Braided Model Research Articles

Dark energy with a shift-symmetric scalar field: Obstacles, loophole hunting and dead ends

We discuss the possibility of a scalar field being the fundamental description of dark energy. We focus on shift-symmetric scalar-tensor theories since this symmetry potentially avoids some fine-tuning problems. We also restrict attention to theories satisfying that the propagation speed of gravitational waves is equal to the speed of light. These considerations lead us to investigate shift-symmetric Kinetic Gravity Braiding theories. Analysing the stability of scalar linear perturbations, we discuss the conditions that seems to be necessary to describe (super) accelerated cosmic expansion without introducing instabilities. However, it has been previously established that the linearised analysis does not guarantee the stability of this non-canonical scalar theory, as potentially dangerous interactions between dark energy fluctuations and tensor perturbations (essentially gravitational waves) appear at a higher order in perturbation theory. Indeed, although we shall point out that the standard proof of absence of dark energy stable braiding models due to this interaction has a possible way-out, we find general arguments suggesting that there are no dark energy stable solutions that can exploit this loophole. Thus, we discuss future research directions for finding viable fundamental descriptions of dark energy. We also provide a dictionary between the covariant version of the theory and that of the Effective Field Theory approach, explicitly computing the parameters in the latter formalism in terms of the functions appearing in the covariant version, and its derivatives. To the best of our knowledge, this is the first time these expressions are explicitly obtained up-to arbitrary order in perturbation theory.

Dynamic modeling and improved PiDiNet edge detection of multi-process mixed braiding net

The morphology of the braided net formed during the laying and braiding processes performed by a hybrid braiding machine significantly affect the formation of the braided fabric and its mechanical properties. However, problems such as yarn accumulation during the braiding process, inability of braided webs to shrink, and yarn skipping remain unsolved. In this study, a dynamics-based braided net model is developed to predict the shape profile of the braided net using the given braiding parameters. In addition, a measurement method based on pixel-by-pixel comparison is proposed for extracting the topography of a braided net using an edge-detection technique. The accuracy of the model is verified by comparing its predictions with the topography of a braided net extracted using edge detection. The proposed model can be used to predict the braiding process and solve the problem of braided nets without shrinking and skipping yarns.

Virtual and analytical self-expandable braided stent treatment models

The Flow Diverter is a self-expandable braided stent that has helped improve the effectiveness of cerebral aneurysm treatment during the last decade. The Flow Diverter's efficiency heavily relies on proper decision-making during the pre-operative phase, which is currently based on static measurements that fail to account for vessel or tissue deformation. In the context of providing realistic measurements, a biomechanical computational method is designed to aid physicians in predicting patient-specific treatment outcomes. The method integrates virtual and analytical treatment models, validated against experimental mechanical tests, and two patient treatment outcomes. In the case of both patients, deployed stent length was one of the validated result parameters, which displayed an error inferior to 1.5% for the virtual and analytical models. These results indicated both models' accuracy. However, the analytical model provided more accurate results with a 0.3% error while requiring a lower computational cost for length prediction. This computational method can offer designing and testing platforms for predicting possible intervention-related complications, patient-specific medical device designs, and pre-operative planning to automate interventional procedures.

Prediction of mechanical properties of 3D tubular braided composites at different temperatures using a multi-scale modeling framework based on micro-CT

It is of great significance to establish a real three-dimensional (3D) tubular braided composites mechanical properties prediction model at different temperatures. In this paper, a multi-scale modeling framework based on micro-computed tomography (micro-CT) is adopted to consider the characteristics of the real yarn cross section, fiber shape deviation and internal defects within the matrix after composite formation, and a realistic trans-scale finite element model for 3D tubular braided composite is established. The micro-scale and macro-scale mechanical properties of 3D tubular braided composites at different temperatures are sequentially simulated by using the elastic-plastic damage model considering temperature and the tractor-separation constitutive model. Comparison with experiments shows that temperature significantly affects the mechanical properties. With the increase of temperature, the overall failure degree of the 3D tubular braided composite under axial compressive load increases significantly, its axial compressive strength and modulus decrease significantly, and the post-peak response of the stress-strain curve gradually flattens. The proposed trans-scale model demonstrates high predictive accuracy.

