Modeling and Dynamic Characteristics of a Novel High-Pressure and Large-Flow Water Hydraulic Proportional Valve

In the field of fully mechanized coal mining equipment, the hydraulic valve used in the hydraulic support is an on/off directional valve. There are many problems caused by the valve such as large pressure shock and discontinuous flow control. Therefore, a novel two-position three-way hydraulic proportional valve suitable for high-pressure and large-flow conditions is proposed to overcome the above problems. The novel valve utilizes a two-stage structure and the displacement follow-up principle is adopted between the pilot stage and the main stage to meet proportional control. In this paper, a simulation model of the novel proportional valve was established after a simplified analysis of the structural principle. Its reliability and the feasibility of the design were verified by the test results under different working conditions. Then, the step response characteristics of the proportional valve under different strokes were predicted and analyzed. Nonlinear characteristics were presented, and the closing time was shorter than the opening time because of the influence of nonlinear flow force. Under different ramp signals, the displacement of the main inlet spool was always approximately equal to the displacement of the pilot stage. Then, the motion relationship between the pilot stage and the main stage was studied, and the influence of the structural parameters on the stability was analyzed.

The Impact of Rolling Stock Heterogeneity on Tram Stop Dwell Time

The prediction of stop dwell time is a major issue in travel speed modeling, i.e., in the definition of travel time for high-frequency and high-ridership rail public transport. This is due to the numerous influential factors associated with stop dwell time, variable both in space and time, such as passenger flow, vehicle and stop design characteristics, and traffic organization. To investigate the impact of the heterogeneity of tram vehicles on stop dwell time, a survey was conducted regarding the tram network of the City of Zagreb. The dwell time at three consecutive island stops served by three different tram vehicle types was analyzed. The stops are located near the city center, in a separate tram corridor, at the far side of signalized intersections. Dwell time was determined and evaluated through the statistical analysis of observed, measured, and video-recorded data. The results show that at stops with up to 200 passengers per hour, the dwell time is around 15 s. For volumes of 20 passengers or less per tram, the dwell time is mostly affected by the tram door opening mechanism and opening/closing time. As the passenger volumes become higher, the number of doors per vehicle becomes more significant.

Association between Nightlife Goers’ Likelihood of an Alcohol Use Disorder and Their Preferred Bar’s Closing Time: A Cross-Sectional Observational Study in Perth, Australia

Introduction and aims: Associations between longer-term alcohol-related conditions and licensed outlet trading hours are not well understood. We investigated the association between nightlife-goers’ likelihood of an alcohol use disorder (AUD) and their preference for bars with special permits to remain open ‘late’ (i.e., spent more time there compared to any other venue) until 2 a.m. or 3 a.m. (Friday; Saturday) or midnight (Sunday) compared to bars with ‘standard’ closing times of midnight (Friday; Saturday) or 10 p.m. (Sunday). Design and methods: A cross-sectional observational study was conducted in four major nightlife areas of Perth, Australia, in 2015–2016. We conducted weekend street intercept surveys outside bars between 8 p.m. and 3 a.m. and screened participants who reported alcohol use prior to the survey and spent more time in a bar than any other venue type (n = 667) regarding their past year drinking pattern using AUDIT-C (n = 459). We used gender-specific logistic regression models to estimate associations between AUDIT-C categories (1–4, low risk; 5–7, hazardous; 8–12, active AUD) and preference for bars with different closing times (late vs. standard). Results: A large proportion of participants were hazardous drinkers or had active AUD (83% males; 65% females), and over half preferred a late to a standard closing bar. We found evidence of a positive association between preference for late closing bars and hazardous drinking females (OR = 3.48; 95% CI 1.47–8.23; p = 0.01), but not for females with active AUD, male hazardous drinkers, nor males with active AUD. Discussion and conclusions: Our study adds new evidence on associations between likelihood of AUD among nightlife-goers and trading hours. With increasing international relaxation of trading hours, evidence that late closing bars may be preferred by hazardous drinking females will be of concern to policymakers wanting to curb alcohol-related harms in the community.

Sensitivity Analysis of Hydraulic Transient Simulations Based on the MOC in the Gravity Flow

The purpose of this study was to evaluate the sensitivity of input parameters to output results when using the method of characteristics (MOC) for hydraulic transient simulations. Based on a gravity flow water delivery project, we selected six main parameters that affect the hydraulic transient simulation and selected maximum pressure as the output parameter in order to perform a parameter sensitivity analysis. The Morris sensitivity analysis (Morris) and the partial rank correlation coefficient method based on Latin hypercube sampling (LHS-PRCC) were both adopted. The results show that the sensitivity of each parameter is the same except for the friction factor. The flow rate and Young’s modulus are positively correlated with the maximum pressure, whereas the pipe diameter, valve closing time, and wall thickness are negatively correlated. It is discussed that the variability of the friction factor comes from the function of the flow and pressure regulating valve. When other conditions of the gravity flow project remain unchanged, the maximum pressure increases with the increase in the friction factor. The flow rate, pipe diameter, and valve closing time are the key parameters that affect the model. Meanwhile, Morris and LHS-PRCC proved to be effective methods for evaluating parameter sensitivity in hydraulic transient simulations.

