https://jcarme.sru.ac.ir/ Journal of Computational & Applied Research in Mechanical Engineering (JCARME) en daily 1 Tue, 01 Jul 2025 00:00:00 +0330 Tue, 01 Jul 2025 00:00:00 +0330 https://jcarme.sru.ac.ir/article_2495.html Numerical techniques for solving dynamic structural problems often encounter significant challenges, including conditional stability, period elongation errors, amplitude decay errors, and the emergence of spurious frequencies. To address these issues, several first-order precise integration methods have been developed; however, these approaches still suffer from errors associated with the inversion of the state matrix. This study employs the singular value decomposition technique to enhance the efficiency of the precise integration method algorithm and eliminate the singularity of the state matrix. The robustness of the proposed method is evaluated across various transient dynamic problems. The results demonstrate that traditional approaches, such as the Newmark method, exhibit substantially larger errors—exceeding 150% in certain cases. Ultimately, the findings emphasize that accurately estimating the dynamic response of multi-degree-of-freedom systems under impact loading requires careful consideration. Conventional methods, including the Newmark average acceleration technique, should therefore not be applied indiscriminately. https://jcarme.sru.ac.ir/article_12598.html Chillers are among the most widely used air-conditioning systems, and improving their thermal performance can significantly reduce energy consumption. In the present study, the effects of Al₂O₃/water and Al₂O₃–TiO₂/water nanofluids on the performance characteristics of a shell-and-tube chiller evaporator were numerically investigated using an Eulerian-Lagrangian Discrete Phase Model (DPM). The influences of nanoparticle volume fraction, inlet fluid temperature, evaporator temperature, mass flow rate, and number of baffles were examined. Three evaporator configurations with 3, 5, and 7 baffles were considered.The results showed that increasing the number of baffles from 5 to 7 enhanced the overall heat transfer coefficient by 6.94%. The addition of Al₂O₃ nanoparticles increased the overall heat transfer coefficient by 5.8%, while the use of Al₂O₃–TiO₂ hybrid nanoparticles resulted in an enhancement of up to 8.8%. Analysis of the performance evaluation criterion (PEC) indicated that nanoparticle volume fractions up to 0.03 provide favorable thermal performance, with an optimum value around 0.02. The results also demonstrated a significant difference between the DPM and conventional single-phase predictions, with a relative discrepancy of approximately 68% in the estimated heat transfer enhancement under the investigated conditions. The findings confirm the potential of nanofluids, particularly hybrid nanofluids, for enhancing the thermal performance of shell-and-tube chiller evaporators. https://jcarme.sru.ac.ir/article_2452.html The hand plays a crucial role in daily activities; injury or paralysis significantly reduces independence. Therefore, robotic hand exoskeletons have been developed to restore motor function safely and effectively. Considering the major role of the hand in daily activities, many researchers have been working on hand rehabilitation exoskeletons. This research presents the design and implementation of a tendon-driven exoskeleton for finger rehabilitation. Continuous passive motion devices are used to maintain and restore the range of motion of the joints. The exoskeleton has been designed to help patients easily perform functional tasks. To achieve this goal, an adjustable thimble mechanism with flexible filament and a finger guide was designed. Also, this design provides the necessary force to fully guide the fingers through the whole range of motion of the joints. The designed mechanism has been modeled and simulated in MATLAB software. It has also been tested on healthy human subjects. Recorded images from the index finger in a complete range of motion have been analyzed to find the finger trajectory during flexion. The metacarpophalangeal joint of the index finger in healthy subjects has a range of motion between 0 and 90 degrees, while the exoskeleton can provide a range of motion between 0 and 94 degrees. Results show that the designed exoskeleton can provide sufficient force and an acceptable range of motion for patients up to level 2 of the Ashworth scale, which is acceptable for most different and functional varieties of continuous passive motion exoskeletons. https://jcarme.sru.ac.ir/article_12597.html The first stage compressor blades of the gas turbine are subject to occasional failure due to their operating conditions. Initial evaluations indicate that microcracks that form in critical areas of the blade during fatigue loading make the blade prone to failure. Therefore, it is of great importance to find the locations of the blade where microcracks are most likely to form. In this study, extensive numerical and analytical investigations were performed to evaluate the observed failures, and Abaqus software was used for finite element analysis of the first stage compressor blade of the gas turbine model. In pursuit of this goal, initially, finite element simulations were conducted on an intact blade, followed by analyses on a blade incorporating a