F. Hajdu

57194498837

Publications - 19

Fire simulation of different complex geometry tree objects using FDS

F. Hajdu Rajmund Kuti Cs Papp

Publication Name: Pollack Periodica

Publication Date: 2025-06-27

Volume: 20

Issue: 2

Page Range: 67-72

Description:

Fire simulations are becoming more and more widely used in fire protection practices. In order to achieve more accurate results, it is inevitable that simulations are always developed. This study investigates the fire behavior of various complex wooden geometries. This research aims to enhance the understanding of fire propagation of different geometries made of wood. The simulations are performed using fire dynamics simulator, which incorporates heat transfer, combustion, and fluid dynamics principles. Key parameters like temperature and heat release rate are analyzed for each of tree geometries. The research contributes to the development of more accurate fire models. It also provides the basis for further development of simulations including more complex geometries.

Open Access: Yes

DOI: 10.1556/606.2024.01225

Global Sensitivity Study of a Duffing-Type Nonlinear Vibration System

F. Hajdu

Publication Name: Strojnicky Casopis

Publication Date: 2024-11-01

Volume: 74

Issue: 2

Page Range: 17-24

Description:

An interesting field of studying nonlinear systems is their sensitivity study. With sensitivity study the most influential parameters on a system can be obtained and then the simplification and improvement of the model will be possible. In this paper the global sensitivity study of a Duffing-type vibration system is carried out with Sobol's variance-based method taking the root mean square of acceleration and the maximum acceleration as output variables. With the sensitivity study it was observed that the parameters of the excitation signal like the amplitude and the angular velocity are the most influential. It was also found that a single parameter has less influence on the system than the parameter combinations. The aim of the research is to carry out the global sensitivity study of a relatively simple nonlinear system. The study is the basis for further research tasks in order to perform the sensitivity study of more complex systems.

Open Access: Yes

DOI: 10.2478/scjme-2024-0021

Comparison of different geometry trees in fire simulation

L. Környei Csaba Hajdu F. Hajdu Rajmund Kuti Dóra Beke

Publication Name: Pollack Periodica

Publication Date: 2024-10-16

Volume: 19

Issue: 3

Page Range: 34-39

Description:

Wildfire simulations can help to better understand the dynamics and effects of forest fires. The basis of wildfire simulation is the tree-burning simulation. In this paper, the fire simulation of 7 different geometry Hungarian trees in the case of arson is presented. It was observed that the trees were burned down fast. The maximum mass loss rate and maximum heat release rate were larger as the tree was larger. The largest intensity fire could be observed in the case of the smallest tree. The maximum temperature was higher in the case of a large crown diameter. The maximum aerosol reached high pollutant concentrations. In the case of large crown height, the maximum CO2 concentration was higher. The results presented in this paper can be the basis of the following forest fire simulations.

Open Access: Yes

DOI: 10.1556/606.2024.01022

One-at-a-Time sensitivity study of a tree burning simulation

L. Környei F. Hajdu Rajmund Kuti

Publication Name: Pollack Periodica

Publication Date: 2024-03-22

Volume: 19

Issue: 1

Page Range: 53-59

Description:

The aim of the research was to carry out the One-at-a-Time sensitivity analysis of a tree burning experiment simulation with a novel fuzzy logic-based method. It was observed that the precent of the remaining tree is sensitive to the moisture content, the crown-base diameter and the tree height. The other variables, which are maximum mass loss rate, maximum heat release rate, and maximum temperature at the top of the tree are moderately sensitive or not sensitive to the selected parameters. The presented results can be used in sensitivity studies and wildfire simulations.

Open Access: Yes

DOI: 10.1556/606.2023.00850

INVESTIGATION OF TRAFFIC INDUCED DYNAMIC RESPONSE OF A BRIDGE

Zoltán Major P. Szalai Péter Horváth F. Hajdu Rajmund Kuti M. Brinissat Antal Apagyi Cs Papp

Publication Name: Strojnicky Casopis

Publication Date: 2023-05-01

Volume: 73

Issue: 1

Page Range: 85-102

Description:

Bridges are special structures that provide a transport connection between areas divided by a physical barrier. Vehicles passing over bridges cause vibrations in the structural elements of the bridge, which can damage these structural elements over time. The aim of our research was to investigate the vibrations generated by vehicles on Hungary's first steel girder welded bridge, which was subjected to the maximum allowable load. In this paper, we describe the measurements we have carried out, analyse the results, present the vehicle-bridge interaction model we have constructed and the computer simulation we have carried out by using it. Our research results are intended to contribute to accident prevention and the safe operation of bridges.

