A note on ‘A bivariate optimal replacement policy for a repairable system’

An error appearing in equation (3) of Y.L. Zhang (J. Appl. Prob., 1994, 31, 1123–1127) has been pointed out by S.H. Sheu (Eur. J. Oper. Res., 1999, 112, 503–516) and the correct expressions (25)–(27) given accordingly on pp. 510–511. However, the derivation of the key expression (27), the long-run expected loss rate, was not presented. The purpose of this note is threefold. First, since a monotone process (e.g. an arithmetic, geometric, or arithmetic–geometric process) approach, as discussed by K.N.F. Leung (Eng. Optimiz., 2001, 33, 473–484), is considered to be relevant, realistic, and appropriate to the modelling of a deteriorating system maintenance problem, it is worth explicitly developing this expression, which is of benefit to the subsequent studies. Secondly, equation (3) in Zhang (1994) Zhang, Y. L. 1994. A bivariate optimal replacement policy for a repairable system. J. Appl. Prob., 31: 1123–1127. [Crossref], [Web of Science ®] , [Google Scholar] is shown to be fundamentally correct and so it can be viewed as an alternative method of formulating similar bivariate cases. Thirdly, although equations (4) and (5) in Zhang (1994) Zhang, Y. L. 1994. A bivariate optimal replacement policy for a repairable system. J. Appl. Prob., 31: 1123–1127. [Crossref], [Web of Science ®] , [Google Scholar] have been logically and correctly derived, both can be readily reduced to their simplest forms which are derived here.     

Comments on ‘A model for determining job throughput times for manufacturing flow line worked Is with finite buffers’

This comment shows that the basic ideas in the paper by Park and Steudel (1991) have already appeared in the literature and in greater generality and have covered more interesting cases     

Comment on ‘Economic analysis of inventory systems’

This paper deals with the problem of designing a hierarchical production planning system, where higher level decisions impose constraints on lower level decisions. This paper supports the choice of a production planning system for a two-stage process. First, analytical models clarify the relationship between production planning rules and the role of buffer inventory level in terms of manufacturing performance. Second, from the results of the analysis, a numerical example is presented on a production planning system designed under various management policies.     

Dynamic analysis of bridge–vehicle system with uncertainties based on the finite element model

A new method of dynamic analysis on the bridge–vehicle interaction problem considering uncertainties is proposed in this paper. The bridge is modeled as a simply supported Euler–Bernoulli beam with Gaussian random elastic modulus and mass density of material with moving forces on top. These forces are time varying with a coefficient of variation at each time instance and they are considered as Gaussian random processes. The mathematical model of the bridge–vehicle system is established based on the finite element model in which the Gaussian random processes are represented by the Karhunen–Loéve expansion and the equations will be solved by the Newmark  -β$\beta$ method. The proposed method is compared with the Monte Carlo method in numerical simulations with good agreements for cases with different vehicle speed and level of uncertainties in the excitation and system parameters. The mean value and variance of the structural responses are found to be very accurate even with large uncertainties in the excitation forces. The proposed method is also found to have superior performance in the computational efficiency compared with the Monte Carlo method.     

Multi‐rate digital control for a cascaded system consisting of two subsystems with different input time delays

Abstract

This paper presents a multi‐rate state‐space control scheme for digital control of a cascaded continuous‐time system with fractional time delays. First, a discrete‐time state‐space representation of a continuous‐time system with a fractional input delay is established. Based on the time‐delay digital modelling, an ideal state reconstructor is also presented such that system states are exactly reconstructed via the measurement histories of inputs and outputs without a state observer. Next, a time‐delay subsystem (designated subsystem 1) with a fast sampling rate is designed to form the inner loop of the overall system, then the designed closed‐loop subsystem 1 is cascaded with a time‐delay open‐loop subsystem 2 with a slow sampling rate. A digital modelling of the time‐delay open‐loop subsystem 2, based on a fast‐rate sampling, is also formed for obtaining the digital modelling of the overall cascaded continuous‐time system by using the block‐pulse function approximation. Then, the fast‐rate overall system is converted into a slow‐rate model via the newly developed model conversion technique. Furthermore, subsystem 2 is separated from the slow‐rate overall system via a linear transformation for achieving a reduced‐order subsystem design. As a consequence, a digital control law is determined on some specific goals for the overall system. The proposed method is suitable for digital control of a multivariable, multi‐rate, time‐delay system in which state variables are not accessible.     

A note on ‘Economic manufacturing quantity in a just-in-time delivery system’

This comment is made on a paper by Golhar and Sarker who showed that it is economically advantageous for a supplier to participate in the just-in-time delivery system. Although the general conclusions are correct, one of the conditions under which the results are obtained is not necessary. Also, the optimal production quantity is not independent of delivery quantity though their interdependency is in a rather indirect manner.     

