Iranian Journal of Science and Technology, Transactions of Mechanical Engineering

The effects of inclined magnetic field on entropy generation in nanofluid over a stretching sheet were investigated in the presence of partial slip and nonlinear thermal radiation. Applying a similarity variable, the governing equations are reduced to a set of nonlinear ODEs. These equations are solved both analytically and numerically by hypergeometric function and Runge–Kutta Gill method with shooting technique, respectively. For Ag–water, magnetic, aligned angle, nanosolid volume fraction and slip parameters on velocity, temperature, skin friction coefficient and reduced Nusselt number were analyzed. The entropy generation for the influence of the same parameters, radiation parameter and the Reynolds number is discussed for Ag nanoparticles. It is observed that the nanosolid volume fraction and slip parameter reduce the entropy generation. But aligned magnetic field enhances the entropy generation.

Decreasing stress in a part or piece of equipment especially in a stress concentration point without increasing thickness or using stronger material is always an interesting issue for design engineers. In this paper, piezoelectric patches were used for stress concentration reduction around various hole sizes in thin-walled cylindrical shells subjected to internal pressure. Applied voltage to piezoelectric patches induces strain on both patch and part and alters stress flow on the part, leading to new distribution of stresses. Three dimensionless effective parameters that include hole and shell diameters as well as shell and piezo patch thicknesses were selected in this investigation. Ant colony optimization was utilized, and attachment of optimal arrangements of piezoelectric patches was derived for various numbers of piezoelectric patches. Using finite element analysis, it was shown that various combinations of these dimensionless parameters (R/t, tp/t and d/D) have different effects on reducing the maximum stress around the hole and up to 20% reduction on maximum stress was achieved during this research. Experimental tests were finally performed to verify finite element results.

In this paper, a modification of the mast, which is the main part of a vortex-induced wind generator was considered in order to improve the performance. Numerical simulations were applied to investigate the change in vortex shedding frequency behind an oscillating structure. Considering the identical vortex shedding frequencies throughout the whole mast, an expression for the characteristic length (ϕ) was defined. The numerical simulations were conducted for an oscillating cylinder at different wind speeds and for different A/D to present a formula for designing of the mast. The FFT was implemented to determine the frequencies. The results showed that for A/D > 0.2, the variations in characteristic length were not significant. It was found that for Re < 2 × 104, the variation in $$\phi /D$$ was considerable and was taken into account in the design of the mast. Using these results, an expression for calculation of the diameter of the mast at different heights was generated. Finally, a small mast with a height of 3 m was designed based on this method. For evaluation of the modified mast, a 3D simulation was conducted. Results showed that the vortex shedding frequencies were the same throughout the whole mast, which is desired.

The pump structure may involve using fins on the impeller discs to reduce axial thrust. The fins are also used to reduce pressure acting on the discharge-side stuffing box, throw mechanical impurities away and protect the seal against mechanical impurities at the pump impeller inlet. Extensive laboratory tests were performed on finned discs at the water centrifugal flow for different fin widths and gaps between fins and the casing and for different water flow rates. The resulting change in power consumption was determined compared to unfinned discs. The analysis results indicate that fitting the disc with fins involves an increase in power consumption. The consumption rise depends on the centrifugal volumetric flow rate, the fin width and the size of the gap. The dependence of power consumption on the gap size is non-monotonic—the gap can be optimized to minimize power consumption. The determination of the rise in the consumption of power resulting from fitting the disc with fins and depending on the centrifugal volumetric flow rate is an original outcome of the analysis presented in this paper. The dependence was defined for fins with different values of width and for different sizes of gap. The presented results of the testing can be used in the analysis of power consumption of both finned and unfinned rotating discs. The analysis of power consumption in the impeller pump axial thrust balancing system using balancing vanes is another example of the application of the obtained results.

To satisfy the maneuverability requirements in a complicated environment, fish have evolved with special segmented muscle to produce undulatory locomotion. Herein, we developed a three-dimensional W-shaped model of musculo-tendinous system to mimic realistic segmented muscle of fish, and directly quantify the relationship between local muscle contraction and the corresponding flexion. By regulating the key parameters of model, the variation in local muscle strain producing prescribed set of kinematics is calculated. Furthermore, the morphological variations of the musculo-tendinous system located in fish caudal region and the distinctions between different swimmers are also discussed. It is found out that for a desired bending curvature, strain of the musculo-tendinous system can be reduced by lengthening the model longitudinally. Thus, if the muscle contraction is fixed, larger amplitude and flexion can be achieved by elongating the W-shaped model. This also explains the morphological diversities of segmented muscle within anguilliform, carangiform, and thunniform. Fish with better swimming ability are likely equipped with relatively longer myomere and shaper pointing cones. Therefore, the musculo-tendinous system amplifies the body curvature, it has functional benefits on fish kinematics. In additionally, this paper may provide some inspirations on the structural design of fish-inspired soft robots.

This paper addresses a simple chattering-free and finite-time convergent robust synchronization scheme for a general class of disturbed master and slave chaotic systems. Unlike traditional variable structure control schemes, the proposed controller does not directly include a switching function, and chattering is avoided. The term including switching function is the input of a low-pass filter where the filtered output is used in the controller. Also, numerical differentiation of master and slave state trajectories is not required to implement the controller. Stability of the proposed controller is established using a Lyapunov stability analysis and the finite-time convergence theories. Simulation results validate the effectiveness and robustness of the proposed control scheme.

Recently, simple shear extrusion (SSE) was introduced to fabricate ultra-fine-grained materials. It was designed for billets with square cross sections and was investigated well previously. This study aims to introduce a new alternative design of simple shear extrusion process with a circular cross section, which is named circular simple shear extrusion (CSSE). Therefore, the finite element analysis is applied for investigating the deformation behavior during the CSSE process. The results show that the CSSE process fills the die with less back-pressure and the strain values are closer to theoretical ones in comparison with SSE with a square cross section. Moreover, this new alternative is needed to lower the extrusion pressure compared to SSE with a square cross section. In addition, the contact pressure and the maximum principal stress in a die with a circular cross section are lower in comparison with the square one which leads to a longer service life of CSSE’s die. Hence, this new geometry will provide more potential in terms of industrial applications.

The objective of the study is to establish a new correlation to estimate the daily air temperature using total solar radiation, atmospheric pressure and relative humidity. Multiple sites are used to test the efficiency of the proposed model. Statistical parameters were used to determine the accuracy in applying the model. Temperature is a physical quantity that manifests itself in the sensation of heat and cold in humans. It comes from the thermal transfer between two bodies that lead to an increasing thermal agitation of the particles that compose matter (molecules or atoms). This agitation causes a permanent vibration (kinetic energy). The propagation of light (solar radiation) in a medium (air) gives rise to the increase in energy. Temperature may be regarded as an indirect measurement of this microscopic agitation of atoms or molecules. The study of weather phenomena (meteorology) such as sunlight, clouds, wind speed and their evolution is in accordance with the measured parameters (pressure, temperature and humidity). The purpose of this study is to predict the evolution of weather with respect to these parameters using mathematical models. The daily air temperature value is the average value of all the instantaneous air temperatures of the day. The mean R2 values range from 0.655 to 0.782, giving good precision. The results showed that the model was more precise and performed reasonably well in various locations.