The earthing segments of electrical power systems play an important role in ensuring human safety. A core function of these earthing systems is to maintain reliable operation and ensure safety for personnel and appara...
The earthing segments of electrical power systems play an important role in ensuring human safety. A core function of these earthing systems is to maintain reliable operation and ensure safety for personnel and apparatus during fault conditions. Earthing electrodes can be buried in the soil to dissipate lightning and fault currents into the earth and limit the effect of any magnitude of voltage and current generated between different contact points to earth structures that may be occupied by people or sensitive electrical equipment. In order to obtain the best design of an electrical system to protect power system installations and ensure human safety against abnormal conditions, it is useful to clarify the behaviour of earthing systems subjected to variable frequency currents. In this paper, a numerical study is thus implemented to investigate the behaviour of earthing electrodes subjected to variable frequency current using the computational software program HIFREQ/FFTSESCDEGS with a uniform equivalent soil model. The effect of soil resistivity and permittivity on the behaviour of earthing electrodes is thus obtained, and the relationship between the length of earthing electrodes and their earthing responses over a wide range of frequencies from DC up to 1MHz is identified.
Solubility phase diagram which consists of information on solute concentration, metastable and saturation limits against temperature, provides helpful insights in designing crystallization process to achieve desired c...
Solubility phase diagram which consists of information on solute concentration, metastable and saturation limits against temperature, provides helpful insights in designing crystallization process to achieve desired crystal size distribution (CSD). Usually, the design of cooling crystallization process involves high supersaturation level at the beginning of the process in the metastable zone that is bounded by metastable and saturation limits. However, this high level of supersaturation causes an increment in both nucleation and crystal growth rates which induce the growth of the seed crystals as well as unwanted secondary nucleation that produce excessive fine crystals. Mitigation by employing proper temperature trajectory or policy along metastable zone to avoid unnecessary long operational time and fine crystals is needed. Thus, the purpose of this paper is to develop and simulate mathematical model of seeded batch crystallization process for the case of potash alum which is mainly used for purification in water treatment. Dynamic response of such process under open-loop operation for three cooling policies which are natural, linear and cubic is performed for evaluating the effect of different cooling policies on CSD. Simulation results based on the dynamic behaviour for all three cooling policies show cubic cooling policy obtained the best performance by achieving mean crystal size of 420 µm from the targeted CSD at 430 µm, and the mean crystal size for fine crystals is the lowest which is 35 µm compared to linear and natural cooling policies, at 40 µm and 55 µm, respectively. This information is prominent in deciding proper temperature trajectory of optimal cooling policy for potash alum crystallization process.
Focused Ion Beam (FIB) and Nano-Imprint Forming (NIF) have gained recently major interest because of their potential to enable the fabrication of precision engineering parts and to deliver high resolution, low-cost an...
Focused Ion Beam (FIB) and Nano-Imprint Forming (NIF) have gained recently major interest because of their potential to enable the fabrication of precision engineering parts and to deliver high resolution, low-cost and high-throughput production of fine sub-micrometre structures respectively. Using computational modelling and simulation becomes increasingly important in assessing capabilities and risks of defects with respect to product manufacturability, quality, reliability and performance, as well as controlling and optimising the process parameters. A computational model that predicts the milling depth as function of the ion beam dwell times and a number of process parameters in the case of FIB milling is investigated and experimentally validated. The focus in the NIF study is on modelling the material deformation and the filling of the pattern grooves during the mould pressing using non-linear large deformation finite element analysis with hyperelastic non-compressive material behaviour. Simulation results are used to understand the risk of imperfections in the pattern replication and to identify the optimal process parameters and their interaction.
This paper is the outcome of a small scale fuel cell project. Fuel cell is an electrochemical device that converts energy from chemical reaction to electrical work. Proton Exchange Membrane Fuel Cell (PEMFC) is one of...
This paper is the outcome of a small scale fuel cell project. Fuel cell is an electrochemical device that converts energy from chemical reaction to electrical work. Proton Exchange Membrane Fuel Cell (PEMFC) is one of the different types of fuel cell, which is more efficient, having low operational temperature and fast start up capability results in high energy density. In this study, a mathematical model of 1.2 W PEMFC is developed and simulated using MATLAB software. This model describes the PEMFC behaviour under steady-state condition. This mathematical modeling of PEMFC determines the polarization curve, power generated, and the efficiency of the fuel cell. Simulation results were validated by comparing with experimental results obtained from the test of a single PEMFC with a 3 V motor. The performance of experimental PEMFC is little lower compared to simulated PEMFC, however both results were found in good agreement. Experiments on hydrogen flow rate also been conducted to obtain the amount of hydrogen consumed to produce electrical work on PEMFC.
System identification or modelling is the process of building mathematical models of dynamical systems based on the available input and output data from the systems. This paper introduces system identification by usin...
System identification or modelling is the process of building mathematical models of dynamical systems based on the available input and output data from the systems. This paper introduces system identification by using ARX (Auto Regressive with eXogeneous input) and ARMAX (Auto Regressive Moving Average with eXogeneous input) models. Through the identified system model, the predicted output could be compared with the measured one to help prevent the motor faults from developing into a catastrophic machine failure and avoid unnecessary costs and delays caused by the need to carry out unscheduled repairs. The induction motor system is illustrated as an example. Numerical and experimental results are shown for the identified induction motor system.
