https://jsfm.shahroodut.ac.ir/ Journal of Solid and Fluid Mechanics en daily 1 Tue, 06 Jun 2017 00:00:00 +0430 Tue, 06 Jun 2017 00:00:00 +0430 https://jsfm.shahroodut.ac.ir/article_944.html In this paper, fist, operation of Ramin power plant cooling towers at present condition and then with packing substitute assumption was simulated. mathematical modeling of heat and mass transfer with Merkel simple assumption in the tower is used. The governing partial differential equations of air and water in the tower packing was derived by using mass and energy balances.Then the governing equation were solved by numerical method. after that tower characteristic was calculated and cooling tower performance in varied ambient condition during several month of a year was simulated and was compared with available experimental data in the power plant. After packing substitute, new operation points are achieved and cooling tower performance in this point is predicted and compared with the operation results of the old packing.The results of simulation show that the range of cooling tower after packing substitute is increased until 5.5 oC relatively and was reached from 10 oc to 15.5 oC at new conditions. https://jsfm.shahroodut.ac.ir/article_3773.html Noise pollution poses a significant threat to human health and ecosystem stability. Carbon-based nanostructures, with their exceptional mechanical strength and unique geometries, offer a promising strategy for nanoscale sound absorption. In this study, molecular dynamics simulations were employed to examine acoustic wave propagation and absorption in argon gas. The model was first validated without an absorber, followed by an analysis of how nanotube diameter, quantity, arrangement, and frequency influence key acoustic parameters, including attenuation, wave number, and absorption coefficient. Findings indicate that larger nanotube diameters enhance effective contact area, while increasing the number of nanotubes shortens molecular free paths, thereby improving absorption. A triangular arrangement maximized absorption by confining space and intensifying gas–wall interactions. Frequency-dependent analysis showed a clear correlation between frequency, attenuation, and absorption, aligning with previous studies and confirming the simulation’s validity. The study is limited to argon gas and single-walled nanotubes of restricted dimensions. Nonetheless, the results underscore the critical role of optimizing nano-absorber geometry and structural parameters for designing effective high-frequency noise-control systems. https://jsfm.shahroodut.ac.ir/article_3770.html In this paper, a multiphysics framework is proposed for the analysis and mitigation of torsion in ionic polymer–metal composite (IPMC) actuators, where both viscoelastic and electroactive effects of the material are considered simultaneously. The governing equations were first derived based on Euler–Bernoulli beam theory and the principle of minimum energy, and then coupled with the Nernst–Planck–Poisson electrochemical relations to obtain the torsional moment induced by ion migration under an electric field. To account for material softening, the mechanical moduli were formulated as combined models dependent on both time and electric field. Numerical simulations reveal that, under an applied voltage of 5 V and a thickness of 1 mm, the shear modulus decreases by nearly 85% within about 10 seconds; however, by introducing transverse stiff layers and symmetric longitudinal excitation, the torsional moment drops to less than 5% of its initial value and the torsional angle is effectively eliminated. A stability analysis was performed through the definition of a specific index that simultaneously captures the influence of time, electric field intensity, and boundary constraints. The numerical results demonstrate that while modulus reduction over time and with higher voltages decreases the shear and bending stiffness and increases viscous energy, the imposition of boundary conditions at the edges suppresses torsion even under severe softening. Geometrical sensitivity analysis further indicated that variations in length and width have only a limited effect on viscous energy, whereas boundary conditions play a decisive role in torsion control. https://jsfm.shahroodut.ac.ir/article_3775.html In this study, fiber-assisted polishing is presented as a method for eliminating undesirable defects caused by abrasives on the surfaces of sensitive components such as prostheses, lenses, and turbine blades. To this end, a polishing tool based on coarse sisal fibers was first fabricated. Subsequently, the performance of this tool on the surface roughness ratio and polishing rate of an artificial femoral head made of 316L stainless steel was investigated. The results indicate that the coarse sisal fiber-based polishing tool effectively and efficiently finishes the surface of the artificial femoral head. Microscopic observations revealed that the main finishing mechanism is the gradual fracturing of sisal fibers and the formation of self-adaptive sisal fibrils that act as soft abrasives. Over a period of 2.5 hours, this process transitioned from the roughing phase to nano-finishing, producing a surface with an average surface roughness (Ra) of 36.96 nm and a mirror-like reflection on the femoral head. Consequently, the sisal fiber-based polishing tool is proposed as an efficient method for surface modification of components with complex geometries in the medical, aerospace, and automotive industries. https://jsfm.shahroodut.ac.ir/article_3772.html In this study, the modeling of the critical manipulation force of particles in three-dimensional space was investigated using the Design of Experiments (DoE) approach. The main objective was to analyze the influence of geometric and control parameters on the critical force required for particle manipulation using an Atomic Force Microscope (AFM). Five key parameters, including particle radius (Rp), cantilever thickness (T), cantilever length (L), cantilever width (W), and tip height (H) were selected as input variables, while the critical forces in the X and Y directions were modeled