In this paper we present numerical results of conceptual design study of an UAV which uses Coanda... more In this paper we present numerical results of conceptual design study of an UAV which uses Coanda Effect for lift production. Results indicate the ability of manuveuring by creating asymmetric flow patterns which lead to uneven lift production and resulting force with horizontal component necessary for establishing forward flight conditions.
Laminated composites have an important application in modern aeronautical structures. They have e... more Laminated composites have an important application in modern aeronautical structures. They have extraordinary properties, like high strength, stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to impact loads. As a consequence of that, impact damage initiation and growth are appearing in them. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date a lot of models for impact damages in laminates have been developed with higher or lower accuracy. Those models can replace real and expensive testing in laminated structures with some approximation. By using specialized software the damage parameters in laminate aircraft structures can be predicted (at certain conditions). In that way numerical simulation of impact on certain laminates can be done and the obtained results from the simulations presented in a form of graphic damage distributions.
Laminated composites have an important application in modern aeronautical structures. They have e... more Laminated composites have an important application in modern aeronautical structures. They have extraordinary properties, like high strength, stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to impact loads. As a consequence of that, impact damage initiation and growth are appearing in them. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date a lot of models for impact damages in laminates have been developed with higher or lower accuracy. Those models can replace real and expensive testing in laminated structures with some approximation. By using specialized software the damage parameters in laminate aircraft structures can be predicted (at certain conditions). In that way numerical simulation of impact on certain laminates can be done and the obtained results from the simulations presented in a form of graphic damage distributions.
Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing... more Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing vibrations in the seat. In order to determine the suitability and potential of cockpit floor -seat connections we conducted an experiment where measurements were taken and seat vibration analysis conducted. Vibrations parameters were measured for maximum engine and propeller speed. This analysis indicates that passive vibrations damping or cockpit floor -seat connections functionality depends on flights profile and vibrations frequency. The connection in question was behaving like a vibration multiplier on the 3 rd and 4 th harmonic as well as on the 3,5 sub-harmonic in individual flight modes on basic propeller rotation frequency, however, it behaved as a vibration silencer on all other frequencies. Analysis of the experimental data has shown that it would be justified to start improving the self adaptive unit for active vibration reduction for pilot seats.
Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing... more Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing vibrations in the seat. In order to determine the suitability and potential of cockpit floor -seat connections we conducted an experiment where measurements were taken and seat vibration analysis conducted. Vibrations parameters were measured for maximum engine and propeller speed. This analysis indicates that passive vibrations damping or cockpit floor -seat connections functionality depends on flights profile and vibrations frequency. The connection in question was behaving like a vibration multiplier on the 3 rd and 4 th harmonic as well as on the 3,5 sub-harmonic in individual flight modes on basic propeller rotation frequency, however, it behaved as a vibration silencer on all other frequencies. Analysis of the experimental data has shown that it would be justified to start improving the self adaptive unit for active vibration reduction for pilot seats.
In this article, a formulation of a point-collocation method in which the unknown function is app... more In this article, a formulation of a point-collocation method in which the unknown function is approximated using global expansion in tensor product Bernstein polynomial basis is presented. Bernstein polynomials used in this study are defined over general interval [a,b]. Method incorporates several ideas that enable higher numerical efficiency compared to Bernstein polynomial methods that have been previously presented. The approach is illustrated by a solution of Poisson, Helmholtz and Biharmonic equations with Dirichlet and Neumann type boundary conditions. Comparisons with analytical solutions are given to demonstrate the accuracy and convergence properties of the current procedure. The method is implemented in an open-source code, and a library for manipulation of Bernstein polynomials bernstein-poly, developed by the authors.
Abstract This paper presents the analysis of the survivability of a heavy transport helicopter ta... more Abstract This paper presents the analysis of the survivability of a heavy transport helicopter tail rotor blade made of composite laminated materials after ballistic damage made by the bullet of 7.9 mm calibre shoulder weapons. Penetrating damages made in the root part of ...
