Bodies In Relative Motion Research Articles

Sliding on vacuum

Bodies in relative motion, separated by nanometres of vacuum, experience a tiny friction force. Experiments involving a conductor–superconductor transition provide essential information for distinguishing the contribution of electrons from that of lattice vibrations in this non-contact form of friction.

Numerical Simulation of Unsteady Rotor Flow Using an Unstructured Overset Mesh Flow Solver

An unstructured overset mesh method has been developed for the simulation of unsteady flow fields around isolated rotors and rotor-fuselage configurations. The flow solver was parallelized for the efficient calculation of complicated flows requiring a large number of cells. A quasi-unsteady mesh adaptation technique was adopted to enhance the spatial accuracy of the solution and to better resolve the rotor wake. The method has been applied to calculate the flow fields around rotor-alone and rotor-fuselage configurations in forward flight. Validations were made by comparing the predicted results with those of measurements. It was demonstrated that the present method is efficient and robust for the prediction of unsteady time-accurate flow fields involving multiple bodies in relative motion.

Moving-body simulations using overset framework with rigid body dynamics

The simulation of flow past bodies in relative motion is a challenging task due to the presence of complex flow features, moving grids, and rigid body movements under the action of external forces and moments. A generalized grid-based overset framework is presented for the simulation of this class of problems. The equations that govern the fluid flows are cast in an integral form and are solved using a cell-centered finite volume upwind scheme. The rigid body dynamics equations are formulated using quaternion and are solved using fourth-order Runge–Kutta (RK) time integration. The overset framework and the six degree of freedom (6-DOF) rigid body dynamics simulators are developed in a library form for easy incorporation into existing flow solvers. The details of the flow solver, the 6-DOF library, and the overset framework are presented in this paper along with the validation results of the developed system.

3차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체들 간의 상대운동 해석기법에 관한 연구

본 연구에서는 3차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체들 간의 상대운동 해석기법에 대한 연구를 수행하였다. 홀 컷팅 과정에서 격자요소를 구성하는 모든 격자점들이 다른 물체의 내부에 위치하는 물체 경계의 격자요소들을 계산에서 제외하였고, 일부분이 다른 물체의 내부에 위치하는 격자요소들은 계산영역에 포함하였다. 비정상 유동의 계산을 위해 계산에서 제외되는 비활성 격자요소들에 내삽과 외삽을 통해 적절한 유동값을 부여하여, 상대운동이 진행됨에 따라 다음 시간단계에서 새롭게 활성 격자로 분류될 때 이전 시간에서의 유동값으로 이용될 수 있도록 하였다. 해석기법을 이용하여 기존에는 해석이 불가능했던 3차원 날개의 내부에서 발사체가 사출되는 운동과 발사체의 동체에서 다수의 핀이 전개되는 운동을 해석하였다. In the present study, A 3-D chimera technique for overlapped bodies in relative motion is studied using unstructured meshes. If all node points of a mesh element at solid boundary are in another body, this element is excluded from computational domain. For computation of unsteady flow, non-active cells have proper variables using interpolation and extrapolation. These variables are used in next time step. The motion of a launching trajectory ejected from a wing and the motion of deploying fins of a trajectory which have not been simulated are computed to conform practicality of this technique.

Parallel universal approach to mesh motion and application to rotors in forward flight

AbstractNumerical simulation of unsteady flows including moving boundaries, whether rigid, prescribed, or deforming, requires the mesh to move/deform also. Many approaches to mesh motion have been considered, but the approach adopted often depends on both the meshing approach used and the proposed application. A universal approach to grid motion is presented here. The method developed has several important properties, the most significant of which is that the scheme requires no grid point connectivity information, i.e. each point can be moved totally independently to its neighbours. This has two major implications: first, it means the scheme is universal, i.e. applicable to any grid type, unstructured, hybrid or structured single‐ and multiblock. Second, and equally as important, is that the scheme is perfectly parallel, as no communication is required between points/blocks. Each block can be updated independently to its neighbours so there is no connectivity data required, and this also means the flow‐solver does not have to carry the grid motion parameterization data in memory. The scheme accounts for moving surface rotations as well as displacements, and this ensures grid quality is preserved by maintaining orthogonality. The method is applied to a four‐bladed lifting rotor in forward flight. This is a particularly challenging unsteady problem as there are multiple bodies in relative motion, each one with its own axis system, as each blade has a cyclic pitch variation. Grid quality is proven to be preserved even when a large deformation case is considered and, significantly, the scheme adds only around 1% to the cost of a flow solution real time step. Copyright © 2006 John Wiley & Sons, Ltd.

