Showing papers in "Journal of Mechanical Science and Technology in 2018"

Machine health management in smart factory: A review

Abstract: In this paper, we present a review of machine health managements for the smart factory. As the Industry 4.0 leads current factory automation and intelligent machines, the machine health management for diagnostic and prognostic purposes are essential, and their importance is getting more significant for the realization of the smart factory in the Industry 4.0. After brief introductions to important concepts and definitions composing smart factory and Industry 4.0, the developments in maintenance strategies towards Prognostics and health management (PHM) of machines are summarized. The review of machine health managements is followed, classifying the references by the monitoring components, types of measurements, as well as PHM tools and algorithms. 94 existing articles are reviewed and summarized in this regard. The implementations of machine health managements within the smart factory are discussed in terms of data connectivity, communications, Cyber-physical system (CPS) and virtual factory, relating them to Internet of things (IoT), cloud computing, and big data management.

Effects of extreme pressure and anti-wear additives on surface topography and tool wear during MQCL turning of AISI 1045 steel

Abstract: The paper presents an original study of the influence of extreme pressure and anti-wear (EP/AW) additives on the surface topography of double-phase steel during turning with different cooling media and variable flow rates. The obtained surface topographies were compared using frequency and fractal analyses for dry, minimum quantity cooling lubrication (MQCL), and MQCL + EP/AW methods. Results showed that the addition of phosphate ester-based additives to an active medium caused the formation of tribofilm on the tool-chip interface and thus a change in the lubricating properties by reducing friction. The tool wear and the formation of the thin-layered tribofilm were also incorporated. The application of the MQCL method with the EP/AW additives led to a decrease in particular surface topography parameters from 8 % to 38 % in comparison with the effects of dry cutting and from 6 % to 35 % in comparison with the effects of machining under MQCL conditions. An exception was the result obtained for the surface roughness height parameter Sp, which was higher than that obtained after the MQCL + EP/AW process for the lowest investigated feed per revolution f = 0.1 mm/rev. This observation was correlated with the uneven formation of the tribofilm on the machined surface. The phosphate ester-based additive used in the MQCL + EP/AW method contributed to achieving tool wear that was less than that obtained by the processes conducted under dry and MQCL conditions.

Design and evaluation of a 7-DOF cable-driven upper limb exoskeleton

Abstract: This paper presents a seven degrees of freedom cable-driven upper limb exoskeleton (CABXLexo-7), which is compact, lightweight, and comfortable for post-stroke patients. To achieve the compactness of exoskeleton, two types of cable-driven differential mechanisms were designed. The cable-conduit mechanisms were applied to transmit the power of motors mounted on the backboard to the corresponding joints, then the whole weight of the exoskeleton could be light to ensure a comfortable motion assistance. In the course of experiments, the surface electromyography signals of major muscles related with the movements of upper limb were collected to evaluate the assistant ability of exoskeleton. The experimental results showed that the activation levels of corresponding muscles were reduced by using the seven degrees of freedom cable-driven upper limb exoskeleton in the course of rehabilitation, and it demonstrated that the exoskeleton can provide effective movements assistance to the post-stroke patients.

Effect of the blade loading distribution on hydrodynamic performance of a centrifugal pump with cylindrical blades

Abstract: The effect of the blade loading distribution on head, radial force and pressure pulsation of a low specific-speed centrifugal pump with cylindrical impeller blades were investigated in the present study. Blade shapes were obtained by adopting the 1D inverse design method, impellers with different blade loading curves were obtained while the distribution of the blade loading was carefully tailored. Threedimensional URANS simulation method based on the Shear stress transport (SST) k-ω turbulence model was employed for the analyzation of flow patterns. Numerical results including the pressure distribution and velocity profile were validated by comparing with the available experimental data, and an acceptable agreement was obtained. Three typical parameters of the blade loading curve, including the location of the fore-loading point (mpre), location of the aft-loading point (mpost) and slope of the rectilinear segment (K), were analyzed. Results showed that the well-designed blade loading curve, such as the fore-loading impeller, can effectively reduce the pressure pulsation amplitude and the radial force. The significant effect of the variation of the aft-loading point on pump hydrodynamic performance was also investigated. Meanwhile, pressure and velocity distributions at different slopes of the blade loading curves show that the fore-loading impeller produces more uniform flow issuing from the impeller than that of the pump with aft-loading impeller, thus reduces the radial force and pressure pulsation of the pump.

