Rigid Assumption Research Articles

Experimental research on the in-plane performance of discontinuous modular diaphragms

Modular steel buildings (MSBs) are assembled from factory-manufactured modules and have been becoming more popular with higher construction efficiency. However, MSBs show quite different in-plane load-transferring behavior from traditional steel frame structures due to the diaphragm discontinuity, and in-depth researches will be needed to acquire better knowledge of its structural behavior. In this paper, the in-plane performance of modular diaphragms was investigated through the half-scaled experiments on the assembled modules, with two types of horizontal connections and double-layer diaphragm structure being taken account. The load–displacement curves, the displacement distribution as well as the strain development were all analyzed and the effects of different horizontal connections as well as double-layer diaphragm on the in-plane performance of diaphragm were discussed. Afterwards, one analytical model will be proposed to evaluate the in-plane transferring ability of modular diaphragms, where two key parameters are defined including displacement inconsistency factor (DIF) and effective lateral stiffness (ELS). The results from experiments and analytical models indicated the modular diaphragms were far from rigid floor assumption and the horizontal connections could make great differences in in-plane load transferring ability of modular diaphragms.

Robustness of structural superlubricity beyond rigid models

Structural superlubricity is a theoretical concept stating that the friction force is absent between two rigid, incommensurate crystalline surfaces. However, elasticity of the contact pairs could modify the lattice registry at interfaces by nucleating local slips, favoring commeasure. The validity of structural superlubricity is thus concerned for large-scale systems where the energy cost of elastic distortion to break the lattice registry is low. In this work, we study the size dependence of superlubricity between single-crystal graphite flakes. Molecular dynamics simulations show that with nucleation and propagation of out-of-plane dislocations and strained solitons at Bernal interfaces, the friction force is reduced by one order of magnitude. Elastic distortion is much weaker for non-Bernal or incommensurate ones, remaining notable only at the ends of contact. Lattice self-organization at small twist angles perturbs the state of structural superlubricity through a reconstructed potential energy surface. Theoretical models are developed to illustrate and predict the interfacial elastoplastic behaviors at length scales beyond those in the simulations. These results validate the rigid assumption for graphitic superlubricity systems at microscale, and reveal the intrinsic channels of mechanical energy dissipation. The understandings lay the ground for the design of structural superlubricity applications.

Strategy for Creating AR Applications in Static and Dynamic Environments Using SLAM- and Marker Detector-Based Tracking

Recently, simultaneous localization and mapping (SLAM) has received considerable attention in augmented reality (AR) libraries and applications. Although the assumption of scene rigidity is common in most visual SLAMs, this assumption limits the possibilities of AR applications in various real-world environments. In this paper, we propose a new tracking system that integrates SLAM with a marker detection module for real-time AR applications in static and dynamic environments. Because the proposed system assumes that the marker is movable, SLAM performs tracking and mapping of the static scene except for the marker, and the marker detector estimates the 3-dimensional pose of the marker attached to the dynamic object. We can place SLAM maps, cameras, and dynamic objects (markers) on the same coordinate system, and we can also accurately augment AR resources in real-time on both the static scene and dynamic objects simultaneously. Additionally, having a static map of the scene in advance has the advantage of being able to perform tracking of static and dynamic environments with mapping disabled. In this paper, we evaluate whether the proposed tracking system is suitable for AR applications and describe a strategy for creating AR applications in static and dynamic environments with a demonstration.

Numerical approach on shear wall analysis of frames due to lateral loads

The purpose of this study is to model and assess non-planar shear wall assemblies of shear wall-frame systems in order to get a better understanding of the behaviour of these assemblies. The development and testing of two separate three-dimensional models of shear wall assemblies with open and closed sections has been completed.According to the classic wide column analogy, a planar shear wall is replaced by an idealised frame structure consisting of a column and stiff beams located at different floor levels in these models, which are based on the broad column analogy. The rigid diaphragm floor assumption, which is often used in the research of multi-story building structures and is widely used in the construction sector, is also taken into consideration. The connections between the stiff beams in the model for open-section shear walls that has been described are released against torsion in order to get the desired results. Apart from simulating closed-section shear walls, a series of equations are utilised to modify the torsional stiffness of the wide columns in order to attain the required torsional stiffness of the structure.Static lateral loads and response spectrum analysis, as well as the suggested approaches, were used to explore a wide range of shear wall systems with a variety of wall-frame geometries, including Flat Plate shear wall assemblies. It is assessed whether or not the conclusions of this research are equivalent to those obtained utilising frequently utilised shear wall modelling methodologies.