Open Access: Yes

DOI: 10.2478/scjme-2023-0007

Stair Climbing Aid Devices as Parts of Sustainable Healthcare

Péter Horváth F. Hajdu Attila Nagy

Publication Name: Chemical Engineering Transactions

Publication Date: 2023-01-01

Volume: 107

Issue: Unknown

Page Range: 325-330

Description:

An important aspect of a sustainable society is the care of elderly people. For a sustainable society, it is necessary to develop cost-effective, culture-appropriate, and sustainable eldercare services, which should guarantee both safety and quality. It is also important to prolong the time in which elderly people can live independently to contribute to sustainable healthcare. For elderly people, a daily activity, climbing stairs, might be difficult. This paper presents an overview of stair-climbing aid devices. The paper introduces the sustainable healthcare of elderly people. Then, different stair-climbing aid devices are explained and analyzed, ranging from passive ones to high-tech stair-climbing exoskeletons. A prototype of a new solution, which is an Intelligent Crutch, is presented. After elaborating on the design criteria, the detailed conceptual design and the working principle of the device are presented. The presented concept fills a gap between expensive and complicated stair climbing aid devices and simple and cheaper solutions. It is cheaper and simpler than the active, complicated stair-climbing devices but performs almost the same function. The device helps elderly and disabled people to climb stairs alone, thus improving the quality of life of the target group. The study concludes with further development tasks in order to help elderly people and contribute to a sustainable society.

Open Access: Yes

DOI: 10.3303/CET23107055

Numerical Examination of a Forest Area Fire

L. Környei Csaba Hajdu F. Hajdu Rajmund Kuti Dóra Beke

Publication Name: Chemical Engineering Transactions

Publication Date: 2023-01-01

Volume: 107

Issue: Unknown

Page Range: 61-66

Description:

An important task of sustainability is the protection of Earth's forests and the prevention of forest fires. In this paper, the numerical examination of a typical Hungarian ash forest fire is presented. The connection between sustainability and forest fire simulations is also discussed. For the simulation, a Fire Dynamics Simulator was selected, and a particle-based model was used. The simulation setup, which includes a random location of trees following Poisson distribution, is also explained. Then, the simulation of a 10x10 m area of ash forest is presented. It was found that in case of arson, the fire spreads rapidly among the trees, and there will be a high-intensity fire in which the forest area burns down in 4 min. The mass loss rate, the temperature, and the heat release rate also increased fast (above 50 kg/s, above 2,000 °C and above 800,000 kW). The aerosol concentration reached a high pollutant concentration (1.3x10-6), and the carbon dioxide concentration also increased significantly (above 14,000 ppm). These changes have a direct effect on climate change. Therefore, it is important to examine them in a simulation environment. The simulation was compared to a pine tree forest simulation, and it could be observed that in the case of the pine tree, the values are similar, but phenomena occur faster. With the computer simulation, it is easier to determine the areas affected by the fire, which also helps fire prevention and firefighting. The aim of the research is to contribute to the prevention and more efficient extinguishment of wildfires and the sustainability of the Earth.

Open Access: Yes

DOI: 10.3303/CET23107011

Examination of effects of indoor fires on building structures and people

L. Környei Csaba Hajdu F. Hajdu Geza Zolyomi Rajmund Kuti Gabriella Lászlo

Publication Name: Heliyon

Publication Date: 2023-01-01

Volume: 9

Issue: 1

Page Range: Unknown

Description:

The scientific study of the harmful effects of indoor fires on building structures and on the environment is a top issue today. Indoor fires frequently occur all over the world. The goal of our research is to examine the effects of an average room fire on the survival possibility of a trapped person and on the building structure, taking into account features of the Eastern European architecture. First, a computational fluid dynamics (CFD) simulation was performed to examine the change of temperature, oxygen, and carbon monoxide concentration in a selected room in a vacant building used for military training. Based on the results, a 1:1 scale fire experiment was carried out with the parameters used in the simulation. The experiment was repeated once with the same settings. It was observed that without the intervention of firefighters, the temperature in the experiment could have rapidly reached 400 °C, as suggested by the simulation, which could have caused structural damage to the building. Furthermore, after 3 min the carbon monoxide concentration reached 400 ppm in both experiments and the simulation, which is a harmful level to people trapped inside the room. Also, in the experiment there was sufficient oxygen at the ground level with what people can survive 3 min.

Open Access: Yes

DOI: 10.1016/j.heliyon.2022.e12720

Experimental study on examining the fire load of a small compartment

F. Hajdu Rajmund Kuti Gabriella Lászlo

Publication Name: Pollack Periodica

Publication Date: 2022-04-30

Volume: 17

Issue: 1

Page Range: 133-138

Description:

In Hungary a lot of people live in condominiums or in block of flats where fire often occurs despite of precise design and effective fire protection arrangements. This means a hazard for the people living there, for the building constructions and also for the environment. A deeper knowledge of the burning process and examining the negative effects of fire load on building constructions with scientific methods are actual questions nowadays. In order to get to know the phenomena more accurately, fire spread in a bedroom was modeled and numerical simulation was carried out, which is presented in this paper in detail. These experiences may help increasing the fire safety and preventing fires in apartments. The simulations were carried out considering the characteristics of the Hungarian architecture.