Numerical study on the internal flow characteristics of an axial-flow pump under stall conditions

Abstract: When an axial-flow pump works in low flow rate conditions, rotating stall phenomena will probably occur, and the pump will enter hydraulic unsteady conditions. The rotating stall can lead to violent vibration, noise, turbulent flow, and a sharp drop in efficiency. This affects the safety and stability of the pump unit. To study the rotating stall flow characteristics of an axial-flow pump, the steady and unsteady internal flow field in a large vertical axial-flow pump was investigated using 3D computational fluid dynamic (CFD) technology. Numerical calculations were carried out using the Reynolds-averaged Navier–Stokes (RANS) solver and Menter's shear stress transport (SST) k-ω turbulence model. Steady flow characteristics including streamline, velocity vector, pressure and turbulent kinetic energy are presented and analyzed. Unsteady flow characteristics are described using post-processing signals for pressure monitoring points in the time and frequency domains. Using Q-criterion, the locations and evolution rules of the core region of the vortex structure in guide vanes under deep stall conditions were investigated. The reliability of the numerical simulation results was verified using the experimental prototype pressure fluctuation test. In this way, typical flow structure and pressure fluctuation characteristics in an axial-flow pump were analyzed, with contrastive analysis in design condition and stall conditions. Finally, the mechanism of low-frequency pressure fluctuation in a pump unit under the stall condition was revealed.

Prediction of ship fuel consumption by using an artificial neural network

Abstract: A smart ship collects various data with large volume, such as voyage, machinery, and weather data. Thus, big data analysis for smart ships is an important technology that can be widely applied to improve ship maintenance, operational efficiency, and equipment life management. In this study, an accurate regression model for the fuel consumption of the main engine by using an artificial neural network (ANN) was proposed by big data analysis including data collection, clustering, compression, and expansion. To obtain an accurate regression model, various numbers of hidden layers and neurons and different types of activation functions were tested in the ANN, and their effects on the accuracy and efficiency of the regression analysis were studied. The proposed regression model using ANN is a more accurate and efficient model to predict the fuel consumption of the main engine than polynomial regression and support vector machine.

Investigation of deep neural network with drop out for ultrasonic flaw classification in weldments

Abstract: Ultrasonic signal classification of defects in weldment, in automatic fashion, is an active area of research and many pattern recognition approaches have been developed to classify ultrasonic signals correctly. However, most of the developed algorithms depend on some statistical or signal processing techniques to extract the suitable features for them. In this work, data driven approaches are used to train the neural network for defect classification without extracting any feature from ultrasonic signals. Firstly, the performance of single hidden layer neural network was evaluated as almost all the prior works have applied it for classification then its performance was compared with deep neural network with drop out regularization. The results demonstrate that given deep neural network architecture is more robust and the network can classify defects with high accuracy without extracting any feature from ultrasonic signals.

