Rotational Displacement Research Articles

Partial Trapeziotrapezoid Resection and Thumb Range of Movement After Trapeziometacarpal Joint Fusion—A Biomechanical Study

Trapeziometacarpal (TMC) joint arthrodesis is an effective treatment for stage III osteoarthritis. Although this procedure alleviates thumb pain and restores grip power and pinch strength, persistent limitation of thumb movement is inevitable. This biomechanical study aimed to investigate the altered kinematics of thumb circumduction motion after TMC joint arthrodesis and subsequent excision of the trapeziotrapezoid (TT) and trapezio-second metacarpal (T-2MC) joint spaces. Eight cadaver upper extremities were mounted on a custom testing apparatus. The hand and carpal bones were fixed to the apparatus, except for the first metacarpal bone, trapezium, and trapezoid. A 50-g load was applied at the tip of the first metacarpal head to generate passive thumb circumduction. An electromagnetic tracking system measured the angular and rotational displacement of the first metacarpal. All specimens were tested in 4 conditions: intact, after simulated TMC joint fusion, after subsequent excision of 3 mm of bone at the TT joint space, and after additional 3 mm resection at the T-2MC joint space. After simulated TMC arthrodesis, the range of angular motion of thumb circumduction decreased to 25% that of the intact thumb. Subsequent resections at the TT and T-2MC joint spaces increased circumduction ranges to 49% (TT joint) and 73% (TT plus T-2MC joints) that of the intact thumb. The range of thumb rotational motion showed a similar trend. Trapeziometacarpal arthrodesis decreased the range of both angular and rotational motion during thumb circumduction. Subsequent resections at the paratrapezial space increased the range of thumb motion, suggesting that hypermobility of the paratrapezial joints increases thumb mobility after TMC joint fusion. Patients with hypermobile paratrapezial joints may have larger thumb movement after TMC joint fusion. Additional resections of the TT and T-2MC joint spaces may further mobilize the thumb in patients who complain of stiffness after TMC fusion.

A Barycenter Control Method for the Bioinspired Forest Chassis Robot on Slope

To improve the stability of forestry chassis on the slope, a chassis-installed barycenter adjustable mechanism (BAM) is designed, and the control method of the counterweight is proposed to make the chassis barycenter move suitably to achieve the design purpose. The kinematic analysis of BAM is carried out, and the relationship between the translation, rotation, and vertical displacement of counterweight and the chassis barycenter is calculated. Furthermore, the variation curves obtained in Matlab show the barycenter can translate 100 mm, rotate from 0 to 360 degrees, and lower about 180 mm in the vertical direction. Adams is adopted to complete the kinematics simulation of the chassis, indicating that the control method can effectively adjust the barycenter position. Finally, experiments are carried out under slope conditions to analyze chassis stability by testing plantar pressure. The results show that forest chassis using the barycenter control method helps keep stable on the slope of 15 degrees, much better than standard normal chassis.

Free Vibration Analysis of Rotating Beams Based on the Modified Couple Stress Theory and Coupled Displacement Field

In this paper, transverse vibration analysis of rotating micro-beam is investigated based on the modified couple stress theory. The simply-supported micro-beam is modeled utilizing Euler-Bernoulli and Timoshenko beam theories. The system is rotating around a fixed axis perpendicular to the axial direction of the beam. For the first time, displacement filed is introduced as a coupled field to the translational field. In other words, the mentioned rotational displacement field is expressed as a proportional function of translational displacement field using first (axial), second (lateral), and third (angular or rotational) velocity factors. Utilizing Hamilton’s approach as a variational method, dynamic-vibration equations of motion of the proposed model are derived. Galerkin’s method is adopted to solve the equation corresponding to the Euler–Bernoulli and Timoshenko beams. For the case considering shear deformation effects, Navier method is chosen. For evaluation of current results and models, they are compared with those available at the benchmark. In this paper; effects of slenderness ratio, axial, lateral, and angular velocity factors, and rotations of the beam on the frequency are reported. Based on the results presented, mentioned factors should be counted in the analysis and design of such rotating micro-systems.

