Comments on “Second-order sliding mode control with experimental application”

In this paper, some points to the stability analysis of the paper [Eker I, Second-order sliding mode control with experimental application, ISA Trans 2010;50:394–405] are presented. It is illustrated that the way the author in [1] proves stability, suffers lack of correct justification. A modification to the stability analysis is presented and the stability conditions are restated. Moreover, some other flaws in the original paper are addressed.     

Use of analytical techniques to reveal the influence of chemical structure of clearcoat on its biological degradation caused by bird-droppings

There are various biological materials which may repetitively deposit on a painted automotive body during its service life, causing possible local defects. This study is an attempt to reveal the mechanism of degradation caused by bird-droppings and to compare the performance of clearcoats having various resin/hardener ratios. Two different testing methods varying in aging conditions, of the effect of natural bird-droppings, were applied to two types of clearcoats. Variations in chemical structure were characterized by the aid of FTIR spectroscopy and DMTA analysis. Also, in order to establish an experimentally viable procedure to assess such an effect, synthetic countertype of bird-droppings (pancreatin) was used to simulate this natural phenomenon.     

Hyperelastic model analysis of stress‐strain behavior in polybutadiene/ethylene‐propylene diene terpolymer nanocomposites

Micromechanics of elastomer nanocomposite samples based on polybutadiene (BR), ethylene‐propylene diene terpolymer (EPDM) hyperelastic matrixes prepared via melt compounding was investigated using uniaxial tensile analysis. Constitutive hyperelastic models, including Polynomial, Yeoh, Ogden, Arruda‐Boyce, and Van der Waals were used to determine material parameters in incompressible isotropic elastic strain‐energy functions on the basis of a nonlinear least squares optimization method by fitting the data obtained from uniaxial classic experiments. Effect of nanoclay (0, 3, 5, 7, and 10 phr) content on the simulation accuracy was investigated. Simulation results compared with the experimental data suggested that the Ogden model as the most consistent model investigated here. J. VINYL ADDIT. TECHNOL., 23:21–27, 2017. © 2015 Society of Plastics Engineers     

A realistic multi-manned five-sided mixed-model assembly line balancing and scheduling problem with moving workers and limited workspace

The assembly line balancing problem can completely vary from one production line to the other. This paper deals with a realistic assembly line for the automotive industry inspired by Fiat Chrysler Automotive in North America and Parskhodro in Iran (both large-scale automotive companies). This problem includes some specific requirements that have not been studied in the literature. For example, the assembly line is five-sided, and workers can move along these sides. Due to the limited workspace, all the sides cannot work simultaneously at one station. First, a mixed integer linear programming model is proposed for the problem. Then, the model is improved to have a tighter linear relaxation. Moreover, an effective logic-based Benders’ decomposition algorithm is developed. After careful analysis of problem’s structure, three propositions are introduced. The master problem is well restricted by eight valid inequalities. Two different sub-problem types are defined to extract more information from the master problem’s solution. In this case, the algorithm adds effective cuts that reduce the solution space to the extent possible at each iteration. Thus, the number of iterations is significantly cut down. The performance of the model and algorithm, as well as improvement made on both, is evaluated.     

Prediction of fatigue crack nucleation life in polycrystalline AA7075‐T651 using energy approach

A crystal plasticity (CP) simulation and an energy‐based model is presented to predict the fatigue nucleation onset for polycrystalline AA 7075‐T651. Different microstructure morphology and grain sizes are employed in the simulations. Using a simple method, statistically stored dislocation (SSD) and geometrically necessary dislocation (GND) as decoupled with crystal plasticity model are estimated using a double round‐notch specimen test data, and CP simulation. The dislocation density parameter approximated from plastic energy density, stored energy density, elastic energy and accumulated slip validated with double hole experimental data. Sensitivity analysis is performed with respect to different microstructures and dislocation density parameters. Roughly, maximum 30% difference between experimental nucleation life and the simulated one is observed. The simulated predictions are in fair agreement with test data. The proposed strategy is suitable to study the scatter of fatigue nucleation life.     

