Rigid Body Model Research Articles

CALIBRATION OF HOLZAPFEL-GASSER-OGDEN COLLATERAL LIGAMENT PROPERTIES IN A HYBRID POST-ARTHROPLASTY KNEE JOINT MODEL FOR LAXITY TESTING

This study aims to create a novel computational workflow for frontal plane laxity evaluation which combines a rigid body knee joint model with a non-linear implicit finite-element model wherein collateral ligaments are anisotropically modelled using subject-specific, experimentally calibrated Holzpfel-Gasser-Ogden (HGO) models.The framework was developed based on CT and MRI data of three cadaveric post-TKA knees. Bones were segmented from CT-scans and modelled as rigid bodies in a multibody dynamics simulation software (MSC Adams/view, MSC Software, USA). Medial collateral and lateral collateral ligaments were segmented based on MRI-scans and are modelled as finite elements using the HGO model in Abaqus (Simulia, USA). All specimens were submitted varus/valgus loading (0-10Nm) while being rigidly fixed on a testing bench to prevent knee flexion. In subsequent computer simulations of the experimental testing, rigid bodies kinematics and the associated soft-tissue force response were computed at each time step. Ligament properties were optimised using a gradient descent approach by minimising the error between the experimental and simulation-based kinematic response to the applied varus/valgus loads. For comparison, a second model was defined wherein collateral ligaments were modelled as nonlinear no-compression spring elements using the Blankevoort formulation.Models with subject-specific, experimentally calibrated HGO representations of the collateral ligaments demonstrated smaller root mean square errors in terms of kinematics (0.7900° +/− 0.4081°) than models integrating a Blankevoort representation (1.4704° +/− 0.8007°).A novel computational workflow integrating subject-specific, experimentally calibrated HGO predicted post-TKA frontal-plane knee joint laxity with clinically applicable accuracy. Generally, errors in terms of tibial rotation were higher and might be further reduced by increasing the interaction nodes between the rigid body model and the finite element software. Future work should investigate the accuracy of resulting models for simulating unseen activities of daily living.

THE CONTRIBUTION OF THE MASTICATORY MUSCLES TO PRODUCTION OF 3D OCCLUSAL LOADS ACROSS THE DENTAL ARCH

Occlusal loading and muscle forces during mastication aids in assessment of dental restorations and implants and jaw implant design; however, three-dimensional bite forces cannot be measured with conventional transducers, which obstruct the native occlusion. The aim of this study was to combine accurate jaw kinematics measurements, together with subject-specific computational modelling, to estimate subject-specific occlusal loading and muscle forces during mastication.Motion experiments were performed on one male participant (age: 39yrs, weight: 82kg) with healthy dentition. Two low-profile magnetic sensors were fixed to the participant's teeth and the two dental arches digitised using an intra-oral scanner. The participant performed ten continuous of chewing on a polyurethane rubber sample of known material properties, followed by maximal compression (clenching). This was repeated at the molars, premolars of both the left and right sides, and central incisors. Jaw motion was simultaneously recorded from the sensors, and finite element modelling used to estimate bite force. Specifically, simulations of chewing and biting were performed by driving the model using the measured kinematics, and bite force magnitude and direction quantified. Muscle forces were then evaluated using a rigid-body musculoskeletal model of the patient's jaw.The first molars generated the largest bite forces during chewing (left: 309 N, right: 311 N) and maximum-force biting (left: 496 N, right: 495 N). The incisors generated the smallest bite forces during chewing (75 N) and maximum-force biting (114 N). The anterior temporalis and superficial masseter muscles had the largest contribution to maximum bite force, followed by the posterior temporalis and medial pterygoid muscles.This study presents a new method for estimating dynamic occlusal loading and muscle forces during mastication. These techniques provide new knowledge of jaw biomechanics, including muscle and occlusal loading, which will be useful in surgical planning and jaw implant design.

