Potential applications of discrete-event simulation and fuzzy rule-based systems to structural reliability and availability

This chapter discusses and illustrates some potential applications of discrete-event simulation (DES) techniques in structural reliability and availability analysis, emphasizing the convenience of using probabilistic approaches in modern building and civil engineering practices. After reviewing existing literature on the topic, some advantages of probabilistic techniques over analytical ones are highlighted. Then, we introduce a general framework for performing structural reliability and availability analysis through DES. Our methodology proposes the use of statistical distributions and techniques – such as survival analysis – to model component-level reliability. Then, using failure- and repair-time distributions and information about the structural logical topology (which allows determination of the structural state from their components’ state), structural reliability, and availability information can be inferred. Two numerical examples illustrate some potential applications of the proposed methodology to achieving more reliable and structural designs. Finally, an alternative approach to model uncertainty at component level is also introduced as ongoing work. This new approach is based on the use of fuzzy rule-based systems and it allows the introduction of experts’ opinions and evaluations in our methodology.

Analysis of dynamic strains in tibia during human locomotion based on flexible multibody approach integrated with magnetic resonance imaging technique

Bone is known to adapt to the prevalent strain environment while the variation in strains, e.g., due to mechanical loading, modulates bone remodeling, and modeling. Dynamic strains rather than static strains provide the primary stimulus of bone functional adaptation. The finite element method can be generally used for estimating bone strains, but it may be limited to the static analysis of bone strains since the dynamic analysis requires expensive computation. Direct in vivo strain measurement, in turn, is an invasive procedure, limited to certain superficial bone sites, and requires surgical implementation of strain gauges and thus involves risks (e.g., infection). Therefore, to overcome difficulties associated with the finite element method and the in vivo strain measurements, the flexible multibody simulation approach has been recently introduced as a feasible method to estimate dynamic bone strains during physical activity. The purpose of the present study is to further strengthen the idea of using the flexible multibody approach for the analysis of dynamic bone strains. Besides discussing the background theory, magnetic resonance imaging is integrated into the flexible multibody approach framework so that the actual bone geometry could be better accounted for and the accuracy of prediction improved.

A full body musculoskeletal model based on flexible multibody simulation approach utilised in bone strain analysis during human locomotion

Load-induced strains applied to bone can stimulate its development and adaptation. In order to quantify the incident strains within the skeleton, in vivo implementation of strain gauges on the surfaces of bone is typically used. However, in vivo strain measurements require invasive methodology that is challenging and limited to certain regions of superficial bones only such as the anterior surface of the tibia. Based on our previous study [Al Nazer et al. (2008) J Biomech. 41:1036–1043], an alternative numerical approach to analyse in vivo strains based on the flexible multibody simulation approach was proposed. The purpose of this study was to extend the idea of using the flexible multibody approach in the analysis of bone strains during physical activity through integrating the magnetic resonance imaging (MRI) technique within the framework. In order to investigate the reliability and validity of the proposed approach, a three-dimensional full body musculoskeletal model with a flexible tibia was used as a demonstration example. The model was used in a forward dynamics simulation in order to predict the tibial strains during walking on a level exercise. The flexible tibial model was developed using the actual geometry of human tibia, which was obtained from three-dimensional reconstruction of MRI. Motion capture data obtained from walking at constant velocity were used to drive the model during the inverse dynamics simulation in order to teach the muscles to reproduce the motion in the forward dynamics simulation. Based on the agreement between the literature-based in vivo strain measurements and the simulated strain results, it can be concluded that the flexible multibody approach enables reasonable predictions of bone strain in response to dynamic loading. The information obtained from the present approach can be useful in clinical applications including devising exercises to prevent bone fragility or to accelerate fracture healing.

Simulation and visualization of fire using extended Lindenmayer systems

This research introduces a method of using Lindenmayer Systems to model the spreading and behavior of fire inside a factory building. The research investigates the use of L-System propagated fires for determining factors such as where the fire is most likely to spread first and how fast. It also looks at an alternative way of storing the Lindenmayer System, not in the form of a string but rather as a graph. A variation on the building and traversal process is also investigated, in which the L-System is traversed depth first instead of breadth first. Results of fire propagation are presented and we conclude that L-Systems are a suitable tool for fire propagation.

Performance study of a daylight guiding system in an office building

This research developed a comprehensive evaluation of a daylight-guiding system in an Australian office building. On-site measurements, simulation and correlation studies have been carried out to identify the daylight contribution from the reflective louvre system. Results show that the system can provide up to 70% additional illuminance for the workplace.

