Estimating the availability of hydraulic drive systems operating under different functional profiles through simulation

Hydraulic drive systems are widely used in a variety of industrial applications where high torque and low speed rotational power are required. The advantages include maximum torque from zero speed, continuously variable speed within wide limits, high reliability and insensitivity to shock loads. A drive system consists of a hydraulic circuit, electric motors, hydraulic pumps, hydraulic motors and auxiliary components. The stress on the components, and hence wear and failure rate, varies with the torque and speed output by the drive. The reliability of a hydraulic drive system of a particular design can therefore vary significantly between installations operating in applications with different functional requirements. Predicting the availability of a drive system in a particular application is useful for several purposes such as optimising the system design and estimating support costs. This paper describes a simulation model, developed to estimate the availability of a hydraulic drive system in a given functional profile, consisting of output torque and speed time phase requirements. It outputs statistics on system availability and component failure rates. As an example, the simulation model is used to compare these statistics for a drive design operating under two distinct operational profiles

An efficient algorithm for computing exact system and survival signatures of K-terminal network reliability

An efficient algorithm is presented for computing exact system and survival signatures of K-terminal reliability in undirected networks with unreliable edges. K-terminal reliability is defined as the probability that a subset K of the network nodes can communicate with each other. Signatures have several advantages over direct reliability calculation such as enabling certain stochastic comparisons of reliability between competing network topology designs, extremely fast repeat computation of network reliability for different edge reliabilities and computation of network reliability when failures of edges are exchangeable but not independent. Existing methods for computation of signatures for K-terminal network reliability require derivation of cut-sets or path-sets which is only feasible for small networks due to the computational expense. The new algorithm utilises binary decision diagrams, boundary set partition sets and simple array operations to efficiently compute signatures through a factorisation of the network edges. The performance and advantages of the algorithm are demonstrated through application to a set of benchmark networks and a sensor network from an underground mine

Modelling cycle for simulation digital twins

Digital twins (DT) form part of the Industry 4.0 revolution within manufacturing and related industries. A DT is a digital model (DM) of a real system that features continuous and automated synchronisation and feedback of optimisations between the real and digital domains. A core technology for predictive capabilities from DT is discrete event simulation (DES). The modelling cycle for developing and analysing DES models is significantly different compared to DM. A DT specific DES modelling cycle is introduced that is evolved from that of DM. The availability of specialised software tools for DT tailored to these differences would benefit industry

Modelling stochastic behaviour in simulation digital twins through neural nets

Discrete event simulation (DES) is a widely used technique for modelling systems where state changes occur at discrete points in time. Stochastic behaviour is represented through random variables associated with probability distributions, from which random variates are sampled during simulation to determine outcomes. However, the distribution of outcomes for an event in the real system being modelled often depend on characteristics of the current system state. This paper proposes the use of artificial neural networks (ANN) to determine the changing conditional distributions of random variables during a simulation. The ANN are pre-trained to predict distributions by learning from example pairs of input feature vectors and random variable outcomes. It enables complex, non-linear dependencies between these features and random variable outcome distributions to be accurately modelled, including distributions that are multi-modal. A major area of application is the development of digital twin models that closely mimic the complex stochastic behaviour of the connected physical twin by learning from the data the real system generates. The benefits of the approach introduced in the paper are demonstrated through a realistic DES model of load-haul-dump vehicle operations in a production area of a sublevel caving mine. Keywords: discrete event simulation; mixture density network; digital twin; artificial neural network; industry 4.0 1. Introduction Discrete event simulation (DES) is a popular modelling approach due to its ability to represent complex, dynamic systems with stochastic behaviour whilst requiring fewer simplifying assumptions compared to analytical models (Banks, 1998). Stochastic behaviour is incorporated in DES by using random variables to represent event outcomes, with outcome probabilities represented by a probability distribution function. Random variables in a DE

Analysis of the contributions to the performance of a functional product design using simulation

Functional products (FP) consist of combined hardware, software and support services that are sold to the customer under performance-based contracts that guarantee a specified level of functional availability. The supplier is responsible for the development, manufacture, support and upgrade of a FP during the contract period. In comparison to a traditional hardware sale only contract, an FP transfers risk from uncertain availability and support costs from the customer to the supplier. This is a major advantage for the customer but means that the supplier must understand and optimise the availability and support costs of a FP design. During product development, simulation can be used to analyse potential FP designs, predict how they will perform and identify possible areas for improvement – providing vital qualitative and quantitative decision support. In this paper, a methodology for analysing a FP design to predict how it will perform and determine the contribution of individual elements of the FP to its overall performance is described. This methodology is then applied to analyse an example of a FP

Maintenance processes modelling and optimisation

A Maintenance Procedure is conducted in order to prevent the failure of a system or to restore the functionality of a failed system. Such a procedure consists of a series of tasks, each of which has a distribution of times to complete and a probability of being performed incorrectly. The inclusion of tests can be used to identify any maintenance errors which have occurred. When an error is identified it can be addressed through a corresponding correction sequence which will have associated costs and add to the maintenance process completion time. A modified FMEA approach has been used to identify the possible tests. By incorporating any selection of tests into the maintenance process it can then analysed using a discrete-event simulation to predict the expected completion time distribution. The choice of tests to perform and when to do them is then made to successfully complete the maintenance objective in the shortest possible time using a genetic algorithm. The methodology is demonstrated by applying it to the repair process for a car braking system. The developed method is suitable for application in abroad range of industries