End Motion Path Analysis of Notched Variable Cross-section Flexible Manipulator Based on 3R Pseudo-Rigid Body Model

A wire-driven planar curved notched flexible manipulator with variable cross-section is designed. Based on the Bernoulli Euler beam equation, the end track and rotation angle of the notched flexible manipulator with variable cross-section after applying force is deduced theoretically. In addition, the 3R pseudo rigid body model is used to calculate the end track and rotation angle, and ABAQUS finite element analysis software is used for motion simulation. Then, MATLAB is used for post-processing to obtain the end track of the flexible manipulator. By comparing the track of the 3R pseudo rigid body model with the ABAQUS simulation track, the relative error is obtained. The conclusion proves that the 3R pseudo rigid body model can effectively simulate the end track of a notched flexible manipulator with variable cross-section after bending, which expands a new method for solving the complex end motion problem of a flexible manipulator with variable cross-section, and also broadens the applicable structure of the 3R pseudo rigid body model.

Collaborative Simulation of Mechanical Structure and Control Systems of Leighton Chajnantor Telescope

Leighton Chajnantor Telescope (LCT) will be moved from the summit of Maunakea, Hawaii to Chajnantor Plateau, Chile and be refurbished there. Strong wind disturbance at the new site will bring great challenges to the servo control of LCT. It is necessary and important to develop a simulation platform that behaves as close as possible to the real telescope for testing the performance of the designed servo controller. In this paper, a collaborative simulation platform of LCT based on Adams and Matlab/Simulink is constructed. On this platform, the mechanical structure model of LCT can be integrated with its control system model such that a collaborative simulation of the mechanical structure and the control system of LCT can be conducted. The mechanical structure model of LCT, which contains both rigid body models (i.e., the mount) and flexible body models (i.e., the primary reflector), is developed by using Adams. The servo system model and the wind disturbance model are constructed by using Matlab/Simulink. By conducting collaborative simulation, the performances of the servo controller based on the rigid body model and the rigid-flexible coupling model of LCT are compared. The comparison shows that the controller designed based on the rigid body model does not perform well when it is employed to control the rigid-flexible coupling model of LCT. However, by readjusting parameters of the servo controller, its performance can be further improved when applied to the rigid-flexible coupling model. Therefore, an LCT model of integrated mechanical structure and control systems is very helpful for analyzing its performance more accurately and designing a better servo controller.

Fluid-structure interaction simulation for performance prediction and design optimization of parafoils

Parachute design is challenging to achieve innovative progress if the dominant role of testing continues, as it will be an increasingly expensive and time-consuming work. The aim of this study is to establish a reliable and efficient design tool using existing advanced numerical modeling methods. This paper presents a numerical method based on two-way coupled fluid-structure interaction (FSI) strategies for predicting aerodynamic and flight performance for parafoil design optimization. The nonlinear finite element method was used for the canopy fabric model and flow field, and the fluid dynamics were solved by Reynolds-averaged Navier-Stokes with the Spalart-Allmaras turbulence model. The FSI simulations are performed to assess the aerodynamic performance and structural deformations of full-scale parafoil canopies. The equilibrium shape of the parafoil canopy under steady gliding states and the relevant flow field were analyzed to enhance confidence and understanding in the performance prediction of new parachutes. Three-dimensional FSI simulation results of parafoils show that the inflation caused flexible bulges of canopy cells, and the maximum lift coefficient increased more than 16% with a higher stall angle of attack than that of the rigid body model. A parafoil with a smaller leading edge inlet or a scaling down area can improve the aerodynamic performance, mainly manifested in a higher lift-to-drag ratio and better anti-stall performance. Finally, the prediction results of parafoil glide performance were verified by flight test data, and the prediction accuracy of the flexible model is more than 10% higher than that of the rigid model. This work makes the simulation tools a step closer to practical application.

Additive Manufactured Piezoelectric-Driven Miniature Gripper

In several cases, it is desirable to have prototypes of low-cost fabrication and adequate performance. In academic laboratories and industries, miniature and microgrippers can be very useful for observations and the analysis of small objects. Piezoelectrically actuated microgrippers, commonly fabricated with aluminum, and with micrometer stroke or displacement, have been considered as Microelectromechanical Systems (MEMS). Recently, additive manufacture using several polymers has also been used for the fabrication of miniature grippers. This work focuses on the design of a piezoelectric-driven miniature gripper, additive manufactured with polylactic acid (PLA), which was modeled using a pseudo rigid body model (PRBM). It was also numerically and experimentally characterized with an acceptable level of approximation. The piezoelectric stack is composed of widely available buzzers. The aperture between the jaws allows it to hold objects with diameters lower than 500 μm, and weights lower than 1.4 g, such as the strands of some plants, salt grains, metal wires, etc. The novelty of this work is given by the miniature gripper’s simple design, as well as the low-cost of the materials and the fabrication process used. In addition, the initial aperture of the jaws can be adjusted, by adhering the metal tips in the required position.

