Showing papers in "Journal of Mechanical Science and Technology in 2016"

Multi-objective optimization of powder mixed electric discharge machining parameters for fabrication of biocompatible layer on β -Ti alloy using NSGA-II coupled with Taguchi based response surface methodology

Abstract: The success of an implant depends upon surface characteristics like roughness, topography, chemistry and hardness. The fabrication of a hard surface in combination with micron-, submicron- and nano-scale surface roughness is a great challenge for biomanufacturing industries. The surface microhardness (MH) needs to be maximized while controlling the Surface roughness (SR). The present research is the first study in which the application of Non-dominated sorting genetic algorithm (NSGA)-II coupled with Taguchi based Response surface methodology (RSM) is used to predict the optimal conditions of Powder mixed electric discharge machining (PMEDM) parameters to fabricate the biocompatible surface on β-phase Ti alloy. Batch vial tests were first carried out in accordance with the L25 orthogonal array. ANOVA analysis gave the significant influencing factors and then mathematical models were developed between input parameters and output responses like SR and MH using Taguchi based RSM technique. These models were then optimized using NSGA-II to obtain a set of Pareto-optimal solutions. From the series of multiple solutions, the best optimal condition to achieve required low SR and high MH was determined, which are 13 A peak current, 5 μs pulse duration, 8% duty cycle (longer pulse-interval) and 8 g/l silicon powder concentration for achieving a required low SR and high MH. The MH considerably increased about 184% compared to the base material, and about 1.02 μm SR can be achieved in combination with micron-, submicron- and nano-scale surface features.

Effect of nano additives (titanium and zirconium oxides) and diethyl ether on biodiesel-ethanol fuelled CI engine

Abstract: The present work is dedicated to the comparative experimental study of biodiesel-ethanol blends in a compression ignition engine using TiO2 (Titanium oxide) nanoparticle, ZrO2 (Zirconium oxide) nanoparticle and DEE (Diethyl ether) additives. The test fuels used are a blend of biodiesel (80%) -ethanol (20%) (denoted as BE), a blend of BE with 25 ppm Titanium oxide nanoparticle (denoted as BE-Ti), a blend of BE with 25 ppm Zirconium oxide nanoparticle (denoted as BE-Zr) and a blend of BE with 50 ml Diethyl ether (denoted as BE-DEE). Addition of nanoparticles increases the oxidation rate, reduces the light-off temperature and creates large contact surface area with the base fuel thereby enhancing the combustion with minimal emissions. Experimental results shown that addition of Titanium nanoparticles increased NOx, HC and smoke with lowered BSFC and CO. Whereas addition of Zirconium nanoparticles increases BSFC and HC emissions with lowered CO, CO2 and smoke emissions in comparison with BE blends. DEE addition to BE blends improved the heat release rate and increased HC, CO emissions were observed with lowered BSFC, NOx and smoke. Simultaneous reduction of NOx and smoke indicates the effect of DEE on Low temperature combustion (LTC).

Influence of tip clearance on pressure fluctuations in an axial flow pump

Abstract: Rotor-stator interaction in axial pumps can produce pressure fluctuations and further vibrations even damage to the pump system in some extreme case. In this paper, the influence of tip clearance on pressure fluctuations in an axial flow water pump has been investigated by numerical method. Three-dimensional unsteady flow in the axial flow water pump has been simulated with different tip clearances between the impeller blade tip and the casing wall. In addition to monitoring pressure fluctuations at some typical points, a new method based on pressure statistics was proposed to determine pressure fluctuations at all grid nodes inside the whole pump. The comparison shows that the existence of impeller tip clearance magnifies the pressure fluctuations in the impeller region, from the hub to shroud. However, the effect on pressure fluctuation in the diffuser region is not evident. Furthermore, the tip clearance vortex has also been examined under different tip clearances.

Effect of magnetic field on thermal conductivity and viscosity of a magnetic nanofluid loaded with carbon nanotubes

Abstract: The present work examines experimentally the effect of magnetic field on the viscosity and thermal conductivity of a hybrid nanofluid containing tetramethylammonium hydroxide (TMAH) coated Fe3O4 nanoparticles and Gum arabic (GA) coated carbon nanotubes (CNTs). The hybrid nanofluid was prepared by using ultrasonic dispersion method. Magnetic field was created by a pair of spaced apart magnet plates. The effect of temperature on the time variation of thermal conductivity under applied magnetic field was also investigated. According to the results of this study, viscosity of the hybrid nanofluid increases with the strength of magnetic field, while it decreases with the increase of temperature. Additionally, it is found that the hybrid nanofluid behaves as a shear thinning fluid at low shear rates while it exhibits Newtonian behavior at high shear rates. Furthermore, results show that when an external magnetic field is applied to the studied magnetic nanofluids, the thermal conductivity experiences a peak.

