Bodies In Relative Motion Research Articles

Динамический анализ двухмассовой механической системы в диссипативной среде с учетом сил инерции

In this paper, a dynamic analysis of a two-mass mechanical system is performed. The aim of this work is to study the effect of the inertial forces of bodies in relative motion within the mechanical system on the motion of this system in a dissipative medium with linear viscous resistance to the motion of one of its bodies (a reference body). The analysis is based on the decomposition of the absolute impulse of the mechanical system into portable and relative components. The resolution shows that the relative inertia forces significantly affect the absolute motion of the mechanical system in a dissipative medium. The equation for such motion is presented, where the total mass of the mechanical system is conditionally concentrated in the reference body. The obtained results and conclusions can be used to solve the problem of two gravitating bodies, one of which is located in a dissipative medium, with the center of mass of the bodies moving relative to the center of the inertial domain. The results are also applicable to three-mass mechanical systems of the inertioid type.

Casimir–Lifshitz Frictional Heating in a System of Parallel Metallic Plates

The Casimir–Lifshitz force of friction between neutral bodies in relative motion, along with the drag effect, causes their heating. This paper considers this frictional heating in a system of two metal plates within the framework of fluctuation electromagnetic theory. Analytical expressions for the friction force in the limiting cases of low (zero) temperature and low and high speeds, as well as general expressions describing the kinetics of heating, have been obtained. It is shown that the combination of low temperatures (T < 10 K) and velocities of 10–103 m/s provides the most favorable conditions when measuring the Casimir–Lifshitz friction force from heat measurements. In particular, the friction force of two coaxial disks of gold 10 cm in diameter and 500 nm in thickness, one of which rotates at a frequency of 10–103 rps (revolutions per second), can be measured using the heating effect of 1–2 K in less than 1 min. A possible experimental layout is discussed.

A Stress-State-Dependent Sliding Wear Model for Micro-Scale Contacts

Abstract Wear is a complex phenomenon taking place as two bodies in relative motion are brought into contact with each other. There are many different types of wear, for example, sliding, fretting, surface fatigue, and combinations thereof. Wear occurs over a wide range of scales, and it largely depends on the mechanical properties of the material. For instance, at the micro-scale, sliding wear is the result of material detachment that occurs due to fracture. An accurate numerical simulation of sliding wear requires a robust and efficient solver, based on a realistic fracture mechanics model that can handle large deformations. In the present work, a fully coupled thermo-mechanical and meshfree approach, based on the momentum-consistent smoothed particle Galerkin (MC-SPG) method, is adapted and employed to predict wear of colliding asperities. The MC-SPG-based approach is used to study how plastic deformation, thermal response, and wear are influenced by the variation of the vertical overlap between colliding spherical asperities. The findings demonstrate a critical overlap value where the wear mechanism transitions from plastic deformation to brittle fracture. In addition, the results reveal a linear relationship between the average temperature and the increasing overlap size, up until the critical overlap value. Beyond this critical point, the average temperature reaches a steady-state value.

Comparison of forming processes for micro textured cups

Friction losses are present in all kinds of technical systems. This is always associated with additional energy consumption, which can be partly avoided as it arises. Energy savings can be achieved by a wide range of approaches. The application of friction reducing coatings on bodies in relative motion is widespread. The coating of parts is however only suitable to a limited extent for the production in large batches. Therefore, research approaches consider alternative methods to achieve friction reductions. A promising approach is the integration of miniaturized pockets on the surface of the component. In lubricated contacts, the lubricant can then accumulate in these indentations. The relative motion between two bodies thus builds up a hydrodynamic pressure and consequently reduces friction. Forming technology is suitable for the efficient production of metallic components in large quantities. The aim of this study is therefore to identify challenges in the integration of micro coining in established forming processes. Two processes from sheet metal forming and bulk metal forming are investigated. In a combined experimental and numerical approach, process-specific challenges are derived regarding the texturing process and the numerical process modelling for combined micro coining. The analysis is carried out on a cup geometry, as used in the automotive sector as tappets in the valve train. The case hardening steel 16MnCr5 (1.7131) is used as workpiece material.