Locally constrained inverse mean curvature flow in GRW spacetimes

<p style='text-indent:20px;'>We obtain the long-time existence and smooth convergence results for the locally constrained inverse mean curvature flow of compact spacelike hypersurface in certain GRW spacetimes. As an application of the convergence result, we establish a weighted Minkowski type inequality for closed spacelike mean-convex hypersurface in de Sitter space under mild rigidity assumption.</p>

Experimental Study on Dynamic Interaction between Large U-Shape Aqueduct and Water

Hydrodynamic interaction between water and structure plays an important role in the evaluation of seismic response of aqueducts in area of high seismicity. This interaction differs in axial, lateral and vertical direction of aqueduct. Both impulsive and convective effects of water exist in lateral direction. In presented study, shaking table tests were conducted with a 1/10 model of U-shape aqueduct, of 30 m long, to study the hydrodynamic interaction. With the analyses of aqueduct and water responses to stationary White Noise excitations as well as non-stationary excitations, impulsive and convective effects of water were deduced quantitatively. Characteristic frequencies and corresponding modes of aqueduct were identified with the transfer functions of acceleration, sloshing frequencies in lateral direction were recognized with the transfer functions of seat force. Impulsive mass was deduced from the alteration in fundamental frequency and the corresponding modal seat forces of the aqueduct with and without water. Convective mass was obtained from the wave height of sloshing and lateral seat forces recorded, or the lateral modal seat force and damping ratio. Comparison was made with those given in simplified methods for rigid structure. Observed hydrodynamic pressure on the structure in the test was smaller than that based on the rigid assumption.

An efficient, localised approach for the simulation of elastic blood vessels using the lattice Boltzmann method

Many numerical studies of blood flow impose a rigid wall assumption due to the simplicity of its implementation compared to a full coupling with a solid mechanics model. In this paper, we present a localised method for incorporating the effects of elastic walls into blood flow simulations using the lattice Boltzmann method implemented by the open-source code HemeLB. We demonstrate that our approach is able to more accurately capture the flow behaviour expected in elastic walled vessels than ones with rigid walls. Furthermore, we show that this can be achieved with no loss of computational performance and remains strongly scalable on high performance computers. We finally illustrate that our approach captures the same trends in wall shear stress distribution as those observed in studies using a rigorous coupling between fluid dynamics and solid mechanics models to solve flow in personalised vascular geometries. These results demonstrate that our model can be used to efficiently and effectively represent flows in elastic blood vessels.

Parametric stability of geared systems with linear suspension in permanent contact regime

The prediction and control of excessive vibration are one of the most important concerns in the design and development of geared systems. For any gear set, parametric resonance is the main source of instability, resulting in the separation of gears in mesh and chaotic behavior. In many works, gears are modeled with rigid mountings, and various analytical and numerical approaches have been used to investigate the dynamic characteristics of the system in different regimes: permanent contact (no impact), free play, single-sided impact, and double-sided impact. Alternatively, in other works, the effect of the deformation of the mountings is included in the dynamic modeling; in almost all these studies, the dynamic characteristic of the system is investigated through direct numerical integration of the governing differential equations, and there is no analytical work to determine the effect of suspension on the parametric resonance of the system. Consequently, in this work, both analytical and numerical approaches, including the Poincare–Lindstedt method and Floquet theory, are used to investigate the dynamic characteristics of a one-stage spur gear pair with linear suspension in the permanent contact regime. It has been shown that, unlike systems with rigid mounting that have one set of unstable tongues, systems with suspension have three sets of unstable tongues. The results show that the additional sets of unstable tongues appear at higher parametric frequencies. Therefore, the rigid mounting assumption is accurate only for systems operating at low speeds; for systems operating at high speeds, the deformation of the suspension must be included in the dynamic modeling, as it significantly contributes to the parametric instability of the system.

