نشریه مهندسی هوانوردی
سال دوازدهم شماره 2 (پاییز 1389)

A hybrid mesh generation method is presented to discretize the computational domain around complex aerodynamic geometries. The idea behind this hybrid method is to combine the orthogonality and regularity of structured grids inside the boundary layer, the efficiency and simplicity of Cartesian grids and the flexibility of unstructured grids for development of an automatic, robust and fast mesh generation method. A series of structured layers is firstly generated around wetted surfaces. Cartesian grids are then constructed using a binary tree data structure covering the rest of the domain. Those Cartesian cells overlapping with the structured grids are then removed. Finally, unstructured triangular cells are generated to fill all empty regions in the domain as a result of the trimming method process. The developed method is used for calculation of a number of laminar and turbulent flow test cases. Results show that the presented grid generation method can compute viscous flows with good accuracy and less computational time.

In this paper the behavior of a flat plate with rotational degree of freedom has been discussed. Because of the mutual influence between rotational plate and airflow, unsteadiness of flow and complexity of vortex flow, there is no proper analytical method resolution for this problem. Also it cant be analyzed by in the numerical solvers based on the Navier_Stokes equations. Therefore, improved Discrete_Vortex method should be used to calculate normal force coefficient and aerodynamic pitching moment. Two modeling were done; free rotation and force rotation. Normal and axial coefficient and aerodynamic moment based on proportion of angle of plate to the flow in steady state and in free rotation and force rotation were calculated. To evaluate the numerical results some experimental test on the plate in wind tunnel were done and the behavior of that plate by experiment method were surveyed. Based on the result, in force rotation regime because of engendering some differential structure in vortex flow (in compare with static position), there are Aerodynamic Hysteresis in normal force and rotational moment that this hysteresis nutritious with decrease in Strohaul number. If any plate with rotational degree of freedom being under the Air flow, may result in being free rotation. This position is occurred when momentary of inertia being between 1.43-5 and angle of attack being little enough. In another values of momentary of inertia, plate enters in free vibration (or damping regime)

Air operations in a broad pattern of a collection of hundreds of warplane and air support aircraft, the efficient communication platform for achieving the goals and guiding its operations, navigation systems are networked. The network according to the mobility pattern of birds as a specific mobile wireless networks is that in addition to advantages such as tolerance against error, reduced impact aggressors during the discovery process to identify and track the data transfer, ability to discover multipath for the exchange of information can have increased reliability. In this paper, systems and protocols designed for having of these advantages, the encoding, encryption, routing and loading several adaptive algorithms are used that increase efficiency and security and finally, increase the ratio of normal delivery package will be sent to the whole package. Simulation results show the proposed algorithm, the average speed packet transfer rates, approximately %1 increase and with increasing percentage of the attacker security, concurrent additional overhead on average % 12 decreases.

Crashworthiness of aircraft and helicopter structures in terms of impact energy absorption is a fundamental design consideration in structural design of such a flight vehicles. In fact, crashworthiness of the lower fuselage structure is often considered as a key factor in assessing damages and hazards encountered in emergency landing cases. This reseach focused on a structural component of a naval utility helicopter, in which an aluminium structural component attached to the seats is considered for re-engineering to achieve an improved safety. This structural component has a significant effect on impact energy in vertical crash of the helicopter to the ground or sea water surface. In this respect, the origional metallic component is repalced by a laminated composite material one, and its effect on structural weight, cost and maintenance and repair are studied. Computer simulations as well as experimental tests are performed to validate the superior characteristics of the re-engineered component. The results show the re-engineered component has improved safety factors, weight and manufacturing cost when compared to the origional one.

Aluminum alloys are widely used in the aircraft industry due to the high strength-to-density ration. Anodic oxidation, which is an electrochemical process to form stable films on the surface of metals, is one of the most unique and widely used methods to improve surface performance such as corrosion and wear resistance. In this report different aircraft Al alloys e. g. 7075-T6، 2024-T3, 6061-T6 are coated by hard anodizing in different thicknesses (25µm, 50µm, 64µm, 76µm, 100µm) using different current densities (2. 6, 3. 2) and, wear properties, micro-hardness, increase in dimensions of samples in sealed and unsealed conditions are studied. Samples were anodized in sulfuric acid. Test results show uniform coating in all alloys and, decrease of wear of samples in sealed beside non-sealed condition. The sealing process has little effect on reduction of hardness of samples. Hardness of all samples is increased with up to 3 mil increase in thickness of coating and, is decreased thereafter and addition of dimensions is increased by increase in current density.

Dynamic behavior of a cracked rotor is simulated under the excitation of unbalance and gravity forces. The shaft is modeled using Timoshenko beam segments supported on two visco elastic bearings, and the attached disks are considered to be solid bodies with point connections to the shaft. The presence of a transverse breathing fatigue crack in the shaft cross section is considered which results in a time dependent stiffness. The model is constructed by using the convenient energy method and the crack effect is implemented as a substructure. Response of the system is calculated using a Harmonic Balance Method (HBM). The calculated system response includes run up response and time response. The obtained results are verified by FEM and a good agreement is observed.

The historical trend in formation and development of high tech. organizations such as active ones in aerospace industry demonstrated that organizations with traditional structures do not show flexibility and competitive strength for being in accordance with surrounding changes and they are accused of being incompetence in economics competition environment. These organizations have come to realize that, to be out of this crisis, they need to be equipped new tools. One of the most important solutions is to create learning processes and to institutionalize the learning organizations. This article deals with the assessing the degree of readiness of the statistical population for transformation to Learning Organization. The main research question includes how much the features and characteristics reported in literature on Learning Organization exist in given statistical population. How is the situation of given statistical population on the dimension and components of Learning Organization. How much has it institutionalized these elements in itself? Data collection was documentُis investigation, in-person questionnaire and Survey–descriptive approach. Concluding results indicate that there is meaningful gap on some components in order to change to Learning Organization. Finally, concerning research findings, some suggestions were presented to scientific society and organizational managers.