مجله مهندسی مکانیک شریف
سال سی و دوم شماره 2 (پاییز و زمستان 1395)

In this work, the modeling and utter and nonlinear dynamical behaviors of uid-conveying pipes in three dimensions are undertaken. All equations of motion are derived assuming an appropriate displacement in nonlinear form using Lagrange principle to circumvent the complex modeling approach given in mentioned references. In previous works on modeling three-dimensional motion of pipe, a complex approach based on inextensibility of pipe was used for derivation of equation of motion. This assumption resulted in nonlinear complex equation of motion and boundary condition. But, here, a simple method is used to obtain equation of motion. Due to three-dimensional motions of pipe, double bending and in-plane displacement eld are assumed. Governing partial dierential equations are discretized by Rayleigh- Ritz's method, and dimensionless form of equation is derived with dening appropriate parameters. The nonlinear equations are solved numerically and its vibration behavior is examined. Due to uid ow, detrimental utter phenomenon occurs, which make system unstable. Dierent types of bifurcations are observed, and the eect of varying parameters on utter is accurately examined. Discussion of how utter occurs and dierent modes of utter are presented. Finally, the eect of design parameters on the system instability and its type is presented. With varying ow velocity, dierent types of nonlinear vibrations are occurred. These behaviors include simple limit cycle oscillations, period doubling, intermittency, and chaos. Also, in some ow velocities, locking motion in a special plane is occurred. The eects of dierent parameters on these nonlinear behaviors are examined. Some new results are presented, which are not previously reported. Obtained results and their comparison with appropriate references show the accuracy of modeling according to the assumed eld displacement. Obtained results show the ecacy of the proposed modeling in capturing all nonlinear behavior phenomenon reported in literature. It is simple to extend the proposed modeling for dierent boundary conditions.

Environmental pollution and energy constraints have made engineers research a new method of ignition in the internal combustion engines. Also, the automotive industries are searching to replace SI and CI engines due to the strict regulations of international organizations actives in the eld of environment. (HCCI) is a suitable method for combustion in SI and CI engines. The HCCI engine uses a premixed air/fuel mixture that is pressed with high compression ratio. In the research, a CFD model has been used for the analysis of HCCI engine. In order to validate the model, we used the experimental results obtained from Dutez engines with Methane fuel and a secondary fuel injection diesel in 270oCAD position. Investigation showed that concordance between the model and experimental results is acceptable. Maximum cylinder pressure decreases with the increase of EGR. With an increase in EGR percentage, the rate of carbon black increases which it results from the incomplete combustion. Therefore, performance of EGR is acceptable within a certain range. Also, an increase of EGR reduces cylinder temperatures. Incomplete combustion causes a part of the air/fuel mixtures to leave the cylinder without participating in the combustion process. As a result, those parts of the air/fuel mixtures leave the cylinder without producing thermal energy. Increase of EGR rate reduces the amount of heat release due to incomplete combustion, but heat release increases even despite non-combustion. This performance is due to the increase of temperature which, in turn, causes the increase of cylinder density. As a result, heat release is produced even despite non-combustion. It is noteworthy that maximum heat releases occur under non-EGR condition. Change in the heat release rate regarding dierent EGR rates shows that the combustion occurs in dierent positions. The increase of EGR greatly reduces NOX emissions. So, EGR system can provide adequate eect on reducing NOX emissions.

In this paper, we investigate the inverse heat conduction method by a set of data extracted from experimental applications has been studied. Two heat transfer classic problems are designed for this purpose and the measured data are utilized as an input to the inverse heat conduction algorithm. In the rst experiment, a stainless steel plate (AISI-304 with length, width, and thickness of 250, 70, and 5 millimeters, respectively) is in proximity to a heater from one surface. Other faces are completely insulated, and the temperature from the bottom insulated surface has been measured with type K thermocouples, which is used to estimate the heater heat ux. There has been low pass Butterworth lter applied to the collected data before the usage in inverse algorithm. These kinds of problems with measurement at the inactive surface are common in inverse heat conduction elds due to the measurement and construction complexities. Second experiment is a bit more sophisticated and designed in order to nd the free convection heat transfer coecient of air adjacent to stainless steel plate. It consists of the previous heater and steel plate, in addition to wood, ber glass, and elastomer insulation layers. The temperatures inside the steel and wood plates are measured, in addition to the ambient air and the last insulation layer temperatures. The calculation is started from the bottom surface and the heat ux lost into environment is calculated, then heat transfer in each layer is estimated one by one until we reach the steel plate on the top, adjacent to air. Sequential function estimation method, due to its online and fast solution, has been used as an inverse heat conduction technique to solve the problems. The results show that inverse heat conduction algorithm has an acceptable accuracy in situations, in which temperature measurement on active surface comes with dif- culties such as high temperatures, harsh environment, construction problems, etc.

