Hussein A. Mansy

Quantitative measurements of three-dimensional structures in the wake of a circular cylinder

The fine scale three-dimensional structures usually associated with streamwise vortices in the near wake of a circular cylinder have been studied at Reynolds numbers ranging from 170 to 2200. Spatially continuous velocity measurements along lines parallel to the cylinder axis were obtained with a scanning laser anemometer. To detect the streamwise vortices in the amplitude modulated velocity field, it was necessary to develop a spatial decomposition technique to split the total flow into a primary flow component and a secondary flow component. The primary flow is comprised of the mean flow and Strouhal vortices, while the secondary flow is the result of the three-dimensional streamwise vortices that are the essence of transition to turbulence. The three-dimensional flow amplitude increases in the primary vortex formation region, then saturates shortly after the maximum amplitude in the primary flow is reached. In the near-wake region the wavelength decreases approximately like Re −0.5 , but increases with downstream distance. A discontinuous increase in wavelength occurs below Re = 300 suggesting a fundamental change in the character of the three-dimensional flow. At downstream distances ( x / D = 10-20), the spanwise wavelength decreases from 1.42 D to 1.03 D as the Reynolds number increases from 300 to 1200.

Gastrointestinal sounds and migrating motor complex in fasted humans

Objective:We investigated the relationships among gastrointestinal sounds, gastrointestinal manometric findings, and small intestinal transit time in healthy fasted humans.Methods:Gastrointestinal sounds acquired with two microphones attached to the upper and lower abdominal walls of healthy subjects were quantified with a computer-aided sound analysis program. Antroduodenal contractions were recorded by manometry. Small intestinal transit time was measured by breath hydrogen testing after intraduodenal administration of lactulose.Results:The sum of the gastrointestinal sound amplitudes (sound index) in both the upper and lower abdomen changed with time, coinciding with the gastric phases of the migrating motor complex. The sound indices in the upper and lower abdomen were 59.0 ± 24.8 and 98.1 ± 21.6 mV/min in phase 1, 95.5 ± 27.9 and 127.4 ± 34.9 mV/min in phase 2, and 132.8 ± 12.4 and 188.5 ± 73.4 mV/min in phase 3, respectively. There were no significant differences among motility phases in terms of the mean duration or frequency of each sound event. Intravenous erythromycin induced phase 3 in the stomach and doubled the sound index. Somatostatin analogue induced phase-3–like clustered contractions in the duodenum, but inhibited antral contractions and decreased the sound index. The small intestinal transit time was shorter and the sound index increased after intravenous metoclopramide, compared with controls. Scopolamine delayed small intestinal transit time and decreased the sound index.Conclusions:This study is the first to document the relationships between gastrointestinal sounds and the migrating motor complex. The chronological relation between antral motility and gastrointestinal sounds, and the dissimilar effects of erythromycin and somatostatin, suggest that antral contractions increase gastrointestinal sounds, perhaps by supplying gas into the intestine.

Oblique and parallel wave interaction in the near wake of a circular cylinder

Detailed velocity measurements have been made to investigate the structure of the low‐frequency vortex dislocations that appear in the indigenous wake of a circular cylinder. It is shown that one mechanism for the production of vortex dislocations is the superposition of two waves with slightly different frequencies, where the higher frequency wave is parallel to the cylinder axis and the lower frequency is an oblique wave. In contrast to the discrete vortex concept that implies discontinuous shedding frequencies, the measured amplitude and phase distribution of the interacting waves are shown to be continuous along the span of the cylinder. Both waves (parent modes) exist simultaneously and overlap in the wake. The difference mode associated with the vortex dislocations is produced by the nonlinear interaction of the parent modes, and its maximum amplitude is at the location where the parent modes have comparable magnitude. The spanwise phase and amplitude distributions of the difference mode are ‘‘predi...

THREE-DIMENSIONAL SUBHARMONIC WAVES DURING TRANSITION IN THE NEAR-WAKE REGION OF A CYLINDER

Detailed quantitative measurements of three‐dimensional subharmonic waves have been obtained with a scanning laser anemometer in the near‐wake region of a circular cylinder. A spatial decomposition technique has been used to separate the secondary three‐dimensional flow from the primary Strouhal vortex flow. The appearance of subharmonic frequencies in the spectrum of the secondary instability field at Reynolds numbers of 300 and above provides experimental evidence consistent with the scenario of a period‐doubling route to turbulence. The basic flow structure of the secondary field responsible for producing the subharmonics is shown to be pairs of counter‐rotating streamwise vortices, which alternate the direction of rotation every Strouhal period.