Fluctuational electrodynamics in and out of equilibrium

Dispersion forces between neutral material bodies are due to fluctuations of the polarization of the bodies. For bodies in equilibrium these forces are often referred to as Casimir–Lifshitz forces. For bodies in relative motion, in addition to the Casimir–Lifshitz force, a lateral frictional force (“quantum friction”, in the zero temperature limit) comes into play. The widely accepted theory of the fluctuation-induced forces is based on the “fluctuational electrodynamics”, when the Maxwell equations are supplemented by random current sources responsible for the fluctuations of the medium polarization. The first part of our paper touches on some conceptual issues of the theory, such as the dissipation-less limit and the link between Rytov’s approach and quantum electrodynamics. We point out the problems with the dissipation-less plasma model (with its unphysical double pole at zero frequency) which still appears in the literature. The second part of the paper is devoted to “quantum friction”, in a broad sense, and it contains some novel material. In particular, it is pointed out that in weakly dissipative systems the friction force may not be a stationary process. It is shown, using an “exact” (nonperturbative) quantum treatment, that under appropriate conditions, an instability can occur when the kinetic energy (due to the relative motion between the bodies) is transformed into coherent radiation, exponentially growing in intensity (the instability gets eventually limited by nonlinear effects). We also discuss a setup when the two bodies are at rest but a constant electric current is flowing in one of the bodies. One may say that only the electron component of one body is dragged with respect to the other body, unlike the usual setup when the two bodies are in relative motion. Clearly, there are differences in the frictional forces between the two setups.

Enhanced decoherence for a neutral particle sliding on a metallic surface in vacuum

Bodies in relative motion, spatially separated in vacuum, experience a tiny friction force known as quantum friction. This force has eluded experimental detection so far due to its small magnitude and short range. Herein, we give quantitative details so as to track traces of the quantum friction by measuring coherences in the atom. We notice that the environmentally induced decoherence can be decomposed into contributions of different signature: corrections induced by the electromagnetic vacuum in presence of the dielectric sheet and those induced by the motion of the particle. In this direction, we show that non-contact friction enhances the decoherence of the moving atom. Further, its effect can be enlarged by a thorough selection of the two-level particle and the Drude-Lorentz parameters of the material. In this context, we suggest that measuring decoherence times through velocity dependence of coherences could indirectly demonstrate the existence of quantum friction.

A note on synthesizing geodesic based contact curves

The paper focuses on synthesizing optimal contact curves that can be used to ensure a rolling constraint between two bodies in relative motion. We show that geodesic based contact curves generated on both the contacting surfaces are sufficient conditions to ensure rolling. The differential geodesic equations, when modified, can ensure proper disturbance rejection in case the system of interacting bodies is perturbed from the desired curve. A corollary states that geodesic curves are generated on the surface if rolling constraints are satisfied. Simulations in the context of in-hand manipulations of the objects are used as examples.

Normal Load and Counter Body Size Influence the Initiation of Microstructural Discontinuities in Copper during Sliding

Near the interface of two contacting metallic bodies in relative motion, the microstructure changes. This modified microstructure leads to changes in material properties and thereby influences the tribological behavior of the entire contact. Tribological properties such as the friction coefficient and wear rate are controlled by the microstructure, while the elementary mechanisms for microstructural changes are not sufficiently understood. In this paper, the influence of the normal load and the size of the counter body on the initiation of a tribologically induced microstructure in copper after a single sliding pass is revealed. A systematic variation in the normal load and sphere diameter resulted in maximum Hertzian contact pressures between 530 MPa and 1953 MPa. Scanning electron microscopy, focused ion beam, and transmission electron microscopy were used to probe the subsurface deformation. Irrespective of the normal load and the sphere diameter, a sharp line-like feature consisting of dislocations, the so-called dislocation trace line, was identified in the subsurface area at depths between 100 nm and 400 nm. For normal loads below 6.75 N, dislocation features are formed below this line. For higher normal loads, the microstructure evolution directly underneath the surface is mainly confined to the area between the sample surface and the dislocation trace line, which itself is located at increasing depth. Transmission Kikuchi diffraction and transmission electron microscopy demonstrate that the misorientation is predominantly concentrated at the dislocation trace line. The results disclose a material rotation around axes roughly parallel to the transverse direction. This study demonstrates the generality of the trace line phenomena over a wide range of loads and contact pressures and the complexity of subsurface processes under a sliding contact and provides the basis for modeling the early stages in the microstructure evolution.