Multi-response optimization of Micro-EDM process parameters on AISI304 steel using TOPSIS

Abstract: The Technique for order preference by similarity to ideal solution (TOPSIS) method of optimization is used to analyze the process parameters of the micro-Electrical discharge machining (micro-EDM) of an AISI 304 steel with multi-performance characteristics. The Taguchi method of experimental design L27 is performed to obtain the optimal parameters for inputs, including feed rate, current, pulse on time, and gap voltage. Several output responses, such as the material removal rate, electrode wear rate, overcut, taper angle, and circularity at entry and exit points, are analyzed for the optimal conditions. Among all the investigated parameters, feed rate exerts a greater influence on the hole quality. ANOVA is employed to identify the contribution of each experiment. The optimal level of parameter setting is maintained at a feed rate of 4 μm/s, a current of 10 A, a pulse on time of 10 μs, and a gap voltage of 10 V. Scanning electron microscope analysis is conducted to examine the hole quality. The experimental results indicate that the optimal level of the process parameter setting over the overall performance of the micro-EDM is improved through TOPSIS.

Diagnosis of compound faults of rolling bearings through adaptive maximum correlated kurtosis deconvolution

Abstract: This paper proposes a new diagnosis method based on Adaptive maximum correlated kurtosis deconvolution (AMCKD) for accurate identification of compound faults of rolling bearings. The AMCKD method combines the powerful capability of cuckoo search algorithm for global optimization with the advantage of Maximum correlated kurtosis deconvolution (MCKD) for impact signal extraction. In contrast to traditional methods, such as direct envelop spectrum, Discrete wavelet transform (DWT), and empirical mode decomposition, the proposed method extracts each fault signal related to the single failed part from the compound fault signals and effectively separates the coupled fault features. First, the original signal is processed using AMCKD method. Demodulation operation is then performed on the obtained single fault signal, and the envelope spectrum is calculated to identify the characteristic frequency information. Verification is performed on simulated and experimental signals. Results show that the proposed method is more suitable for detecting compound faults in rolling bearings compared with traditional methods. This research provides a basis for improving the monitoring and diagnosis precision of rolling bearings.

Generation of electrical energy using lead zirconate titanate (PZT-5A) piezoelectric material: Analytical, numerical and experimental verifications

Abstract: Energy harvesting is the process of attaining energy from the external sources and transforming it into usable electrical energy. An analytical model of piezoelectric energy harvester has been developed to determine the output voltage across an electrical circuit when it is forced to undergo a base excitation. This model gives an easy approach to design and investigate the behavior of piezoelectric material. Numerical simulations have been carried out to determine the effect of frequency and loading on a Lead zirconate titanate (PZT-5A) piezoelectric material. It has been observed that the output voltage from the harvester increases when loading increases whereas its resonance frequency decreases. The analytical results were found to be in good agreement with the experimental and numerical simulation results.

Experimental analysis on neat mustard oil methyl ester subjected to ultrasonication and microwave irradiation in four stroke single cylinder Diesel engine

Abstract: Transesterification of fatty acid using the application of ultrasound stirring and microwave irradiation has been used of late for biodiesel production from various vegetable oil and animal fats. However analysis on influence of these techniques on performance, combustion and emission aspects has received little attention. In this work, transesterification of mustard oil with methanol was performed using ultra sound stirring (42 kHz /170 W, 80 W) and microwave irradiation (230v AC, 50 Hz, 900 W). Reaction time, conversion rate, fuel properties, performance, emission and combustion characteristics were compared with conventional transesetrification. Results indicated that Mustard oil methyl ester subjected to ultrasonication and microwave irradiation (MOMESUM) has 5.71% more yield than conventional transesterification process. It was also observed that BTE for MOMESUM is improved by 5.84% with 5.14% reduction in BSFC when compared to MOME. CO, HC, NOx and Smoke emission was found to decrease by 11.39%, 3.81%, 7.99% and 5.3% respectively for MOMESUM.

