Comparison of modal characteristic of wrapped and winded composite tubes from carbon prepreg

Constructions based on long fiber composite frames gaining significant and irreplaceable position through almost all traffic sectors. The aim of this presented work is a study of composite rods made by two ways from pre impregnated fibres. In technical practice, one can find applications of so called “prepregs”, especially for so-called wrapping, which is a gradual helical layering of wide tapes. This is a quite simply method with a good quality of final parts, but the using is limited only for straight shapes. Therefore, a method called winding, which is a simultaneous deposition of larger number of fiber filaments was used to handle the problem for curved shapes and fluently changed cross-sections. Even though this method could expand the using of presaturated fibres, in a real case compared with wrapped parts there is evident imperfect alignment and mutually storing of placed fibers. This could be mainly caused by a significant tortuosity and stickiness of the individual fiber strands. The objective the carried work was to experimentally compare the vibrational - modal behavior of two almost identical rods. One was winded and the second kind was wrapped with the same structure of layers, weight and curing parameters. The results of the two compared tubes, that should be theoretically identical, were significantly different. Another step was compilation of a numerical model and verify its suitability for parts created with the two mentioned production methods. The numerical model was in a good agreement with the empirical obtained from the experiment with wrapped parts. However, the using of this standard model also for winded tube is questionable, because of the significantly differences in founded natural frequencies

Study of the acoustic attenuation in plaster composites in dependency on added fiber reinforcement

The current trend, with regards to the cost and energy savings, is to combine properties of basic materials and try to obtain so called synergic effect with that we could get significant amplification of their individual properties. The aim of this article is to assess whether this required improvement of the physical properties occurs also for fiber-reinforced construction materials, whose study has been the author work devoted for a long time. This work is focused on assessment of changes in the acoustic attenuation of the basic plaster composites with addition of some high strength fiber reinforcement. The chosen plasters materials are commonly used in building constructions (gypsum, lime-cement, cement). Into those materials that in our case has become the matrix, some basalt and glass fiber dispersion of length 8.5 and 12 mm have been added. An impedance tube was used to the test of materials acoustic absorption. The results show the very good acoustic absorption for all of the tested samples regardless on the ratio of used reinforcement

Characteristic comparison of wound and wrapped composite tubes made from carbon prepreg using modal analysis

The lightweight constructions are nowadays often based on composite materials. The best benefits are possible to obtain especially with a dispersion in the form of long fibres. In this study, the main properties of two almost identical composite rods manufactured from preimpregnated carbon fibres using two different methods will be compared. The first one is called “wrapping” which is helical layering of one wide tape in each ply. The main benefit of this method is good quality of final parts, but we are limited only by straight shapes. The second way “winding”, it is simultaneous deposition of several thinner fiber filaments. This method could handle the problem of curved shapes and fluently variable cross-sections. The disadvantage of this method is imperfect alignment of the placed fibers. This could be caused by a significant tortuosity and stickiness of the individual fiber strands. The goal of the carried work was to experimentally compare the vibrational transfer of these two almost identical rods with the same structure of layers, weight and curing parameters. Based on the certified properties of the base fibres and known boundary conditions, the material model and simulation of the vibrational response was created. The results of the empirical model compared with the experimental on the wrapped part were in good agreement. However, the use of this model also for the wound tubes is questionable, because of the found differences in natural frequencies and a shape of the transfer function. As part of the analytical study also the sensitivity analysis on the mesh quality has been done. As the conclusion is possible to say, that for determination of the main modes the mesh in a solved model could be just standard – it means without visible defects. Changes in the results achieved by improving the mesh quality are just really small. The more significant problem is that with using the contemporary knowledge and methods, it is not possible to simply create analytical model of the wound parts. The only option is trying to adjust the mechanical properties of base materials according to the empirical results

Thermal properties of highly structured composite and aluminium sheets in an aerodynamic tunnel

This article deals with the thermodynamic behaviour of heat shields - structured metal and composite plates. Experiments have been carried out in a wind tunnel with an additional heating, which simulates the heat source from engine or exhaust pipe and simultaneously the airflow generated during a car movement. The tested sheets with hexagonal structure were a standard commercial made of aluminium and a second manufactured by replication (lamination, diffusion) from glass fabric. The airflow in a parallel way along the sheets was analysed experimentally in order to determine the heat transfer efficiency between surfaces of sheets and surrounding airflow. The temperature on the sheets was chosen to observe the effects of different sheets material, various heat power and airflow velocity. During the experiment a thermal input below the sheets and airflow velocity through the tunnel have been changed. The thermal field distribution on the metal sheet is different than in case of composite sheet. For the composite material the thermal field distribution was more homogeneous. This article describe briefly also methods of obtaining real composite geometry based on scanned data and their reconstruction for using in some future numerical models

Thermal properties of highly structured composite and aluminium sheets in an aerodynamic tunnel

