Scientia Iranica
Volume:31 Issue: 4, Mar-Apr 2024

Obtaining the required surface finish and geometric accuracy together with attaining high production rate is a challenge in finishing of the inner surfaces of steel pipes and bushes. One of the promising techniques for finishing the surface of metal parts is electrochemical machining. In this paper, the surface roughness and dimensional inaccuracy of the inner surface of a CK45 steel bush were controlled electrochemically. For this, a special electrochemical finishing machine was constructed. The effect of electric potential difference along with temperature, flow rate and concentration of electrolyte on the material removal rate, surface roughness and dimensional accuracy were investigated. Box Behnken design (BBD) was used for designing the experiments. Analysis of variance (ANOVA) was performed for validating the experimental models. Also, multi-objective optimization was performed using response surface methodology (RSM) to achieve a predetermined level of surface roughness and dimensional accuracy along with maximizing the material removal rate.

Intervertebral disc (IVD) carries compressive loads and resists the tensile and shear stress, produced during bending and rotational movements. Hence, identifying its mechanical behavior has always encouraged researchers to propose various models for this tissue. Both viscoelastic and hyperelastic behavior have been observed regarding the IVD. Therefore, this study aims at mechanically characterizing the tissue using the existing hyper- and viscoelastic constitutive models and further discuss the best ones. Three stress relaxation tests were performed on ten ovine cervical IVD samples to evaluate their viscoelastic behavior. Models with linear, quasi-linear, and nonlinear behavior were implemented. For the hyperelastic response, another test was carried out using a load with a constant strain rate to fit seven previously suggested hyperelastic constitutive models to our recorded data. All tests were performed as uniaxial compression. Calculations were made using isotropy and incompressibility assumptions. Results approved the nonlinearity of the tissue’s viscoelastic behavior since the linear models predicted divergent responses for different strain inputs. However, modified superposition theory, featuring a time- and strain-dependent relaxation function, was the most accurate model to predict the IVD response at different strain levels. As for hyperelasticity, Mooney-Rivlin, Yeoh, and Veronda-Westmann models fitted the experimental data with higher R2 values.

Localization of the delamination is an essential task that is conducted by various destructive and non-destructive approaches, which may require time, experts, and cost. Various intelligent non-destructive techniques are utilized to reduce time consumption, the need for expertise, and expenditures for localizing compositing delaminations. Yet, developing an accurate, robust, and low-cost intelligent delamination identification technique becomes a challenging task due to the anisotropy and the variation in the fiber orientation of the composites. Based on those issues, it is aimed to develop an effective intelligent model to localize delaminations in composite plates. This study measures the performance of the Bagging and Boosting techniques on delamination localization in thin composite plates. To validate the effectiveness of the proposed approaches; cross-ply, angle-ply, and quasi-isotropic composite plates having 2400 different delamination cases are considered. The bagging and boosting models are trained with the vibrational characteristics of the healthy and delaminated composite structures. The free vibration analysis is conducted for those structures to obtain the first five natural frequencies and the corresponding mode shapes. For this purpose, Classical Plate Theory is employed by using Finite Element Analysis. It is concluded that both bagging and boosting techniques are robust, precise, and accurate in localizing delamination.

In this paper, a conceptual model is proposed to investigate the nonlinear dynamics of the transverse vibrations of the floating wind turbine. The conceptual models are the best tools to capture the most important phenomena in the dynamic response of the systems. First, the surge dynamics of the TLP platform is modeled as a nonlinear spring. Then the fore-aft motions of the wind turbine is modeled as a spring-mass system. Then simulations are carried out to evaluate the time response of the proposed model. Afterward, the FAST code is utilized to verify the proposed model. The internal resonance and its combinations with the primary resonance are studied by the multiple time scale method. Finally, the frequency response curve is obtained and the effect of the various parameters of the system on the amplitude and the stability of the oscillations are investigated.

Friction stir welding of Titanium sheets is carried out under air and water environment and the tensile properties of the joints made are measured. The tool rotational speed and tool traversing speed which significantly influence the tensile properties of the welded joints are considered as input process parameters. This work deals with the application of Analytic hierarchy process to calculate the weights of the relative importance of the output responses using the pairwise comparison of responses and checked for the consistency and acceptability of the assumed comparison. Also, the VIKOR optimization technique, a multi-response multi criterion method, is used for determining the optimum process parameters. From the VIKOR optimization method, it is observed that the higher tool rotational speed and lower tool traversing speed are the optimum process parameters in both conventional and under water FSW. The results from the experimental measurements and the study of microstructure supports the results obtained from VIKOR optimization method.

The compound parabolic concentrator (CPC) is designed and its optical and thermal analysis is performed in ANSYS. The CPC sizing and the optimal mass flow rate by maximum power point tracking (MPPT) method in MATLAB are determined. The radiative transfer equation is solved by Discrete Ordinate (DO) and Mont Carlo (MC) models and the deduced radiative flux divergence is applied as a source term in Navier-Stokes equations to model heat transfer. Results indicate that MC is faster than DO with lower computational cost and higher accuracy. The optimal mass flow rate at each time-variable solar radiation is calculated from MPPT control and entered as the inlet boundary condition for 3D CFD model. The absorbed useful power by MPPT is about 4% higher than the constant mass flow rate case. Reduction of the convective heat transfer by locating the evacuated tube collectors inside a cavity leads to 12% more power and 25% temperature enhancement in 3D model with respect to MPPT-based analytical results. Then, the evacuated collector in a cavity with MPPT control has about 16% power gain.