Open Access: Yes

DOI: 10.1556/606.2021.00422

Heat radiation effects on insulating materials used in buildings

F. Hajdu Rajmund Kuti Gabriella Lászlo

Publication Name: Pollack Periodica

Publication Date: 2021-12-31

Volume: 16

Issue: 3

Page Range: 108-113

Description:

In recent years, in order to increase the energy efficiency of older buildings in Hungary, several tenders have supported the modernization of the thermal insulation. Various thermal insulation materials have been installed on walls, on slab and on floor. Unfortunately there are cases where thermal insulation materials are not installed in accordance with the construction permit or the manufacturer's instructions, which poses a serious danger in case of a fire. During the research the effects of heat on the behavior of Expanded PolyStyrene, a thermal insulation material often used in Hungary is examined. Laboratory tests and computer simulations were carried out, which are presented in detail in this paper. The aim of the research is to contribute to increase the fire safety of buildings.

Open Access: Yes

DOI: 10.1556/606.2021.00377

Modelling and Sensitivity Analysis of Nonlinear Firefighting Systems Using Maple

F. Hajdu Rajmund Kuti G. Molnárka

Publication Name: Communications in Computer and Information Science

Publication Date: 2021-01-01

Volume: 1414

Issue: Unknown

Page Range: 234-251

Description:

Mathematical modelling and numerical simulations have greatly contributed to the development of technical sciences in the recent decades. With powerful tools, like Maple, the examination of ever newer engineering applications in simulation environment was made possible. This paper gives an overview of mathematical modelling and numerical examination of nonlinear fire truck suspension systems using Maple. The examined models are the suspension system of a heavy-duty fire truck with different degrees of freedom and a special double-cabin fire truck suspension system with a crew compartment. The construction of mathematical models, their implementation to Maple and the numerical simulation results are explained. Detailed One-at-a-Time sensitivity analysis results using a novel fuzzy logic based evaluation method developed in Maple are also presented. With the proposed method an extended parameter range can be examined and the parameters can be easily compared. From the sensitivity analysis it was concluded that the spring characteristics and the road models greatly affect simulation results.

Open Access: Yes

DOI: 10.1007/978-3-030-81698-8_16

Fuzzy logic based sensitivity study of nonlinear systems

Csaba Hajdu F. Hajdu

Publication Name: Gpmc 2020 2nd IEEE International Conference on Gridding and Polytope Based Modeling and Control Proceedings

Publication Date: 2020-11-19

Volume: Unknown

Issue: Unknown

Page Range: 19-24

Description:

A fuzzy logic based One-at-a-Time sensitivity study method of nonlinear systems is proposed in this paper. The advantage of the method is that it can be used for a wider parameter examination range. With the use of fuzzy logic a smooth evaluation of sensitivity study could be achieved and the degree of sensitivity of parameters could be easily compared. The method was tested with 2 case studies: The sensitivity study of a nonlinear Duffing-type vibration system and a vehicle simulation using an open-source physics simulator. With the simulation results it was shown that the method can be used effectively for sensitivity study of nonlinear systems in an extended examination range.

Open Access: Yes

DOI: 10.1109/GPMC50267.2020.9333818

Testing output variables for sensitivity study of nonlinear vibration systems

F. Hajdu G. Molnárka

Publication Name: Pollack Periodica

Publication Date: 2020-08-01

Volume: 15

Issue: 2

Page Range: 70-81

Description:

In this study the detailed One-at-a-Time sensitivity analysis of nonlinear massspring- damper systems is carried out with numerical simulation. The degree of sensitivity was measured with a sensitivity index and based on its sensitivity Fuzzy-sets were established. The sensitivity of a parameter then can be expressed by the membership to the Fuzzy-sets. In this study the root mean square of acceleration, the maximum amplitude of acceleration and the peak frequency were chosen as output variables to measure sensitivity. With this research it was proven, that the root mean square of acceleration and the peak frequency can be used for sensitivity study of nonlinear vibration systems effectively.