Fault diagnosis method of rolling bearing using principal component analysis and support vector machine

Abstract: To effectively extract the fault feature information of rolling bearings and improve the performance of fault diagnosis, a fault diagnosis method based on principal component analysis and support vector machine was presented, and the rolling bearings signals with different fault states were collected. To address the limitation on effectively dealing with the raw vibration signals by the traditional signal processing technology based on Fourier transform, wavelet packet decomposition was employed to extract the features of bearing faults such as outer ring flaking, inner ring flaking, roller flaking and normal condition. Compared with the previous literature on fault diagnosis using principal component analysis (PCA) and support vector machine (SVM), one-to-one and one-to-many algorithms were taken into account. Additionally, the effect of four kernel functions, such as liner kernel function, polynomial kernel function, radial basis function and hyperbolic tangent kernel function, on the performance of SVM classifier was investigated, and the optimal hype-parameters of SVM classifier model were determined by genetic algorithm optimization. PCA was employed for dimension reduction, so as to reduce the computational complexity. The principal components that reached more than 95 % cumulative contribution rate were extracted by PCA and were input into SVM and BP neural network classifiers for identification. Results show that the fault feature dimensionality of the rolling bearing is reduced from 8-dimensions to 5-dimensions, which can still characterize the bearing status effectively, and the computational complexity is reduced as well. Compared with the raw feature set, PCA has a higher fault diagnosis accuracy (more than 97 %), and a shorter diagnosis time relatively. To better verify the superiority of the proposed method, SVM classification results were compared with the results of BP neural network. It is concluded that SVM classifier achieved a better performance than BP neural network classifier in terms of the classification accuracy and time-cost.

Characterization & evaluation of Al7075 MMCs reinforced with ceramic particulates and influence of age hardening on their tensile behavior

Abstract: Aluminium has a massive demand in the areas of automobile, aerospace and diverse engineering applications in order to furnish the requirement in those fields But this technological evolution needs something more than aluminium Materialogists are struggling hard to find out a material which owns sound mechanical and thermal properties and also superior than aluminium in each extent Metal matrix composite (MMC) is a solution Generally, metal matrix composites contain a low density material, ie aluminium or magnesium, reinforced with fibers or particulate of a ceramic material, ie silicon carbide or graphite They show greater specific strength, high stiffness, elevated operating temperature, and superior wear resistance, along with the possibility to customize these properties for a specific use In this study, Al 7075 is taken as a base matrix material, whereas ceramic materials like SiC, Al2O3, B4C and TiB2 are used as reinforcements There are different methods available for fabricating metal matrix composite materials and in this work, stir casting technique, which is a liquid state process, is used Four different MMC specimens were produced with 15 % SiC, 15 % Al2O3, 15 % B4C and 15 % TiB2 Mechanical properties ie tensile strength, hardness, and impact strength were studied for the prepared specimens The results were charted and presented graphically to describe these materials characteristics

Nanofluid thin film flow and heat transfer over an unsteady stretching elastic sheet by LSM

Abstract: This study is carried out on the unsteady flow and heat transfer of a nanofluid in a stretching flat plate. Least square method is implemented for solving the governing equations. It also attempts to demonstrate the accuracy of the aforementioned method compared with a numerical one, Runge-Kutta fourth order. Furthermore, the impact of some physical parameters like unsteadiness parameter (S), Prandtl number (Pr) and the nanoparticles volume fraction (ϕ) on the temperature and velocity profiles is scrutinized carefully. Accordingly, the results obtained from this study reveal that the temperature enhances by means of augmenting the nanoparticles volume fraction. At η ∈ {0, 0.5}, the velocity decreases as a result of a rise in nanoparticles volume fraction and at η ∈ {0.5, 1}, an opposite treatment takes place. Moreover, velocity distribution augments by raising the S value, however an inverse trend is observed in temperature values. Moreover, the local skin friction coefficient indicated a notable rise by increasing the S parameter as well as a steady decrease by rising ϕ. Finally, water-Alumina nanofluid demonstrated better heat transfer enhancement compared to other types of nanofluids.