A coefficient of restitution model for particle–surface collision of particles with a wide range of mechanical characteristics

The coefficient of restitution describes the energy dissipation resulting from particle-particle and particle–surface interactions in solid–fluid flows. The energy loss depends on the mechanical characteristics of the solid phase, therefore, to correctly predict the behavior of these systems it is necessary to use reliable coefficient values based on the properties of the particles. This paper investigated the energy dissipation in particle–surface collisions using 7 types of particles with a wide range of mechanical properties (Young's modulus between 1.38 × 10⁴ and 2.83 × 10⁹ Pa). Three empirical equations have been proposed to calculate the coefficient of restitution based on the impact velocity and the compressional wave velocity. The experimental results presented an inverse relation between the impact velocity and the coefficient of restitution. This effect was more pronounced for less elastic particles. The models presented an accurate fit to the experimental data and statistical analysis showed that the Power model presented the greater capacity to predict the coefficient of restitution from generic data. The experimental results showed the predominant effect of mechanical characteristics on the coefficient of restitution. In addition, the proposed equations are proved to be precise tools for predicting particle coefficients of restitution with a wide range of elasticity modulus at low velocities.     

A formal control-theoretic model of a human–automation interactive manufacturing system control

This paper describes a human–automation interactive manufacturing system and presents a formal model for describing and controlling the system. The model presented in this paper considers a system from two perspectives: structural and operational perspectives. Human and an automated controller are considered agents that cooperate to achieve given goals by executing assigned tasks. A human–automation interaction is described with a particular communication model between two agents that exchanges messages. A system control schema and human tasks are modelled separately and then integrated in a formal manner using a modified communicating finite state machine framework. An interface model that coordinates the message exchanges between two agents is then introduced. An automated shop floor control system with a human material handler is modelled with the proposed framework and a simple illustrative example is provided.     

Effect of cannibalism on a predator–prey system with nutritional value: a model based study

Enrichment of a simple predator–prey system results in the destruction of stable steady state and further enrichment leads to the extinction of the species, which is a classical problem in ecology and known as the paradox of enrichment. The Paradox of enrichment is a controversial issue. Most theoretical studies show the destabilization of predator–prey system due to enrichment, but there is a discrepancy between the empirical evidence and theoretical predictions. In spite of the debate and cross-debate, research is still being carried out on the paradox of enrichment (16 papers and nearly 500 citations in 2008), which in general does not include the effect of cannibalism. Here we present a simple predator–prey system in the presence of cannibalism among predators and offer a novel resolution to the paradox of enrichment. The concept of nutritional value is introduced by many authors to resolve the issue. It is observed that even in the face of sufficient enrichment the system remains stable in the vicinity of critical nutritional value. In the case of a lower cannibalism rate we also observe similar kinds of behaviour, but for a higher cannibalism rate, the system remains always stable and does not depend upon the nutritional value of prey, i.e. paradox of enrichment does not hold at all in such a situation. We also observe that cannibalism can have a positive as well as a negative effect on population abundance, depending on the cannibalism rate.     

Construction of algorithm for calculation of the flow rate of a gas–liquid mixture in a horizontal pipeline for the microprocessor of an information measurement system

Features of an algorithm for calculation of the flow rate of the liquid phase of a gas–liquid mixture with the use of a variable pressure-drop flow meter with constricting devices are considered. Corresponding dependences for use in calculating the concentration of liquid in a mixture and a correction factor based on the readings of the flow meter for use in determining the flow rate of a single-phase flow are obtained.     

A novel shortened electrospun nanofiber modified with a ‘concentrated’ polymer brush

Abstract

We report the fabrication of shortened electrospun polymer fibers with a well-defined concentrated polymer brush. We first prepared electrospun nanofibers from a random copolymer of styrene and 4-vinylbenzyl 2-bromopropionate, with number-average molecular weight M_n=105 200 and weight-average molecular weight M_w=296 700 (M_w/M_n=2.82). The fibers had a diameter of 593±74 nm and contained initiating sites for surface-initiated atom transfer radical polymerization (SI-ATRP). Then, SI-ATRP of hydrophilic styrene sodium sulfonate (SSNa) was carried out in the presence of a free initiator and the hydrophobic fibers. Gel permeation chromatography confirmed that M_n and M_w/M_n values were almost the same for free polymers and graft polymers. M_n agreed well with the theoretical prediction, and M_w/M_n was relatively low (<1.3) in all the examined cases, indicating that this polymerization proceeded in a living manner. Using the values of the graft amount measured by Fourier transform infrared spectroscopy, the surface area, and M_n, we calculated the graft density σ as 0.22 chains nm^?2. This value was nearly equal to the density obtained on silicon wafers (σ=0.24 chains nm^?2), which is categorized into the concentrated brush regime. Finally, we mechanically cut the fibers with a concentrated poly(SSNa) brush by a homogenizer. With increasing cutting time, the fiber length became shorter and more homogenous (11±17 μm after 3 h). The shortened fibers exhibited excellent water dispersibility owing to the hydrophilic poly(SSNa) brush layer.     

