<p>The rolling isolation system (RIS) studied in this dissertation functions on the principle of a rolling pendulum; an isolated object rests on a steel frame that is supported at its corners by ball-bearings that roll between shallow steel bowls, dynamically decoupling the floor motion from the response of the object. The primary focus of this dissertation is to develop predictive models that can capture experimentally-observed phenomena and to advance the state-of-the-art by proposing new isolation technologies to surmount current performance limitations. To wit, a double RIS increases the system's displacement capacity, and semi-active and passive damped RISs suppress the system's displacement response.</p><p>This dissertation illustrates the performance of various high-performance isolation strategies using experimentally-validated predictive models. Effective modeling of RISs is complicated by the nonholonomic and chaotic nature of these systems which to date has not received much attention. Motivated by this observation, the first part of this dissertation addresses the high-fidelity modeling of a single, undamped RIS, and later this theory is augmented to account for the double (or stacked) configuration and the supplemental damping via rubber-coated bowl surfaces. The system's potential energy function (i.e. conical bowl shape) and energy dissipation model are calibrated to free-response experiments. Forced-response experiments successfully validate the models by comparing measured and predicted peak displacement and acceleration responses over a range of operating conditions.</p><p>Following the experimental analyses, numerical simulations demonstrate the potential benefits of the proposed technologies. This dissertation presents a method to optimize damping force trajectories subject to constraints imposed by the physical implementation of a particular controllable damper. Potential improvements in terms of acceleration response are shown to be achievable with the semi-active RIS. Finally, extensive time-history analyses establish how the undamped and damped RISs perform when located inside biaxial, hysteretic, multi-story structures under recorded earthquake ground motions. General design recommendations, supported by critical-disturbance spectra and peak-response distributions, are prescribed so as to ensure the uninterrupted operation of vital equipment.</p> / Dissertation

<p>The main objectives of this research are: (i) to elaborate a unified nonlinear viscoelastic model for rubber-like materials, in finite strain, accounting for material softening under deformation, and for damage induced anisotropy, (ii) to conceive, implement and test, simple, robust and efficient frictional rolling and sliding contact algorithms, in steady-state, as alternatives to existing, general purpose, contact solving strategies, (iii) to develop and verify high fidelity and computationally efficient modeling tools for isotropic and anisotropic viscoelastic objects in steady-state motion, (iv) to investigate, numerically and through experimentation, the influence of various material parameters, including material nonlinearities such at the Payne effect and the Mullins effect, as well as geometric parameters and contact surface conditions, on viscoelastic rolling resistance, and (iv) to explore, analytically and through experimentation, the conditions under which favorable mechanical synergies occur between material components and develop novel composites with improved structural performances.</p><p>A new constitutive model that unifies the behavioral characterizations of rubber-like materials in a broad range of loading regimes is proposed. The model reflects two fundamental aspects of rubber behavior in finite strain: (i) the Mullins effect, and (ii) hyper-viscoelasticity with multiple time scales, including at high strain rates. Suitable means of identifying the system's parameters from simple uniaxial extension tests are explored. A directional approach extending the model to handle softening induced anisotropy is also discussed.</p><p>Novel, simple, and yet robust and efficient algorithms for solving steady-state, frictional, rolling/sliding contact problems, in two and three dimensions are presented. These are alternatives to powerful, well established, but in particular instances, possibly `cumbersome' general-purpose numerical techniques, such as finite-element approaches based on constrained optimization. The proposed algorithms are applied to the rolling resistance of cylinders and spheres.</p><p>Two and three-dimensional boundary element formulations of isotropic, transversely isotropic, and fully orthotropic, compressible and incompressible, viscoelastic layers of finite thickness are presented, in a moving frame of reference. The proposed formulations are based on two-dimensional Fourier series expansions of relevant mechanical fields in the continuum of the layers and support any linear viscoelastic material model characterized by general frequency-domain master-curves. These modeling techniques result in a compliance matrix for the upper boundary of the layers, including the effects of steady-state motion. Such characterizations may be used as components in various problem settings to generate sequences of high fidelity solutions for varying parameters. These are applied, in combination with appropriate contact solvers, to the rolling resistance of rigid cylinders and spheres.