Range observer‐based formation control for heterogeneous spatial underactuated vehicle networks

AbstractIn this work, we solve the distributed formation control problem for heterogeneous spatial underactuated vehicle networks subject to switching topologies. We consider the spatial rigid body model of underwater and aerial vehicles with one translational actuator for propulsion and three rotational actuators, without any simplification. A distributed finite‐time sliding mode observer is designed to estimate the ranges between vehicles based on the bearing angles, and thus, the control design does not require relative position or distance measurements. A coordinate transformation is proposed to define continuous reference velocity trajectories under switching topologies. Then, based on the cascade structure, a distributed formation protocol is presented which guarantees the global asymptotic convergence for the closed‐loop system. The formation controller has a simple structure, requires only neighbor‐to‐neighbor information exchange, and all the measurements may be obtained using simple onboard sensors. Numerical simulations for a group of heterogeneous spatial underactuated vehicles including autonomous underwater vehicles and quadrotors are presented.

Subject-specific computational modeling of acromioclavicular and coracoclavicular ligaments.

Disruption of the acromioclavicular joint is a common injury. Despite the different surgical procedures described for treating this injury, complications such as loss of reduction and failure of fixation remain unacceptably high. We developed a computer model of the acromioclavicular joint to better understand the biomechanical contributions of the ligaments that are typically injured. Six fresh frozen human cadaveric shoulders were tested on an AMTI VIVO 6-degree of freedom test platform to measure force-displacement in inferior translation, anteroposterior translation, and internal rotation before and after sequentially transecting the coracoclavicular and acromioclavicular ligaments. These data were used to construct computer models of each specimen. Three-dimensional computed tomographic scans were used to generate a rigid-body dynamics model using the AnyBody Modeling System. The scapula and clavicle were connected by the acromioclavicular joint capsule, the conoid ligament, and the trapezoid ligament. Subject-specific ligament properties were calculated by matching computer predictions to experimental force-displacement data. The calculated free lengths of the conoid, trapezoid, and acromioclavicular ligaments were 13.5 (±3.2), 11.8 (±2.4), and 11.0 (±2.7) mm, respectively. The calculated stiffnesses of the conoid, trapezoid, and acromioclavicular ligaments were 34.3 (±6.3), 28.4(±3.2), and 33.8 (±8.2) N/mm, respectively. Root mean square deviation (RMSD) of predicted force-displacement curves relative to experimental force-displacement curves (during inferior and anteroposterior translation) was less than 1 mm. For validation of subject-specific models, after ligament properties were calculated, the RMSD of the predicted torque over 15° of internal rotation was 12% of maximum rotational torque (average for 6 specimens). Acromioclavicular disruption results in multidirectional instability, which requires careful consideration of the individual contributions of the injured ligaments. In addition, variations in patient anatomy can significantly affect the biomechanical stability of the reconstruction. Subject-specific models can enhance our understanding of the individual and collective biomechanical contributions of the injured soft tissues to the multiaxial stability of the acromioclavicular joint. These models may also be useful for analyzing and assessing biomechanical stability after various types of surgical reconstruction.

Investigating the Orientation of an Interfacially Adsorbed Monoclonal Antibody and Its Fragments Using Neutron Reflection.

Interfacial adsorption is a molecular process occurring during the production, purification, transport, and storage of antibodies, with a direct impact on their structural stability and subsequent implications on their bioactivities. While the average conformational orientation of an adsorbed protein can be readily determined, its associated structures are more complex to characterize. Neutron reflection has been used in this work to investigate the conformational orientations of the monoclonal antibody COE-3 and its Fab and Fc fragments at the oil/water and air/water interfaces. Rigid body rotation modeling was found to be suitable for globular and relatively rigid proteins such as the Fab and Fc fragments but less so for relatively flexible proteins such as full COE-3. Fab and Fc fragments adopted a 'flat-on' orientation at the air/water interface, minimizing the thickness of the protein layer, but they adopted a substantially tilted orientation at the oil/water interface with increased layer thickness. In contrast, COE-3 was found to adsorb in tilted orientations at both interfaces, with one fragment protruding into the solution. This work demonstrates that rigid-body modeling can provide additional insights into protein layers at various interfaces relevant to bioprocess engineering.

