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This paper demonstrates how a strain energy transition approach can be used to remove artificial buckling modes that often occur in stability constrained topology optimization problems. To simulate the structural response, a nonlinear large deformation hyperelastic simulation is performed, wherein the fundamental load path is traversed using Newton’s method and the critical buckling load levels are estimated by an eigenvalue analysis. The goal of the optimization is to minimize displacement, subject to constraints on the lowest critical buckling loads and maximum volume. The topology optimization problem is regularized via the Helmholtz PDE-filter and the method of moving asymptotes is used to update the design. The stability and sensitivity analyses are outlined in detail. The effectiveness of the energy transition scheme is demonstrated in numerical examples.

Objective: To identify differences between asymptote- and rate-based methods for estimating age and size at growth cessation in linear craniofacial measurements. Design: This is a retrospective, longitudinal study. Five linear measurements were collected from lateral cephalograms as part of the Craniofacial Growth Consortium Study (CGCS). Four estimates of growth cessation, including 2 asymptote- (GCasym, GCerr) and 2 rate-based (GCabs, GC10%) methods, from double logistic models of craniofacial growth were compared. Participants: Cephalometric data from participants in 6 historic longitudinal growth studies were included in the CGCS. At least 1749 individuals (870 females, 879 males), unaffected by craniofacial anomalies, were included in all analyses. Individuals were represented by a median of 11 images between 2.5 and 31.3 years of age. Results: GCasym consistently occurred before GCerr and GCabs consistently occurred before GC10% within the rate-based approaches. The ordering of the asymptote-based methods compared to the rate-based methods was not consistent across measurements or between males and females. Across the 5 measurements, age at growth cessation ranged from 13.56 (females, nasion-basion, GCasym) to 24.39 (males, sella-gonion, GCerr). Conclusions: Adolescent growth cessation is an important milestone for treatment planning. Based on our findings, we recommend careful consideration of specific definitions of growth cessation in both clinical and research settings since the most appropriate estimation method may differ according to patients’ needs. The different methods presented here provide useful estimates of growth cessation that can be applied to raw data and to a variety of statistical models of craniofacial growth.

This study proposes a method for camera calibration using the properties of conic asymptotes, which are combined with the projective invariance, images of the asymptotes, and image of the absolute points to obtain the vanishing line. Constraints for the image of the absolute conic are obtained from a set of orthogonal vanishing points, the homography, and images of the circular points. The proposed calibration algorithm is compared with several other research methods, and its effectiveness and robustness are verified within a certain error range from the results of simulated and real experiments for different eccentricities without loss of generality.

The visual system efficiently processes complex and redundant information in a scene despite its limited capacity. One strategy for coping with the complexity and redundancy of a scene is to summarize it by using average information. However, despite its importance, the mechanism of averaging is not well understood. Here, a distributed attention model of averaging is proposed. Human percept for an object can be disturbed by various sources of internal noise, which can occur either before (early noise) or after (late noise) forming an ensemble perception. The model assumes these noises and reflects noise cancellation by averaging multiple items. The model predicts increased precision for more items with decelerated increments for large set-sizes resulting from late noise. Importantly, the model incorporates mechanisms of attention, which modulate each item's contribution to the averaging process. The attention in the model also results in saturation of performance increments for small set-sizes because the amount of attention allocated to each item is greater for small set-sizes than for large set-sizes. To evaluate the proposed model, a psychophysical experiment was conducted in which observers' ability to discriminate average sizes of two displays was measured. The observers' averaging performance increased at a decreasing rate with small set-sizes and it approached an asymptote for large set-sizes. The model accurately predicted the observed pattern of data. It provides a theoretical framework for interpreting behavioral data and leads to an understanding of the characteristics of ensemble perception.

The structures in thermal environment often suffer from severe thermal expansion, potentially leading to buckling failure. This study aims to address this issue by proposing multi-material topology optimization for thermomechanical buckling problems. The density-based model with the rational approximation of material properties (RAMP) is adopted here for parameterization of multiple materials. The sensitivities of thermomechanical compliance and buckling are derived through the adjoint technique. The globally convergent version of the method of moving asymptotes (GCMMA) is employed to solve the non-monotonic topology optimization problem. In this study, two numerical examples are presented to illustrate the effectiveness of the proposed method, in which the total volume of multi-materials is minimized subject to thermoelastic compliance and buckling constraints. The examples exhibit significant difference in the final topologies for mechanical buckling and thermomechanical buckling optimization. The study demonstrates the importance of thermomechanical buckling criteria for the design of structures operating in a temperature-varying environment.