Development of combustion strategy for the internal combustion engine fueled by ammonia and its operating characteristics

Abstract: Focusing on the possibility of using ammonia as a hydrogen carrier, a combustion strategy for pure ammonia as an engine fuel to convert the stored energy into a usable form has been proposed, which uses ammonia itself as a combustion promotor. Under this strategy, the conditions of sufficiently high temperature and pressure to cause the spray combustion of ammonia are obtained by the auto-ignition of a mixture of pilot-injected ammonia and air. To confirm the feasibility and the operating characteristics of an engine with the proposed ammonia combustion strategy, engine modeling has been conducted, the combustion strategy has been simulated, and a parametric study has been performed. To analyze the NO production mechanisms in an engine with the proposed combustion strategy, the NO production process has been classified into four phases, and the NO production in each phase has been analyzed under various start of injection timing and fuel amounts.

CFD analysis of the brake disc and the wheel house through air flow: Predictions of Surface heat transfer coefficients (STHC) during braking operation

Abstract: Braking system is one of the basic organs to control a car. For many years, the disc brakes have been used in automobiles for safe retardation of the vehicles. During braking, enormous amount of heat will be generated, and for effective braking, sufficient heat dissipation is essential. The specific air flow surrounding the brake rotor depends on the thermal performance of the disc brake and hence, the aerodynamics is an important in the region of brake components. A CFD analysis is carried out on the braking system as the study of this case, to make out the behavior of air flow distribution around the disc brake components using ANSYS CFX software. The main object of this work is to calculate the heat transfer coefficient (h) of the full and ventilated brake discs as a function of time using the CDF analysis, which will be used later in the transient thermal analysis of the disc in ANSYS Workbench 11.0.

Compound fault diagnosis of bearings using improved fast spectral kurtosis with VMD

Abstract: The fast spectrum kurtosis (FSK) algorithm can adaptively identify resonance bands of a signal, and fault characteristics can be extracted by analyzing the selected frequency bands. However, in practical applications, the bearing failure may be composed of various faults (inner ring/outer ring/rolling element) and the faults may be located in different resonant bands. Due to the interference between different fault components and noise, the weak components may be submerged when FSK is used to deal with compound fault signals. To improve the accuracy of an FSK processing compound fault located in different resonance bands, an improved FSK method combined with the variational mode decomposition (VMD) is proposed. First, the parameters (number of components K / penalty factor α ) in the VMD decomposition are selected, and the original compound fault signal is preprocessed by VMD decomposition, so that the original signal is decomposed into K variational intrinsic mode function (VIMF) components. The resonance center bands of these signals are different from each other, so the different fault information is located in different VIMF. Finally, each VIMF component is calculated by FSK. Through the simulated and experimental analysis, the method can accurately identify the resonance bands, and identify the weak fault characteristics of compound bearing fault.

Optimal design of an MR damper valve for prosthetic knee application

Abstract: In this work, a magnetorheological (MR) damper valve is designed with the primary objective of controlling swing-phase damping in an above-knee prosthesis. Initially, a swing phase model of the desired single axis knee incorporating MR damper was modelled. The control parameters that govern damping force and displacement of the damper were identified and optimized to enable the prosthetic knee to produce near normal swing phase trajectory for ground walking as obtained from experimental data. Then, the MR damper valve is optimally designed by selecting typical performance indices of the damper for the intended application. A multi-objective optimization problem is formulated where the MR damper valve is constrained in a desired cylindrical volume defined by its radius and height. Effects of the geometrical design variables of the valve are analytically investigated by mapping finite element analysis (FEA) numerical responses with response surface method (RSM). The results show that the MR damper with designed damper valve enables the prosthetic knee to achieve near to normal swing phase trajectory, and compare to the existed MR damper, up to 71 % reduction by weight has been achieved.