Design, Modeling, and Evaluation of a Hybrid Driven Knee-Ankle Orthosis With Shape Memory Alloy Actuators

Abstract This paper demonstrates the mechanical design, analysis, and evaluation of a knee-ankle orthosis (KAO) for lower limb rehabilitation, including shape memory alloy (SMA) actuators and DC brushless motor actuators. First, the mechanical structure of the KAO is detailed, including the actuator system, transmission mechanism, monitoring device, and processing method of SMA actuators. Next, the dynamic model of SMA spring actuators in the phase transition process is established based on the thermal constitutive model of SMA. In addition, the dynamic output response of the knee joint under three working states is analyzed, and the rotation angle of SMA soft actuator during bending is described by pseudo rigid body model. Finally, the output of SMA actuator is preliminarily evaluated through experiments. The experimental results show that the maximum displacement of SMA spring actuator is 54.36 mm, the maximum restoring force during phase transformation is 4.14 N, and the maximum rotation angle of SMA soft actuator is 43.18 deg. The experimental results are consistent with the theoretical model.

A Real-Time Planning and Control Framework for Robust and Dynamic Quadrupedal Locomotion

Legged locomotion poses significant challenges due to its nonlinear, underactuated and hybrid dynamic properties. These challenges are exacerbated by the high-speed motion and presence of aerial phases in dynamic legged locomotion, which highlights the requirement for online planning based on current states to cope with uncertainty and disturbances. This article proposes a real-time planning and control framework integrating motion planning and whole-body control. In the framework, the designed motion planner allows a wider body rotation range and fast reactive behaviors based on the 3-D single rigid body model. In addition, the combination of a Bézier curve based trajectory interpolator and a heuristic-based foothold planner helps generate continuous and smooth foot trajectories. The developed whole-body controller uses hierarchical quadratic optimization coupled with the full system dynamics, which ensures tasks are prioritized based on importance and joint commands are physically feasible. The performance of the framework is successfully validated in experiments with a torque-controlled quadrupedal robot for generating dynamic motions.

Vehicle Dynamics and Train-Induced Ground Vibration—Theoretical Analyses and Simultaneous Vehicle, Track, and Soil Measurements

Ground vibrations near railway lines are generated by the forces that are acting between wheel and rail. It seems to be a straight forward assumption that the vehicle dynamics are important for the level and the frequencies of the excitation forces. Different vehicle dynamics phenomena are analysed for their role in the excitation of ground vibrations: rigid body modes of the bogies, elastic (bending) modes of the car body, and elastic modes of the wheelset. The theoretical analyses use rigid body models, simplified elastic models, and detailed elastic models. Some of these problems are vehicle–track interaction problems where 3D finite-element boundary-element models have been used for the track and soil. It is shown that the rigid or flexible vehicle modes are well in the frequency range of ground vibrations (4 to 100 Hz). They have an influence on the excitation force but the additional forces are rather small and can be neglected in ground vibration prediction. The theoretical results are checked by experimental results of a simultaneous measurement of vehicle, track, and ground vibrations.

Joint Localization and Environment Sensing of Rigid Body With 5G Millimeter Wave MIMO

Accurately localizing a target in three-dimensional (3D) space assisted with the fifth generation (5G) wireless systems in an indoor environment could enable a wide variety of new applications, including precise control for factory automation, self-maneuver of the vehicle and so on. However, controlling a target in 3D space relies on a rigid body modelling with six degrees of freedom, which dramatically increases the localization difficulty and complexity. Furthermore, for radio-based localization methods, the lack of line-of-sight (LOS) and the existence of reflection points in the environment will also influence the rigid body localization process. To improve the rigid body localization accuracy as well as unravel useful environmental information from the received signal, a novel rigid body joint active localization and environment sensing scheme is proposed in this paper. Specifically, the multi-path effect of millimeter wave (mm-wave) signal with a single reflection can be exploited to enhance the rigid body localization accuracy, and it can also be utilized to locate the reflection points, which further enables a new way for environmental sensing. Hence, we first propose a two-step hierarchical compressive sensing algorithm to extract the angular and distance information of the LOS (if available) and single-bounce specular reflections. Then a particle swarm optimization (PSO) based method is derived to recover the posture of the rigid body and the location of reflection points. The Cramér-Rao lower bound (CRLB) on angle, rigid body posture and reflection points position uncertainty is also analyzed. The simulation results demonstrate that the proposed scheme can achieve high accuracy rigid body localization and locate the reflection points around the rigid body even under obstructed-line-of-sight (OLOS) conditions in an indoor scene.

