Maple Toolbox for Switched Stabilizing Controller

This paper is celebrating the increment of interest in the application of  computer algebra in control system analysis. A Maple toolbox for stabilizing state feedback controllers for a class of switched system is presented. The attention is focused on finding the existence of common Lyapunov function  (CLFs), as this ensures stability for arbitrary switching sequences between several subsystems. The system considered here are restricted to second order linear  systems. In order to find the common Lyapunov function and the ability of the Maple software, the toolbox is proved to be less computational demanding compared to a lot of methods that has been solved by Linear Matrix Inequalities (LMI)

Numerical Simulation of Heat Transfer Performance of Water: Ethylene Glycol Mixture (W:EG) Through Turbine-Like Decaying Flow Swirler

The propeller-type swirler has been mentioned several times in the literature as one of the decaying flow swirlers designed to improve heat transfer performance while maintaining a low friction factor. However, the distance travelled by swirling flow varies according to the swirler’s design configuration. As a result, the purpose of this paper is to investigate the heat transfer performance and friction factor of a new turbine-like decaying flow swirler (TDS). The distance traversed and decays downstream the tube by the created swirling flow will then be determined. The TDS is a rigid turbine or compressor consist of four twisted blades at 172.2° set at the entrance of a fully developed 1.5 m tube with a dimensionless length (L/D) of 93.75. A 60:40% water and ethylene glycol mixture was employed as a working fluid for the turbulent flow with Reynolds numbers ranging from 4583 to 35,000. The results indicate that the maximum relative heat transfer is 1.16 and the highest relative friction factor is 1.47 at the lowest Reynolds number tested. For Reynolds numbers less than and equal to 10,136, the thermal hydraulic performance achieved unity. The obtained relative heat transfer is deemed to be poor in comparison to several publications. The swirl flow finally entirely decays after L/D = 70.32 after being visualised through the vortex core and cross-sectional plane of the tube, contributing to a reduced heat transfer performance. In conclusion, TDS performance can be optimised for a lower dimensionless length using the same design configuration, or the design configuration should be modified to increase the generated swirl flow intensity

Effect of diameter, twist angle, and blade count on the thermal-hydraulic performance of a decaying twisted swirler

Inserting a decaying swirler into a heat exchanger has been shown to improve heat transfer with minimal effect on the friction factor. The study analyses the effect of diameter, twist angle, and blade count on the thermal-hydraulic performance of a Decaying Twisted Swirler (DTS) in a horizontally heated tube. The diameter, twist angle, and DTS's blade count are examined for 13.5 mm–15.5 mm with a 0.5 mm interval, 0°–360° with a 60° gap, and 2 to 6 blades, respectively. The Nusselt number, friction factor, and thermal-hydraulic performance are examined for Reynolds numbers between 4583 and 35000. The relative Nusselt number and friction factor increase as DTS diameter and twist angle increase, reaching a maximum value at Re = 4583. Despite this, the relative Nusselt number dispersed as the blade count increased. The relative friction factor increases as the blade count increases. Maximum relative Nusselt number and friction factor reached 1.64 and 3.25, respectively with DTS's 15.5 mm diameter, 360° angle, and 4 blades. Nonetheless, the thermal-hydraulic performance is greatest when the DTS has a diameter of 15.5 mm, a twist angle of 180°, and 2 blades with 1.17

Thermo-Hydraulic Performance of Heated Tube with Twisted Delta Winglet Swirler Insert: A Numerical Simulation

