International Journal of Information Technologies and Systems Approach, 2012
This paper looks at the established Systems Dynamics (SD) methods applied to Software projects in... more This paper looks at the established Systems Dynamics (SD) methods applied to Software projects in order to simplify them. These methods are highly non-linear and contain large numbers of variables and built in decisions. A SIMULINK version of an SD model is used here and conclusions are made with respect to the initial main controlling factors, compared to a NASA project. The eigenvalues of the linearised system indicate that the important factors are the hiring delay time, the assimilation time and the employment time. This illustrates how the initial state of the system is at best neutrally stable with control only being achieved with complex non-linear decisions. The purpose is to show the minimum level of complexity required for “good” simulation of project behaviour considering the Abdel-Hamid software project model and three simpler versions. These models give clues to the decision structures that are necessary for good agreement with reality.
This paper uses nonlinear eigenvalues to examine the behaviour of three well studied nonlinear sy... more This paper uses nonlinear eigenvalues to examine the behaviour of three well studied nonlinear systems that exhibit chaos. The nonlinear eigenvalue analysis method has been widely used in System Dynamics to study the relative dominance of feedback loops. The method used here is to compute nonlinear eigenvalues using a Taylor expansion about the equilibrium solutions with a Hessian matrix expansion to obtain nonlinear eigenvalues with state variables in the algebraic solution and then substitute state values computed via a Simulink model. Examination of limit cycle and chaos are made for forced 2D systems such as the Duffing and Van der Pol equation and for a 3D system, the Lorenz equations. The eigenvalue variation with time shows a repeating root variation for limit cycles that is intermittently varied for the forced chaos conditions. This behaviour is not the same for the Lorenz system. These results illustrate how the roots of a system can change when chaos is present.
Simulation of a flexible robot link using ACSL; a Fortran based simulation language is described ... more Simulation of a flexible robot link using ACSL; a Fortran based simulation language is described based on the finite difference solution of a Lagrange-Euler formulation. The manipulator was controlled by classical PD and Fuzzy PD controllers. The step responses of the simulation of the model were validated with correlation coefficients. It was shown that the correlation coefficient of the simulation is greater than 78%. Simulation with the fuzzy controller can achieve correlation coefficients of 99%. The impact to the subject is to show the effectiveness of simple validation techniques to modelling approaches, now taken up by other users.
A simple simulation using SIMULINK is presented to model the thermal/control behaviour of a domes... more A simple simulation using SIMULINK is presented to model the thermal/control behaviour of a domestic gas boiler. The simulation was the first step in a research programme to investigate the efficacy of control using an oxygen sensor. A brief review of boiler control is used to outline current practice and research developments. Ratio control in several forms has been investigated. Performance improvements using control incorporating an Oxygen sensor are examined. These indicate that a modest fuel saving of the order of 5% is possible from the addition of the sensor to the control loop. The performance of the sensor is insensitive to small changes in position and to a 10% variation in the time constant of the sensor. The fuel air ratio varies throughout the heating cycle with only a small period when either system achieves accurate control Keywords-Boiler contr; ratio control; oxygen sensor; SIMULINK; PID control
This paper describes the problem of human monitoring or supervision of automation. It includes a ... more This paper describes the problem of human monitoring or supervision of automation. It includes a review of current research describing how automation monitoring increases the chances of error if the operator is not involved in the control process. A qualitative systems model is developed because of the lack of sufficient data to completely describe the causal pathways and provide a numerical simulation. This leads to a number of research strands for which data is not available or needs to be improved.
This paper describes a control systems approach to the management of inventory. Normal inventory ... more This paper describes a control systems approach to the management of inventory. Normal inventory operation is an example of proportional control. Several control algorithms including Pseudo-Derivative Feedback (PDF), Proportional, Integral and Derivative (PID) and Feedforward control are used in this paper to produce a more sophisticated form of inventory operation that can easily reduce stock levels by up to 80% compared to 20-30% with MRP and hence reduce cost. Settling times are reduced by a factor of 50%. Modelling was achieved using the Simulink simulation package using equations developed by Ferris and Towill for a single level industrial system model rather than a conventional System Dynamics computer package. The best controller is shown to be a PID controller with Feedforward. This controller did not cause any significant oscillatory inventory level changes. These techniques compare well with other investigators using control strategies. This has special significance for JI...
