Primljeno (Received): 20xx-xx-xx Prihvaćeno (Accepted): 20xx-xx-xx Abstract This paper focuses on the sizing of solar combisystems with adsorption seasonal storage to target autonomous solar space heating. Two main configurations of the combisystem are simulated, including one or two tanks. The influence of the seasonal storage on the sizing of the tanks is also discussed. The analysis is conducted in simulation using the TRNSYS program. Results show that performances of the system with two tanks are better (2 to 4 % with seasonal storage) but some improvements should be possible for the single tank configuration. The sizing of the sensible storage is nearly independent of the solar collectors area if there is a seasonal storage. The sensible storage size increase with the collectors area without adsorption storage.
In this work are compared performances of five different robot control algorithms. The following controllers under consideration are: PD controller, PID controller, analytical fuzzy controller, classical adaptive controller and adaptive controller based on neural network. The mentioned controllers are used to control two different robot configurations with two rotational degrees of freedom (in horizontal and vertical plane). The basic performances for control algorithms comparisons are: tracking error, rate of convergence, robustness on structural changes of control object, complexity of stability criterion and complexity of implementation.
This paper presents semi-analytical solution for the problem of elastic impact of two beams. The solution is based on the finite element discretization of the structure and equation of motion solution using diagonalization method for solving a system of differential equations. This procedure avoids temporal discretization typical for numerical methods, and in this way eliminates influence of the time-step size on the solution and numerical stability problems that can occur if time step isn’t defined properly. Computer code is developed for calculation, and application of the procedure is illustrated with the case of collision of communication bridge between two floating objects and safety structure called arrestor. The results are compared to those obtained by numerical procedure using the same discretization of the continuum and applying energy conservation principle. Very good agreement of the results obtained by three methods is achieved.
High costs, irrational consumption of thermal energy and low efficiency are often characteristics of sawn timber drying by warm humid air in chamber drying kilns. A weak link between technological planning with the sawn timber mass dynamics in the systems with more drying kilns is the most common reason that influences considerably the economy of timber thermal processing and the heat source pre- dimensioning. Lack of experimental research and usage of general relations are common reasons for insufficient practical compliance and connection of drying thermal needs and the heat source capacity. Air heater thermal load has been researched during the sawn oak timber drying, 25 mm thick, as well as 32 mm and 50 mm thick beech, by applying of appropriate regimes during all the stages in more cycles of convective drying. Current thermal needs have been measured and registered in relation to maximal values during the characteristic intervals of each drying cycle. The exact values have been shown, while the defined correlation polynome has been used to describe a graphic and mathematical model of thermal load in all intervals of tested sawn timber drying cycles. An analytical procedure for determination of total maximal thermal needs of more drying kilns has been suggested based on timber moisture decreasing and technological drying planning. Using a characteristic example, its applicability and contribution to an optimal thermal source dimensioning has been shown.
Dredgers are special sea floating vessels used for removing sea bottom material in order to: reshape harbor underwater areas and waterways, assembling pipelines, preparing sand beaches and coasts to handle with erosion impact, oil resources exploitation, forming man-made islands… This paper is based on selection of heat treatment parameters of sheaves, surface errors determination method and surface damages recovery. Om test samples made out of same material (GS30Mn5) built—up welding test was carried out of (SMAW procedure) by fluting prepared damage area. Next step was induction hardening using various parameters. Determination of cracks appearance was done by magnet method. By recording cross section structure as well as hardness measuring it has been determined that besides certain level of energy input (electrical current frequency) surface layer properties of sheave edge depend also about choosing proper cooling medium. Satisfying hardness values (320400 HB) were achieved combining air and water cooling simultaneously with avoiding cracks appearance. Parameters selected that way should ensure long working period of ropes (hardness 500550 HB) as well as safe dredgers performance.