A fast and accurate method for the seismic response analysis of reinforced concrete frame structures considering Beam-Column joint deformation

Many previous investigations of reinforced concrete (RC) frame structures have demonstrated that beam-column joints may experience significant nonlinearities under earthquake excitations. However, most available analysis methods assume that the joint region remains rigid. Because joint failure may result in strength and stiffness losses and even induce structural collapse, it is difficult for an analytical model with a rigid joint assumption to obtain an accurate prediction of the structural nonlinear response. The behavior of a joint is mainly affected by the shear deformation of the joint core and bond-slip of beam longitudinal reinforcements in the joint. Although many different types of modeling approaches have been presented to effectively represent the behavior mechanism of beam-column joints, the introduction of joint models inevitably increases the complexity of the analytical model of the global structure and the effort of the solution process. Therefore, achieving highly efficient analysis on the premise of accurately predicting the seismic response of RC frame structures is still a topic that deserves investigation. This study presents an efficient analysis method for the accurate evaluation of the nonlinear response of RC frames considering the effect of beam-column joint deformation based on the concept of local inelasticity separation. The proposed method captures the bond-slip behavior at beam ends by adding inelastic rotation hinge mechanisms to the ends of the existing inelasticity-separated fiber beam-column model and uses a sliding hinge mechanism to simulate the inelastic shear response of the joint core. A small number of additional inelastic degrees of freedom that are separated from the global displacement degrees of freedom of the structure is introduced to describe both the inelastic rotation behavior and the inelastic deformation of the proposed bond-slip hinge mechanism and the sliding hinge mechanism. Consequently, the Woodbury formula can be utilized for nonlinear iterative solutions to avoid updating the global stiffness matrix, thus significantly improving the computational efficiency. The exactness of the proposed method is verified against experimental data, and its application is illustrated through a seismic response analysis example.

Investigation of the effects of shot overlap and rigid body assumptions on surface layer characteristics in shot peening simulation

As an important mean of shot peening (SP) research, finite element simulation has been widely and successfully employed in estimating the surface characteristic and residual stress distribution after SP treatment. In this study, the effects of shot overlap and rigid body assumptions on dimple geometry and residual stress distribution in depth were discussed via the validated ordered dimple pattern and stochastic dimple pattern SP models for quenched and tempered 42CrMo steel. The results show that shot overlap assumption has a great influence on the surface plastic deformation of peened material. The simulated value of plastic deformation is much larger than the experimental value, which results in the residual stress of the overlapping shot SP model deviating from the actual result seriously. For the prediction of the residual stress distribution, the shot must be set as an elasto-plastic body when the number of shot is large. The shot can be set as a rigid body for the aim of reducing the calculation time when the number of shots is small. In addition, the influence of material hardness on residual stress and equivalent plastic strain (PEEQ) was investigated via simulating the residual stress and PEEQ of different hardness materials treated by SP process . • It is necessary to choose the non-overlapping shot in SP simulation when the dimple geometry and residual stress distribution is predicted. • It is more accurate to choose elasto-plastic shot in SP model for the dimple geometry prediction. • The shot can be set as a rigid body when the number of shot is small.

Experimental Study on Seismic Instability of Pile-Supported Structure Considering Different Ground Conditions

The stability of pile-supported structures under earthquake loads involves complex dynamic soil–structure interaction (SSI). A series of large-scale shaking table experiments was performed to investigate the seismic performance and SSI of pile-supported structures considering different ground conditions. Lateral soil resistance and dynamic displacements of superstructures located in nonliquefiable and liquefiable sites as well as a rigid foundation were measured during shaking tests. The measured responses were analyzed to investigate the P-Δ effect on structural stability. It was observed that the soil lateral resistance to the pile cap at the nonliquefiable site was large and represented the main component of the lateral bearing capacity resisting structure overturning. On the other hand, the lateral resistance of liquefied soil on piles was insignificant and the lateral bearing capacity was derived primarily from soil resistance to pile cap. The analysis of the measured dynamic displacements demonstrated that the seismic instability of the structure was mainly due to the P-Δ effect caused by the rotation of the foundation, especially in liquefied sites. In addition, comparison with the results of base shears and bending moments with the rigid base assumption allows for an in-depth discussion of the effect of SSI on structural seismic design.