Perturbations and stability conditions of k-essence and kinetic gravity braiding models in two-field measure theory

We study cosmological perturbations for k-essence and kinetic gravity braiding models in the context of the two-field measure theory (TMT). Considering scalar perturbations and the uniform field gauge, we obtain the sound speed of the fields and present a stability analysis by means of the kinetic matrix and the mass eigenvalues. For k-essence models, in the two-field measure theory, the speed of propagation of the field is modified completely due to the new measure field and it gives rise to crucial differences with respect to the case without new measure. The stability analysis gives a physical viable model for the Universe. For the kinetic gravity braiding models in the two-field measure theory we get that, in general, the speed of perturbations is equal to the speed of light which is a consequence of the properties of the new measure field. In the latter case, there is always a ghost field. Furthermore, we calculate general expressions for the mass eigenvalues and find, for an explicit example, the existence of tachyonic instabilities.

Design and Finite Element Analysis of Artificial Braided Meniscus Model.

Currently, artificial meniscus prostheses are mostly homogenous, low strength, and difficult to mimic the distribution of internal fibers in the native meniscus. To promote the overall mechanical performance of meniscus prostheses, this paper designed a new artificial braided meniscus model and conducted finite element analysis. Firstly, we designed the spatial fiber interweaving structure of meniscus model to mimic the internal fiber distribution of the native meniscus. Secondly, we provided the detailed braiding steps and forming process principles based on the weaving structure. Thirdly, we adopted the models of the fiber-embedded matrix and multi-scale methods separately for finite element analysis to achieve the reliable elastic properties. Meanwhile, we compared the results for two models, which are basically consistent, and verified the accuracy of analysis. Finally, we conducted the comparative simulation analysis of the meniscus model and the pure matrix meniscus model based on the solved elastic constants through Abaqus, which indicated a 60% increase in strength.

Trans-scale elastic–plastic damage analysis of 3D tubular braided composites with void defects

Three-dimensional (3D) tubular braided composites exhibit irreversible plastic deformation and nonlinear behavior due to the void defects and plastic effects of the matrix. Therefore, this paper establishes an elastic–plastic damage constitutive model of 3D tubular braided composites with defects, which is coupled with plastic effects and damage accumulation. Firstly, 3D tubular braided composite models with defects are established by sequential trans-scale analysis method to transfer the mechanical properties of the component materials. Then, according to the brittleness of the fiber or yarn and the plasticity of the matrix, the elastic and elastic–plastic damage model of the fiber and the matrix are established, respectively. On this basis, an interface element is established to characterize the mechanical properties of the interface with the tractor-separation constitutive model. Finally, the finite element results of the axial compression properties of 3D tubular braided composites coupled with the porosity and plasticity of the matrix, the longitudinal shear nonlinearity of the yarn and the bilinear constitutive relationship of the interface are in good agreement with the experimental results.

High‐fidelity modeling of the braiding process for generating the realistic mesostructure of preforms in braided composites

AbstractAn accurate method for modeling the braided preforms is vital for the mesoscopic performance analysis of tubular composites. This study proposed a high‐fidelity virtual braiding model for the general braiding process, which further considers the fiber‐level deformation of the yarns during the braiding process to generate the realistic mesostructure of preforms in tubular composites. The method uses the digital element approach previously proposed for weaving processes to model the braiding yarn. The whole braiding process, including the deposition zone and convergence zone, is incorporated into the model to account for the effect of interaction in these zones on the preform mesostructure. Two braiding processes were simulated with the proposed virtual braiding method. The simulated geometry of the braided preforms and the yarn paths in the convergence zone agree well with the reported experimental results. To facilitate the performance analysis of braided composite structures, further automated generation of solid cell instances based on the obtained braided preforms was studied. Importantly, this work could reduce the considerable effort required for characterizing the mesostructure via the costly micro‐CT scans for braided composites, and the generated geometry of the braided preform is more precise than the widely used highly idealized models.

A Review of Numerical Modelling of Morphodynamics in Braided Rivers: Mechanisms, Insights and Challenges

In the past decade, the numerical modelling of braided river morphodynamics has experienced a significant advance due to the increasing computer power and the development of numerical techniques. Numerical models are quite efficient in exploring scenarios with different settings, and they can be applied to investigate the complicated physics laws of natural braided rivers and manage complex river engineering problems. However, braided river models are far from fully developed, e.g., the representation of flow and sediment transport, model sensitivity, essential effects of sediment transport, bank erosion and vegetation, and require intensive refinement and validation to enhance their prediction accuracy. The recent application of advanced field measurement techniques offers model development a new chance by providing abundant measurement data of a high quality. The present study reviews the essential mechanisms and applications of typical braided river models; compares their accuracy; discusses the recent progress, advantages and shortcomings; and illustrates the challenges and future research trends.