A goal-oriented dual-weighted adaptive finite element approach for the optimal control of a nonsmooth Cahn–Hilliard–Navier–Stokes system

This paper is concerned with the development and implementation of an adaptive solution algorithm for the optimal control of a time-discrete Cahn–Hilliard–Navier–Stokes system with variable densities. The free energy density associated with the Cahn–Hilliard system incorporates the double-obstacle potential which yields an optimal control problem for a family of coupled systems in each time instant of a variational inequality of fourth order and the Navier–Stokes equation. A dual-weighted residual approach for goal-oriented adaptive finite elements is presented which is based on the concept of C-stationarity. The overall error representation depends on primal residuals weighted by approximate dual quantities and vice versa as well as various complementarity mismatch errors. Details of the numerical realization of the adaptive concept and a report on the numerical tests are given.     

Effect of constrained layers on vibrational characteristics of a composite sandwich system��A finite element based critical investigation

The main aim of this paper is to investigate the effect of various constrained layers (viscoelastic layer (VEL), electro-rheological fluid (ERF), and magneto-rheological fluid (MRF)) over natural frequency and the damping loss factor with two different fiber orientations (0° and 90°) for a Graphite/Epoxy (GR/E) composite sandwich shaft disc system. The finite element technique is used to investigate the natural frequency and loss factor for various combinations. Furthermore, the vibrational characteristics of the composite sandwich shaft disc system are compared with those of the base structure without constrained layers. The study shows that introducing various constrained layers reduces the magnitude of natural frequency by up to 80%. The results also show that GR/E composite with 90° fiber orientation acquires the highest frequency reduction. Among the proposed layers, VEL has the highest damping loss factor.     

Corrigendum to ‘Evaluation of normalisation methods for uniaxial bias extension tests on engineering fabrics’

This short communication is intended to correct certain erroneous conclusions drawn in the recently published paper by Härtel and Harrison (2014). The investigation of Härtel and Harrison (2014) was intended to evaluate the performance of normalisation methods for the uniaxial bias extension test. Predictions of two published theories for rate-independent behaviour were examined. New conclusions drawn in light of the error found in Härtel and Harrison (2014) are presented and corrected results are provided.     

Comments on ‘vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme’

Zanoni, Mazzoldi, and Jaber [Zanoni, S., L. Mazzoldi, and M. Y., Jaber. 2014. Vendor-managed inventory with consignment stock agreement for single vendor–single buyer under the emission-trading scheme. International Journal of Production Research 52 (1): 20–31] consider a joint economic lot size problem under the vendor-managed inventory with consignment stock agreement and an emission-trading scheme. They show that the total cost of the system is a jointly convex function by simply showing that every element of the Hessian is positive. Noticing this mistake, we analyse the same problem in this technical note. We first provide a closed-form solution when the production rate is given. In order to avoid a complete search over all possible production rates, we then develop an efficient continuous approximation algorithm. Computational experiment shows that the approximation algorithm is effective and efficient.     

The cumulative capability ‘sand cone’ model revisited: a new perspective for manufacturing strategy

The cumulative capability or the ‘sand cone’ model (Ferdows and De Meyer 1990, Lasting improvements in manufacturing performance: in search of a new theory. Journal of Operations Management, 9(2), 168–184) has been central in the debate on relations among dimensions of manufacturing performance. The central thesis of this model is that manufacturing performance is cumulative and sequential, with quality performance forming the foundation. An implicit assumption underlying the model is that the indirect effects of quality leading to delivery, then to flexibility and finally cost are stronger than direct effects among these same performance dimensions. Despite its frequent use, the sand cone model has not been empirically tested for direct and indirect effects or for the sequence of effects. Most tests have used correlations or regression relationships that only establish positive relationships among dimensions, not the specific sand cone sequence. We conduct two new tests of the actual sequence of the sand cone theory using data from 189 manufacturing plants. We do not find universal support for the sand cone theory, since some plants in our data appear to be following the sand cone sequence, while others are not. Our empirical tests support other limited evidence in the literature that a contingency theory is needed rather than an outright rejection or acceptance of the sand cone model.