Layered dynamic probabilistic networks for spatio-temporal modelling

In applications such as tracking and surveillance in large spatial environments, there is a need for representing dynamic and noisy data and at the same time dealing with them at different levels of detail. In the spatial domain, there has been work dealing with these two issues separately, however, there is no existing common framework for dealing with both of them. In this paper, we propose a new representation framework called the Layered Dynamic Probabilistic Network (LDPN), a special type of Dynamic Probabilistic Network (DPN), capable of handling uncertainty and representing spatial data at various levels of detail. The framework is thus particularly suited to applications in wide-area environments which are characterised by large region size, complex spatial layout and multiple sensors/cameras. For example, a building has three levels: entry/exit to the building, entry/exit between rooms and moving within rooms. To avoid the problem of a relatively large state space associated with a large spatial environment, the LDPN explicitly encodes the hierarchy of connected spatial locations, making it scalable to the size of the environment being modelled. There are three main advantages of the LDPN. First, the reduction in state space makes it suitable for dealing with wide area surveillance involving multiple sensors. Second, it offers a hierarchy of intervals for indexing temporal data. Lastly, the explicit representation of intermediate sub-goals allows for the extension of the framework to easily represent group interactions by allowing coupling between sub-goal layers of different individuals or objects. We describe an adaptation of the likelihood sampling inference scheme for the LDPN, and illustrate its use in a hypothetical surveillance scenario.

Dynamic shot suggestion filtering for home video based on user performance

This paper presents novel additions to our existing amateur media creation framework. The framework provides at-capture guidance to enable the home movie maker to realize their aesthetic and narrative goals and automation of post-production editing. A common problem with the amateur filming context is its contingent nature, which often results in the failure to gain footage vital to the user's goals, even with at-capture software embedding. Accordingly, we have modelled minimizing the difference between target and captured footage at a given time during filming as a probability distribution divergence problem. We apply two policies of feedback to the user on their performance, passive communication via a suggestion desirability measure, and active filtering of undesirable suggestions. We demonstrate the framework using each policy with a simulation of various user and filming situations with promising results.

Fuzzy simulation of pedestrian walking path considering local environmental stimuli

Pedestrian steering activity is a perception-based decision making process that involves interaction with the surrounding environment and insight into environmental stimuli. There are many stimuli within the environment that influence pedestrian wayfinding behaviour during walking activities. However, compelling factors such as individual physical and psychological characteristics and trip intention cause the behaviour become a very fuzzy concept. In this paper pedestrian steering behaviour is modelled using a fuzzy logic approach. The objective of this research is to simulate pedestrian walking paths in indoor public environments during normal and non-panic situations. The proposed algorithm introduces a fuzzy logic framework to predict the impact of perceived attractive and repulsive stimuli, within the pedestrian's field of view, on movement direction. Environmental stimuli are quantified using the social force method. The algorithm is implemented in a simulated area of an office corridor consist of a printer and exit door. Stochastic simulation using the proposed fuzzy algorithm generated realistic walking trajectories, contour map of dynamic change of environmental effects in each step of movement and high flow areas in the corridor.

Prospective randomized controlled trial comparing dynamic hip screw and screw fixation for undisplaced subcapital hip fractures

Background
Neck of femur fractures (NOFFs) are a common cause of morbidity and mortality in our community. Minimally displaced intracapsular fractures are treated with internal fixation by a two-hole dynamic hip screw (DHS) or three partially threaded cancellous screws. Data to support the superiority of one are limited. This prospective randomized controlled trial compares outcomes with these two fixation methods.

Methods
We prospectively recruited patients over 50 years, with an acute fracture subcapital NOFF, who walked and lived independently, and were cognitively intact. They were randomized into DHS or cancellous screw groups and followed up for 2 years (overall 75.9%). Outcomes of mortality, revision, loss of fixation, avascular necrosis, surgical complications, WOMAC, Harris hip score and SF-12 were measured.

Results
We recruited 62 patients (31 DHS, 29 cancellous screws, 2 failed consent). Six deaths (19.3%) were seen in each group. A total of 3.2% of DHS (1 out of 31) and 10.3% (3 out of 29) of cancellous screw patients required re-operation (P = 0.272). There was no statistical significant difference in patient satisfaction, quality of life (QoL), radiological union or osteonecrosis. There are trends towards better functional scores and QoL in cancellous screws, particularly at 1 year (P = 0.0061), but with a higher re-operation rate. There was a combined mortality and transition to institutional care of 40.0% (24 out of 60) at 2 years.

Conclusions
This study found no difference in outcomes between DHS and cancellous screws in the treatment of subcapital NOFFs in a fit, independent population, but we found a high level of physical decline in previously fit, independently ambulating patients. A large, multicentre trial will be required to differentiate between these two fixation methods.

Dynamic control of skilled and unskilled labour task assignments

Efficient allocation of skilled and non-skilled workers allow a company to improve productivity and usually requires an understanding of personnel capability, operating conditions and resource availability. This paper examines a labour control strategy that optimises labour skill level, utilisation, task execution time and processing error. The proposed controller manages different labour groups in a multiple work cell environment, providing real-time job assignment, as well as guiding and navigation features. These features can be used to enhance the performance of existing MRP-based or Just-In-Time production systems. A discrete event simulation-based manufacturing model has been developed to assess the performance of the labour controller. Experiments conducted for the selected production scenarios have demonstrated a productivity improvement when using the proposed control. A second experiment has shown that when a skilled labour uses the labour controller to guide them through the job, their utilisation also increases. The proposed controller also has potential application in other domains, such as minimising the shopping time at a supermarket

A mathematical model of neuromuscular adaptation to resistance training and its application in a computer simulation of accommodating loads