A relativistic paradox and its resolution or who drives the entropy current between two bodies in relative motion?

We discuss a paradox from the field of relativistic thermodynamics: two heat reservoirs of the same proper temperature move against each other. One is at rest in the inertial reference frame S A, the other in S B. For an observer, no matter in which of the two reference frames he is at rest, the temperatures of the two reservoirs are different. One might, therefore, conclude that a thermal engine can be operated between the reservoirs. However, the observers in S A and S B do not agree upon the direction of the entropy flow: from S A to S B, or from S B to S A. The resolution of the paradox is obtained by taking into account that the ‘drive’ of an entropy current is not simply a temperature difference, but the difference of a quantity that depends on both temperature and velocity.

Determination of a contact length dependent friction function in micro metal forming

Abstract The coefficient of friction, which determines the process force in the micro range, can be described by a pressure dependent friction function. In this work, this friction function is transferred into a contact length-dependent one. The resulting course is characteristic for lubricated contact of two bodies in relative motion to each other. This allows to identify solid friction and mixed friction during forming. Moreover, these areas can be used to identify a minimum contact length of lC,min = 17 μm at the transition from solid to mixed friction, in accordance with roughness measurements. This point is also found for different punch velocities, which proves that there is a minimum contact length required to form so-called lubrication pockets improving the friction behaviour of two contact partners. Thus, this work presents a method that numerically, analytically and experimentally determines the effective size of lubrication pockets of a given material with a given surface structure.

Calculation of the Braking Temperature on a Brake Disc of Light Passenger Aircraft Using FEM and Newcomb Models

The friction of two bodies in relative motion is accompanied by several phenomena such as elevation of temperature. The aim of this work is to calculate the braking temperature of the brake disc of an aircraft during the landing phase, using a calculation code based on Finite Element Method (FEM) and the analytical method of Newcomb. This investigation uses two kinds of disc — full and real disc (original version mounted on the aircraft) — and three braking disc materials such as the cast irons FG15, FG20 and FG25. The result showed that the numbers of holes and slots existing in the real disc has no influence on the braking temperature compared to the full disc. On the other hand, all brake disc materials have almost the same thermal behavior. Both models, analytical and numerical, provided acceptable results.

Towards detecting traces of non-contact quantum friction in the corrections of the accumulated geometric phase

The geometric phase can be used as a fruitful venue of investigation to infer features of the quantum systems. Its application can reach new theoretical frontiers and imply innovative and challenging experimental proposals. Herein, we take advantage of the geometric phase to sense the corrections induced while a neutral particle travels at constant velocity in front of an imperfect sheet in quantum vacuum. As it is already known, two bodies in relative motion at constant velocity experience a quantum contactless dissipative force, known as quantum friction. This force has eluded experimental detection so far due to its small magnitude and short range. However, we give details of an innovative experiment designed to track traces of the quantum friction by measuring the velocity dependence of corrections to the geometric phase. We notice that the environmentally induced corrections can be decomposed in different contributions: corrections induced by the presence of the dielectric sheet and the motion of the particle in quantum vacuum. As the geometric phase accumulates over time, its correction becomes relevant at a relative short timescale, while the system still preserves purity. The experimentally viable scheme presented would be the first one in tracking traces of quantum friction through the study of decoherence effects on a NV center in diamond.