V-shaped notch, and subsequently, applying stress analysis, the critical positions that are the main candidates for the formation and initiation of microcracks in the blade were determined. In addition, a new critical plane fatigue model was applied to evaluate and investigate the fatigue behaviour of the compressor blade. Then, through coding in MATLAB software, the plane that suffered the maximum damage based on the critical plane fatigue model was determined and its direction was calculated for the critical positions of the compressor blade. Finally, the compressor blade fatigue life was determined based on this criterion and compared with traditional critical plane fatigue criteria such as Brown-Miller and SWT, and the reduction in life due to foreign object damage to the blade was determined and compared to an intact blade. https://jcarme.sru.ac.ir/article_2537.html The occurrence of the cavitation phenomenon in hydraulic structures operating under high flow velocities remains a critical challenge. Efficient mitigation strategies may include increasing air concentration and optimizing the geometric design, such as minimizing sharp changes in flow direction and reducing local vortices. The Seymareh dam bottom outlet, operating under high water heads, is prone to cavitation due to its velocity and pressure fields. This study numerically investigates the effects of geometric modifications on cavitation risk reduction. Results showed that removing lateral expansion increases cavitation indices on outlet walls, while designing a concave curved bed elevates pressure and cavitation indices on the bed surface. Nonetheless, implementing both modifications together completely suppresses cavitation risk. The numerical analysis was conducted under single-phase flow conditions, without considering air entrainment, which, in practice, could further improve outlet safety. These findings could provide useful insights for geometric design approaches to control cavitation in high-velocity hydraulic structures. https://jcarme.sru.ac.ir/article_12594.html This study investigates crack formation and rupture in a newly developed "SCDA expansion forming", which utilizes the pressure generated by a soundless chemical demolition agent (SCDA). The research integrates experimental analysis and finite element analysis (FEA) to examine the forming of a 1 mm thick St12 low-carbon steel sheet into a dome shape. The experimental phase involved using Green Rock SCDA within a rigid steel die under test conditions of 75°C temperature, 25% water content, and 300 g mixture mass. The corresponding FEA was performed in Abaqus, applying the forming limit diagram (FLD) damage model criteria to predict necking instability and crack formation. The results from both the simulation and the experimental tests demonstrated that rupture occurs in the areas between the dome's center and its corners. FEA revealed that the maximum plastic strain and stress are concentrated in these central regions, leading to localized thinning and eventual failure. The experimental findings confirmed the location of the crack, thereby validating the accuracy of the numerical model. Analysis of the fracture surface via scanning electron microscopy (SEM) indicated a ductile fracture mechanism, characterized by dimples formed through a combination of shear and tensile modes. https://jcarme.sru.ac.ir/article_2451.html Electrochemical machining (ECM) is an effective method for machining CMSX-4 superalloy, a single-crystal nickel-based superalloy, due to its unique performance in metal machining. The microstructure of this superalloy consists of three phases: gamma (γ), gamma prime (γ'), and carbide. The gamma prime phase is distributed cubically and homogeneously in the gamma field without any boundaries. It is essential to maintain this microstructure after the production process. In the present study, ECM was performed on a CMSX-4 superalloy workpiece. The microstructure of the workpiece was then investigated before and after ECM using scanning electron microscopy and energy-dispersive spectroscopy analysis from two sides. The results showed that no changes were observed in the CMSX-4 microstructure after ECM process. The single-crystal structure and the distribution of the gamma prime phase were maintained after this machining process, indicating that ECM is an effective machining method for CMSX-4 superalloy without compromising its critical microstructural features. https://jcarme.sru.ac.ir/article_2546.html Computational models/methods are regularly used by the engineering community to evaluate the optimal set of solutions with respect to the defined performance criteria. In the case of multi-objective optimization problems, the set of Pareto front or optimal solutions needs to be evaluated with a simple and effective search methodology to help the decision maker select the best parameters/factors. In this study an attempt has been made to optimize the content of MWCNTs, cutting speed, and feed rate to minimize delamination factor and thrust force during drilling of MWCNTs reinforced GFRP nano-composite. Entropy-weighted TOPSIS and BHARAT approaches are implemented successfully for evaluating optimal parameters. Experimental result analysis suggests that feed rate being the major contributing factor for affecting delamination