International Journal of Engineering - Transactions C: Aspects 

Abstract: This paper develops a model for the closed-loop supply chain network design with disruption risk. By considering supply disruption, two factors including extra inventory and lateral transshipment are used as resilience strategies. The main purpose is to reduce the supply chain costs due to the location decisions, quantity of products between different levels and lost sale. Disruption in a supply is assumed completely by different scenarios, and then the problem is formulated by a mixed-integer programming model. Furthermore, a two-stage stochastic approach is implemented to tackle uncertainty. Finally, a sensitivity analysis is carried out to examine the effects of the resilience strategies on the structure of the supply chain and to propose some managerial insight for using the model in real world situations.

Abstract: A complete investigation on the free vibration and stability analysis of beams made of functionally graded materials (FGMs) containing open edge cracks utilizing four beam theories, Euler-Bernoulli, Rayleigh, shear and Timoshenko, is performed here. It is assumed that the material properties vary along the beam thickness exponentially and the cracked beam is modeled as two segments connected by two mass-less springs, extensional and rotational spring. Afterward the equations of motion for the free vibrations and buckling analysis are established and solved analytically for clamped-free boundary conditions. A detailed parametric study is also performed to examine the influences of the location and depth of the crack, material properties and slenderness ratio of the beam on the free vibration and buckling characteristics of cracked FGM beams for each of the four engineering beam theories.

Abstract: In this paper, a size-dependent formulation for the Bernoulli-Euler beam is developed based on a new model of couple stress theory presented by Hadjesfandiar i and Dargush. The constitutive equation obtained in this new model, consists of only one length scale parameter that is capable of capturing the micro-structural size effect in predicting the mechanical behavior of the structure. Having one length scale parameter is claimed to be an advantage of the model in comparison with the classical couple stress theory. The governing equations and boundary conditions of the Bernoulli-Euler beam are developed using the variational formulation and the Hamilton principle. The static bending and free vibration problems of a Bernoulli-Euler beam with various boundary conditions are solved. Numerical results demonstrate that the value of deflection predicted by the new model is lower than that of the classical theory. It is also found that natural frequencies obtained by the present couple stress model are higher than those predicted by the classical theory. The differences between results obtained by the present model and the classical theory become significant as the thickness of the beam gets close to the length scale parameter of the beam material

Abstract: In this paper, a comprehensive model for hub location-routing problem is proposed which no network structure other than connectivity is imposed on the backbone (i.e. Network between hub nodes) and tributary networks (i.e. Networks which connect non-hub nodes to hub nodes). This model is applied in public transportation, telecommunication and banking networks. In this model locating and routing is considered simultaneously and it has a multiple allocation strategy to allocate non-hub nodes to hub nodes. In addition, non-hub nodes can connect directly to each other. The objective of the proposed model is minimizing costs of establishing a network and transferring flows. To expedite solving the proposed model and improve the lower bound, which gain from linear relaxation, a number of preprocessing tests and valid inequalities are presented which have relatively good performance in the proposed model. Their performance is analyzed by implementing them on the test problems. Results show that using all preprocessing tests and valid inequalities is the best approach to solve the problem among all proposed approaches in this paper.

Abstract: One of the important problems in reducing of pollutant emission from DI and IDI diesel engines is trade-off between soot and NOx. Split injection is one of the most powerful tools that makes the chance to shift the trade-off curve closer to origin. At the present work, the effect of split injection on the combustion process and emissions of a cylinder IDI diesel engine under the specifications of 5.9 kW maximum engine power and engine speed of 730 rpm has been investigated. The studies of injection timing and split injection parameters, including the delay dwell and the fuel quantity injected between injection pulses are carried out. Three different split injection schemes, in which 10, 20 and 25% of total fuel injected in the second pulse, have been considered. The numerical results show that 25% of total fuel injected in the second pulse which is accompanied with the 20oCA delay dwell between injections, reduces the total soot and NOx emissions effectively in IDI diesel engines. The predicted values of combustion process and emissions by the model at baseline engine show a good agreement with the corresponding experimental data. This agreement makes the model a reliable tool that can use for exploring new engine concepts.