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Papers by Inneke VAN NIEUWENHUYSE

Research paper thumbnail of The role of specialized hospital units in infection and mortality risk reduction among patients with hematological cancers

PLOS ONE, 2019

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Research paper thumbnail of Simulation of emergency department operations: a comprehensive review of KPIs and operational improvements

Computers & Industrial Engineering

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Research paper thumbnail of Construction of fast retrieval model of e-commerce supply chain information system based on Bayesian network

Information Systems and e-Business Management

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Research paper thumbnail of Research on agricultural supply chain system with double chain architecture based on blockchain technology

Future Generation Computer Systems

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Research paper thumbnail of Comparison of Kriging-based algorithms for simulation optimization with heterogeneous noise

European Journal of Operational Research, 2017

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Research paper thumbnail of A queueing model for a two-stage stochastic manufacturing system with overlapping operations

International Journal of Flexible Manufacturing Systems, 2005

This paper presents analytical expressions for estimating average process batch flow times throug... more This paper presents analytical expressions for estimating average process batch flow times through a stochastic manufacturing system with overlapping operations. It is shown that the traditional queueing methodology cannot be directly applied to this setting, as the use of the overlapping operations principle causes the arrival process of sublots at the second stage to be a non-renewal process. An embedded

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Research paper thumbnail of Buffer sizing in multi-product multi-reactor batch processes: Impact of allocation and campaign sizing policies

European Journal of Operational Research, Jun 1, 2007

ABSTRACT This paper studies the impact of management policies, such as product allocation and cam... more ABSTRACT This paper studies the impact of management policies, such as product allocation and campaign sizing, on the required size of the finished goods inventories in a multi-product multi-reactor batch process. Demand, setup and batch processing times for these products are assumed to be stochastic, and the inventory buffer for every product type needs to be such that target customer service levels are met. To perform this analysis, we develop a queueing model that allows us to explicitly estimate service levels as a function of the buffer size, and the allocation/campaign sizing policies. This model can be used to evaluate the service level given an existing buffer configuration, as well as to determine the buffer sizes required across products to meet a pre-specified service level. It also allows us to formulate a number of insights into how product allocation decisions and campaign planning policies affect buffer sizing decisions in symmetric production systems.

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Research paper thumbnail of The Vehicle Routing Problem: State of the Art Classification and Review

Computers & Industrial Engineering, 2015

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Research paper thumbnail of Order batching in multi-server pick-and-sort warehouses

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Research paper thumbnail of G-RAND: A phase-type approximation for the nonstationary G(t)/G(t)/s(t)+G(t) queue

ABSTRACT We present a Markov model to analyze the queueing behavior of the nonstationary G(t)/G(t... more ABSTRACT We present a Markov model to analyze the queueing behavior of the nonstationary G(t)/G(t)/s(t)+G(t) queue. We assume an exhaustive service discipline (where servers complete their current service before leaving) and use acyclic phase-type distributions to approximate the general interarrival, service, and abandonment time distributions. The time-varying performance measures of interest are: (1) the expected number of customers in queue, (2) the variance of the number of customers in queue, (3) the expected number of abandonments, and (4) the virtual waiting time distribution of a customer arriving at an arbitrary moment in time. We refer to our model as G-RAND since it analyzes a general queue using the randomization method. A computational experiment shows that our model allows the accurate analysis of small- to medium-sized problem instances.

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Research paper thumbnail of Lean operations management gekwantificeerd

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Research paper thumbnail of Optimizing campaign sizing policies: an application to a real-life setting

This paper presents an integrated production inventory model that enables to capture the tradeoff... more This paper presents an integrated production inventory model that enables to capture the tradeoffs between average inventory, production capacity and customer service level in a semiprocess industry setting. The model includes different features that are specific for such a setting, such as differences in reactor yield and quality requirements across products, the need for cleaning reactors when switching between product

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Research paper thumbnail of A branch-and-bound algorithm for shift scheduling with stochastic nonstationary demand

Computers & Operations Research, 2015

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Research paper thumbnail of The impact of lot sizing on queuing delays, an educational software tool

It is now widely accepted that both large and small lot sizes can cause long lead times and conse... more It is now widely accepted that both large and small lot sizes can cause long lead times and consequently bad customer service in terms of late deliveries. The impact of the lot size on the lead time consists of a convex relationship, implying an optimal lot size minimising average lead time. In order to educate people with this undoubtedly correct, but yet controversial issue, we developed an educational software tool which helps to clarify the important determinants and allows for self-tuition experimentation. Therefore, in the first section we explain why this phenomenon is so important and how it can be applied in practice. In the second section, we introduce a small example and explain the theoretical foundations of the model. The third section describes the graphical user interface.

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Research paper thumbnail of On the sum of independent zero-truncated Poisson random variables

The objective of this article is to derive the density function and cumulative distribution funct... more The objective of this article is to derive the density function and cumulative distribution function for random variables which may be written as the sum of independent (either identical or non-identical) zerotruncated Poisson random variables. The obtained expressions may be particularly useful for modelling purposes, especially in view of linking common purchase quantity models from the marketing literature to stochastic production-inventory models from the operations management literature.

