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Residual unbalance in hand-held power tool rotors transmits undesirable vibrations to the hand of its operator. These vibrations can be effectively suppressed using a one plane automatic dynamic balancer (ADB). This balancing device consists of several balls constrained to move inside a sealed cylindrical ball-race unit partially filled with oil. One of the hand-held power tools is an angle grinder. This study introduces the design of an ADB for eliminating vibration of a grinder based on the achieved design parameters. A physical model of the system is derived for a Jeffcott rotor with an ADB. Utilizing Lagrange's method, the nonlinear equations of motion for an autonomous system in polar coordinate system is derived. Further, the equilibrium position and the linear variational equations are obtained by the perturbation method. Moreover, the dynamic stability of the system in the neighborhood of the equilibrium positions is investigated by the Routh-Hurwitz criteria. The results of the stability analysis provide the design requirements for the ADB to achieve balancing of the system. In addition, time responses are presented by the generalized-alpha method. Employing the modal analysis method the equivalent damping and stiffness coefficients are achieved. Finally, the ADB is designed and manufactured by solving the equations of motion governed on identified unbalanced grinder. To evaluate and identify the performance of the ADB, vibration levels are measured in cases of with balancer, without balancer, and are compared with a typical commercial ADB.

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In the paper, a three-axis power transmission system is modeled mathematically and simulated by software. In mathematically method, a system consisting of three flexible shafts with different rotation axis which connected through two universal joints is investigated via a three degree-of-freedom model. The stability is analyzed by means of a monodromy matrix technique. This is verified by comparing the results with dynamic analytical software AdamsView simulation and the results of the previous research. Then, the effects of rotational velocity, non-aligned angles, shaft's properties (stiffness and damping) on the stability are investigated. Finally, the stability charts constructed on various parameters is presented. It is observed that decreasing shaft stiffness and universal joint angle due to more stability, while decreasing shaft damping has the opposite effect.

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In this work, governing equations of the feed line, cut-off valve, and the starter system are analyzed mathematically and numerically. In the mathematical solution, the stability of the valve system is considered using the Laplace transform along with the linearization of the equations of the system. According to parameter design of the feed pipe–valve system, the system demonstrates the stable behavior in the effective parameter of the valve system on the basis of the Nyquist and Bode stability criterion. In the numerical solution, the steady state behavior of the cut-off valve is simulated during the cut-command. Then the rate of the pressure variation, mass flow rate through of the valve, gas pressure of the starter system, and the upstream pressure of the valve (water hammer) are considered based on the valve's poppet motion. The comparison of the simulation results with the experimental data depicts only 13 percent error in the mass flow rate through of the valve. In the last time of the closing valve, there is no variation in the mass flow rate in the valve due to the excessive loss factor of the valve when the valve approximately is closed. The results show that the closure of the cutoff valve shall be provided in accordance with allowable maximum pressure of the hydraulic shock on the established

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Rotating machines are one of the kinds of mechanical systems that widely used in industry. The way of connecting axis and vibration of system are among the items that are always discussed in these systems. In the paper, a mechanical rotating system is modeled. In the model, a system consisting of two flexible axes (shafts) with different rotation axis which connected through a cardan joint is investigated via two degrees of freedom model. The stability of the model is analyzed by means of a monodromy matrix technique. The model is verified by comparing the results with the results of the previous researches and different natural frequencies. Then the effects of different system parameters such as axis rotational velocity, cardan angle, shaft's properties (stiffness and damping) on the stability of system are investigated. Also manner and conditions of each parameter on the stability of system are discussed. Finally, the stability charts constructed on various system parameters is presented. It is observed that decreasing shaft stiffness and cardan joint angle due to more stability, while decreasing shaft damping has the opposite effect.

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In this article, Monte Carlo simulation method is used in conjunction with finite elements (FEs) for probabilistic free vibration and stability analysis of pipes conveying fluid. For fluid-structure interaction, Euler-Bernoulli beam model is used for analyzing pipe structure and plug flow model for representing internal fluid flow in the pipe. By considering structural parameters of system as random fields, the governing deterministic partial differential equation (PDE) of continuous system is transformed into a stochastic PDE. The continuous random fields are discretized by mid-point and local average discretization methods; then, by Monte Carlo simulations in each iteration loop, every distributed-parameter PDE having stochastic lumped-parameters is transformed into a deterministic distributed-parameter PDE. Each PDE is transformed into a system of deterministic ordinary differential equations (ODEs) by using FEs. Accordingly, all of the deterministic and stochastic parameters of system are discretized. For free vibration analysis, the eigenvalue problem is solved for investigating the complex-valued eigenvalues and critical eigenfrequencies. Consequently, having complex eigenfrequencies and divergence points, the statistical responses of stochastic problem are obtained like expected values, standard deviations, probability density functions, and the probability of occurrence for divergence instabilities.