Page 1. 583 Application of Fuzzy Logic in Solving Problems from the Area of Reliability and Maint... more Page 1. 583 Application of Fuzzy Logic in Solving Problems from the Area of Reliability and Maintenance of Aircraft Systems Milenko Zivaljevi~ and Bogko Ra~uo Aeronautical Department, Faculty of Mechanical Engineering ...
This paper presents a method for determination of optimum positions of single wind turbines withi... more This paper presents a method for determination of optimum positions of single wind turbines within the wind farms installed on arbitrary configured terrains, in order to achieve their maximum production effectiveness. This method is based on use of the genetic algorithm as optimization technique. The wind turbine aerodynamic calculation is unsteady, based on the blade modeled as a vortex lattice and a free-wake type airflow behind the blade. Optimization method is developed for two different fitness functions. Both functions use the total energy obtained from the farm as one of the key variables. The second also involves the total investments in a single wind turbine, so the optimization process can also include the total number of turbines as an additional variable. The method has been tested on several different terrain configurations, with special attention paid to the overall algorithm performance improvements by selecting certain genetic algorithm parameters.
Tailoring dielectric properties of engineering materials has become very important since many rad... more Tailoring dielectric properties of engineering materials has become very important since many radio wave propagation problems and remote sensing applications depend on correct values of these material properties. Prediction of material dielectric constant and loss tangent is of paramaunt importance. Polymer matrix composite materials are excellent candidates for these applications. In this paper analytical method for material dielectric constant and loss tangent prediction is preseneted. The model is experimentally verified for E-glass fibers embedded in epoxy matrix. Test results for 100 kHz to 1 MHz frequency range are presented.
: In this paper experimental results of structural vibratory testing for the light multipurpose h... more : In this paper experimental results of structural vibratory testing for the light multipurpose helicopter main rotor blade of composite laminated materials are presented. The aim of the main rotor blade vibratory testing was to define the basic aeroelastic properties of the blade. This testing included determination of the natural oscillation modes and natural frequency of the structure in oscillations, as well as defining the blade structural damping. The measurement was performed for three different full-scale models with two different types of cores of the main rotor blade: Nomex (phenolic honeycomb) and Rohacell (polyurethane foam), and the results are presented in this paper. KEYWORDS: Structural damping, phenolic honeycomb, polyurethane foam, vibratory characteristics of the helicopter main rotor blade made of composite laminated materials.
: In this paper the design, fabrication and analysis of behavior by full-scale ver-ification test... more : In this paper the design, fabrication and analysis of behavior by full-scale ver-ification testing for the tail rotor blade of composite laminated materials for a heavy transport helicopter is given. The verification test program for the tail rotor blade encompassed static and dynamic test-ing. The static tests of the blade involved experimental evaluation of torsional and flexional blade stiffness and its elastic axis position. Dynamic tests involved testing of vibratory charac-teristics and testing of blade fatigue characteristic. In structural vibration tests natural frequen-cy, vibration modes and damping ratio for the structure were measured. The fatigue analysis of the structure of blade root section was performed after fatigue test cycles for detection of laminate separation, tolerance and distortion of crossections of structure.
Aluminium alloys are used in many applications (e.g. engine blocks) exploiting their low density,... more Aluminium alloys are used in many applications (e.g. engine blocks) exploiting their low density, mechanical properties, corrosion resistibility and processability. Sand casting is a widely used process for aluminium alloys casting. The changes of temperature distribution in the alloy during the cooling influence residual stresses in the part, resulting in shape change. Therefore, additional process of thermal stress relief has to be involved, raising the temperature of the part by several hundred degrees under carefully controlled conditions, holding at the high temperature until the bulk of the stresses removes, and then slowly cooling the part in order to prevent introducing new residual stresses. For some parts, this has to be done several times during the manufacturing process (2, 3). This paper presents the results of a numerical simulation of the temperature, temperature gradient and thermal flux distribution changes in the aluminium casting and mold during the solidification...
