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791.
Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure
loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds
of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been
carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening
or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and
the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In
this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap
existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the
hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while
the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the
error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting
in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation
results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters
in a throttle governing system with a hydraulic butterfly valve. It also determines the type and specification of the hydraulic
butterfly valve and the design of motion parameters of the transported fluid. 相似文献
792.
Sloshing phenomenon in the liquid cargo carriers has caught the attention of researchers as the interaction between the sloshing
waves and structure is one of the key point and difficulty in the study of sloshing. In this paper, we captured the free surface
with a volume of fluid (VOF) method and then calculated the motions and responses of the structure by adopting the Reynolds-averaged
Navier-Stokes (RANS) equations for the whole fluid domain. With the use of user defined functions (UDF) in Fluent, the interaction
between fluid and structure was then simulated. As a reasonable simplification, the authors studied the response of a single
cantilever in a tank under sloshing loads; Further study should pay more attention to the mechanisms of interaction between
sloshing waves and elastic structures. 相似文献
793.
For the large-scale application requirements of the belt-type networks, the mathematical modeling as well as quantitative
analysis for the scalability of the network based on average path length is completed in this paper, and the theorem for the
scale scalability of the belt-type networks is derived. The theorem provides a calculation formula for the upper limit of
node scale theory of the belt-type networks and a calculation formula for the upper limit of single node load theory. 相似文献
794.
The rapid and continuing changes in travel and mobility needs in India over the last decade necessitates the development and
use of dynamic models for travel demand forecasting rather than cross-sectional models. In this context, this paper investigates
mode choice dynamics among workers in Chennai city, India over a period of five years (1999–2004). Dynamics in mode choice
is captured at four levels: exogenous variable change, state-dependence, changes in users’ sensitivity to attributes, and
unobserved error terms. The results show that the dynamic models provide a substantial improvement (of over 500 log-likelihood
points and ρ2 increases from 44% to 68%) over the cross-sectional model. The performance was compared using two illustrative policy scenarios
with important methodological and practical implications. The results indicate that cross-sectional models tend to provide
inflated estimates of potential improvement measures. Improving the Level of Service (LOS) alone will not produce the anticipated
benefits to transit agencies, as it fails to overcome the persistent inertia captured in the state-dependence factors. The
results and models have important applications in the context of growing motorization and congestion management in developing
countries.
相似文献
P. BhargaviEmail: |
795.
Annual electric bike (e-bike) sales in China grew from 40,000 in 1998 to 10 million in 2005. This rapid transition from human-powered
bicycles, buses and gasoline-powered scooters to an all-electric vehicle/fuel technology system is special in the evolution
of transportation technology and, thus far, unique to China. We examine how and why e-bikes developed so quickly in China
with particular focus on the key technical, economic, and political factors involved. This case study provides important insights
to policy makers in China and abroad on how timely regulatory policy can change the purchase choice of millions and create
a new mode of transportation. These lessons are especially important to China as it embarks on a large-scale transition to
personal vehicles, but also to other countries seeking more sustainable forms of transportation.
相似文献
Christopher CherryEmail: |
796.
SUICheng-cheng YANGYong-tian JIARong-zhen 《船舶与海洋工程学报》2004,3(1):52-56
Real-time modeling and simulation of flight system are the key parts of simulator. After describing the architecture of simulator for a newer fighter, author presents the composition of flight system and its mathematic models. In this paper, aircraft is regarded as an elastic flight body. And a new integrated algorithm which can remedy the shortcoming of Euler method and four-element method is used to calculate the Eulerian angles of aircraft. Finally, the software implementation of the flight system is given in the paper. 相似文献
797.
Jaegu Kang Sanghyun Chu Jeongwoo Lee Gyujin Kim Kyoungdoug Min 《International Journal of Automotive Technology》2018,19(1):27-35
In this research, the effects of three operating parameters (Diesel injection timing, propane ratio, and exhaust gas recirculation (EGR) rates) in a diesel-propane dual fuel combustion were investigated. The characteristics of dual-fuel combustion were analyzed by engine parameters, such as emission levels (Nitrogen oxides (NOx) and particulate matter (PM)), gross indicated thermal efficiency (GIE) and gross IMEP Coefficient of Variance (CoV). Based on the results, improving operating strategies of the four main operating points were conducted for dual-fuel PCCI combustion with restrictions on the emissions and the maximum pressure rise rate. The NOx emission was restricted to below 0.21 g/kWh in terms of the indicated specific NOx (ISNOx), PM was restricted to under 0.2 FSN, and the maximum pressure rise rate (MPRR) was restricted to 10 bar/deg. Dual-fuel PCI combustion can be available with low NOx, PM emission and the maximum pressure rise rate in relatively low load condition. However, exceeding of PM and MPRR regulation was occurred in high load condition, therefore, design of optimal piston shape for early diesel injection and modification of hardware optimizing for dual-fuel combustion should be taken into consideration. 相似文献
798.
We test a copula-based joint discrete–continuous model to unravel mode choice and travel distance decisions in a joint framework for school trips. This framework explicitly accounts for common unobserved factors that may affect both the mode choice and travel distance. Joint estimation of the models makes a significant difference in the effect of travel distance on willingness to walk to school. The absolute value of the travel distance coefficient in the mode choice model increases by 22% when a joint formulation is adopted instead of the conventional single estimations. We find a significant decrease of 19% in the coefficient of travel safety perception in the joint mode choice model compared to the single model. This underscores the impact of model specification, in terms of the variable effect interpretation and policy assessments. The effect magnitude of several policy-sensitive variables is discussed and compared with previous studies. Particularly, we indicate that the probability of walking is reduced by 0.85% due to a 1% increase in travel distance; accordingly, it propels parents to select non-active modes, particularly school bus. This study also demonstrates how addressing parental concerns about travel safety could double the propensity to walk to school. 相似文献
799.
Offshore jacket-type platforms are attached to the seabed by long batter piles. In this paper, results from a finite element analysis, verified against experimental data, are used to study the effect of the pile’s inclination angle, and its interaction with the geometrical properties of the pile and the geotechnical characteristics of the surrounding soil on the behavior of the inclined piles supporting the jacket platforms. Results show that the inclination angle is one of the main parameters affecting the behavior of an offshore pile. We investigated the effect of the inclination angle on the maximum von Mises stress, maximum von Mises elastic strain, maximum displacement vector sum, maximum displacement in the horizontal direction, and maximum displacement in the vertical direction. The pile seems to have an operationally optimal degree of inclination of approximately 5°. By exceeding this value, the instability in the surrounding soil under applied loads grows extensively in all the geotechnical properties considered. Cohesive soils tend to display poorer results compared to grained soils. 相似文献
800.
Fayyaz Ahmad Taek Soo Jang Jinsoo Park Hong Gun Sung 《Journal of Marine Science and Technology》2016,21(2):240-250
We address in this article, how to calculate the restoring characteristic and the excitation of a nonlinear forced oscillating system. Under the assumption that the forced nonlinear oscillator has a periodic solution with period \(T=2\pi / \omega\), we constructed a system of linear equations by introducing time-dependent multipliers. The periodicity assumption helps simplify the system of linear equations. The stability and uniqueness are also presented for the inverse problem. Numerical testing is conducted to show the effectiveness of our presented methodology. 相似文献