Scientia Iranica
Volume:29 Issue: 3, May & Jun 2022

In the current study, two different vessels with a single step and two steps are experimentally and numerically studied. The considered speeds are 8 and 9 m/s, equivalent to beam Froude numbers of 3.44 and 3.86. The experimentally measured parameters include bow rise-up, trim, and vessel’s resistance. On the other hand, numerical simulations of fluid flow around the vessel at 10 m/s and 12 m/s speeds are conducted using STAR-CCM+ software. Two-phase flow is analyzed using finite volume method and volume of fluid technique. Moving mesh approach through the Overset technique is applied for discretization of the domain. Based on the experimental results, it is observed that addition of the transverse step enhances the vessel’s stability and reduces its trim. It is also concluded that the resistance of a single stepped high-speed vessel reduces, compared to a vessel of without step. Meanwhile, numerical studies indicate that as the second step moves away from the transom, the resistance increases, and trim decreases. It is also concluded that both single-step and two-step models are stable at speeds up to 12 m/s.

In this paper, the effects of flapping flexible vortex generators in a two dimensional turbulent free convection airflow in a double-pass solar air heater are discussed. Two thin elastic winglets, used here as vortex generators, are attached on two absorber walls near the inlet section with the attack angle of 65o. This novel concept is demonstrated using transient numerical simulation of the flow field by the finite element method with considering the Fluid-Solid Interaction. In this work, an extensive comparison is made between four different configurations. The absorber and outlet temperatures, as well as flow rate and velocity field, are discussed in detail and the numerical findings reveal considerable thermal performance enhancement in comparison with conventional parallel double pass heater. The improvement up to 54% in the ∆T ̅=T ̅_out-T_in , from 13 to 20 o C, while reducing 33.6% flow rate. The present numerical results are validated against the experimental and numerical data reported in the literature.

Importance of maneuverability as a main feature of safety for a marine craft is broadly recognized. Mathematical modeling together with Maneuver Hydrodynamic Coefficients (MHCs) is employed for maneuverability simulation. Generally, experimental, analytical and numerical methods are employed for extraction of MHCs which 2D+t approach is recently employed. In this study, roll restoring MHCs of planing hulls are evaluated by the 2D+t approach. Running attitude of planing boats alters during any kind of maneuver due to forward speed change. This study presents a simple and applicable PMM procedure for consideration of running attitude to extract MHCs. In this procedure at a given forward speed, the planing hull is restrained to PMM apparatus in a fixed running attitude resulted from conventional resistance test at the same forward speed. This procedure is employed by 2D+t method for prismatic planing hulls in a set of forward speeds in roll condition. It has resulted three regression formulae for Y_ϕ, K_ϕ and N_ϕ as function of dead-rise angle and Froude number. The result of this study can be directly used in simulation of maneuvers via mathematical model. Moreover, this approach may be followed for other MHCs related to sway and yaw motions in future work.

In this study, factors affecting average shot velocity in the SMAT process were investigated numerically. The numerical model was developed by using the finite element method. The effects of frequency, amplitude, and projection distance parameters on shot velocity were simulated. Response Surface Methodology was used to evaluate the simulation results. ANOVA tables were used for statistical evaluation. Moreover, the regression equations derived from simulation results were compared with the theoretical equations. Besides, the effect of the amount of shot in the SMAT chamber on the speed of the shot is simulated. The results showed that apart from frequency and amplitude, projection distance also had a significant impact on shot velocity.

Two methods which are computationally simple and easy to apply are developed by using state dependent Riccati equation (SDRE) approach and approximating sequence of Riccati equation (ASRE) approach to control active suspension system in the presence of nonlinear spring and damper. Additionally, effectivenesses of the both control methods developed by utilizing two recently introduced SDRE and ASRE techniques are compared. First, methodologies of both approaches are presented. After that, nonlinear dynamics of the vehicle suspension system is described in terms of conveniently selected state variables for better control performance. Then, a cost function is written by using suspension and tire deflections, sprung mass velocity and acceleration, and unsprung mass velocity variables to improve ride quality, suspension deflection, and tire deflection. Additionally, a convenient representation of this cost function in terms of state variables is obtained to realize better control. A bump expressed as sinusoidal function and roughness of the road expressed as white noise are taken into consideration as the disturbances from the road. Finally, quarter vehicle suspension system equivalent model of Ford Fiesta Mk2 is used as an example and simulations obtained by using the developed control methods are checked against the performance requirements and corresponding passive suspension system.

