Studies of exit pressure recovery coefficient and its effects on dynamic characteristics of annular water seals

Rotordynamic instability and vibration due to fluid forces within annular seals are well-known phenomenons that can occur in pumps as well as in turbines. Traditional theoretical predictions for the fluid reaction forces and equivalent dynamic characteristics of annular seals are computationally efficient compared with CFD method. Exit pressure loss coefficient is one of the main factors that influence the precisions of theoretical analysis. In this paper, exit pressure recovery coefficients at three different static eccentricity ratios under different operating conditions are investigated using CFD method. The numerical result shows that exit coefficient increases exponentially with the ratio of circumferential velocity to axial velocity at all these three eccentricity ratios. Besides, an analysis method for annular plain seals with the introduction of exit pressure recovery coefficient varied with operating conditions is proposed based on the previous analysis results. Comparisons are made between theoretical predictions calculated by the two methods with and without exit coefficient over a wide range of pressure drops and running speeds. The result suggests that damping coefficients are much more sensitive to the change of the exit boundary conditions compared to stiffness coefficients. In addition, the new prediction results of cross-coupled stiffness and direct damping coefficient show relatively smooth change with the increase of velocity ratio than the previous results

Nonlinear characteristics and stability optimization of rotor-seal-bearing system

A nonlinear rotor-seal-bearing system model, including the Muszynska nonlinear seal force model and nonlinear oil-film force model based on short bearing assumption, is proposed in this paper. The non-dimensional dynamic motion equations of the system are also established and solved by fourth order Runge-kutta method. The nonlinear dynamic characteristics of the system are analyzed with the help of bifurcation diagrams, spectrum waterfall diagrams, axis orbit diagrams, Poincaré maps and amplitude spectrums. The effect of rotor speed, seal clearance, seal length and seal radius on the nonlinear characteristics of the system is also explored. The genetic algorithm (GA) is applied to optimize the stability of the system. The numerical results demonstrate that the rotor-seal-bearing system contains many motion forms, such as periodic, multi-periodic and quasi-periodic motions. Lower rotor speed, proper seal clearance and seal radius, larger seal length are of benefit to the stability of rotor-seal-bearing system. The minimum instability rotor speed changing from 1970 rad/s to 2110 rad/s indicates the GA is an effective optimization method of improving the stability of rotor-seal-bearing system

Drug-induced anaphylaxis in China: a 10 year retrospective analysis of the Beijing Pharmacovigilance Database

Background Few studies on the causes of drug-induced anaphylaxis (DIA) in the hospital setting are available. Objective We aimed to use the Beijing Pharmacovigilance Database (BPD) to identify the causes of DIA in Beijing, China. Setting Anaphylactic case reports from the BPD provided by the Beijing Center for Adverse Drug Reaction Monitoring. Method DIA cases collected by the BPD from January 2004 to December 2014 were adjudicated. Cases were analyzed for demographics, causative drugs and route of administration, and clinical signs and outcomes. Main outcome measure Drugs implicated in DIAs were identified and the signs and symptoms of the DIA cases were analyzed. Results A total of 1189 DIA cases were analyzed. The mean age was 47.6 years, and 732 (61.6%) were aged from 18 to 59 years. A total of 627 patients (52.7%) were females. There was a predominance of cardiovascular (83.8%) followed by respiratory (55.4%), central nervous (50.1%), mucocutaneous (47.4%), and gastrointestinal symptoms (31.3%). A total of 249 different drugs were involved. DIAs were mainly caused by antibiotics (39.3%), traditional Chinese medicines (TCM) (11.9%), radiocontrast agents (11.9%), and antineoplastic agents (10.3%). Cephalosporins accounted for majority (34.5%) of antibiotic-induced anaphylaxis, followed by fluoroquinolones (29.6%), beta-lactam/beta-lactamase inhibitors (15.4%) and penicillins (7.9%). Blood products and biological agents (3.1%), and plasma substitutes (2.1%) were also important contributors to DIAs. Conclusion A variety of drug classes were implicated in DIAs. Patients should be closely monitored for signs and symptoms of anaphylaxis when medications are administered especially with antibiotics, TCM, radiocontrast and antineoplastic agents

Conservation and diversification of the miR166 family in soybean and potential roles of newly identified miR166s

Identity between pre-miR166s in soybean. (TIF 5906 kb

Simulation study of the Gilbert Damping in Ni80Fe20/Nd Bilayers: comparison with experiments.

We present an experimental and computational investigation the Neodymium thickness dependence of the effective damping constant (α_eff) in Ni80Fe20/Neodymium (Py/Nd) bilayers. The computational results show that the magnetic damping is strongly dependent on the thickness of Nd, which is in agreement with experimental data. Self consistent solutions of the spin accumulation model and the local magnetisation were used in the simulations. It was not possible to obtain agreement with experiment under the assumption of an enhanced damping in a single Py monolayer. Instead, it was found that the enhanced damping due to spin pumping needed to be spread across two monolayers of Py. This is suggested to arise from interface mixing. Subsequently, the temperature dependence of the effective damping was investigated. It is found that, with increasing temperature, the influence of thermally-induced spin fluctuations on magnetic damping becomes stronger with increasing Nd thickness

Research on Rotordynamic Characteristics of Pump Annular Seals Based on a New Transient CFD Method

Pump annular seals can cause fluid reaction forces that have great effects on the vibration characteristic and stability of a pump system. For this reason, it is important to study rotordynamic characteristics of annular seals. In this paper, a new transient computational fluid dynamics (CFD) method with dynamic mesh is proposed to investigate rotordynamic characteristics of the pump annular seal. The reliability of the transient CFD method is validated by comparison with the results from the experiment and the bulk-flow method, and the relationship between the seal length and rotordynamic characteristics is investigated by the transient CFD method. The results indicate that direct stiffness decreases sharply even turns to negative as the seal length increases, this phenomenon may change the direction of fluid force on the rotor surface and affect supporting condition of the pump rotor. With the increasing seal length, the whirl frequency ratio gradually increases, which would weaken the stability of the pump rotor system

Original data used in figures of the paper

The data file includes all the experimental and theoretical data shown in Figure 5 to Figure 9