Prediction of Tensile Strain Capacity for X52 Steel Pipeline Materials Using the Extended Finite Element Method

Strain-based design (SBD) plays an important role in pipeline design and assessment of pipelines subjected to geo-hazards. Under such hazards, a pipe can be subjected to substantial plastic strains, leading to tensile failure at locations of girth weld flaws. For SBD, the finite element method (FEM) can be a reliable tool to calculate the tensile strain capacity (TSC) for better design in pipelines. This study aims to investigate the ductile fracture properties for specific vintage pipeline steel (API 5L grade of X52) using the extended finite element method (XFEM). Eight full-scale tests were simulated using the commercial finite element analysis software ABAQUS Version 6.17. Maximum principal strain is used to assess the damage initiation using the cohesive zone model (CZM) when the crack evolution is evaluated by fracture energy release. A proper set of damage parameters for the X52 materials was calibrated based on the ability of the model to reproduce the experimental results. These experimental results included the tensile strain, applied load, endplate rotation, and crack mouth opening displacement (CMOD). This study describes a methodology for validation of the XFEM and the proper damage parameters required to model crack initiation and propagation in X52 grades of pipeline.

Modeling and Evaluation of Adaptive Super Twisting Sliding Mode Control in Lower Extremity Exoskeleton

In this paper, an integrated human-in-the-loop simulation paradigm for the design and performance analysis of a 6 DOF lower extremity exoskeleton is presented. An adaptive Super Twisting Sliding Mode Controller (ASTSMC) is designed for the trajectory tracking control of the exoskeleton by considering the human motion as reference trajectory. The dynamic model, that include linear and rotational displacement of hip, knee and ankle joints of both the legs is developed using Lagrange energy formulation. The position and angular velocity error of the wearer and the exoskeleton are being considered to establish the control law. Super twisting SMC is a robust control scheme that works effectively in the presence of external disturbances and parameter variations. However, the STSMC introduces chattering in the closed loop because of its high gain, to overcome this drawback, an adaptive STSMC is proposed for the control of exoskeleton against unknown disturbances without chattering. An adaptation scheme using Lyapunov criterion is derived that ensures the stability of the system in closed loop. The performance of the proposed control strategy is verified by implementing on the integrated CAD model of the exoskeleton along with the wearer. The effectiveness of the controller is tested under wind disturbance of varying velocity and direction. The results demonstrate improved tracking performance of the proposed control scheme with least error and less control effort compared to constant gain STSMC in normal and uneven terrain.

An Examination of Equations Relating Motorcycle Impact Speed to Struck Vehicle Post-Impact Rotational Displacement

<div class="section abstract"><div class="htmlview paragraph">When a motorcycle collides with a passenger vehicle, the impact can cause a change in the translational and rotational velocities of the struck vehicle. If these velocity changes, or the magnitude of the translation and rotation of the struck vehicle can be quantified, then these can potentially be used to calculate the impact speed of the motorcycle. There are several methods that could be used for this analysis. The most general and comprehensive solution will be to use one of the widely-accepted accident reconstruction simulation programs - PC-Crash, HVE (the EDSMAC4 or SIMON modules), Virtual CRASH, or VCRware. However, these simulation programs can be time-consuming to apply and not everyone has access to them. It would be useful to have simple formulas for obtaining a reasonable estimate of the motorcycle impact speed based on the observed post-impact translation and rotation of the struck vehicle. All the more useful if a method could be based on the struck vehicle rotation alone. And, in fact, several such methods exist in the literature.</div><div class="htmlview paragraph">This paper tests these methods for obtaining an initial estimate of a motorcycle’s impact speed based on the struck vehicle’s post-impact rotation alone. The accuracy of the methods is assessed and the sensitivity of the methods to various parameters are discussed. This paper demonstrates that the initial translational velocity of the struck vehicle significantly affects the magnitude of the struck vehicle’s post-impact angular displacement. Thus, methods that consider both the translation and rotation of the struck vehicle are more accurate than methods that rely on the struck vehicle rotational displacement alone.</div></div>

Validation of Inertial Sensing-Based Wearable Device for Tremor and Bradykinesia Quantification.