</p><p>The problem of a viscoelastic sphere moving across a rigid surface is significantly more complicated than that of a rigid indenter on a viscoelastic plane. The additional difficulties raised by the former may explain why previous work on this topic is so sparse. A new boundary element formulation for the multi-layered viscoelastic coating of a rigid sphere is developed. The model relies on the assumption of a relatively small contact surface in order to decouple equilibrium equations in the frequency domain. It is applied in combination with an adapted rolling contact solving strategy to the rolling resistance of a coated sphere.</p><p>New modeling approaches yielding rolling resistance estimates for rigid spheres (and cylinders) on viscoelastic layers of finite thicknesses are also introduced, as lower-cost alternatives to more comprehensive solution-finding strategies, including those proposed in this work. Application examples illustrate the capabilities of the different approaches over their respective ranges of validity.</p><p>The computational tools proposed in this dissertation are verified by comparison to dynamic finite element simulations and to existing solutions in limiting cases. The dependencies of rolling resistance on problem parameters are explored. It is for instance shown that, on orthotropic layers, the dissipated power varies with the direction of motion, which suggests new ways of optimizing the level of damping in various engineering applications of very high impact. Interesting lateral viscoelastic effects resulting from material asymmetry are unveiled. These phenomena could be harnessed to achieve smooth and `invisible' guides across three-dimensional viscoelastic surfaces, and hence suggest new ways of controlling trajectories, with a broad range of potential applications.</p><p>A new experimental apparatus is designed and assembled to measure viscoelastic rolling resistance. Experiments are conducted by rolling steel balls between sheets of rubber. Principal sources of measurement error, specific to the device, are discussed. Rolling resistance predictions are obtained using the computational tools presented in this dissertation, and compared to the measurements. Interesting conclusions are drawn regarding the fundamental influence of the Payne effect on viscoelastic rolling friction.</p><p>The work presented in this dissertations finally touches on the mechanical behavior of casing-infill composite tubes, as potential new lightweight structural elements. The axial behavior of composite circular tubes is addressed analytically. The influence of material parameters and geometry on structural performances are revealed and presented in original graphical forms. It is for instance shown that significantly improved overall stiffness and capacity at yield can be obtained using a moderately soft and highly auxetic infill, which further highlights the need to develop new lightweight auxetic materials, without compromising their stiffness. It is furthermore concluded that limited mechanical synergies can be expected in metal-polymer composite tubes, within the linear range of the materials involved. This prediction is confirmed by a bending experiment conducted on an Aluminum-Urethane composite tube. The experiment however reveals unexpected and quite promising mechanical synergies under large deformations. This novel composite has a potential influence on the design and performance of lightweight protecting structures against shocks and accelerations due to impacts, which justifies that it be characterized further.</p> / Dissertation

Compostos elastoméricos a base de borracha natural (NR) e copolímero de butadieno-estireno (SBR) utilizados na banda de rodagem de pneus são tradicionalmente reticulados com enxofre. O uso de peróxidos e co-agentes na reticulação desses compostos ainda é um desafio a se superar com relação às propriedades viscoelásticas requeridas, de extrema importância para um bom desempenho e vida útil dos pneus. Neste trabalho foi avaliado o uso de peróxidos sem e com co-agentes na reticulação de compostos NR/SBR com o intuito de avaliar a eficiência destes na manutenção das propriedades relevantes em relação a um composto tradicionalmente usado na confecção de banda de rodagem de pneus. Onze formulações com diferentes sistemas de reticulação foram preparadas, sendo uma de referência. Foram avaliadas propriedades físicas como dureza, densidade, tração, resistência ao rasgamento, resiliência, abrasão e DPC, e o comportamento dos compostos de NR/SBR com relação ao inchamento em tolueno. As propriedades dinâmicomecânicas dos compostos NR/SBR foram analisadas por DMA e RPA. Os compostos NR/SBR contendo somente peróxidos não apresentaram propriedades comparáveis ao composto de referência vulcanizado com enxofre. Os compostos contendo os sistemas peróxidos/co-agentes, BIS F 40 A-Retilink T40 (composto 10) e BIS F 40 A-Retilink TA 70 (composto 11) apresentaram os melhores resultados. O composto 10 e o composto de referência (composto 1) apresentaram valores similares de tan d a 60°C e tan d a 0°C (DMA), os quais estão correlacionados às propriedades de resistência ao rolamento e tração no molhado, respectivamente. Os resultados mostraram a possibilidade de uso de certos sistemas peróxido/co-agente em compostos de NR/SBR, em substituição ao sistema com enxofre, sem perda de propriedades, tendo como vantagem a redução de componentes na formulação, redução de tempo de processamento, e consequentemente custo da produção de