Analytical modeling of spindle-tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindleholdertool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modication methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is veried by comparing the natural frequencies of an example spindleholdertool assembly obtained from the model with those obtained from a nite element software

A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone

Finite Element Simulation of Dense Wire Packings

A finite element program is presented to simulate the process of packing and coiling elastic wires in two- and three-dimensional confining cavities. The wire is represented by third order beam elements and embedded into a corotational formulation to capture the geometric nonlinearity resulting from large rotations and deformations. The hyperbolic equations of motion are integrated in time using two different integration methods from the Newmark family: an implicit iterative Newton-Raphson line search solver, and an explicit predictor-corrector scheme, both with adaptive time stepping. These two approaches reveal fundamentally different suitability for the problem of strongly self-interacting bodies found in densely packed cavities. Generalizing the spherical confinement symmetry investigated in recent studies, the packing of a wire in hard ellipsoidal cavities is simulated in the frictionless elastic limit. Evidence is given that packings in oblate spheroids and scalene ellipsoids are energetically preferred to spheres.Comment: 17 pages, 7 figures, 1 tabl

A Numerical and Experimental Investigation of a Special Type of Floating-Slab Tracks

This thesis presents a research study on the dynamic behavior of a special type of FST used in recently built subway system in Doha, Qatar. The special FST has a continuous concrete slab with periodic grooves for which the track can be modeled as periodic structure with a slab unit having two elements with different cross sections. Extensive numerical and experimental investigations were conducted on a multi-unit full-scale mockup track. The numerical investigations were carried out using both a fast running model based on the Dynamic Stiffness Method and a detailed Finite Element model. In the experimental campaign, experimental vibration test was performed to identify the actual vibration response of the mockup track. Results from the experimental investigations were then used for verifying the numerical models and carrying out a model updating exercise for the fast running model. The model updating process was carried out according to an automated hybrid optimization approach. Finally, the updated model was extended to an infinite model and used in a parametric study to investigate the influence of varying groove’s thickness on the dynamic behavior of the special track with infinite length for both bending and torsion scenarios. The parametric study suggested that reducing the thickness below 50% of the full thickness of the slab significantly affects the dynamic behavior of the special FST

Finite element for the analysis of rotor-dynamic systems that include gyroscopic effects

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis presents new finite element formulations for the analysis of rotor-dynamic systems that include the effects of gyroscopic influence. Euler-Bernoulli finite elements have been created for both shaft and propeller descriptions. In addition to the gyroscopic effects, centrifugal stiffening has been considered for the propeller elements. The principle of virtual work has been used to determine the equations of motion and formulate element matrices. The proposed element matrices have been incorporated in the VIBRATIO suite of vibration analysis software in order to test the formulations. The software uses an innovative hybrid modelling technique that enables the user to analyse various dynamic problems including rotating beam elements with rigid body attachments. A model of a ship's drive shaft has been created in VIBRATIO for comparison against a verified ANSYS model. Results for forced vibration shaft analysis show excellent correlation between VIBRATIO's Euler shaft formulation and ANSYS's Timoshenko formulation. Incremental analyses of propeller systems using the novel gyroscopic formulation show gyroscopic effects of flexible blade attachments, and also the changing mode shapes and frequencies due to centrifugal stiffening. Results show gyroscopic and centrifugal stiffening effects must not be ignored for an accurate propeller analysis.This work was financially supported by Brunel University

Analysis of a Thin-Walled Curved Rectangular Beam with Five Degrees of Freedom

A study of a thin-walled curved rectangular box beam under torsion and out-of-plane bending is documented in this thesis. A new one-dimensional theory that takes into account warping and distortion in the beam cross-sections is the main focus. Existing available theories for thin-walled curved beams lack rigorous theoretical development, and most have ignored the effects of warping and distortion. A higher order theory including two additional degrees of freedom corresponding to warping and distortion was derived. The conventional three degrees of freedom model was compared with the new five degrees of freedom model. The variation of beam thickness to control and decrease the high distortion variable is investigated