Among the various methods for enhancing heat transfer in a heat exchanger, a passive method of inserting a continuous swirler inside a heated tube provides a secondary flow along the fluid that reduces the thickness of the thermal boundary layer, thus increasing the efficiency of convection heat transfer performance. The research’s primary goal is to conserve energy, materials, and money by operating efficient heat exchanger equipment. However, the continuous swirler along the fluid flow creates a persistent obstruction, which amplifies the friction factor and increases the working fluid’s energy loss. As a result, this research presented the twisted delta winglet swirler (TDWS), a new design of a decaying swirler that uses delta winglets twisted to 180° to produce a swirling flow along the tube. The swirler comprises four twisted delta winglets arranged in a circle with a diameter 6% smaller than the tube and a length of L/D=2.2. It was placed at the entrance to a heated tube test section with a diameter of 0.016 m and a length of L/D=93.75. The Reynolds Stress Model was used to simulate the flow domain with a water-ethylene glycol mixture was chosen as the working fluid. TDWS transformed the uniform inlet flow from potential energy to high kinetic energy, resulting in a high intensity of swirling flow downstream of the circular tube up to L/D=46.88 before decaying and reaching a steady state. Compared to other decaying swirlers, TDWS obtained one of the lowest relative friction factors, 1.36, with this flow. The maximum global relative Nusselt number increased by only 11% because this value considered the area where the flow reached a steady state. Since the TDWS is a decaying swirler, the thermal-hydraulic performance reached unity along the tube. However, the optimal performance of TDWS in the plain tube with a length of L/D=93.75 can be found if the dimension or geometric configuration of the TDWS is modified, or two or more TDWS may be placed in an array orientation

Thermal conductivity and dynamic viscosity of mono and hybrid organic- and synthetic-based nanofluids: A critical review

Thermal conductivity and dynamic viscosity are two critical properties of nanofluids that indicate their heat transfer performance and flow. Nanofluids are prepared by dispersing mono or several organic or synthetic nanoparticles in selected base fluids to form mono or hybrid nanofluids. The qualitative and quantitative stability measurement of nanofluids will then be addressed, followed by a detailed discussion on how the dispersion of nanoparticles in water (W), ethylene glycol (EG), and themixture of W:EG 60:40%by volume affects the thermal conductivity and dynamic viscosity ratio. The data comparison demonstrated that the thermal conductivity ratio increases with increasing normalized concentrations, the bulk temperature of nanofluids, and the smaller nanoparticle size. The dynamic viscosity ratio is multiplied by the normalized concentration increase. Nevertheless, as the bulk temperature climbed from 0 to 80°C, the dynamic viscosity ratio was scattered, and the dynamic viscosity ratio trend dropped with increasing particle size. While the majority of nanofluids enhanced thermal conductivity ratio by 20%, adding carbon-based nanoparticles to synthetic nanofluid increased it by less than 10%. The disadvantage of nanofluids is that they multiply the dynamic viscosity ratio of all nanofluids, which increase power consumption and reduces the efficiency of any mechanical system

A study on the applicability of symbolic computation in stabilising control design for switched systems

This thesis examines the problem of designing controllers for switched systems that assures stability of the overall system. The switched systems here refer to systems whose dynamic behaviour changes from time to time. Stability concepts for continuous time and discrete event systems cannot be used to assure stability of switched systems as mode switching sequence and dwell time influences the stability of the overall system. One method of ensuring stability of switched systems is by proving the existence of a Common Lyapunov Function for the system. However, finding a Common Lyapunov Function is not trivial. Most methods that have been introduced to solve this problem involve the formulation of the system dynamic model and constraints into a Linear Matrix Inequality (LMI) structure. Then, computational methods are used to solve the LMI problem. Two problems arise from using LMIs to find solutions. Firstly, available LMI solvers use numerical computation which raises the possibility of rounding off errors. Secondly, the computational burden would be quite heavy, especially if the switched system comprises of a large number of subsystems or the subsystems are of a high order. The Haris-Rogers method is an alternative approach that has been previously developed for designing controllers based on the existence of a Common Lyapunov Function. In this approach, the problem is reduced to solving two sets of Linear Inequalities (LI), hence reducing the computational burden, as compared to methods that use LMIs. To overcome rounding off errors, symbolic computation methods should be used. However, this would require more computational power compared to numerical computation methods. In this study, a Switched System Control Design Toolbox employing symbolic computation based on the Haris-Rogers solution method was developed using the Maple software. A switched system with four second order subsystems was used as a test case and the toolbox successfully found a Common Lyapunov Function and subsequently designed the controller. For comparison, an LMI based method was tested with the same switched system using Maple and also three numerical LMI solvers, namely cvx, LMI Solver and Yalmip. Only Yalmip successfully generated a correct solution, while LMI Solver generated an incorrect solution since the controller obtained was clearly unstable. Maple and cvx failed to generate any controller. The Haris-Rogers method was also tested for the same switched system using cvx, LMI Solver and Yalmip, and all three produced correct results. All computational work and testing were performed on a system running Intel Core i5 2.67 GHz, 64-bit operating system with 2 GB RAM