bandas de rodagem. / Rubber compounds based on natural rubber (NR) and styrene-butadiene rubber (SBR) used on tire tread are traditionally crosslinked with sulfur. The use of peroxides and co-agents in crosslinking of these compounds is still a challenge to be achieved, considering the required viscoelastic properties which are extremely important for a good tire performance and lifetime. In this work it was evaluated the use of peroxide systems with and without co-agents as crosslinking agents for NR/SBR compounds, with the aim of evaluating the efficiency of maintaining the key properties related to the traditionally used in the manufactory of tire tread. Eleven formulations with different systems were prepared, a one as a reference. Physical properties such as hardness, density, tensile strength, tear, resilience, abrasion and compression set and the behavior of NR/SBR compounds in relation of swelling Toluene were evaluated. The dynamic mechanical properties of the NR/SBR cured compounds were analysed by DMA and RPA. The NR/SBR compounds cured with only peroxide had poorer properties when compared to the reference compound vulcanized with sulfur. On the other hand, the compounds cured with proxide/co-agents, BIS F40 plus Retilink T40 (compound 10) or plus T70A (compound 11) showed better results.The compound 10 and the reference compound (compound 1) showed similar results of tan d 60 °C and tan d 0 °C (DMA), which are correlated to rolling resistance and wet traction, respectively. The results demonstrate the possibility of using a peroxide/co-agent as a cure system in NR/SBR compound instead of a sulfur-cured compound for tire tread applications, without the loss of desirable properties, lower processing times and consequently reducing manufacturing costs.

Compostos elastoméricos a base de borracha natural (NR) e copolímero de butadieno-estireno (SBR) utilizados na banda de rodagem de pneus são tradicionalmente reticulados com enxofre. O uso de peróxidos e co-agentes na reticulação desses compostos ainda é um desafio a se superar com relação às propriedades viscoelásticas requeridas, de extrema importância para um bom desempenho e vida útil dos pneus. Neste trabalho foi avaliado o uso de peróxidos sem e com co-agentes na reticulação de compostos NR/SBR com o intuito de avaliar a eficiência destes na manutenção das propriedades relevantes em relação a um composto tradicionalmente usado na confecção de banda de rodagem de pneus. Onze formulações com diferentes sistemas de reticulação foram preparadas, sendo uma de referência. Foram avaliadas propriedades físicas como dureza, densidade, tração, resistência ao rasgamento, resiliência, abrasão e DPC, e o comportamento dos compostos de NR/SBR com relação ao inchamento em tolueno. As propriedades dinâmicomecânicas dos compostos NR/SBR foram analisadas por DMA e RPA. Os compostos NR/SBR contendo somente peróxidos não apresentaram propriedades comparáveis ao composto de referência vulcanizado com enxofre. Os compostos contendo os sistemas peróxidos/co-agentes, BIS F 40 A-Retilink T40 (composto 10) e BIS F 40 A-Retilink TA 70 (composto 11) apresentaram os melhores resultados. O composto 10 e o composto de referência (composto 1) apresentaram valores similares de tan d a 60°C e tan d a 0°C (DMA), os quais estão correlacionados às propriedades de resistência ao rolamento e tração no molhado, respectivamente. Os resultados mostraram a possibilidade de uso de certos sistemas peróxido/co-agente em compostos de NR/SBR, em substituição ao sistema com enxofre, sem perda de propriedades, tendo como vantagem a redução de componentes na formulação, redução de tempo de processamento, e consequentemente custo da produção de bandas de rodagem. / Rubber compounds based on natural rubber (NR) and styrene-butadiene rubber (SBR) used on tire tread are traditionally crosslinked with sulfur. The use of peroxides and co-agents in crosslinking of these compounds is still a challenge to be achieved, considering the required viscoelastic properties which are extremely important for a good tire performance and lifetime. In this work it was evaluated the use of peroxide systems with and without co-agents as crosslinking agents for NR/SBR compounds, with the aim of evaluating the efficiency of maintaining the key properties related to the traditionally used in the manufactory of tire tread. Eleven formulations with different systems were prepared, a one as a reference. Physical properties such as hardness, density, tensile strength, tear, resilience, abrasion and compression set and the behavior of NR/SBR compounds in relation of swelling Toluene were evaluated. The dynamic mechanical properties of the NR/SBR cured compounds were analysed by DMA and RPA. The NR/SBR compounds cured with only peroxide had poorer properties when compared to the reference compound vulcanized with sulfur. On the other hand, the compounds cured with proxide/co-agents, BIS F40 plus Retilink T40 (compound 10) or plus T70A (compound 11) showed better results.The compound 10 and the reference compound (compound 1) showed similar results of tan d 60 °C and tan d 0 °C (DMA), which are correlated to rolling resistance and wet traction, respectively. The results demonstrate the possibility of using a peroxide/co-agent as a cure system in NR/SBR compound instead of a sulfur-cured compound for tire tread applications, without the loss of desirable properties, lower processing times and consequently reducing manufacturing costs.