Neurologists judge the severity of Parkinsonian motor symptoms according to clinical scales, and their judgments exist inconsistent because of differences in clinical experience. Correspondingly, inertial sensing-based wearable devices (ISWDs) produce objective and standardized quantifications. However, ISWDs indirectly quantify symptoms by parametric modeling of angular velocities and linear accelerations nd trained by the judgments of several neurologists through supervised learning algorithms. Hence, the ISWD outputs are biased along with the scores provided by neurologists. To investigate the effectiveness ISWDs for Parkinsonian symptoms quantification, technical verification and clinical validation of both tremor and bradykinesia quantification methods were carried out. A total of 45 Parkinson's disease patients and 30 healthy controls performed the tremor and finger-tapping tasks, which were tracked simultaneously by an ISWD and a 6-axis high-precision electromagnetic tracking system (EMTS). The Unified Parkinson's Disease Rating Scale (UPDRS) prescribed parameters obtained from the EMTS, which directly provides linear and rotational displacements, were compared with the scores provided by both the ISWD and seven neurologists. EMTS-based parameters were regarded as the ground truth and were employed to train several common machine learning (ML) algorithms, i.e., support vector machine (SVM), k-nearest neighbors (KNN), and random forest (RF) algorithms. Inconsistency among the scores provided by the neurologists was proven. Besides, the quantification performance (sensitivity, specificity, and accuracy) of the ISWD employed with ML algorithms were better than that of the neurologists. Furthermore, EMTS can be utilized to both modify the quantification algorithms of ISWDs and improve the assessment skills of young neurologists.

Relationship between rotational disc displacement of the temporomandibular joint and the dentoskeletal morphology.

ObjectiveThe purpose of this study was to evaluate the relationship between rotational disk displacement (DD) of the temporomandibular joint (TMJ) and the dentoskeletal morphology.MethodsWomen aged > 17 years were included in this study. Each subject had a primary complaint of malocclusion and underwent routine cephalometric examinations. They were divided into five groups according to the findings on sagittal and coronal magnetic resonance images of their TMJs bilateral normal disk position, bilateral anterior DD with reduction (ADDR), bilateral rotational DD with reduction (RDDR), bilateral anterior DD without reduction (ADDNR), and bilateral rotational DD without reduction (RDDNR). Twenty-three cephalometric variables were analyzed, and the Kruskal–Wallis test was used to evaluate differences in the dentoskeletal morphology among the five groups.ResultsPatients with TMJ DD exhibited a hyperdivergent pattern with a retrognathic mandible, unlike those with a normal disk position. These specific skeletal characteristics were more severe in patients exhibiting DD without reduction than in those with reduction, regardless of the presence of rotational DD. Rotational DD significantly influenced horizontal and vertical skeletal patterns only in the stage of DD with reduction, and the mandible exhibited a more backward position and rotation in patients with RDDR than in those with ADDR. However, there were no significant dentoskeletal differences between ADDNR and RDDNR.ConclusionsThe results of this study suggest that rotational DD of TMJ plays an important role in the dentoskeletal morphology, particularly in patients showing DD with reduction.

Translational and rotational ground motion simulations in homogeneous reduced micropolar half-space

The present article focusses on determining the response of reduced micropolar half-space subjected to specific loading conditions. Analytical expressions for translational and rotational displacements are derived for the half-space subjected to impulses using the method of potentials. The derived analytical expressions are numerically evaluated to determine the response of reduced micropolar half-space subjected to buried impulses acting in both horizontal and vertical directions. The derived Green’s functions are further used to obtain the surface translations and rotations for the half-space subjected to earthquake force. Parametric analysis is carried to understand the effect of additional material parameters of the reduced micropolar medium on the surface ground motions. Finally, ground motions are simulated for 2012 Wutai, Taiwan, earthquake by modelling the medium as a homogeneous reduced micropolar half-space consisting of rock material properties.

