Correct Kinematics Research Articles

Compensating attenuation effects in full-waveform inversion with dissipation-dispersion decoupling

Seismic attenuation poses challenges to velocity model building from acoustic/elastic full-waveform inversion (FWI). In particular, when constructing the FWI gradient for velocity inversion, recent studies have indicated that the high-attenuation structure could distort the gradient by damping the amplitudes and shifting the kinematic phases, resulting in an imbalanced update and thus unreliable velocity model. These Q effects are particularly significant in the reflection acquisition geometry due to the “double-damping” issue. Here, we develop a Q-compensated FWI algorithm for constructing a Q-free FWI gradient. By using a recently developed viscoacoustic wave propagator, this compensation can be done conveniently by keeping the dispersion term and flipping the dissipation term in the wave equation when we simulate the forward and time-reversed adjoint wavefields. The resultant gradient obtained by interacting these two wavefields has correct kinematics and Q-free amplitudes. This Q-compensated FWI can balance the update between Q- and no- Q-areas, which we determine using synthetic examples. In addition, we illustrate how to take advantage of the dissipation-dispersion decoupling to determine the anomalous Q value in the Q model building workflow via Q-compensated reverse time migration.

Modeling matrix crack/delamination interaction in a double edge notch tension specimen via a divisible cohesive element with damage state mapping

This work investigates the simulated kinematics of matrix crack/delamination interaction in predictions of damage progression of a double edge notch tension specimen. Based on previous work, a divisible cohesive element (Div-CE) is implemented in a three-dimensional finite-element (FE) framework with the Floating Node Method (FNM). Unlike conventional cohesive elements (CEs), the Div-CE captures the correct kinematics when matrix cracks and delaminations interact. First, the Div-CE implementation is generalized to prevent artificial healing, which can occur under non-monotonic loading conditions. When elements are split to represent cracks with the FNM, the proposed Div-CE scheme handles the complex partitioning and integration of the resulting cohesive-zone sub-elements. Furthermore, as additional cracks interact and partitions are updated, damage state variables are also updated and mapped to new partitions, which prevents artificial healing, yielding a general formulation. The proposed element formulation is verified using single-element models demonstrating its generality and accuracy. Second, the approach is applied to the modeling of a double edge notch tension specimen. The results obtained with Div-CEs at the ply interface are compared to those obtained with only conventional CEs, and both are compared to the experiments. Overall, the simulated mechanical response and damage morphology, which exhibited extensive matrix crack/delamination interaction, agreed closely to that which was observed experimentally. Notably, the simulations using Div-CEs produced consistently correct damage morphologies with meshes three times coarser than those performed with conventional CEs. Furthermore, contrary to previous studies, the results obtained suggest that the correct failure morphology can be captured without including shear-nonlinearity.

An integrated yield-line approach to tensile and compressive membrane actions in thin lightly-reinforced concrete slabs

In this paper a recently developed method of analysis is used to examine the effects of rotational and normal continuity at parallel edges on the large-deflection behaviour of lightly reinforced rectangular concrete slabs. The method makes the conventional assumption of an optimal yield-line mechanism at infinitesimal deflection, and subsequently ensures equilibrium of the flat facets of the mechanism using the correct kinematics as the deflection increases. For slabs which are only supported transversely at their edges the method was developed to model the development of tensile membrane action, which enhances the slab’s load capacity as its deflection increases, This has particular practical applications in the resistance of buildings to hazard loads, particularly fire. The fracture ductility of reinforcing mesh crossing yield lines is used to monitor the progressive fracture of the mesh across the yield-line cracks. This progressive fracture causes the enhancement of load capacity to have natural limits, depending largely on the bond characteristics of the bars at a discrete crack-face.When rotational continuity at parallel edges is modelled as an extension to the technique, by forcing plastic hinges to develop along these edges as part of the yield-line mechanism, this enhances the yield-line failure load of the slab, but has no effect on either the geometry of the yield line or the additional load capacity at any value of deflection. However, if these edges are assumed also to be fully restrained so that there can be no outward movement of the slab, the initial yield-line mechanism is immediately subject to compressive membrane action. This can generate a very high initial load capacity, which rapidly declines as the deflection increases, but may subsequently rise slowly as tensile membrane action develops. However, it is essential in all cases that reinforcement has high ductility across yield lines if any significantly rising load capacity is to be generated as the deflection rises.