Data analysis and modeling of small-angle neutron scattering data with contrast variation from bio-macromolecular complexes.

Small-angle neutron scattering (SANS) with contrast variation (CV) is a valuable technique in the structural biology toolchest. Accurate structural parameters-e.g., radii of gyration, volumes, dimensions, and distance distribution(s)-can be derived from the SANS-CV data to yield the shape and disposition of the individual components within stable complexes. Contrast variation is achieved through the substitution of hydrogen isotopes (1H for 2H) in molecules and solvents to alter the neutron scattering properties of each component of a complex. While SANS-CV can be used a stand-alone technique for interrogating the overall structure of biomacromolecules in solution, it also complements other methods such as small-angle X-ray scattering, crystallography, nuclear magnetic resonance, and cryo-electron microscopy. Undertaking a SANS-CV experiment is challenging, due in part to the preparation of significant quantities of monodisperse samples that may require deuterium (2H) labeling. Nevertheless, SANS-CV can be used to study a diverse range biomacromolecular complexes including protein-protein and protein-nucleic acid systems, membrane proteins, and flexible systems resistant to crystallization. This chapter describes how to approach the data analysis and modeling of SANS data, including: (1) Analysis of the forward scattering (I(0)) and calculation of theoretical estimates of contrast; (2) Analysis of the contrast dependence of the radius of gyration using the Stuhrmann plot and parallel axis theorem; (3) Calculation of composite scattering functions to evaluate the size, shape, and dispositions of individual components within a complex, and; (4) Development of real-space models to fit the SANS-CV data using volume-element bead modeling or atomistic rigid body modeling.

A simplified model for whole-body angular momentum calculation.

The capability to monitor gait stability during everyday life could provide key information to guide clinical intervention to patients with lower limb disabilities. Whole body angular momentum (Lbody) is a convenient stability indicator for wearable motion capture systems. However, Lbody is costly to estimate, because it requires monitoring all major body segment using expensive sensor elements. In this study, we developed a simplified rigid body model by merging connected body segments to reduce the number of body segments, which need to be monitored. We demonstrated that the Lbody could be estimated by a seven-segment model accurately for both people with and without lower extremity amputation.

Simulation and Initial Experiment of a Twist-Tilt Quadcopter for Fully Actuated Motion

Although conventional quadcopters are well developed and are used in many applications, they are limited to 4 degree-of-freedom motion. For instance, the underactuated quadcopters cannot hover with inclined roll or pitch angles. To achieve fully actuated 6 degree-of-freedom motion, this paper presents a design, construction, and initial experimental results of an overactuated twist-and-tilt quadcopter configuration proposed in the group's previous work. The copter is comprised of four rotors, where each rotor's twist and tilt angles are independently adjustable over one full rotation by servo actuators. The copter weighs 5.78kg and is designed to carry an additional 5kg payload. A comprehensive multi-body virtual plant simulation model was also created with identified parameters from the rotor-arm drive dynamics to verify the control, which is designed based on a lumped single rigid body model. Also, an experimental rig was constructed to facilitate flight testing in a small physical space with safety to both the copter and environment. The initial experimental results for 6 degree-of-freedom motion is then presented.