Female kinematics and muscle responses in lane change and lane change with braking maneuvers

Objective The primary aim of this article is to extensively study female occupant kinematics and muscle activations in vehicle maneuvers potentially occurring in precrash situations and with different seat belt configurations. The secondary aim is to provide validation data for active human body models (AHBMs) of female occupants in representative precrash loading situations. Methods Front seat female passengers wearing a 3-point seat belt, with either standard or pre-pretensioning functionality, were subjected to multiple autonomously carried-out lane change and lane change with braking maneuvers while traveling at 73 km/h. This article quantifies the head center of gravity and T1 vertebra body (T1) linear and rotational displacements. This article also includes surface electromyography (EMG) data collected from 38 muscles in the neck, torso, and upper and lower extremities, all normalized by maximum voluntary contraction (MVC). The raw EMG data were filtered, rectified, and smoothed. Separate Wilcoxon signed-rank tests were performed on EMG onset and amplitude as well as peak displacements of head and T1 considering 2 paired samples with the belt configuration as an independent variable. Results Significantly smaller lateral and forward displacements for head and T1 were found with the pre-pretensioner belt versus the standard belt (P < .05). Averaged muscle activity, mainly in the neck, lumbar extensor, and abdominal muscles, increased up to 16% MVC immediately after the vehicle accelerated in the lateral direction. Muscles in the right and left sides of the body displayed differences in activation time and amplitude relative to the vehicle’s lateral motion. For specific muscles, lane changes with the pre-pretensioner belt resulted in earlier muscle activation onsets and significantly smaller activation amplitudes compared to the standard belt (P < .05). Conclusions The presented results from female passengers complement the previously published results from male passengers subjected to the same loading scenarios. The data provided in this article can be used for validation of AHBMs of female occupants in both sagittal and lateral loading scenarios potentially occurring prior to a crash. Additionally, our results show that a pre-pretensioner belt decreases muscle activation onset and amplitude as well as forward and lateral displacements of head and T1 compared to a standard belt, confirming previously published results.

Analysis of a curved Timoshenko nano-beam with flexoelectricity

A Timoshenko beam model is applied for the analysis of the flexoelectric effect for a curved nano-beam. This theory transforms the beam to a 1-d problem along the beam axis. The electric intensity vector for the open-circuit condition can be expressed by mechanical quantities, namely strains and strain gradients. The variational principle is applied to derive the system of ordinary differential equations (ODEs) for the beam deflection, cross-section rotation, and in-plane displacement. A numerical solution based on the Taylor series expansion with Cartesian coordinate along the beam is proposed for the system of ODEs. A convergence analysis with respect to the number of terms in the Taylor series expansion is performed. Numerical results for the beam deflection, rotation, in-plane displacement, and induced electric intensity vector are presented for various flexoelectric coefficients and the beam curvature.

Abstract PS15-02: Permanent marker free surface-guided breast radiotherapy: Implementing a new technique