Experimental evaluation of waste plastic oil and its blends on a single cylinder diesel engine

Abstract: The aim of the present work to investigate the performance of oil derived from the waste plastic on diesel engine. Waste plastic fuel (WPF) is derived from the waste plastics by catalytic pyrolysis. Test were employed to completely characterize the Fuel by determining the physical, chemical and spectroscopic like FTIR, GC-MS properties of WPF and WPF-diesel blends in different proportions and to evaluate the performance and emission characteristics of these fuel and their blends on a single cylinder diesel engine and finally the results were compared with reference test fuel diesel. It is observed that the engine can operate with neat WPF and their blends without any modification and can be used as an alternative fuel for diesel engine. However, it is found that WPF10D90 (10% waste plastic oil and 90% diesel fuel) shows similar results as compare to diesel.

Flexible vibration analysis for car body of high-speed EMU

Abstract: The resonance of the flexible vibration of car body, which has not been detected before on a passenger coach, occurred recently on a high-speed Electric multi units (EMU) when the train was running at 300 km/h on Beijing-Shanghai line. In this investigation, the force transmission from track to car body via suspensions is elaborated first with possibly induced factors briefly discussed. Both the measurements and experiments in field and in laboratory were conducted to evaluate the resonances and the excitation as well as transmission. Moreover, a three-dimensional railroad vehicle model was built in a computational non-linear Multibody system (MBS) framework, in which the car body flexibility was modeled using Finite element (FE) method. The model was validated and shows good agreements with measurements. Furthermore, the measured wheel and rail profiles were used to analyze the wheel/rail interaction for both new and worn states. The effects of the wheel-rail contact conditions on stabilities, dynamics and riding comforts were also examined. Feasible solutions were promoted to avoid the resonance and following by validating tests. It shows that the high frequency excitation arises from the hunting motion of bogie that closes to the modals of the car body, leads to the resonance of the structure of the car.

Oil film stiffness and damping in an elastohydrodynamic lubrication line contact-vibration

Abstract: An elastohydrodynamic lubrication line contact-vibration model is proposed to study the stiffness and damping of the oil film existed in the EHL contact region. An initial mutual approach between interacting surfaces, which deviates from the steady-state balanced position, is assumed under the free contact-vibration to predict the response of the mutual approach. An inertia term, which represents the acceleration of the gap motion, is added to the classical force balance equation to form the equation of motion of the mutual approach. Response of the mutual approach is solved based upon the solving of the contact-dynamic model. The oil stiffness is calculated according to the natural frequency of the response under damped and non-damped conditions, the latter of which represents dry contact conditions. The oil film damping is calculated in terms of the principle of the energy conservation which utilizes the whole history of response compared with the log decrement method. Effect of the normal load, the rolling speed and the amplitude of the regular sinusoidal surface waviness on the oil film stiffness, the contact stiffness and the oil film damping are studied. The study provides an insight on the oil film dynamic characteristics of lubricated contact-vibration problems which appear in gears, bearings, etc. The results show that the oil film damping factor decreases with the increasing normal load as well as the increasing rolling speed. The oil film stiffness increases with the normal load and decreases with the rolling speed. Also, compared to the contact stiffness, the oil film stiffness makes less contribution to the total stiffness. The surface waviness amplitude has little effect on the oil film stiffness and the oil film damping.

Effect of surface treatment on mechanical properties of glass fiber/stainless steel wire mesh reinforced epoxy hybrid composites

Abstract: This paper investigates the effect of surface treatment for glass fiber, stainless steel wire mesh on tensile, flexural, inter-laminar shear and impact properties of glass fiber/stainless steel wire mesh reinforced epoxy hybrid composites. The glass fiber fabric is surface treated either by 1 N solution of sulfuric acid or 1 N solution of sodium hydroxide. The stainless steel wire mesh is also surface treated by either electro dissolution or sand blasting. The hybrid composites are fabricated using epoxy resin reinforced with glass fiber and fine stainless steel wire mesh by hand lay-up technique at room temperature. The hybrid composite consisting of acid treated glass fiber and sand blasted stainless steel wire mesh exhibits a good combination of tensile, flexural, inter-laminar shear and impact behavior in comparison with the composites made without any surface treatment. The fine morphological modifications made on the surface of the glass fiber and stainless steel wire mesh enhances the bonding between the resin and reinforcement which inturn improved the tensile, flexural, inter- laminar shear and impact properties.

