Proposal of a coast-down model including speed dependent coefficients for the retarding forces

Coast-down techniques are widely used on bicycles and motorized vehicles in order to estimate retarding forces and respective coefficients. The mathematical model behind coast-down data analysis is usually based on the assumption that both drag and rolling resistance coefficients do not depend on the vehicle speed. This assumption restricts the model validity to the specifically tested range of speeds and provide averaged values for the force coefficients. In the attempt to overcome this limit, the proposal of a complete polynomial equation of motion is developed, evaluated and discussed on a human powered vehicle case study. The analysis points out that the extended model is adequate for experimental data fitting and could potentially provide a more reliable power-speed prediction outside the testing range. However, the expressions included in the model in order to account for speed dependent coefficients is a first approximation with limited capability to represent these complex phenomena. As a consequence, further experimental testing is needed in order to achieve a validation. Advantages and side effects of both the classical and the complete polynomial models are discussed, concluding that the two approaches could be complementary and could answer different needs that specifically depend on the purpose of the coast-down analysis

Deep Cryogenic treatment: a bibliographic review

The use of cryogenic treatment (CT) to improve mechanical properties of materials has been developed from the end of the Sixties. At the present time, the initial mistrust about CT has been cleared up and many papers about different materials reporting laboratory tests results, microstructural investigations and hypothesis on CT strengthening mechanisms have been published. The removal of retained austenite combined with fine dispersed η-carbides precipitation have been widely observed and their effects on mechanical properties have been measured. In addition, some recent studies have pointed out a different mechanism for fatigue strengthening of stainless steels, which involves nano-martensite formation during the CT. The present paper summarizes the state of art about CT, focusing on methods, parameters, results and assumed microstructural mechanisms, in order to get a starting point for new researches to com

Finite Element Thermo-Structural Methodology for Investigating Diesel Engine Pistons with Thermal Barrier Coating

Traditionally, in combustion engine applications, metallic materials have been widely employed due to their properties: castability and machinability with accurate dimensional tolerances, good mechanical strength even at high temperatures, wear resistance, and affordable price. However, the high thermal conductivity of metallic materials is responsible for consistent losses of thermal energy and has a strong influence on pollutant emission. A possible approach for reducing the thermal exchange requires the use of thermal barrier coating (TBC) made by materials with low thermal conductivity and good thermo-mechanical strength. In this work, the effects of a ceramic coating for thermal insulation of the piston crown of a car diesel engine are investigated through a numerical methodology based on finite element analysis. The study is developed by considering firstly a thermal analysis and then a thermo-structural analysis of the component. The loads acting on the piston are considered both separately and combined to achieve a better understanding of their mutual interaction and of the coating effect on the stress state. The thermal analysis pointed out a decrease of temperature up to 40°C in the upper part of the piston for the coated model. Despite the lower deformations induced by the reduced thermal load, the stiffening effect provided by the TBC results in higher peak stress. However, the lower temperature field inside the piston compensates by allowing higher yielding stresses for the component and reducing the impact on the safety factor. The methodology is validated by comparison of the model results with numerical data available from the literature; limitations and potential future improvements are also discussed

CFD analysis of internal ventilation in high-speed Human Powered Vehicles

When dealing with fully faired Human Powered Vehicles (HPVs) for speed or endurance record attempts, the need for internal ventilation of the rider arises. Different solutions have been proposed in the literature and in practice by designers and builders of these bicycles. The present paper proposes an analytical approach to design the frontal air inlet according to the VO 2 max of the rider in speed competitions. A 3D computational fluid dynamics (CFD) model is presented to analyze the external and internal flow interaction with respect to three design parameters: the presence of wheel-covers, the location of the rear vent and its geometry. The CFD results predict the wheel-covers save 23 W of aerodynamic power at 125 km/h. A secondary but significant design parameter is the rear vent position, that can provide a further reduction of 11 W at 125 km/h if properly located. Finally, the effect of the rear vent geometry was below the model confidence level, resulting in a likely negligible design parameter

Ciclismo: fisica e fisiologia - 10 risposte della scienza al ciclista curioso

Consumo di ossigeno e di calorie, potenza ed energia sviluppate, efficienza del motore umano, soglia anaerobica ed acido lattico, velocità ascensionale, pedalata rotonda e a stantuffo, spinta sui pedali, produzione e dispersione del calore corporeo, le resistenze esterne contro cui la bicicletta deve farsi strada, le modifiche morfologiche e fisiologiche che intervengono con l'età, le risposte dei sistemi respiratorio e cardio-vascolare all'esercizio fisico, e tanto altro: per ogni concetto si trova qui una dettagliata spiegazione, attinta dalla fisica e dalla fisiologia

Design and Construction of a Moving Cassette Electronic Gear-Shift for Human Powered Vehicles