Abstract Background:It is standard practice in our centre for patients to be given permanent skin marks during breast radiotherapy planning, for use as reliable landmarks in daily reproduction of their positioning for treatment. However, these permanent marks (tattoos) may have a significant psychological impact on patients (1). In recent years, there have been technological advances in surface-guided radiotherapy techniques (SGRT) which may provide improved set-up accuracy compared to permanent markers.Aims:1. To evaluate if surface-guided set-up is as good, if not better, than set-up with permanent markers alone.2. To safely implement a permanent marker (PM) free, surface-guided set-up technique.Methods:A pilot study was conducted with tangents-only breast patients treated in free breathing (FB). All treatments were delivered on Varian TrueBeam linear accelerators, with patients immobilised on a couch indexed breast board. The study group (n=20) were set up using PMs with adjustments guided by the AlignRT® SGRT system to optimise patient positioning. Imaging (MV tangent images) was performed as per standard protocol on fractions 1-3, 8 and 12. Additional imaging was performed if indicated. The translational and rotational displacements calculated by the TrueBeam verification system for this group were compared to average displacements calculated for patients set up using PMs alone (the control group, n=20). Encouraged by the results of the pilot study, the centre moved to safely roll-out the PM-free technique to include additional applications. The step-wise approach taken will be described.Results:The mean displacements calculated from the verification imaging are shown in Table 1 below: SGRT set-up demonstrated statistically-significant improvements compared to PM set-up alone with respect to lateral, vertical and total translational displacements. Longitudinal displacements favoured PM set-up alone but this did not reach statistical significance. Rotational displacements favoured SGRT set-up and the results reached statistical significance.Given the improved set-up accuracy with SGRT, and the wish to reduce the psychological morbidity of radiotherapy for our breast cancer patients, the centre moved to safely implement a PM free SGRT technique along agreed timelines as shown in Table 2: Conclusions:Our pilot study demonstrated that surface-guided radiotherapy (SGRT) set-up is as good, if not better, than set-up with permanent markers (PM) alone in tangent-only free-breathing patients. Subsequent further analysis showed improved consistency of set-up guided by PM plus SGRT for all breast set-ups (to include nodal regions and DIBH). We have described our step-wise approach to setting up PM free radiotherapy delivery for breast cancer patients, which has additional advantages in maintaining social distancing in the COVID19 era.Refs1. Psychosocial impacts of radiation tattooing for breast cancer: a critical review. B Clow et al. Displacement20 patients PM only (106 #s)20 patients PM + SGRT (114 #s)Statistical significanceLateral (mm)2.271.56yesVertical (mm)2.692yesLongitudinal (mm)1.441.53noTotal translation/Vector (mm)4.13.21yesPitch (0)0.610.42yesYaw (0)0.670.53yes Development stageDetailDateSet up tangents only FB patients using PM + SGRTPatients set up using PM + SGRT – pilot study showed comparable or better than PM alone (see Table 1)Oct 2018Breast Working Party decision to use PM + SGRT for all set-upsTo build on SGRT experience from pilot study to include all breast set-ups (nodal regions &amp; Deep Inspiration Breath Hold, DIBH)Sept 2019Site visit to Birmingham, UKRadiographer-led visit to observe PM free breast techniqueOct 2019Report to Breast Working Party about PM + SGRT guided set upReport showed improved consistency using SGRT and reduction in displacements for all set-upsNov 2019Site Visit to Inverness, UKMulti-disciplinary team (ClinOnc/Rad/Dosimetry) attended Inverness to review PM free CT, Planning &amp;TreatmentMarch 2020Need to Improve Social distancing from COVID19Increased use of SGRT to maintain social distancing in RT treatment room at outbreak of pandemicMarch 2020Removal of breast bordersTo simplify set up processMay 2020Use treatment capture images to resolve set up issues + use SGRT for electron sets with PMsStaff will have time to practice SGRT set up without using PMs before the PM-free technique is implemented26th May 2020New CT protocol for DIBHThis allows fusion of scans so that patients can be set up in FB and monitored during treatment in DIBH8th June 20201st PM free Tangent only FB patient treatedMean translational displacements (mm) 0.05 Vert/0 Long/0.04 LatMean rotational displacements (o) Pitch 1.3/Roll 0/Yaw 0.917th June 2020 Citation Format: Christy Goldsmith, Deirdre Dobson, Adam Littler, Elinor Sawyer, Georgina Moriggi, Roshni Chauhan. Permanent marker free surface-guided breast radiotherapy: Implementing a new technique [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS15-02.