An experimental study on the cavitation vibration characteristics of a centrifugal pump at normal flow rate

Abstract: Cavitation is a challenging flow abnormality that leads to undesirable effects on the energy performance of the centrifugal pump and the reliable operation of the pump system. The onset and mechanism of a phenomenon that results in unsteady cavitation must be realised to ensure a reliable operation of pumps under the cavitation state. This study focuses on cavitation instability at normal flow rate, at which point the unsteady cavitation occurs as the available net positive suction head (NPSHa) falls below 5.61 m for the researched pump. An ameliorative algorithm–united algorithm for cavitation vibration analysis is proposed on the basis of short time Fourier transform (STFT) and Wigner–Ville distribution (WVD). The STFT–WVD method is then tested using vibration data measured from the centrifugal pump. The relationship between vibration and suction performance indicates that the inception and development of cavitation can be effectively detected by the distribution and intensity of the united algorithm at the testing points. Intermediate frequency components at approximately 6 kHz fluctuate initially with the development of cavitation. A time–frequency characteristic is found to be conducive to monitoring the cavitation performance of centrifugal pumps.

Machining of CFRP/Ti6Al4V stacks under minimal quantity lubricating condition

Abstract: Light weight and high strength materials like carbon fiber reinforce plastics (CFRP), Titanium alloys (Ti) and stacks (CFRP/Ti, CFRP/Al, CFRP/Al/Ti) are being extensively used in commercial aircraft. Drilling process on the aircraft components was carried out to facilitate the assembly process. Drilling operations are made under dry condition which leads to tool wear and poor hole quality. In this paper study on drilling of CFRP/Ti6Al4V stacks under minimum quantity lubrication (MQL) using LRT 30 oil with varying flow rate, spindle speed and feed rate have been carried out using three modified drill tool made of solid carbide (K 20) coated with TiAlN. The recital of the tools were evaluated based on hole quality, burr height, thrust force, chip formation and tool wear. It was found that TG1 tool performance was better by producing minimum burr height while drilling Ti. TG2 recital was better by producing minimum force and better hole quality.

Static stiffness characteristics of a new non-pneumatic tire with different hinge structure and distribution

Abstract: To eliminate the potential risk factors of the conventional inflatable tire, a creative non-pneumatic tire named “ME-wheel” was developed. Based on the analysis of the bearing characteristics, four types of ME-wheel with varying hinge structures and distributions were designed. The static stiffness characteristics of these four ME-wheels were investigated by numerical simulations and experiments. The hyperelasticity and incompressibility of the rubber material were described by the Mooney–Rivlin model, and the multilayer rubber-cord composites were modeled by the rebar layer. The nonlinear finite element model of the ME-wheel, which included nonlinear property of the material, contact condition, and anisotropy of rubber-cord composites, was validated by the load characteristic test. Stiffness characteristic tests of these four types of ME-wheel and a pneumatic tire, including vertical, longitudinal, lateral, and torsional stiffness, were carried out using a low speed flatbed test bench. A sufficient comparison and analysis were made between the experimental data and simulation data. The research results provided some theoretical and technical verification on the performance and structural optimization of the ME-wheel.

A central composite design based fuzzy logic for optimization of drilling parameters on natural fiber reinforced composite

Abstract: Machining of polymeric composite is inevitable during assembly of components. In view of making holes on structural composites, drilling is essential and a study to optimize the machining parameters is very important. The present study has been made to investigate the defaces and cutting forces associated during drilling of natural fiber reinforced plastics. Plastic composite has been manufactured using chemically treated vetiveria zizanioides as the reinforcement and polyester as the matrix. The composite has been drilled several times on the basis of central composite design. Speed and feed rate of the spindle, point angle and diameter of the tool are considered as the input parameters. Deface of each hole during entry and exit, thrust force and torque have been measured as the output parameters. A fuzzy model has been created and a comparative study between the central composite design and fuzzy model is made. The design has been optimized with the objective of minimizing the output parameters and a set of confirmatory experiments have been conducted. The central composite model has been validated by comparing it with the fuzzy model and confirmatory runs. The comparison presented only a minimal error and hence the modeling by central composite design and fuzzy are consummate.

