Marko Delimar

Influence of the acetabular cup position on hip load during arthroplasty in hip dysplasia

Placement of the acetabular cup during total hip arthroplasty is of great importance because usually every deviation from the ideal centre of rotation negatively influences endoprosthesis survival, polyethylene wear and hip load. Here we present hip load change in respect to various acetabular cup positions in female patients who underwent total hip replacement surgery due to hip dysplasia. The calculation suggests that, in the majority of cases, for every millimeter of lateral displacement of the acetabular cup (relative to the ideal centre of rotation) an increase of 0.7% in hip load should be expected and for every millimeter of proximal displacement an increase of 0.1% in hip load should be expected (or decreased if displacement is medial or distal). Also, for every millimeter of neck length increase, 1% decrease is expected and for every millimeter of lateral offset, 0.8% decrease is expected. Altogether, hip load decreases when the cup is placed more medially or distally and when the femoral neck is longer or lateral offset is used.RésuméLe positionnement de la cupule acétabulaire durant la réalisation d’une prothèse totale de hanche est très important car une déviation de la position idéale du centre de rotation peut influer de façon négative sur la survie, sur l’usure et sur les vecteurs de forces au niveau de la hanche. Nous présentons une étude qui permet de visualiser les vecteurs de forces en fonction des différentes positions de la cupule chez des patients de sexe féminin qui ont bénéficié d’une prothèse totale de hanche mise en place pour dysplasie. Les calculs permettent de penser que dans la majorité des cas chaque millimètre de latéralisation de la cupule augmente de 0,7% la charge au niveau de la hanche et que chaque déplacement proximal l’augmente de 0,1%. Ainsi chaque augmentation millimétrique de la longueur du col peut entraîner une diminution de 1% des forces, de même en ce qui concerne chaque millimètre d’offset latéral qui permet d’obtenir une diminution de 0,8%. En conclusion, les charges diminuent au niveau de la hanche quand la cupule est placée de façon plus médiane ou distale et quand les longueurs du col fémoral ou de l’offset son utilisées.

Technical limitations towards a SuperGrid — A European prospective

In the search for a more sustainable energy supply, renewable energy sources are increasingly introduced into the power system. However, most of these sources are located far from the load centers, and the existing power system is getting overloaded. A supergrid is by many seen as a viable solution that allows a massive integration of these renewable energy sources into the European power system. By connecting energy sources that are located far from each other and by offering enhanced control, balancing services can be delivered. The geographic spread in its turn allows a more diversified energy portfolio. In the meanwhile it increases the security of supply. Although the supergrid has gotten much attention, it cannot be built yet. While the basic technology might seem available, several technical limitations still exist. This paper first describes the potential and need for a supergrid. The paper focuses on a meshed, multi-terminal VSC HVDC, and it is explained why this relatively new technology is believed to be the best suitable one for such a grid. Next the different difficulties or challenges that still exist are addressed.

A literature review with statistical analysis of electricity price forecasting methods

In todays liberalized and competitive power market, electric utilities, power producers and traders are exposed to increasing price risks and volatility. The growing reliance on renewable sources and their dependence on weather, nuclear uncertainty, market coupling and global financial instability are contributing to importance of accurate price forecast. Considering the fact that power markets are not equally developed, different price forecasting methods have arose. This paper provides an overview of notable price forecasting methods that have been published in research papers. The paper also includes statistical review of applied methods embracing timeframe, geographical background, statistical errors and other specific data. Finally, results are discussed with respect to qualitative and quantitative statistical analysis, with emphasis on the price forecasting accuracy.

Artificial neural networks in power system topology recognition

This paper presents an artificial neural network based model for identifying anomalies in the reported power system topology. The results obtained using a multilayer perceptron with backpropagation learning algorithm are presented and discussed.

Profit maximization of a hydro producer in a day-ahead energy market and ancillary service markets

Water is scarce resource with uncertain availability. Hence finding an optimal production schedule for hydro producer is usually a complex task and it is necessary to carefully balance the timing of water use. This paper addresses the self-scheduling problem for a price-taker hydro producer. The goal is maximizing the profit of a hydro producer through participating in the day-ahead energy and ancillary service markets. The spinning reserve and regulation market are considered as ancillary service markets. The self-scheduling problem of hydro producer is formulated and solved as a mixed integer linear programming problem. Model is deterministic and three-dimensional relationship between the power produced, the water discharged, and the head of associated reservoir is accounted. Real hydropower system Vinodol is considered.

Short term hourly forecasting of gas consumption using neural networks

This paper presents a neural network based model for forecasting gas consumption for residential and commercial consumers. A feedforward neural network with sigmoid nodes and one hidden layer was trained by backpropagation. The model was validated on real data from a distribution area covering 7% of the total consumption in Croatia, consisting mostly of residential and commercial consumers.

Shipboard Microgrids: A Novel Approach to Load Frequency Control

Due to the fast development of renewable energy systems and the severe limitations enforced by the marine pollution protocol, the utilizing of wind turbines (WTs), solar generation, sea wave energy (SWE), and energy storage systems (ESS) in marine vessel power systems have been attracting a lot of attention. Hence, a marine vessel power system with photovoltaic, WT, SWE, and ESS can be considered as a specific mobile islanded microgrid. Consequently, the main target of this paper is to design a new optimal fractional order fuzzy PD+I load frequency controller (LFC) for islanded microgrids in a ship power system. Since the performance of the controller depends on its parameters, the optimization of these coefficients can play a significant role in improving the output performance of the LFC control. Accordingly, a modified black hole optimization algorithm is utilized for the adaptive tuning of the coefficients of noninteger fuzzy PD+I controller. The performance of the shipboard microgrid is evaluated by utilizing real-world wind power fluctuation and solar radiation data. Finally, the extensive studies and hardware-in-the-loop simulations are applied to prove that the proposed controller can track the reference frequency with lower deviation as well as it is more robust in comparison with the prior-art controllers utilized in the case studies.

Short term power system planning with water value and energy trade optimisation

This paper emphasises the importance of a well planned unit commitment model in coordination with water value evaluation to achieve optimal economic results for genco. The existing water value models are examined and customized for the developed power system model. Linear programming methods are used to achieve optimal economic performance for hydro and thermal power plants production and the power exchange is calculated. Several scenarios of short term planning with emphasis on water value and power market exchanges are presented.

Real-time student assessment using a system of RF clickers

The paper presents an analysis of a one-semester technical course ldquoElectrical facilitiesrdquo. The goal of the paper is to show how a system of real-time knowledge testing at undergraduate level, using a radio-frequency clicker system and conventional knowledge assessment methods, was implemented on a single course at the University of Zagreb. Using statistical analysis, students are clustered in groups to show the influence of clickers on the student population. It is shown that clickers have a favorable impact on students and work in accordance with each studentpsilas abilities, as confirmed using conventional assessment methods.

Optimal MRAS speed estimation for induction generator in wind turbine application

This paper propose improved sensorless vector control of squiral cage induction generator for variable speed wind energy conversion system. The rotational speed of the induction generator is estimated with the Model Reference Adaptive System - MRAS observer. The estimated rotational speed is used as the feedback of the control loop in the converter control system. Proportional integral controller in the MRAS observer is optimized via Genetic Algorithm, Partical Swarm Optimization and Simulated Annealing. Comparative analise of the optimal speed estimation of induction generator is also presented. The performance of the sensorless controled variable speed wind turbine drive is evaluated through simulation in Matlab/Simulink. Experimental results are gained via laboratory model based on dSpace DS1104 digital control card.