Obnovljivi izvori energije su za Primorsko-goransku županiju osobito važno tematsko podrucje. Kako zbog potrebe smanjivanja emisija staklenickih plinova tako i zbog potrebe smanjenja velike ovisnosti o neobnovljivim izvorima energije. Kroz rad se daje pregled provedenih aktivnosti Primorsko-goranske županije u cilju osiguranju prostornoplanskih preduvjeta kojima ce se potaknuti i olaksati implementacija obnovljivih izvora energije, a osobito izgradnja vjetroelektrana. Navedeno, u konacnici, može biti dobar model za primjenu i u ostalim hrvatskim, europskim pa i svjetskim regijama. U samom radu se posebno razlaže predloženi model odabira potencijalnih lokacija za smjestaj vjetroelektrana izrađen od strane Energetskog instituta Hrvoje Požar kao i najnovije Europske smjernice koje tretiraju navedenu problematiku.
This paper presents welding current influence on spreading of electromagnetic field in TIG welding process. The quality of welding is analyzed by „Fast Fourier Transformation“ (FFT) on recorded current. Electric and magnetic field are measured using an instrument „Macshek ESM – 100 3D Fieldmeter“ [1]. Welding current is recorded using the On-line monitoring system [2]. Recording parameters of these two devices have synchronization time on On-line interface over hardware pin and interrupt routine in LabView software platform. Scale, resolution and synchronization of measured signals are additionally analyzed in Matlab.
Waste is one of the key issues of the modern civilisation and represents the result of our way of life. After the occurrence of bovine spongiform encephalopathy and the ban to feed animals with bone meals, new technologies of animal waste processing are developed, as well as animal waste uses for energy purposes. Certain parts of this waste, such as brains and spinal cord, are deemed high-risk substances and can be infected with prions ; their treatment is therefore only possible in strictly controlled conditions. Tests against effects of hydrolysis were conducted on samples of first class animal waste, bovine brains, in circumstances of different temperatures and hydrolisation duration, using the designed and built experimental laboratory reactor for alkaline hydrolysis. Production of hydrolysed substance biogas is monitored using the existing laboratory biogas circuit. Large potentials of hydrolyzates utilisation for energy purposes is featured by the analysis and systematisation of quantified results of the research, and the method used can be successfully applied for the pre-treatment of high-risk biological substances in biogas production.
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An innovative concept is suggested for ship ballast water management using continuous flow-trough method in ships double bottom. The idea was to create a ship who will not carry ballast water containing invasive marine organisms from one destination to another but who will navigate through it keeping the necessary hydrostatic characteristics using always local ambient water. Authors have suggested the solution which can obtain satisfactory results based on tree-dimensional CFD simulations.
The continually ephemeral demands of the shipbuilding market has forced shipyard management to be ready for change in order to maintain competitiveness. Applying principles of lean manufacturing in various degrees has proven to produce positive results in many industries including the shipbuilding industry. The concept of lean quality stresses the importance of quality which is one of the pillars and principles of lean manufacturing. The panel-block assembly line is a key production area where applying the lean quality concept can ease the decision making process for shipyard management with regards to changes in production. This includes analyzing various methods of block assembly in order to determine which method is best for the present state of shipyard technology and which method should eventually be chosen for the future. This paper shows that improving the methodology of the panel-block assembly line process alone will not yield better production results. Methodology must be in par with technology in order to bring about improvements. Finally, a Monte Carlo risk analysis clearly illustrates the results of the methods and allows shipyard management the ability to make decisions which have minimal risk both in the present and in the future.
Achievements of professor Liscic in heat treatment and surface engineering of metals have been described.
The editorial is dedicated to three-hundredth anniversary of the birth of one of the greatest Croatian minds, a scientists and humanists, Ruđer Boskovic (Ruggiero Joanes Boscovich).
The main goal of each technologist is the prediction of technological parameters by fulfilling the set design and technological demands. The work of the technologist is made easier by acquired knowledge and previous experience. A plan of input-output data was made by using the hybrid system of modelling ANFIS (Adaptive Neuro-Fuzzy Inference System) based on the results of seam tube production. This plan is the prerequisite for generating the system of fuzzy logic. The generated system can be used to estimate the output (speed of polishing) based on the given input (external tube diameter, oval shaping of the tube after the first phase of production, gradation of belts for grinding or polishing, condition of belts - time of usage, pressure of belts).The more precise predictions of technological time provided by the model supplement the previously defined manufacturing operations, replace the predictions based on the technologists' experience and form the basis on which to plan production and control delivery times. The work of technologists is thus made easier and the production preparation technological time shorter.