In this examination, a sensitivity analysis is implemented using response surface strategies to control the Walters-B nanofluid stagnant point flow caused by a Riga surface. An electromagnetic actuator is known as Riga-surface. The Buongiorno model is used to construct the mathematical model, which includes a Newtonian heating condition as well as radiation effects. Via the fundamental laws of mass, momentum, and energy, transformation is incorporated to obtain nonlinear ordinary differential equations. To solve the governing system, the numerical shooting approach along with Runge-Kutta scheme is used to solve the governing system. A comparison with existing research is made, and the results are obtained to be in strong agreement. Focusing on the response of local Nusselt number to variation of input variables, an experimental structure is incorporated by sensitivity analysis. As underline, the LNN is quite sensitive to radiation number rather than other parameters of interest. Meanwhile, it is demonstrated that sensitivity of LNN to Brownian number decreases with growing thermophoresis number but sensitivity value is also vary from positive to negative for all values of Brownian number. The results are assumed to provide a tentative guidance for possible lab-based experiments.

In the present article, the vibrational behavior of buckled functionally graded (FG) circular plates with clamped and simply-supported edge conditions is described. Considering von Kármán’s assumptions, the geometric nonlinearity is incorporated into the Kirchhoff plate theory and the nonlinear governing equations of motion are then derived using Hamilton’s principle. Critical buckling load and linear natural frequencies are first calculated using the generalized differential quadrature (GDQ) method. Afterward, the postbuckling characteristics of the circular plate are obtained via solving the nonlinear governing equations, directly. By several comparative studies, the reliability of the presented model is revealed. Finally, the fundamental natural frequency of the plate is evaluated for prebuckled and postbuckled configurations. The effects of material property and boundary conditions on the static bifurcation diagram and the natural frequency of the initial undeflected and bucked plate are studied. It is found that the trend of the fundamental natural frequency changes with the applied radial load around the prebuckled configuration is unlike the one around the buckled configuration.

BASHTI implant-less technique has been proposed as an alternative to conventional tendon repair methods. This study aims to evaluate the strength of this technique under biceps loading conditions with different fixation strategies. Twelve specimens with bovine tendons and Sawbones were constructed using two different insertion methods; in Group 1, 4 samples were prepared using a hand-hammer with a hitting frequency of 300 beats per minute (BPM), while Group 2 included eight specimens with insertion using an auto-hammer applying a frequency of 3600 BPM. Both groups were tested under a cyclic loading followed by a pull-out until the failure. All the samples completed the cyclic step without failure. At the pull-out step, for Group 1, the strength was 251±31 N, and the stiffness was 10.3±0.8 N/mm, while these values were 183±35 N and 10.5±3.0 N/mm, respectively for Group 2. It was concluded that the BASHTI structure for biceps tendon reconstruction had a suitable strength and the insertion process had no effect on its behavior under cyclic loading. It was also proved that variations in the insertion frequency significantly affect the structure's maximum strength (p-value = 0.038). Still, its influence on the stiffness was insignificant (p-value = 0.91).

In this study a technique has been addressed in order to model and optimize AWJM process. The required data for modeling and optimization purposes has been achieved using orthogonal array Taguchi (OA-Taguchi), D-optimal techniques and their combination based on design of experiments (DOE) approach. Water pressure, abrasive flow rate, machining speed, and machining gap are the process variables considered in this study. To evaluate the process, surface roughness (SR) has been taken into account as the process characteristic. Regression modeling using which has been turned into a widely used method has been employed to establish a relationship between process input variables and output characteristic. Analysis of variance (ANOVA) has been employed to evaluate the adequacy of the proposed models among which the most fitted and proper ones selected as the authentic representative of the process and considered as the process objective function to be optimized. Next, to optimize the objective function in order to get the desired characteristic (SR), the proposed model has been embedded into simulated annealing (SA) algorithm. Based on the computational results (less than 4% error), the proposed procedure is quite effective in modeling and optimization of the process.

Depletion of freshwater resources and reduction of rainfall in arid areas causes water scarcity, which is intensified by population and urbanization growth. In this study, a small-scale solar thermal/desalination combisystem using nanofluid-based direct absorption solar collectors and humidification-dehumidification desalination unit is proposed to supply domestic hot water, space heating, and freshwater demands of a residential building. The dynamic simulation of the system performance in the Hot-Dry climate zone is done using TRNSYS-MATLAB co-simulator. The results indicate that using the proposed combisystem reduces 94.3% and 17% of annual energy consumption for providing domestic hot water and space heating demands, respectively. The freshwater demand is supplied in the range of 11.3% to 100%. In the case of using a flat plate solar collector, the solar fraction for domestic hot water and space heating demands in comparison with nanofluid-based direct absorption solar collectors reduces by 3.7% and 1.7%, respectively. Furthermore, the produced freshwater reduces 18% on average. The payback time using nanofluid-based direct absorption and flat plate solar collectors are 6.4 and 7.8 years, respectively.