Motion Equations for the Ball and Beam and the Ball and Arc Systems

Abstract Presently, most derivations of the equations of motion for the ball and beam and ball and arc systems model the ball as a point mass. Other derivations apply assumptions related to the ball that lack physical justification. To understand fully the impact the ball has on the equations of motion and controller design, equations of motion are needed that stem from a derivation invoking few assumptions. At that point, simplifying assumptions applied in a consistent manner are possible. This paper derives the equations of motion for each mechanical system using fewer assumptions than what appears in the literature. The development then applies the assumptions needed to convert the derived dynamics to the well-used equations of motion seen in the literature. The presentation shows that some ball and beam models appearing in the literature do not stem from consistent assumptions or correct kinematics. Incorrect kinematics are also present in some of the ball and arc dynamic models. This paper also introduces dimensionless quantities to the dynamic equations of both systems rendering them in dimensionless form. Such formulations allow for comparisons between different systems through the size of the dimensionless quantities. The dimensionless systems are the means used to demonstrate that the equations of motion of each system are the same as the radius of the arc grows without bound. Finally, the paper shows that comparisons between different ball and beam models using these dimensionless numbers are now possible.

Optimization of compressive loading parameters to mimic in vivo cervical spine kinematics in vitro

The human cervical spine supports substantial compressive load in vivo. However, the traditional in vitro testing methods rarely include compressive loads, especially in investigations of multi-segment cervical spine constructs. Previously, a systematic comparison was performed between the standard pure moment with no compressive loading and published compressive loading techniques (follower load – FL, axial load – AL, and combined load – CL). The systematic comparison was structured a priori using a statistical design of experiments and the desirability function approach, which was chosen based on the goal of determining the optimal compressive loading parameters necessary to mimic the segmental contribution patterns exhibited in vivo. The optimized set of compressive loading parameters resulted in in vitro segmental rotations that were within one standard deviation and 10% of average percent error of the in vivo mean throughout the entire motion path. As hypothesized, the values for the optimized independent variables of FL and AL varied dynamically throughout the motion path. FL was not necessary at the extremes of the flexion–extension (FE) motion path but peaked through the neutral position, whereas, a large negative value of AL was necessary in extension and increased linearly to a large positive value in flexion. Although further validation is required, the long-term goal is to develop a “physiologic” in vitro testing method, which will be valuable for evaluating adjacent segment effect following spinal fusion surgery, disc arthroplasty instrumentation testing and design, as well as mechanobiology experiments where correct kinematics and arthrokinematics are critical.

Evaluation of Femoral-Tibial Flexion Gap in Total Knee Arthroplasty with Everted or Lateralized Patella.

Intraoperative patellar position (eversion, lateralization, or in situ) influences the ligamentous balancing in knee flexion and thereby the correct positioning of the femoral component during total knee arthroplasty. The correct ligament balancing is crucial when, as in our experience, prostheses with medial pivot design are used. It was shown that the flexion gap in the normal knee is not rectangular and that the lateral compartment is significantly slacker than the medial. Therefore, to obtain a correct kinematics of a medial pivot anatomical prosthesis, it is essential to recreate an anatomical flexion gap slacker in the lateral compartment. We conducted a prospective study on a consecutive series of 87 total knee prostheses. The objective of this study is to evaluate the femoral external rotation angle in each patient with everted patella as well as with pure subluxated patella. The purpose of this study is to offer guidance about the optimal femoral rotation angle to achieve best outcomes of a knee replacement. The evaluation was done using an instrument developed by Medacta International (Switzerland) with our direct collaboration (Tensor, Medacta, Switzerland) and standardizing the basic conditions of each patient (knee 90 degrees flexed, medial transquadricipital surgical access, lateral displacement of the patella, tourniquet inflated at 250 mm Hg, spinal anesthesia). Each group was subdivided into subgroups according to gender, preoperative varus or valgus deformity, and patellar height. Our study advises against evaluating the flexion gap with everted patella due to high risk of underestimation of the lateral compartment laxity (differences up to + 3 degrees with pure subluxated patella compared with everted patella).