Effects of wave nonlinearity on submerged flexible vegetation dynamics and wave attenuation

Dynamic characteristics and wave attenuation mechanism of flexible vegetation have propelled to the forefront in investigations of coastal engineering. Given that existing studies of wave nonlinearity are mainly restricted to rigid vegetation assumptions, this study was undertaken to quantitatively determine the effect of wave nonlinearity on submerged flexible vegetation dynamics as well as wave attenuation based on flexible vegetation dynamic model and experimental results. Meanwhile, the influence of different wave theories along with different determination methods of characteristic wave velocity was evaluated quantitatively. Results reveal that wave nonlinearity exerts substantial nonlinear and nonmonotonic effects upon flexible vegetation dynamics and wave attenuation rate. The maximum horizontal force, stem tip excursion, and wave height attenuation rate increase as the dimensionless Ursell number increases on the whole under the present investigation conditions. Moreover, it is suggested that different wave theories and determination methods of characteristic wave velocity can result in slight discrepancies of flexible vegetation dynamics, which may further affect wave attenuation by flexible vegetation. Determining the impacts of wave nonlinearity, wave theory, and characteristic wave velocity provides clearer insight into the wave attenuation mechanism of flexible vegetation, which is of great benefit to the flexible vegetation dynamics and related wave attenuation model improvement.

Spatial interpolation of coal properties using geographic quantile regression forest

Inaccuracies in spatial modelling of coal properties can impact coal resource and reserve estimates. Geostatistical methods which account for compositional data have previously been recommended as a preferred method for modelling of coal properties. These methods can quantify uncertainty, can use auxiliary information to improve estimates, and ensure that compositional data (such as coal proximate analysis) is modelled in a mathematically consistent way. However, geostatistical methods have drawbacks in that have rigid statistical assumptions about the distribution and stationarity of the target variable and require variogram interpretation which can be onerous when then number of domains and target variables are numerous. Due to these drawback, inverse distance weighting (a simple deterministic method) remains the most popular method for modelling coal properties in Australian resource estimates. To address the drawbacks of geostatistical methods, a machine learning approach based on the quantile regression forest algorithm is proposed as an alternative method to spatially model coal properties. This newly proposed method, accounts for spatial arrangement of data, requires minimal pre-processing steps, can quantify uncertainty and can easily incorporate auxiliary information of various types. To evaluate the performance of this method, the accuracy of predictions of coal proximate analysis properties, and coal density are compared to the predictions of inverse distance weighting and regression kriging. All methods incorporate isometric log ratio transform and back-transform of data in order to account for the compositional nature of coal proximate analysis. Data from an active coal mine in the Bowen Basin, Queensland Australia was used as basis of the results. A unique feature of the mine site in this basin is the presence of intrusion which impacts coal quality properties to various degrees. Using evaluation metrics from leave-one-out cross-validation, this paper demonstrates that quantile regression forest has higher accuracy, lower bias and higher precision than inverses distance weighting across all coal properties. The paper also shows that results of the new method are very similar or better than regression kriging. It is also demonstrated that the prediction maps produced by quantile regression forest could be used to more accurately map out coal impacted by intrusion compared to inverse distance weighting, and that inverse distance weighting overestimates the impact of intrusion and intrusion extent. A drawback of the method compared to inverse distance weighting, is that it is more computationally demanding, less intuitive and is currently not available in existing geological packages.

Quasi-static compressive behaviour of 3D-printed origami-inspired cellular structure: experimental, numerical and theoretical studies

ABSTRACT This paper proposed a novel periodic cellular structure by introducing re-entrant hexagon-shaped honeycombs and Miura origami geometry. The large-scale multi-layer metallic specimens were manufactured by a selective laser melting (SLM) system and tested for the first time. The compression deformation and energy absorption characteristics under quasi-static load were investigated thoroughly, considering three loading directions and various geometric parameters. The results show that this novel structure has balanced mechanical properties in the three loading directions. Among them, the z-direction is the best bearing direction. Moreover, this structure exhibits an obvious three-dimensional negative Poisson's ratio effect during the compression process. Besides the experimental study, the numerical investigation base on ANSYS/LS-DYNA was carried out to provide an accurate and effective simulation method. Predictive formulas for the critical energy absorption indexes were derived by theoretical analysis based on the rigid folding assumption, validated to be well-matched with the experimental results.

