The effect of structural variations on the dynamic behaviour of a system

This report analyses a way of defining the most suitable changes for attenuating structural vibration. The following are studied: —the possibility of singling out the most suitable modification area by way of energy considerations; —the importance of the modification area, the modifications themselves being equal; —the applicability and validity of the perturbation formulae as a rapid means of forecasting.Two structures are investigated.     

Economic lot sizing in a production system with random demand

An extended economic production quantity model that copes with random demand is developed in this paper. A unique feature of the proposed study is the consideration of transient shortage during the production stage, which has not been explicitly analysed in existing literature. The considered costs include set-up cost for the batch production, inventory carrying cost during the production and depletion stages in one replenishment cycle, and shortage cost when demand cannot be satisfied from the shop floor immediately. Based on renewal reward process, a per-unit-time expected cost model is developed and analysed. Under some mild condition, it can be shown that the approximate cost function is convex. Computational experiments have demonstrated that the average reduction in total cost is significant when the proposed lot sizing policy is compared with those with deterministic demand.     

Modelling of air damping effect on the performance of encapsulated MEMS resonators

Microsystem Technologies - The dynamic performance of a micro-resonator depends on its energy loss mechanism which is quantified by Q-factor (Quality factor). This paper presents numerical...     

On the performance of the base-stock inventory system under a compound Erlang demand distribution

In this paper, we propose a new method for determining the optimal base-stock level in a single echelon inventory system where the demand is a compound Erlang process and the lead-time is constant. The demand inter-arrival follows an Erlang distribution and the demand size follows a Gamma distribution. The stock is controlled according to a continuous review base-stock policy where unfilled demands are backordered. The optimal base-stock level is derived based on a minimization of the total expected inventory cost. A numerical investigation is conducted to analyze the performance of the inventory system with respect to the different system parameters and also to show the outperformance of the approach that is based on the compound Erlang demand assumption as compared to the classical Newsboy approach. This work allows insights to be gained on stock control related issues for both slow and fast moving stock keeping units.     

Modelling the impact of study behaviours on academic performance to inform the design of a persuasive system

Information technology is deeply ingrained in most aspects of everyday life and can be designed to influence users to behave in a certain way. Influencing students to improve their study behaviour would be a useful application of this technology. As a preamble to the design of a persuasive system for learning, we collected data to identify the study behaviours of students and recent alumni. We then developed two models to measure which behaviours have the most significant impact on learning performance. Current students reported more foundational behaviours whereas alumni demonstrated more higher-order thinking traits.     

The effect of system parameter variations on natural frequencies

In the paper the relationships between variations of mass and stiffness matrices of system and variation of natural frequencies vector are analysed. Results are applied to finite element method and to stiff finite element method. The example of influence of masses and mass inertia moments variations of support beam on its natural frequencies illustrates the analysis.     

The effect of a database feedback system on user performance

Abstract

There are two main approaches to improving the effectiveness of database interfaces. One is to raise the level of abstraction for the content of the user-database interaction. The relational model belonging to the logical level has replaced the hierarchical and network models that belong to the lower physical level. It is likely that the relational model will eventually be replaced by models belonging to the even higher conceptual level, such as entity relationship models and object-oriented models. The second approach is to enhance the actual interaction process. This can be done by providing better feedback to the user. Feedback can be in the form of more comprehensible error messages, and the provision of a natural language interpretation of user's query. Such a feedback system was developed, and its effectiveness tested in an experiment. The results showed that the feedback system enhanced user performance greatly. Specifically, users who used the feedback system were 12.9% more accurate than those without the feedback system. They were also 41.2% more confident of their answers, and they took 29.0% less time than those without the feedback system.     

The effect of a database feedback system on user performance

There are two main approaches to improving the effectiveness of database interfaces. One is to raise the level of abstraction for the content of the user-database interaction. The relational model belonging to the logical level has replaced the hierarchical and network models that belong to the lower physical level. It is likely that the relational model will eventually be replaced by models belonging to the even higher conceptual level, such as entity relationship models and object-oriented models. The second approach is to enhance the actual interaction process. This can be done by providing better feedback to the user. Feedback can be in the form of more comprehensible error messages, and the provision of a natural language interpretation of user's query. Such a feedback system was developed, and its effectiveness tested in an experiment. The results showed that the feedback system enhanced user performance greatly. Specifically, users who used the feedback system were 12.9% more accurate than those without the feedback system. They were also 41.2% more confident of their answers, and they took 29.0% less time than those without the feedback system.     

The effect of performance failure and task demand on the perception of mental workload

An experiment was conducted to investigate the effects of incipient performance failure on subjective workload response. Unknown to the participants, there were two levels of demand embedded in the PC-based flight simulation performance task. These were included to assess whether task-naive subjects could distinguish variations in load in the face of repetitive performance failure. Results confirmed that participants were able to distinguish this change in load level under such circumstances and that failure resulted in higher perceived workload than did successful performance. Within these differences were significant effects dependent upon subject gender. In general, female participants performed more poorly and rated workload higher than their male counterparts. It is concluded that the experience of failure presents a significant source of workload in systems operation.     

