Maximum External Pressure Research Articles

Mathematical modeling of corneal hysteresis

Mathematical modeling of the deformation of the eyeball under the external pressure applied to the cornea in a bounded area and gradually increasing and then decreasing according to a given law is performed. This relationship corresponds to the change in applied pressure in the ocular response analyzer (ORA) used in clinic. An approach pre-viously developed by the authors is applied, based on representing the cornea as a soft two-dimensional surface and the scleral region as a zero-dimensional element. Since the process under consideration occurs very quickly (lasting several tens of milliseconds), it cannot be considered as purely elastic. The Voigt viscoelasticity of the cornea is taken into account, the smallness of the strain relaxation time allowing us to consider the solu-tion as a correction to a similar purely elastic problem considered at the previous stage of research. The behavior of two parameters characterizing the asymmetry of the system's response to a symmetrical action is studied. These are the delay time of the moment of maximum flattening of the cornea in the apical region during unloading compared to the moment of its flattening during loading and the difference in external pressures at which these flattenings are reached (corneal hysteresis). Their values obtained from the simula-tion are of the same order as the same values determined experimentally. It is shown that hysteresis increases with increasing strain relaxation time and with increasing maximum external pressure.

Effects of ignition location and vent area on the external explosion in vented hydrogen explosions

In the current study, effects of vent area and ignition location on vented stoichiometric hydrogen-air mixture explosion were experimentally and numerically investigated. Internal and external pressure-time curves and flame behavior were focused. For low vent coefficient Kv = 4, the maximum internal pressure results from the vent rupture for front ignition and the external explosion for center ignition and rear ignition. The maximum internal pressure for IL4 is larger than those for other ignition locations. The maximum internal pressure is induced by the internal chemical reaction and increases monotonically with Kv for different ignition locations, and the maximum internal pressure occurs at center ignition as Kv ＞ 4. Mach disk in external flame begins to appear when Kv increases to 12.75 for front ignition and 8.65 for other ignition locations. External pressure histories show two pressure peaks P1 and P2 for center and rear ignitions. Although the pressure peak P1 results from the leading pressure wave, the pressure peak P2 is induced by the venting flame and external explosion for center ignition and rear ignition, respectively. Only one pressure peak was recorded for center ignition. For front ignition and IL2, the maximum external pressure increases with Kv while it firstly increases and then decreases for center ignition, IL4 and rear ignition, the critical value is Kv = 17.36 for center ignition and IL4 while it is Kv = 8.65 for rear ignition.

Investigation of the length-to-diameter ratio of ducts effect on the oscillation propagation behavior and vented characteristics for propane-air vented explosions

The effects of length-to-diameter (L/D) ratio on oscillation propagation behavior and vented characteristics of propane explosions have been explored in a rectangular explosion duct. The results show that as the L/D ratio increased, the turbulence of the internal flame was enhanced, and the flame area and gas reaction rate increased sharply, which promoted the appearance of the Mach diamond structure in the vented flame. Due to heat and energy loss, the maximum reduced pressure (Pred) decreased with the increase of L/D ratio, but the maximum pressure rise rate ((dp/dt)max) and the deflagration index (KG) still increased significantly. Besides, the venting diameter (Dv) where the maximum external pressure was obtained increased with the L/D ratio, and the critical venting diameters of the vented propane-air explosions to reach the equilibrium venting state under different L/D ratios were determined. An empirically modified model of Pred was established by introducing the L/D ratio and vent coefficient KV, and the maximum relative error of this model is 137% lower than that of the international standard model. The excellent performance of the results would provide a new idea for the venting safety design of the large L/D ratio duct in process industry applications.

