Model verification and validation (V&V) is one of the most important activities in simulation mod... more Model verification and validation (V&V) is one of the most important activities in simulation modelling. Model validation is especially challenging for Agent-Based Simulation (ABS). Techniques that can help to improve V&V in simulation modelling are needed. This paper proposes a V&V technique called Test-Driven Simulation Modelling (TDSM) which applies techniques from Test-Driven Development in software engineering to simulation modelling. The main principle in TDSM is that a unit test for a simulation model has to be specified before the simulation model is implemented. Hence, TDSM explicitly embeds V&V in simulation modelling. We use a case study in maritime search operations to demonstrate how TDSM can be used in practice. Maritime search operations (and search operations in general) are one of the classic applications of Operational Research (OR). Hence, we can use analytical models from the vast search theory literature for unit tests in TDSM. The results show that TDSM is a useful technique in the verification and validation of simulation models, especially ABS models. This paper also shows that ABS can offer an alternative modelling approach in the analysis of maritime search operations.
Two of the crucial parts in the process of performing a simulation study are validation and verif... more Two of the crucial parts in the process of performing a simulation study are validation and verification. The reason is these techniques help on increasing the confidence in the model, since it is not possible to demonstrate its absolute validity in all contexts. This paper presents the results of a white-box validation performed in an agent-based simulator for population dynamics. The tool provides a way to simulate the demographic evolution of large populations in a parallel environment. The purpose is to obtain population projections that can be used afterwards for policy analysis. Although the tool has been studied in terms of performance and scalability, its validation hasn’t been addressed. With a white-box validation we expect to increase the confidence of policy analysers and social scientists in our simulation model.
Police command and control centres are the main point of contact for the public who require help.... more Police command and control centres are the main point of contact for the public who require help. Like other areas of UK public services, police forces are set targets for their performance. Some of these targets relate to the speed at which they respond to calls for assistance from the public. In this paper we share our experience in improving the performance of command and control centres of a UK Police Force; a project which started as a classical simulation exercise and ended up with a significant reorganisation in a UK Police Force.
This paper deals with the application of modern software development tools on simulation developm... more This paper deals with the application of modern software development tools on simulation development. Recently, Agile Software Development (ASD) methods enjoy an increasing popularity. eXtreme Programming (XP) techniques, one of the techniques which belong to the ASD group of methods is a software development method which improves software quality and responsiveness of software projects through introducing short development cycles and a Test Driven Development (TDD) philosophy throughout the development. In this paper, we particularly pay attention to the application of the TDD by approaching simulation development from a test-first perspective. This study consists of a feasibility study of applying the TDD technique in simulation development in its various levels, say, acceptance and unit testing. Moreover, a simulation case study of a surgical ward has been considered, designed and implemented using the AnyLogic simulation toolkit. Our study differs from the mainstream in many ways. It addresses the feasibility of Test-Driven Simulation Development in Visual Interactive Modelling and Simulation (VIMS) environments as well as providing an insight into how the test-first concept can further help with the choice of components and acceptance testing.
SIMULATION: Transactions of The Society for Modeling and Simulation International
This paper advocates the use of a formal framework for analyzing simulation performance. Simulati... more This paper advocates the use of a formal framework for analyzing simulation performance. Simulation performance is characterized based on the three simulation development process boundaries: physical system, simulation model, and simulator implementation. Firstly, we formalize simulation event ordering using partially ordered set theory. A simulator implements a simulation event ordering, and incurs implementation overheads when enforcing event ordering at runtime. Secondly, we apply our formalism to extract and formalize the simulation event orderings of both sequential and parallel simulations. Thirdly, we propose the relation stricter and a measure called strictness for comparing and quantifying the degree of event dependency of simulation event orderings respectively. In contrast to the event parallelism measure, strictness is independent of time.
Simulation modeling is one of the analytic techniques commonly used for transportation management... more Simulation modeling is one of the analytic techniques commonly used for transportation management; it includes such activities as route planning and post-operation analysis. One of the simulation methods, agent-based simulation, has become increasingly popular due to the availability of good micro-level data collected through technologies such as GPS-enabled devices and road sensors. This paper presents the design and implementation of an agent-based simulation tool that can be used to analyse vehicle routing algorithms. We demonstrate how the tool can be used in practice by implementing two vehicle routing algorithms: shortest-path and LANTIME. LANTIME is an algorithm that can be used to minimize CO 2 emissions.
