Motion Deformation Research Articles

Targeted Deformable Motion Compensation for Vascular Interventional Cone-Beam CT Imaging.

Cone-beam CT has become commonplace for 3D guidance in interventional radiology (IR), especially for vascular procedures in which identification of small vascular structures is crucial. However, its long image acquisition time poses a limit to image quality due to soft-tissue deformable motion that hampers visibility of small vessels. Autofocus motion compensation has shown promising potential for soft-tissue deformable motion compensation, but it lacks specific target to the imaging task. This work presents an approach for deformable motion compensation targeted at imaging of vascular structures. The proposed method consists on a two-stage framework for: i) identification of contrast-enhanced blood vessels in 2D projection data and delineation of an approximate region covering the vascular target in the volume space, and, ii) a novel autofocus approach including a metric designed to promote the presence of vascular structures acting solely in the region of interest. The vesselness of the image is quantified via evaluation of the properties of the 3D image Hessian, yielding a vesselness filter that gives larger values to voxels candidate to be part of a tubular structure. A cost metric is designed to promote large vesselness values and spatial sparsity, as expected in regions of fine vascularity. A targeted autofocus method was designed by combining the presented metric with a conventional autofocus term acting outside of the region of interest. The resulting method was evaluated on simulated data including synthetic vascularity merged with real anatomical features obtained from MDCT data. Further evaluation was obtained in two clinical datasets obtained during TACE procedures with a robotic C-arm (Artis Zeego, Siemens Healthineers). The targeted vascular autofocus effectively restored the shape and contrast of the contrast-enhanced vascularity in the simulation cases, resulting in improved visibility and reduced artifacts. Segmentations performed with a single threshold value on the target vascular regions yielded a net increase of up to 42% in DICE coefficient computed against the static reference. Motion compensation in clinical datasets resulted in improved visibility of vascular structures, observed in maximum intensity projections of the contrast-enhanced liver vessel tree. Targeted motion compensation for vascular imaging showed promising performance for increased identification of small vascular structures in presence of motion. The development of autofocus metrics and methods tailored to vascular imaging opens the way for reliable compensation of deformable motion while preserving the integrity of anatomical structures in the image.

Analysis of retraction performance of aircraft landing gear in high and low temperature environment

Abstract In order to solve the problem that the internal mechanism parameters of the aircraft landing gear are difficult to measure and retractable, the retractable performance of the landing gear under high and low temperature environments is studied. This paper simplifies the retractable mechanism of the landing gear by analyzing the motion mechanism of the aircraft landing gear. The degree of freedom of the retractable mechanism is calculated to verify the accuracy of the simplified rear landing gear retraction mechanism. The simulation model of landing gear retraction mechanism under high and low temperature environment is constructed by Patran. The component deformation and shaft clearance of the retractable mechanism under low temperature (-55°C) and high temperature (74°C) environments are analyzed from the overall and detail dimensions. The quantitative effect of ambient temperature on the deformation of the retractable mechanism of the landing gear is studied. Then Adams is used to establish the kinematics simulation model of the retractable mechanism, and the friction coefficient of the kinematic pair under different ambient temperatures is incorporated. Based on the historical data of the high and low temperature environmental test of the landing gear, the correctness of the model is verified. The influence of the environmental temperature on the driving torque, movement angle and movement time of the retractable mechanism is quantified. The problem that the deformation parameters and motion characteristics of the retractable mechanism of the landing gear are difficult to measure is solved, and the research method of retractable performance of the landing gear mechanism under different ambient temperatures is formed.

Combining Solid-State Shear Milling and FFF 3D-Printing Strategy to Fabricate High-Performance Biomimetic Wearable Fish-Scale PVDF-Based Piezoelectric Energy Harvesters.