A hybrid artificial immune algorithm for a realistic variant of job shops to minimize the total completion time

This paper investigates an extended problem of job shop scheduling to minimize the total completion time. With aim of actualization of the scheduling problems, many researchers have recently considered realistic assumptions in their problems. Two of the most applied assumptions are to consider sequence-dependent setup times and machine availability constraints (MACs). In this paper, we deal with a specific case of MACs caused by preventive maintenance (PM) operations. Contrary to the previous papers considering fixed or/and conservative policies, we consider flexible PM operations, in which PM operations may be postponed or expedited as required. A simple technique is employed to schedule production jobs along with the flexible MACs caused by PM. To solve the given problem, we present a novel meta-heuristic method based on the artificial immune algorithm (AIA) incorporating some advanced features. For further enhancement, the proposed AIA is hybridized with a simple and fast simulated annealing (SA). To evaluate the proposed algorithms, we compare our proposed AIA with three well-known algorithms taken from the literature. Finally, we find that the proposed AIA outperforms other algorithms.     

A study on integrating sequence dependent setup time flexible flow lines and preventive maintenance scheduling

This paper investigates flexible flow line problems with sequence dependent setup times and different preventive maintenance policies. The optimization criterion is the minimization of makespan. The contribution of this work could be divided into two parts: (1) Since the proposed integrating methods in the literature are often not only complicated but also problem-specific, we have been thinking of providing a technique simple to implement, yet easily extendible to any other machine scheduling problems to overcome the foregoing drawbacks. (2) In order to tackle the problem, we propose a novel variable neighborhood search (VNS) as well as the adaptations of some existing high performing metaheuristics in the literature. The proposed VNS uses advanced neighborhood search structures. In order to evaluate the algorithms, a benchmark is established with the meticulous care. All the results illustrate that the VNS outperforms the other algorithms.     

A Novel Method of Gait Synthesis for Bipedal Fast Locomotion

Common methods of gait generation of bipedal locomotion based on experimental results, can successfully synthesize biped joints’ profiles for a simple walking. However, most of these methods lack sufficient physical backgrounds which can cause major problems for bipeds when performing fast locomotion such as running and jumping. In order to develop a more accurate gait generation method, a thorough study of human running and jumping seems to be necessary. Most biomechanics researchers observed that human dynamics, during fast locomotion, can be modeled by a simple spring loaded inverted pendulum system. Considering this observation, a simple approach for bipedal gait generation in fast locomotion is introduced in this paper. This approach applies a nonlinear control method to synchronize the biped link-segmental dynamics with the spring-mass dynamics. This is done such that while the biped center of mass follows the trajectory of the mass-spring model, the whole biped performs the desired running/jumping process. A computer simulation is done on a three-link under-actuated biped model in order to obtain the robot joints’ profiles which ensure repeatable hopping. The initial results are found to be satisfactory, and improvements are currently underway to explore and enhance the capabilities of the proposed method.     

Finite element analysis of a thermoplastic elastomer melt flow in the metering region of a single screw extruder

The flow of a thermoplastic elastomer melt in the metering region of a single screw extruder was studied by the use of a mathematical model. In this model the continuous penalty finite element scheme was combined with generalized Newtonian rheological model to solve the governing equations of continuity and momentum in three-dimensional Cartesian coordinate system. A non-isothermal flow regime was assumed and the energy equation was solved by a streamline upwind Petrov–Galerkin method. The nonlinear nature of the derived set of working equations was also treated using the well-known Picard’s iterative technique. The applicability of this model has been verified by the comparison between the results of the computer simulation of the flow of a NBR/PP thermoplastic elastomer in the metering zone of a single screw extruder with experimentally measured data at different process conditions. These comparisons show that there are very good agreements between the model predictions and experimental data.     

Wireless mesh networks channel reservation: modelling and delay analysis

In order to overcome the negotiation procedure bottleneck of the standard DCF in wireless mesh networks, the authors propose a new channel reservation function (CRF) that reduces the negotiation overhead of the DCF, which as a result reduces the overall transmission delay effectively without of any extra bandwidth consumption. Furthermore, the authors provide an analytical model for the proposed scheme for which the simulation results measure the amount that the new method can reduce the average total delay for both regular and fragmented mesh topologies demonstrating superiority of the new method over the classic 802.11 solution. Additionally, the authors extend the scheme to multichannel CRF upon which the proposed method can be used for multichannel applications.