This paper describes the investigation of the effects on profitability of production for an Autom... more This paper describes the investigation of the effects on profitability of production for an Automatic Pipeline, Variable Inventory and Order Based Production Control System (APVIOBPCS) production system using as an example electronic RAM production. The investigation includes varying the order up to inventory and WIP using PID control to illustrate the profit gain from using control analysis. The results show that greater PID gains for a controlled production system will increase profitability. The value of desired inventory level increases profitability with a defined optimum value
A non-linear mathematical model for the roll-yaw behaviour of a ship is used to predict capsize o... more A non-linear mathematical model for the roll-yaw behaviour of a ship is used to predict capsize of a small tanker which sank in the North Sea some years ago. This capsize problem was initially simulated on an analogue computer by the Danish Maritime Authorities as well as being tank tested. The problem was simulated using the digital package SIMULINK, which produced comparable results indicating instability in waves of just less than 3 m in height. Validation of the results is attempted and a discussion of possible improvements to the model is given. Simulated responses of the tanker with simple hydrodynamic fin stabilisers show that capsize could have been prevented by this means in waves up to 7 m in height. Active PID control using a simple full span elevon is used to show a factor of ten reduction in roll angle to much greater waves. This work is of use to ship designers illustrating that stability can be enhanced for a fraction of the cost of major redesign of the ship hull and...
A non-linear mathematical model, for the roll-yaw behaviour of a ship, is used to predict the pre... more A non-linear mathematical model, for the roll-yaw behaviour of a ship, is used to predict the prevention of capsize of a small ship. The problem was simulated using the digital package SIMULINK. Simulated responses of the ship with simple hydrodynamic fin stabilisers show that capsize could have been prevented by this means in waves up to 7 m in height. Active control using a simple full span control flap is used to show a reduction in roll angle to much greater waves. These results are compared to the use of cycloidal propeller propulsion to provide lateral thrust and hence roll control, which showed that this method can also reduce the roll. In order for successful roll reduction with a cycloidal propeller the response time constant is determined. In this example the roll reduction is greater in the fin example but this ability falls off rapidly with forward speed. Roll control using the cycloidal propeller has the advantage of retaining its' effectiveness at low or zero speed...
International Journal of Information Technologies and Systems Approach
This paper compares established Systems Dynamics (SD) models of software projects with models of ... more This paper compares established Systems Dynamics (SD) models of software projects with models of agile development. A new minimal SIMULINK™ agile project model was created and compared to a Waterfall model of a NASA project. Results are presented to enable project managers to predict the performance of future agile project processes. The model includes the time to generate the requirements and a function to provide requirements volatility. These models show that for the same productivity and fraction of errors that are satisfactory, the overall development staff costs are similar for agile and waterfall projects and the undiscovered rework is less for the agile project. This model generally supports empirical observations that shorter time-box iterations yield a shorter overall project completion.
Variation of installed industrial capacity has been found to follow a cyclic pattern. This paper ... more Variation of installed industrial capacity has been found to follow a cyclic pattern. This paper discusses the application of control theory to the problem of the timely acquisition of extra production capacity. The control system based model presented here is compared with a System Dynamics model proposed by Sterman. Key differences are the method of implementing rational decisions about deployment of extra capacity and the use of a nonlinear APVIOBPCS inventory model. Benefits of this new model are a more measurable process and the ability to select parameter values to optimise capacity deployment. Simulation of the model indicates that the results found by Sterman underestimate the production backlog and time taken to reach equilibrium. The use of a Proportional, Integral, and Derivative (PID) controller in the capacity control loop model illustrates that it is possible not only to alter the backlog levels but at the same time to reduce the sales force and improve the revenue. Th...
Proceedings of 1993 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS '93), 1993
Conventional robots are unable to handle heavy loads as flexing in the loaded link chain results ... more Conventional robots are unable to handle heavy loads as flexing in the loaded link chain results in severe positioning errors. This paper discusses the development of an optoelectronic system which controls the overall movement of a two-link robot while simultaneously correcting for the effects of load-induced structural deflections
Software Engineering Research, Management and Applications 2012, 2012
Over the years, software has become ubiquitous in business processes from payroll systems to airl... more Over the years, software has become ubiquitous in business processes from payroll systems to airline reservation systems. Software plays a vital role in facilitating business processes. Given the importance of these software systems, managing their quality is essential to the success of the business processes they support. Because quality attributes are important predictors of software quality as to provide a better understanding of the related features acquired for each software quality attribute, those features can be manipulated to improve the quality of a software project and determine the desired functional requirements necessary to satisfy the associated business processes. Accordingly, customer needs should be completely elicited in developing the software application then traced and referred back to throughout the software development process during the early requirements analysis phase. The proposed questionnaire empowers software developers to capture the functional reliability requirements and specify reliability related features for a software system.