Development of a rotatable similar simulation experimental system for steep coal seam mining

Purpose Currently, the existing similar simulation is still limited in the following aspects: un-rotatable laboratory devices, the difficulty in the pavement on steep seams and great error of the experimental data. Design/methodology/approach To address above-mentioned problems, this study combined theoretical analysis and numerical simulation and developed a rotatable experimental system for similar simulation on steep coal seam mining on the premise of ensuring experimental safety. Findings The present experimental system mainly consists of the model support, the rotation system and the bearing system. By taking into account the experimental requirements and actual laboratory space, the sizes of the model support and the bearing system were determined. Considering the requirements in space limit and rotation stability, the rotation mode of vertical sliding on the left side and the horizontal sliding on the lower side was designed. Originality/value Using programmable logic controller automatic angle control technology, the rotation angle, velocity and displacement of the model can be automatically adjusted and controlled so as to achieve safe rotation and precise control. Finally, the calculation method of the mass of the required similar materials for paving the coal strata at different inclination angles and in different horizons was analyzed, and the related mass proportion calculation software was developed.

Improved progressive collapse resistance of irregular reinforced concrete flat slab buildings under different corner column failures

As the flat slab building with irregular geometric configurations is commonly designed to advance urban development and for architectural demands, its behaviour to resist progressive collapse must be examined. The building's progressive collapse occurs when one or more vertical structural load-bearing elements such as columns are removed due to an extreme load caused either by natural or manmade hazards. The present analytical research examines the failure criteria and improvement in the progressive collapse resistance of five and ten-storey irregular R.C flat slab building by incorporating perimeter beams along with strengthened perimeter columns in the building. The progressive collapse study is conducted by removing different corner columns on the ground floor as per the GSA guidelines (2003) and assessing the spread of damage. Static analysis is performed using the structural analysis program ETABS 2016. For each case, the results have been taken in terms of demand capacity ratio (DCR) at critical sections and, chord rotation and joint displacement at locations of removal of columns. The results showed that the presence of strengthened columns provides sufficient stiffness and the perimeter beam provides load paths for the building's gravity loads, thus making it resistive to progressive collapse under column failure.

Tilt errors of translational accelerometers attached to dynamic systems with tilt motion caused by the system response

Translational inertia sensors - like the accelerometer - can measure the translational acceleration but they are incapable of distinguishing between translational and tilt motions. As an accelerometer tilts, it will measure a component of the gravitational acceleration along with the translational acceleration of the sensors. This results in a tilt error on the measured acceleration that masks the actual translational acceleration. In this paper, tilt error is studied for accelerometers attached to linear, stationary, and dynamic systems where the tilt motion origins from the system response. Mathematical formulations of the tilt errors are introduced where an impulse and frequency response function matrix for the measured acceleration from accelerometers is derived. It is proven that the tilt error is pollution by the rotational displacement on the translational acceleration of the accelerometers. Thus, the displacement of a dynamic system merges with its acceleration in the presence of tilt errors and the level of tilt error depends on the system and the excitation. In this paper, a method is introduced to reduce the tilt error. Both theory and tilt reduction are verified on a test-specimen in the laboratory.

Dynamic analysis of multi point winding hoisting system under non synchronous movements of wire ropes in deep well

Taking the multi point winding hoisting system with depth of 1000 m, drum radius of 0.4 m, drum radius difference of 0.1 mm as the research background, a model of multi point winding hoisting system under non synchronous movement of wire ropes is established, and the mathematical model is deduced by Lagrange equation. Then the dynamic characteristic of super deep multi point winding hoisting system under non synchronous movements of wire ropes is analyzed. The results show that: the rotational displacement of mass block is 5°, the rotational velocity is 0.07 °/s in the stage of constant speed. The rope length difference reaches 0.07 m, the tension of each wire rope changes 333 N, accounted for about 7 % of the average tension. And with the length difference increasing 35 mm, the force differences increasing 320 N, which indicates that the length difference has great impact on the tension difference of wire ropes. Finally, the mathematical model is verified through experiment.

