Ruslan Krenzler

Ruslan Krenzler

Dr

About

20
Publications
5,884
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125
Citations
Introduction
I am a researcher in the field mathematical modelling, in particular queueing systems and operations research.

Publications

Publications (20)
Article
Full-text available
We investigate a fundamental model from open-pit mining, which is a cyclic system consisting of a shovel, traveling loaded, unloading facility, and traveling back empty. The interaction of these subsystem determines the capacity of the shovel, which is the fundamental quantity of interest. To determine this capacity one needs the stationary probabi...
Preprint
Full-text available
Exponential single server queues with state dependent arrival and service rates are considered which evolve under influences of external environments. The transitions of the queues are influenced by the environment's state and the movements of the environment depend on the status of the queues (bi-directional interaction). The structure of the envi...
Article
Full-text available
In robotic mobile fulfillment systems, human pickers don’t go to the inventory area to search for and pick the ordered items. Instead, robots carry shelves (called “pods”) containing ordered items from the inventory area to picking stations. At the picking stations, pickers put ordered items into totes; then these items are transported to the packi...
Chapter
We present models for performance analysis of IPTV services. The main topic is to model the interplay of the restricted number of channels, the larger number of available programs to be transmitted over the channels, and the concurrent access of many users to the same program, resp. channel (multicast services). In a simple Engset-like model we com...
Article
We investigate a new class of separable systems which exhibit a product-form stationary distribution. These systems consist of parallel production systems (servers) at several locations, each with a local inventory under base stock policy, connected with a common supplier network. Demand of customers arrives at each production system according to a...
Preprint
Full-text available
We consider a semi-open queueing network (SOQN), where a customer requires exactly one resource from the resource pool for service. If there is a resource available, the customer is immediately served and the resource enters an inner network. If there is no resource available, the new customer has to wait in an external queue until one becomes avai...
Preprint
Robotic mobile fulfillment systems (RMFSs) are a new type of warehousing system, which has received more attention recently, due to increasing growth in the e-commerce sector. Instead of sending pickers to the inventory area to search for and pick the ordered items, robots carry shelves (called "pods") including ordered items from the inventory are...
Article
Full-text available
In a robotic mobile fulfillment system, robots bring shelves, called pods, with storage items from the storage area to pick stations. At every pick station there is a person-the picker-who takes parts from the pod and packs them into boxes according to orders. Usually there are multiple shelves at the pick station. In this case, they build a queue...
Presentation
Full-text available
Presentation for OR2018 conference.
Article
We investigate a fundamental model from open-pit mining which is a cyclic system consisting of an (unreliable) shovel, trucks travelling loaded, unloading facility, and trucks travelling back empty. The interaction of these subsystems determines the mean number of trucks loaded per time unit - the capacity of the shovel, which is a fundamental quan...
Article
We investigate queueing networks in a random environment. The impact of the evolving environment on the network is by changing service capacities (upgrading and/or degrading, breakdown, repair) when the environment changes its state. On the other side, customers departing from the network may enforce the environment to jump immediately. This means...
Article
We consider a two-echelon production-inventory system with a central supplier connected to production systems (servers) at several locations, each with a local inventory. Demand of customers arrives at each production system according to a Poisson process and is lost if the local inventory is depleted. To satisfy a customer’s demand, a server at th...
Article
We consider a single server system with infinite waiting room in a random environment. The service system and the environment interact in both directions. Whenever the environment enters a prespecified subset of its state space the service process is completely blocked: Service is interrupted and newly arriving customers are lost. We prove a produc...
Article
Full-text available
We develop randomized modifications of Markov chains and apply these modifications to the routing chains of customers in Jacksonian stochastic networks. The aim of our investigations is to find new rerouting schemes for non standard Jackson networks which hitherto resist computing explicitly the stationary distribution. The non standard properties...
Conference Paper
We develop a separable model for a referenced node in a fault tolerant (disruption tolerant) wireless sensor network, which encompasses the message queue of the node and an inner and an outer environment for describing details of the transmission protocols. We prove that the system has steady state of product form for the queue and its environment....
Article
Full-text available
We consider a single server system with infinite waiting room in a random environment. The service system and the environment interact in both directions. Whenever the environment enters a prespecified subset of its state space the service process is completely blocked: Service is interrupted and newly arriving customers are lost. We prove an if-an...
Article
Full-text available
We consider a single server system with infinite waiting room in a random environment. The service system and the environment interact in both directions. Whenever the environment enters a specific subset of its state space the service process is completely blocked: Service is interrupted and newly arriving customers are lost. We prove an if-and-on...

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Cited By

Projects

Projects (5)
Project
We consider a queueing system, which consists of a single server system under a first-come, first-served regime with infinite waiting room, in a random environment, where the queueing system and the environment interact in both directions. Special cases of the model are the queueing-inventory systems with perishable items (server = production system, environment = inventory-replenishment subsystem).
Project
We investigate a new class of separable systems which exhibit a product form stationary distribution. These systems consist of parallel production systems (servers) at several locations, each with a local inventory under base stock policy, connected with a common supplier network. Demand of customers arrives at each production system according to a Poisson process and is lost if the local inventory is depleted (“lost sales”). To satisfy a customer’s demand a production server needs raw material from the associated local inventory. The supplier network is a classical queueing network. We perform cost analysis to find the optimal base stock levels.
Project
The RMFS gives rise to a new combination of decision problems that have to be solved and coordinated effectively to ensure overall performance. Those decision problems include multi robot path planning, multi robot task allocation, order batching, replenishment batching, item storage assignment and bucket storage assignment problems. In short these decide (in the same order) which paths the robots use, how the tasks are allocated to the different robots, which orders are assigned to which output-station, which incoming items are distributed from which input-station, which new items are put on which bucket and where to park the buckets when bringing them back to the inventory. Most of these naturally have to be decided in an online sense while they also can be mapped to NP-hard optimization problems. Moreover, they have to cooperate well and efficiently. At this, the main goal of this project is to use as few equipment as possible while still managing the item throughput, respectively not making the order pickers wait.