Reactive Powder Concrete-Filled Steel Tube (RPC-FST) is a new composite section with ultra-high strength, good plasticity and ductility to withstand blast loading. This paper is devoted to introduce an analytical method for evaluating the damage level of RPC-FST column suffered fire attack and the following blast load. The damage indexes of RPC-FST column has experienced ISO-834 standard fire and subsequent blast load are predicted using Pressure-Impulse (P-I) diagram. The analytical approaches are proposed based on equivalent Single Degree of Freedom (SDOF) model, in which the damping dissipation, thermal effect and axial load are included. In order to clarify the influences of temperature distribution and explosive charge on the damage index, an inclusive P-I function, characterized by three variables: pressure, impulse and fire duration, is presented. Then blast-resistant results of four fire-damaged RPC-FST columns are employed to validate the reliabilities of presented method. Parametric analysis is conducted to investigate the impacts of damping ratio and ductility ratio on the structural damages. It is demonstrated that a larger damping would lead to better structural blast-resistance. The asymptote value of quasi-static zone tends to smaller as the ductility ratio increases, either the asymptote value of impulse zone, which results in a larger safe area for structural member. In addition, the damaged level is governed by impulse load as scaled distance decreases. The analytical damage indexes are well validated by experimental data.

Interlaminar endoscopic lumbar discectomy (IELD) is an efficient surgical treatment for lumbar disc herniation. However, this minimally invasive procedure requires a considerable learning curve that has not yet been standardized. This review aimed to evaluate the learning curve's characteristics, including the cutoff point required to achieve technical proficiency and to discuss appropriate training methods.We systematically searched the core databases (PubMed, Embase, and Cochrane Library) for clinical studies that evaluated the learning curve using quantitative data. We performed a quality assessment using the Newcastle-Ottawa scale. We also compared descriptive statistics, including operative time and other variables before and after the cutoff point.Six studies reporting 302 cases of IELD were selected from 7188 screened articles. The cutoff point was randomly set in 3 studies and determined as the curve's asymptote in 3 studies. The mean value for the cutoff point was 22.17 ± 12.40 cases (range: 10-43 cases) and mainly determined based on the operative time, which was shorter in the late group than that in the early group (P0.05). The cutoff points were not significant for patient outcome parameters such as pain score, functional result, surgical failure, or complications.The evidence of published studies regarding the learning curve for the IELD technique is insufficient. The reported cutoff points may be significant only for task efficiency. Moreover, they may not represent the asymptote of the curve. Future studies should evaluate the actual plateau points using patient outcome data.

A methodology for obtaining the optimal structure and distribution for the gradient properties of a material in order to reduce the stress level in a soldered joint was constructed. The developed methodology was based on a combination of topological optimization methods (the moving asymptotes method) and the finite elements method, it was first implemented to solve problems of optimizing soldered joints. Using the proposed methodology, a number of problems were solved, allowing one to obtain optimal structural characteristics, in which a decrease in stress is revealed. Designing compounds using this technique will provide more robust designs. The proposed technique can be applied to a wide class of practical problems.

This work presents a design of a system-on-chip for the telemetry of photovoltaic curves of a nanosatellite in real time, based on the work reported by Gutierrez et al. [1]. In this type of application, the limitation of memory and communication bandwidth makes it difficult to store and transmit the whole I-V characteristic curve of any solar section in real time. The proposed solution is based on the real-time calculation of the equivalent single diode model of the solar section. Thus, once the parameters calculated, recorded and transmitted, regardless of the operating conditions, the specific curve could be reproduced later. The system is based on a 32-bit LEON3 microprocessor core implemented in a FPGA. LEON microprocessors were originally designed by the European Space Agency for use in space projects requiring high reliability. Moreover, in order to design the system as simple and reliable as possible, among all the methods available in the literature to extract the five parameters of the equivalent model (Iph, Is, n, Rs and Rsh), the method Asymptote Oblique (OA) [2] was chosen for its simplicity and precision. These parameters (Iph, Is, n, Rs, Rsh) are recorded and transmitted to the ground for later reproduction using the following equation: I= I p h − I s ( e V + I R s n V T − 1 ) − V + I R s R s h ( 1 ) In summary, the final system consists of three blocks: 1) LEON3 microprocessor, as shown in Figure 1, which executes the OA method to obtain PV characteristic values from the detected values. 2) Electronic load, as shown in Figure 2 to set the PV output voltage to a value defined by SoC LEON3. 3) Acquisition interface, as shown in Figure 3 which allows to obtain the value of the voltage and the current of a pilot cell and to adapt them to values that can be acquired by the digital system.

There are renewed interests in grid-stiffened composite structures due to the high structural stability and damage tolerance enabled by multiple intersected stiffeners . The limited design space of repeated straight grid patterns has been remarkably expanded by introducing non-uniform curved grid-stiffened composite structures (NCGCs). In this work, curved stiffener layout optimization for NCGCs with a central cutout is investigated to maximize the critical buckling load under a given weight constraint. The design framework is developed by calling ABAQUS for simulating stiffened models and using numerical sensitivities in order to adopt gradient-based optimization algorithm, where the computational time depends not only on simulation but also the number of design variables. To increase the efficiency, an improvement is proposed based on globally convergent method of moving asymptotes (GCM), as one of the most popularly used structural optimization algorithms, by relaxing the conservativeness (CR-GCM) with an additional relaxation factor and an adaptive limit of the iteration number . Numerical examples show that optimal curved stiffeners around the cutout have the ability to remarkably increase the structural buckling load and the proposed CR-GCM demonstrates the ability of better balancing the computational efficiency and convergence in the optimization process.