factor and thrust force. The optimized levels for MWCNTs, cutting speed and feed rate are 3 (1%), 3 (75 mm/min), and 1 (0.1 mm/rev), respectively, as obtained by both methods. Comparative analysis of entropy-weighted TOPSIS and BHARAT approach has been performed in relation to multi-criteria decision-making problems. The evaluated Pearson's and Spearman's correlation coefficient for both methods are 0.98, suggesting a high correlation between both methods. https://jcarme.sru.ac.ir/article_2410.html Rolling bearings are critical components of rotating machinery, and their health status directly affects the operational reliability of equipment. This paper proposes an optimized wavelet-SVM fault diagnosis method based on multi-source vibration signal fusion: Three-channel inputs are constructed by synchronously collecting vibration signals from the drive end and fan end, along with their differential signals; Wavelet packet decomposition is utilized to extract frequency-domain features such as unit node energy entropy and wavelet coefficient standard deviation, while dimensionless indicators independent of rotational speed (kurtosis factor/waveform factor/impulse factor) are introduced to enhance time-domain characterization; The fused features are input into an RBF-SVM classifier after dimensionality reduction via PCA (retaining 99% variance, reducing dimensions from 102 to 4). Experiments indicate that on the CWRU dataset, this method achieves 97.0% precision, 96.9% recall, and an F1-score of 96.9% (representing a 2.9% improvement over single-source input methods); Although there is a 2.4% absolute accuracy gap compared to deep learning solutions, it possesses significant edge advantages—memory usage is only 12KB and inference latency is 0.6ms—providing a high-precision, low-cost embedded solution for rotating machinery fault diagnosis https://jcarme.sru.ac.ir/article_2538.html This study investigates the effects of tool rotational speed and traverse speed on the microstructural development and mechanical characteristics of friction stir welded (FSW) AA6082-T6 aluminum alloy joints. Welding was performed at rotational speeds of 710, 1000, and 1400 rpm and traverse rates of 14, 28, and 56 mm/min to elucidate the correlation between process parameters, relative heat input, and joint performance. The macrostructural analysis verified the presence of robust weld production devoid of macroscopic flaws across all parameter combinations. Optical microscopy demonstrated polished equiaxed grains in the stir zone, indicative of deformation-induced recrystallization during solid-state processing, while the redistribution of Mg2Si and Al6Mn containing phases facilitated microstructural homogenization. Mechanical tests indicated that hardness and tensile strength typically rose with higher rotational and traverse rates, reaching peak values of 73.77 HV and 111.77 MPa at 1400 rpm and 56 mm/min, respectively. Impact toughness attained a peak value of 13.00 Nm at 1000 rpm and 14 mm/min, where modest heat input and strain rate facilitated a more ductile fracture behavior. The results suggest that joint behavior is determined by the equilibrium between temperature exposure and plastic deformation, rather than by a singular predominant factor. A balance between strength and impact toughness was achieved within the current parameter range of 1000–1400 rpm and 14–56 mm/min, offering practical guidelines for the optimization of AA6082-T6 friction stir welds. https://jcarme.sru.ac.ir/article_2444.html Cancer is a common and often devastating disease affecting many individuals. This condition is frequently perceived as incurable; however, scientific advancements have shown that most cancers are treatable if detected early. The first step in diagnosing cancer is often identifying circulating tumor cells in the bloodstream. Separator devices are employed for the identification of cancer cells. Currently utilized devices are often bulky and marker-based and may come with a biohazard exposure risk. The advancement of micro elector mechanical systems (MEMS) has given rise to smaller devices capable of markerless separation; however, these devices have not yet attained the performance level of conventional devices. Designing a device that can reliably isolate these rare cells is a challenging task. Designing a device that can reliably isolate cancer cells with a high degree of confidence is crucial. In this study, we present a method for model preparation capable of simulating multiple physics. Subsequently, we introduce an optimization process for mesh size. We aim to investigate the design parameters for a novel cell separation device based on buoyancy and a chevron channel. This device has the potential to increase the purity of separators by 10% increase overall acoustic pressure and decrease shear drag. Chevron channel flow pattern if properly aligned can contribute to cell separation of acoustic radiation force or counteract it if necessary. Utilizing buoyancy force for cell separation based on cell density is a prominent feature of acoustic-chevron separator devices. Finally, chevron channel capabilities and design constraints are discussed. https://jcarme.sru.ac.ir/article_2433.html The cooling system used in brushless direct current motors employs an air-cooling mechanism with fins on the