Sliding channel cladding connections for precast structures subjected to earthquake action

The traditional seismic design of precast frame buildings concerns the calculation of the frame, considering the cladding panels as non-structural added masses without stiffness, assuming they are connected so to not interact with the frame. Under seismic excitation, the cladding connections are subjected to complex multi-directional actions, depending on the panel static scheme, all of which involve relative motion between cladding and structure. The correct kinematics of these connections in decoupling the panels from the structure has rarely been demonstrated, and accidental coupling may result in dangerous sudden increase of forces and subsequent failure of the connections. This is also confirmed by post-earthquake field observations on precast structures, which are characterised by pronounced deformation under seismic loading due to their flexibility. An innovative panel-to-structure sliding connection conceived to allow for an effective cladding-structure decoupling has been tested to check its correct kinematics within a uniaxial test apparatus, imposing displacement histories with application of constant normal force. The experimental results of cyclic tests with a tailored test protocol are presented, and static and dynamic friction coefficients are experimentally evaluated. A cyclic test on a full-scale precast prototype equipped with sliding panel connections has been carried out, checking the global behaviour of such systems and their installation peculiarities. Design rules for the evaluation of seismic actions arising within the proposed panel arrangements are finally provided, accounting for the experimentally evaluated friction coefficients.

A finite-difference approach for solving pure quasi-P-wave equations in transversely isotropic and orthorhombic media

Starting from the dispersion relation and setting S-wave velocity along symmetry axes to zero, pseudoacoustic-wave equations have been proposed to describe the kinematics of acoustic wavefields in transversely isotropic (TI) and orthorhombic media. To date, the numerical stability of the pseudoacoustic-wave equations has been improved by developing coupled systems of wave equations; however, most simulations still suffer from S-wave artifacts that are the fundamental solutions of the fourth- and sixth-order partial differential equations. Pure quasi-P-wave equations accurately describe the traveltimes of P-waves in TI and orthorhombic media and are free of S-wave artifacts. However, it is difficult to directly solve the pure quasi-P-wave equations using conventional finite-difference schemes due to the presence of pseudo-differential operators. We approximated these pseudo-differential operators by algebraic expressions, whose coefficients can be determined by minimizing differences between the true and approximated values of the pseudo-differential operators in the wavenumber domain. The derived new coupled systems involve modified acoustic-wave equations and a Poisson’s equation that can be solved by conventional finite-difference stencils and fast Poisson’s solver. Several 2D and 3D numerical examples demonstrate that the simulations based on the new systems are free of S-wave artifacts and have correct kinematics of quasi-P-waves in TI and orthorhombic media.

LHC collider phenomenology of minimal universal extra dimensions

We discuss the collider phenomenology of the model of Minimal Universal Extra Dimensions (MUED) at the Large hadron Collider (LHC). We derive analytical results for all relevant strong pair-production processes of two level 1 Kaluza–Klein partners and use them to validate and correct the existing MUED implementation in the fortran version of the Pythia event generator. We also develop a new implementation of the model in the C++ version of Pythia. We use our implementations in conjunction with the Checkmate package to derive the LHC bounds on MUED from a large number of published experimental analyses from Run 1 at the LHC. Program summaryProgram title:Pythia6 MUED and Pythia8 MUEDProgram Files doi:http://dx.doi.org/10.17632/fkvcgdw9j6.1Licensing provisions: CC0 1.0Programming language: Fortran and C++Journal reference of previous version: Comput. Phys. Comm. 181 (2010) 122–127Does the new version supersede the previous version?: YesReasons for new version: The Minimal Universal Extra Dimension (MUED) model was implemented in the Pythia6 event generator from version 6.4.18 onwards. The new version now allows for different masses for various level 1 KK excitations, modified and corrected subroutines to handle the kinematics and squared matrix elements. A new production process has been added. Additionally the model is now made available in the Pythia8 event generator.Summary of revisions: The Minimal Universal Extra Dimension (MUED) model implementation in the Pythia6 event generator now allows for different masses for various level 1 KK excitations. These may appear both in the final states and in the propagators of t∕u channel contributions. Routines handling the kinematics and squared matrix elements are suitably modified to incorporate correct kinematics and ensure proper interferences of diagrams. For some processes, corrections in the expressions for the existing squared matrix elements have been made. A new subprocess qq̄→g1∗g1∗ has been added. A couple of production modes (which originally had some subprocesses lumped together) are now split to handle different masses of doublet and singlet KK excitations.Nature of problem: The ongoing run of the Large Hadron Collider (LHC) at CERN continues to look for new physics Beyond the Standard Model (BSM). For many years, the only complete models which were seriously investigated by the LHC collaborations, were different versions of low energy supersymmetry: mSUGRA, gauge-mediated SUSY, anomaly-mediated SUSY, etc. The MUED model provides an interesting and motivated alternative to supersymmetry, with unique and challenging collider phenomenology. In order to study the MUED model, it was implemented in the fortran version Pythia6 general purpose event generator from version 6.4.18 onwards. The MUED model is not available in the C++ version of Pythia8.Solution method: The new implementation validates and fixes the backward compatibility and some issues in the current Pythia6 version. The model has now been implemented in the Pythia8 event generator.

