small-diameter tube is applied to some parts of industry such as a PIG and it is also expected to be developed for future engineering applications. As a first step to considering a multibody system, this study focused on elucidating the flow characteristics around a single rigid body and understanding the effect of a bypass hole. The model considered has been a single rigid body moving at a constant velocity in a narrow tube. Assuming that the flow is steady axisymmetric laminar flow, the fluid flow around the body has been experimentally observed and numerically analyzed. A Rankine’s combined vortex was observed around the body and it was also observed that a layer of fluid near the top wall has characteristics of the boundary layer. Furthermore, a minimum allowable thickness of a bypass hole to cause the successful front-drive effect was obtained.

Abstract The added mass coefficient is an important parameter when calculating the flow induced vibration (FIV) in heat exchangers. The calculation method of the added mass coefficient for tube bundles in triangular and square arrays had been presented in relevant standards which like GB/T 151. Presently, concentric arrays of tube bundles are applied extensively in the heat exchangers at nuclear power plants. However, the method for calculating the added mass coefficient of tube bundles in concentric arrays has not been given in these standards. In this paper, in order to calculate the added mass coefficient of a central flexible tube surrounded by rigid tubes in concentric arrays, the fluid-structure interaction models of tube bundles has been established by ANSYS CFX. The influence of the circumferential and radial distance of the tube bundles on the added mass coefficient has been studied by calculating the natural frequency. The results are expected to provide the calculation reference for added mass coefficient of the tube bundles in concentric arrays. The coupling vibration of tube bundles in concentric arrays has been studied by the other model which is made up of all the flexible tubes, and the coupling vibration of the tube bundles is simulated by the rigid wall motion of ANSYS CFX. According to simulation results, there exists a band of amplitude peaks in the coupling vibration of the tube bundles. It is shown that as the circumferential and radial distance increases, the band of amplitude peaks becomes narrow.

A rigid body moving with fluid in a narrow tube is expected to be developed for future engineering applications such as a capsule endoscopy, and it is also applied to some parts of industry. This paper deals with the flow characteristics around a single rigid body with a hole in its center and transient motion of the body when the body is influenced by pressure force from upstream. The model considered the width of the gap between the body and the wall is smaller than a diameter of a tube so that the force on the body can be numerically and analytically estimated as a viscous friction force. It was assumed that the flow is axisymmetric, laminar and taken to be Newtonian and incompressible. It was obtained that, with the hole in its center, the terminal velocity of the body becomes smaller than the average velocity at the inlet. Moreover, because there is a stagnation on the body, the pressure increases behind the body.