비정렬 중첩격자기법을 이용한 유도무기의 기체분리운동 모사

본 연구에서는 비행중인 유도무기의 기체분리에 대한 수치적 해석을 수행하였다. 기체의 정확한 분리운동을 모사하기 위해 삼차원 공간에서 각각의 물체가 연결되어 움직이는 6자유도 운동방정식을 유도하였으며, 물체를 둘러싼 격자계의 독립적인 처리를 위해 개발된 비정렬 중첩격자기법과 연계하였다. 개발된 해석기법은 유도무기의 받음각이 0도와 5도인 경우의 기체분리운동 해석에 적용되었으며, 이를 통해 본 연구에서의 해석기법이 다중 물체간의 상대운동이 있는 비정상 유동장을 해석하는데 효과적임을 알 수 있었다. In this study, numerical simulation of airframes separating from a missile system has been preformed. For the time-accurate trajectory simulation, six D.O.F equations of motion of multiply connected bodies were derived and these equations have been coupled with the unstructured overset mesh technique for the treatment of independent mesh blocks moving with each body component. Applications were made for the simulation of the airframe separation at missile angles of attack of 0 and 5 degrees. It was demonstrated that the present method is efficient and robust for the prediction of unsteady time-accurate flow fields involving multiple bodies in relative motion.

2차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체간의 상대운동 해석기법 개발

본 연구에서는 2차원 비정렬 중첩격자계를 이용한 서로 겹쳐진 물체간의 상대운동 해석기법을 개발하였다. 물체들이 교차되는 교차점에서 가장 가까운 거리에 있는 각 격자계의 물체 경계면에 위치한 격자점들을 교차점으로 이동시키고, 이 교차점을 기준으로 계산영역에 포함되는 격자와 계산에서 제외되는 격자가 구분되도록 하였다. 비정상 유동의 계산을 위해 계산에서 제외되는 비활성 격자점에 적절한 유동값을 부여하여, 상대운동이 진행됨에 따라 새롭게 활성 격자점으로 분류될 때 이전 시간에서의 유동값으로 이용될 수 있도록 하였다. 해석기법의 검증을 위해 단순플랩의 진동에 따른 에어포일 주위의 유동을 해석하여 타 연구자의 해석결과와 비교하였고, NACA0012 에어포일의 내부에서 사출되는 발사체의 운동에 대하여 해석을 수행하였다. In the present study, a 2-D chimera technique for overlapped bodies in relative motion is developed using unstructured triangular meshes. The solid boundary nodes located next to the intersecting point between bodies are merged to the intersecting point to assure accurate representation of the intersecting region. In order to assign proper value of flow variables at the nodes located out of the computational field, interpolation is conducted for non-active nodes. For validation, the motions of a NACA64A006 airfoil and a NACA0012 airfoil with a plane flap are computed and the results are compared with other simulations. The motion of a launching missile ejected from a NACA0012 airfoil is also simulated.

Parallel remeshing of unstructured volume grids for CFD applications

AbstractThis paper presents a new approach towards the parallel local remeshing of unstructured tetrahedral grids on distributed memory parallel computers based on the message passing paradigm (MPI). The overall remeshing approach consisting of the parallel determination of the regions to be remeshed and the parallel local surface and volume remeshing is described in detail. An application of the remeshing algorithms in a time‐accurate simulation of bodies in relative motion demonstrates the capabilities of the approach. Copyright © 2006 John Wiley & Sons, Ltd.