International Journal of Information Technologies and Systems Approach, 2012
This paper looks at the established Systems Dynamics (SD) methods applied to Software projects in... more This paper looks at the established Systems Dynamics (SD) methods applied to Software projects in order to simplify them. These methods are highly non-linear and contain large numbers of variables and built in decisions. A SIMULINK version of an SD model is used here and conclusions are made with respect to the initial main controlling factors, compared to a NASA project. The eigenvalues of the linearised system indicate that the important factors are the hiring delay time, the assimilation time and the employment time. This illustrates how the initial state of the system is at best neutrally stable with control only being achieved with complex non-linear decisions. The purpose is to show the minimum level of complexity required for “good” simulation of project behaviour considering the Abdel-Hamid software project model and three simpler versions. These models give clues to the decision structures that are necessary for good agreement with reality.
This paper uses nonlinear eigenvalues to examine the behaviour of three well studied nonlinear sy... more This paper uses nonlinear eigenvalues to examine the behaviour of three well studied nonlinear systems that exhibit chaos. The nonlinear eigenvalue analysis method has been widely used in System Dynamics to study the relative dominance of feedback loops. The method used here is to compute nonlinear eigenvalues using a Taylor expansion about the equilibrium solutions with a Hessian matrix expansion to obtain nonlinear eigenvalues with state variables in the algebraic solution and then substitute state values computed via a Simulink model. Examination of limit cycle and chaos are made for forced 2D systems such as the Duffing and Van der Pol equation and for a 3D system, the Lorenz equations. The eigenvalue variation with time shows a repeating root variation for limit cycles that is intermittently varied for the forced chaos conditions. This behaviour is not the same for the Lorenz system. These results illustrate how the roots of a system can change when chaos is present.
Simulation of a flexible robot link using ACSL; a Fortran based simulation language is described ... more Simulation of a flexible robot link using ACSL; a Fortran based simulation language is described based on the finite difference solution of a Lagrange-Euler formulation. The manipulator was controlled by classical PD and Fuzzy PD controllers. The step responses of the simulation of the model were validated with correlation coefficients. It was shown that the correlation coefficient of the simulation is greater than 78%. Simulation with the fuzzy controller can achieve correlation coefficients of 99%. The impact to the subject is to show the effectiveness of simple validation techniques to modelling approaches, now taken up by other users.
A simple simulation using SIMULINK is presented to model the thermal/control behaviour of a domes... more A simple simulation using SIMULINK is presented to model the thermal/control behaviour of a domestic gas boiler. The simulation was the first step in a research programme to investigate the efficacy of control using an oxygen sensor. A brief review of boiler control is used to outline current practice and research developments. Ratio control in several forms has been investigated. Performance improvements using control incorporating an Oxygen sensor are examined. These indicate that a modest fuel saving of the order of 5% is possible from the addition of the sensor to the control loop. The performance of the sensor is insensitive to small changes in position and to a 10% variation in the time constant of the sensor. The fuel air ratio varies throughout the heating cycle with only a small period when either system achieves accurate control Keywords-Boiler contr; ratio control; oxygen sensor; SIMULINK; PID control
This paper describes the problem of human monitoring or supervision of automation. It includes a ... more This paper describes the problem of human monitoring or supervision of automation. It includes a review of current research describing how automation monitoring increases the chances of error if the operator is not involved in the control process. A qualitative systems model is developed because of the lack of sufficient data to completely describe the causal pathways and provide a numerical simulation. This leads to a number of research strands for which data is not available or needs to be improved.
This paper describes a control systems approach to the management of inventory. Normal inventory ... more This paper describes a control systems approach to the management of inventory. Normal inventory operation is an example of proportional control. Several control algorithms including Pseudo-Derivative Feedback (PDF), Proportional, Integral and Derivative (PID) and Feedforward control are used in this paper to produce a more sophisticated form of inventory operation that can easily reduce stock levels by up to 80% compared to 20-30% with MRP and hence reduce cost. Settling times are reduced by a factor of 50%. Modelling was achieved using the Simulink simulation package using equations developed by Ferris and Towill for a single level industrial system model rather than a conventional System Dynamics computer package. The best controller is shown to be a PID controller with Feedforward. This controller did not cause any significant oscillatory inventory level changes. These techniques compare well with other investigators using control strategies. This has special significance for JI...