Big rip in shift-symmetric Kinetic Gravity Braiding theories

We revise the future fate of a group of scalar-tensor theories known as kinetic gravity braiding models. As it is well-known, these theories can safely drive the expansion of the universe towards a future de Sitter state if the corresponding Lagrangian is invariant under constant shifts in the scalar field. However, this is not the only possible future state of these shift-symmetric models as we show in this letter. In fact, future cosmic singularities characterized by a divergence of the energy density can also appear in this framework. We present an explicit example where a big rip singularity is the only possible future fate of the cosmos.

Mechanical property analysis and design parameter optimization of a novel nitinol nasal stent based on numerical simulation.

Background: A novel braided nasal stent is an effective alternative to nasal packing after septoplasty that can be used to manage the mucosal flap after septoplasty and expand the nasal cavity. This study aimed to investigate the influence of design parameters on the mechanical properties of the nasal stent for optimal performance. Methods: A braided nasal stent modeling method was proposed and 27 stent models with a range of different geometric parameters were built. The compression behavior and bending behavior of these stent models were numerically analyzed using a finite element method (FEM). The orthogonal test was used as an optimization method, and the optimized design variables of the stent with improved performance were obtained based on range analysis and weight grade method. Results: The reaction force and bending stiffness of the braided stent increased with the wire diameter, braiding density, and external stent diameter, while wire diameter resulted as the most important determining parameter. The external stent diameter had the greatest influence on the elongation deformation. The influence of design parameters on von-Mises stress distribution of bent stent models was visualized. The stent model with geometrical parameters of 25mm external diameter, 30° braiding angle, and 0.13mm wire diameter (A3B3C3) had a greater reaction force but a considerably smaller bending stiffness, which was the optimal combination of parameters. Conclusion: Firstly, among the three design parameters of braided stent models, wire diameter resulted as the most important parameter determining the reaction force and bending stiffness. Secondly, the external stent diameter significantly influenced the elongation deformation during the compression simulation. Finally, 25mm external diameter, 30° braiding angle, and 0.13mm wire diameter (A3B3C3) was the optimal combination of stent parameters according to the orthogonal test results.

Facies and architectural analysis of Paleogen fluvial deposits of the measured section of Rambangnia and Air Napalan Rivers in Palembang Sub-basin

Paleogene fluvial deposits have an important problem as pre-rift deposits, which occur before or at the same time as the formation of the basin. The research results on facies analysis and interpretation of the depositional environment of Paleogene deposits located in the Garba Hills will later explain and describe the history of the formation and stratigraphic evolution of sedimentary rocks in the South Sumatra Basin, reflected in the lithological and facies characteristics. The facies analysis was carried out on a stratigraphic cross-section with a thickness of ± 107.37 meters and ± 11.06 meters on the measurement path of the Rambangnia River and Air Napalan River, which are located in the Ogan Komering Ulu area, South Sumatra. Seven lithofacies developed on two measured paths are matrix supported gradded gravel (Gmg), gravel matrix supported Massive (Gmm), through cross-bedded (St), massive sandstone (Sm), horizontally bedded sandstones (Sh), parallel laminated siltstone and claystone (F1), massive siltstones and mudstones (Fsm). Asosiasi fasies didapatkan berupa Sedimentary Gravity Flow (SG), Gravel Bars (GB), Sandy Bedforms (SB), channel (CH), Overbank fine (FF). The interpretation of the depositional environment shows a fluvial environment, the type of braided river with a gravel braided rivers model with sedimentary gravity flows.Paleogene fluvial deposits have an important problem as pre-rift deposits, which occur before or at the same time as the formation of the basin. The research results on facies analysis and interpretation of the depositional environment of Paleogene deposits located in the Garba Hills will later explain and describe the history of the formation and stratigraphic evolution of sedimentary rocks in the South Sumatra Basin, reflected in the lithological and facies characteristics. The facies analysis was carried out on a stratigraphic cross-section with a thickness of ± 107.37 meters and ± 11.06 meters on the measurement path of the Rambangnia River and Air Napalan River, which are located in the Ogan Komering Ulu area, South Sumatra. Seven lithofacies developed on two measured paths are matrix supported gradded gravel (Gmg), gravel matrix supported Massive (Gmm), through cross-bedded (St), massive sandstone (Sm), horizontally bedded sandstones (Sh), parallel laminated siltstone and claystone (F1), massive siltstones and mudstones (Fsm). Asosiasi fasies didapatkan berupa Sedimentary Gravity Flow (SG), Gravel Bars (GB), Sandy Bedforms (SB), channel (CH), Overbank fine (FF). The interpretation of the depositional environment shows a fluvial environment, the type of braided river with a gravel braided rivers model with sedimentary gravity flows.