High-performance flexible piezoelectric polymer-ceramic composites are in high demand for increasing wearable energy-harvesting applications. In this work, a strategy combining solid-state shear milling (S3M) and fused filament fabrication (FFF) 3D-printing technology is proposed for the fabrication of high-performance biomimetic wearable piezoelectric poly(vinylidene fluoride) (PVDF)/tetraphenylphosphonium chloride (TPPC)/barium titanate (BaTiO3) nanocomposite energy harvesters with a biomimetic fish-scale-like metamaterial. The S3M technology could greatly improve the dispersion of BaTiO3 sub-micrometer particles and the interfacial compatibility, resulting in better processability and piezoelectric performance of the nanocomposites. Typically, the FFF 3D printed energy harvester incorporating 30 wt % BaTiO3 showed the highest piezoelectric outputs with an open-circuit voltage of 11.5 V and a short-circuit current of 220 nA. It could hence drive nine green LEDs to work normally. In addition, a 3D-printed biomimetic wearable energy harvester inspired by an environmentally adaptive fish-scale-like metamaterial was further fabricated. The fish-scale-like energy harvester could harvest energy through different deformation motions and successfully recharge a 4.7 μF capacitor by being mounted on a bicycle tire and the tire's rolling. This work not only provides a 3D printing strategy for designing diversified and complex geometric structures but also paves the way for further applications in flexible, wearable, self-powered electromechanical energy harvesters.

Synthetic 4DCT(MRI) lung phantom generation for 4D radiotherapy and image guidance investigations.

PurposeRespiratory motion is one of the major challenges in radiotherapy. In this work, a comprehensive and clinically plausible set of 4D numerical phantoms, together with their corresponding “ground truths,” have been developed and validated for 4D radiotherapy applications.MethodsThe phantoms are based on CTs providing density information and motion from multi‐breathing‐cycle 4D Magnetic Resonance imagings (MRIs). Deformable image registration (DIR) has been utilized to extract motion fields from 4DMRIs and to establish inter‐subject correspondence by registering binary lung masks between Computer Tomography (CT) and MRI. The established correspondence is then used to warp the CT according to the 4DMRI motion. The resulting synthetic 4DCTs are called 4DCT(MRI)s. Validation of the 4DCT(MRI) workflow was conducted by directly comparing conventional 4DCTs to derived synthetic 4D images using the motion of the 4DCTs themselves (referred to as 4DCT(CT)s). Digitally reconstructed radiographs (DRRs) as well as 4D pencil beam scanned (PBS) proton dose calculations were used for validation.ResultsBased on the CT image appearance of 13 lung cancer patients and deformable motion of five volunteer 4DMRIs, synthetic 4DCT(MRI)s with a total of 871 different breathing cycles have been generated. The 4DCT(MRI)s exhibit an average superior–inferior tumor motion amplitude of 7 ± 5 mm (min: 0.5 mm, max: 22.7 mm). The relative change of the DRR image intensities of the conventional 4DCTs and the corresponding synthetic 4DCT(CT)s inside the body is smaller than 5% for at least 81% of the pixels for all studied cases. Comparison of 4D dose distributions calculated on 4DCTs and the synthetic 4DCT(CT)s using the same motion achieved similar dose distributions with an average 2%/2 mm gamma pass rate of 90.8% (min: 77.8%, max: 97.2%).ConclusionWe developed a series of numerical 4D lung phantoms based on real imaging and motion data, which give realistic representations of both anatomy and motion scenarios and the accessible “ground truth” deformation vector fields of each 4DCT(MRI). The open‐source code and motion data allow foreseen users to generate further 4D data by themselves. These numeric 4D phantoms can be used for the development of new 4D treatment strategies, 4D dose calculations, DIR algorithm validations, as well as simulations of motion mitigation and different online image guidance techniques for both proton and photon radiation therapy.

Weak curvature asymptotics for Debye layers as electrohydrodynamic discontinuities.

Important microfluidic phenomena, such as droplet deformation and cell motion, are impacted by the formation of Debye layers at charged interfaces. Previous studies examined interface problems with leaky dielectrics or the formation of diffuse charge layers. In most cases, the results are derived for weakly curved spherical geometries. Moreover, many studies of streaming-potential phenomena at fluid-solid interfaces lack a macroscale description of effects that are higher than first order. An asymptotic methodology capturing both complex surface geometries and an accurate description of higher-order phenomena is presented in this study. For this purpose, we consider a generic streaming-potential problem. As a result, the complex three-dimensional electrohydrodynamics in the Debye layer are entailed in two-dimensional discontinuity conditions. The latter contain a free parameter, the layer thickness, which mathematically represents the discontinuity position within the Debye layer. It can be used to derive an alternative definition of the Debye thickness capturing the influence of the ζ potential. We introduce a virtual particle whose outer boundary envelopes the solid particle plus a fraction of the Debye layer. It interacts with the macroscopic flow while incorporating the detailed electrohydrodynamics inside the layer.