Parametric Study of Multiple Configurations of Pico Hydrokinetic Turbines using CFD

This paper aims to study the river flow characteristics over pico hydrokinetic turbines with variation of arrangement using computational fluid dynamics (CFD) software. This study is required to obtain the optimum spacing and angle between the turbines which leads to higher turbine effective utilisation and performance in terms of power generated. In this study, a river model is created in CFD software to simulate the water flow over the turbines as they are placed in a river to obtain the water flow characteristic. Different types of array arrangements are simulated in the river model. Multiple turbines are used to accumulate more power. The turbine model which consists of eight turbines is arranged in series with different spacing, ranging from a size of diameter (1D) to four times diameter (4D) of turbine is simulated to identify the optimum spacing between the turbines. Then, the simulation is continued using a sufficient spacing of 0.5D with angles ranging of 10° to 60° from datum of original position to minimise the disruption of the aquatic environment. The velocity profiles of each turbine are obtained and analysed. The 4D spacing and 40° angle displayed higher average velocities compared to other arrangements. Thus, from this study, the 4D and 40° are deduced as the optimum spacing and angle, respectively

Stability of a Switched Linear System

Hybrid systems are dynamic systems that arise out of the interaction of continuous state dynamics and discrete state dynamics. Switched systems, which are a type of hybrid system, have been given much attention by control systems research over the past decade. Problems with the controllability, observability, converseability and stabilizability of switched systems have always been discussed. In this paper, the trend in research regarding the stability of switched systems will be investigated. Then the variety of methods that have been discovered by researchers for stabilizing switched linear systems with arbitrary switching will be discussed in detail

Parametric study of multiple configurations of pico hydrokinetic turbines using CFD

This paper aims to study the river flow characteristics over pico hydrokinetic turbines with variation of arrangement using computational fluid dynamics (CFD) software. This study is required to obtain the optimum spacing and angle between the turbines which leads to higher turbine effective utilisation and performance in terms of power generated. In this study, a river model is created in CFD software to simulate the water flow over the turbines as they are placed in a river to obtain the water flow characteristic. Different types of array arrangements are simulated in the river model. Multiple turbines are used to accumulate more power. The turbine model which consists of eight turbines is arranged in series with different spacing, ranging from a size of diameter (1D) to four times diameter (4D) of turbine is simulated to identify the optimum spacing between the turbines. Then, the simulation is continued using a sufficient spacing of 0.5D with angles ranging of 10° to 60° from datum of original position to minimise the disruption of the aquatic environment. The velocity profiles of each turbine are obtained and analysed. The 4D spacing and 40° angle displayed higher average velocities compared to other arrangements. Thus, from this study, the 4D and 40° are deduced as the optimum spacing and angle, respectively

Parametric study of multiple configurations of pico hydrokinetic turbines using CFD

This paper aims to study the river flow characteristics over pico hydrokinetic turbines with variation of arrangement using computational fluid dynamics (CFD) software. This study is required to obtain the optimum spacing and angle between the turbines which leads to higher turbine effective utilisation and performance in terms of power generated. In this study, a river model is created in CFD software to simulate the water flow over the turbines as they are placed in a river to obtain the water flow characteristic. Different types of array arrangements are simulated in the river model. Multiple turbines are used to accumulate more power. The turbine model which consists of eight turbines is arranged in series with different spacing, ranging from a size of diameter (1D) to four times diameter (4D) of turbine is simulated to identify the optimum spacing between the turbines. Then, the simulation is continued using a sufficient spacing of 0.5D with angles ranging of 10° to 60° from datum of original position to minimise the disruption of the aquatic environment. The velocity profiles of each turbine are obtained and analysed. The 4D spacing and 40° angle displayed higher average velocities compared to other arrangements. Thus, from this study, the 4D and 40° are deduced as the optimum spacing and angle, respectively