The current study aims to identify the equivalent linear dynamics of an autonomous underwater vehicle in the horizontal plane to be able to design an appropriate linear controller. Autonomous underwater vehicles are increasingly being used to provide researchers with a simple, low-cost, and rapid response capability to collect pertinent environmental data. They are fairly stable platforms with little roll and pitch. Nevertheless, dynamic coupling and non-linearities make it a challenging task to perform identication process, stability analysis, and control design. Here, for the rst time, the frequency response analysis and the CIFER software, which utilizes strong mathematical algorithms, are employed to solve this problem. Advanced features such as the Chirp-z transform and composite window optimization are also used to extract high-quality frequency responses and best t equivalent transfer functions. After formulating the problem, a frequency sweep input is designed and applied to the rudder controller in the nonlinear simulation and transfer functions for the heading angle and the rate of turn are derived. In addition, these transfer functions are obtained by perturbed equations of motion to be compared with the transfer functions from CIFER. To evaluate the accuracy of the identied models, time domain responses from a zig-zag test are compared with the responses predicated by the identied model and the linearized model. The results show that this model is in good agreement with the analytical linear model and performs signicantly better in presence of noise, thanks to the precise spectral functions and windowing technique. The robustness of the proposed method and transfer functions are also assessed by evaluation of the coherence function and altering the window size, frequency bandwidth, and input commands. The results also show that in a specic frequency range, nonlinear terms are negligible, and the turn rate could be easily predicted by the time derivative of the heading angle.

Boundary layer profle on the upper surface of a supercritical airfoil in pitching motion has been experimentally investigated. Measurements were performed using a boundary layer having total pressure slim tubes positioned at 25% of the chord from the leading edge on the upper surface. In the static mode, the eect of the angle of attack ranging from -3 to 14 degrees and for freestream velocities of 40 m/s to 70 m/s were investigated, where for the dynamic case eects of oscillation amplitude varied between 3 and 10 degrees, reduced frequencies from 0.007 to 0.0313, and mean angles of attack between -3 and 6 degrees, on the boundary layer prole were studied for one oscillation cycle. Time series of each pressure signals acquired from the pressure sensors were processed after ltering and corrections. To study the amplitude of the dominated frequency in the velocity prole, Fast Fourier Transformation on the pressure signals acquired from each rake was used. The results indicate hysteresis loops for boundary layer thickness during upstroke and downstroke states and extension of width of hysteresis loops at higher reduced frequency. In addition, boundary layer thickness is decreased as the angle of attack is increased in the upstroke portion of the motion.

In this paper, the purpose is to compensate the errors of velocityandposition,existingatthestartingtimeofstar sensor work in an integrated inertial/celestial navigation system. In an inertial navigation system, there exists attitude error at launch moment. Moreover, while integrating gyros and accelerometers outputs, errors grow in estimation of attitude, velocity, and position on vehicle. On the other hand, because of earth's atmosphere eects, celestial navigation cannot be implemented for a while after launch moment. Then, pure inertial navigation is carried out at this interval. Consequently, large errors of velocity and position exist at starting time of integration. The estimation and integration are carried out using unscented Kalman lter through which current attitude and the gyros xed bias can be estimated accurately. To precise integration, nonlinear navigation equations have been used and propagated implementing an accurate discretization method. Moreover, in all sequences of navigation and estimation, quaternions have beenusedtodealwithattitude. Thiswillreducecomputation costs and immunize integrated system from singularity. Since quaternions have their own vector space, some considerations are applied to estimation procedure which includes sigma point's calculation, propagation, and calculating mean and covariance. On the other hand, velocity and position errors are not observable in anintegratedinertial/celestialnavigationsystem. Then, in this paper, using nonlinear navigation equations and implementing back-propagation and smoothing, initial attitude and accelerometers xed bias are estimated accurately. In addition, the vehicles attitude is acquired at prior time steps while back-propagating. By carrying out a new parallel navigation based on vehicles attitude at prior moments and taking out gyros and accelerometers xed biases, velocity and position errors are com pensated. To demonstrate the validity and performance of the proposed method, navigation of a LEO launch vehicle has been simulated. Results admit great compensations in velocity and position errors.