Compostos elastoméricos a base de borracha natural (NR) e copolímero de butadieno-estireno (SBR) utilizados na banda de rodagem de pneus são tradicionalmente reticulados com enxofre. O uso de peróxidos e co-agentes na reticulação desses compostos ainda é um desafio a se superar com relação às propriedades viscoelásticas requeridas, de extrema importância para um bom desempenho e vida útil dos pneus. Neste trabalho foi avaliado o uso de peróxidos sem e com co-agentes na reticulação de compostos NR/SBR com o intuito de avaliar a eficiência destes na manutenção das propriedades relevantes em relação a um composto tradicionalmente usado na confecção de banda de rodagem de pneus. Onze formulações com diferentes sistemas de reticulação foram preparadas, sendo uma de referência. Foram avaliadas propriedades físicas como dureza, densidade, tração, resistência ao rasgamento, resiliência, abrasão e DPC, e o comportamento dos compostos de NR/SBR com relação ao inchamento em tolueno. As propriedades dinâmicomecânicas dos compostos NR/SBR foram analisadas por DMA e RPA. Os compostos NR/SBR contendo somente peróxidos não apresentaram propriedades comparáveis ao composto de referência vulcanizado com enxofre. Os compostos contendo os sistemas peróxidos/co-agentes, BIS F 40 A-Retilink T40 (composto 10) e BIS F 40 A-Retilink TA 70 (composto 11) apresentaram os melhores resultados. O composto 10 e o composto de referência (composto 1) apresentaram valores similares de tan d a 60°C e tan d a 0°C (DMA), os quais estão correlacionados às propriedades de resistência ao rolamento e tração no molhado, respectivamente. Os resultados mostraram a possibilidade de uso de certos sistemas peróxido/co-agente em compostos de NR/SBR, em substituição ao sistema com enxofre, sem perda de propriedades, tendo como vantagem a redução de componentes na formulação, redução de tempo de processamento, e consequentemente custo da produção de bandas de rodagem. / Rubber compounds based on natural rubber (NR) and styrene-butadiene rubber (SBR) used on tire tread are traditionally crosslinked with sulfur. The use of peroxides and co-agents in crosslinking of these compounds is still a challenge to be achieved, considering the required viscoelastic properties which are extremely important for a good tire performance and lifetime. In this work it was evaluated the use of peroxide systems with and without co-agents as crosslinking agents for NR/SBR compounds, with the aim of evaluating the efficiency of maintaining the key properties related to the traditionally used in the manufactory of tire tread. Eleven formulations with different systems were prepared, a one as a reference. Physical properties such as hardness, density, tensile strength, tear, resilience, abrasion and compression set and the behavior of NR/SBR compounds in relation of swelling Toluene were evaluated. The dynamic mechanical properties of the NR/SBR cured compounds were analysed by DMA and RPA. The NR/SBR compounds cured with only peroxide had poorer properties when compared to the reference compound vulcanized with sulfur. On the other hand, the compounds cured with proxide/co-agents, BIS F40 plus Retilink T40 (compound 10) or plus T70A (compound 11) showed better results.The compound 10 and the reference compound (compound 1) showed similar results of tan d 60 °C and tan d 0 °C (DMA), which are correlated to rolling resistance and wet traction, respectively. The results demonstrate the possibility of using a peroxide/co-agent as a cure system in NR/SBR compound instead of a sulfur-cured compound for tire tread applications, without the loss of desirable properties, lower processing times and consequently reducing manufacturing costs.