Energy, exergy and exergoeconomic analysis of solar-assisted vertical ground source heat pump system for heating season

Abstract: The purpose of this study is to evaluate the experimental performance of a solar assisted vertical ground source heat pump system (VGSHP) for the winter climatic conditions of Mardin, which is in the South-Eastern Anatolia region of Turkey. For this aim, an experimental analysis was performed on solar assisted VGSHP system, which was designed to meet the heating needs of an experimental room, during the heating season (10.01.2013/03.31.2014). The experimentally obtained results were used to calculate energy, exergy and exergoeconomic analyses of the system and its components. The energy efficiency, exergy efficiency and exergoeconomic factors of the entire system were 67.36 %, 27.40 % and 60.51 %, respectively. In this study, the system was proposed for disseminating the use of alternative technologies supported by renewable energy systems and it has been tested for the first time in Mardin to meet its heating needs with convectional systems. The experimental results showed that the proposed solar assisted VGSHP system can be used for residential heating in Mardin and similar regions. As a result, it has been detected that the system is very effective in both reducing energy consumption and decreasing emissions of green-house gases.

Adaptive control of a vehicle-seat-human coupled model using quasi-zero-stiffness vibration isolator as seat suspension

Abstract: We propose the quasi-zero-stiffness (QZS) vibration isolator as seat suspension to improve vehicle vibration isolation performance. The QZS vibration isolator is composed of vertical spring and two symmetric negative stiffness structures used as stiffness correctors. A vehicle-seat-human coupled model considering the QZS vibration isolator is established as a three degree-of-freedom (DOF) model; it is composed of a quarter car model and a simplified 1 DOF model combined vehicle seat and human body. This model considers the changing mass of the passengers and sets the total mass of the vehicle seat and human body as an uncertain parameter, which investigates the overload and unload conditions in practical engineering. To further improve the vehicle ride comfort, a constrained adaptive backstepping controller law based on the barrier Lyapunov function (BLF) is presented. The dynamic characteristic of the active vehicle-seathuman coupled model under shock excitation was analyzed using numerical method. The results show that the designed controller law can isolate the shock excitation transmitted from the road to the passengers effectively, and both the vehicle and seat suspension strokes remain in the allowed stroke range.

Numerical investigation of heat transfer and friction factor in ribbed triangular duct solar air heater using Computational fluid dynamics (CFD)

Abstract: The Computational fluid dynamics (CFD) based analysis is carried out to investigate the thermal and hydraulic performance of circular rib roughened triangular passage Solar air heater (SAH) The circular ribs were provided over the absorber plate The roughness parameter such as relative roughness pitch (P/e) and relative roughness height (e/D) varies from 4 to 20 and 0015 to 006 (in four sets), respectively, the Reynolds number (Re) varies from 4000 to 18000 The flow governing equations were solved using commercial ANSYS (Fluent) software The predicted Nusselt number (Nu) and friction factor (f) are validated with the available experimental results The thermal and hydraulic performance of roughened duct is estimated in the form of Nusselt number and friction factor, respectively The Thermohydraulic performance parameter (TPP) is also evaluated depending on the friction factor (f) and Nusselt number (Nu) values for SAH The maximum Thermohydraulic performance parameter (TPP) is observed at Reynolds number of 15000 in case of relative roughness pitch (P/e) and relative roughness height (e/D) value of 12 and 006, respectively

A mixed FEM and lumped-parameter dynamic model for evaluating the modal properties of planetary gearboxes

Abstract: Planetary gearboxes are extensively used in mechatronic applications due to their compactness and high reduction ratios. The complex kinematic of such systems and the requirement of low-vibration-gears suggest studying these gearboxes with appropriate dynamic models. To this purpose, a planar lumped parameter model with 18 degrees of freedom was implemented. Model parameters such as the stiffness of the bearings and the gear meshes were calculated using dedicated FEM simulations. Two different gearbox configurations were simulated and experimentally tested. The compared results showed a good agreement. The main goal of the research was to assess the validity of such methodology for the prediction of the system eigenfrequencies. Additionally, from a kinematic analysis of the gearbox it was possible to individuate the self-excitation frequencies. The overlapping of these self-excited frequencies with the eigenfrequencies of the system was individuated as the major cause of the gearbox noise.