A modelling and simulation approach for linking design activities to business decisions

The business environment of the manufacturing industry is changing from a hardware-based product focus to a process and function focus. A current industrial interest is the development and sale of functions. This function could be realised as a product based on hardware, software and services, and may be sold as a function rather than as hardware. This function view is referred to as Functional Products (FP). The new focus for the customer is on value rather than hardware. This presents new challenges for how engineering hardware design may best be carried out. Sale of functional products requires a changed business model in which the price of the functional product is related to the functionality of the product itself; hence the name functional product. The supplier can in such a scenario no longer sell maintenance and spare parts. Instead, these activities become a cost, thus motivating the supplier to increase process efficiency, decrease internal production cost by using less energy per produced unit andincrease knowledge about use-cases. The researcher's challenge is how to create new knowledge regarding functional product development for academic as well as for industrial benefit. The research question was formulated as: How may methods or tools for design process modelling and simulation be developed to support functional product development? Four case studies were carried out in Swedish industry. Case study 1 was carried out in cooperation with Hägglunds Drives AB. Case study 2 was carried out in cooperation with companies Hägglunds Drives AB, Volvo Aero and Volvo Car Corporation. Case study 3 was carried out in cooperation Volvo Aero and Case study 4 was carried out in cooperation with nine industrial companies during the formation of the Faste Laboratory, Centre for Functional Product Innovation. Results include the need for integrating product development process and company strategy for functional product development and the identification of the need for new methods and tools to enable better understanding of technology and business processes. The research shows the possibility of evaluating cost and time of development before doing the actual product development work by modelling and simulating the design process. Thus, the knowledge that previously was implicit in the work process is made explicit and possible to manipulate for a desired outcome. Linking the future business cases to work processes by modelling and simulation enables knowledge re-use and work-process predictions concerning cost and time. Hence, modelling and simulation of work processes results in better knowledge of company development capacity earlier than before, thus allowing shorter reaction time to changes in the business domain

Hardware design as a basis for functional product development

The business environment in manufacturing industry is changing from a hardware based product focus to a process and function focus. A current industrial interest is the development and sale of functions. This function could be realised as a product based on hardware, software and services and may be sold as a function rather than as hardware. This function view is referred to as Functional Products (FP). The new focus is on value for the customer rather than on hardware for the customer. This change creates new challenges for how engineering design of the hardware may best be carried out. To develop a functional product, several parties need to be involved in the particular project. These parties are suggested to be supplier, seller, sub- contractor, customer and end user. Since the functional product is not only consisting of hardware but also of services the relations between manufacturers and customers will change. Product development will be carried out in networks to an increasing degree where assignments, activities of, and relations between involved parties will be continuously changing. This thesis introduces the area of functional products and related literature from a hardware engineering design perspective. It starts from a holistic approach and introduce the area of functional products in relation to traditional hardware design and development. Product and process issues considered to be important are raised and discussed; value of hardware product versus value of functions, increased need for integration, communication and collaboration over cross-disciplinary borders, increased need for simulation support to be able to increase the predictability of design concepts. Simulation as an activity to verify the capabilities of the hardware product must be taken for granted in functional product business negotiation. Elongated needs exploration and identification stage are likely early on in functional product development. The concept verification stage in product development of functional products is suggested to increase until such times when integrated simulation support has been developed to support system simulation of functional products. Additionally, issues brought forward in this thesis include: -Suggestions on processes necessary for functional product development -Changes in value for the customer and ownership of the hardware with the introduction of the FP concept - Questions have been raised for how the engineering design activities actually will be affected with the introduction of functional products The thesis is seen as exploratory rather than verifying and invites discussion of the issues raised here, in order for these issues to be developed further.Godkänd; 2004; 20060925 (cira)Service Concept Design - NFF

User-driven design of a flexible distance education environment : rationale, lessons learned and future implications

This paper discusses the challenges inherent in distributed education and presents the development of a distance education environment to meet the needs of educators and geographically dispersed students at Luleå University of Technology in northern Sweden. The design rationale and experiences from teaching in the environment are discussed. During the course of the research, several prerequisites for quality distance education were identified, one of which is the main topic of this paper. Here, the needs identified by the educators who are to se the created environment are discussed. Those needs have led to the design of the environment, including physical spaces, tools and technologies. Our results indicate that it is now possible to design a highly useful environment for distributed education at a much lower cost-to-quality ratio than only a few years ago. Such a system may be created in a way that allows teachers to earn to use the environment selfsufficiently. Thereby, the need for support staff is greatly diminished. The results indicate that the use of appropriate methods and tools lets teachers work in a distributed environment in a way that closely resembles their normal way of work in a teaching situation. In addition, a strategy for future development of the environment, based on the results presented here and on previous research, is suggested.Godkänd; 2008; 20071207 (maglof