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In this study, a vertically placed double-acting pneumatic cylinder controlled by two On/Off solenoid valves is applied for the purpose of the lower limb rehabilitation. Because of the different physical conditions and degrees of disability of patients and changes of the system dynamic parameters, admittance control strategy is used to compliantly interact between users and actuator. To analyze the stability, a linear model of the servo-pneumatic system is developed and its continuous transfer function is derived. Due to the exponential functions in the continuous transfer function of the system, the necessary transformations are used to achieve the discrete closed-loop transfer function of the system. In this way, the determination of the stable performance boundaries of the admittance control parameters related to changes in other dynamic parameters of the system is possible by root locus analysis of the discrete closed-loop system. These dynamics parameters include equivalent mass, damping and stiffness of the actuator and leg impedance and the proportional and differential gains of the inner loop position controller. Good correspondence is observed between the analytical and experimental stability limits of the system. Analytical results for appropriate choice of the admittance control and other dynamic parameters of the servo-pneumatic system are applicable to get smoothly and stable performance during the rehabilitation process.

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The stability analysis of workpiece in fixtures is considered as one of the stages of the fixture verification system. The stability of free-form workpieces in fixtures is affected by different agents including weight, locators, clamps and machining wrenches. In this study, a mathematical model has been presented for part stability analysis based on the minimum norm principle that led to a non-linear quadratic optimization problem. The solution to this problem is the reaction forces at the contact points between workpiece and locators. The study includes the workpiece stability analysis at the loading stages, determination of stability span for workpiece and the investigating the effect of the base locators distances on the workpiece stability through examples. A turbine blade model was incorporated as the case study to evaluate the suggested model capabilities in stability analysis. The loading procedure of this part into the fixture was categorized into sequential stages and its stability was investigated in contact with the locators. The results included the stability span of [15°-58°] for the workpiece on base locators, increased stability by the distanced base locators and the confirmation of the main locating plan through the stability verification at the loading stages. The results showed the model efficiency and accuracy in analyzing the free-form part stability in contact with the fixture elements. The proposed dexterous model can be integrated into the CAFD platform to be used at the early stages of locating and clamping system design applications.

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Twenty promising barley lines were evaluated at seven research stations in Iran, during two cropping seasons. The analysis of variance on grain yield data showed mean squares of environments, genotypes and Genotype×Environment Interaction (GEI) as significant, respectively accounting accounted for 60.38, 4.52 and 35.09% of treatment combination sum of squares. To find out the effects of GEI on grain yield, the data were subjected to Additive Main effects and Multiplicative Interaction (AMMI) and Sites Regression (SREG) GGE biplot analysis. Mega-environmental investigation is the most suitable way to utilize GEI. "Which-won-where" pattern was followed with three distinct mega-environments found in the barley assessment. Entries G5 and G6 showed general adaptability while G7 and G13 exhibited specific adaptation to Neishabour and Esfehan, respectively. Considering both techniques, genotype G1 revealed high grain yield along with yield stability. With regard to barley assessment, Esfehan was identified as a location with larger main effects interaction, making it a less predictable location for barley variety evaluation. The results finally indicated that AMMI and GGE biplot are informative methods to explore stability and adaptation pattern of genotypes in practical plant breeding and in subsequent variety recommendations. In addition, finding mega-environments help to identify the must suitable barley cultivars that can be recommended for areas within the mega-environment in either one or more test locations.

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Jig and fixture design for workpieces with freeform geometry has more complexity in comparison with the polyhedral parts. The locating and clamping system design construct the basis of the jig and fixture design activities. In this study, a theoretical analysis is suggested for automatic design of clamping points for freeform workpieces. The clamping design is performed in three main stages which the clamping application points are determined through the first two principles and being verified through the last stage. The mentioned principles consist of: (1) the minimum quantity of clamps, (2) the maximum clamping force components on the locating directions and (3) the workpiece static stability under the external wrenches. After mathematical modeling, the suggested analysis was implemented into the already designed CAFD framework by the authors. Three machining models were chosen as case studies to evaluate the capabilities of the implemented system in robust design of clamping layout. The minimum quantity of clamps (single clamp for two case studies and double clamp for the third one) was designed by the developed method that verified the robustness and reliability of the suggested and implemented clamping system design model. The automatic design of clamping scheme for workpieces (regardless of the geometry) beside its capability in integration with the other modules of fixture design activities provides the opportunity for the system to be used in industrial applications.