Rolling element bearings absolute life prediction using modal analysis

Abstract: In this paper, the authors introduce an experimental procedure for predicting the fatigue life of each individual rolling element bearing separately using vibration modal analysis. The experimental procedure was developed based on a statistical analysis. A statistical analysis was performed to find an empirical model that correlates the dynamic load capacity of rolling bearings to their dynamic characteristics (Natural frequencies and damping). These dynamic characteristics are obtained from the frequency response function of each individual bearing that results from vibration modal analysis. A modified formula to the already known Lundberg-Palmgren life formula is proposed for rolling element bearings. Given the modified formula, one can predict the fatigue life of each individual rolling element bearing based on its dynamic characteristics. The paper compares the results from the modified formula with those from Lundberg-Palmgren formula. The modified formula provides an accurate prediction for the fatigue life of each individual bearing based on its dynamic characteristics. The experimental validation of the modified formula is considered for future work. Therefore, it can be used in various applications of rolling element bearings in machinery systems.

Inertial forces acting on a gyroscope

Abstract: Gyroscopic devices for navigation and control systems are widely applied in various industries, such as shipping and aerospace A remarkable property of gyroscopes is that their axes can be maintained within a particular space This interesting property of a spinning disc mounted on an axle is represented by a mathematical model formulated based on L Euler’s principle of change in angular momentum Nevertheless, numerous publications and analytical approaches in known gyroscope theories do not correspond to practical tests on gyroscopes A simple rotating disc creates problems that do not have long-term solutions Recent investigations in this area have demonstrated that the origin of gyroscope properties is more sophisticated than that described in known hypotheses Researchers have not considered the action of inertial forces produced by the mass elements and center mass of the spinning rotor that create internal resistance and precession torques Resistance torque is established through the actions of centrifugal and Coriolis forces Precession torque is established through the actions of common inertial forces and a change in angular momentum These internal torques act simultaneously and interdependently on two axes and represent the fundamental principles of gyroscope theory Equations for internal inertial torques of a spinning disc have been formulated through mathematical analysis and differential and integral equations These calculus methods provide a basis for understanding the rates of change in inertial forces acting on a gyroscope and include the use of functions, their derivatives, and integrals in modeling the physical processes in gyroscopes This paper presents mathematical models for several internal inertial torques generated by the load torque acting on a spinning rotor These models can describe all gyroscope properties and represent their novelty for machine dynamics and engineering

Bayesian degradation assessment of CNC machine tools considering unit non-homogeneity

Abstract: Field reliability assessment and prediction is critical for the estimation, operation and health management of CNC machine tools. The classical methods for field reliability of CNC Machine Tools assessment and prediction are challenged with the issues of expensive reliability tests, small sample size and unit non-homogeneity. In order to solve these problems, this paper introduces a degradation analysis based reliability assessment method for CNC machine tools under performance testing. Since the degradation is an independent increment process, the gamma process is employed to characterize the degradation process of CNC machine tools. The random effects are introduced to accommodate performance degradation model with unit non-homogeneity. The parameters of model are updated by Bayesian estimation approach. As a case study, the CNC Machine Tools is studied to illustrate the approach. And the proposed method is demonstrated precise for practical use.

Multidisciplinary robust design optimization based on time-varying sensitivity analysis

Abstract: The performance of complex mechanical systems often degrades over time primarily due to time-varying uncertainties. Improving the design of such systems entails addressing time-varying uncertainties through Multidisciplinary design optimization (MDO). In this study, a multidisciplinary robust design optimization method that is based on time-varying sensitivity analysis is proposed. First, the indices for the time-varying reliability sensitivity of limit state functions are calculated by combining sensitivity analysis and an empirical correction formula. The propagation effects of these time-varying uncertainties are qualified by combining the simplified implicit uncertainty propagation and sequential quadratic programming methods. Finally, the robust design method is integrated with MDO to reduce the effects of time-varying uncertainties. The feasibility and effectiveness of the proposed method are illustrated with a mathematical problem and an engineering example.