In this article, the design and implementation of an electronic bicycle gear-shift with moving cassette is presented. The niche context where the needs developed is explained and the project evolution over two versions is described. Technical aspects considered in the design phase are discussed and detailed explanations of hardware layout and control software logic are given. Performance of the two implemented versions are compared through data recorded during the target competition (pedaling cadence and torque), highlighting the higher reliability of the second design thanks to mechanical simplification and a more stable position feedback. An additional comparison with cadence data from other competitors in a speed-challenge competition is then presented to highlights the main benefit obtained: a reduced variance in cadence that enables the rider to pedal at his optimal rate since the early stage and through the whole run-up. Finally, the current development of the project under a Proof of Concept grant is presented by discussing its potential application on the standard bicycle market, the need for an assessment of its value proposition and the main obstacles to overcome for complying (or not) with the current market standards. The article offers an overview of practical aspects to be considered when designing high-speed human powered vehicle transmissions, including technical details of an innovative solution and critical considerations about the possibility of such a specific design to develop within the standard bicycle market

PulsaR design: CFD comparative study of speed-record Human Powered Vehicles

High speed Human Powered Vehicles (HPVs) are specifically designed in order to race at the World Human Powered Speed Challenge (WHPSC), an event taking place in Nevada, with the purpose of pushing streamlined bike technology to the limits. The poster shows the comparative CFD analysis made during the design process of PulsaR. The prototype was built in the 1st semester of 2015 and raced at the WHPSC in September after about 850 km of testing. Andrea Gallo achieved the Italian Speed Record at 116.19 km/h, becoming the 24th fastest rider in the history of this discipline

Numerical Study of Power Loss and Lubrication of Connecting Rod Big-End

A hydrodynamic lubrication analysis for connecting rod big-end bearing is conducted. The effects of engine speed, operating condition, lubricant viscosity and oil temperature on tribological performance of big-end bearing have been examined. Force equilibrium is solved to define instantaneous eccentricity between journal and bearing to have accurate estimation of oil film thickness at interface of connecting rod big-end bearing and crankpin. Connecting rod big-end is treated as π film hydrodynamic journal bearing and finite difference scheme is applied to calculate generated hydrodynamic pressure and frictional power loss at each crank angle. Beside the development of analytical formulation, well-known Mobility model introduced by Booker has been employed to be compared with the analytical model. The presented analytical model reduces the complexity and the numerical effort with respect to Mobility method, thus shortening the computation time. The simulation results show good agreement between analytical model, Mobility approach and experimental data

Correlation between Microstructural Alteration, Mechanical Properties and Manufacturability after Cryogenic Treatment: A Review

Cryogenic treatment is a supplemental structural and mechanical properties refinement process to conventional heat treatment processes, quenching, and tempering. Cryogenic treatment encourages the improvement of material properties and durability by means of microstructural alteration comprising phase transfer, particle size, and distribution. These effects are almost permanent and irreversible; furthermore, cryogenic treatment is recognized as an eco-friendly, nontoxic, and nonexplosive process. In addition, to encourage the application of sustainable techniques in mechanical and manufacturing engineering and to improve productivity in current competitive markets, cryo-treatment can be considered as a promising process. However, while improvements in the properties of materials after cryogenic treatment are discussed by the majority of reported studies, the correlation between microstructural alteration and mechanical properties are unclear, and sometimes the conducted investigations are contradictory with each other. These contradictions provide different approaches to perform and combine cryogenic treatment with pre-and post-processing. The present literature survey, mainly focused on the last decade, is aimed to address the effects of cryogenic treatment on microstructural alteration and to correlate these changes with mechanical property variations as a consequence of cryo-processing. The conclusion of the current review discusses the development and outlines the trends for the future research in this field

Industry 4.0 Impact on Evolution of Product Development: The Bicycle Saddle Case Study

The emerging new technologies, the rapid change of market demand, and the influence of society moved the companies to be innovative and to improve their product as continuously as effectively. Therefore, the need for smart manufacturing systems and smart products arises to allow the manufacturer satisfying current customer needs, within a context of highly competitive market. The Industry 4.0 initiative provides a base toward the smart manufacturing, aimed at producing the smart and highly connected product. This study analyzes the role of Industry 4.0 technologies in the product development process. Particularly, it investigates how the whole life cycle of product is conceived, to comply with the Industry 4.0 main features. The paper focuses upon a customized bike saddle, assumed as a case study. The saddle comfort depends on many factors, including the rider anatomy. Therefore, it raises the necessity of profound customization to satisfy the user needs. Artificial intelligence techniques, such as data mining for market research, deep learning for customized design, and additive manufacturing technologies, as the stereolithography for 3D printing, concur all to enable the implementation of the Industry 4.0 paradigm, and to innovate significantly the product