Polymer matrix composite materials are excellent candidates for applications requiring exact diel... more Polymer matrix composite materials are excellent candidates for applications requiring exact dielectric properties, such as radio wave propagation and remote sensing applications. In this paper analytical method for material dielectric constant and loss tangent prediction is presented. Model is experimentally verified for E-glass fibers embedded in DER 324 epoxy matrix, for 100 KHz frequency.
In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The... more In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The construction of the blade is fully composite with the honeycomb core. The approach to determining structure mode shapes and natural frequencies is presented. Modified blade consists of core material, 3D unidirectional composite spar and thin carbon composite facesheets as blade skin. To determine the stiffness of the honeycomb core, the equivalent mass approach was used. Several methods of eigenvalue extraction have been investigated in order to find optimal method which can be used in dynamic analysis of composite structures containing honeycomb cores. Among all extraction methods investigated, it was found that combined Lanczos method is most effective in terms of accuracy and CPU time for eigenvalue extraction in composite structures with honeycomb core having large number of degrees of freedom. Strain energies for first four mode shapes of modified helicopter blade have been calcula...
Like their metal counterparts, composites are damage-prone. To restore the load bearing capacity ... more Like their metal counterparts, composites are damage-prone. To restore the load bearing capacity of damaged composite structure suitable repair technique has to be applied. Repair techniques, developed over the years, for metallic structures, are not directly applicable to composites; therefore, adequate and efficient composite repair techniques have to be developed. The extent of damage induced determines whether the deteriorated composite component needs to be repaired or replaced. The choice between replacing or repairing a structural component is governed by a number of factors such as the availability of spares, feasibility of repair, structural integrity requirements and inspection requirements for the repair. In most cases, component replacement is not economically feasible solution; thus, repair is the only viable solution. The article presents application of PMI (Polymethacrylimide) syntactic foam, as a repair material for damaged high density honeycomb core, in sandwich st...
In this paper we present numerical results of conceptual design study of an UAV which uses Coanda... more In this paper we present numerical results of conceptual design study of an UAV which uses Coanda Effect for lift production. Results indicate the ability of manuveuring by creating asymmetric flow patterns which lead to uneven lift production and resulting force with horizontal component necessary for establishing forward flight conditions.
Laminated composites have an important application in modern aeronautical structures. They have e... more Laminated composites have an important application in modern aeronautical structures. They have extraordinary properties, like high strength, stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to impact loads. As a consequence of that, impact damage initiation and growth are appearing in them. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date a lot of models for impact damages in laminates have been developed with higher or lower accuracy. Those models can replace real and expensive testing in laminated structures with some approximation. By using specialized software the damage parameters in laminate aircraft structures can be predicted (at certain conditions). In that way numerical simulation of impact on certain laminates can be done and the obtained results from the simulations presented in a form of graphic damage distributions.
Laminated composites have an important application in modern aeronautical structures. They have e... more Laminated composites have an important application in modern aeronautical structures. They have extraordinary properties, like high strength, stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to impact loads. As a consequence of that, impact damage initiation and growth are appearing in them. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date a lot of models for impact damages in laminates have been developed with higher or lower accuracy. Those models can replace real and expensive testing in laminated structures with some approximation. By using specialized software the damage parameters in laminate aircraft structures can be predicted (at certain conditions). In that way numerical simulation of impact on certain laminates can be done and the obtained results from the simulations presented in a form of graphic damage distributions.
Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing... more Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing vibrations in the seat. In order to determine the suitability and potential of cockpit floor -seat connections we conducted an experiment where measurements were taken and seat vibration analysis conducted. Vibrations parameters were measured for maximum engine and propeller speed. This analysis indicates that passive vibrations damping or cockpit floor -seat connections functionality depends on flights profile and vibrations frequency. The connection in question was behaving like a vibration multiplier on the 3 rd and 4 th harmonic as well as on the 3,5 sub-harmonic in individual flight modes on basic propeller rotation frequency, however, it behaved as a vibration silencer on all other frequencies. Analysis of the experimental data has shown that it would be justified to start improving the self adaptive unit for active vibration reduction for pilot seats.
Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing... more Original scientific paper Improving aircraft pilot comfort requires continuous work in decreasing vibrations in the seat. In order to determine the suitability and potential of cockpit floor -seat connections we conducted an experiment where measurements were taken and seat vibration analysis conducted. Vibrations parameters were measured for maximum engine and propeller speed. This analysis indicates that passive vibrations damping or cockpit floor -seat connections functionality depends on flights profile and vibrations frequency. The connection in question was behaving like a vibration multiplier on the 3 rd and 4 th harmonic as well as on the 3,5 sub-harmonic in individual flight modes on basic propeller rotation frequency, however, it behaved as a vibration silencer on all other frequencies. Analysis of the experimental data has shown that it would be justified to start improving the self adaptive unit for active vibration reduction for pilot seats.
In this article, a formulation of a point-collocation method in which the unknown function is app... more In this article, a formulation of a point-collocation method in which the unknown function is approximated using global expansion in tensor product Bernstein polynomial basis is presented. Bernstein polynomials used in this study are defined over general interval [a,b]. Method incorporates several ideas that enable higher numerical efficiency compared to Bernstein polynomial methods that have been previously presented. The approach is illustrated by a solution of Poisson, Helmholtz and Biharmonic equations with Dirichlet and Neumann type boundary conditions. Comparisons with analytical solutions are given to demonstrate the accuracy and convergence properties of the current procedure. The method is implemented in an open-source code, and a library for manipulation of Bernstein polynomials bernstein-poly, developed by the authors.
Abstract This paper presents the analysis of the survivability of a heavy transport helicopter ta... more Abstract This paper presents the analysis of the survivability of a heavy transport helicopter tail rotor blade made of composite laminated materials after ballistic damage made by the bullet of 7.9 mm calibre shoulder weapons. Penetrating damages made in the root part of ...
Page 1. 583 Application of Fuzzy Logic in Solving Problems from the Area of Reliability and Maint... more Page 1. 583 Application of Fuzzy Logic in Solving Problems from the Area of Reliability and Maintenance of Aircraft Systems Milenko Zivaljevi~ and Bogko Ra~uo Aeronautical Department, Faculty of Mechanical Engineering ...
This paper presents a method for determination of optimum positions of single wind turbines withi... more This paper presents a method for determination of optimum positions of single wind turbines within the wind farms installed on arbitrary configured terrains, in order to achieve their maximum production effectiveness. This method is based on use of the genetic algorithm as optimization technique. The wind turbine aerodynamic calculation is unsteady, based on the blade modeled as a vortex lattice and a free-wake type airflow behind the blade. Optimization method is developed for two different fitness functions. Both functions use the total energy obtained from the farm as one of the key variables. The second also involves the total investments in a single wind turbine, so the optimization process can also include the total number of turbines as an additional variable. The method has been tested on several different terrain configurations, with special attention paid to the overall algorithm performance improvements by selecting certain genetic algorithm parameters.
Tailoring dielectric properties of engineering materials has become very important since many rad... more Tailoring dielectric properties of engineering materials has become very important since many radio wave propagation problems and remote sensing applications depend on correct values of these material properties. Prediction of material dielectric constant and loss tangent is of paramaunt importance. Polymer matrix composite materials are excellent candidates for these applications. In this paper analytical method for material dielectric constant and loss tangent prediction is preseneted. The model is experimentally verified for E-glass fibers embedded in epoxy matrix. Test results for 100 kHz to 1 MHz frequency range are presented.