and analyzed as output responses. Based on the results from 27 designed experiments and the statistical analysis of the derived regression model, it was found that cantilever thickness and particle radius had the most significant impact on increasing the critical manipulation force, whereas increasing the cantilever length and tip height led to a reduction in this force. The 3D surface plots revealed that the interaction effects between the parameters were considerable, and the overall manipulation performance strongly depended on the appropriate combination of geometric and physical properties. Additionally, residual analysis confirmed the normal distribution of errors and the high accuracy of the model (R² > 99%). The findings of this study can serve as a foundation for the optimal design and development of advanced manipulation tools. https://jsfm.shahroodut.ac.ir/article_3776.html The present study experimentally investigates the effect of flexible wing sweep-back angle on the aerodynamic characteristics and the thrust and lift coefficients. The experiments were conducted at Reynolds numbers of 42,000 to 170,000, which is the flight range for natural birds with dimensions close to pigeons. The model consists of two parts of rigid (at root) and flexible (at tip) and the oscillation is provided by an electro-mechanical system. The results show that increasing the speed at dimensionless frequencies less than 0.2 has caused a decrease in the wing lift. The thrust coefficient versus speed graph at angles of attack of zero to 6 degrees is completely different from angles of attack greater than 6 degrees; So that at an angle of attack of 3 degrees, the changes in speed were less than 10 percent; But at an angle of attack of 18 degrees, the thrust coefficient decreased by 50 percent as the speed increased from 5 to 20 meters per second. Also, the flexibility of the wing has caused the dynamic pressure difference of the flow to change the shape of the wing and ultimately reduce the lift coefficient of the wing. Likewise, the flow structure from an angle of attack of 9 degrees onwards is such that it is not capable of producing propulsive force. https://jsfm.shahroodut.ac.ir/article_3774.html This paper focuses on the numerical simulation and analysis of forced convection heat transfer of a paraffin-alumina nanofluid in a porous channel under an external magnetic field. To this aim, the dimensionless form of the Darcy-Brinkman-Forchheimer equations are solved under local thermal non-equilibrium conditions. The simulations are performed using the thermal lattice Boltzmann method with a single relaxation time scheme, incorporating distribution functions for velocity, nanofluid temperature, and porous medium temperature in an unsteady state condition. In this paper, the effects of parameters such as magnetic field angle, Darcy number, porosity, nanoparticle volume fraction, and Hartmann number on the average Nusselt number, degree of local thermal non-equilibrium, and melting fraction at different time intervals are investigated. The results show that the optimal melting performance occurs at the magnetic field angle of 90°, the Darcy number of 0.001, the porosity of 0.5, the Hartmann number of 30, the nanoparticle volume fraction of 4%, and the Reynolds number of 200, leading to a melting fraction of approximately 88.91% within less than an hour. Conversely, the weakest performance corresponds to the Hartmann number of 50, which increases the required time to reach the melting fraction of 85% to about 198.83 minutes. Furthermore, it is observed that an increase in the average Nusselt number is accompanied by an increased local thermal non-equilibrium. https://jsfm.shahroodut.ac.ir/article_3769.html In this paper , a new method is presented for analyzing the forward kinematics problem of planar parallel mechanisms based on a combination of interval analysis and a refinement process. In the first step , the kinematic equations of each chain of parallel mechanism are derived by applying the relevant kinematic constraints. Then , the forward kinematics problem is solved with the desired accuracy using a combination of interval analysis and mean-value form. For validation purposes , the results of the proposed method are compared with those obtained from the resultant method. The implementation of the proposed approach on a 3- RRR planar parallel mechanism demonstrates its capability to accurately estimate the position and orientation of the moving platform. The main advantage of this method is its high accuracy with reasonable computational efficiency , which makes it a promising option for solving the forward kinematics problem of planar parallel mechanisms. https://jsfm.shahroodut.ac.ir/article_3771.html Bolt loosening in mechanical joints remains one of the critical challenges in maintaining the structural integrity of industrial systems. In this study, a novel approach is proposed for monitoring the loosening status of bolts in a multi-bolt joint using low-sampling-rate acoustic emission (AE) signals. An experimental setup consisting of a four-bolt connection was designed, and acoustic signals were recorded under sixteen different bolt-tightening configurations. To analyze the signals, Mel-frequency cepstral coefficients (MFCCs) were extracted as feature vectors, and the root mean square deviation (RMSD) index was employed to quantify signal variations. The results showed that bolt loosening led to a noticeable increase in RMSD compared to the healthy state. However, no significant correlation was observed between the number of loosened bolts and RMSD values. Subsequently, five classification scenarios were designed, and the performance of a feedforward neural network was evaluated. The highest classification accuracy of 94.44% was achieved in the scenario where connections with one loosened bolts or more were separated from the rest. The proposed method, while relying on simple hardware and lightweight data, demonstrated high accuracy in the early detection of bolt loosening and shows strong potential for integration into continuous structural health monitoring systems in industrial environments.