Experimental investigation of the vented propane-air explosion characteristics at elevated static activation pressures in a large L/D duct

The flame behavior and pressure characteristics of vented propane-air explosions at elevated static activation pressures (Pstat) were investigated in a duct with a length-to-diameter (L/D) ratio of 7. The impact of the discharge traction and the coupling effect of the internal flame front and pressure waves on the flame propagation behavior were captured. The effect of increasing Pstat on the vented flame length and width under a fixed vent was weak. The influences of Pstat on the pressure profiles and maximum reduced pressure (Pred) were investigated. The increase of Pstat mitigated the blocking effect of external explosion on Pred and further promoted the discharge pressure drop rate to be controlled within the limit of the discharge capacity of the vent. The formation mechanisms of the two main external pressure peaks were analyzed. For the larger Dv conditions, the sensitivity of high Pstat to the increase of maximum external pressure was higher than that of low Pstat. A modified model of Pred was developed considering the effects of elevated Pstat and vent coefficient KV, which is proved to have a good performance in vented explosion ducts with a large L/D ratio.

Effects of ignition location on the characteristics of dust explosion venting at elevated static activation pressure

The effect of ignition location on the pressure characteristics of vented dust explosion was investigated in a 20 L chamber. For internal pressure, the proportion of the venting mixture with different ignition locations coupled with the wall quenching effect dominated the internal pressure curves. Besides, the maximum pressure rise rate was controlled by the residual amount of the fuel and induced turbulence. For external pressure, the ignition location dominated the delay time of the external explosion and the number of pressure peaks. Furthermore, the generation mechanism of pressure peaks was revealed by external pressure curves together with the visualization of the flow field. Eventually, it was found that both the internal and external maximum pressure with central ignition was larger than rear-end ignition and then the front-end. The corresponding dynamic mechanism was theoretically revealed, and a dimensionless prediction model for venting size and maximum external pressure was established.

Analysis of external pressure on the left calf in the Lloyd-Davies position during colorectal surgery.

Well-leg compartment syndrome (WLCS) is a potentially life-threatening postoperative complication related to the Lloyd-Davies surgical position, which can place increased external pressure on the calf region. We conducted this study to analyze external pressure changes, by applying a leg holder system to the left calf region of patients placed in the Lloyd-Davies position during laparoscopic surgery. The study participants were 50 patients who underwent laparoscopic surgery for colorectal cancer in the Lloyd-Davies position. We assessed the maximum external pressure (MEP) on the left calf region using a pressure-distribution measurement system. Intraoperative measurements were taken continuously, and the MEP was evaluated with the patient horizontal and every 30min during surgery in the head and right-down tilt position. The intraoperative MEP increased gradually when the patient was in the head and right-down tilt position and decreased when the patient was returned to the horizontal position. The MEP was higher in patients aged < 60years, those who were obese, and those with a thick calf circumference. Both body mass index (BMI) and the maximum left calf circumference (MLCC) were found to correlate with the MEP. In addition to a high BMI, which is a well-known risk factor for WLCS, a high MLCC should be considered another risk factor, especially for patients under 60years.

IBEX Ribbon Separation Using Spherical Harmonic Decomposition of the Globally Distributed Flux

Abstract Remote imaging of plasmas in the heliosphere and very local interstellar medium is possible with energetic neutral atoms (ENAs), created through the charge exchange of protons with interstellar neutral atoms. ENA observations collected by the Interstellar Boundary Explorer (IBEX) revealed two distinctive sources. One source is the globally distributed flux (GDF), which extends over the entire sky and varies over large spatial scales. The other source encompasses only a narrow circular band in the sky and is called the IBEX ribbon. Here, we utilize the observed difference in spatial scales of these two ENA sources to separate them. We find that linear combinations of spherical harmonics up to degree ℓ max = 3 can reproduce most of the ENA fluxes observed outside the ribbon region. We use these combinations to model the GDF and the difference between the observed fluxes and the GDF yields estimation of the ribbon emission. The separated ribbon responds with a longer time delay to the solar wind changes than the GDF, suggesting a more distant source of the ribbon ENAs. Moreover, we locate the direction of the maximum plasma pressure based on the GDF. This direction is 17°.2 ± 0°.5 away from the upwind direction within the plane containing the interstellar flow and interstellar magnetic field vectors. This deflection is consistent with the expected position of the maximum external pressure at the heliopause. The maps with separated ribbon and GDF are posted concurrently with this paper and can be used to further study these two sources.