Accelerating full-waveform inversion with attenuation compensation

The calculation of the gradient in full-waveform inversion (FWI) usually involves crosscorrelating the forward-propagated source wavefield and the back-propagated data residual wavefield at each time step. In the real earth, propagating waves are typically attenuated due to the viscoelasticity, which results in an attenuated gradient for FWI. Replacing the attenuated true gradient with a [Formula: see text]-compensated gradient can accelerate the convergence rate of the inversion process. We have used a phase-dispersion and an amplitude-loss decoupled constant-[Formula: see text] wave equation to formulate a viscoacoustic FWI. We used this wave equation to generate a [Formula: see text]-compensated gradient, which recovers amplitudes while preserving the correct kinematics. We construct an exact adjoint operator in a discretized form using the low-rank wave extrapolation technique, and we implement the gradient compensation by reversing the sign of the amplitude-loss term in the forward and adjoint operators. This leads to a [Formula: see text]-dependent gradient preconditioning method. Using numerical tests with synthetic data, we demonstrate that the proposed viscoacoustic FWI using a constant-[Formula: see text] wave equation is capable of producing high-quality velocity models, and our [Formula: see text]-compensated gradient accelerates its convergence rate.

Yield-line plasticity and tensile membrane action in lightly-reinforced rectangular concrete slabs

The paper provides the systematic derivation of a new analytical approach to tensile membrane action of lightly-reinforced thin concrete slabs at large deflections. The basic motivation for the work comes from the recent use of tensile membrane action as an enhancement, in the fire condition, of the capacity of the thin concrete slabs which are normally made composite with downstand steel beams, at temperatures which have substantially degraded the contribution of these steel beams. The method accepts as a premise that such slabs form a pattern of localized yield lines as an initial small-deflection failure mechanism, and that these yield lines retain their positions as subsequent deflection occurs. As the slab deflects, maintaining the correct kinematics of the articulation and displacement of the system of slab facets, interacting across the yield lines, is extremely important to the horizontal equilibrium of the slab. In this process it becomes necessary to re-think the basic assumption of traditional yield-line theory that any local cross-section of unit width along a yield line equilibrates the force of its concrete compression block with the yielded steel’s tension force, producing constant plastic moment capacities for the mesh in either direction along any yield line. In the approach set out in this paper only overall equilibrium of the system of facets needs to be maintained. As in normal rigid-plastic analysis, concrete acts only when compressed, and then at its compressive strength, and steel acts at its tensile yield strength whilst it remains intact. However, steel in either direction can fracture when the local crack-width causes its local strain to exceed its fracture ductility. When the rebar crossing the diagonal yield lines begins to fracture this generally indicates that the slab’s capacity is about to reduce with further deflection. The paper does not attempt to address how a rebar’s free length across a discrete crack is generated, or the limiting crack widths implied, but this is shown in a range of examples to be a major issue if tensile membrane action is to be used in practice to enhance the capacity of slabs, for example in hazard loading situations. It is important that principles be established in future to quantify this aspect of rebar ductility.