Orientador: José Maria Campos Dos Santos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-27T18:02:49Z (GMT). No. of bitstreams: 1 Gali_MarcosRodolfo_M.pdf: 8846565 bytes, checksum: b82ad0724e54e69642945eea2e744eaf (MD5) Previous issue date: 2015 / Resumo: Em 2012, Rhyne & Cron desenvolveram um modelo analítico para estimar a mínima Resistência ao Rolamento (RR) para pneus destinados aos veículos de passageiro. Os parâmetros estudados pelos autores foram a área de contato, a espessura e a largura da rodagem, o raio da cintura metálica, o módulo elástico do composto da banda de rodagem, a carga vertical imposta, a pressão de inflação do pneu e a área efetiva de contato do pneu com o solo. Para o fator área de contato, os autores simplificaram a abordagem matemática que defini a interação entre o pneu e o pavimento, não considerando a área total formada devido à deformação na região de interação com o pavimento (que muda com a pressão interna do pneu e com a carga imposta sobre o mesmo). O objetivo do presente estudo foi desenvolver um modelo analítico baseado no modelo de Rhyne & Cron, para estimar a resistência ao rolamento de pneus de carga, considerando a área de contato formada na região de interação entre o pneu e o pavimento. Os modelos analíticos foram implementados em MatLab versão R2008a para obtenção das curvas de resistência ao rolamento e compará-las com as curvas obtidas através de modelo numérico que interagiu com um modelo de elementos finitos (FEM). Os resultados dos modelos analíticos e numéricos foram validados e comparados com resultados experimentais obtidos em laboratório segundo condições da norma ISO 28.580. Os resultados obtidos através do modelo analítico proposto mostraram uma satisfatória correlação comportamental quando comparados com as curvas experimentais, sendo uma ferramenta interessante durante o desenvolvimento do projeto do pneu, pois permite ter uma estimativa da resistência ao rolamento / Abstract: In 2012, Rhyne & Cron developed an analytical model to estimate the minimum Rolling Resistance (RR) for tires intended for passenger vehicles. The parameters studied by the authors were the contact area, the thickness and width of the tread, the radius of the metal belt, elastic modulus of the tread compound, the imposed vertical load, the tire inflation pressure and effective contact area tire with ground. For contact area's factor, the authors simplified the mathematical approach that define the interaction between the tire and the ground, not considering the total area formed due to deformation in the interaction region with the ground (which changes with the tire internal pressure and the imposed load). The objective of this study was to develop an analytical model based on the Rhyne & Cron model to estimate the truck tires' rolling resistance, considering the contact area formed at the interaction region between the tire and the pavement. The analytical models were implemented in MatLab R2008a version to obtain the rolling resistance curves and compare them with the curves obtained through numerical model that interacted with a finite element model (FEM). The results of analytical and numerical models were validated by comparison with experimental results obtained according ISO 28580 standard. The obtained results using the proposed analytical model showed a satisfactory behavioral correlation when compared with the experimental curves, being an interesting tool for the development of tire design because it allows having an estimation of the rolling resistance / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

We consider first the single-track bicycle model and state relations between the tires’ lateral forces and the turning radius. From the tire model, a relation between the lateral forces and slip angles is obtained. The extra rolling resistance forces from cornering are by linear approximation obtained as a function of the slip angles. The bicycle model is validated against the Magic-formula tire model from Adams. The bicycle model is then applied on an optimization problem, where the optimal velocity for a track for some given test cases is determined such that the energy loss is as small as possible. Results are presented for how much fuel it is possible to save by driving with optimal velocity compared to fix average velocity. The optimization problem is applied to a specific laden truck. / Vi betraktar först den enspåriga cykelmodellen och ställer upp samband mellan däckens sidokrafter och kurvradien. Genom däcksmodellen fås ett samband för hur sidokrafterna beror av slipvinklarna. De extra rullmotståndskrafterna för kurvor fås via linjär approximation som funktion av slipvinklarna. Cykelmodellen valideras mot en däcksmodell från Adams. Cykelmodellen tillämpas sedan på ett optimeringsproblem där den optimala hastigheten längs en bana för några givna testfall bestäms så att energiförlusten blir så liten som möjligt. Resultat presenteras för hur mycket bränsle det är möjligt att spara genom att köra med optimal hastighet jämfört med fix medelhastighet. Optimeringsproblemet tillämpas på en specifik lastad lastbil.