Agent-Based Modelling and Simulation (ABM/S) is still struggling to become one of the main stream... more Agent-Based Modelling and Simulation (ABM/S) is still struggling to become one of the main stream simulation methods in Operational Research (OR) and Management Science (MS), despite its generally accepted usefulness when it comes to representing human behaviour in human-centric systems. In other fields, as for example Business Studies, Economics, and Social Science, it is flourishing. One of the technical differences between ABM/S and the well-established OR/MS simulation methods System Dynamics Simulation (SDS) and Discrete Event Simulation (DES) is that ABM/S traditionally uses an equation based modelling approach while SDS and DES use a graphical notation for the model description. We believe that having a graphical notation for ABM/S would help establish it in OR/MS. The Unified Modelling Language (UML) is a graphical notation commonly used in software engineering for the purpose of software design. Use case and state machine diagrams, which are part of the UML notation seem to lend themselves particularly well to ABM/S. In this paper we introduce UML to the OR/MS community. First we explain step-by-step how to use UML for developing ABM/S models. Then we demonstrate the application of this graphical notation by presenting two conceptual models we built for real world OR/MS case studies.
Cloud-based simulation (CBS) is one of the new grand challenges in modelling and simulation (M&S)... more Cloud-based simulation (CBS) is one of the new grand challenges in modelling and simulation (M&S). However, the work on web-enabled M&S is not new. A case in point is web-based simulation (WBS). Given the similarities between WBS and CBS, it is important to learn from WBS. Despite advancements in WBS research, its commercial applicability and adoption by users has not grown to the desired extent. This is partly due to the strong emphasis on WBS as a technological tool instead of a socio-technological tool in which users, their needs and circumstances are considered. To understand the needs and perception from practitioners on CBS, we conducted a survey. The results show that practitioners have a good exposure to cloud applications and mobile gadgets. There also appears to be evidence of a need for CBS that provides fast response time, effective communication tools and functionalities to share, store and retrieve models.
The computer power required in the simulation of mutually cooperating systems in the physical sci... more The computer power required in the simulation of mutually cooperating systems in the physical sciences is huge. Therefore, it is common to simulate one system and treat others as parameters or environmental conditions to the simulated system. Macro-micro interlocked (MMI) simulation framework has been proposed to simulate such cooperating systems. In this paper, we study the feasibility of applying this framework on the simulation of macro-micro economic model. This simulation allows us to observe the system's behaviour at the macro and micro levels concurrently. Policy changes at the macroeconomic level may affect the behaviour of the entities at the microeconomic level. Similarly, the behaviour changes at the microeconomic level may affect the macroeconomic system. We implement an MMI simulation library suitable for execution on a cluster of PCs. At this early stage, the experiment shows a promising result which provides us with a foundation to experiment with a larger model.
Research in parallel simulation has been around for more than two decades. However, the number of... more Research in parallel simulation has been around for more than two decades. However, the number of papers reporting on its application to real world problems is limited. At the 2002 PADS conference, researchers discussed the need to go beyond synchronization and performance issues and, in particular, to demonstrate that parallel simulation could be used in real world applications outside military and network simulations. Since then, we have seen an increase in the number of papers on parallel simulation applications in areas such as operations management and the physical sciences. This paper presents a parallel discrete-event demographic simulation tool which has been developed using sik parallel simulation library. A number of experiments have been conducted to evaluate the simulation performance. The result shows that good event parallelism can be achieved.
Changes in demographic and regulations in social care in England are expected to alter the social... more Changes in demographic and regulations in social care in England are expected to alter the social care landscape and increase pressure on people working in the adult social care sector, especially those who deliver direct care services. While significant work has been done to understand the demand side of the adult social care system, work on the supply side is considerably limited and analysis has been dominated by methods such as macro- and micro-simulation. This paper demonstrates that system dynamics modelling can be used to understand the dynamics of the social care workforce who deliver direct care services in the formal sector, specifically, to identify the main feedback loops that govern the dynamics of the system, to identify sensitive and influential factors, and to show non-linearity in the system. Therefore, system dynamics should play a more important role in the analysis of adult social care system.