A large corpus of data obtained by means of empirical study of neuromuscular adaptation is currently of limited use to athletes and their coaches. One of the reasons lies in the unclear direct practical utility of many individual trials. This paper introduces a mathematical model of adaptation to resistance training, which derives its elements from physiological fundamentals on the one side, and empirical findings on the other. The key element of the proposed model is what is here termed the athlete’s capability profile. This is a generalization of length and velocity dependent force production characteristics of individual muscles, to an exercise with arbitrary biomechanics. The capability profile, a two-dimensional function over the capability plane, plays the central role in the proposed model of the training-adaptation feedback loop. Together with a dynamic model of resistance the capability profile is used in the model’s predictive stage when exercise performance is simulated using a numerical approximation of differential equations of motion. Simulation results are used to infer the adaptational stimulus, which manifests itself through a fed back modification of the capability profile. It is shown how empirical evidence of exercise specificity can be formulated mathematically and integrated in this framework. A detailed description of the proposed model is followed by examples of its application—new insights into the effects of accommodating loading for powerlifting are demonstrated. This is followed by a discussion of the limitations of the proposed model and an overview of avenues for future work.

Formulation and simulation of a 3D mechanical model of embryos for microinjection

The understanding of cell manipulation, for example in microinjection, requires an accurate model of the cells. Motivated by this important requirement, a 3D particlebased mechanical model is derived for simulating the deformation of the fish egg membrane and the corresponding cellular forces during microrobotic cell injection. The model is formulated based on the kinematic and dynamic of spring- damper configuration with multi-particle joints considering the visco-elastic fluidic properties. It simulates the indentation force feedback as well as cell visual deformation during microinjection. A preliminary simulation study is conducted with different parameter configurations. The results indicate that the proposed particle-based model is able to provide similar deformation profiles as observed from a real microinjection experiment of the zebrafish embryo published in the literature. As a generic modelling approach is adopted, the proposed model also has the potential in applications with different types of manipulation such as micropipette cell aspiration.

Haptics interface for modelling and simulation of flexible cables

Virtual reality systems are becoming a must for product and process design, training practices and ergonomic analysis in many manufacturing industries. The automotive sector is considered to be the leader in applying virtual reality (VR) solutions for real-world, non-trivial, problems. Although, a number of commercial 3D engineering tools for digital mockups exist, most of them lack intuitive direct manipulation of the digital mockups. The majority of these 3D engineering tools are constrained to the interaction mainly with rigid objects which is just half the story. To bridge this gap, we have developed a haptics interface for modelling and simulation of flexible objects. The graphical and haptic user interface developed allows the creation of multiple one dimensional (1D) flexible objects, such as hoses, cables and harnesses. The user is required to provide the mechanical properties of the material such as Young's modulus, Poisson's ratio, material density, damping factors, as well as dimensional properties such as length, and inner and outer diameters of the flexible object. Flexilution solver is employed to estimate and simulate the dynamic behaviour of flexible objects in response to external user interaction, whereas Nvidia's generic physics engine is used to simulate the behaviour of rigid objects. A generic communication interface is developed to accommodate a variety of devices without the reconfiguration of the simulation platform.

Modelling daylight for preserving identity : simulation of daylight levels for successful intervention in historic buildings

Historical listed buildings have their own unique cultural identity, which is one of the criteria used by decision mechanisms for their statutory protection. The identity of many of these buildings is often related to their tangible features/components, such as period characteristics (geometry, size, colour, form, and shape), materials and construction. Daylight is one of the in/tangible elements that have contributed to the distinctiveness of many historical buildings, yet when constructing preservation schemes of historical buildings, daylight is rarely introduced or considered as one of the components that shape the character of buildings. One of the reasons is the limited number of credible simulation studies that identify such interrelationships. As many of these buildings were originally designed to accommodate different activities to today's requirements, maintaining the quality of daylight that originally contributed to their visual identity can be a very challenging task, especially if the building is to be adapted to accommodate a different activity. In this paper we will discuss the conflict between maintaining the original visual identity of historical buildings and meeting the visual requirements of restored buildings. The paper discusses the visual performance of a traditional bathhouse (Hammam) in the city of Bursa in Turkey. The change in the visual performance of the selected case study will be discussed in terms of daylight conditions. The paper explores the possibility of maintaining the original daylight conditions of renovated historical buildings while meeting the visual requirements of the new use.

An effective VAR planning to improve dynamic voltage profile of distribution networks with distributed wind generation

This paper proposes an effective VAR planning based on reactive power margin for the enhancement of dynamic voltage stability in distribution networks with distributed wind generation. The analysis is carried over a distribution test system representative of the Kumamoto area in Japan. The detailed mathematical modeling of the system is also presented. Firstly, this paper provides simulation results showing the effects of composite load on voltage dynamics in the distribution network through an accurate time-domain analysis. Then, a cost-effective combination of shunt capacitor bank and distribution static synchronous compensator (D-STATCOM) is selected to ensure fast voltage recovery after a sudden disturbance. The analysis shows that the proposed approach can reduce the size of compensating devices, which in turn, reduces the cost. It also reduces power loss of the system.