This paper describes the investigation of the effects on profitability of production for an Autom... more This paper describes the investigation of the effects on profitability of production for an Automatic Pipeline, Variable Inventory and Order Based Production Control System (APVIOBPCS) production system using as an example electronic RAM production. The investigation includes varying the order up to inventory and WIP using PID control to illustrate the profit gain from using control analysis. The results show that greater PID gains for a controlled production system will increase profitability. The value of desired inventory level increases profitability with a defined optimum value
A non-linear mathematical model for the roll-yaw behaviour of a ship is used to predict capsize o... more A non-linear mathematical model for the roll-yaw behaviour of a ship is used to predict capsize of a small tanker which sank in the North Sea some years ago. This capsize problem was initially simulated on an analogue computer by the Danish Maritime Authorities as well as being tank tested. The problem was simulated using the digital package SIMULINK, which produced comparable results indicating instability in waves of just less than 3 m in height. Validation of the results is attempted and a discussion of possible improvements to the model is given. Simulated responses of the tanker with simple hydrodynamic fin stabilisers show that capsize could have been prevented by this means in waves up to 7 m in height. Active PID control using a simple full span elevon is used to show a factor of ten reduction in roll angle to much greater waves. This work is of use to ship designers illustrating that stability can be enhanced for a fraction of the cost of major redesign of the ship hull and...
A non-linear mathematical model, for the roll-yaw behaviour of a ship, is used to predict the pre... more A non-linear mathematical model, for the roll-yaw behaviour of a ship, is used to predict the prevention of capsize of a small ship. The problem was simulated using the digital package SIMULINK. Simulated responses of the ship with simple hydrodynamic fin stabilisers show that capsize could have been prevented by this means in waves up to 7 m in height. Active control using a simple full span control flap is used to show a reduction in roll angle to much greater waves. These results are compared to the use of cycloidal propeller propulsion to provide lateral thrust and hence roll control, which showed that this method can also reduce the roll. In order for successful roll reduction with a cycloidal propeller the response time constant is determined. In this example the roll reduction is greater in the fin example but this ability falls off rapidly with forward speed. Roll control using the cycloidal propeller has the advantage of retaining its' effectiveness at low or zero speed...
International Journal of Information Technologies and Systems Approach
This paper compares established Systems Dynamics (SD) models of software projects with models of ... more This paper compares established Systems Dynamics (SD) models of software projects with models of agile development. A new minimal SIMULINK™ agile project model was created and compared to a Waterfall model of a NASA project. Results are presented to enable project managers to predict the performance of future agile project processes. The model includes the time to generate the requirements and a function to provide requirements volatility. These models show that for the same productivity and fraction of errors that are satisfactory, the overall development staff costs are similar for agile and waterfall projects and the undiscovered rework is less for the agile project. This model generally supports empirical observations that shorter time-box iterations yield a shorter overall project completion.
Variation of installed industrial capacity has been found to follow a cyclic pattern. This paper ... more Variation of installed industrial capacity has been found to follow a cyclic pattern. This paper discusses the application of control theory to the problem of the timely acquisition of extra production capacity. The control system based model presented here is compared with a System Dynamics model proposed by Sterman. Key differences are the method of implementing rational decisions about deployment of extra capacity and the use of a nonlinear APVIOBPCS inventory model. Benefits of this new model are a more measurable process and the ability to select parameter values to optimise capacity deployment. Simulation of the model indicates that the results found by Sterman underestimate the production backlog and time taken to reach equilibrium. The use of a Proportional, Integral, and Derivative (PID) controller in the capacity control loop model illustrates that it is possible not only to alter the backlog levels but at the same time to reduce the sales force and improve the revenue. Th...
Proceedings of 1993 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS '93), 1993
Conventional robots are unable to handle heavy loads as flexing in the loaded link chain results ... more Conventional robots are unable to handle heavy loads as flexing in the loaded link chain results in severe positioning errors. This paper discusses the development of an optoelectronic system which controls the overall movement of a two-link robot while simultaneously correcting for the effects of load-induced structural deflections
Software Engineering Research, Management and Applications 2012, 2012
Over the years, software has become ubiquitous in business processes from payroll systems to airl... more Over the years, software has become ubiquitous in business processes from payroll systems to airline reservation systems. Software plays a vital role in facilitating business processes. Given the importance of these software systems, managing their quality is essential to the success of the business processes they support. Because quality attributes are important predictors of software quality as to provide a better understanding of the related features acquired for each software quality attribute, those features can be manipulated to improve the quality of a software project and determine the desired functional requirements necessary to satisfy the associated business processes. Accordingly, customer needs should be completely elicited in developing the software application then traced and referred back to throughout the software development process during the early requirements analysis phase. The proposed questionnaire empowers software developers to capture the functional reliability requirements and specify reliability related features for a software system.
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Papers by Anthony White