In this paper, the accuracy of integrated inertial-radar navigation systems used for autonomous landing of unmanned air vehicles is studied. These navigation systems use the inertial instruments as the main navigation and the radar data as the navigation aids. The radar system provides the position and velocity measurements with respect to the runway coordinate system. Navigation of aircrafts is classied to \terminal" and \non-terminal" phases. The terminal phase involves the parts of ight which are related to arrival and departure from a runway. The requirements of the navigation system in the terminal phase are more complicated than the non-terminal phase. The nal condition of the nonterminal phase will be set as the initial condition of the terminal phase. Thus, the designer of the navigation system should consider the interaction of these two phases. In this study, the accuracy of an integrated navigation system with velocity matching algorithm is analyzed during the landing phase of a xed wing aircraft. The relation between accuracy of inertial instruments, ight parameters, and accuracy of integrated navigation are extracted in the form of dierential equations. The initial conditions of these equations are calculated from the terminal phase parameters. The mentioned dierential equations can not be solved analytically. Thus, based on the nominal behavior of an aircraft in the landing phase, some reasonable assumptions are made and the equations are solved in a closed form. The analytical solutions are used to express the accuracy of the integrated navigation in the terminal phase. The designer of the navigation system of an aircraft can use the analytical results obtained in this study to select the accuracy of the aircraft inertial instruments. In order to verify the analytical results, landing phase of a famous unmanned air vehicle, Shadow-200, which uses a system named \TALS" as the navigation aids, is simulated numerically. It is shown that the analytical results are well matched with the numerical ones.

Increasing the buckling strength-to-weight ratio is of particular importance in aerospace, mechanical, nuclear, and civil engineering. Corrugated structures with trapezoidal geometric pattern have higher amount of the buckling strength-to-weight ratio with respect to other similar structures; hence, these generations of structures are widely used in several industries. Static stability of corrugated cylindrical structures with trapezoidal geometric pattern was investigated here under axial loading for simply supported boundary condition. Using rst-order shear deformation theory of Mindlin, equilibrium equations of the problem were derived. Mechanical proper ties of corrugated cylindrical structure were achieved by the mechanical properties of equivalent orthotropic circular cylinder. Then, critical buckling load was obtained for both simple circular and corrugated cylinders. The present analytical results are validated by the nite element models. These validations report very good agreement between the present results and those obtained by the nite element analysis. Eect of dierent parameters including number of corrugations, cylinder thickness, cylinder length, cylinder radius, corrugation angle, and shape factor was investigated numerically on buckling behavior of corrugated cylindrical structure. The results of nite element reveal that buckling mode shapes can be divided into two types as local and global buckling modes. Graphical shapes of local and global modes are presented to make the better physical sense. In this article, the present analytical method can solve the global buckling problem of a corrugated cylinder. According to the comparison between present modeling results and those obtained by nite element analysis, increasing the corrugation angle and cylinder radius and decreasing the number of corrugations, the cylinder thickness, the cylinder length, and shape factor led to an increase in the buckling load of corrugated cylinder with respect to circular cylinder on the condition that local buckling had not been occurred. The present results and procedure can help engineers and designers to achieve a best performance for their structures, especially related to aerospace structures.