Curvature Theory on Contact and Transfer Characteristics of Enveloping Curves

Abstract In differential geometry, a curve is characterized by the curvature properties and so is a point trajectory in curvature theory. However, due to the rolling and sliding between contact curves, the characterization of enveloping curves embedded on rigid bodies in relative motion is not complete without the transfer rate of the contact point. This paper presents the new perspectives on not only the curvature characteristics but also the transfer characteristics between enveloping curves embedded on rigid bodies. The paper contains three parts. First, a pair of enveloping curves can be described by a point trajectory which traces two curves simultaneously. Second, the paper treated instant center as a tracing point, which traces the moving centrode and the fixed centrode on each of the bodies. This characterizes the rolling between centrodes and the transfer rate of the instant center on each of centrodes. The treatment can extend the instant center transfer velocity to any higher order. The third part is about the rolling and sliding between enveloping curves embedded on rigid bodies motion. A kinematic model to describe the transfer rate of contact point based on the motion of the instant center is proposed. The detailed curvature and transfer properties of line- and circle-envelopes are presented. Due to the simple treatment, this might be the first paper that successfully achieved the curvature properties of circle-envelopes. The method offers the vital kinematic aspect of enveloping curves distinctly different from the conventional curvature theory and enveloping theory.

Mechanical dissipation from charge and spin transitions in oxygen-deficient SrTiO3\xa0surfaces

Bodies in relative motion separated by a gap of a few nanometers can experience a tiny friction force. This non-contact dissipation can have various origins and can be successfully measured by a sensitive pendulum atomic force microscope tip oscillating laterally above the surface. Here, we report on the observation of dissipation peaks at selected voltage-dependent tip-surface distances for oxygen-deficient strontium titanate (SrTiO3) surface at low temperatures (T = 5 K). The observed dissipation peaks are attributed to tip-induced charge and spin state transitions in quantum-dot-like entities formed by single oxygen vacancies (and clusters thereof, possibly through a collective mechanism) at the SrTiO3 surface, which in view of technological and fundamental research relevance of the material opens important avenues for further studies and applications.

Parametrical experimental and numerical analysis on friction-induced vibrations by a simple frictional system

This paper presents an experimental and numerical analysis on friction-induced vibrations arising from the frictional contact between two bodies in relative motion. The sliding contact has been reproduced within a mechanical system characterized by a simple dynamics, in order to better distinguish between the dynamic response of the system and the broadband excitation coming from the contact. The effects of some parameters, mainly relative velocity, roughness and normal load, on the magnitude and frequency content of the induced vibrations are investigated, also by comparing results from experimental measurements and simulations. A distinction between weak and strong coupling is recovered by the experimental results. Finally, accounting for the contribution of the roughness to the contact-induced vibrations, a conceptually innovative method to implement the effect of the roughness in the numerical simulation is proposed.

Design and analysis of a task-based parallelization over a runtime system of an explicit finite-volume CFD code with adaptive time stepping

FLUSEPA (registered trademark in France No. 134009261) is an advanced simulation tool which performs a large panel of aerodynamic studies. It is the unstructured finite-volume solver developed by Airbus Safran Launchers company to calculate compressible, multidimensional, unsteady, viscous and reactive flows around bodies in relative motion. The time integration in FLUSEPA is done using an explicit temporal adaptive method. The current production version of the code is based on MPI and OpenMP. This implementation leads to important synchronizations that must be reduced. To tackle this problem, we present the study of a task-based parallelization of the aerodynamic solver of FLUSEPA using the runtime system StarPU and combining up to three levels of parallelism. We validate our solution by the simulation (using a finite-volume mesh with 80 million cells) of a take-off blast wave propagation for Ariane 5 launcher.

An overset mesh approach for 3D mixed element high-order discretizations

A parallel high-order Discontinuous Galerkin (DG) method is used to solve the compressible Navier–Stokes equations in an overset mesh framework. The DG solver has many capabilities including: hp-adaption, curved cells, support for hybrid, mixed-element meshes, and moving meshes. Combining these capabilities with overset grids allows the DG solver to be used in problems with bodies in relative motion and in a near-body off-body solver strategy. The overset implementation is constructed to preserve the design accuracy of the baseline DG discretization. Multiple simulations are carried out to validate the accuracy and performance of the overset DG solver. These simulations demonstrate the capability of the high-order DG solver to handle complex geometry and large scale parallel simulations in an overset framework.