: In this paper experimental results of structural vibratory testing for the light multipurpose h... more : In this paper experimental results of structural vibratory testing for the light multipurpose helicopter main rotor blade of composite laminated materials are presented. The aim of the main rotor blade vibratory testing was to define the basic aeroelastic properties of the blade. This testing included determination of the natural oscillation modes and natural frequency of the structure in oscillations, as well as defining the blade structural damping. The measurement was performed for three different full-scale models with two different types of cores of the main rotor blade: Nomex (phenolic honeycomb) and Rohacell (polyurethane foam), and the results are presented in this paper. KEYWORDS: Structural damping, phenolic honeycomb, polyurethane foam, vibratory characteristics of the helicopter main rotor blade made of composite laminated materials.
: In this paper the design, fabrication and analysis of behavior by full-scale ver-ification test... more : In this paper the design, fabrication and analysis of behavior by full-scale ver-ification testing for the tail rotor blade of composite laminated materials for a heavy transport helicopter is given. The verification test program for the tail rotor blade encompassed static and dynamic test-ing. The static tests of the blade involved experimental evaluation of torsional and flexional blade stiffness and its elastic axis position. Dynamic tests involved testing of vibratory charac-teristics and testing of blade fatigue characteristic. In structural vibration tests natural frequen-cy, vibration modes and damping ratio for the structure were measured. The fatigue analysis of the structure of blade root section was performed after fatigue test cycles for detection of laminate separation, tolerance and distortion of crossections of structure.
Aluminium alloys are used in many applications (e.g. engine blocks) exploiting their low density,... more Aluminium alloys are used in many applications (e.g. engine blocks) exploiting their low density, mechanical properties, corrosion resistibility and processability. Sand casting is a widely used process for aluminium alloys casting. The changes of temperature distribution in the alloy during the cooling influence residual stresses in the part, resulting in shape change. Therefore, additional process of thermal stress relief has to be involved, raising the temperature of the part by several hundred degrees under carefully controlled conditions, holding at the high temperature until the bulk of the stresses removes, and then slowly cooling the part in order to prevent introducing new residual stresses. For some parts, this has to be done several times during the manufacturing process (2, 3). This paper presents the results of a numerical simulation of the temperature, temperature gradient and thermal flux distribution changes in the aluminium casting and mold during the solidification...
Polymer matrix composite materials are excellent candidates for applications requiring exact diel... more Polymer matrix composite materials are excellent candidates for applications requiring exact dielectric properties, such as radio wave propagation and remote sensing applications. In this paper analytical method for material dielectric constant and loss tangent prediction is presented. Model is experimentally verified for E-glass fibers embedded in DER 324 epoxy matrix, for 100 KHz frequency.
In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The... more In the present study, modal analysis has been performed on modified Gazelle helicopter blade. The construction of the blade is fully composite with the honeycomb core. The approach to determining structure mode shapes and natural frequencies is presented. Modified blade consists of core material, 3D unidirectional composite spar and thin carbon composite facesheets as blade skin. To determine the stiffness of the honeycomb core, the equivalent mass approach was used. Several methods of eigenvalue extraction have been investigated in order to find optimal method which can be used in dynamic analysis of composite structures containing honeycomb cores. Among all extraction methods investigated, it was found that combined Lanczos method is most effective in terms of accuracy and CPU time for eigenvalue extraction in composite structures with honeycomb core having large number of degrees of freedom. Strain energies for first four mode shapes of modified helicopter blade have been calcula...
Like their metal counterparts, composites are damage-prone. To restore the load bearing capacity ... more Like their metal counterparts, composites are damage-prone. To restore the load bearing capacity of damaged composite structure suitable repair technique has to be applied. Repair techniques, developed over the years, for metallic structures, are not directly applicable to composites; therefore, adequate and efficient composite repair techniques have to be developed. The extent of damage induced determines whether the deteriorated composite component needs to be repaired or replaced. The choice between replacing or repairing a structural component is governed by a number of factors such as the availability of spares, feasibility of repair, structural integrity requirements and inspection requirements for the repair. In most cases, component replacement is not economically feasible solution; thus, repair is the only viable solution. The article presents application of PMI (Polymethacrylimide) syntactic foam, as a repair material for damaged high density honeycomb core, in sandwich st...
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