Ultra-stretchable dual-network ionic hydrogel strain sensor with moistening and anti-freezing ability

Ionic hydrogel strain sensors are widely used in wearable electronic devices because of their excellent stretchability and responsiveness. However, ordinary ionic hydrogels are easy to dry during working under low temperatures, which severely limit their service life and application areas. Herein, we constructed a dual-network ionic conductive hydrogel based on the alginate/polyacrylamide dual-network hydrogel via solvent replacement treatment, which can be further applied as the wearable strain sensors. The solvent replacement process is by soaking the dual-network hydrogel in LiCl/CaCl2/glycerin/water solution, in which divalent cations Ca2+ ions cross-linking with the alginate chain to further toughen the dual-network, thus obtaining high stress of ~0.81 MPa and a high ionic conductivity (>19.4 mS/cm), and the mixed salt solution of glycerin/water provides excellent moisture for >30 days and frost resistance even under −80 °C ultralow temperature. Impressively, the resulting hydrogel sensor demonstrates excellent sensitivity and cyclic stability in detecting tensile deformation and human motion in a range of sizes. This work provides a feasible method for the construction of high-strength, moisturizing, antifreeze, and durable hydrogel sensors with high sensitivity and a wide range of detection capabilities, and provides a new idea for the application of electronic skin and intelligent wearable devices.

An aero-hydro coupled method for investigating ship collision against a floating offshore wind turbine

Ship collision hazards with floating offshore wind turbines (FOWTs) has been identified and the dynamic responses of FOWT under ship collision scenarios are necessary to be investigated. This paper develops a numerical solver to address the challenge of considering wind-wave loads in the ship-FOWT collision analysis. The user-defined load subroutine, LOADUD, in LS-DYNA is utilized to model the wind, wave and mooring loads. A simplified aerodynamic model considering blade pitch strategy is used and the hydrodynamic loads are calculated based on potential-flow theory with a linear wave kinematic model. The mooring forces are considered with a linearized model. The implementation of the coupled solver is verified by conducting free decay test, wave-only and wind-only analysis, respectively and comparing them with the reference values. Good agreement has been achieved, indicating that the aero-hydro coupling effects can be accurately simulated by the numerical solver. With the developed method and solver, cases of ship collision with a spar-type floating wind turbine are simulated and both local structural deformation and global motions in 6DOF are obtained. The influence of velocity, flexibility of tower, deformability of the ship, wind-wave loads are further discussed. It is found that the impact velocity can greatly affect the structural responses and a high-speed impact can directly lead to tower collapse. By comparing the cases of ship collision with FOWT, and those with fixed-support wind turbine, the flexibility of wind turbine tower is found to rarely influence the energy dissipation under collision scenario of FOWT, while it is important for the collision scenario of fixed-support wind turbine. The wind-wave condition can be more hazardous as a smaller impact velocity can lead to structures collapsing. This is because, even though the structure can withstand the ship collision, the residual strength may not be enough for the following wind loads, which can result in the structure to finally collapse. Additionally, the proposed fully coupled method is used to validate one of the authors’ previous studies, which is a decoupled method regarding the ship-FOWT collision analysis [1]. The external dynamic results from two methods are compared and discussed. Good agreement is reached between two methods for low-velocity impact but for high-speed collision or collisions with serious deformation, limitations of decoupled method can be found because some basic assumptions of them are violated. The proposed method and solver can be used to evaluate the crashworthiness of FOWT during the engineering design phase.