This article deals with the thermodynamic behaviour of heat shields - structured metal and composite plates. Experiments have been carried out in a wind tunnel with an additional heating, which simulates the heat source from engine or exhaust pipe and simultaneously the airflow generated during a car movement. The tested sheets with hexagonal structure were a standard commercial made of aluminium and a second manufactured by replication (lamination, diffusion) from glass fabric. The airflow in a parallel way along the sheets was analysed experimentally in order to determine the heat transfer efficiency between surfaces of sheets and surrounding airflow. The temperature on the sheets was chosen to observe the effects of different sheets material, various heat power and airflow velocity. During the experiment a thermal input below the sheets and airflow velocity through the tunnel have been changed. The thermal field distribution on the metal sheet is different than in case of composite sheet. For the composite material the thermal field distribution was more homogeneous. This article describe briefly also methods of obtaining real composite geometry based on scanned data and their reconstruction for using in some future numerical models

Study and verification of the superposition method used for determining the pressure losses of the heat exchangers

This paper deals with study of the pressure losses of the new heat convectors product line. For all devices connected to the heating circuit of the building, it‘s required to declare a tabulated values of pressure drops. The heat exchangers are manufactured in a lot of different dimensions and atypical shapes. An individual assessment of the pressure losses for each type is very time consuming. Therefore based on the resulting data of the experiments and numerical models, an electronic database was created that can be used for calculating the total values of the pressure losses in the optionally assembled exchanger. The measurements are standardly performed by the manufacturer Licon heat hydrodynamic laboratory and the numerical models are carried out in COMSOL Multiphysics. Different variations of the convectors geometry cause non-linear process of energy losses, which is proportionately about 30% larger for the smaller exchanger than for the larger types. The results of the experiments and the numerical simulations were in a very good conjuncture. Considerable influence of the water temperature onto the total size of incurred energy losses has been proven. This is mainly caused by the different ranges of the Reynolds number depending on the viscosity of the used liquid. Concerning to the tested method of superposition, it is not possible to easily find the characteristic values appropriate for the each individual components of the heat exchanger. Every of the components behaves differently, depend on the complexity of the exchanger. However, the correction coefficient, depended on the matrix of the exchanger, that is suitable for the entire range of the developed product line has been found

Optimization of the heat output of wall convectors with using an unconventional slumped glass cover

This paper deals with study of a new shape of the glass cover of heat convectors. Design of the heat convectors is characterized by the low water volume, highly variable geometry, adjustable heat output and the pressure losses that arise when the fluid flow through the exchanger. Based on a new concept of a slumped glass cover of the exchanger have been created some numerical models and also carried out experiments in order to find and optimize an appropriate shape. The glass materials are very specific mainly due to their specific shaping abilities and technological capabilities of manufacturing. The aim is to determine an appropriate shape and a curvature of the glass body and also the position and size of the exchanger. It has been found a significant dependence of the heat exchanger position on to the total heat output of an entire device. Simultaneously has been proved also the dependence of a shape of the cover plate, to the total heat output, that is more considerably for natural than for the forced convection

Optimization of the heat output of wall convectors with using an unconventional slumped glass cover

This paper deals with study of a new shape of the glass cover of heat convectors. Design of the heat convectors is characterized by the low water volume, highly variable geometry, adjustable heat output and the pressure losses that arise when the fluid flow through the exchanger. Based on a new concept of a slumped glass cover of the exchanger have been created some numerical models and also carried out experiments in order to find and optimize an appropriate shape. The glass materials are very specific mainly due to their specific shaping abilities and technological capabilities of manufacturing. The aim is to determine an appropriate shape and a curvature of the glass body and also the position and size of the exchanger. It has been found a significant dependence of the heat exchanger position on to the total heat output of an entire device. Simultaneously has been proved also the dependence of a shape of the cover plate, to the total heat output, that is more considerably for natural than for the forced convection

Study and verification of the superposition method used for determining the pressure losses of the heat exchangers

This paper deals with study of the pressure losses of the new heat convectors product line. For all devices connected to the heating circuit of the building, it‘s required to declare a tabulated values of pressure drops. The heat exchangers are manufactured in a lot of different dimensions and atypical shapes. An individual assessment of the pressure losses for each type is very time consuming. Therefore based on the resulting data of the experiments and numerical models, an electronic database was created that can be used for calculating the total values of the pressure losses in the optionally assembled exchanger. The measurements are standardly performed by the manufacturer Licon heat hydrodynamic laboratory and the numerical models are carried out in COMSOL Multiphysics. Different variations of the convectors geometry cause non-linear process of energy losses, which is proportionately about 30% larger for the smaller exchanger than for the larger types. The results of the experiments and the numerical simulations were in a very good conjuncture. Considerable influence of the water temperature onto the total size of incurred energy losses has been proven. This is mainly caused by the different ranges of the Reynolds number depending on the viscosity of the used liquid. Concerning to the tested method of superposition, it is not possible to easily find the characteristic values appropriate for the each individual components of the heat exchanger. Every of the components behaves differently, depend on the complexity of the exchanger. However, the correction coefficient, depended on the matrix of the exchanger, that is suitable for the entire range of the developed product line has been found

Development of an anti-flood board to protect the interiors and exteriors of the infrastructure

This article deals with the development of an anti-flood board to protect the interior and exterior of various infrastructures, such a houses, cottages or industrial buildings. It was designed prototypes and assembled numerical simulations. In Central Europe and in particular in the Czech Republic, floods are an integral part of the natural water cycle and cause great loss of life and great property damage. The development of new types of mobile anti-flood boards is very important as the design solution is developed for flood protection with regard to minimizing weight, cost of production, easy manipulation, simplicity and speed of installation