Neutrino mass and kinetic gravity braiding degeneracies

Modified theories of gravity yield an effective dark energy in the background dynamics that achieves an accelerated expansion of the universe. In addition, they present a fifth force that induces gravitational signatures in structure formation, and therefore in the matter power spectrum and related statistics. On the other hand, massive neutrinos suppress the power spectrum at scales that also modified gravity enhances it, so a degeneration of these effects has been recognized for some gravity models. In the present work, we study both effects using kinetic gravity braiding (nKGB) models to find that in spite of some degeneracies, the role of the fifth force at very large scales imprints a bump in the matter power spectrum as a distinctive signature of this model and, therefore, acts as a smoking gun that seems difficult to match within the present knowledge of power spectra. These models result interesting, however, since the n = 1 presents no H 0 tension, and all nKGB studied here present no σ 8 tension and, in addition, a null neutrino mass is excluded.

Is local H 0 at odds with dark energy EFT?

Local H_0 determinations currently fall in a window between H 0 ∼ 70 km/s/Mpc (TRGB) and H 0 ∼ 76 km/s/Mpc (Tully-Fisher). In contrast, BAO data calibrated in an early ΛCDM universe are largely consistent with Planck-ΛCDM, H 0 ∼ 67.5 km/s/Mpc. Employing a generic two parameter family of evolving equations of state (EoS) for dark energy (DE) w DE(z) and mock BAO data, we demonstrate that if i) w DE(z = 0) < -1 and ii) integrated DE density less than ΛCDM, then H 0 increases. EoS that violate these conditions at best lead to modest H 0 increases within 1σ. Tellingly, Quintessence and K-essence satisfy neither condition, whereas coupled Quintessence can only satisfy ii). Beyond these seminal DE Effective Field Theories (EFTs), we turn to explicit examples. Working model agnostically in an expansion in powers of redshift z, we show that Brans-Dicke/f(R) and Kinetic Gravity Braiding models within the Horndeski class can lead to marginal and modest increases in H 0, respectively. We confirm that as far as increasing H 0 is concerned, no DE EFT model can outperform the phenomenological two parameter family of the DE models. Evidently, the late universe may no longer be large enough to accommodate H 0, BAO and DE described by EFT.

Tucson Shares Blueprint for Crisis System Success

Tucson Shares Blueprint for Crisis System Success

Numerical Simulation and Experimental Study on Axial Stiffness and Stress Deformation of the Braided Corrugated Hose

To explore the mechanical properties of the braided corrugated hose, the space curve parametric equation of the braided tube is deduced, specific to the structural features of the braided tube. On this basis, the equivalent braided tube model is proposed based on the same axial stiffness in order to improve the calculational efficiency. The geometric model and the Finite Element Model of the DN25 braided corrugated hose is established. The numerical simulation results are analyzed, and the distribution of the equivalent stress and frictional stress is discussed. The maximum equivalent stress of the braided corrugated hose occurs at the braided tube, with the value of 903MPa. The maximum equivalent stress of the bellows occurs at the area in contact with the braided tube, with the value of 314MPa. The maximum frictional stress between the bellows and the braided tube is 88.46MPa. The tensile experiment of the DN25 braided corrugated hose is performed. The simulation results are in good agreement with test data, with a maximum error of 9.4%, verifying the rationality of the model. The study is helpful to the research of the axial stiffness of the braided corrugated hose and provides the base for wear and life studies on the braided corrugated hose.

Multi-scale simulation of temperature on braided fibers reinforced composite plate considering the fluctuations