This paper presents a pressure-impulse (P-I) diagram method for predicting failure modes of reactive powder concrete (RPC) one-way slabs subjected to blast loading. This method involves two loosely-coupled single-degree-of-freedom (SDOF) models and the proposed failure criteria. Motion functions, resistance functions and dynamic mechanical properties of RPC are considered in predicting the dynamic response of RPC one-way slabs. Deformation of RPC one-way slabs predicted using a theoretical approach correlate well with the explosion test results. According to previous studies, the flexural-shear failure of structural members occurs at high pressures and impulses. However, analysis results show that only shear failure occurs under these conditions once the shear fracture criterion is introduced. A new shear failure region is found in the P-I diagram. Parametric studies show that the asymptotes of P-I curves increase with increasing slab depth, longitudinal reinforcement ratio, and RPC compressive strength, and decreasing slab length and load level. When the boundary condition changes from clamped to simply-supported, the asymptote values of flexural P-I curves decrease, while the asymptote values of shear P-I curves increase. In addition, the applicability of the improved P-I diagrams approach in practical evaluation is illustrated through a case study.

In the current contribution for the first time a mechanistic model is presented that can be used for analysing and optimising the mechanical performance of straight wall structures in 3D printing processes. The two failure mechanisms considered are elastic buckling and plastic collapse. The model incorporates the most relevant process parameters, which are the printing velocity, the curing characteristics of the printing material, the geometrical features of the printed object, the heterogeneous strength and stiffness properties, the presence of imperfections, and the non-uniform dead weight loading. The sensitivity to elastic buckling and plastic collapse is first explored for three basic configurations, namely i) a free wall, ii) a simply-supported wall and iii) a fully-clamped wall, which are printed under linear or exponentially-decaying curing processes. As demonstrated for the specific case of a rectangular wall lay-out, the design graphs and failure mechanism maps constructed for these basic configurations provide a convenient practical tool for analysing arbitrary wall structures under a broad range of possible printing process parameters. Here, the simply-supported wall results in a lower bound for the wall buckling length, corresponding to global buckling of the complete wall structure, while the fully-clamped wall gives an upper bound, reflecting local buckling of an individual wall. The range of critical buckling lengths defined by these bounds may be further narrowed by the critical wall length for plastic collapse. For an arbitrary wall configuration the critical buckling length and corresponding buckling mode can be accurately predicted by deriving an expression for the non-uniform rotational stiffness provided by the support structure of a buckling wall. This has been elaborated for the specific case of a wall structure characterised by a rectangular lay-out. It is further shown that under the presence of imperfections the buckling response at growing deflection correctly asymptotes towards the bifurcation buckling length of an ideally straight wall. The buckling responses computed for a free wall and a wall structure with a rectangular lay-out turn out to be in good agreement with experimental results of 3D printed concrete wall structures. Hence, the model can be applied to systematically explore the influence of individual printing process parameters on the mechanical performance of particular wall structures, which should lead to clear directions for the optimisation on printing time and material usage. The model may be further utilised as a validation tool for finite element models of wall structures printed under specific process conditions.

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In this paper, an analytical model for determining the iso-damage curves for framed monolithic glass panels subjected to blast loading is proposed. Two typical damage levels corresponding to different conditions in GSA/ISC are classified, namely (a) the glass crack limit and (b) glass fragments invading with a certain velocity. The nonlinear dynamic responses and failure modes of framed monolithic glass under different blast loadings are firstly analysed numerically. Then critical states of glass panel in both impulsive region and quasi-static region of the pressure-impulse (P-I) diagram are defined. Based on the energy balance approach, an analytical method is proposed for determining the pressure asymptote and the impulse asymptote of framed monolithic glass for different damage levels. The proposed method is verified through comparison with published experimental data and numerical results. The method can be applied for any framed monolithic glazing with different dimension and thickness and provides a practical approach for engineering design and hazard level estimation of framed monolithic glass against blast loading.

In this study an elastoplastic hardening model for quasibrittle materials is presented. The yield surface exhibits hyperbolic meridians while its shape on the deviatoric plane is described by an elliptic function. The proposed hardening mechanism is controlled by the slope of the asymptotes of the hyperbolic meridians and thus by the mobilized friction of the material. The yield surface is capped during the first stages of hardening and opens up before reaching the peak strength. On the deviatoric plane the hardening is non-uniform producing changes in both the size and the shape of the yield surface. The proposed plastic potential is related with the yield function through a simple modification of its volumetric part. The model is equipped with a hardening rule that is a monotonically increasing elliptic function of the hardening parameter. The latter is given in its rate form and it is pressure dependent. A proposed ductility rule controls this pressure dependency and leads to brittle behavior in tension and ductile behavior at high confinement compression. All the parameters have physical interpretation and are directly related with measurable mechanical properties of the material in the lab. Most of them could be identified from a uniaxial compression test. The predictions of the model are compared against experimental datasets and it is shown that exhibit very good agreement.

