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171.
Parviz?GhadimiEmail author Alireza?Bolghasi Mohammad?A.?Feizi Chekab Rahim?Zamanian 《船舶与海洋工程学报》2015,14(3):334-342
It is the traditional belief that sound transmission from water to the air is very weak due to a large contrast between air and water impedances. Recently, the enhanced sound transmission and anomalous transparency of air-water interface have been introduced. Anomalous transparency of air-water interface states that the sound generated by a submerged shallow depth monopole point source localized at depths less than 1/10 sound wavelength, can be transmitted into the air with omni-directional pattern. The generated sound has 35 times higher power compared to the classical ray theory prediction. In this paper, sound transmission through air-water interface for a localized underwater shallow depth source is examined. To accomplish this, two-phase coupled Helmholtz wave equations in two-phase media of air-water are solved by the commercial finite element based COMSOL Multiphysics software. Ratios of pressure amplitudes of different sound sources in two different underwater and air coordinates are computed and analyzed against non-dimensional ratio of the source depth (D) to the sound wavelength (λ). The obtained results are compared with the experimental data and good agreement is displayed. 相似文献
172.
Miha Moškon Štefan Novak Marino Medeot Iztok Lebar Bajec Nikolaj Zimic Miha Mraz 《先进运输杂志》2013,47(4):447-460
Fuzzy approach of optimal resource assignment regarding the given demands in the scope of transportation will be presented in the article. The basis of the research is the crisp solution which is also presented in the article. The basic solution was upgraded in order to be able to handle vaguely (i.e. fuzzily) defined requirements and resource properties. The optimal resource configuration is calculated with the aid of Hungarian algorithm which uses the data calculated with the fuzzy methods for its inputs. The approach described is presented on the example of a military convoy formation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
173.
Obrad Babić Milica Kalić Goran Pavković Slavica Dožić Mirjana Čangalović 《运输规划与技术》2013,36(3):257-280
Abstract When disturbances make it impossible to realise the planned flight schedule, the dispatcher at the airline operational centre defines a new flight schedule based on airline policy, in order to reduce the negative effects of these perturbations. Depending on airline policy, when designing the new flight schedule, the dispatcher delays or cancels some flights and reassigns some flights to available aircraft. In this paper, a decision support system (DSS) for solving the airline schedule disturbances problem is developed aiming to assist decision makers in handling disturbances in real-time. The system is based on a heuristic algorithm, which generates a list of different feasible schedules ordered according to the value of an objective function. The dispatcher can thus select and implement one of them. In this paper, the possibilities of DSS are illustrated by real numerical examples that concern JAT Airways' flight schedule disturbances. 相似文献
174.
Air separators provide safe, clean, and appropriate air flow to engines and are widely used in vehicles with large engines such as ships and submarines. In this operational study, the separation process inside a Ranque–Hilsch vortex tube cleaning (cooling) system is investigated to analyze the impact of the operating gas type on the vortex tube performance; the operating gases used are air, nitrogen, oxygen, carbon dioxide and nitrogen dioxide. The computational fluid dynamic model used is equipped with a three-dimensional structure, and the steady-state condition is applied during computations. The standard k–ε turbulence model is employed to resolve nonlinear flow equations, and various key parameters, such as hot and cold exhaust thermal drops, and power separation rates, are described numerically. The results show that nitrogen dioxide creates the greatest separation power out of all gases tested, and the numerical results are validated by good agreement with available experimental data. In addition, a comparison is made between the use of two different boundary conditions, the pressure-far-field and the pressure-outlet, when analyzing complex turbulent flows inside the air separators. Results present a comprehensive and practical solution for use in future numerical studies. 相似文献
175.
Lakshitha?T.?Premathilake Poojitha?D.?YapaEmail author Indrajith?D.?Nissanka Pubudu?Kumarage 《船舶与海洋工程学报》2016,15(4):433-441
Recent progress in calculating gas bubble sizes in a plume, based on phenomenological approaches using the release conditions is a significant improvement to make the gas plume models self-reliant. Such calculations require details of conditions Near the Source of Plume (NSP); (i.e. the plume/jet velocity and radius near the source), which inspired the present work. Determining NSP conditions for gas plumes are far more complex than that for oil plumes due to the substantial density difference between gas and water. To calculate NSP conditions, modeling the early stage of the plume is important. A novel method of modeling the early stage of an underwater gas release is presented here. Major impact of the present work is to define the correct NSP conditions for underwater gas releases, which is not possible with available methods as those techniques are not based on the physics of flow region near the source of the plume/jet. We introduce super Gaussian profiles to model the density and velocity variations of the early stages of plume, coupled with the laws of fluid mechanics to define profile parameters. This new approach, models the velocity profile variation from near uniform, across the section at the release point to Gaussian some distance away. The comparisons show that experimental data agrees well with the computations. 相似文献
176.