A study on avoiding joint limits for inverse kinematics of redundant manipulators using improved clamping weighted least-norm method

Abstract: A general method is presented for the inverse kinematics resolution of redundant manipulators with joint limits. The success of avoiding joint angular position limits of the original clamping weighted least-norm method is ascribable to the strength of the repulsive potential field function. However, the repulsive potential field function may lead to excessive joint angular velocities that can exceed the corresponding limits. We propose an improved clamping weighted least-norm method that adds an elastic field function into the original method for the sake of sustaining the constraints of joint angular velocity limits. Moreover, for hierarchical task-level construction, the priority of avoiding joint angular velocity limits is lower than that of avoiding joint angular position limits. To adequately illustrate the effectiveness of the proposed method, case studies were performed in comparison with other methods in singular configurations of a redundant manipulator.

Terminal sliding mode control for full vehicle active suspension systems

Abstract: In current study, a terminal sliding mode control approach different from the conventional sliding mode control is proposed for active suspension system, which has an ability to reach the sliding surface in a finite time to achieve a high control accuracy. A full vehicle active suspension model is adopted with consideration of system uncertainties. The terminal sliding mode controller (TSMC) is systematically designed to force motion trajectories of vehicle body to accurately track the ideal reference model, and the controller parameters are tuned by a novel kidney-inspired algorithm (KA) for better control performance. The thought of designing an adaptive scheme for the reference model is one of the main contribution of this work. Simulation results clearly show the strength of adaptive scheme. The effectiveness and the strong robustness in stabilizing the attitude of the vehicle and improving the ride comfort are the main positive features of the proposed TSMC.

Design and analysis of a new magneto rheological damper for washing machine

Abstract: In this article, a new magneto rheological (MR) sponge damper is proposed for suppression of vibrations in a washing machine. The article presents design optimization of geometric parameters of MR sponge damper (MRSD) using the finite element analysis (FEA) and first order derivative techniques for a washing machine. The article explains the hysteresis behavior and the relationship of damping force with input current for the proposed MRSD. Moreover, the characteristics of the MRSD such as energy dissipation and equivalent damping coefficient are investigated experimentally in terms of input current and excitation amplitude. The passive dampers installed in washing machine are ineffective in reducing unwanted vibrations at resonant frequencies due to real time unbalanced mass. For this purpose, a test setup is established in order to compare the performance of passive dampers with the proposed MRSDs in a washing machine. It is noticed that MRSDs reduce average vibrations of 75.61 % in a low frequency band, whereas in a high frequency band, the MRSDs lessen average vibrations of 30.57 % in a washing machine. In order to determine the performance of proposed design MRSD, a detailed comparison of the performance parameters, such as total damping force, passive force, maximum average vibrations after suppression by MR dampers, maximum current and power ratings is provided with the existing designs of MR damper for washing machine from the literature.

Recent advances in finite element modeling of the human cervical spine

Abstract: The human cervical spine is a complex structure that is the most frequently injured site among all spinal injuries. Therefore, understanding of the cervical spine injury and dysfunction, and also biomechanical response to external stimuli is important. Finite element (FE) modeling can help researchers to access the internal stresses and strains in the bones, ligaments and soft tissues more realistically, and it has been widely adopted for spine biomechanics research. Although in recent years numerous techniques have been developed, there are no recent literature reviews on FE models of the cervical spine. Our objective was to present recent advances in FE modeling of the human cervical spine in terms of component modeling, material properties, and validation procedures. Model applications and further development are also discussed. The integration of new technologies will allow us to generate more accurate and comprehensive model of the cervical spine, which can increase efficiency and model applicability. Finally, the FE modeling can help to facilitate diagnosis, treatment, and prevention technologies for cervical spine injuries.