Open Access: Yes

DOI: 10.1556/606.2020.15.2.7

Investigation of swings caused by sudden wind loads during operation of an aerial ladder

Péter Horváth F. Hajdu Rajmund Kuti

Publication Name: Fme Transactions

Publication Date: 2020-01-01

Volume: 48

Issue: 2

Page Range: 351-356

Description:

In Hungary, as in other countries around the world, intervention firefighting units often use a mechanically operated aerial ladder for highaltitude rescue tasks. The safe operation of the equipment is only possible under strict safety regulations and requires a high level of expertise from the operating staff. During each intervention, extraordinary events such as sudden wind gusts can occur, which can cause extreme overload of the structural members of aerial ladders and have adverse effects on the equipment that can lead to malfunctions and-even worse-to accidents. Therefore it is important to study the consequences of external influences on aerial ladders during operation. The examination was performed on a widely used Magirus M32-L aerial ladder. The reason for choosing this type of aerial ladder is because it has a wide operating range, therefore test results can be a good starting point for other similar equipment as well. In this paper the development of our beam model and the performed finite element simulations are presented. The aim of the research is to develop a model based on geometrical measurement data that is suitable for studying the effects of wind gusts on the ladder structure. With our research, we aim to contribute to the safe operation of aerial ladders and to prevent possible accidents.

Open Access: Yes

DOI: 10.5937/FME2002351H

One-at-a-time sensitivity study of a nonlinear fire truck suspension model

F. Hajdu Rajmund Kuti G. Molnárka

Publication Name: Fme Transactions

Publication Date: 2020-01-01

Volume: 48

Issue: 1

Page Range: 90-95

Description:

In this paper the detailed OAT (one-at-a-time) sensitivity analysis of a nonlinear fire truck suspension system is carried out with numerical simulation. As output to measure sensitivity the RMS of acceleration was chosen, which can be calculated with numerical simulations easily. The degree of sensitivity was measured with a sensitivity index and based on it sensitivity Fuzzy-sets were established. The membership of each parameter to the Fuzzy sets is calculated and based on it, it was determined which parameters are the most sensitive. With the presented results it is shown that the proposed method is suitable for testing mathematical models as well.

Open Access: Yes

DOI: 10.5937/fmet2001090H

Parameter identification of a fire truck suspension for vibration analysis

P. Szalai F. Hajdu Rajmund Kuti Péter Mika

Publication Name: Pollack Periodica

Publication Date: 2019-01-01

Volume: 14

Issue: 3

Page Range: 51-62

Description:

In case of field measurement it is essential to determine the measurement conditions. With accurate parameter identification credible measurement and simulation results can be achieved. In this paper the parameter identification of a CSD-755-10 heavy-duty fire truck suspension for vibration analysis is presented, which is an important base-point for further research.

Open Access: Yes

DOI: 10.1556/606.2019.14.3.6

Numerical examination of nonlinear oscillators

F. Hajdu

Publication Name: Pollack Periodica

Publication Date: 2018-12-01

Volume: 13

Issue: 3

Page Range: 95-106

Description:

The numerical examination of nonlinear oscillators is presented in this paper. First some methods of nonlinear system modeling are described then the numerical creation of phase-plane, bifurcation diagrams and Poincaré sections are expounded in detail. The next part of the paper is the numerical examination of nonlinear oscillators, like the Duffing-Holmes oscillator and a mechatronic semi-active suspension system. The paper concludes with further development tasks.

Open Access: Yes

DOI: 10.1556/606.2018.13.3.10

Parallelization of numerical examination of nonlinear systems using maple

F. Hajdu G. Molnárka

Publication Name: Civil Comp Proceedings

Publication Date: 2017-01-01

Volume: 111

Issue: Unknown

Page Range: Unknown

Description:

In this work we present possibilities of the parallelization of numerical examination and simulation of nonlinear systems, especially creating phase-plane diagrams in parallel. For construction of such diagrams Maple was used because it provides algorithms for solving differential equations and two models for parallelization. These are the Task programming model and the Grid programming model. The paper describes the development, the test and the comparison of the parallel programs created according to the two parallelization models. Even using a simple desktop with low number of processors a relative good speedup with a good efficiency could be achieved in both cases. It was also examined how the problem size affects the speedup and the efficiency.

Open Access: Yes

DOI: DOI not available

Determination of Measurement Parameters for Vibration Analysis by Bus

P. Szalai Péter Horváth F. Hajdu Rajmund Kuti M. Brinissat Antal Apagyi Cs Papp

Publication Name: Strojnicky Casopis

Publication Date: 2022-11-01

Volume: 72

Issue: 2

Page Range: 189-200

Description:

From the point of view of field examinations, especially in the case of measurements done by instruments, it is crucially important to determine measurement conditions. Accurate identification of parameters enables accurate and certified measurement results to be achieved. In our work, we represent the determination of measurement conditions for harmful vibrations occurring during urban road transport of an Ikarus 55 type long-haul bus. This is a favourable basis for further vibration analysis regarding other buses.

Open Access: Yes

DOI: 10.2478/scjme-2022-0028