상대운동이 있는 물체주위의 비정상 유동해석을 위한 병렬화된 비정렬 중첩격자기법 개발

비정상 유동의 모사를 위한 병렬화된 비정렬 중첩격자기법을 개발하였다. 비정렬 격자계에서 효율적이고 강건하게 쓰일 수 있는 탐색방법과 병렬경계에서 유동적으로 변하는 데이터의 수를 처리할 수 있는 자료구조를 제안하였다. 격자계간의 정보전달을 위한 삽간경계면을 정의하였고, 공간상의 이차정확도를 유지하기 위한 삽간방법 및 물체내부에 위치하는 삽간점에 대한 처리방법을 제안하였다. 개발된 해석코드의 검증을 위해 Eglin/Pylon 형상에서 분리되는 스토어의 궤적을 해석하여 실험치와 비교하였고, 다 물체간의 상대운동이 있는 비정상유동의 적용을 위해 세 개의 스토어 분리에 대한 해석을 수행하였다. An unstructured parallel overset mesh method has been developed for the simulation of unsteady flows around multiple bodies in relative motion. For this purpose, an efficient and robust search method is proposed for the unstructured grid system. A new data-structure is also proposed to handle the variable number of data on parallel sub-domain boundary. The interpolation boundary is defined for data communication between grid systems. An interpolation method to retain second-order spatial accuracy and to treat the points inside the neighboring solid bodies are also suggested. A single store separating from the Eglin/Pylon configuration is calculated and the result is compared with experimental data for validation. Simulation of unsteady flows around multiple bodies in relative motion is also performed.

Introduction to Tribology

Introduction to Tribology

Tribology and Its Many Facets: From Macroscopic to Microscopic and Nano-scale Phenomena

The key features of tribology – interfacial phenomena of interacting bodies in relative motion – are as origin of friction and wear scientifically interesting and have important applications in technology and engineering. The interfacial interactions have been studied in various theoretical and experimental approaches. Depending on the scope of the investigation and the nature of the tribological solid/fluid/solid or solid/solid system under study, these approaches apply contact mechanics, hydrodynamics, and rheology as well as solid state physics and chemistry. Accordingly, also various experimental techniques have been used, ranging from Coulomb's classical tribometer to the contemporary atomic force microscope.

Unsteady aerodynamic loads on high speed trains passing by each other

In order to study unsteady aerodynamic loads on high speed trains passing by each other 350km/h, three-dimensional flow fields around trains during the crossing event are numerically simulated using three-dimensional Euler equations. Roe’s FDS with MUSCL interpolation is employed to simulate wave phenomena. An efficient moving grid system based on domain decomposition techniques is developed to analyze the unsteady flow field induced by the restricted motion of a train on a rail. Numerical simulations of the strain passing by on the double-track are carried out to study the effect of the train nose-shape, length and the existence of a tunnel on the crossing event. Unsteady aerodynamic loads-a side force and a drag force-acting on the train during the crossing are numerically predicted and analyzed. The side force mainly depends on the nose-shape, and the drag force depends on tunnel existence. Also. a push-pull (i.e. impluse force) force successively acts on each car and acts in different directions between the neighborhood cars. The maximum change of the impulsive force reaches about 3 tons. These aerodynamic force data are absolutely necessary to evaluate the stability of high speed multi-car trains. The results also indicate the effectiveness of the present numerical method for simulating the unsteady flow fields induced by bodies in relative motion.

Hybrid FEM/MOM formulation for eddy current problems with moving conductors

In this paper a hybrid formulation for the analysis of electromagnetic fields distribution in systems with conductors in motion is presented. Conductive bodies in relative motion are enclosed in a fictitious surface attached to the conductors. The equivalence theorem is applied to these surfaces and the continuity of tangential components of electric and magnetic fields, taking into account the motional effects, is imposed using the Method Of Moments (M.O.M.). The distribution of electromagnetic fields inside each surface is obtained by means of a Finite Elements Method (F.E.M.) analysis. No re-meshing is required inside and the motional effects are taken into account by means of the boundary conditions. A relevant characteristic of the proposed method is that only a part of the matrices, (namely those involved in the application of MOM), have to be recalculated at each step. The proposed formulation has been tested by comparison with other numerical results.