Dynamic modeling of rotating blades system based on transfer matrix method of multibody system

Due to the coupling between the stator and the blades, the vibration characteristics of rotating blades play an important role in the structural reliability of rotating machinery. The computational modeling challenge lies in achieving the coupling of the rotating bending-torsional blade with the stator. To perform rapid and accurate vibration characteristics analysis, the Transfer Matrix Method of Multibody System (MSTMM) is proposed to study the multibody dynamics models of single rotating beam and rotor-stator coupled system. The models are verified by comparison with finite element method (FEM) results. Using the beam model, rotating blades pure bending and torsion frequencies can be simply computed, these are the key parameters for establishing critical instability dynamic models, such as 2D aerofoil or blade flutter models. By computing the vibration characteristics with varying rotating speed, the influence of the blade rotation is illustrated. The computational results show that, the influence of rotation is greater on the frequencies associated with the bending rather than with the one of the torsion mode, hence the adjacent natural frequencies may intersect. At the veering point, the mode shape of bending-torsion coupling mode changes greatly, compared with that of other rotation speeds. In addition, asymmetric modes can be observed in the rotor-stator coupled model due to the coupling of elastic deformation and rigid body motion. The modeling process is simple and rapid, only assembling the transfer matrix of each element like building blocks. This proposed model can be applied to compute coupled/uncoupled bending-torsional frequencies of helicopter and wind turbine blades, and the results can provide useful guidance for the modeling of rotating machinery.

Property enhancement in relaxor-PbTiO3 single crystals by alternating current poling: Evaluation of intrinsic and extrinsic contributions

Piezoelectric activity has always been the most concerned performance for PbTiO3-based relaxor ferroelectrics. Recently, the alternating current poling (ACP) method has been developed as a simple and economical technique to optimize piezoelectric performance. However, the mechanism of the ACP method is still debatable. In this work, we carried out the ACP on the 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3 single crystal, a noticeable piezoelectric improvement of 20% has been achieved in comparison with the direct current poled sample, meanwhile, the dielectric loss is reduced by 26%. We found that the ACP sample demonstrates a uniform domain pattern with a large domain size dominated by 109° domain walls, in contrary to the complicated domain structures which contain both 109° and 71° domains in the DCP sample. With this uniform and simple domain structure, the crystal lattice is weakly constrained and very susceptive to external stimulation, resulting in enhanced piezoelectric response in ACP poled sample. Meanwhile, dielectric loss is reduced for the low domain wall density. The current work gives a comprehensive description of the ACP poled samples, including the microscopic domain structure, the quantitative estimation of contributions arise from lattice deformation and domain wall motions, and reveals the interactions between domain structure and the macro performance, which provide important guidelines for the design of high-performance ferroelectrics utilizing domain tailoring techniques.

Two-color resonance enhanced two-photon ionization and mass analyzed threshold ionization spectroscopy of <i>p</i>-chlorobenzonitrile

The vibrational features of <i>p</i>-chlorobenzonitrile in its first electronically excited state S<sub>1</sub> and cationic ground state D<sub>0</sub> have been investigated by two-color resonance enhanced two-photon ionization and mass analyzed threshold ionization spectroscopy. The excitation energy of S<sub>1</sub> ← S<sub>0</sub> and the ionization energy of <sup>35</sup>Cl and <sup>37</sup>Cl isotopomers of <i>p</i>-chlorobenzonitrile are determined to be 35818 ± 2, and 76846 ± 5 cm<sup>–1</sup>, respectively. These two isotopomers have similar vibrational features. Most of the active vibrations in the S<sub>1</sub> and D<sub>0</sub> states are related to the motions of the in-plane ring deformation. The stable structures and vibrational frequencies of <i>p</i>-chlorobenzonitrile are also calculated by the B3LYP/aug-cc-pVDZ method for the S<sub>0</sub> and D<sub>0</sub> states, and TD-B3LYP/aug-cc-pVDZ method for the S<sub>1</sub> state. The changes in the molecular geometry are discussed in the S<sub>1</sub> ← S<sub>0</sub> photoexcitation process and the D<sub>0</sub> ← S<sub>1</sub> photoionization process. The comparisons between the transition energy of <i>p</i>-chlorophenol, <i>p</i>-chloroaniline, <i>p</i>-chloroanisole, and <i>p</i>-chlorobenzonitrile with those of phenol, anisole, aniline, and benzonitrile provide an insight into the substitution effect of Cl atom.

