This paper analyzes the interdependency across two critical infrastructures of transportation and motor fueling supply chains, and investigates how vulnerability to climatic extremes in a fueling infrastructure hampers the resilience of a transportation system. The proposed model features both a bi-stage mathematical program and an extension to an ‘α-reliable mean-excess’ regret model. The former aspect allows decision makers to optimize the pre-disaster asset prepositioning against the maximum post-disaster system resilience. The latter aspect of the proposed model devalues the impact of ‘low-probability, high-cost’ sub-scenarios upon model results. The model reveals the reliance of post-disaster urban mobility on the interdependent critical infrastructure of motor fueling supply chains. The results also suggest how investment in the fueling infrastructure’s vulnerable elements protects urban mobility while the transportation network is stressed or under attack. 相似文献
A numerical method for solving 3D unsteady potential flow problem of ship advancing in waves is put forward. The flow field is divided into an inner and an outer domain by introducing an artificial matching surface. The inner domain is surrounded by ship wetted surface and matching surface as well as part of the free surface. The free surface condition for the inner domain is formulated by perturbation about the double-body flow or uniform incoming flow assumption. The outer domain is surrounded by matching surface and the rest free surface as well as infinite far-field radiation boundary. The free surface condition for the outer domain is formulated by perturbation about uniform incoming flow. The simple Green function and transient free surface Green function are used to form the boundary integral equation (BIE) for the inner and outer domains, respectively. Taylor Expansion Boundary Element Method (TEBEM) is utilized to solve the double-body flow and inner domain and outer domain unsteady flow BIE. Matching conditions for the inner domain flow and outer domain flow are enforced by the continuity of velocity potential and normal velocity on the matching surface. Direct pressure integration on ship wetted surface is used to obtain the first-order and second-order wave forces (moments). The numerical predictions on the displacement, added resistance, sway mean drift force and yaw mean drift moment of the modified KVLCC2 ship at different forward speeds are investigated by the proposed TEBEM method. It is also compared with the other numerical results. The physical tank experiment results are also developed to validate the accuracy of numerical tank results. Compared with the experiment solutions, a good agreement can be obtained by TEBEM method.
The highly globalized and competitive nature of the shipping industry poses serious governance challenges. Recently, the use of voluntary measures, such as corporate social responsibility (CSR) initiatives, has been explored in terms of moving towards environmentally and socially responsible as well as safe shipping industry practices. Limited attention has been paid on the role of stakeholders such as consumers, employees, NGOs, and academia in pressuring the shipping industry towards greater environmental and social responsibility. Here, by applying stakeholder theory and drawing on examples of already materialized stakeholder actions and multi-stakeholder initiatives, we study the potential ways that stakeholders can promote CSR in the shipping industry: we explore the resource dependencies between stakeholders, the stakeholder influence strategies, and the importance of multi-stakeholder pressure. We show that stakeholders can gain more power by using indirect strategies such as working via and/or in alliances with NGOs, trade unions, banks and financers, and/or different national or international regulatory bodies, as well as with the industry itself. Our results reveal the potential of multi-stakeholder pressure and action to promote the adoption of CSR activities, support the transparency, legitimacy, and enforcement of the practices, as well as widen the scope and focus of CSR initiatives and practices by focusing on a broad range of social and environmental issues. Finally, stakeholder pressure can push towards improved regulations. The study suggests that increased attention needs to be paid on the multi-stakeholder demands, especially considering the accentuated importance of effective maritime governance in the future. 相似文献
Experiments regarding the modification of the foil geometry and/or active or passive mass injection in the vortex core have been performed to investigate the possibility of inhibiting tip vortex cavitation. The ejection at very low flow rates of drag-reducing polymer solutions at the tip of hydrofoils and propeller blades has demonstrated effectiveness as a tip vortex cavitation inhibitor. This paper reports the results obtained with an elliptical hydrofoil, of 8cm maximum chord and 12cm haif-span, operating at Reynolds numbers, of =106, much larger than those previously reported in the literature. Lift coefficients and critical cavitation numbers were determined for a variety of flow and polymer solution ejection conditions. Tangential and axial components of the mean velocity as well as velocity fluctuations along the vortex path were also measured. At 12.5 m/s free stream velocity and a variety of angles of attack, the ejection of a 500 ppm aqueous solution of a drag-reducing polymer at a flow rate of about 5 cm3/s leads to a decrease of up to 30% in the cavitation number. This occurs without modification of the lift coefficient and, hence, of the midspan bound circulation of the foil. Moreover, water injection does not cause any appreciable change in the cavitation numbers. The tangential velocity profiles along the vortex path during polymer ejection indicate that the potential region remains the same, while the viscous core dimension increases, and the maximum tangential velocity decreases substantially as compared to the no ejection or water ejection experiments. Thus, the pressure coefficients at the vortex axis are smaller than for the no ejection or water ejection cases and cause the reduction of the critical cavitation numbers. It is speculated that this inhibition effect is due only to swelling of the polymer solution when exiting the ejection orifice.List of symbols
a
core radius (distance to the vortex axis for maximum tangential velocity)
-
C1
lift coefficient
-
cmax
maximum chord
-
Cp
pressure coefficient at the vortex axis
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Cpmin
minimum pressure coefficient at the vortex axis
-
de
diameter of the ejection port
-
m
ejection flow rate
-
P
reference pressure
-
Pv
vapor pressure
-
V
free stream velocity
-
Va
axial velocity
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Vt
tangential velocity
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vr
radial component of the velocity resulting from jet swelling
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x
downstream distance from the tip of the foil
-
y, r
distance to the vortex axis
-
angle of attack
- r
difference between the swollen jet and the ejection port radii
-
boundary layer thickness
-
tip vortex intensity
-
d(
de)
desinent cavitation number (with ejection)
-
i(
ie)
inception cavitation number (with ejection)
-
ii
normal stresses
-
viscosity
-
v
kinematic viscosity
-
p
specific mass 相似文献
A mathematical model for the steering control of an automobile is described. The structure of the model derives from linear optimal discrete time preview control theory but it is non-linear. Its parameter values are obtained by heuristic methods, using insight gained from the linear optimal control theory. The driver model is joined to a vehicle dynamics model and the path tracking performance is demonstrated, using moderate manoeuvring and racing speeds. The model is shown to be capable of excellent path following and to be robust against changes in the vehicle dynamics. Application to the simulation of manoeuvres specified by an ideal vehicle path and further development of the model to formalise the derivation of its parameter values and to put it to other uses are discussed. 相似文献
This paper considers a method for estimating vehicle handling dynamic states in real-time, using a reduced sensor set; the information is essential for vehicle handling stability control and is also valuable in chassis design evaluation. An extended (nonlinear) Kalman filter is designed to estimate the rapidly varying handling state vector. This employs a low order (4 DOF) handling model which is augmented to include adaptive states (cornering stiffnesses) to compensate for tyre force nonlinearities. The adaptation is driven by steer-induced variations in the longitudinal vehicle acceleration. The observer is compared with an equivalent linear, model-invariant Kalman filter. Both filters are designed and tested against data from a high order source model which simulates six degrees of freedom for the vehicle body, and employs a combined-slip Pacejka tyre model. A performance comparison is presented, which shows promising results for the extended filter, given a sensor set comprising three accelerometers only. The study also presents an insight into the effect of correlated error sources in this application, and it concludes with a discussion of the new observer's practical viability. 相似文献