At hub airports, dominant airlines/alliance coordinate their flights in time with the aim of increasing the number (and quality) of connections, thus producing a wave‐system in traffic schedules. This paper addresses the impact of concentrating aircraft into waves on airport apron capacity. Existing models for apron capacity estimation are based on the number of stands, stand occupancy time, and demand structure, differing between representative groups of aircraft served at an airport. Criteria for aircraft grouping are aircraft type and/or airline and/or type of service (domestic, international, etc.). Modified deterministic analytical models proposed in this paper also take into account the wave‐system parameters, as well as runway capacity. They include the impact of these parameters on the number of flights in wave, stand occupancy time, and consequently apron capacity. Numerical examples illustrate the difference between apron capacity for an origin–destination airport and a hub airport, under the same conditions; utilization of the theoretical apron capacity at a hub airport, given the wave‐system structure; and utilization of the apron capacity at a hub airport when point‐to‐point traffic is allowed to use idle stands. Furthermore, the influence of different assignment strategies for aircraft stands in the case of hub airports is also discussed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
177.
Mirko Čorić Joško Deur Li Xu H. Eric Tseng Davor Hrovat 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2016,54(7):1004-1030
A collocation-type control variable optimisation method is used in the paper to analyse to which extent the fully active suspension (FAS) can improve the vehicle ride comfort while preserving the wheel holding ability. The method is first applied for a cosine-shaped bump road disturbance of different heights, and for both quarter-car and full 10 degree-of-freedom vehicle models. A nonlinear anti-wheel hop constraint is considered, and the influence of bump preview time period is analysed. The analysis is then extended to the case of square- or cosine-shaped pothole with different lengths, and the quarter-car model. In this case, the cost function is extended with FAS energy consumption and wheel damage resilience costs. The FAS action is found to be such to provide a wheel hop over the pothole, in order to avoid or minimise the damage at the pothole trailing edge. In the case of long pothole, when the FAS cannot provide the wheel hop, the wheel is travelling over the pothole bottom and then hops over the pothole trailing edge. The numerical optimisation results are accompanied by a simplified algebraic analysis. 相似文献
178.
179.
Zeqi?Lu Tiejun?YangEmail author Michael?J.?Brennan Xinhui?Li Zhigang?Liu 《船舶与海洋工程学报》2014,13(3):291-298
Motivated by the need for improving the isolation performance, many research studies have been performed on isolators with nonlinear characteristics. Based on the shape of their phase portrait, such devices can be configured as either a mono-or bi-stable isolator. This paper focuses on investigating the relative performance of these two classes under the same excitations. Force transmissibility is used to measure the isolation performance, which is defined in terms of the RMS of the ratio of the transmitted force to the excitation force. When the system is subjected to harmonic excitation, it is found that the maximum reduction of the force transmissibility in the isolation range using Quasi-Zero stiffness is achieved. When the system is subjected to random excitation, it has the same effect of Quasi-Zero stiffness. Further, optimum damping can be changed with stiffness and has minimum value. 相似文献
180.
Assessing the impact of characteristics of the built environment on travel behavior can yield valuable tools for land use
and transportation planning. Of particular interest are planning models that can estimate the effects of ‘smart growth’ planning.
In this paper, a post-processor method of quantifying and searching for relationships among many aspects of travel behavior
and the built environment is developed and applied to the Buffalo, NY area. A wide scope of travel behavior is examined, and
over 50 variables, many of which are based on high-detail data sources, are examined for potentially quantifying the built
environment. Linear modeling is then used to relate travel behavior and the built environment, and the resulting models may
be applied in a post-processor fashion to travel models to provide some measure of sensitivity to built environment modifications.
The study’s findings demonstrate that mode choice is highly correlated to measures of the built environment, and that many
of the principles of smart growth appear to be a valid way to encourage non-vehicle travel. Home-based VHT and VMT appear
to be affected by the built environment to a lesser degree. 相似文献