A lightweight design approach for an EMU carbody using a material selection method and size optimization

Abstract: This study proposes a weight reduction design approach for urban transit carbody using a material selection method and size optimization. First, the material selection method, which uses specific stiffness and strength indices to predict the weight reduction rate, is set up when the materials of the under-frame and roof structure are substituted. The CFRP was chosen as the best weight reduction material in terms of the material selection method but was not appropriate for application to an urban transit carbody as a thin panel because of out-of-plane deformation. Therefore, we applied CFRP-AL honeycomb sandwich composites to the under-frame and roof structures, and the size optimization method was subsequently applied to derive a lightweight composite hybrid carbody design. Finally, the proposed approach was applied to an urban transit carbody, i.e., a Korean electrical multiple units carbody made of aluminum extrusion profiles. The weight of the optimized composite hybrid carbody design was 29.0% lighter than that of the original K-EMU. The resulting composite hybrid carbody design satisfied the design guidelines of the Performance test standard for K-EMU according to the corresponding FE simulations.

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

Abstract: We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.

Effect of twist morphing wing segment on aerodynamic performance of UAV

Abstract: The design space for morphing wings is incredibly broad and allows for a wide range of improvements versus fixed wing aircrafts such that each type of morphing can be useful for different purposes. This work introduces a novel concept for a twist morphing wing segment where only a segment of the wing is actuated which causes a rotation of the tip of the wing while the base segment fixed. The morphing segment consists of a smart soft composite structure made from PDMS and PLA which is actuated by multiple embedded SMA wires. This structure was implemented in a UAV-sized wing and was tested both in still-air conditions and in an open-type wind tunnel to determine the actual impact of this mode of actuation. Results show that this concept can improve the aerodynamic properties of the wing, particularly at low angles of attack.

Wake vortex interaction effects on energy extraction performance of tandem oscillating hydrofoils

Abstract: An energy extracting technology based on tandem oscillating hydrofoils from flow field is presented in this paper. Numerical simulation were performed to optimize the spatial arrangement for tandem oscillating hydrofoils, the position of the downstream hydrofoil relative to the wake vortex shed by the upstream hydrofoil is seen as critical. Optimized position of the two hydrofoils improves the energy extraction performance through positive interactions between the downstream hydrofoil and the wake vortices of the upstream hydrofoil, and the highest energy extraction efficiency reaches 53.8%. The downstream hydrofoil has a slight impact on the energy extraction performance of the upstream hydrofoil, and the contribution from the upstream hydrofoil is usually slightly inferior to the single hydrofoil results. Leading edge vortex (LEV) is formed and shed from the upstream hydrofoil, which is seen as critical in the energy transformation between the fluid and the energy extraction device. For different reduced frequencies, the energy extraction of a single hydrofoil is heavily influenced by the dynamics of vortex forming and shedding. The investigation was also undertaken over a wide range of kinematic parameters, including hydrofoil separation distance and reduced frequency. Results reveal that energy extraction of tandem oscillating hydrofoils shows better performance than a single hydrofoil for optimal reduced frequency and suitable hydrofoil separation distance.

Design, analysis and fabrication of polyamide/ hydroxyapatite porous structured scaffold using selective laser sintering method for bio-medical applications

Abstract: Both medical and engineering sciences play a vital role in human health diagnose and treatment. In this scientific world, the technology of alternative bone scaffold is one of the remedial sources for bone loss treatment. This research paper focuses on the design and analysis of porous scaffold made of additive manufacturing process. Various types of biocompatible materials with different characteristics are used for this bone scaffold. In order to have high load bearing capacity, a material composition of biocompatible Polyamide (PA) combined with Hydroxyapatite (HA) is used in this research work. HA has the character of greater cell seeding growth of tissue cells and hence added in the composition. The porous scaffold models with different configuration of cubical pore, spherical pore, shifted cubical pore, shifted spherical pore are designed using Solidworks software with a pore size of 800 microns and the porosity ranging from 40 % to 70 %. All the CAD models are analyzed using ANSYS software. Based on the static structural analysis, the shifted cubical scaffold posses lesser stress concentration, and thus selected for fabrication using Selective Laser Sintering machine. The specimens are fabricated in three different build orientations and the load bearing strength is found out using experimentation. The different material composition of 100 %PA, 95 %PA: 5 %HA, 90 %PA: 10 %HA and 85 %PA: 15 %HA are considered for this study.