EFFECTS OF TWO TYPES OF CONTROLLABLE DEFORMATION ON ENERGY EXTRACTION OF A FLEXIBLE HYDROFOIL

Energy extraction capacity of controllably flexible hydrofoil was studied under two identified deformation modes. Deformation modes, flexure parameters (flexure amplitude  and flexure coefficient ) and motion parameters (reduced frequency f* and pitching amplitude 0) were investigated to understand the effects of controllably flexible deformation on energy extraction. The results reveal that deformation modes affect the effective angle of attack and vortex structure, which influence hydrodynamic performance. The energy extraction capacity improves from the deformation mode 2 to the rigid hydrofoil and then to the deformation mode 1. Under the deformation mode 1, lift, moment and power coefficients are increased obviously with the increase of , while they increase slightly with . Power coefficients and efficiency are sensitive to , which influences the development of leading-edge vortices. The flexible coefficient  affects the wake structure, which has less impact on variation of force coefficient. As the increase in f*, averaged power coefficients firstly increase and then decrease. Further, the optimal f* is subjected to 0. Interestingly, a critical reduced frequency f*s, which is generally increase with increasing 0, was found under three modes. The condition that f* > f*s. is a prerequisite for subsequent adjustments of flexure modes and parameters according to different requirement of power coefficient under different tidal currents. The range of high efficiency () is: deformation mode 1 (36.1%<<54.3%) > rigid hydrofoils (34.2%<<41%) > deformation mode 2 (26.9%<<30.3%).

Population-based 3D respiratory motion modelling from convolutional autoencoders for 2D ultrasound-guided radiotherapy.

Radiotherapy is a widely used treatment modality for various types of cancers. A challenge for precise delivery of radiation to the treatment site is the management of internal motion caused by the patient's breathing, especially around abdominal organs such as the liver. Current image-guided radiation therapy (IGRT) solutions rely on ionising imaging modalities such as X-ray or CBCT, which do not allow real-time target tracking. Ultrasound imaging (US) on the other hand is relatively inexpensive, portable and non-ionising. Although 2D US can be acquired at a sufficient temporal frequency, it doesn't allow for target tracking in multiple planes, while 3D US acquisitions are not adapted for real-time. In this work, a novel deep learning-based motion modelling framework is presented for ultrasound IGRT. Our solution includes an image similarity-based rigid alignment module combined with a deep deformable motion model. Leveraging the representational capabilities of convolutional autoencoders, our deformable motion model associates complex 3D deformations with 2D surrogate US images through a common learned low dimensional representation. The model is trained on a variety of deformations and anatomies which enables it to generate the 3D motion experienced by the liver of a previously unseen subject. During inference, our framework only requires two pre-treatment 3D volumes of the liver at extreme breathing phases and a live 2D surrogate image representing the current state of the organ. In this study, the presented model is evaluated on a 3D+t US data set of 20 volunteers based on image similarity as well as anatomical target tracking performance. We report results that surpass comparable methodologies in both metric categories with a mean tracking error of 3.5±2.4mm, demonstrating the potential of this technique for IGRT.

Grayscale Stereolithography of Gradient Hydrogel with Site‐Selective Shape Deformation

AbstractHydrogels can convert external stimuli into shape deformation and mechanical motion, leading to the potential applications in intelligent devices and soft robotics. However, it is difficult to control the site‐selective shape deformation in a single hydrogel system in comparison with the traditional bilayer actuators with difference in structure or composition across the thickness. Here, a strategy to achieve the programmable shape deformation of hydrogel from a single precursor by grayscale stereolithography is proposed. The designed grayscale patterns can govern the spatially gradient crosslinking density of hydrogels, which leads to the heterogeneity in physicochemical performance, especially swelling ability. As a result, the swelling mismatch inducing the nonuniform internal stresses can drive the printed hydrogels to deform as the expected shape in three dimensions although there is no apparent asymmetric features and bilayer configuration. Grayscale light intensity and exposure time, as the digital printing codes can parametrically regulate the predictable shape deformation. More importantly, hydration and dehydration characterizations can endow the reversible feature of shape deformation hydrogel, benefiting to design the hydrogel actuators and sensitive devices. It is believed that integration of the advanced grayscale stereolithography together with the functional hydrogels uncovers a facile strategy to broad opportunities for sensors, soft robots, actuators, and so on.