Modelling of palm oil production using fuzzy expert system

The production of crude palm oil and palm kernel is a complex problem due to the influence of processing variables and environmental factors. These processing variables influence the amount of crude palm oil and palm kernel losses during processing. Instead of mathematical model, fuzzy logic approach provides a simpler and easier mechanism to describe the relationships between the processing variables and the amount of crude palm oil and palm kernel losses. In this study, four fuzzy expert system models were developed for each palm oil processing station. An approximation of centre of gravity method for defuzzification is also proposed to enable the development of the model using Microsoft^®Excel. For comparison purpose, the models were also developed using MATLAB^®. Results obtained from the Excel model are found to be very close to the results from MATLAB.     

On the effect of a configuration choice on the performance of a mirrored storage system

In this paper, we study the effect of various configuration choices on the performance of a mirrored disk array. We introduce a large class of semistructured configurations which provide good seek minimization and bandwidth. We study their properties with respect to both online and offline mirroring algorithms. We also prove a theorem concerning the load balancing capabilities of random or semistructured configurations with several data copies. We show that almost the entire bandwidth of the storage system can be exploited once we increase the number of copies. In an appendix we explain a common error which appears in much of the literature concerning this subject.     

Modelling of the inventory replenishment problem with a two-segment piecewise linear demand

The classical inventory replenishment problem with a linear function in demand uses a ‘single-segment’ linear function as its demand and can be modelled by a simple algorithm. Moreover, this article extends the algorithm to provide a heuristic solution for the inventory replenishment model with a two-segment linear function in demand called the ‘two-segment piecewise linear demand model’. In addition, this article proposes a general procedure for solving both models. Meanwhile, several examples taken from the literature illustrate our algorithm for these two models with convincing results. Furthermore, this study shows that when the demand is a two-segment piecewise linear function over time, it is better to use the proposed algorithm rather than devising a decoupled solution approach by treating segments separately. Finally, a sensitivity analysis of two factors, demand and cost, is performed. The model is highly extensible and applicable, so it can serve as an inventory planning tool to solve the replenishment problem.     

Driving monotonous routes in a train simulator: the effect of task demand on driving performance and subjective experience

Although monotony is widely recognised as being detrimental to performance, its occurrence and effects are not yet well understood. This is despite the fact that task-related characteristics, such as monotony and low task demand, have been shown to contribute to performance decrements over time. Participants completed one of two simulated train-driving scenarios. Both were highly monotonous and differed only in terms of the level of cognitive demand required (i.e. low demand or high demand). These results highlight the seriously detrimental effects of the combination of monotony and low task demands and clearly show that even a relatively minor increase in cognitive demand can mitigate adverse monotony-related effects on performance for extended periods of time. Monotony is an inherent characteristic of transport industries, including rail, aviation and road transport, which can have adverse impact on safety, reliability and efficiency. This study highlights possible strategies for mitigating these adverse effects. Practitioner Summary: This study provides evidence for the importance of cognitive demand in mitigating monotony-related effects on performance. The results have clear implications for the rapid onset of performance deterioration in low demand monotonous tasks and demonstrate that these detrimental performance effects can be overcome with simple solutions, such as making the task more cognitively engaging.     

Investigating the effect of variations in the test development process: a case from a safety-critical system

Variation is inherent to a process, and process management demands understanding the nature of variation in quantitative terms, for evaluation and prediction purposes. This understanding requires the identification of process indicators that build the system of variation. To utilize quantitative techniques to understand and improve a software process, more indicators are needed than in a manufacturing process. The need to identify the indicators of a software process and the lack of a generic approach to assess the ability of a software process for quantitative management encouraged us to carry out a sequence of studies that resulted in the development of an Assessment Approach for Quantitative Process Management (A²QPM). This paper explains an application of the A²QPM to the test development process of an avionics software project and presents the results. The study aimed at understanding the effect of the test design stage and the effect of internal reviews as verification activities in test development, with respect to process productivity and product quality measures. The measurement data collected during the execution of the processes were analyzed by control charts to observe the evidence of process stability. The mean values of measurement data were utilized to make performance comparisons between the various executions of the test development process. The results showed that process productivity was unaffected, but the test procedure quality was positively influenced by the application of test design and internal reviews. The utilization of the A²QPM as a guide for the quantitative implementation enabled the systematic evaluation of the test development process and measures prior to analysis. This resulted in the identification of process clusters having stable variation.     

Optimal production planning for a multi-product closed loop system with uncertain demand and return

We study the production planning problem for a multi-product closed loop system, in which the manufacturer has two channels for supplying products: producing brand-new products and remanufacturing returns into as-new ones. In the remanufacturing process, used products are bought back and remanufactured into as-new products which are sold together with the brand-new ones. The demands for all the products are uncertain, and their returns are uncertain and price-sensitive. The problem is to maximize the manufacturer's expected profit by jointly determining the production quantities of brand-new products, the quantities of remanufactured products and the acquisition prices of the used products, subject to a capacity constraint. A mathematical model is presented to formulate the problem and a Lagrangian relaxation based approach is developed to solve the problem. Numerical examples are presented to illustrate the model and test the solution approach. Computational results show that the proposed approach is highly promising for solving the problems. The sensitivity analysis is also conducted to generate managerial insights.