A data set of ventral-aspect insect radar cross-sections (RCSs) and polarization patterns, measured at X band (9.4 GHz, linear polarization) in laboratory rigs, has been collated from a number of sources. The data have been analysed to identify relationships between RCS parameters (one representing size and two the polarization-pattern shape) and the insects’ masses and morphological dimensions and forms. An improved mass-estimation relationship, with appropriate asymptotes for very small and very large insects, is presented. This relationship draws only on the RCS size parameter and it is shown that incorporating one or both of the RCS shape parameters provides little additional benefit. Small insects have polarization-pattern shapes that fall within a relatively limited region of the range of parameter values allowed by electromagnetic scattering theory. Larger insects have shapes that extend beyond this region, following a broad trajectory as size and mass increases; at masses above ~0.6 g, the pattern becomes ‘perpendicular’, with maxima when the E-field is orthogonal to the body axis rather than parallel to it. RCS shape can be used to infer morphological form for small insects (

Radial frequency (RF) patterns, which are sinusoidal modulations of a radius in polar coordinates, are commonly used to study shape perception. Previous studies have argued that the detection of RF patterns is either achieved globally by a specialized global shape mechanism, or locally using as cue the maximum tangent orientation difference between the RF pattern and the circle. Here we challenge both ideas and suggest instead a model that accounts not only for the detection of RF patterns but also for line frequency patterns (LF), i.e. contours sinusoidally modulated around a straight line. The model has two features. The first is that the detection of both RF and LF patterns is based on curvature differences along the contour. The second is that this curvature metric is subject to what we term the Curve Frequency Sensitivity Function, or CFSF, which is characterized by a flat followed by declining response to curvature as a function of modulation frequency, analogous to the modulation transfer function of the eye. The evidence that curvature forms the basis for detection is that at very low modulation frequencies (1-3 cycles for the RF pattern) there is a dramatic difference in thresholds between the RF and LF patterns, a difference however that disappears at medium and high modulation frequencies. The CFSF feature on the other hand explains why thresholds, rather than continuously declining with modulation frequency, asymptote at medium and high modulation frequencies. In summary, our analysis suggests that the detection of shape modulations is processed by a common curvature-sensitive mechanism that is subject to a shape-frequency-dependent transfer function. This mechanism is independent of whether the modulation is applied to a circle or a straight line.

This study uses an Implicit Level Set Algorithm (ILSA) to model the propagation of planar hydraulic fractures in situations when their progress is determined by an interplay of fluid viscosity, rock fracture toughness, and fluid leak-off into the formation. One of the key features of our approach is the use of the three-process tip asymptotic solution both as a propagation condition and to capture the multiscale behavior in a weak sense. Using this special tip asymptote is necessary because the validity region of the classical square root fracture opening solution (stemming from linear elastic fracture mechanics) is often limited to a small zone near the fracture tip, which can only be captured by a very fine mesh. In addition, this validity zone depends on the velocity of fracture propagation, so that slow and fast portions of the fracture front may experience different near-tip behavior. The multiscale tip asymptotic solution, on the other hand, has an increased validity region, which makes it possible to capture the near-tip multiscale behavior on a coarse mesh and yields a computationally efficient algorithm. The presence of leak-off also complicates the model considerably as it involves a delay term containing the trigger time history, which depends on the earlier fracture front positions. Moreover, the leak-off from tip elements in which the fracture front speed changes significantly requires special treatment. This three-process asymptotic solution is used to solve the fully coupled integro-delay-PDE model for a propagating planar hydraulic fracture by using a level set algorithm in conjunction with the tip asymptotic solution to locate the moving fracture front and to capture multiscale behavior. Firstly, the developed algorithm is validated against a reference solution for an axisymmetric hydraulic fracture. Secondly, a set of numerical examples involving three stress layers is presented to illustrate the variation of the multiscale near-tip behavior along the fracture perimeter and the need to use the multiscale asymptotic solution in a hydraulic fracturing simulator.

Reinforced concrete (RC) column systems are widely used in protective structures designed to resist blast events. Development of correlations between explosive load and the resulting damage in concrete elements are significant for incorporation of blast load in design and also for pre and post-damage assessments. The main purpose of this research is to organizing correlations between explosive load and damage. These correlations are being expressed in Pressure-Impulse diagrams. The damage level is calculated based on the residual axial load-carrying capacity of the damaged RC column. Finite element modeling in LS-DYNA is used to analyze the structures and calculate the damage level for each explosive phenomenon. The Arbitrary Lagrangian Eulerian (ALE) method is used to simulate the explosive loads in the reinforced concrete column. The results demonstrated that increase the column size cause to increase in pressure and impulsive asymptotes and lead to enhanced the pressure-impulse (P-I) diagram.