High Level Architecture provides a standard for abstraction, design, construction, development an... more High Level Architecture provides a standard for abstraction, design, construction, development and operation of distributed computer simulation systems. This paper focuses on the latest version of the standard, i.e. IEEE1516:2010. Users who are not familiar with distributed computer programming may find it difficult to create HLA-compliant models using a tool that assumes some familiarities with distributed computer programming. Hence, a tool that can help such users is useful, especially in encouraging more people to develop HLA-compliant models. We have developed HLAVA Framework that encapsulates the detailed steps of main HLA interfaces such as the methods for creating logical processes, and management thereof, synchronization methods, and communication protocols -in fact, the framework is a simulation kernel for the distributed simulation logical process, which is compliant with (among others) the HLA standard, but due to a simple interface has only about 10 methods, which have ...
The verification and validation of a simulation model is one of the most important steps in simul... more The verification and validation of a simulation model is one of the most important steps in simulation modelling. This paper proposes an approach to the verification and validation of a simulation model called the Test-Driven Simulation Modelling (TDSM) that is based on the concept of Test-Driven Development in software engineering. TDSM makes use of two unit test suites, verification suite and validation suite. This paper demonstrates how a unit test can be used to verify and validate a simulation model. This is followed by a discussion on how to carry out TDSM using the two unit test suites. We use tools called SharpSim simulation library and NUnit in this paper but the concept of TDSM can be implemented using similar tools.
Whilst trust is an increasingly popular subject amongst management scholars, very few scholars ha... more Whilst trust is an increasingly popular subject amongst management scholars, very few scholars have attempted to address the public-business trust relationship. However, it is the loss of public trust in business (and the need to restore it) which appears to be of the most concern in practice. This paper discusses the perspective of a group of experienced business consultants on factors that drive public trust in a business organisation and examines the causal structure of these drivers in order to determine public trust. The focus group design was influenced by group model building practices. The key insights include how they perceive the importance of competence over characters, how they identify trust drivers, and how they perceive the interplays between trust drivers, trustworthiness dimensions and the moderating factors. A causal loop diagram is used to map the key insights into a conceptual model.
Police command and control centres are the main point of contact for the public who require help.... more Police command and control centres are the main point of contact for the public who require help. Like other areas of UK public services, police forces are set targets for their performance. Some of these targets relate to the speed at which they respond to calls for assistance from the public. In this paper we share our experience in improving the performance of command and control centres of a UK Police Force; a project which started as a classical simulation exercise and ended up with a significant reorganisation in a UK Police Force.
A central problem in managing risk is dealing with social processes that either exaggerate or und... more A central problem in managing risk is dealing with social processes that either exaggerate or understate it. A longstanding approach to understanding such processes has been the social amplification of risk framework. But this implies that some true level of risk becomes distorted in social actors' perceptions. Many risk events are characterised by such uncertainties, disagreements and changes in scientific knowledge that it becomes unreasonable to speak of a true level of risk. The most we can often say in such cases is that different groups believe each other to be either amplifying or attenuating a risk. This inherent subjectivity raises the question as to whether risk managers can expect any particular kinds of outcome to emerge. This question is the basis for a case study of zoonotic disease outbreaks using systems dynamics as a modelling medium. The model shows that processes suggested in the social amplification of risk framework produce polarised risk responses among different actors, but that the subjectivity magnifies this polarisation considerably. As this subjectivity takes more complex forms leaves problematic residues at the end of a disease outbreak, such as an indefinite drop in economic activity and an indefinite increase in anxiety.
Though manpower planning models have been part of OR for many years, and simulation has 4 always ... more Though manpower planning models have been part of OR for many years, and simulation has 4 always been acknowledged as a potential approach, there are few reported applications of its 5 use. In this case-based study we report on a micro-simulation model that exploits the 6 structure of the European Commission's appraisal and promotion rules, and includes 7 regression-based sampling schemes which allow for non-normal error terms to represent 8 behavioural factors that led to the need for a new system. With a suitably parsimonious 9 formulation the 20,000 person model runs very effectively, and the transparency associated 10 with simulation proves an important factor in the successful use of the model as the basis for 11 designing a promotion box system that was implemented across the Commission in 2009. 12
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Papers by Bhakti S Onggo
the model, since it is not possible to demonstrate its absolute validity in all contexts. This paper presents the results of a white-box validation performed in an agent-based simulator for population dynamics. The tool provides a way to simulate the demographic evolution of large populations in a parallel environment. The purpose is to obtain population projections that can be used afterwards for policy analysis. Although the
tool has been studied in terms of performance and scalability, its validation hasn’t been addressed. With a white-box validation we expect to increase the confidence of policy analysers and social scientists in our simulation model.