Occurrence Of Negative Pressure Research Articles

Numerical simulation of water entry problems considering air effect using a multiphase Riemann-SPH model

The water entry is a classic fluid-structure interaction problem in ocean engineering. The prediction of impact loads on structure during the water entry is critical to some engineering applications. In this paper, a multiphase Riemann-SPH model is developed to investigate water entry problems. In this model, a special treatment, a cut-off value for the particle density, is arranged to avoid the occurrence of negative pressure. A remarkable advantage of the present multiphase SPH model is that the real speed of sound in air can be allowed when simulating water-air flows. In the present work, considering the air effect, several typical water entry problems are studied, and the evolution of multiphase interface, the motion characteristic of structure and complex fluid-structure interactions during the water entry are analyzed. Compared with the experimental data, the present multiphase SPH model can obtain satisfactory results, and it can be considered as a reliable tool in reproducing some fluid-structure interaction problems.

Large Eddy Simulation of diesel injector opening with a two phase cavitation model

In the current paper, indicative results of the flow simulation during the opening phase of a Diesel injector are presented. In order to capture the complex flow field and cavitation structures forming in the injector, Large Eddy Simulation has been employed, whereas compressibility of the liquid was included. For taking into account cavitation effects, a two phase homogenous mixture model was employed. The mass transfer rate of the mixture model was adjusted to limit as much as possible the occurrence of negative pressures. During the simulation, pressure peaks have been found in areas of vapour collapse, with magnitude beyond 4000bar, which is higher that the yield stress of common materials. The locations of such pressure peaks corresponds well with the actual erosion location as found from X ray scans.

Survey of pressure management in water distribution systems

A survey was conducted to assess pressure management practices in water distribution systems. Most of the surveyed utilities agreed on the need to avoid low‐pressure episodes (< 20 psi). However, 56% of the utilities had no requirements for the maximum pressure delivered to customers, and 67% did not manage peak pressures in their systems. Only 13% of surveyed systems conducted pressure monitoring at critical locations—e.g., sites of highest or lowest pressure. Approximately 50% of systems reported at least one occurrence of negative pressure during the previous year; however, many more incidents of low and/or negative pressure may have gone undetected. The authors recommend that distribution system pressures be monitored in at least two locations in each pressure zone, representing the highest and lowest pressures. The recording interval could be set to 5–10 min with a 10‐s sampling interval. Impulse recording (when available) should be enabled to capture momentary pressure changes.

S114032 高速スラスト空気軸受の高剛性化メカニズムの実験的検討([S11403]機素潤滑設計部門 第17回卒業研究コンテスト(3))

Hydrodynamic thrust air bearings have a lot of advantages such as low environmental load, low frictional loss and maintenance-free. Therefore, hydrodynamic thrust air bearings are extremely effective against saving of energy gain recognition in machine industry. On the other hand, the bearing stiffness of hydrodynamic thrust air bearings is considerably low compared to the stiffness of oil bearings. Therefore, optimization of groove geometry proposed by Hashimoto was carried out to maximize bearing stiffness based on conventional spiral grooved bearings. As a result, an optimized bearing which has new original groove geometry was found out. The optimized bearings have been proven through experiments to have a much higher bearing stiffness compared to conventional spiral grooved bearings. However, the mechanism of enhancement of bearing stiffness is still not obvious. Consequently, this paper describes the consideration about mechanism of high-stiffness through the measurement of pressure distribution and load carrying capacity. As a result, occurrence of negative pressure was confirmed where the optimized bearings periphery. Furthermore, it is found that the optimized bearing stiffness was advanced because the load carrying capacity of optimized bearing increase exponentially at the near of floating point.

A Pulsatile Cardiopulmonary Bypass System that Prevents Negative Pressure at the Membrane Oxygenator

Negative pressure is a problem in pulsatile cardiopulmonary bypass (CPB). To avoid this, the authors designed a pulsatile CPB system containing a Sarns centrifugal pump (CP) and a Univox membrane oxygenator, in which the inertial flow is not obstructed by the CP. In both an in vitro study and a clinical study, negative pressure was not observed in the arterial line of the CPB circuit when this system was used. When a roller pump (RP) was used, however, instead of a CP, negative pressure did occur. In a clinical study using this system, mean pulse pressure was 36 mmHg and hemolysis, expressed as the rate of rise in plasma free hemoglobin from 10 to 70 min of CPB, was 26.2 mg/dl/hr, which did not exceed that seen with a pulsatile CPB using an RP instead of a CP. The hemolysis seen in the study caused no clinical problems. Thus, pulsatile CPB using a CP and Univox membrane oxygenator should be considered for clinical use to prevent the occurrence of negative pressure.