Moving Morphable Component (MMC) based topology optimization approach is an explicit algorithm since the boundary of the entity explicitly described by its functions. Compared with other pixel or node point-based algorithms, it is optimized through the parameter optimization of a Topological Description Function (TDF). However, the optimized results partly depend on the selection of related parameters of Method of Moving Asymptote (MMA), which is the optimizer of MMC based topology optimization. Practically, these parameters are tuned according to the experience and the feasible solution might not be easily obtained, even the solution might be infeasible due to improper parameter setting. In order to address these issues, a Machine Learning (ML) based parameter tuning strategy is proposed in this study. An Extra-Trees (ET) based image classifier is integrated to the optimization framework, and combined with Particle Swarm Optimization (PSO) algorithm to form a closed loop. It makes the optimization process be free from the manual parameter adjustment and the reasonable solution in the design domain is obtained. In this study, two classical cases are presented to demonstrate the efficiency of the proposed approach., 25 pages,13 figures,8 tables

The B-plane is a fundamental tool to analyze planetary encounters of small bodies and spacecraft flybys. In this paper, we review the B-plane formulation with a full derivation of its coordinates and their partial derivatives, which allow the mapping of orbital uncertainties onto the B-plane. We find that this mapping can be sensitive to variations in the inbound asymptote, especially for low-velocity encounters, and to non-Keplerian dynamics for distant encounters. Under linearity assumptions, we show how to derive close approach boundaries and impact probabilities from the orbital uncertainty mapped onto the B-plane.

In this article a formal model of associative learning is presented that incorporates representational and computational mechanisms that, as a coherent corpus, empower it to make accurate predictions of a wide variety of phenomena that, so far, have eluded a unified account in learning theory. In particular, the Double Error Dynamic Asymptote (DDA) model introduces: (a) a fully connected network architecture in which stimuli are represented as temporally clustered elements that associate to each other, so that elements of one cluster engender activity on other clusters, which naturally implements neutral stimuli associations and mediated learning; (b) a predictor error term within the traditional error correction rule (the double error), which reduces the rate of learning for expected predictors; (c) a revaluation associability rate that operates on the assumption that the outcome predictiveness is tracked over time so that prolonged uncertainty is learned, reducing the levels of attention to initially surprising outcomes; and critically (d) a biologically plausible variable asymptote, which encapsulates the principle of Hebbian learning, leading to stronger associations for similar levels of cluster activity. The outputs of a set of simulations of the DDA model are presented along with empirical results from the literature. Finally, the predictive scope of the model is discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

The classification performance of deep neural networks has begun to asymptote at near-perfect levels. However, their ability to generalize outside the training set and their robustness to adversarial attacks have not. In this paper, we make progress on this problem by training with full label distributions that reflect human perceptual uncertainty. We first present a new benchmark dataset which we call CIFAR10H, containing a full distribution of human labels for each image of the CIFAR10 test set. We then show that, while contemporary classifiers fail to exhibit human-like uncertainty on their own, explicit training on our dataset closes this gap, supports improved generalization to increasingly out-of-training-distribution test datasets, and confers robustness to adversarial attacks., Comment: In Proceedings of the 2019 IEEE International Conference on Computer Vision (ICCV)

There has been considerable research effort into image registration and regression, which address the problem of determining correspondence primarily through estimating models of structural change. There has been far less focus into methods which model both structural and intensity change. However, medical images often exhibit intensity changes over time. Of particular interest is MRI of the early developing brain, where such intensity change encodes rich information about development, such as rapidly increasing white matter intensity during the first years of life. In this paper, we develop a new spatiotemporal model which takes into account both structural and appearance changes jointly. This will not only lead to improved regression accuracy and data-matching in the presence of longitudinal intensity changes, but also facilitate the study of development by direct analysis of appearance change models. We propose to combine a diffeomorphic model of structural change with a Gompertz intensity model, which captures intensity trajectories with 3 intuitive parameters of asymptote, delay, and speed. We propose an optimization scheme which allows to control the balance between structural and intensity change via two data-matching terms. We show that Gompertz parameter maps show great promise to characterize regional patterns of development.

