When the body is running at fully immersed condition in viscous fluid, there are two components of resistance, i.e. frictional resistance and form drag. When it is near the free surface, the additional drag encountered to the body which is wave-making drag. This paper is presents the hydrodynamic performance of high-speed Unmanned Underwater Vehicle (UUV) in fully immersed condition.We did 1000000 (cells) fluid mesh around the body using Navier Stokes (N-S) equations and appropriate boundary conditions. The calculations of drag and lift have been obtained at various speeds and attack angle. The k-e model is used to solve the N-S equations. We firstly calculated for the sphere and the results of pressure distributions and drag are very good and satisfactory with the experimental data. The calculations are extended to the UUV and the pressure distributions and drag are shown in good agreement with data.

The first purpose of this study is to investigate different methods of making viscous cellulose (in non-aqueous solvent) and strengthening tissue by cross-linking synthesis. The second goal is coupling with PVC. To coat viscovellulose on polyvinylchloride (PVC) surface in this study, instead of water, organic solvents as ethylenediamine and ethylene glycol were used to synthesize viscous cellulose. In the first method, gelatinization of cellulose was performed in ethylene glycol solvent and cellulose tissue was reinforced with ester crosslink by additives such as phthalic anhydride and polyvinyl alcohol. In the second method, cellulose was aminolyzed in ethylenediamine and an amide cross-link was formed by using terephthalic acid. In the third method, cellulose acetate tissue was reinforced with polyvinyl acetate and borax. Finally; it was rubberized with acetone solvent. In the final step, the viscose cellulose samples of each method were coated with a layer of PVC paste. To compare the quality of coupling methods, the tensile test and moisture absorption test were used. Based on the obtained results, the first (ester crosslink) and second method (amide crosslink) had better tensile strength (with tensile device) and moisture absorption (with volatile meter) was more than the others. The tensile strength of the first method and its moisture absorption was more than other methods. Also, intrinsic viscosity [η ] of viscocellulose: PVC paste (1: 1ratio) showed that the third method (cellulose acetate and polyvinyl acetate paste) has the highest homogeneity and adhesion with PVC paste. The advantage of these methods is that for the synthesis of viscous cellulose, ethylene glycol solvent is used instead of water solvent and for activation energy, a microwave beam is used instead of heater heat. The importance of microwave beams for this research method is proved by the DSC method.

In some aerospace vehicles, the tracking sensors which act in a tracking loop as stabilizer are mounted on a two degree of freedom gyro. The gyro must align its rotor axis with the line of sight in order to remove tracking errors. The tracking precision and sensitivity are functions of the gyros performance. One of the main factors in reducing the precision and producing instabilities is nutation vibration. This fluctuating motion, which is a dynamical inherent property of the system, is related to the gyro lateral moment of inertia, the length of gyro and its rotating speed. In order to investigate the capabilities of nutation damper and removing the wobble motion of a freely processing body, this paper analyzes a ring damper partially filled with viscous liquid with taking into account the behavior of the damper and its subsystems. The equations of motion for the dynamical motion of gyro, are obtained using Lagrangian approach, taking into account the friction of dampers and interaction of the liquid with the system equations of motion.