Equal Channel Angular Rolling (ECAR) is a continuous severe plastic deformation process. In this process, severe shear strains are applied to the sheet. This strain increases the yield or ultimate strength of sheet without signicant change in sheet dimension. In this article, the eect of ECAR process on mechanical properties and fatigue life of manufactured sheets will be studied. Four Al-5083 samples have been prepared and annealed for obtaining stress-free samples. Three samples have been rolled by ECAR process with 1, 2, and 3 pass of rolling, respectively. Mechanical tests including tensile test, hardness, and axial fatigue tests have been carried out on prepared samples. Fatigue tests have been implemented according to strain-based approach with constant strain ratio and 0.5 Hz frequency of loading. Strain ratio (ratio of minimum strain to maximum strain in each cycle) is selected which equals 0.75. All of the tests have been carried out in a controlled laboratory condition. Fatigue life of samples is dened as the total of cycles before complete rupture of samples. Results show that the ultimate tensile strength (UTS) of samples increases with increasing the pass of rolling. Also, the maximum elongation of samples decreases. Maximum elongation was 17% in annealed sample, while it decreases to 10% in sample with three pass of rolling. The hardness of samples has been measured by Vickers micro harness test. The hardness of samples increases at higher pass of rolling. Fatigue test results show that fatigue life of Al-5083 samples decreases in manufactured sheets of equal channel angular rolling process.

Cold roll forming is one of the most complex forming processes in which quality of products is highly dependent on the process parameters. Estimation of forming torque and power in the cold roll forming process is one of the most important parameters. Eective parameters on the forming torque and forming power are investigated in the present study. These parameters are rolls geometry, sheet thickness, sheet width, strength of sheet, andformingangle. So, theformingprocessissimulated in the nite element software Abaqus for both
at and angled geometry of the top roll. Simulation results show that with yield strength, sheet thickness, and increase of roll angle, forming torque and power will increase. Also, the rolls force increase and the forming torque decrease with sheet width increasing. The results of this study show that the forming torque and power for the top roll with
at geometry is lesser than the top roll with angled top roll. Due to easier process of manufacturing of
at rolls, this type of rolls geometry can be used for channel sections. The eect of thickness and width of sheet is investigated experimentally on the forming torque and power. Numerical results are veried by experimental results of the present study. Results show that forming torque and power increase with yield strength, then forming angle and sheet thickness increase as well. Therefore, engineers can consider the eects of these parameters on the forming torque, forming power, and selecting proper type of motors. Edge longitudinal strain of numerical simulations of the present study is veried by numerical results of Lindgeren, 2007 [8]. This comparison shows that numerical results of the present study is near to the results of Lindgeren, 2007. Results show that edge longitudinal strain decreases with the increase of yield strength. These results also show that the increase of edge longitudinal with the increase of roll forming angle.

In recent decades, there have been great eorts to simulate ow in hydrocarbon reservoirs and oil recovery processes. Compositional model is one of the most advanced models for this purpose. In this model, nonlinear mass conservation equations for multicomponent ow have to be solved along with thermodynamic equilibrium constraints. In most compositional simulators, an equation of state is used to determine phase behavior of hydrocarbon mixtures. In this article, an ecient two-phase compositional model for both immiscible and miscible uid ows in porous media is presented. In this model, the mass conservation equations are discretized using a cell-centered control volume method. The solution algorithm employs the so-called Implicit Pressure Explicit Saturation (IMPES) method. To determine the thermodynamic state of the mixture, the equation of state must be solved at each time step for each computational cell. These computations consume considerable time in a compositional simulation. Compositional space is parameterized with tie-line variables, and this parameterized space is used to reduce the number of times the equation of state must be solved. To parameterize compositional space, a few supporting tie-lines are needed, which were obtained adaptively during simulation process. The tie-line space is discretized using these supporting tie-lines and a Delaunay triangulation procedure. In the rest of discretized tie-line space, thermodynamic properties are calculated using linear interpolation. It is important to note that the equation of state is solved only at the supporting points used to discretize the tie-line space. Since tie-lines do not exist in the super-critical region, the space is represented based on overall compositions and equation of state. In this work, the used method keeps continuity of tie-line variables and overall compositions with respect to the change of the mixture state from sub-critical to super-critical space, and vice versa. The performance of the proposed approach is assessed using a number of homogeneous one-dimensional multicomponent problems. Numerical results show200e that the proposed method has acceptable accuracy and signi cantly reduces the total number of ash calculations needed in a compositional simulator.