Numerical and experimental research on the rock-breaking process of tunnel boring machine normal disc cutters

Abstract: A common drawback presented by several numerical rock-breaking studies was that the rocks beneath disc cutters were cut off excessively while the rocks between disc cutters remained, which usually resulted in a smaller cutter spacing than the proper value. To overcome this limitation, the constitutive equations of different rock parts were defined separately using VUMAT, an ABAQUS-based material subroutine. The constitutive model of rock was an application of the Drucker-Prager yield criterion coupled with the Lemaitre damage model. Full-scale rock-breaking tests on a rotary cutting machine were conducted, and 25 groups of orthogonal numerical simulations were carried out. By comparing the normal force, rolling force, and specific energy of numerical results with those of experimental results, the optimal values of the defined parameters D c1, k, and B were determined to be 9☓10-4, 0.1 and 0.8, respectively. With the presented numerical method and the determined parameters, the influences of cutter spacing on normal force, rolling force, and specific energy were studied. Both the normal and rolling forces of the first cutting generally remained constant, whereas the forces of the second cutting generally increased linearly with the cutter spacing. The optimal cutter spacing for the studied rock type (Hard sand rock collected from West Qinling tunnel) was approximately 72 mm, which was in accordance with the cutter spacing of the tunnel boring machine applied in this tunnel project.

3D finite element simulation of temperature distribution, residual stress and distortion on 304 stainless steel plates using GTA welding

Abstract: In the present study, the distortion induced in rectangular plate of AISI 304 SS during autogenous GTA welding process is measured experimentally and further validated using Finite element (FE) analysis. The thermal histories are measured at fixed locations over the surface of the plate and the results are compared with FE analysis. The Gaussian surface and Volumetric heat source models are simulated and transient heat transfer analysis is performed. The heat source models have been tested with two different speeds. The effectiveness of change in thermal histories of the heat sources have been studied and reported. In FE analysis, the sequentially coupled thermomechanical analysis is performed using the thermal histories as input and the distortion of the plates are predicted and compared with experimental measurements. The large and small displacement theories are employed for the above purpose and the effectiveness of the theories are reported. The edge deformation of the plates have been measured and validated for both the theories. The residual stress and distortion at the mid span are predicted and discussed. The results predicted using large displacement theory is in good agreement with measured values.

Mass production of CNTs using CVD multi-quartz tubes

Abstract: Carbon nanotubes (CNTs) have become the backbone of modern industries, including lightweight and heavy-duty industrial applications. Chemical vapor deposition (CVD) is considered as the most common method used to synthesize high yield CNTs. This work aims to develop the traditional CVD for the mass production of more economical CNTs, meeting the growing CNT demands among consumers by increasing the number of three particular reactors. All reactors housing is connected by small channels to provide the heat exchange possibility between the chambers, thereby decreasing synthesis time and reducing heat losses inside the ceramic body of the furnace. The novel design is simple and cheap with a lower reacting time and heat loss compared with the traditional CVD design. Methane, hydrogen, argon, and catalyzed iron nanoparticles were used as a carbon source and catalyst during the synthesis process. In addition, CNTs were produced using only a single quartz tube for comparison. The produced samples were examined using XRD, TEM, SEM, FTIR, and TGA. The results showed that the yield of CNTs increases by 287 % compared with those synthesized with a single quartz tube. Moreover, the total synthesis time of CNTs decreases by 37 % because of decreased heat leakage.

Application of different surrogate models on the optimization of centrifugal pump

Abstract: An optimization process for impellers was carried out based on numerical simulation, Latin hypercube sampling (LHS), surrogate model and Genetic algorithm (GA) to improve the efficiency of residual heat removal pump. The commercial software ANSYS CFX 14.5 was utilized to solve the Reynolds-averaged Navier-Stokes equations by using the Shear stress transport turbulence model. The impeller blade parameters, which contain the blade inlet incidence angle Δβ, blade wrap angle φ, and blade outlet angle β 2, were designed by random sample points according to the LHS method. The efficiency predicted under the design flow rate was selected as the objective function. The best combination of parameters was obtained by calculating the surrogate model with the GA. Meanwhile, the prediction accuracies of three surrogate models, namely, Response surface model (RSM), Kriging model, and Radial basis neural network (RBNN), were compared. Results showed that the calculated findings agree with the experimental performance results of the original pump. The RSF model predicted the highest efficiency, while the RBNN had the highest prediction accuracy. Compared with the simulated efficiency of the original pump, the optimization increased efficiency by 8.34% under the design point. Finally, the internal flow fields were analyzed to understand the mechanism of efficiency improvement. The optimization process, including the comparison of the surrogate models, can provide reference for the optimization design of other pumps.