New techniques in seismic design of structural systems are based on flexibility and energy dissipation approach. In this approach, the role of energy dissipaters is quite important. The behaviors of these devices and the way they dissipate energy have always been a concern for many researchers to improve the efficiency of these important parts of the structural systems. There has been a large number of investigations on behavioral aspects of energy dissipating devices capable of using in seismic design of structural systems.The concept of adding dissipating supplemental devices to a structure assumes that much of the energy imposed to the structure from a transient will be absorbed, not by the structure itself, but rather by supplemental damping elements. Among them, viscous devices have received considerable attention. The behavior of these energy dissipaters are dependent, not only on the relative velocity, but also on a large number of other parameters including relative displacement, compressibility of fluid, internal friction etc.The behavior of viscous devices are also dependent on the frequency of excitation and their thermal conditions. Determination of mechanical characteristics of these devices is usually based on experimental studies including cyclic tests in different amplitudes and frequencies.In this study, a new type of viscous dashpot in which the main body of the device has been made of contractible steel bellows (developed in IIEES) is chosen for experimental studies. The viscous device has the capacity of 500 kN and axial deformability of ±150mm. The tests have been carried out using an actuator capable of providing axial forces up to 300 kN in cyclic tests with displacement range of ±120mm. Axial forces on dashpot and resulted deformations on the device during experiments have been used to find the relationships between applied forces and induced relative displacement and velocity on the device.According to the results, the dashpot shows a dominant viscous behavior. It also represents a small frictional behavior in order of 10 kN (on average). The device also shows a frictional feature that is proportional to its internal fluid pressure. This feature is due to a small asymmetry in manufacturing some parts of the device, but it can be used later to improve the behavior of contractible dashpots. To be able to develop a model for this device, the test results are used in the form of cyclic behavior and time series. The time series results show the fact that there is not a linear proportionality between forces and velocity experienced by the dashpot in all the range of excitation frequencies. In addition, according to the test results, damping constants for this device is also dependent on the excitation frequency. Different types of behavioral models have been examined for the device. The proper model is proposed based on the three element type Maxwell model. The model can be further improved to represent the pressure dependent frictional forces in this dashpot.

In this research, applications of the Boundary Element Method to viscous flow are investigated. The BEM formulation allows a boundary-only solution for linear stokes flow. For higher speed flows in which the non-linear convective effects cannot be ignored, a volume integral must be retained. The proposed formulation is based on analogy between Navier's equations in elastostatics and Navier-Stokes equations expressed by using a penalty function. By using penalty function formulation, pressure term is eliminated and Navier-Stokes equations are converted to Navier equations in elastostatics. In many previous works, potential fundamental solution was used for solving viscous fluid flow with BEM but in this research elastostatics fundamental solution is used. Finally, some two-dimensional examples are provided to validate the presented approach. It is found that the boundary element method gives accurate solutions and it is more economical than other methods since the application of the method requires discretization only on the boundaries of the domain and thus it reduces the spatial dimensions of the problem by one.

In the present study, nonlinear vibration of coupled carbon nanotubes (CNTs) in presence of surface effect is investigated based on nonlocal Euler-Bernoulli beam (EBB) theory. CNTs are embedded in a visco-elastic medium and placed in the uniform longitudinal magnetic field. Using von Karman geometric nonlinearity and Hamilton’s principle, the nonlinear higher order governing equations are derived. The differential quadrature (DQ) method is applied to obtain the nonlocal frequency of coupled visco-CNTs system. The effects of various parameters such as the longitudinal magnetic field, visco-Pasternak foundation, Knudsen number, surface effect, aspect ratio and velocity of conveying viscous are specified. It is shown that the longitudinal magnetic field is responsible for an up shift in the frequency and an improvement of the instability of coupled system. Results also reveal that the surface effect and internal conveying fluid plays an important role in the instability of nano coupled system. Also, it is found that trend of figures have good agreement with previous researches. It is hoped that the nonlinear results of this work could be used in design and manufacturing of nano/micro mechanical system in advanced nanomechanics applications where in this study the magnetic field is a controller parameter.

In this paper, nonlinear simulation of viscous fingering instability of miscible displacement involving nanofluid is investigated. Using vorticity and stream functions and the spectral method governing equations are obtained. Due to the fractality of fluid-fluid interface in instability phenomena, by using box counting method, its fractal dimension is calculated in different parameters such as deposition rate, mobility ratio and diffusion rates. The results show that increasing the deposition rate reduces the complexity of finger patterns and the diffusion rate of nanofluid has no effect on complexity of finger patterns while increasing the diffusion rate of displaced fluid has significant effect on patterns and makes it more complicated. The fractal analysis also shows that the effect of mobility ratio depends on the deposition rate.  By considering deposition rate, although the mobility ratio has no effect on fractal dimension and effective time is constant and equal to 275, start time of instability is delayed by 25 units. It can be concluded that fractal analysis of viscous fingering phenomena can be considered as one of the instability characteristics.