Estimation of properties of near-wellbore damaged zone made by drilling, completion, injection, and other operations is a challenging issue in reservoir engineering. Researchers have proposed dierent methods to predict reduction in damaged zone permeability; however, few studies have focused on the prediction of the damaged zone radius and its permeability. In this study, a simple and practical method is proposed to predict the damaged zone properties, i.e., radius and permeability, based on pressure drawdown test data. In this approach, pressure derivative curves for a homogenous reservoir as a base case and a reservoir with spatial permeability variation based on Composite Reservoir model are compared. Eventually, the pressure data points were used for comparison from a drawdown test in a synthetic reservoir model. This spatial permeability variation represents a permeability anomaly. Permeability anomaly makes pressure derivative curve deviate from base curve for corresponding homogenous reservoirs. The parameters of permeability anomaly such as size, orientation, and location have dierent eects on pressure derivative curve. In reservoir with simple permeability heterogeneity that has a single permeability anomaly, originating location and end location of an anomaly can be predicted by pressure derivative curve. In this study, damaged area radius of a damaged homogeneous reservoir, causing a single anomaly in permeability, is calculated by means of pressure derivative curve, known correlations, and the result from pressure wave propagation concept in reservoir. Short-term pressure data is used to measure the damaged permeability. The method has been validated in a synthetic cylindrical reservoir generated by numerical simulation, as well as in an actual reservoir. For the actual reservoir example, validation is made by comparing the results with Skin Factor model. The proposed method is suggestive of its ability to predict the damaged radius and permeability very well.

Regarding the variability nature of the solar ray in a day, application of a thermal storage system seems necessary to accompany the solar system. Latent heat energy storage in a solar water heater can occur in a phase-change material. These materials are generally encapsulated in a container and positioned in the water container. Shape, material type, and size of the encapsulating container have direct eect on the eciency of the storage system. In this paper, eort has been made to investigate experimentally the encapsulation diameter eect on the storage system eciency. Industrial paran with 5- 7% fat was used as a phase-change material. They were encapsulated in aluminum tubes of 6, 10, and 12 mm diameter. The thicknesses of the capsules in all diameters are 1mm. For each tube size, a set of tests was carried out. For each test, 88 capsules with 280 mm height containing the paran were used. As a result, for capsules with 6, 10, and 12mm diameter, 281.6gr, 1126.4gr, and 1760gr of paran were used, respectively. The results show that the rate of energy storage using aluminum tubes of 6, 10, and 12 mm with phase-change material in comparison to when using no phase-change material, improved energy storage eciency by 4.4, 15.3, and 11.2%, respectively. With regard to the fact that by reduction of capsule diameter, the rate of surface area to the volume increases; hence, heat transferring surface area increases. Therefore, it is expected that by reducing the capsule diameter, density of energy storage will increase. Consequently, by reducing the capsule diameter, total paran mass will decrease. Hence, by considering these two factors, maximum rate of energy storage occurs when the capsule diameter is 10mm.

A signicant part of the total annual energy consumption is used in buildings. The most part of the energy consumption in buildings is due to the HVAC systems. As a result, the eciency of air conditioning systems plays an important role in energy saving. In the recent years, variable refrigerant ow (VRF) systems have become popular, especially for commercial buildings, due to their high eciency and their ability in simultaneous heating and cooling. In this research, VRF systems are investigated from the second law of thermodynamic point of view; the eect of design parameters and the refrigerant type on the system performance is studied. At rst, the thermodynamic cycle of VRF systems is modeled. Comparison of the numerical results with the available experimental data shows that the developed model can predict the system behavior with reasonable good accuracy. Based on the results, the coecient of performance (COP), the exergy destruction, and the exergy eciency of the VRF system are evaluated to investigate the system eectiveness. The results indicate that the compressor and the condenser are responsible for the most exergy destruction in the system, while the exergy destruction in the sub-cooling heat exchanger and the expansion valve is the least. In addition, the refrigerant type is an important parameter which may aect the system performance. Considering the importance of the sub-cooling heat exchanger, the eect of the heat exchanger on system performance has also been investigated. It has been found that the eect of the subcooling heat exchanger depends on the refrigerant type. In the systems using R-134a and R-407c, the heat exchanger improves the system eectiveness; if R-22 and R-410a are used as a refrigerant, the system performance decreases. The results of this paper are useful in getting a better understanding of the VRF systems and in designing more ecient ones.