Thermodynamic modeling of stress–strain behavior of saturated sand considering temperature effect

Based on the thermodynamic process of granular matter, considering the influence of temperature on energy dissipation at the mesoscopic level, a thermodynamic constitutive model, which can describe the thermal properties of saturated sand, is proposed in this paper. The model adopts the idea of double entropy theory, which introduces the concept of granular entropy to reflect the energy dissipation at the mesoscopic level. The energy dissipative structure composition and the related migration coefficient relationships are determined theoretically. Combined with the thermodynamic differential equation and the conservation and entropy increase equations, the thermodynamic identity is established; then, the mathematical expression of effective stress, plastic deformation, and granular temperature motion including the temperature effect are deduced accordingly. The relationship between the mesoscopic energy dissipation process caused by temperature change and macro-mechanical behavior is established by means of migration coefficient relationships and the energy function model. In addition, the dilatancy equation considering the state parameters is combined with the model parameters, so the stress–strain behavior of saturated sand considering the temperature effect can be described. The ability of the model to describe the thermal properties of saturated sand is verified by comparing the simulation results with the heating-induced volume change and triaxial undrained shear test results.

OD99 - One-shot learning for Diffeomorphic deformable medical image registration and periodic motion tracking

OD99 - One-shot learning for Diffeomorphic deformable medical image registration and periodic motion tracking

FORMATION OF CRUSHING ZONE AT THE LEVEL OF TAMPING IN THE CONDITIONS OF MASS EXPLOSIONS

The purpose of the work is to study the sequence of formation of the fracture zone in the area of the array above the ends of the system of adjacent charges in connection with the technological parameters of their mutual location. The task of works is the analytically substantiate the dependence of the value of the undamaged area of the array at the level of the bottomhole on the parameters of the system of downhole charges, taking into account the phenomenon of the edge effect. 
 Research results. Data on the dimentions of the part of the massif in the lborewhole that does not participate in the mass deformation motion of the rock during the formation of adjacent downhole funnels are obtained. It is assumed that this area between adjacent charges is the source of the oversized fraction. 
 Originality. The process of formation of the destroyed zone in space above the end of the boreholeis considered step by step: generation of the shock wave front, the symmetry of which is close to spherical, formation of the loosenning funnel system in the second stage, which does not adjacent charges of the total front of the stress wave from the explosion of downhole charges detonated from their bottom. Behind him moves the deformation front of a complex structure. It is assumed that this front in the system of two adjacent charges acquires a shape similar to a vertical wedge inverted by the base towards the free surface. The expected result of such a step-by-step deformation process is the desired degree of crushing of the rock mass at the level of the tamping. 
 Conclusions and practical implications. Theoretically and calculatedly obtained and recommended rational parameters of the location of the system of well charges of limited length to reduce the size of the non-destructive region of the rock mass at the level of the tamping, which improves the design of mass explosions in mountain slopes.

Some Issues on Crystal Plasticity Models Formulation: Motion Decomposition and Constitutive Law Variants

In this paper, kinematic relations and constitutive laws in crystal plasticity are analyzed in the context of geometric nonlinearity description and fulfillment of thermodynamic requirements in the case of elastic deformation. We consider the most popular relations: in finite form, written in terms of the unloaded configuration, and in rate form, written in terms of the current configuration. The presence of a corotational derivative in the relations formulated in terms of the current configuration testifies to the fact that the model is based on the decomposition of motion into the deformation motion and the rigid motion of a moving coordinate system, and precisely the stress rate with respect to this coordinate system is associated with the strain rate. We also examine the relations of the mesolevel model with an explicit separation of a moving coordinate system and the elastic distortion of crystallites relative to it in the deformation gradient. These relations are compared with the above formulations, which makes it possible to determine how close they are. The results of the performed analytical calculations show the equivalence or similarity (in the sense of the response determined under the same influences) of the formulation and are supported by the results of numerical calculation. It is shown that the formulation based on the decomposition of motion with an explicit separation of the moving coordinate system motion provides a theoretical framework for the transition to a similar formulation in rate form written in terms of the current configuration. The formulation of this kind is preferable for the numerical solution of boundary value problems (in a case when the current configuration and, consequently, contact boundaries, are not known a priori) used to model the technological treatment processes.