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To evaluate genotype × environment interaction (GEI) of grapevine, 20 genotypes of grapevines with Russian origin were evaluated at one location in Urmia and four locations in Takestan (two locations under full irrigation and two locations under drought stress). This research was performed in a randomized complete block design with three replications and three vines in each plot, in 2012-2013 season. Data on fruit yield (kg/vine) of the grapevine genotypes grown at different test locations were recorded and subjected to stability analysis by nonparametric methods. Result of the combined ANOVA revealed that variances due to genotypes, environments, and genotype-environment interactions were highly significant. Significant genotypic variance indicated genetic diversity among genotypes yield. The highest S_i⁽¹⁾ and S_i⁽²⁾ mean absolute rank was observed for genotypes Ramfi TCXA, Apozoski Ramfi, X45 and Anapiski Ramfli, indicating the high instability of these genotypes. Among the individual Z values, it was found that genotypes Ramfi TCXA, Uzbakestan Moscat, Bli Ramfi, Apozoski Ramfi and Anapiski Ramfli were significantly stable relative to the others, of which the Z_i⁽¹⁾ and Z_i⁽²⁾ values were greater than the table χ²_{(0.05, 1)}(3.84). The genotypes Skieve and Gezgiski Ramfi ranked the first and second, respectively, according to S_i⁽³⁾, while, according to S_i⁽⁶⁾, genotypes Skieve and Uzbakestan Moscat ranked the first and second, respectively. Genotypes Uzbakestan Moscat, Bli Ramfi and Kishmish Ramfi Azos, respectively, had the highest stability and lowest changes in different environments and were recommendable as stable genotypes in different areas. But, it should be noted that yield of these genotypes was moderate. Genotype Muscat had a high yield and moderate stability. As a result, these genotypes (Uzbakestan Moscat, Bli Ramfi, Skieve, Muscat and Kishmish Ramfi Azos) indicated greater resistance to environmental fluctuation and, therefore, increasing specificity of adaptability to low yielding environments.

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Network Control Systems (NCS) arise in many real-world applications and they have been an active area over recent decades. Using NCSs instead of traditional controllers has led to significant decrease in costs, weight and power of installations, also increase in reliability of control systems. Despite these advantages, NCSs confront various challenges, such as time varying delays and data packet dropouts in control data transfer which leads to instability. In this paper, the stability analysis and stabilizing with state feedback are studied for NCSs which includes time varying delays in state equations. This goal is achieved by introducing a new functional and using the Lyapunov-Krasovskii approach. Then, an accurate estimation of derivative of functional is obtained by applying Wirtinger and Reciprocally convex combination inequalities. In the proposed method, a stability criterion is derived with less conservatism and complexity. Afterwards, the problem of controller design is examined in which the state feedback controller is designed based on stability criterion. Finally, the dynamic model of the satellite as an examples is used to demonstrate the advantages of proposed method which illustrates our proposed method has desirable influence in decreasing conservatism of results and leading to better performance.

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Today, oil journal bearings are widely used as an efficient support for rotary systems in various industries. When these bearings are used by loading in high speed conditions, whirling disturbances in the rotor motion status leading to collisions and abrasion is probable. Designing specific geometric shapes or applying industrial lubricants with different new combinations can affect the journal bearings ability to maintain their dynamic stability in critical situations. From this view, the use of non-circular bearings and non-Newtonian fluids in the field of lubrication has recently been heavily taken into consideration. In the present study by choosing non-Newtonian lubricant simulated by power law fluid model, the effects of design parameters such as eccentricity ratio, aspect ratio and power law index on dynamic stability of noncircular two, three and four lobe bearings are investigated. For this purpose, assuming the limited cycle oscillations of the rotor around the equilibrium point after damping the effects of initial imposed disturbances and using finite element numerical method to solve the governing equations, stability range of the system in form of linear dynamic analysis characteristics is determined based on the whirl frequency ratio and critical mass parameter. The results indicate that by increasing the power law index and decreasing aspect ratio, the dynamic range of bearing support will be developed. Also, by increasing the number of noncircular bearings lobes with power law lubricant and providing the system's positioning conditions in high values of eccentricity ratio, more ability to damping dynamic disturbances can be achieved.

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In this paper, the instability of wave motion on the surface of liquid sheet emanating from a swirl injector exposed to inner and outer air streams, before the breakup is considered using the linear instability analysis by a perturbation method. The forces acting on a liquid gas interface in sprays, including surface tension, pressure, inertia force, centrifugal force and viscous force, lead to grow the disturbances originated from inside the injector on the outgoing liquid sheet. Interaction between these forces ultimately breaks up the jet into the ligaments. The linear instability analysis used in the present study is different from prior analysis. A cylindrical liquid sheet has been considered in previous studies but the present study implements the linear instability on a conical annular liquid sheet. Due to the complexity of derived governing equations a semi-analytical and numerical method was utilized in the solution procedure. The present model is capable to solve governing equations for the liquid jet with large range of spray angle. The predicted results compared with the prior studies results and experiments. The results of the current model in comparison with prior models have better accordance with experimental data. Also, the results show that the improved linear theory (the present model) predicts the breakup length better than linear theory.