Abstract In this research, generation of a short and smooth path in three-dimensional space with obstacles for guiding an Unmanned Underwater Vehicle (UUV) without collision is investigated. This is done by utilizing spline technique, in which the spline control points positions are determined by Imperialist Competitive Algorithm (ICA) in three-dimensional space such that the shortest possible path from the starting point to the target point without colliding with obstacles is achieved. Furthermore, for guiding the UUV in the generated path, an Interval Type-2 Fuzzy Logic Controller (IT2FLC), the coefficients of which are optimized by considering an objective function that includes quadratic terms of the input forces and state error of the system, is used. Selecting such objective function reduces the control error and also the force applied to the UUV, which consequently leads to reduction of energy consumption. Therefore, by using a special method, desired signals of UUV state are obtained from generated three-dimensional optimal path such that tracking these signals by the controller leads to the tracking of this path by UUV. In this paper, the dynamical model of the UUV, entitled as "mUUV-WJ-1" , is derived and its hydrodynamic coefficients are calculated by CFD in order to be used in the simulations. For simulation by the method presented in this study, three environments with different obstacles are intended in order to check the performance of the IT2FLC controller in generating optimal paths for guiding the UUV. In this article, in addition to ICA, Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC) are also used for generation of the paths and the results are compared with each other. The results show the appropriate performance of ICA rather than ABC and PSO. Moreover, to evaluate the performance of the IT2FLC, optimal Type-1 Fuzzy Logic Controller (T1FLC) and Proportional Integrator Differentiator (PID) controller are designed and applied to the UUV and compared with each other. The simulation results show the superiority of the IT2FLC than the other two controllers.

In this paper, a scaled 3D ship under shock loading is modeled and analyzed by finite element method. By using of shock factor, there is no need to have different tests or even numerical simulation. Shock factor is an important parameter which clarifies shock severity. It was found that although the new shock factor introduced by Yao et al. (2009), when constant, predict the response better than older shock factor, but for varying values of shock factors, the older would predict better. It is also found that costly and time-consuming experiments can be avoided by proper finite element modeling, yet the errors can remain within an acceptable range. The results of the present work can be used as benchmarks for future works.

Bending analysis of functionally graded single walled carbon nano tubes is presented in this paper. Carbon nano tubes are modeled as Euler-Bernoulli beam theory in this study. Harmonic differential quadrature (HDQ) method is used to discretize the governing equations. In order to show the accuracy of present work, the results are compared with those of other existing results. Then the effects of different parameters such as power law index, inner and outer radius of nano tubes and length nano tubes of are studied, too.

In this paper, free vibration of functionally graded nonuniform straight-sided plates with circular and non-circular cutouts has been investigated. Moreover, thermal effects on free vibration analysis and the effects of various parameters on natural frequencies of these plates were evaluated. The material properties were assumed to be graded across thickness, which vary according to the linear distribution law. The investigated parameters in this study are: (1) cutout size (2) type of loading (3) different boundary conditions. It should be mentioned that the obtained results of thermal effect on free vibration of the FG nonuniform straight-sided plates (such as skew and trapezoidal plates) with cutouts have not been studied yet. Therefore, the results of this investigation can be implemented in future studies.