The correlation of macro deformation and micro kinematics for dense granular material subjected to shearing

In the study, biaxial shearing tests were carried out through the numerical simulations based on the discrete element method to examine the correlation of macro deformation and micro kinematics characterization in contact scale. The contact motions were decomposed into three independent types, i.e., contact deformation, contact rolling and rigid-body motion. The simulated dense sample can qualitatively reproduce the experimental outcomes for the stress–strain and volumetric relationship. From the micro to macro scale, it is found that the particle nonaffine displacement and particle rotation have strong spatial correlations with development of the shear band and the different contact motions have different influences on the sample deformation. That is, the contact deformation dominates the whole sample deformation, while the contact rolling and the rigid-body rotation have relatively small contributions to the volume change during the whole shearing process. The external loading is mostly supported by the strong contact forces in the sample, but the dilation deformation is more obvious in the weak contact force network. In strong contact force network, the contact deformation mainly induces contraction for the sample; the rigid-body rotation and contact rolling also contribute to contraction slightly; hence, the overall deformation in the strong contact force network is contraction. In the weak contact force network, the contact deformation creates dilation; the contact rolling has a small contribution to contraction, and the rigid-body rotation has no contribution to the volume change; thus, the overall dilation for the sample in the weak contact force network is observed.

Nonlinear Helicopter Rigid-Elastic Coupled Modeling with Its Applications on Aeroservoelasticity Analysis

This paper represents a new mathematical model for helicopters with flexible fuselages. The theory connects the two commonly separated research areas of flight, dynamics and structural dynamics, by considering all necessary effects of a flexible fuselage on helicopter flight dynamic characteristics. They are rigid-elastic couplings of the flexible fuselage between six rigid-body degrees of freedom and elastic deformations, along with inertial and kinematic couplings between subcomponents and the fuselage. This is achieved by using the floating frame theory and deriving the acceleration coupling matrices of subcomponents analytically. In addition, the obtained formulation is explicitly decoupled such that all unknown absolute accelerations could be obtained in a single step without iterations, which could improve computational efficiency greatly. This model is suited for aeroservoelastic analysis, and is particularly suited for heavy lift helicopters (HLH) because they usually have slower turning rotors and more flexible fuselages due to their larger scale, leading to closer frequency ranges between rigid body motions and high-frequency rotor and structural modes. The model is validated before being applied to a numerical example of a sample HLH with a feedback loop for stability augmentation. The results show that the feedback loop connects actuators, fuselage deformation, and rigid body motion and induces divergent oscillation, which is the aeroservoelastic instability that cannot be predicted without the additional sensor measurements feedback caused by dynamic deformation. Since the 10-second step response could be calculated in three seconds, the presented helicopter mathematical model is expected to be used in real-time simulations or even further in pilot-in-the-loop simulations, ultimately helping with the design of modern helicopters with nonnegligible fuselage flexibility.

Decomposition of Longitudinal Deformations via Beltrami Descriptors

We present a mathematical model to decompose a longitudinal deformation into normal and abnormal components. The goal is to detect and extract subtle abnormal deformation from periodic motions in a video sequence. It has important applications in medical image analysis. To achieve this goal, we consider a representation of the longitudinal deformation, called the Beltrami descriptor, based on quasiconformal theories. The Beltrami descriptor is a complex-valued matrix. Each longitudinal deformation is associated to a Beltrami descriptor and vice versa. To decompose the longitudinal deformation, we propose to carry out the low rank and sparse decomposition of the Beltrami descriptor. The low rank component corresponds to the periodic motions, whereas the sparse part corresponds to the abnormal motions of a longitudinal deformation. Experiments have been carried out on both synthetic and real video sequences. Results demonstrate the efficacy of our proposed model to decompose a longitudinal deformation into regular and irregular components.