Power system stabilizer (PSS) is used in synchronous generator excitation control system for damping electromechanical oscillations. The objective of the PSS is to generate a stabilizing signal, which produces a torque damping component on the generator rotor. Created torque component must be in phase with speed deviation. Today’s power system stabilizers (IEEE types) use speed deviation and/or acceleration of synchronous generator as input signals and are based on a phase compensation method. This paper compares the performance of IEEE type PSS1A and PSS2B stabilizers. The algorithms of stabilizers were implemented into the DSP based digital control system and tested in a laboratory environment on an 83kVA, 50Hz synchronous generator connected by transmission lines to the power system. The stabilizers’ performance was compared in cases of voltage and active power change. In case of voltage change, both stabilizers performance is satisfactory, whilst in the case of active power change, only the PSS2B satisfies. The PSS1A stabilizer generates an unwanted stabilizing signal and causes variations in voltage and reactive power.
In general, computer tools for ergonomic CAD do not assist designer with higher level advice when performing ergonomic design. Designer has to possess expert knowledge and experience in many fields of engineering design including ergonomics in order to deliver successful designs. Such multi-levelexperts are rare and usually occupied. Two alternative ways are used to substitute these experts: teams of experts covering different areas of knowledge are established or some intelligent computer programs with expert knowledge are applied. In the second case, expert knowledge has to be collected, organized and encoded into the knowledge base of the system. An intelligent decision support system has been developed in order to overcome this bottleneck. This paper presents a knowledge base, containing ergonomic design knowledge specific for hand tools design. A pneumatic hammer handle design is used as a case study to show how ergonomic design knowledge built in the system is used to improve the ergonomic value of the product.
One of the main disadvantages of composite materials like glass or carbon fiber reinforced composites in use today is their inability to be recycled. After the end of a product or part life cycle, there is no way to separate the fibers from the matrix, or to recycle them except for deposition or shredding. Bio- polymer based composites have an increasing and bright future due to their recyclability, reproduction capability, available sources and economic factors without the fundamental loss of mechanical properties. This paper deals with natural – bamboo fiber reinforced composite material design and its basic mechanical properties testing.
CFD analysis of heavy fuel oil combustion in a 6.7 MW cylindrical vertically-fired furnace has been carried out. The furnace supplies process heat in the Oil refinery of the National oil company (INA) in Rijeka-Croatia. The motivation of the work was to improve the performance of the combustion process by changing fuel and burner parameters. The commercial CFD-code Fluent is used to model transport and reaction in the furnace. The chosen CFD models for heavy fuel oil spray combustion are compared with measurement data found in the literature and good agreement is achieved. The combustion process is investigated through the influence of different parameters: air-fuel ratio, fuel oil droplet diameter, spray cone half-angle and burner swirl number. It is determined that the best performance of the combustion process is achieved for an air-fuel ratio of 1.15. The droplet diameter should be neither too small nor too large: medium-sized droplets (~100 μm) mix well with air and reside in the furnace the right amount of time for complete burnout to occur. Small spray cone half-angles deteriorate mixing between air and fuel which is reflected in higher CO concentrations. The burner’s swirl number influences the mixing rate of air and fuel: a small swirl number is not desired as it elongates the flame, increases flue gases temperatures and reduces the furnace heating output.
In the present conditions of market globalization and thereby increasing market competition, purchasing department and management structure of the company, in addition to answer the questions what, how many and when to buy at what price, also must answer the question about appropriate supplier. Supplier selection as well as the efficient inventory control can bring significant savings to company. For the purpose of systematic evaluation of suppliers, criteria and multiple criteria AHP model (analytic hierarchy process) for selecting the best supplier have been proposed in the paper. The model is illustrated by the example of supplier selection to purchase parts for assembly of the agricultural machine. Multiple criteria and systematic quantitative approach to the supplier selection problem, significantly improve decision making process.