motor heatsink. The optimal performance of brushless direct current motor cooling is not yet fully understood, necessitating an analysis of the cooling process. This study employs two methods, experimental and simulation, to investigate cooling efficiency. The results indicate that the temperatures of the winding and heatsink increase with the electric motor's rotation speed. The highest temperature recorded with a thermocouple was 94℃ at 2000rpm. Validation of the simulation results against the experimental results showed a 2% deviation, indicating their validity. Based on these findings, three new heatsink designs, namely modif 1, modif 2, and modif 3, were developed. Simulation results revealed that modif 3, a combination of axial and radial heatsink shapes, exhibited the most effective temperature transfer. Therefore, it can be inferred that higher motor rotation speeds can lead to increased motor heat. The study concludes that a combination heatsink design is capable of reducing temperatures in brushless direct current motors, as demonstrated through CFD simulations on electric motor prototypes. https://jcarme.sru.ac.ir/article_2416.html In this study, relationship between effect of machining parameters on machining characteristics and surface morphology was studied in electrochemical machining (ECM). The characteristics were Material Removal Rates (MRR), Over Cut (OC), Surface Roughness (SR) and surface morphology. The results show that MRR is increased by increasing current but OC is decreased. Increasing concentration causes to increase MRR, OC and SR. Also, the analysis of surface morphology shows that the electrolyte type affects the dissolution mechanism and surface layer formation in ECM. There are cavities in NaCl and KCl that their diameter, depth and distribution on the machined surface are changed by parameters and their diameters were 4μm to 9μm. Increasing ion concentration causes to enhance the diameter size and depth of created cavities on work piece but their uniform distribution decreases, while the current has a reverse effect on them. On the other hand, an oxide layer is formed on the machined surface in NaNO3 and by increasing current and concentration, breaking and the anion cavity effect are increased on this layer. So, increasing the MRR and SR is due to this phenomenon in NaNO3. https://jcarme.sru.ac.ir/article_2480.html This study presents a non-invasive method for detecting mechanical faults in a single-phase AC electromotor using processed acoustic signals. Sound data were collected via a USB-connected microphone installed in the motor's electrical casing under diverse operating conditions. Ten statistical features were extracted from the acoustic signals and used as input to three classification algorithms: Linear Discriminant Analysis (LDA), Quadratic Discriminant Analysis (QDA), and Support Vector Machine (SVM). Model performance was evaluated using confusion matrix metrics, including specificity, accuracy, precision, and sensitivity. Among the classifiers, SVM outperformed others, achieving average values of 99.54, 99.16, 97.15, and 96.17, respectively, with 10-fold cross-validation confirming its superior consistency (99.88% specificity, 99.17% accuracy). The findings confirm that acoustic signal analysis is a reliable and cost-effective tool for real-time fault diagnosis in electromotors. Defects may be accurately found in the electromotor by using acoustic analysis to monitor its status. The proposed framework is adaptable to other rotating machinery through retraining, offering a valuable solution for predictive maintenance in industrial applications. https://jcarme.sru.ac.ir/article_2490.html A comprehensive investigation has been conducted into the direct internal reforming planar type solid oxide fuel cell (DIR-PSOFC) through numerical analysis. The mathematical modeling of DIR-PSOFC is achieved through the implementation of conservation equations and a comprehensive electrochemical model. The synthesis gas fuel is introduced into the fuel channel, where both carbon monoxide (CO) and hydrogen (H2) undergo electrochemical oxidation. Gas flows are treated as plug flows with a co-flow configuration. Results of the simulation are then compared with and without the inclusion of carbon monoxide electrochemical oxidation. This comparison encompasses temperature fluctuations along the cell's longitudinal axis and the mole fraction variations of all gaseous species along the cel length, in addition to the electrical performance of the SOFC. It has been demonstrated that CO accounts for only 20% of the total current density. The contribution of CO to the generation of electric current at the inlet is 15%. At the point of maximum current density, the value is 16.17%. The cell operating voltage, power density, and fuel efficiency have been demonstrated to exhibit an enhancement, with an augmentation observed from 0.68 to 0.75 V, 3411.396 to 3739.130 W/m2, and 45.83% to 50.23%, respectively, when CO is used as a reactant in the anode side TPB. It has been determined that the electrochemical reaction of CO results in elevated heat generation within the cell, which in turn enhances the operating temperature. Consequently, the activation and ohmic losses are diminished, thereby improving the local current density and cell operating voltage.