The direct simulation based on the braided model of a whole fibers reinforced composite (FRC) component puts forward too high request on the calculating ability. So a multi-scale simulating method of the temperature on braided FRC plate is built in this paper, considering the temperature fluctuations of braided structures. The effective model of braided plate and the periodic braided structure are built, to obtain the homogenized temperature field and the fluctuations of temperature, respectively. The Fourier series is applied to build the functions of temperature fluctuations. Then the reconstructed temperature field of braided FRC plate could be obtained based on the homogenized temperature field and the functions of temperature fluctuations. Finally, the temperature field with fluctuations based on the braided model of whole plate is also simulated and compared with the reconstructed temperature field, to validate the accuracy of multi-scale thermal analysis method. Additionally, the experiment of temperature test on the braided FRC plate is also carried out to validate the accuracy of simulation, which presented good accuracy. The results show that, the temperature distribution of the braided FRC plate has significant fluctuating characteristics, the temperature in the region with braided yarns is relatively lower comparing with that in the matrix region, and the distributions of fluctuations are highly similar to the braided structures. The homogenized model based on the effective thermal conductivities could not obtain the temperature fluctuations of braided FRC plate. The maximum temperature difference between the braided model and the homogenized model reaches 25.37 K. Finally the maximum relative variation between the reconstructed temperature distribution and the temperature distribution based on the braided model is 3.18%, so the multi-scale thermal analysis method in this paper has good accuracy in simulating the temperature distribution of braided FRC plate with fluctuations.

Research on Biaxial Damage Evolution Characteristics of Flexible Woven Composite Film

The flexible braided composite film structures have been widely used in many fields such as near space aerostats, inflatable wings, flexible spacecraft due to their unique advantages such as small folding volume, light weight, high specific strength, excellent comprehensive performance, etc. However, the space environment is so harsh, and the flexible film structure composite material could be easily affected by various environmental factors such as long-term sunlight, ultraviolet radiation and space particle impact. So the weathering damage evolution characteristics directly determine the use life and working efficiency. The typical biaxial fiber reinforced laminated flexible composite material was studied with the damage mode, and the composite meso-mechanical theory was also used to construct the braided composite mechanics model during the damage process. The damage model of the warp and weft fiber bundles with the base film layer was introduced into the independent flexible film composite component damage degree, and the damage evolution model of the damage-containing composite material characterized by the mesoscopic component parameters was also established. Moreover, the load-bearing stress characteristics of each component under different damage conditions were calculated and analysed. The research results could provide an effective theoretical reference for the weathering optimization design and the improvement of the service life of flexible film woven composite structures.

Sandbody architecture analysis of braided river reservoirs and their significance for remaining oil distribution: A case study based on a new outcrop in the Songliao Basin, Northeast China

The reservoir architecture analysis of braided rivers, especially falling-silt seam forms, has played a key role in predicting remaining oil distributions. However, no studies have used architecture analyses that document braided river outcrops and researched the tapping of the few remaining oil distributions based on outcrops in the Songliao basin, northeast China. In this paper, the architecture characteristics and remaining oil distribution of braided river reservoirs are studied using a combination of an outcrop, modern deposition and subsurface well data. The new 8–13 m thick Lower Cretaceous Quantou Formation outcrop of the Songliao basin is a braided fluvial succession arranged in one large fining-upward cycle. Eight facies (Gt, St, Sm, Sh, Sp, Sw, Fl and Fm), four architecture elements (CH, DA, LV, and FF), and three orders of bounding surfaces (third-, fourth-, and fifth-order) are recognized. A new distribution pattern of falling-silt seams and a braided river architecture model are presented according to the analysis of the outcrop. In the mid-channel bar, the falling-silt seams thin from the mid-bar to the bar tail following the flow direction. Each falling-silt seam is oriented tangentially to the basal surface of the mid-channel bar, and the upper falling-silt seam extends farther than the lower one. In a Daqing Oilfield exploitation block in the Songliao basin, while channels and bars are the main reservoir units, they have different remaining oil distribution patterns. For bars, water injection wells located at the mid-bar, zonal injection technology, the drilling of horizontal wells, and proper well patterns are proposed. Fourth-order bounding surfaces, single braided channels, stacking patterns, and the lateral blocking of levees and floodplains are the key factors affecting the remaining oil distribution in channels.

Multi-scale damage mechanics method for predicting fatigue life of plain-braided C/SiC composites

In order to predict fatigue life of plain-braided C/SiC composites, a fiber bundle unit cell model and a braided unit cell model were established based on the meso-structure of two-dimensional braided C/SiC composites. First, different failure modes were considered and a progressive damage model of the two-dimensional braided C/SiC composite was established. Based on the results obtained by on-axis uniaxial tensile tests, the damage process of the unit cell model during off-axis tension was analyzed. In fatigue damage analysis, the uniaxial tensile fatigue experimental data of the plain-braided C/SiC composite standard specimen were used to fit the fatigue damage evolution equation of the fiber bundle. The fatigue damage results obtained by the model under uniaxial, biaxial, and shear loading were analyzed and fitted to obtain the equivalent stress equation and anisotropic macro-damage evolution equation. Finally, the life of the plain-braided C/SiC composite was estimated under random loading.