Analytical prediction of buckling collapse for reinforced thermoplastic pipes based on hoop stress analysis of crushed rings

Reinforced thermoplastic pipes (RTPs) can experience collapse under external pressure. The maximum external pressure that RTPs can resist before buckling collapse must be considered in engineering practice. To predict the critical pressure of RTPs, a new analytical model is proposed by analyzing the hoop stress distributions of crushed rings. The model is made under the assumption that the maximum hoop stress equals the critical stress when pipes collapse. Different from the previously reported studies, focusing on axial compression, the critical stress of cylinders' buckling under crushing loads is formulated. With regard to the material anisotropy of RTPs, the equivalent stiffness method is applied to obtain the homogenized hoop elastic modulus in the proposed model. The effectiveness of the proposed model is verified by eigenvalue analyses on solid models and continuum shell models. Compared with numerical methods and Timoshenko and Gere (1961), the proposed model was found to give accurate critical pressures and hoop stress distributions. Furthermore, the optimal range for fiber’s winding angle is obtained, and the effect of thickness-radius ratios on critical pressure and the disproportionate motions of singularity points are also discussed.

Numerical Investigation on Critical Tunnel Length of Maximum External Pressure Change of High-Speed Train

This study describes the numerical investigations to estimate the critical tunnel length. A one-dimensional compressible unsteady non-homentropic flow model, and method of characteristics of generalized Riemann variables is adopted. Then, the critical tunnel length of 1) maximum positive pressure change, 2) maximum negative pressure change and 3) peak-peak pressure change is obtained. The difference between obtained critical tunnel length of maximum positive pressure change and maximum negative pressure change and that from formulas of EN 14067-5 and other scholar is investigated. The comparison shows that the critical tunnel length by our method is close to the formulas. In addition, the critical tunnel length of peak-peak pressure change which is more helpful to the fatigue design of train body and components is delivered. The method in this paper has been proved to be an efficient approach to obtain the critical tunnel length.

Imperfection sensitivity of pressured buckling of biopolymer spherical shells.

Imperfection sensitivity is essential for mechanical behavior of biopolymer shells [such as ultrasound contrast agents (UCAs) and spherical viruses] characterized by high geometric heterogeneity. In this work, an imperfection sensitivity analysis is conducted based on a refined shell model recently developed for spherical biopolymer shells of high structural heterogeneity and thickness nonuniformity. The influence of related parameters (including the ratio of radius to average shell thickness, the ratio of transverse shear modulus to in-plane shear modulus, and the ratio of effective bending thickness to average shell thickness) on imperfection sensitivity is examined for pressured buckling. Our results show that the ratio of effective bending thickness to average shell thickness has a major effect on the imperfection sensitivity, while the effect of the ratio of transverse shear modulus to in-plane shear modulus is usually negligible. For example, with physically realistic parameters for typical imperfect spherical biopolymer shells, the present model predicts that actual maximum external pressure could be reduced to as low as 60% of that of a perfect UCA spherical shell or 55%-65% of that of a perfect spherical virus shell, respectively. The moderate imperfection sensitivity of spherical biopolymer shells with physically realistic imperfection is largely attributed to the fact that biopolymer shells are relatively thicker (defined by smaller radius-to-thickness ratio) and therefore practically realistic imperfection amplitude normalized by thickness is very small as compared to that of classical elastic thin shells which have much larger radius-to-thickness ratio.