Numerical investigation of the hydrodynamic interaction between two underwater bodies in relative motion

The hydrodynamic interaction between an Autonomous Underwater Vehicle (AUV) manoeuvring in close proximity to a larger underwater vehicle can cause rapid changes in the motion of the AUV. This interaction can lead to mission failure and possible vehicle collision. Being self-piloted and comparatively small, an AUV is more susceptible to these interaction effects than the larger body. In an aim to predict the manoeuvring performance of an AUV under the effects of the interaction, the Australian Maritime College (AMC) has conducted a series of computer simulations and captive model experiments. A numerical model was developed to simulate pure sway motion of an AUV at different lateral and longitudinal positions relative to a larger underwater vehicle using Computational Fluid Dynamics (CFDs). The variables investigated include the surge force, sway force and the yaw moment coefficients acting on the AUV due to interaction effects, which were in turn validated against experimental results. A simplified method is presented to obtain the hydrodynamic coefficients of an AUV when operating close to a larger underwater body by transforming the single body hydrodynamic coefficients of the AUV using the steady-state interaction forces. This method is considerably less time consuming than traditional methods. Furthermore, the inverse of this method (i.e. to obtain the steady state interaction force) is also presented to obtain the steady-state interaction force at multiple lateral separations efficiently. Both the CFD model and the simplified methods have been validated against the experimental data and are capable of providing adequate interaction predictions. Such methods are critical for accurate prediction of vehicle performance under varying conditions present in real life.

Computational fluid dynamics re-mesh method to generating hydrodynamic models for maneuvering simulation of two submerged bodies in relative motion

Một phương tiện ngầm tự hành (AUV) hoạt động gần tới một tầu lớn hơn chịu ảnh hưởng các lực thủy động học đáng kể cần một cơ cấu điều khiển thích nghi để duy trì quỹ đạo chuyển động ở mức cho phép. Do vậy điều quan trọng là người thiết kế biết được các đặc tính thủy động học của phương tiện ngầm trong tình huống này để có thể phát triển các thuật toán điều khiển thích hợp với động thái của nó. Điều này đòi hỏi việc phát triển các mô phỏng động thái của phương tiện ngầm khi hoạt động gần một tầu lớn hơn, các thuật toán điều khiển và tương tác động học giữa hai vật thể. Bài báo này trình bày phương pháp tạo ra một mô hình thủy động học trọn vẹn của các phương tiện ngầm sử dụng phần mềm ANSYS CFX gói mã Động học Chất lỏng Tính toán (CFD), và có thể tương tác mô hình này với các thuật toán điều khiển phương tiện ngầm trong môi trường mô phỏng. Điểm chính yếu của phương pháp là cách tái thiết lập mạng tại đó mạng biến dạng cục bộ xung quanh các vật thể dùng phương trình chất lỏng mô tả có dạng Lagrangian-Eulerian tự chọn và tái thiết lập mạng khi sự biến dạng có ảnh hưởng rất đáng kể đến chất lượng của mạng. Phương pháp này khắc phục được những hạn chế gây ra bởi phương pháp biến dạng mạng thuần túy. Việc đánh giá phương pháp sơ bộ ban đầu được dựa trên hai mặt trơn tru chuyển động tương đối với nhau. Qua đó cho thấy phương pháp này có thể mô phỏng đầy đủ động thái chất lỏng xung quanh các vật thể. Bài báo này cũng trình bày các công việc tiếp theo tập trung vào một phương tiện ngầm sáu bậc tự do (6-DOF) được mô hình hóa trong phần mềm CFD để thu được động thái thủy động học tương tác với hệ thống điều khiển trong môi trường MATLAB.

Molecular dynamics simulation of atomic-scale frictional behavior of corrugated nano-structured surfaces

Surface morphology is one of the critical parameters that affect the frictional behavior of two contacting bodies in relative motion. It is important because the real contact area as well as the contact stiffness is dictated by the micro- and nano-scale geometry of the surface. In this regard, the frictional behavior may be controlled by varying the surface morphology through nano-structuring. In this study, molecular dynamics simulations were conducted to investigate the effects of contact area and structural stiffness of corrugated nano-structures on the fundamental frictional behavior at the atomic-scale. The nano-structured surface was modeled as an array of corrugated carbon atoms with a given periodicity. It was found that the friction coefficient of the nano-structured surface was lower than that of a smooth surface under specific contact conditions. The effect of applied load on the friction coefficient was dependent on the size of the corrugation. Furthermore, stiffness of the nano-structure was identified to be an important variable in dictating the frictional behavior.