There are few data regarding the effect of aging on pressure asymptote (Pasymptote) and time constant (Tau) of exponential diastolic aortic pressure (AoP) decay in normal human heart. To investigate this issue, we analyzed high-fidelity AoP, measured by use of a catheter-tipped manometer in 71 normal subjects who underwent diagnostic cardiac catheterization but who were found to have normal coronary artery and LV function. Subjects who had hypertension, diabetes or renal disease were excluded. There were 49 men and 22 women, ranging in age from 20 to 80 years. We analyzed diastolic AoP sampled every 5 ms from the point of minimal dP/dt to the top of ECG-R waves of the next beat, and estimated Tau and Pasymptote by the exponential best fitting with a variable Pasymptote results. Systolic AoP were significantly increased with age, but mean and diastolic AoP remained unchanged. Pasymptote was 58.5 ± 8.1 mmHg and Tau was 436 ± 105 msec. Pasymptote show no significant age-related change, but strongly and positively correlated with systolic, diastolic and mean AoP (R2 = 0.39, 0.70 and 0.66, respectively). For Tau, it was weakly and positively related with both age and AoP (Age: R2 = 0.20, AoP: R2 = 0.08–0.20). Conclusion: We documented Pasymptote and Tau of the Windkessel with the beating heart in normal humans. Tau was associated with aging, whereas Pasymptote, which increased with the level of AoP, did not vary with aging per se, at least until the ninth decade. These data may provide insight into the understanding of AoP physiology.

This study develops a topology optimization approach for design of carbon fiber reinforced plastic (CFRP) laminated components with different failure criteria to reduce the risk of structural failure. The discrete material and thickness optimization (DMTO) method is adopted to parameterize the design variables of thickness and orientation of CFRP composites, which is driven by the Method of Moving Asymptote (MMA) algorithm. A large number of local constraints associated with the failure criteria are aggregated in terms of a p-norm function. Analytical sensitivities are derived with respect to the design variables. In this study, a battery hanging structure in electrical vehicle (EV) is exemplified; and a DMTO based design is prototyped and validated through the in-house experimental tests first. To prevent different failure modes, the Hashin, Hoffman and Tsai-Wu failure criteria are then imposed as the design constraints together with manufacturing requirements in the optimization. A comparative study is performed for the design with and without such failure criteria. The results demonstrate that the maximum failure index of the optimized structure with the Tsai-Wu failure criterion decreases the most by 40%; and follows by the Hashin and Hoffman criteria by 24% and 33%, respectively. Finally, the CFRP structure is also optimized to design a so-called double-double laminates for demonstrating the generality of the proposed method. The study is anticipated to gain in-depth understanding of how the failure criteria would affect the design of fiber reinforced composite structures to ensure structural integrity.

Photonic chip is a kind of integrated device that uses light as a carrier for information transportation and processing. Owing to its advantages of small size, lightweight, and low power consumption, photonic chip has become the most popular research topic nowadays. The beam splitter is a vital part of on-chip integration. For conventional beam splitting elements, Y-type and tree-branch output are the main elements, which are usually realized by interference principles. However, it is appropriate only for simple conventional beam splitter because the propagation direction of light cannot achieve large angle deflection. In the case of relay loading, optical amplification, pumping, and frequency upconversion, the vertical loading is often required without affecting the main optical path. To complete the large-angle deflection beam splitting, one needs to add a mirror to realize it or use a right-angle mirror structure for geometric double-sided reflection and splitting in traditional ways, but these structures are relatively complicated and difficult to complete on-chip integration. Based on previous work on inversely designed multi-channel wavelength routers and wide spectrum efficient focusing devices by using the intelligent algorithm, and combining the years of research on the coherent superposition theory of multi-scattering of the disordered medium, a large angle beam splitter that can realize from the near-infrared band is designed through using the intelligent algorithm. The beam splitter structure is based on AMTIR-1 glass, the part to be etched is air. The composition of AMTIR-1 is Ge33As12Se55. And the size of the structure is only 1 μm × 2 μm. The beam splitter can achieve 180° linear separation of beams in a range from 800 nm to 1100 nm, the beam splitting ratio of the entire waveband is approximately 1∶1, and the gross beam splitting efficiency is stable between 85% and 92%. Compared with several conventional structures with the same size, the efficiency of the beam splitter designed by this algorithm is higher. At the same time, the algorithm has the advantages of fast computation speed and small computation amount, and it can be completed only by ordinary personal computers without the support of hardware such as workstations. This intelligent algorithm can also be applied to the design of various passive photonic devices such as optical polarization splitters, routers, optical isolators, etc., providing an idea and reference for the design of integrated micro-nano photonic devices on high-density sheets.

