Sharif Digital Repository

Designing of an efficient emergency ventilation system is one of the main approaches to prevent the perilous fire in tunnel phenomenon. For this purpose, firstly, fire behavior and its heat release rate should be investigated. Knowing about temperature distribution and smoke movement is the second step. One of the most considerable factors in smoke control is critical velocity. It means the minimum velocity to prevent backlayering flow. If longitudinal ventilation velocity were less than this amount, smoke and hot gases originated from the fire can enter the upstream zone. This may cause lack of oxygen and decrease visibility for the passengers when they are escaping from the fire field. In... 

Polypropylene block copolymer is used in different industries like pipe productions. This copolymer has proper mechanical properties, specially it has good impact strength, but in some applications it’s elastic modulus (stiffness) is not enough and that leads to some problemes in servise. Nucleating agents influence crystalline structure and properties and also the mechanical properties by controlling the crystallization process. Nanoparticles also have a beneficial effects on physical and mechanical properties. In this study, the effect of adding two types of α-phase nucleating agents (commercial names NA11 and DMDBS) in the form of masterbatch wt 5% with a carrier of polypropylene block... 

Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by... 

At present, with some exceptions, the contracts are awarded based on the least proposed price. The records show that this method has not been successful especially for the infrastructure projects. In other words the projects awarded this way have been completed with time and cost overruns. Most of the times, such projects have not satisfied the stakeholders' expectations or have had problems during operation phase. The goal of this research is to suggest a method for selecting the most suitable contractor, considering the proposed price as well as incorporating the delay and other risks based on Contractors' actual past performance in the completed projects. Before selecting the Contractor,...