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Research paper thumbnail of An adapted queueing model for estimating replenishment lead times in make-to-stock batch process industries

In this paper, we consider the problem of estimating the average and variance of replenishment le... more In this paper, we consider the problem of estimating the average and variance of replenishment lead time in a multi-product multi-reactor batch process with a base-stock inventory policy. The methodology used for this purpose is queueing theory. Although the body of knowledge on queueing theory has primarily been adopted in discrete manufacturing processes, we show that it is also applicable in semi-process industries. However, adequate changes to the models must be made in order to capture the specificities of this type of industry (such as batch processing, product allocation and campaign sizing).

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Research paper thumbnail of Estimating process batch flow times in a two-stage stochastic flowshop with overlapping operations

This paper focuses on modelling the impact of lot splitting on average process batch flow times, ... more This paper focuses on modelling the impact of lot splitting on average process batch flow times, in a two-stage stochastic flowshop. It is shown that the traditional queueing methodology for estimating flow times cannot be directly applied to a system with lot splitting, as the arrival process of sublots at the second stage is not a renewal process. Consequently, an embedded queueing model is developed in order to approximate the average flow time of the flags through the system; from the flow time of the flags, the flow time of process batches can then be derived. The model turns out to yield very satisfactory results, and provides a tool to quantify the reduction in flow time that can be obtained by overlapping operations at different processing stages. Moreover, it allows to model the trade-off between flow time improvement and gap time occurrence by using it within the scope of a cost model.

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Research paper thumbnail of Staffing and scheduling under nonstationary demand for service: A literature review

Omega, 2015

ABSTRACT

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Research paper thumbnail of Simulation optimization in inventory replenishment: A classification

IIE Transactions, 2015

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Research paper thumbnail of Use of Simulation for Improving the Output Rate: An Industrial Application

Our research focuses on improving the output rate of a single product CONWIP system. The system h... more Our research focuses on improving the output rate of a single product CONWIP system. The system has zero intermediate buffer capacity but may use time buffers which result from minimum and maximum processing times on each workstation. The transport between the different workstations is accomplished by a single resource (a bridge crane), constituting the bottleneck of the system. Since no mathematical approach exists to model this problem, we use simulation. To determine the parameters for the simulation scenarios, we rely on CONWIP, queueing and Factory Physics® literature. We apply the model to an industrial case. The results reveal major improvements in the output rate. The decision framework used, appears to be valuable for other real-life performance improvement applications based on simulation. The results also generate generic insights in improving production performance in similar systems.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The role of specialized hospital units in infection and mortality risk reduction among patients with hematological cancers

PLOS ONE, 2019

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Simulation of emergency department operations: a comprehensive review of KPIs and operational improvements

Computers & Industrial Engineering

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Construction of fast retrieval model of e-commerce supply chain information system based on Bayesian network

Information Systems and e-Business Management

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Research on agricultural supply chain system with double chain architecture based on blockchain technology

Future Generation Computer Systems

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Comparison of Kriging-based algorithms for simulation optimization with heterogeneous noise

European Journal of Operational Research, 2017

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A queueing model for a two-stage stochastic manufacturing system with overlapping operations

International Journal of Flexible Manufacturing Systems, 2005

This paper presents analytical expressions for estimating average process batch flow times throug... more This paper presents analytical expressions for estimating average process batch flow times through a stochastic manufacturing system with overlapping operations. It is shown that the traditional queueing methodology cannot be directly applied to this setting, as the use of the overlapping operations principle causes the arrival process of sublots at the second stage to be a non-renewal process. An embedded

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Buffer sizing in multi-product multi-reactor batch processes: Impact of allocation and campaign sizing policies

European Journal of Operational Research, Jun 1, 2007

ABSTRACT This paper studies the impact of management policies, such as product allocation and cam... more ABSTRACT This paper studies the impact of management policies, such as product allocation and campaign sizing, on the required size of the finished goods inventories in a multi-product multi-reactor batch process. Demand, setup and batch processing times for these products are assumed to be stochastic, and the inventory buffer for every product type needs to be such that target customer service levels are met. To perform this analysis, we develop a queueing model that allows us to explicitly estimate service levels as a function of the buffer size, and the allocation/campaign sizing policies. This model can be used to evaluate the service level given an existing buffer configuration, as well as to determine the buffer sizes required across products to meet a pre-specified service level. It also allows us to formulate a number of insights into how product allocation decisions and campaign planning policies affect buffer sizing decisions in symmetric production systems.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The Vehicle Routing Problem: State of the Art Classification and Review

Computers & Industrial Engineering, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Order batching in multi-server pick-and-sort warehouses