Fluid‐structure interaction: Insights into biomechanical implications of endograft after thoracic endovascular aortic repair

Thoracic endovascular aortic repair (TEVAR) has developed to be the most effective treatment for aortic diseases. This study aims to evaluate the biomechanical implications of the implanted endograft after TEVAR. We present a novel image-based, patient-specific, fluid-structure computational framework. The geometries of blood, endograft, and aortic wall were reconstructed based on clinical images. Patient-specific measurement data was collected to determine the parameters of the three-element Windkessel. We designed three postoperative scenarios with rigid wall assumption, blood-wall interaction, blood-endograft-wall interplay, respectively, where a two-way fluid-structure interaction (FSI) method was applied to predict the deformation of the composite stent-wall. Computational results were validated with Doppler ultrasound data. Results show that the rigid wall assumption fails to predict the waveforms of blood outflow and energy loss (EL). The complete storage and release process of blood flow energy, which consists of four phases is captured by the FSI method. The endograft implantation would weaken the buffer function of the aorta and reduce mean EL by 19.1%. The closed curve area of wall pressure and aortic volume could indicate the EL caused by the interaction between blood flow and wall deformation, which accounts for 68.8% of the total EL. Both the FSI and endograft have a slight effect on wall shear stress-related-indices. The deformability of the composite stent-wall region is remarkably limited by the endograft. Our results highlight the importance of considering the interaction between blood flow, the implanted endograft, and the aortic wall to acquire physiologically accurate hemodynamics in post-TEVAR computational studies and the deformation of the aortic wall is responsible for the major EL of the blood flow.

Predictive processing models and affective neuroscience

The neural bases of affective experience remain elusive. Early neuroscience models of affect searched for specific brain regions that uniquely carried out the computations that underlie dimensions of valence and arousal. However, a growing body of work has failed to identify these circuits. Research turned to multivariate analyses, but these strategies, too, have made limited progress. Predictive processing models offer exciting new directions to address this problem. Here, we use predictive processing models as a lens to critique prevailing functional neuroimaging research practices in affective neuroscience. Our review highlights how much work relies on rigid assumptions that are inconsistent with a predictive processing approach. We outline the central aspects of a predictive processing model and draw out their implications for research in affective and cognitive neuroscience. Predictive models motivate a reformulation of “reverse inference” in cognitive neuroscience, and placing a greater emphasis on external validity in experimental design.

In vitro pulsatile flow study in compliant and rigid ascending aorta phantoms by stereo particle image velocimetry

The aorta is a high risk region for cardiovascular disease (CVD). Haemodynamic patterns leading to CVD are not well established despite numerous experimental and numerical studies. Most overlook effects of arterial compliance and pulsatile flow. However, rigid wall assumptions can lead to overestimation of wall shear stress; a key CVD determinant. This work investigates the effect of compliance on aortic arch haemodynamics experiencing pulsatility. Rigid and compliant phantoms of the arch and brachiocephalic branch (BCA) were manufactured. Stereoscopic particle image velocimetry was used to observe velocity fields. Higher velocity magnitude was observed in the rigid BCA during acceleration. However, during deceleration, the compliant phantom experienced higher velocity. During deceleration, a low velocity region initiated and increased in size in the BCA of both phantoms with irregular shape in the compliant. At mid-deceleration, considerably larger recirculation was observed under compliance compared to rigid. Another recirculation region formed and increased in size on the inner wall of the arch in the compliant during late deceleration, but not rigid. The recirculation regions witnessed identify as high risk areas for atherosclerosis formation by a previous ex-vivo study. The results demonstrate necessity of compliance and pulsatility in haemodynamic studies to obtain highly relevant clinical outcomes.

