---

Abstratct- In this paper, first, a number of emerging technologies for rapid manufacturing of components are introduced and their application in manufacturing aeronautical structural components is discussed. Then, a novel method for generation of sectional contour curves directly from the cloud point data is presented. The proposed method computes contour curves for rapid prototyping model generation through adaptive slicing, data points reducing and B-spline curve fitting. The Proposed procedure was programmed in MATLAB software package to perform all computational effort in a single software system. The method has been applied to a wing-fuselage connector component of an existing fighter aircraft to create its layered model for rapid manufacturing. 3D comparison of the developed model and the digitized cloud point data reveals that 95% of the data points have a maximum deviation of 0.5 mm, which is a reasonable accuracy compared to the component size. The simplicity and effectiveness of the proposed method, as demonestarted by our experiments, confirms that the algorithm can be practically used for rapid prototype manufaturing of aeronautical structural components with an adequate accuracy.

---

The need for complex surfaces in CAD motivates researchers for methods which can produce smooth and visually pleasing surfaces. In this research, a new method is presented for creating compatible cross-sectional curves for surface fitting to certain sections or lofting. In this method, the distribution of sections' data points along with basis knot vectors are improved in order to reach a desired smooth surface. In compatibility process, the section curves' degrees and their knot vectors must be set equal before implementing lofting process. Based on proposed algorithm, in this research, the constructed smooth and faired surfaces can be used in many engineering applications such as reverse engineering, biomedical engineering, quality control, etc. The main focus of the method is improvement of data points' distributions and their assigned parameters in a way that by a few iterations, data points' distribution are improved in order to reach a common knot vector for all cross-sectional curves. The method is implemented on some benchmarking examples and its efficiency are confirmed. In addition, the amount of final data points' deviation from the initial section curve is analyzed using the vigorous Hausdorff method. It is worth mentioning that the quality of obtained final surface is visually pleasing. In order to quantitatively confirm that the proposed method will result in smooth and fair surfaces, MVS is used. Finally the application of the method in modeling the root joint zone of a wind turbine blade is presented.

---

Shape optimization of free form shell structures with different objective and constraint functions including the stress constraint is the subject of this article. To construct the geometry B-Splines are employed that allow generating smooth free form geometries with a small number of parameters which are considered as the design variables of the optimization problem. For analysis, the finite element method by using the Wilson’s quad shell element is employed. For shape optimization, in each step of the optimization process the mesh generation, finite element analysis, sensitivity analysis and geometry update steps are repeated until convergence. Maximization of the stiffness of structure with volume constraint and the minimization of the weight of structure with the von Misses stress constraint are the addressed problems of this article. In both kinds of problems, the applicates of the control points are considered as the design variables of the shape optimization problem and the sequential quadratic programming (SQP) is employed to solve the optimization problem. Since in this approach, the derivatives of the objective and constraint functions are needed, the sensitivity analysis is carried out in each step by the finite difference method. The quality and smoothness of the obtained results together with the convergence graphs of the presented examples are indicative of the usefulness and efficiency of the proposed approach for shape optimization of shell structures.

---

In this paper, optimal trajectories of soft landing on the Moon are designed based on different landing strategies. For this purpose, the problem of soft landing is defined as an optimal control problem to minimize fuel consumption and solved by a combinational direct method. The used solution method in this paper is a combination of direct collocation method, nonlinear programming, differential flatness and B-spline curves. In this method, by using differential flatness, dynamic equations of landing are expressed by the minimum number of state variables in the minimum dimensional space. Also, state variables are approximated by B-spline curves, and control points of these curves are considered as optimization variables of the nonlinear programming problem. By simultaneously using of differential flatness and B-spline curves, the number of variables and constraints of the optimal control problem decrease significantly and the problem is solved with high accuracy and speed. In the paper, three different strategies for soft landing on the Moon are investigated. These strategies are defined based on direct or indirect landing from the parking orbit and separation of horizontal braking and vertical descent phases. According to achieved optimal trajectories, by indirect landing from an intermediate orbit, the space vehicle can be landed on the Moon with the minimum fuel consumption. Also, by separation of horizontal braking and vertical descent phases, a more applicable landing trajectory can be achieved.

---

Solving the governing equations of a system is the most important issues that is always discussed in science and engineering fields. Since there are few equations that have analytical solution, many numerical methods have been proposed for solving the equations that have no analytical solutions. Numerical methods are developed by the advent of computers. Today, with using computers and these methods together, complicated equations in diverse areas can be resolved. Several numerical methods such as finite element method (FEM), finite difference method (FDM) and meshless (MFree) method have been suggested for solving partial differential equations. In this study, Isogeometric analysis method is engaged as a numerical method. Isogeometric analysis was developed by Hughes in 2005 in order to eliminate the gap between the world of finite element analysis and computer modeling. This method uses the same basis functions, in the process of modelling. Isogeometric method provides the possibility of simulation in irregular and complex geometry domains and also removes errors due to the multiple elements. Two variable NURBS basis functions are defined by B-spline basis functions. B-spline basis functions are calculated by the Cox–de Boor recursion. In this study, Birjand aquifer is modeled in two dimensions by the Isogeometric analysis using four-point Gauss integration method. The mentioned aquifer is defined by 1274 points and 836 control elements. After creating the geometry of the aquifer by control points and knot vector, NURBS basis functions and their derivatives were calculated. Then, with using input information, such as hydraulic conductivity coefficients, boundary conditions, precipitation rates and the sources and sinks, water table is computed. In order to allocate hydraulic conductivity coefficients of the aquifer, the domain is divided by the GIS software to multiple homogeneous Thiessen. According to the location of NURBS elements in the aquifer, a value has been assigned to NURBS elements. In Birjand aquifer there are boundary conditions with constant head. For enforcing the boundary conditions, 83 points of control points were defined as fixed head. There are 190 wells in the Birjand aquifer, the Extracted water from the wells were used as the discharge rate in the model. Also, 15 percent of the amount of rainfall was considered as the recharge rate in 2011-2012 period, the value of recharge rate is 0.0000727 m/day based on rain gauges. In order to ensure the accuracy of modeling the results of Isogeometric method is compared with finite difference method solutions and observation data, the relative mean error of Isogeometric method is 0.000256. With using Isogeometric method the consumed time for running the MatLab code is around 400 seconds. In order to evaluate the model, three criteria is calculated. Mean error (ME), mean absolute error (MAE) and root mean square error (RMSE) whose values are 0.09, 0.34, and 0.459 respectively. The values of the error and computation time has shown the power of this method in modeling of groundwater flow. Finally, Birjand aquifer groundwater balance was calculated using the input values, extracted water and water storage in plain. By studying the model balance and actual balance of aquifer and comparing them with each other, it is determined that the change in the volume of the aquifer in the time period considered is close to that of the aquifer, which indicates the accuracy of the model.