Bookmarks Related papers MentionsView impact

Research paper thumbnail of G-RAND: A phase-type approximation for the nonstationary G(t)/G(t)/s(t)+G(t) queue

ABSTRACT We present a Markov model to analyze the queueing behavior of the nonstationary G(t)/G(t... more ABSTRACT We present a Markov model to analyze the queueing behavior of the nonstationary G(t)/G(t)/s(t)+G(t) queue. We assume an exhaustive service discipline (where servers complete their current service before leaving) and use acyclic phase-type distributions to approximate the general interarrival, service, and abandonment time distributions. The time-varying performance measures of interest are: (1) the expected number of customers in queue, (2) the variance of the number of customers in queue, (3) the expected number of abandonments, and (4) the virtual waiting time distribution of a customer arriving at an arbitrary moment in time. We refer to our model as G-RAND since it analyzes a general queue using the randomization method. A computational experiment shows that our model allows the accurate analysis of small- to medium-sized problem instances.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Lean operations management gekwantificeerd

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Optimizing campaign sizing policies: an application to a real-life setting

This paper presents an integrated production inventory model that enables to capture the tradeoff... more This paper presents an integrated production inventory model that enables to capture the tradeoffs between average inventory, production capacity and customer service level in a semiprocess industry setting. The model includes different features that are specific for such a setting, such as differences in reactor yield and quality requirements across products, the need for cleaning reactors when switching between product

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A branch-and-bound algorithm for shift scheduling with stochastic nonstationary demand

Computers & Operations Research, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The impact of lot sizing on queuing delays, an educational software tool

It is now widely accepted that both large and small lot sizes can cause long lead times and conse... more It is now widely accepted that both large and small lot sizes can cause long lead times and consequently bad customer service in terms of late deliveries. The impact of the lot size on the lead time consists of a convex relationship, implying an optimal lot size minimising average lead time. In order to educate people with this undoubtedly correct, but yet controversial issue, we developed an educational software tool which helps to clarify the important determinants and allows for self-tuition experimentation. Therefore, in the first section we explain why this phenomenon is so important and how it can be applied in practice. In the second section, we introduce a small example and explain the theoretical foundations of the model. The third section describes the graphical user interface.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of On the sum of independent zero-truncated Poisson random variables

The objective of this article is to derive the density function and cumulative distribution funct... more The objective of this article is to derive the density function and cumulative distribution function for random variables which may be written as the sum of independent (either identical or non-identical) zerotruncated Poisson random variables. The obtained expressions may be particularly useful for modelling purposes, especially in view of linking common purchase quantity models from the marketing literature to stochastic production-inventory models from the operations management literature.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of An adapted queueing model for estimating replenishment lead times in make-to-stock batch process industries

In this paper, we consider the problem of estimating the average and variance of replenishment le... more In this paper, we consider the problem of estimating the average and variance of replenishment lead time in a multi-product multi-reactor batch process with a base-stock inventory policy. The methodology used for this purpose is queueing theory. Although the body of knowledge on queueing theory has primarily been adopted in discrete manufacturing processes, we show that it is also applicable in semi-process industries. However, adequate changes to the models must be made in order to capture the specificities of this type of industry (such as batch processing, product allocation and campaign sizing).

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Estimating process batch flow times in a two-stage stochastic flowshop with overlapping operations

This paper focuses on modelling the impact of lot splitting on average process batch flow times, ... more This paper focuses on modelling the impact of lot splitting on average process batch flow times, in a two-stage stochastic flowshop. It is shown that the traditional queueing methodology for estimating flow times cannot be directly applied to a system with lot splitting, as the arrival process of sublots at the second stage is not a renewal process. Consequently, an embedded queueing model is developed in order to approximate the average flow time of the flags through the system; from the flow time of the flags, the flow time of process batches can then be derived. The model turns out to yield very satisfactory results, and provides a tool to quantify the reduction in flow time that can be obtained by overlapping operations at different processing stages. Moreover, it allows to model the trade-off between flow time improvement and gap time occurrence by using it within the scope of a cost model.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Staffing and scheduling under nonstationary demand for service: A literature review

Omega, 2015

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Simulation optimization in inventory replenishment: A classification

IIE Transactions, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Use of Simulation for Improving the Output Rate: An Industrial Application

Our research focuses on improving the output rate of a single product CONWIP system. The system h... more Our research focuses on improving the output rate of a single product CONWIP system. The system has zero intermediate buffer capacity but may use time buffers which result from minimum and maximum processing times on each workstation. The transport between the different workstations is accomplished by a single resource (a bridge crane), constituting the bottleneck of the system. Since no mathematical approach exists to model this problem, we use simulation. To determine the parameters for the simulation scenarios, we rely on CONWIP, queueing and Factory Physics® literature. We apply the model to an industrial case. The results reveal major improvements in the output rate. The decision framework used, appears to be valuable for other real-life performance improvement applications based on simulation. The results also generate generic insights in improving production performance in similar systems.

Bookmarks Related papers MentionsView impact