Buckling collapse study for the carcass layer of flexible pipes using a strain energy equivalence method

When a flexible pipe is subjected to high external hydraulic pressure, the innermost carcass layer serves to resist buckling and collapse. The maximum external pressure that the carcass layer can withstand before buckling collapse must be considered during pipe design. To study this problem, a strain energy equivalence method is proposed to transform a representative volume element (RVE) of the carcass layer, which has a complex geometry, into a homogeneous shell with an equivalent thickness. To obtain the strain energy, a finite element model of the RVE is developed, and the analytical equations for the homogeneous shell are derived for the same uniform-strain boundary conditions. Radial compression tests on three different carcass layer test pieces are performed to verify the safety and effectiveness of the proposed equivalence method. The strain energy equivalence method is found to give conservative results when compared to other equivalence approaches. The advantages of the method for designing a collapse-resistant carcass layer in engineering practice are also discussed.

Effects on external pressures caused by vented explosion of methane‐air mixtures in single and connected vessels

An experimental apparatus was built to study the external pressure caused by vented explosions of methane and air mixtures. In some circumstances, two peak points of external pressure induced by vented explosion appear. One of the peaks is caused by the vented flow from the vessel while the other one is due to the vented flow from the vessel or external explosion. Both the maximum external pressure and pressure rising rate increase with initial pressure, explosion venting pressure and vent diameter of the vented vessel. The maximum external pressure and pressure rising rate decrease with the volume of the vessel. The maximum pressure and the maximum pressure increase rate occur when the methane concentration is 9.5%. Compared with explosion outside one single big vessel, explosion outside the connected vessels is more severe. The external pressure caused by ignition in the center of the small vessel is higher than that in the center of the big vessel while the external pressure rising rate caused by ignition in the center of the small vessel is lower than that in the center of the big vessel. © 2014 American Institute of Chemical Engineers Process Saf Prog 33: 385–391, 2014

축방향 및 원주방향 관통균열이 존재하는 나선형 전열관의 파손 외압 평가

Once-through helically coiled steam generator tubes subjected to external pressure are of interest because of their application to advanced small- and medium-sized integral reactors, in which a primary coolant with a relatively higher pressure flows outside the tubes, while secondary water with a relatively lower pressure flows inside the tubes. Another notable point is that the values of the mean radius to thickness ratio of these steam generator tubes are very small, which means that a thick-walled cylinder is employed for these steam generator tubes. In the present paper, the maximum allowable pressure of helically coiled and thick-walled steam generator tubes with through-wall cracks under external pressure is investigated based on a detailed nonlinear three-dimensional finite element analysis. In terms of the crack orientation, either circumferential or axial through-wall cracks are considered. In particular, in order to quantify the effect of the crack location on the maximum external pressure, these cracks are assumed to be located in the intrados, extrados, and flank of helically coiled cylinders. Moreover, an evaluation is also made of how the maximum external pressure is affected by the ovality, which might be inherently induced during the tube coiling process used to fabricate the helically coiled steam generator tubes.

Tailoring of Composite Reinforcements for Weight Reduction of Offshore Production Risers

The use of composite materials in offshore engineering for deep sea oil production riser systems would lead to weight savings and improvement in fatigue and corrosion resistance. This paper examines the weight saving potentials offered by varying fibre orientations, stacking sequences, fibre matrix combinations and liner materials for deep sea riser tubulars. Four main load cases, recommended by design standards for the local design of composite offshore risers, are considered in the analysis using three-dimensional finite element modelling: maximum internal pressure, axial tension, top tension with external pressure and maximum external pressure.

Microstructure and mechanical properties of pulsed electric current sintered B4C–TiB2 composites