Symmetry of interacting modes in a cylinder wake

The cross‐flow symmetry properties of interacting nonlinear disturbances have been studied experimentally in the wake of a circular cylinder. It is shown using modal decomposition that the interaction between two symmetric or two antisymmetric modes produces symmetric combination modes, while the interaction between a symmetric and an antisymmetric mode produces antisymmetric combination modes.

Flow meter based on the trapped vortex pair fluidic oscillator

A new type of fluidic flow meter is presented, which relies on the hydrodynamic instability resulting from the interaction of a pair of vortices for its operation. The vortices are confined to a convergent channel section of the device and oscillate along approximately elliptical trajectories. The output of the oscillator is a fluctuating pressure signal whose frequency is linearly proportional to the flowrate. One particular configuration of the fluidic oscillator operates over the range 0.227–7.135 (m3/h) with a maximum pressure drop of 63 mm of water and a calibration linearity better than±2.9%. Experiments with both air and water have shown that the fluidic oscillator calibrations are similar when plotted as Strouhal number against Reynolds number.

The effect of abdominal palpation on gastrointestinal sounds (GIS) in healthy subjects: a quantitative investigation using computerized analysis

The effect of abdominal palpation on gastrointestinal sounds (GIS) in healthy subjects: a quantitative investigation using computerized analysis

Choice of operating parameters in heart sound removal from bowel sounds using adaptive filtering

This study is aimed at enhancing bowel sound (or gastrointestinal acoustic phenomena-[GAP]) analysis in an anesthetized rat model. The measured signal at the rats abdominal wall primarily contains infrequent GAP activities against a strong background of ongoing heart sounds (HS). The bandwidth of GAP events overlaps with that of HS rendering use of fixed band-pass filters inadequate. Therefore, an adaptive filter (AF) is necessary. Because no reference signal is readily available, the reference signal is generated by exploiting the low variability in HS properties. Effects of the adaptation parameter and filter order on SNR and GAP distortion due to filtering are discussed. The GAP waveform distortions were minimum for a filter dimension of 1 to 5 points and an adaptation parameter of 5 to 20% of the value at the onset of filter instability. Typical overall SNR enhancement by HS removal with the current system was 25 to 30 dB for a wide range of adaptation parameters and filter dimensions. It is concluded that an AF system can be implemented to study GAP activity in anesthetized rats.

Modeling sound transmission and reflection in the pulmonary system and chest with application to diagnosis of a collapsed lung

Experimental studies have shown that a pneumothorax (collapsed lung) substantially alters the propagation of sound introduced at the mouth of an intubated subject and measured at the chest surface. Thus, it is hypothesized that an inexpensive diagnostic procedure could be developed for detection of a pneumothorax based on a simple acoustic test. In the present study, theoretical models of sound transmission through the pulmonary system and chest region are reviewed in the context of their ability to predict acoustic changes caused by a pneumothorax, as well as other pathologic conditions. Such models could aid in parametric design studies to develop acoustic means of diagnosing pneumothorax and other lung pathologies. Extensions of previously developed simple models of the authors are presented that are in more quantitative agreement with experimental results and that simulate both transmission from the bronchial airways to the chest wall, as well as reflection in the bronchial airways. [Research supporte...

Radiation impedance of a finite circular piston vibrating normal to an isotropic viscoelastic half‐space with application to medical diagnosis

In a recent study [J. Acoust. Soc. Am. 106, 3678–3686 (1999)], a new analytical solution was developed and validated experimentally for the problem of surface wave generation on a linear viscoelastic half‐space by a rigid circular disk located on the surface and oscillating normal to it. The results of that study suggested that, for the low audible frequency range, some previously reported values of shear viscosity for soft biological tissues may be inaccurate. Those values were determined by matching radiation impedance measurements with theoretical calculations reported previously [J. Acoust. Soc. Am. 23, 707–714 (1951)]. In the current study, the new derivation is extended to the calculation of radiation impedance. Comparisons are made with prior theory and experiments to determine which theory is more accurate and what range of values for shear viscosity is more accurate. Measurement of skin surface radiation impedance has been studied by a few researchers for rapid, nonintrusive diagnosis of a variet...