Irregular and suppressed elastic deformation by a structural twist in cellulose nanofibre models

The elastic responsiveness of single cellulose nanofibres is important for advanced analysis of biological tissues and their use in sophisticated functional materials. However, the mechanical responsiveness derived from the twisted structure of cellulose nanofibres (CNFs) has remained unexplored. In this study, finite element simulations were applied to characterize the deformation response derived from the torsional structure by performing tensile and bending tests of an unconventionally very long and twisted rod model, having the known dimensional parameters and properties of CNFs. The antagonistic action of two types of structural elements (a contour twist and a curvilinear coordinate) was found to result in an irregular deformation response but with only small fluctuations. The contour twist generated rotational displacements under tensile load, but the curvilinear coordinate suppressed rotational displacement. Under bending stress, the contour twist minimized irregular bending deformation because of the orthotropic properties and made the bending stress transferability a highly linear response.

Identification of real translational and rotational displacements of six-axial shakers with only six measured linear accelerations

Qualification tests on the vibrations of on-board equipment depend on the ability of the shaker used to reproduce as precisely as possible the excitation profiles stipulated by standards, given that real operational conditions are generally multiaxial. Using a set of six measured linear accelerations the original method proposed permits determining real six-axial shaker displacements combining three translations and three rotations. Thus, this method, named REDEAT (REal Displacement from Experimental Acceleration with inverse Technique), is useful for introducing these real displacements in the numerical simulation in view of experimentally validating the dynamic behavior model of on-board equipment. Moreover, the REDEAT method evaluates the deviation between real and intended forced displacements. Its principle resides in solving a system of nonlinear time-differential equations expressed, by resorting to numerical integration combining Newmark and Newton–Raphson schemes. In order to overcome the classical divergence issue inherent to the use of numerical integration, data processing tools are employed, consisting of the application of successive high pass filters and window functions. The REDEAT method is applied to a hydraulic 6-DOF shaker equipped with accelerometers and gyroscopes, through a combination of two harmonic rotations and a full 6-DOF random motion. In addition, the influence of the method’s parameters and of the six input accelerograms chosen from twelve is investigated.

Natural vibration characteristics determination of elastic beam with attachments based on a transfer matrix method

The transfer matrix method for multibody system takes into account the accuracy of the equations of motion and the efficiency of the algorithm. Especially if a system is composed of flexible and rigid components, transfer matrix method for multibody system reduces the dynamics problem to an overall transfer equation which only involves boundary state vectors. The state vectors at the boundary are made up of rotation angles, displacements, shear forces, and bending moments, which are normally half known and half unknown. The proposed transfer matrix method for multibody system of multibody system dynamics to determine the vibration characteristics is easy to formulate, systematic to apply, and simple to code. The purpose of this study is to introduce a modeling and simulation idea of beam with attachments based on transfer matrix method for multibody system. Numerical results for several examples of beam with attachments are presented to demonstrate the validity of this method.

Motion and its Effects on the Cement Mantle – A Biomechanical Analysis of Femoral Stem Displacement during Implant Cementation

Background: It is a common notion that motion of a femoral component during cementation should be avoided as it may weaken the cement mantle. We created an in vitro model of cemented femoral components and subjected them to varying rotational motion during the cement curing process, to measure the effect on the pullout strength of the stem. Methods: 21 sawbones femurs were separated into four groups. The first group served as control and was cemented in a standard fashion. The remainder of the stems were divided into groups and subjected to angular rotational displacement within the cement mantle during curing . Anteroposterior and lateral radiographs were obtained of each model to evaluate for cement defects. Pullout strength testing was performed. Results: Despite rotational displacement, no cement defects were noted on imaging. The control stems showed an average pullout strength of 3735.79N. The experimental groups showed a trend for lower failure loads but it was not statistically significant (P=0.063). Of the 21 stems tested, three encountered cement mantle failure and associated stem pullout and the remainder failed by peripros-thetic fracture. Conclusion: Despite conventional thinking that rotational displacement during the cementing process leading to disruption of the cement mantle integrity, this was not borne out in our study. This should give surgeons confidence that in the set-ting of unintended rotational displacement of a femoral stem, returning the stem to its original position does not significantly compromise the integrity of the cement mantle or the pullout strength of the femoral implant. Small displacement of the femoral stem with prompt correction during cement curing does not cause evident cement mantle defects or a loss of femoral stem pullout strength.