Monolithic B4C, TiB2 and B4C–TiB2 particulate composites were consolidated without sintering additives by means of pulsed electric current sintering in vacuum. Sintering studies on B4C–TiB2 composites were carried out to reveal the influence of the pressure loading cycle during pulsed electrical current sintering (PECS) on the removal of oxide impurities, i.e. boron oxide and titanium oxide, hereby influencing the densification behavior as well as microstructure evolvement. The critical temperature to evaporate the boron oxide impurities was determined to be 2000°C. Fully dense B4C–TiB2 composites were achieved by PECS for 4min at 2000°C when applying the maximum external pressure of 60MPa after volatilization of the oxide impurities, whereas a relative density of 95–97% was obtained when applying the external pressure below 2000°C. Microstructural analysis showed that B4C and TiB2 grain growth was substantially suppressed due to the pinning effect of the secondary phase and the rapid sintering cycle, resulting in micrometer sized and homogeneous microstructures. Excellent properties were obtained for the 60vol% TiB2 composite, combining a Vickers hardness of 29GPa, a fracture toughness of 4.5MPam1/2 and a flexural strength of 867MPa, as well as electrical conductivity of 3.39E+6S/m.

Non-invasive measurement of bladder pressure using an external catheter.

Previous studies showed that, on the basis of a combination of maximum flow rate and isovolumetric bladder pressure, objectively diagnosing infravesical obstruction is possible. In this study, we validated a newly developed external catheter to measure non-invasively this pressure, which avoids the risk of damaging or infecting the urethral and bladder wall as occurs with invasive urodynamics. To evaluate the external catheter, we simultaneously recorded the internal bladder pressure signal (measured invasively) and the external pressure signal (measured non-invasively) in 40 non-obstructed and obstructed patients. Additionally, we tested whether the external pressure depended on bladder volume in five healthy volunteers. The simultaneously measured internal bladder pressure and external pressure showed good agreement in the non-obstructed patients. There was less agreement in the obstructed group. Nevertheless, the external pressure in these patients was significantly higher than in the non-obstructed patients. The maximum external pressure depended significantly on the bladder volume in all volunteers. We concluded that isovolumetric bladder pressure can be measured non-invasively with the external catheter. In non-obstructed patients, this pressure accurately represents the internal bladder pressure. We think that it is possible to distinguish between obstructed patients and patients with a weak detrusor by combining the non-invasively measured isovolumetric bladder pressure with a separately measured maximum flow rate. Neurourol. Urodynam. 18:455-475, 1999.

Optimal Design of Laminated Cylindrical Pressure Vessels for Maximum External Pressure

Finite element solutions are presented for the optimal design of hemispherically and flat-capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius, and wall thickness, as well as bending-twisting coupling and hybridization on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fiber angles and maximum buckling pressures for various vessel geometries are made with those for a hybrid pressure vessel. The well-known golden section method is used to compute the optimum angle in each case.

STRENGTH CHARACTERISTICS of PRESSURIZED CANS

ABSTRACTTo study the strength advantages of pressurized cans used for food packaging, two indicators of can strength, maximum axial load and maximum external pressure, were investigated experimentally. Unbeaded 303 × 406 steel cans having several thicknesses and tempers with various internal pressures were tested. Also tested were beaded steel cans and aluminum cans with 206 × 406 dimensions. Failure of the cans was by both buckling and yielding. the results indicated that steel can thicknesses could be significantly reduced, and beading eliminated, by using internal pressure to supplement can strength.

Note on the collapse of magnetic interstellar clouds

view Abstract Citations (453) References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Note on the collapse of magnetic interstellar clouds. Mouschovias, T. Ch. ; Spitzer, L., Jr. Abstract Virial-theorem expressions for clouds on the verge of gravitational collapse are fitted to numerical values obtained with exact equilibrium computations for magnetic interstellar isothermal clouds subject to the pressure of the intercloud medium. The minimum mass needed for gravitational collapse is 0.53 times the virial-theorem value obtained for a homogeneous magnetic sphere, while the maximum external pressure, Pm, at which equilibrium is possible is 0.60 times the virial-theorem value. Subject heading: interstellar: magnetic fields Publication: The Astrophysical Journal Pub Date: December 1976 DOI: 10.1086/154835 Bibcode: 1976ApJ...210..326M Keywords: Cloud Physics; Gravitational Collapse; Interstellar Gas; Interstellar Magnetic Fields; Magnetic Clouds; Critical Mass; Virial Theorem; Astrophysics full text sources ADS |