Modeling and optimization of geometrical characteristics in laser trepan drilling of titanium alloy

Abstract: Laser drilling has become an alternative to drilling precise holes in advanced difficult-to-cut superalloys. Due to better hole quality and capability to generate macro-size holes, laser trepan drilling is becoming more popular as compared with laser percussion drilling. This paper presents a study of laser trepan drilling process performance in terms of geometrical quality characteristics, such as hole taper and circularity for drilling small diameter hole in difficult-to-cut Titanium alloy sheet. Due to involvement of different process parameters such as laser power, pulse width, pulse frequency, workpiece thickness, material composition, cutting speed, stand of distance and assist gas pressure, the laser cutting is a highly nonlinear and complex process. To handle this nonlinearity and complexity, genetic algorithm has been applied for the optimization. We used assist gas pressure, pulse width, pulse frequency and trepanning speed as input process parameters. The effect of significant process parameters on hole characteristics are discussed on the basis of data obtained through a well designed orthogonal array experimental matrix. Reliable empirical models have been developed for different quality characteristics. Improvements of 49% and 8% have been registered in hole taper and circularity, respectively, at optimum level of process parameters.

Flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves: Analysis and optimization

Abstract: This paper investigates the potential of flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves. A dynamic model is developed to analyze the pumping dynamics of the pump and validated by experimental results. The effects of cross-angle on the flow ripples in the outlet and inlet ports, and the piston chamber pressure are investigated. The effects of pressure relief grooves on the optimal solutions obtained by a multi-objective optimization method are identified. A sensitivity analysis is performed to investigate the sensitivity of cross-angle to different working conditions. The results reveal that the flow ripples from the optimal solutions are smaller using the cross-angle and pressure relief grooves than those using the cross-angle and ordinary precompression and decompression angles and the cross-angle can be smaller. In addition, when the optimal design is used, the outlet flow ripples sensitivity can be reduced significantly.

Multiresponse optimization of cryogenic drilling on Ti-6Al-4V alloy using topsis method

Abstract: Multiresponse optimization of process parameters in drilling is focused in this article using the TOPSIS technique to obtain minimum cutting temperature (T), thrust force (Ft), torque (Mt) and surface roughness (Ra), Circularity (Cir), Cylindricity (Cyl). The experiments were performed on Titanium alloy Ti-6Al-4V in different cooling environments: Wet cooling and cryogenic cooling conditions. Liquid nitrogen (LN2) as a coolant is used in cryogenic machining. The control factors selected were machining environments, cutting speed (Vc) and feed rate (f). Eighteen experiments were conducted in wet and cryogenic LN2 conditions based on L18 orthogonal array, respectively. The optimization results indicate drilling at Vc = 40 m/min and f = 0.02 mm/rev which is of the lowest value in cryogenic LN2 condition. A better performance is achieved too. The optimum multiresponses show that TOPSIS method is the most effective performance in the drilling process.

Multi-point optimization on meridional shape of a centrifugal pump impeller for performance improvement

Abstract: A wide operating band is important for a pump to safely perform at maximum efficiency while saving energy. To widen the operating range, a multi-point optimization process based on numerical simulations in order to improve impeller performance of a centrifugal pump used in nuclear plant applications is proposed by this research. The Reynolds average Navier Stokes equations are utilized to perform the calculations. The meridional shape of the impeller was optimized based on the following four parameters; shroud arc radius, hub arc radius, shroud angle, and hub angle as the design variables. Efficiencies calculated under 0.6Q d, 1.0Q d and 1.62Q d were selected as the three optimized objectives. The Design of experiment method was applied to generate various impellers while 35 impellers were generated by the Latin hypercube sampling method. A Response surface function based on a second order function was applied to construct a mathematical relationship between the objectives and design variables. A multi-objective genetic algorithm was utilized to solve the response surface function to obtain the best optimized objectives as well as the best combination of design parameters. The results indicated that the pump performance predicted by numerical simulation was in agreement with the experimental performance. The optimized efficiencies based on the three operating conditions were increased by 3.9 %, 6.1 % and 2.6 %, respectively. In addition, the velocity distribution, pressure distribution, streamline and turbulence kinetic energy distribution of the optimized and reference impeller were compared and analyzed to illustrate the performance improvement.

