Modeling in Engineering
Year:2011 | Volume:9 | Issue:26|Papers Count:7

In this research, inspection of bonding between aluminum and composite layer is simulated. To this aim, propagation of vertical wave in layers and their connection, which is created by vertical wave probe, was modeled. This simulation is performed by ABAQUS finite element software. There are three layers in finite element model, which the middle one is cohesive. To show the effect of disbond on the output signals, cohesive layer is modeled with and without hole. The results of simulated output signals were compared to test results, which was performed with nondestructive vertical wave probe, to verify the simulations.The test specimen was made of aluminum bonded to composite.In a special zone in the test specimen, dispond test was performed to compare the signals from complete bonding and nonbonding. There was good agreement between simulation and test results.

State estimation is a key tool in energy management system for monitoring, control and static security analysis of power systems.Weighted least square, as a conventional method for solving state estimation problem, has deficiencies such as ill-conditioning of gain matrix and slow detection of bad data. Designing of state estimator by using artificial neural network can overcome the numerical results and converge to desirable state more rapidly with respect to weighted least square method. However, errors in measured data would result to bias in state estimation procedure.In this paper, with the aim of mitigation of bad data effect, a state estimator based on artificial neural network was presented that can improve the ability of proposed method. Efficiency of the proposed method has been investigated on two test systems with 9 and 14 buses. The results confirm abilities of the proposed method in solving state estimation problem.

In this paper, wheel-rail contact problem in the presence of rail surface crack is investigated. The reason for investigating this problem is significant effect of wheel-rail contact on stress intensity factors. In this research, by using finite element method and a commercial software, wheel-rail is modeled under partial slip rolling condition. Contact elements are used to model the interactions between the wheel-rail contact surfaces and the crack surfaces. Stress intensity factors are calculated through a numerical displacement extrapolation method. The effects of crack orientation, crack length, friction coefficient and contact on the stress intensity factors are studied. The results indicate that KII has greater values than KI. Therefore, shear mode may dominate the tip behavior in this wheel-rail contact problem. As the wheel passes over, the complicated crack edge deformation changes the direction of interfacial shear stress and this causes variation in KII. Fluctuation in KII is the main factor of fatigue crack propagation in the wheel-rail contact problem.

Increase of strength to weight ratio is one of the main aims in pressure vessel reinforcement. Wire-winding is a safe technique which can be used to reinforce pressure vessels by introducing compression prestress. The purpose of this paper is analytical and numerical investigation of reinforcement effect on CNG vessels by using wire-winding technique. This process increases working pressure to weight ratio in aluminum vessels wound by steel wire in comparison to full-steel vessels. In this work, first, the wire winding method was explained. Next, by considering synchronic yield in the CNG vessel and number of wire layers, maximum internal pressure is calculated. For this purpose, an analytical solution based on Tresca yield criteria is used. Then, the problem is simulated by finite element software. Finally, the obtained results are compared with the analytical results. It is shown that in reinforcement of aluminum vessel by winding five layers, the maximum ratio of working pressure to weight can increase 55% in comparison with full-steel vessels. Also, maximum error between analytical and numerical results was about 3%.

Hybrid buildings, which consist of two different structural systems in height, don’t show good seismic response. Use of reinforced concrete (RC) frames for lower stories and steel frames for upper stories is an example of hybrid buildings and under the earthquake loads, steel frames may slip on lower concrete parts. In this paper, linear and nonlinear behavior of 5, 10 and 15 story buildings that have RC frames with shear walls in lower stories and steel frames with bracings in upper stories is investigated. Analytical results show that using transition story between two different parts of hybrid structures improves the seismic behavior of these buildings. Transition story, which is located in the transition level, is a composite (steel-concrete) story with composite columns, shear walls and steel bracings.Number of these transition stories is dependent on the height of the building and applied loads. The best position of this story is at one-third of the height of hybrid building from top. Moreover, with using transition story in hybrid structures, axial and shear forces at transition level decrease and ductility increases.

Anti-lock braking system (ABS) is an automobile safety system that allows the wheels on a motor vehicle to maintain tractive contact with the road surface according to driver inputs. It is reported that this system can be considered as one of the most important options in vehicle safety and consequently, concentration upon this system can be extremely useful. In conventional anti-lock braking systems, the braking force is generated by hydraulic pressure and then is applied to the driven wheels through hydraulic circuits. Whereas, the fundamental of braking force generation in EMABS is thoroughly different. In this paper, basic concepts of electromagnetic anti-lock braking system are introduced and some of its important advantages in comparison with conventional anti-lock braking systems are presented. In EMABS, a portion of braking force is generated by using an electromagnetic relay and is transmitted into braking shoes through hydraulic circuits. It should be noted that the initial pressure of braking force in EMABS is also generated by a hydraulic booster and it causes the locking of driven wheels. Afterward, the performance of electromagnetic anti-lock system will be started and the locked wheel will be released.