Correlation of structure parameters and performance characteristics of alloy steels for shipbuilding

The article presents the results of a study of the relationship between strength and performance (temperatures of ductile-brittle transition Tdb and zero plasticity NDT, critical opening at the crack tip CTOD at a test temperature of —40°C) on the structure parameters of thick plate products made of low-carbon low-alloy steels with different contents of basic alloying and microalloying elements.

Identification of critical moving characteristics in high speed on/off valve based on time derivative of the coil current

This article focuses on accurate identification of the critical moving characteristics of the high speed on/off valve. Typically, there are two strategies for identifying the critical moving characteristics, including calculation strategy based on force balance and strategy for detecting the coil current’s certain points. However, the accuracy of the two above strategies needs to be improved. Therefore, to improve the identification accuracy of the high speed on/off valve’s critical moving characteristics, an identification strategy for detecting the time derivative of the coil current is proposed. First, a mathematical model of the high speed on/off valve (including electromagnetic sub-model and mechanical-fluid sub-model) is established. And on this basis, relationship between the coil current’s derivative and the valve’s critical moving characteristics is analyzed which reveals the changing rule of the coil current’s derivative causing by the ball valve’s moving. Finally, the changing rule of the coil current’s derivative is verified by the comparative simulations and experiments, which also indicate that, with the proposed identification strategy, the maximum identification error of the critical opening/closing time is only within 6%, and the maximum identification error of the total opening/closing time is still small (2.9%), compared to other identification strategies in the previous literatures.

Scientific and technological bases for creation of cold-resistant steel with a guaranteed yield strength of 315–750 MPa for the Arctic. Part 1: Principles of alloying and requirements for sheet metal structure

The results of the choice of rational alloying and microalloying of cold-resistant steels with a guaranteed yield strength of 315–750 MPa are presented on the basis of the established interrelationship of phase transformations, structure, mechanical properties and performance characteristics when varying the content of basic alloying elements. Quantitative requirements for various structural parameters and their maximum permissible difference in sheet metal thickness up to 100 mm have been developed, depending on the strength category, manufacturing technology (thermomechanical treatment with accelerated cooling, hardening from separate furnace or rolling heating with high temperature tempering), which provide guaranteed characteristics of strength, cold resistance (impact work KV at test temperature –60 ... –80°С, critical temperatures of viscousbrittle transition Ткand zero ductility NDT) and crack resistance under the criterion of the critical opening in the top CTOD fracture.

Effects of recruitment/derecruitment dynamics on the efficacy of variable ventilation

Variable (or noisy) ventilation (VV) has been demonstrated in animal models of acute lung injury to be superior to constant (or conventional) ventilation (CV), in terms of improved gas exchange and mitigation of lung injury, for reasons that are not entirely clear. We hypothesized that the efficacy of VV is related to the fact that recruitment and derecruitment of lung units are dynamic processes. To test this hypothesis, we modeled the lung computationally as a symmetrically bifurcating airway tree terminating in elastic units. Each airway was fully open or completely closed, at any point in time, according to its pressure history. The model is able to accurately mimic previous experimental measurements showing that the lungs of mice injured by acid aspiration are better recruited after 60 min of VV than CV. The model also shows that recruitment/derecruitment dynamics contribute to the relative efficacy of VV, provided lung units open more rapidly than they close once a critical opening or closing pressure threshold has been crossed. We conclude that the dynamics of recruitment and derecruitment in the lung may be important factors responsible for the benefits of VV compared with CV.

The spreading phase in Lighthill's model of the Weis-Fogh lift mechanism

Lighthill's analysis (J. Fluid Mech., vol. 60, 1973, p. 1) of the Weis-Fogh lift mechanism is extended to include the spreading phase of the cycle. Lighthill proposed a two-dimensional inviscid irrotational analytical model to compute the circulation around two flat plates (the wings) as they open out, in opposite directions, about a common centre of rotation taken to be at the point of contact of an edge of each plate (the ‘opening phase’). At a critical opening angle, the plates separate and move apart horizontally (the ‘spreading phase’). During this second phase, the fluid region becomes doubly connected and is not analysed by Lighthill. It can, however, also be studied analytically and the results are presented here. We also extend a similar analysis, in an application to turbomachinery, due to Furber & Ffowcs Williams (J. Fluid Mech., vol. 94, 1979, p. 519).

Cavitating flow in non-circular opening spool valves with U-grooves

Cavitating flow in non-circular opening spool valves with U-grooves has been investigated in this article. Multifarious cavitating properties, including acoustic cavitation, morphologic cavitation, and discharge performance with cavitation, are investigated, the correlations of which are discussed. The critical opening condition in each valve is obtained based on the analysis of a throttling model. It is found that the cavitating properties show remarkable differences in the two situations when the opening is larger and smaller than the critical opening. Additionally, cavitation impacts on the discharge performance are investigated with the assistance of acoustic and visual detection.

Modeling the dynamics of recruitment and derecruitment in mice with acute lung injury

Lung recruitment and derecruitment contribute significantly to variations in the elastance of the respiratory system during mechanical ventilation. However, the decreases in elastance that occur with deep inflation are transient, especially in acute lung injury. Bates and Irvin ( 8 ) proposed a model of the lung that recreates time-varying changes in elastance as a result of progressive recruitment and derecruitment of lung units. The model is characterized by distributions of critical opening and closing pressures throughout the lung and by distributions of speeds with which the processes of opening and closing take place once the critical pressures have been achieved. In the present study, we adapted this model to represent a mechanically ventilated mouse. We fit the model to data collected in a previous study from control mice and mice in various stages of acid-induced acute lung injury ( 3 ). Excellent fits to the data were obtained when the normally distributed critical opening pressures were about 5 cmH2O above the closing pressures and when the hyperbolically distributed opening velocities were about an order of magnitude greater than the closing velocities. We also found that, compared with controls, the injured mice had markedly increased opening and closing pressures but no change in the velocities, suggesting that the key biophysical change wrought by acid injury is dysfunction of surface tension at the air-liquid interface. Our computational model of lung recruitment and derecruitment dynamics is thus capable of accurately mimicking data from mice with acute lung injury and may provide insight into the altered biophysics of the injured lung.