Numerical modeling of liquid sloshing in flexible tank with FSI approach

PurposeThe paper aims to present a numerical modeling procedure for the analysis of liquid sloshing in a flexible tank subjected to an external excitation, with taking into account the effects of fluid–structure interaction (FSI).Design/methodology/approachA numerical model based on coupling a two-phase flow solver and an elastic solid solver is developed in OpenFOAM code. The Arbitrary Lagrangian–Eulerian formulation is adopted for the two-phase Navier–Stokes equations in a moving domain. The volume of fluid (VOF) method is applied for the air–liquid interface tracking. The finite volume method is used for the spatial discretization of both the fluid and the structure dynamics equations. The FSI coupling problem is solved by an explicit coupling scheme. The model is validated for linear and nonlinear sloshing cases. Then, it is used to analyze the effects of the liquid sloshing on the dynamic response of the tank and the effects of the tank flexibility on the liquid sloshing.FindingsThe obtained results show that the flexibility of the tank walls amplifies the amplitude of the sloshing and increases the fluctuation period of the air–liquid interface. Furthermore, it is found that the bending moment acting on the tank walls may be underestimated when rigid walls assumption is adopted as usually done in sloshing tank modeling. Also, tank walls flexibility causes a phase shift in the free surface dynamic response.Originality/valueA review of previous studies on liquid sloshing in flexible tanks revealed that FSI effects have not been clearly and comprehensively analyzed for large-amplitude liquid sloshing. Many physical and numerical aspects of this problem still require clarifications and enhancements. The added value of the present work and its originality lie in the investigation of large-amplitude liquid sloshing in flexible tanks by using a staggered coupling approach. This approach is carried out by an original combination of a linear solid solver with a two phase fluid solver in OpenFOAM code. In addition, FSI effects on some response quantities, identified and analyzed herein, have not been found in the previous works.

Optimization and variational principles for the shear strength reduction method

AbstractIn this paper, a modified shear strength reduction method (MSSR) and its optimization variant (OPT‐MSSR) are suggested. The idea of MSSR is to approximate the standard shear strength reduction to be more stable and rigorous from the numerical point of view. The MSSR method consists of a simplified associated elasto‐plastic model completed by the strength reduction depending on the dilatancy angle. Three Davis' modifications suggested by Tschuchnigg et al. (2015) are interpreted as special cases of MSSR and their factors of safety are compared. The OPT‐MSSR method is derived from MSSR on the basis of rigid plastic assumption, similarly as in limit analysis. Using the variational approach, the duality between the static and kinematic principles of OPT‐MSSR is shown. The numerical solution of OPT‐MSRR is obtained by performing a regularization method in combination with the finite element method, mesh adaptivity and a damped Newton method. In‐house codes (Matlab) are used for the implementation of this solution concept. Finally, two slope stability problems are considered, one of which follows from analysis of a real slope. The softwares packages Plaxis and Comsol Multiphysics are used for comparison of the results.

SmartFFR, a New Functional Index of Coronary Stenosis: Comparison With Invasive FFR Data.

Aims: In this study, we evaluate the efficacy of SmartFFR, a new functional index of coronary stenosis severity compared with gold standard invasive measurement of fractional flow reserve (FFR). We also assess the influence of the type of simulation employed on smartFFR (i.e. Fluid Structure Interaction vs. rigid wall assumption).Methods and Results: In a dataset of 167 patients undergoing either computed tomography coronary angiography (CTCA) and invasive coronary angiography or only invasive coronary angiography (ICA), as well as invasive FFR measurement, SmartFFR was computed after the 3D reconstruction of the vessels of interest and the subsequent blood flow simulations. 202 vessels were analyzed with a mean total computational time of seven minutes. SmartFFR was used to process all models reconstructed by either method. The mean FFR value of the examined dataset was 0.846 ± 0.089 with 95% CI for the mean of 0.833–0.858, whereas the mean SmartFFR value was 0.853 ± 0.095 with 95% CI for the mean of 0.84–0.866. SmartFFR was significantly correlated with invasive FFR values (RCCTA = 0.86, pCCTA < 0.0001, RICA = 0.84, pICA < 0.0001, Roverall = 0.833, poverall < 0.0001), showing good agreement as depicted by the Bland-Altman method of analysis. The optimal SmartFFR threshold to diagnose ischemia was ≤0.83 for the overall dataset, ≤0.83 for the CTCA-derived dataset and ≤0.81 for the ICA-derived dataset, as defined by a ROC analysis (AUCoverall = 0.956, p < 0.001, AUCICA = 0.975, p < 0.001, AUCCCTA = 0.952, p < 0.001).Conclusion: SmartFFR is a fast and accurate on-site index of hemodynamic significance of coronary stenosis both at single coronary segment and at two or more branches level simultaneously, which can be applied to all CTCA or ICA sequences of acceptable quality.