3-D Viscous Flow Solutions Over Bodies in Relative Motion

A space-time finite element method based on the Arbitrary Lagrangian-Eulerian description of the incompressible Navier-Stokes Equations is developed. The developed method is used for predicting the flows past bodies in relative motion. The governing equations are expressed in a fixed frame of reference, wherein the terms related to grid motion are included. Superparametric space-time elements are used in the discretization of the domain in which, finite elements are both allowed to move and deform in (i) simple and (ii) automatic manner. The equations for the rigid body motion are integrated to calculate the trajectory of the moving object under aerodynamic and gravitational forces. The code developed here is first tested on the flow about a drifting and falling sphere which starts to move at Reynolds number of 104 from a steady state. To study the flows about the bodies in relative motion, store-separation from a wing problem is investigated as a turbulent flow for the Reynolds number of 2.5 x 106 based on the length of the store.

NUMERICAL SIMULATION OF THE PHENOMENA DUE TO THE PASSING-BY OF TWO BODIES USING THE UNSTEADY BOUNDARY ELEMENT METHOD

In this paper a numerical analysis was made to investigate the aerodynamic forces surrounding two bodies in relative motion in a fluid at rest in three dimensions. The unsteady boundary element method was employed in the numerical calculations. This method is very convenient for obtaining an approximate expression of the velocity potential, especially for practical use. The passing-by of two spheres in an incompressible perfect fluid which extends to infinity is treated by the present method. The resultant pressure coefficients on two spheres passing each other in opposite directions are calculated and discussed numerically. Numerical examples are presented to show the validity of the present method. The method is also applied to the calculation of the passing-by of two trains in an open area in order to investigate its applicability.

Implicit Method for the Computation of Unsteady Flows on Unstructured Grids

An implicit method for the computation of unsteady flows on unstructured grids is presented. Following a finite difference approximation for the time derivative, the resulting nonlinear system of equations is solved at each time step by using an agglomeration multigrid procedure. The method allows for arbitrarily large time steps and is efficient in terms of computational effort and storage. Inviscid and viscous unsteady flows are computed to validate the procedure. The issue of the mass matrix which arises with vertex-centered finite volume schemes is addressed. The present formulation allows the mass matrix to be inverted indirectly. A mesh point movement and reconnection procedure is described that allows the grids to evolve with the motion of bodies. As an example of flow over bodies in relative motion, flow over a multi-element airfoil system undergoing deployment is computed.

Heat flow in relativistic equilibrium thermodynamics

An attempt is made to clarify a thought experiment introduced by P. T. Landsberg concerning the relativistic heat flow between bodies in relative motion. It is shown that if the problem is analyzed within the covariant thermodynamics developed by R. Balescu, supplemented by the second law of thermodynamics as proposed here, then such heat flow considerations do not fix the transformation of temperature as Landsberg contends. Instead, the transformation of temperature is left as being purely a matter of definition.

On relativistic thermodynamics

The thermodynamics of moving bodies is developed from first principles. To do this, it is necessary to augment the laws of thermodynamics with a new principle, which asserts the impossibility of thermal equilibrium between bodies in relative motion. Clausius' theorem is generalized to heat flow between moving systems, and leads naturally to the identification of heat and temperature as Lorentz scalars. The formulation of relativistic statistical mechanics is carried out and the correspondence with classical quantities is made. The quantum distribution laws are generalized to the relativistic case, and are found to differ from their accepted relativistic form.

On the Relativistic Theory of Heat Conduction and Temperature

The relativistic theory of heat and temperature is investigated on the stand point of elementary case study and by means of the exact equation of motion of continuous body. It is shown that a kind of heat conduction between two bodies in relative motion is theoretically possible and the conduction temperature must be a relativistic invariant. The considerations on the thermodynamical variables in the presence of heat current also lead to the scalar thermodynamics, where the invariance of the thermodynamical temperature is shown in the same meaning as the invariance of the nonrelativistic temperature.

The second law of thermodynamics and special relativity

The physical equivalence of the two major formulations of comoving, relativistic thermodynamics is stressed. Relativistic thermodynamics is generalized so that heat conduction between bodies in relative motion can be described. This new theory becomes equivalent to the earlier formulations of relativistic thermodynamics when limited to heat transfer between comoving bodies. For the first time, relativistic thermodynamics is developed in a manner which is formally identical to classical thermodynamics, e.g., an invariant quantity, called the generalized entropy, is shown to be an exact differential as a consequence of a generalized Clausius' and a generalized Kelvin's postulate. While engaged in generalizing relativistic thermodynamics a theory of frictionless heat conduction is presented, relativistic friction is discussed, and new types of Carnot cycles are described.