This paper presents a mathematical model of synchronisation of multiple people during cyclic activities such as walking, running, jumping and bouncing. Providing that quality models of individual loading for these act...
This paper presents a mathematical model of synchronisation of multiple people during cyclic activities such as walking, running, jumping and bouncing. Providing that quality models of individual loading for these activities do exist, the sync model is the key component towards an urgently needed yet reliable model of artificial dynamic loading due to multiple active occupants. A model proposed here describes the effect of external and internal factors on the crowd dynamics. The former includes periodic external stimuli on the body motion of individuals, such as perceptible vibration of the ground and music beats. The later addresses the mutual interaction between individuals, such as possibility to see, hear or touch each other. modelling approach is inspired by the existing models of coupled pendulums while the governing equations feature Mathieu-type behaviour. For the sake of simplicity and efficiency, the model is kept linear and deterministic. All modelling parameters have a physical interpretation and their values can be calibrated to match experimental measurements.
The complexity of architecture is continuously growing. Therefore, it is necessary to develop a new construction system with complicated topology using less human work. A fibre-concrete is very promising material to s...
The complexity of architecture is continuously growing. Therefore, it is necessary to develop a new construction system with complicated topology using less human work. A fibre-concrete is very promising material to solve those problems. However, design methods of fibre-concrete load bearing structures such as columns are not well developed. Therefore, a new numerical simulation framework is proposed for analysis of fibre-concrete structures macro scale. The method can take into account non-linear post-cracking behaviour of fibre concrete. This includes local fibre orientation in thin elements, anisotropic continuum damage models on different scales, efficient meso-scale fibre orientation prediction tools and others. The proposed method is used to analyse building's columns where part of structural elements is made from fibre-concrete. The effectiveness of fibre-concrete is estimated and proposed a guideline for optimal design using fibre-concrete.
The article deals with problem of human gait modelling. human gait analysis is used for various human identification tasks and for various purposes in medicine. Lagrange equations of the second kind in many research a...
The article deals with problem of human gait modelling. human gait analysis is used for various human identification tasks and for various purposes in medicine. Lagrange equations of the second kind in many research are used to model gait. We use a model of an anthropomorphic mechanism of five links to describe human movements. The mathematical model is implemented in the form of software that uses input data on the kinematics of a real gait. An important result of the study is the creation of an algorithm for calculating model parameters that best reproduce the gait of a particular person. Our approach is based on the application of a genetic algorithm to minimize a new special objective function, which depends on discrete generalized coordinates that depend on time. The dynamic picture significantly improves the quality of the model, which is able to reproduce the subtle features of the human gait.
The potential for using wave energy is very high. According to various estimates, the energy of the world's ocean waves can range from 146 TWh/year to 29,500 TWh/year. A number of mathematical models have been dev...
The potential for using wave energy is very high. According to various estimates, the energy of the world's ocean waves can range from 146 TWh/year to 29,500 TWh/year. A number of mathematical models have been developed for the wave parameters analysis. The mathematical description of wave behaviour is a very complex process. Not least this is due to the complexity of the interaction of the wind that forms the waves with the water surface. As for the Black Sea, the mean annual wave power flux in this region can reach 4.8 kW/m. Such conclusions were made on the basis of modelling; the input was data on bathymetry of the region, wind speed and its direction. The obtained results on significant wave height, wave length and period were compared with the data obtained from the satellite. Many devices that convert wave energy into electrical energy have been developed. The choice of a particular device is based on a number of factors, including the installation site characteristics, weather conditions and economic opportunities. The article proposes a simple mathematical model of a wave, representing it in the form of a sinusoid. It is possible to estimate the wave energy conversion theoretical potential in a given region by analysing the obtained values of the energy received by the converter working surface (for example, turbine blade) after interacting with the wave. Calculations were carried out using the parameters of the Black Sea waves near the Crimean peninsula in winter.
Finite element modelling and analysis is an alternative way to study human fracture behaviour in biomechanics field compared to experimental test in laboratory. The aim of this study is to analyse the stress intensity...
Finite element modelling and analysis is an alternative way to study human fracture behaviour in biomechanics field compared to experimental test in laboratory. The aim of this study is to analyse the stress intensity factor (K) and strain energy release rate (J-integral) when three-point bending test and tensile test are applied on a two-dimensional (2D) cortical bone model developed by using finite element software with different applied loads and crack-to-width ratios. Two methods are used to to evaluate the values of K and J-integral which are Displacement Extrapolation Method (DEM) and CINT method. The values then been compared with other theoretical expression done by other researchers for validation purposes. It has been proved that by using CINT method, the error is very small compared to DEM method. As a result, stress intensity factor values increased as crack-to-width ratio increased and strain energy release rate also increased as crack-to-width ratio and loads increased. It can be concluded that finite element analysis can be used to study the fracture behaviour of human cortical bone. Therefore, researchers can easily study the behaviour of cortical bone using simulation instead of mechanical experiment.
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