Numerical validation of pressure and flow characteristics across a control valve in a feed line

This work is intended to understand the variation of pressure and flow at the pump inlet of liquid rocket engine. The opening and closure of the valve upstream of the pump features complex phenomenon. The opening and closing of the valve cause pressure and flow variations at the pump inlet which may lead to combustion instabilities in combustion chamber of engine, hydraulic transients in feedlines, and off-design operation of turbo-pumps which are fundamental to the efficient testing and operation of engine. A numerical model to predict the pressure and flow transients across a control valve for different rate of opening in fluid feed systems has been developed using first-order finite difference technique. In case of flow in pipes, the velocity and pressure is governed by momentum and continuity equations. A computer code for the prediction of fluid transients is developed based on method of characteristics for one-dimensional fluid flow in pipelines and compared with test data for validation. The control valve is considered to be in-line with the feed line and modeled based on the valve coefficient vs. percent opening of valve. This model can subsequently be used to predict the effect of opening/closing time of the valve on pressure surges across the control valve and corresponding flow rate in the feedline for different opening of the valve.

Water Hammer Control Using Additional Branched HDPE Pipe

In pressurised pipeline systems, various water hammer events commonly occur. This phenomenon can cause extensive damage or even lead to a failure of the pumping system. The aim of this work is to experimentally re-examine the possibility of using an additional polymeric pipe, installed at the downstream end of the main pipeline, to control water hammer. A previous study on this topic investigated additional polymeric pipes connected to the hydraulic system with a short joint section of the same diameter as the main pipeline. In the current research, a different method of including an additional pipe was considered which involved connecting it with a pipe of a smaller diameter than the main pipeline. Three additional HDPE pipes, with different volumes, were investigated. The performance of the devices was studied for hydraulic transients induced by both rapid and slow, manual valve closures. Experimental results show that the additional polymeric pipe can provide significant pressure surge damping during rapid water hammer events. As the valve closing time lengthens, the influence of the additional pipe on the maximum pressure increase is reduced. The additional HDPE pipe does not provide notable protection against hydraulic transients induced by slow valve closure in terms of reducing the first pressure peak. No relationship between the volume of the additional pipe and the damping properties was noticed. The observed pressure oscillations were used to evaluate a one-dimensional numerical model, in which an additional pipe is described as a lumped parameter of the system. The viscoelastic properties of the device were included using the one element Kelvin–Voigt model. Transient flow equations were solved with the implicit method of characteristics. Calculation results demonstrate that this approach allows one to reasonably reproduce unsteady flow oscillations registered during experiments in terms of the maximum pressure increase and pressure wave oscillation period.

SIMULATION OF DOOR MOVEMENT WITH A CLOSING MECHANISM

The work objective is to determine the parameters of the closing mechanism that provide the specified characteristics of the door movement. Research method: computer simulation of the movement of a door with a lock mechanism as a multi-mass dynamic system, taking into account the mechanical characteristics and contact interaction of the lock mechanism. Research results and novelty. Computer dynamic models of a door with a door closer and a door with a spring have been developed. The moments of the door opening force, the closing time of the door, the angular velocity of the door at the time of impact with the frame are considered as the criteria for the quality of the door closing mechanism. Formulas are obtained that determine the permissible values of stiffness and deformation of the door closer spring according to the specified moments of the door opening force. The movement of doors with a door closer and with a spring is compared. The parameters of the closing mechanism providing the specified characteristics of the door movement of the considered example are determined. It is shown that with the same values of the opening force moments, the speed of impact with the frame in the case of the door closer is less than the door with a spring. Conclusions: The developed computer dynamic models of a door with a door closer and a door with a spring make it possible to determine the characteristics of the door movement taking into account the inertial and mechanical characteristics of the door closer and spring mechanisms. The permissible values of stiffness and deformation of the door closer spring can be determined by the specified moments of the door opening force in two positions. It is established that the forces of air resistance and friction in the hinges of the door cannot create the moment of resistance necessary for smooth closing of the door without a strong impact on the frame with a limited closing time. The quality criteria that minimize the closing time and the speed of impact of the door with the frame are contradictory. The choice of optimal parameters of the door closing mechanism is possible if one of the criteria is replaced by a restriction. The developed formulas and computer models are recommended for use in the design of devices that restrict the movement of doors.

Twentieth Century Linguistics at Closing Time

This chapter appraises the state of linguistics at the end of the twentieth century in the wake of the Generative/Interpretive Semantics episode. The period saw a huge upswing in Noam Chomsky’s influence with the dominance of his Government and Binding/Principles and Parameters model, but also the development of multiple other competing and intersecting formal models, all of which did away with Chomsky’s totemic concept, the transformation: Relational Grammar (RG), Lexical-Functional Grammar (LFG), Generalized Phrase Structure Grammar (GPSG), and so many more that Frederick Newmeyer tagged the lot of them Alphabet Grammars (AGs). Alongside these frameworks came George Lakoff’s most far-reaching and influential development, with philosopher, Mark Johnson, “Conceptual Metaphor Theory” (a label the author rejects).