Numerical simulation of cavitation surge and vortical flows in a diffuser with swirling flow

Abstract: The strong swirling flow at the exit of the runner of a Francis turbine at part load causes flow instabilities and cavitation surges in the draft tube, deteriorating the performance of the hydraulic power system. The unsteady cavitating turbulent flow in the draft tube is simplified and modeled by a diffuser with swirling flow using the Scale-adaptive simulation method. Unsteady characteristics of the vortex rope structure and the underlying mechanisms for the interactions between the cavitation and the vortices are both revealed. The generation and evolution of the vortex rope structures are demonstrated with the help of the iso-surfaces of the vapor volume fraction and the Qcriterion. Analysis based on the vorticity transport equation suggests that the vortex dilatation term is much larger along the cavity interface in the diffuser inlet and modifies the vorticity field in regions with high density and pressure gradients. The present work is validated by comparing two types of cavitation surges observed experimentally in the literature with further interpretations based on simulations.

Parameter design for cut surface characteristics in abrasive waterjet cutting of Al/SiC/Al2O3 composite using grey theory based RSM

Abstract: The abrasive mixed waterjet was successfully employed to cut many materials including austenitic steel, inconel and glass for a variety of industrial applications. The present work focusses on studying the surface roughness, striation zone and striation angle in Abrasive waterjet cutting (AWJC) of Al/SiC/Al2O3 composite. The water pressure, traverse speed, abrasive flow rate and stand-off distance were included as the dominant parameters in the study. The features of striation zone (length and angle) and surface roughness were observed as the responses for each of the cutting trials planned as per Taguchi’s L18 orthogonal array. Parameter design was performed using the grey theory based response surface methodology (g-RSM) by following the method of simultaneous optimization to forecast the optimal cutting condition. All the studied parameters and their interactions were found to have a substantial effect on the observed responses. Significant improvements were observed in the responses obtained with the optimal parameter setting predicted by the g-RSM approach. The Atomic force microscopy (AFM) images and P-profile plots were also studied to observe the texture of the cut surface.

Diagnosing planetary gear faults using the fuzzy entropy of LMD and ANFIS

Abstract: The small size, low weight, and large transmission ratio of planetary gear have resulted in large-scale use, low speed, and heavy-duty mechanical systems. Poor working conditions of planetary gear lead to frequent occurrence of faults. A method is proposed for diagnosing faults in planetary gear based on fuzzy entropy of Local mean decomposition (LMD) and Adaptive neuro-fuzzy inference system (ANFIS). The original vibration signal is decomposed into six Product function (PF) components and a residual using LMD. Given that decomposed PF components contain the main fault feature information, fuzzy entropy is used to reflect the complexity and irregularity of each PF component. The fuzzy entropies of each PF component are defined as the input of the ANFIS model, and its parameters and membership functions are adaptively adjusted based on training samples. Finally, fuzzy inference rules are determined, and the optimal ANFIS model is obtained. Testing samples are used to verity the trained ANFIS model. The overall fault recognition rate reaches 88.8%, and the fault recognition rate for gear with wear reaches 96%. Therefore, the proposed method is effective at diagnosing planetary gear faults.

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

Abstract: We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.

Quantification of defects depth in glass fiber reinforced plastic plate by infrared lock-in thermography

Abstract: The increasing use of composite materials in various industries has evidenced the need for development of more effective nondestructive evaluation methodologies in order to reduce rejected parts and to optimize production cost. Infrared thermography is a noncontact, fast and reliable non-destructive evaluation technique that has received vast and growing attention for diagnostic and monitoring in the recent years. This paper describes the quantitative analysis of artificial defects in Glass fiber reinforced plastic plate by using Lockin infrared thermography. The experimental analysis was performed at several excitation frequencies to investigate the sample ranging from 2.946 Hz down to 0.019 Hz and the effects of each excitation frequency on defect detachability. The four point method was used in post processing of every pixel of thermal images using the MATLAB programming language. The relationship between the phase contrast with defects depth and area was examined. Finally, phase contrast method was used to calculate the defects depth considering the thermal diffusivity of the material being inspected and the excitation frequency for which the defect becomes visible. The obtained results demonstrated the effectiveness of Lock-in infrared thermography as a powerful measurement technique for the inspection of Glass fiber reinforced plastic structures.