Friction modulation in limbless, three-dimensional gaits and heterogeneous terrains

Motivated by a possible convergence of terrestrial limbless locomotion strategies ultimately determined by interfacial effects, we show how both 3D gait alterations and locomotory adaptations to heterogeneous terrains can be understood through the lens of local friction modulation. Via an effective-friction modeling approach, compounded by 3D simulations, the emergence and disappearance of a range of locomotory behaviors observed in nature is systematically explained in relation to inhabited environments. Our approach also simplifies the treatment of terrain heterogeneity, whereby even solid obstacles may be seen as high friction regions, which we confirm against experiments of snakes ‘diffracting’ while traversing rows of posts, similar to optical waves. We further this optic analogy by illustrating snake refraction, reflection and lens focusing. We use these insights to engineer surface friction patterns and demonstrate passive snake navigation in complex topographies. Overall, our study outlines a unified view that connects active and passive 3D mechanics with heterogeneous interfacial effects to explain a broad set of biological observations, and potentially inspire engineering design.

Features of dynamic problems with friction calculation by means of an «ADAMS» package

Актуальность поднимаемых в статье вопросов обусловлена широким применением программных комплексов для численного эксперимента в области механики и необходимостью верификации полученных результатов. В представленной работе отражены возможности программного пакета виртуального моделирования ADAMS для численного анализа динамических задач с учетом трения. В качестве объекта исследования рассмотрено устройство кривошипно-шатунного механизма, имеющего в своём составе фрикционную муфту. Для демонстрации возможностей моделирования задач с учетом трения в ПК ADAMS приведены различные примеры, верифицирующие аналитические решения с численными. Для исследования работы муфты была подтверждена зависимость момента сил трения от относительной скорости и смоделирована работа кривошипно-шатунного механизма. Отдельно была рассмотрена задача о получении коэффициентов трения качения, которые в результате моделирования в ПК ADAMS, оказываются значительно меньше своих предельных коэффициентов трения качения. The relevance of the issues raised in the article is due to the widespread use of software systems for numerical experiments in the field of mechanics and the need to verify the results obtained. Possibilities of the virtual modeling software package ADAMS for the numerical analysis of dynamic tasks taking into account friction are reflected in work. As an object of a research the device of the crank-conrod mechanism in corporating the frictional coupling is considered. For demonstration of tasks taking into account friction modeling opportunities in an ADAMS package various examples verifying analytical decisions with numerical are given. For a research of the coupling the dependence of the friction forces moment operation on relative speed was confirmed and operation of the crank-conrod mechanism is simulated. The task about receiving coefficients of swing friction which as a result of modeling in an ADAMS package, appear much less than the limit coefficients of swing friction was separately considered.

Some Aspects of Shear Behavior of Soft Soil–Concrete Interfaces and Its Consequences in Pile Shaft Friction Modeling

This paper examines the stiffness degradation and interface failure load on soft soil–concrete interface. The friction behavior and its variability is investigated. The direct shear tests under constant normal load were used to establish parameters to hyperbolic interface model which provided a good approximation of the data from instrumented piles. Four instrumented piles were used to obtain reference soil–concrete interface behavior. It was found that the variability of the friction characteristics is the highest for organic clays and the lowest for organic silts. The intact samples exhibit lower shear strength than reconstituted ones. The adhesion varies significantly depending on interface and soil type, which can result in high scatter of the skin friction prediction. The analysis of parameters variability can be used to determine the upper and lower bound of friction behavior on the interface at constant normal load condition. The backward shearing results in decrease in shear strength up to 40% of the precedent forward phase but higher initial stiffness by a factor of between 2 and 3. Presented research provides basic shear and stiffness parameters for four soft soils (organic clay, organic silt, peat, and silty loam) and gives information about variability of interface characteristics.

Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

Study on Friction in Automotive Shock Absorbers Part 2: Validation of Friction Simulations via Novel Single Friction Point Test Rigs

The most important change in the transition from partial to high automation is that the vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorbers with two friction types. The intended viscous friction dissipates the chassis’ vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In the current article, the simulation approach introduced in part 1 of this study is validated against a single friction point and full damper friction measurements. To achieve that, a friction measurement method with novel test rigs has been developed, which allows for reliable determination of the friction behavior of each single friction point, while appropriately resembling the operating conditions of the real damper. The subsequent presentation of a friction simulation using friction model parameters from different geometry shows the general applicability of the overall friction investigation methodology. Accordingly, the presented simulation and measurement approaches enable the investigation of dynamic friction in automotive shock absorbers with significantly increased development efficiency.

Nonlinear Frictional Dynamics on Rolling Contact

The rolling machine element is indispensable for realizing high-precision and high-speed relative motion. In addition, its positioning accuracy is approaching the nanometer order, and its importance is expected to increase in the future. However, since the rolling elements and the raceways are mechanically in contact, various nonlinear phenomena occur. This complicated phenomenon must be clear by theoretically and experimentally. This chapter describes the nonlinear friction behavior occurred with rolling contact condition and its effect on the dynamics of bearings. First, the characteristics of the non-linear friction caused by rolling machine elements and the nonlinear friction modeling method using the Masing rule are described. From the numerical analysis using the friction model, it is clarified that the motion accuracy decreases due to sudden velocity variation caused by nonlinear friction. Also, the author show that the resonance phenomenon and force dependency of the dynamic characteristics of rolling machine element due to the nonlinear friction. Finally, the author indicates nonlinear friction influences on the dynamic characteristics in the directions other than the feed direction.