Analysis of knee functional flexion axis in navigated TKA: identification and repeatability before and after implant positioning

Providing correct rotational alignment of femoral component in total knee arthroplasty (TKA) is mandatory to achieve correct kinematics, good ligament balance and patellar tracking. The purpose of this study was to evaluate potential clinical applications of functional flexion axis (FFA) by analysing the differences between pre- and post-implant placement. This evaluation was supported by the analysis of repeatability, assessing the robustness of the proposed method. Anatomical acquisitions and passive kinematics were acquired on 87 patients undergoing TKA using a commercial navigation system. Knee FFA was estimated, before and after implant positioning, from three flexion-extension movements between 0 and 120°. The angle between FFA and transepicondylar axis was analysed in frontal and axial planes. Repeatability coefficient and intraclass correlation coefficient (ICC) were used to analyse the reliability and the agreement in identifying the axis. The analysed angle presented differences between pre- and post-operative conditions only in the frontal plane (from -8.3±5.5° to -2.8±5.3°) (p<0.0001). There was good intraobserver reliability and agreement. Repeatability coefficient ranged between 4.4° (3.7-4.9°) and 3.4° (2.9-3.8°), the ICC between 0.87 (0.83-0.91) and 0.93 (0.90-0.95) and the standard deviation ranged between 1.3 and 1.0°. The present study demonstrated that TKA affected the estimation of FFA only in the frontal plane. This method reported good repeatability, demonstrating its usefulness for clinical purposes particularly to evaluate rotational positioning of the femoral component in the axial plane. Case series, Level IV.

Polishing and local planarization of plastic spherical capsules using tumble finishing

A new method (a variant of tumble finishing) for polishing and achieving local planarization on precision spherical, plastic capsules is described. Such capsules have niche applications, such as ablators used in high-peak-power laser targets for fusion energy research. The as-manufactured ablators contain many shallow domes (many 100's of nm high and a few 10's of μm wide) on the outer surface which are undesirable due to contributions to instabilities during implosion. These capsules were polished (i.e., tumble finished) by rotating a cylindrical vial containing the capsule, many borosilicate glass or zirconia media, and an aqueous-based colloidal silica polishing slurry. During tumble finishing, the relative media/capsule motions cause multiple, random sliding spherical–spherical Hertzian contacts, resulting in material removal, and possibly plastic deformation, on the capsule. As a result, the domes were observed to locally planarize (i.e., converge to lower heights). Utilizing the correct kinematics (i.e., the characteristics of the media/capsule motions), as controlled by the vial rotation rate and the fill fraction of media and slurry, the high velocity downward circumferential media motions were avoided, preventing fracturing of the fragile capsules. Also, the resulting post-polished surface roughness on the capsule was found to scale with the initial media surface roughness. Hence, pre-polishing the media greatly reduced the roughness of the media and thus the roughness of the polished capsule. A material removal model is described based on the Preston model and spherical–spherical Hertzian contacts which shows reasonable agreement with measured average removal rates of 35±15nm/day and which serves as a valuable tool to scale the polishing behavior with changes in process variables. Narrow domes were observed to planarize more rapidly than wider domes. A local planarization convergence model is also described, based on the concept of workpiece–lap mismatch where the local pressure, and hence removal, varies with the gap at the interface contact. The calculated rate and shape evolution of various size isolated domes compares well with the experimental data.

Precise calculation of the two-step process forK−d→πΣnin theΛ(1405) resonance region

The reaction K- d -> pi Sigma N is investigated taking into account single scattering and the two-step process due to Kbar N -> pi Sigma rescattering. The influence of some common approximations are examined. It is found that the treatment of the kinematics in the Green's function that appears in the loop integral of the rescattering process has a rather strong impact on the resulting lineshape of the pi Sigma invariant mass spectrum. Specifically, a calculation with correct kinematics where the three-body unitarity cut due to the nK- p threshold occurs at the physical value yields a pronounced peak in the invariant mass spectrum at this threshold and, at the same time, suppresses the signal in the region of the Lambda(1405) resonance. On the other hand, an approximation applied in past calculations shifts that threshold down and, consequently, leads to an accidental and therefore erroneous enhancement of the signal of the Lambda(1405) in the pi Sigma invariant mass spectrum.

RETRACTED ARTICLE: Fracture analysis using an enriched meshless method

Crack propagation and fatigue fracture is studied with an enriched meshless method. This method uses an intrinsic enrichment of the meshless weighting functions such that the correct crack kinematics can be described. The major advantage of the method is its simplicity, especially with respect to implementation. The method is applied to problems in elastostatics where analytical and experimental data is available. We show the higher accuracy of our method in comparison to standard methods for two problems with analytical solutions. Finally, we show the accuracy of the method for interacting flaws.