Finite element simulation of an upliftable rigid frame bridge under earthquakes: Experimental verification

Under strong earthquakes, the shallow foundation bridge would experience partial or temporary separation of foundation from the support, hereafter termed as uplift. The uplift can activate rigid-like body movements and cut off the energy transfer of earthquake motions to the upper structure. However, most of the previous studies focus on the theoretical analysis using over simplified rigid body models, and some analyses often have applicable limitations because of their specific assumptions. Experimental research using a shaking table is time-consuming and expensive. In this paper, a finite element model (FEM) of an upliftable rigid frame bridge is developed and verified by a series of shaking table tests. The experimental bridge model is designed according to a similarity of 1:10 based on a viaduct in Auckland. The model has two kinds of foundation forms: fixed foundation and upliftable foundation, the corresponding FEM of the bridges with a fixed and an upliftable foundation is established. In the numerical investigation, the behavior of rocking of the structure due to the uplift between the foundation and the support was considered by Winkler springs. The proposed FEM was verified through the shaking table test results. It shows that the FEM is consistent with the experimental results and can be used to evaluation the displacement, acceleration and bending moment of bridges with an upliftable foundation.

Design and Load Kinematics Analysis of Rollover Rehabilitation Mechanism Fitting Human Motion Curve.

Supine rollover plays an important role in the prevention of pressure sores in long-term bedridden patients. It is of great significance to study the mechanism of human supine rollover movement and to design the rehabilitation rollover mechanism in line with man-machine cooperation. In human supine rollover movement, shoulder and hip are the key parts of force application. Based on anatomical theory, the motion trajectory information of shoulder and hip skeletal rehabilitation parts is collected by combining optical motion capture and rigid body modeling. Following a kinematics simulation analysis, the simulation curve was compared with the experimental curve track; the numerical difference was small. It is proved that the simulation model is correct, and it is also shown that the designed rehabilitation rollover mechanism can better reproduce the natural rolling motion state of the human body. It can meet the requirements of human-machine synergistic assisted lateral roll rehabilitation aids and provides a solution for pressure sore prevention.

Simplified analytical procedure to calculate the impact behaviour of steel parking-structure columns

The steel supporting frame of automatic mechanical garages is called a parking structure. Presently, for these novel structures, the design codes are without giving detailed guidelines to predict the response of their impacted column. Thus, this paper presents a simplified analytical procedure to calculate the impact behaviour of the column. The proposed method is based on the co-rotational rigid body model and follows the energy-balance principle. Compared with the previous analytical method, it specially targets the parking-structure column and can be used to conveniently and quickly calculate the column transverse displacement with considering the effects of the surrounding structural members and axial loads on the column. The research covers the situation where the column is subjected to the impacts at a low velocity, critical velocity, and overcritical velocity. Primarily, an approach is developed to simplify the overall parking structures. On that basis, the calculation formula for the critical impact velocity, i.e. the velocity that results in the formation of plastic hinges in the column, is derived. To predict the behaviour of the column under the impact beyond the critical impact velocity, the simplified analytical procedure is provided and then its accuracy is examined by validated numerical models. Eventually, according to the procedure, some suggestions are given to improve the design of the column after parametric analyses. It is recommended that control the axial-load levels of the column, particularly the column with a small section area, as well as set stiffeners on the column within the height of 1000 – 1500 mm.

Detailed analysis of particle–substrate interaction based on a centrifugal method

• Experiments to remove particles adhering to inclined substrates in a centrifuge. • Analyses using point-mass and rigid-body models. • Elucidation of the particle removal mechanism based on rolling rather than friction. • Determination of particle–substrate adhesion force and effective contact radius. • Estimation of the removal fraction curves at different inclination angles. The interaction between particles and inclined substrates in a centrifuge was investigated theoretically and experimentally. First, the balance of the force acting on a particle adhering to the substrate, with an inclination angle from 0 to 90° to the horizontal, was formulated separately in the normal and tangential directions. The adhesion force was then derived based on the point-mass model as a function of the angular velocity. Next, the balance of the moments of the forces acting on a particle adhering to the substrate was formulated; theoretical equations for the adhesion force and the effective contact radius were then derived from the angular velocities, obtained at any two inclination angles, based on the rigid-body model. Finally, the removal fraction curves of spherical/nonspherical particles with median diameters of less than 10 µm were experimentally obtained by increasing the angular velocity at each inclination angle. The experimentally obtained angular velocities were substituted into the theoretical equations to compare the point-mass and rigid-body models. The effects of the particle shape on the adhesion force and effective contact radius and that of the inclination angle on the removal fraction curves based on the theoretical equation were also investigated.