Pressure-Impulse (P-I) models as graphical representations are frequently adopted to evaluate damage of structures subjected to extreme loads. The main objectives of this research is to derive analytical formulas to propose pressure (P0) and impulsive (I0) asymptotes of RC columns at different levels of damages, and to develop P-I models and empirical equations of RC columns for prediction and assessment of blast induced damages using an advanced numerical modeling approach. An innovative technique to predict the residual capacity of RC columns when subjected to detonation events is essential to measure the column axial capacity after blast loads. This study can offer a methodology for a reliable, simple and accurate dynamic analysis to study the residual capacity of columns under blast detonation. Available literature mainly focused on the simulation of explosion loads by using simplified pressure time histories to develop P-I curves and rarely simulated the actual explosive. Therefore, there is a gap in the literature concerning general relation between blast damage of columns with different explosive loading conditions for a reliable and quick evaluation of column behavior subjected to blast loading. In this paper, the Arbitrary Lagrangian Eulerian (ALE) technique is implemented to simulate high fidelity blast pressure propagations. The numerical model is calibrated and validated by comparing the results from blast field tests performed by other researchers. To develop the designated P-I curves, damage assessment criteria are used based on the residual capacity of column. Intensive investigations are implemented to assess the effect of column dimension, concrete and steel properties, reinforcement ratio and axial load index on the P-I diagram of RC columns. The produced P-I models can be applied by designers to predict the damage of new columns and to assess existing columns subjected to different blast load conditions.

The pressure-impulse (P-I) diagram method is used in practice (for civilian and military applications) for predicting the level of damage sustained by structures when subjected to blast loads and for assessing the imposed loading regime. Each P-I curve is associated with a certain structural configuration as well as a specific form of blast load and level of damage sustained. When assessing the effect of different parameters (associated with the form of the imposed load and the design of the structure considered) on structural performance, a series of new P-I curves need to be derived. This paper presents an extended P-I diagram method, which is based on derivation of complementary diagrams that can define the effect of two parameters (e.g., the level of axial loading imposed onto a column and the level of damage sustained) on the quasi-static and impulsive asymptotes, thus governing the positions of P-I curves in the diagram plane. The extended P-I diagram method is presented in dimensional and normalised forms. The dimensional form simplifies the derivation of new P-I curves, while the normalised form simplifies the procedure adopted for assessing the behaviour of a certain structure when subjected to a new set of loads. The application of the proposed method is demonstrated in both forms using a typical reinforced concrete (RC) column subjected to a blast load. The column is modelled using finite element analysis capable of accounting for the nonlinear behaviour of concrete and steel. A novel method is proposed for material modelling of concrete. The new material model is validated at both material and structural levels against relevant experimental data. P-I diagrams are initially derived for the axially unloaded column, while complementary diagrams are derived for the column loaded by different axial forces. The framework of the extended P-I diagram method employed for the derivation of new P-I curves and the assessment of the level of damage sustained by the column when subjected to different loading conditions is provided herein.

This paper presents a gradient-based framework to optimize the film-cooling performance of heat bearing components in gas turbines. We examine a representative periodic component with very low porosity (below 1 % ) and optimize the shape of an inclined hole on the wall of a combustor for maximum cooling effectiveness, here defined as the normalized average decrease of downstream temperature. The shape boundary of the hole is parameterized using the coordinates of its control points here describing the design variables. Geometric constraints are introduced on the void area, symmetry relations and relative motion between planes along the line of extrusion. The cooling effectiveness is numerically evaluated through a RANS (Reynolds-Averaged Navier-Stokes)-based computational fluid dynamics (CFD) analysis. The Method of Moving Asymptotes (MMA) is adopted as the optimizer, with gradients computed using the adjoint method. Nine case studies with initial hole geometry of circular and elliptical shape as well as various inclination angles converge to a family of V-shapes that achieve more than 120 % increase in cooling effectiveness. The automation of the workflow presented in this paper can be implemented in CFD-based optimization of other single and multi-objectives problems.

The robust and precise control of piezoelectric stages is quite challenging due to the existence of strong hysteresis nonlinearity. In this paper, the dynamics of a piezoelectric stage is identified as a second-order linear system preceded by an input hysteresis characterized by the Prandtl–Ishlinskii (PI) model. Then, a control strategy based on the uncertainty and disturbance estimator (UDE) is developed to mitigate the effect of hysteresis nonlinearity and improve the performance of the positioning control of the piezoelectric stage, without the detailed model of the hysteresis except the slope information of the PI hysteresis asymptotes. Moreover, the stability analysis of the closed-loop system with the UDE-based controller is provided. Extensive experimental studies are carried out on a Physik Instrumente P-753.31c piezoelectric stage to demonstrate that the UDE-based controller can achieve excellent performance in trajectory tracking and disturbance rejection, compared to the proportional–integral–derivative (PID) controller and a disturbance-observer-based controller.

As opposed to the conventional 2D (circular/elliptical crack) and 1D (linear crack) models for earthquake rupture, which are, respectively, for small‐to‐large earthquakes and mega‐earthquakes, Vere‐Jones’ branching crack model describes the extreme case when the entire rupture process is completely controlled by randomness. This article discusses the similar features between the conventional source models and Vere‐Jones’ branching crack model, which include (a) the magnitude–frequency relation, (b) the source time function, and (c) the rupture duration–seismic moment relation. We proved that the Gutenberg–Richter magnitude–frequency relation holds as an asymptote for more general cases of branching processes. The branching crack model shows that the variance of observed rupture durations is relatively larger for small magnitudes and gives a scaling relation of T ∝ M 1/2 between the rupture duration T and the seismic moment M of an earthquake. Moreover, the stochastic property of the branching process explains why the earthquake magnitude cannot be determined until the entire source process is completed. The results in this article imply that the randomness caused by many unknown factors in the complex environments of earthquake sources cannot be ignored, and it can be effectively described by Vere‐Jones’ branching crack model. We conclude that the earthquake rupture is at least an intermediate process between the conventional deterministic model and the stochastic branching crack model if its mechanism is not completely controlled by randomness, as described by the latter.