Considering the more and more important issues concerning the climate changes and the global warming, the automotive industry is paying more and more attention to vehicle concepts with full electric or partly electric propulsion systems. The introduction of electric power sources allow the designers to implement more advanced motion control systems in vehicle, such as active suspensions. An example of this concept is the Autonomous corner module (ACM), designed by S. Zetterström. The ACM is a modular based suspension system that includes all features of wheel control, such as control of steering, wheel torque and camber individually, using electric actuators. With a good control strategy it is believed that is it possible to reduce the fuel consumption and/or increase the handling properties of the vehicle. In particular, camber angle has a significant effect on vehicle handling. However, very few efforts have been done in order to analyse its effects on tire dissipated energy. The aim of this study is to develop a new tire model, having as starting point the simple Brush Tire model, in order to analyse the tire behaviour, in terms of forces generated and energy dissipated, for different dynamic situations. In order to reach this scope, the characteristic equations of the rubber material are implemented in a 3D Multi-Line brush tire model. In this way the energy dissipated, thus the rolling resistance force, can be studied and analysed, considering also the tire geometry. From the results of this work it is possible to assert that the angular parameters (e.g. camber angle) affect the power losses in rolling tires, as well as the tire geometry influences their rolling resistance. Thus, using a good control strategy, it is possible to reduce the power losses in tires.

In Sweden fall-related injuries among the elderly lead to over a thousand deaths and close to 300.0000 hospital visitations annually. Fall related injuries can in many cases lead to serious head injuries along with other fractures. The elderly are more prone to fall and sustain an injury because of conditions such as osteoporosis and weak muscles. Researchers at KTH from the Division of Neuronic Engineering have developed a special floor that absorbs energy from an impact which can reduce the severity of injury when a person falls. There has been research done on the floor focusing on hip fractures which have shown good results. The floor has been set up in an elderly home in Stureby, Stockholm, Sweden, however further testing is needed to fully develop the floor to its maximum capacity. One goal of this master thesis was to investigate certain obstacles with the floor which arose during testing in Stureby. One of the challenges was that the floor had greater rolling resistance since it is softer than a normal concrete floor. The experiment was done by using a dynamo meter to measure the force needed to move a test wagon with a fixed weight and different sizes of wheels. Another goal of this thesis was to investigate head impacts on the KTH floor. That was done in a helmet testing lab at Mips helmet company. There a dummy head was dropped from various heights and the acceleration was measured. The 1st principle strain of the brain was calculated from the collected data. Other companies have created similar floors so it was a part of the thesis to compare the KTH floor with its competitors. The results from the rolling resistance showed that by increasing the width and diameter of the wheels there was less force needed to move the test wagon. Further tests are needed to investigate the problem regarding the indentation issues seen on the floor set up in Stureby. Some research has already begun with different types of linoleum and glue. In the head impact studies, the KTH floor showed the best results of all tested floors when dropped from 60 cm. However, when dropped from 100 cm a competitor floor showed better results in the resultant translational acceleration.

Fall-related injuries are common problems in elderly care in particular. These can cause brain damage and hip fractures, which in many cases can be serious. To reduce or mitigate the damage, various safety measures have been developed. One of them concerns a change in the surroundings, more specifically, the floor. At KTH within the Division of Neuronic Engineering, research has been done on how the impact of the case can be minimized and a shock absorbing floor (SAF) was developed. Diving problems with this type of flooring are that heavy medical beds sink into the floor, which means increased rolling resistance and thus long-term damage to both the floor and the medical staff. The aim of this thesis was to investigate how much rolling resistance can be minimized by building a downscaled hovering device based on hovercraft technology. The purpose was to enable the device to possibly be mounted under hospital beds and create a lifting force. To evaluate the performance, force measurements were performed on KTH SAF with different weights and with the use of a dynamometer. The results showed that the device reduced rolling resistance by up to 57.4% with additional weight. Four axial fans were used together with manual control of the speed of each fan. The selected components were made taking into account, in particular, cost, weight and dimensions and can thus also be limiting factors for this thesis. For future work, effective soundproofing is needed for this solution to be possible to be implemented in a hospital environment. Furthermore, studies needs to be carried out for a full-scale prototype to confirm that an equally large reduction in rolling resistance can be achieved.