Avian Wing Geometry and Kinematics

The avian wing geometry of a seagull, merganser, teal, and owl extracted from noncontact surface measurements using a three-dimensional laser scanner is presented. The geometrical quantities, including the camber line and thickness distribution of the airfoil, wing planform, chord distribution, and twist distribution, are given in convenient analytical expressions. The avian wing kinematics is recovered from videos of a level-flying seagull, crane, and goose based on a two-jointed arm model in which three characteristic angles are expressed in the Fourier series as a function of time. Therefore, the flapping avian wing with the correct kinematics can be computationally generated for the aerodynamic study of flapping flight.

Finite point method: a new approach to model the inflation of side curtain airbags

Since its invention in the early 1990's, the side curtain airbag has become an important part of the occupant restrain system. In order to optimize the design of these devices more efficiently, Computer Aided Engineering (CAE) is often used. While usual simulation tools have proven their usefulness with certain types of airbags, the specificity of a side curtain airbag highlighted some of their limitations. The widely adopted uniform pressure method can simulate the behavior of a side curtain airbag after its full deployment, but is unable to capture the correct inflation kinematics at the early stage due to the great difference of pressure and temperature from one end of the airbag to the other end. As the result of coupling a Computational Fluid Dynamics (CFD) code with a Finite Element (FE) code, the Finite Point Method (FPM) is able to simulate the gas dynamics inside the airbag, thus results in more realistic inflation kinematics. In this paper, the simulation of a side curtain airbag by FPM and the results validation are discussed in detail. The good correlation of both flat airbag and folded airbag simulations with test data proved FPM's capability to help the side curtain airbag design by reducing the number of physical tests. Such a time and cost effective tool also provides a better chance for airbag design optimization.

Investigation of saddle point electrons in positron–atom ionization collisions

We investigate the appearance of fingerprints of saddle-point electrons in the ionization of atoms and molecules by positron impact. We calculate the quintuple differential cross section by means of a continuum distorted wave approximation that employs the correct kinematics. We find a clear structure located at precisely the energy and emission angle where a saddle-point electron is supposed to appear. Unmistakable signatures of this structure can also been pinpointed in the projectile dispersion and the recoiling of the target ion.

Theory of differential offset continuation

I introduce a partial differential equation to describe the process of prestack reflection data transformation in the offset, midpoint, and time coordinates. The equation is proved theoretically to provide correct kinematics and amplitudes on the transformed constant‐offset sections. Solving an initial‐value problem with the proposed equation leads to integral and frequency‐domain offset continuation operators, which reduce to the known forms of dip moveout operators in the case of continuation to zero offset.

Surface-related multiple elimination on wide-tow marine data

Surface-related multiples typically correspond to the largest component of multiple energy on marine seismic data because the surface is an almost perfect reflector with a reflectivity close to unity and, thus, their elimination is a major goal of seismic processing. Recent work has shown surface-related multiple elimination (SRME) to be effective in attenuating surface-related multiples, particularly in complex geology which may include diffracting features. Figure 1 shows the basic idea behind SRME. A surface-related multiple is recorded at receiver X r due to a shot at location Xs. The event is a surface-related multiple because it undergoes at least one downward reflection at the surface, in this case at A, during its propagation. One readily sees that this surface-related multiple event is the composition of two events: one recorded at A due to a shot at Xs and a second recorded at Xr due to a shot at A. Thus the basic operation in SRME is a spatio-temporal convolution of the data with itself. This gives the correct kinematics of the surface-related multiples, but not their amplitudes. The exact prediction is given by a cross-convolution of the data with the surface-related multiple-free version of the data and with proper accounting for directivity, ghosts, and the obliquity factor. In an iterative formulation, the (i+1)th estimate of the multiples is the cross-convolution of the data U with the ith estimate of the multiple-free data U(i). Figure 1. Basic concept behind SRME. SRME does not require any subsurface information, nor does it make any assumptions about seismic events such as hyperbolicity or moveout separation between primaries and multiples. As a result, SRME can handle arbitrarily complex multiples (including, in particular, diffracted multiples). In fact, SRME appears to be the only effective approach to attenuating diffracted multiples and this …