Fan impellers are usually designed considering that the pumped air is incompressible and homogeneous, i.e. its density remains constant. When the incompressibility hypothesis can lead to significant errors, as in the case of high pressure fans, the analysis of the air flow can be made by considering that the air undergoes a polytropic process of constant polytropic exponent. In this paper, the concept of polytropic process of variable exponent depending on impeller radius is introduced, in order to better approximate the phenomena that take place inside blade passages. Numerical results obtained for an impeller of a high pressure fan without spiral casing suggest that the pumped air undergoes two different processes: an expansion in the first part of the impeller and the usual compression in the second part. The two processes are reflected in the strong variation of the polytropic exponent, which shows a vertical asymptote where the change of the process takes place. The results also suggest that high pressure fan impellers could consist of two stages, each stage being designed according to the process that takes place inside it: expansion or compression.

This paper proposes a novel optimization design method for circuit analog absorbers consisting of resistor-loaded square-loop arrays. First, new precise equivalent circuit models (ECMs) for square-loop-array-based absorbers are derived through the synthetic asymptote method. The presented models are applicable for multilayered absorber with printed single or double SLAs on each layer. Then, the combination of this ECM and conventional genetic algorithm (GA) is proposed and provided a fast and efficient way to design broadband and low-profile SLA absorbers. For demonstration, four absorbers are designed and optimized. Finally, the agreement between the simulated and measured reflection coefficients indicates the validity of the presented method.

The p–I diagram of a frame beam subjected to blast loading is established, including the elastic lateral restraint and inertia offered by the rest of the structure, the development of nonlinear membrane action and also, the bending-tension (M−N) interaction that develops in the plastic hinges. The analytical procedures to compute the asymptotes in the p–I diagram as well as a parametric study on the p–I diagram are provided. A dimensional analysis of the problem reveals that, under the considered assumptions, four dimensionless parameters mainly influence the required ductility of the beam. Two of them are related to the behavior of the indirectly affected part (the lateral restraint and mass). Another one is related to the mechanical properties of the investigated beam (i.e. the ratio of the bending to axial resistance). The last parameter incorporates scales of the geometry and of the deformed configuration at the onset of the plastic mechanism.

Stiffened shells are widely used in aerospace structures such as launch vehicles and aircraft wings. This paper presents a novel two-scale topology optimization method to design the innovative grid-stiffened pattern for maximizing the critical buckling load of thin-walled cylindrical shells. On the micro-scale, the asymptotic homogenization method is employed to calculate the general stiffness coefficients of the cell. On the macro-scale, the maximum critical buckling load is set as the objective to drive the topology optimization on the micro-scale. Besides, the repeated eigenvalues are considered both in the sensitivity analysis of buckling loads and the optimization solver with a sub-problem based on the Method of Moving Asymptotes (MMA). Through the optimization, we can obtain the optimal configuration of the grid-stiffened cell. In this paper, an illustrative example of the grid-stiffened cylindrical shell for maximizing the critical buckling load is carried out to validate the effectiveness of the proposed optimization method. In comparison to the optimal orthogrid shell, the critical buckling load with the optimal pattern obtained by the proposed optimization method have a dramatically increase of 21.7%. It can be concluded that the proposed method has huge potential to design the configuration of the grid-stiffened cell of cylindrical shells.

Two very different cities (Berlin and Copenhagen), with two different stories and two different environments, have two different architectures, namely, the Reichstag building in Berlin and the Treetop Experience in Copenhagen, that are differentially designed. Two geometric shapes, an ellipsoid and a hyperboloid of one sheet, are used to interpret the different architectures. A common architectural element in both architectures is a spiral walkway that allows for the buildings’ usability without barriers. In this work, the two observed objects are presented in their respective environment, history and purpose. The shapes are interpreted, which reveals their geometric aspects that are associated with the functional and emotional effects of their architectural forms. Parameterization is the main mathematical tool through which the characteristic shapes are studied and mathematically expressed, using Linear Algebra and the Parametric Geometry of surfaces that are ideally close to the studied architectural objects. Moreover, the free and open-source programming language ASYMPTOTE is used for their virtualization, the model’s reliability is assessed, and the analysis of the model’s behavior is presented.

The characterization of the fatigue behaviour of aluminium alloys is still capturing the attention of researchers. As it is well known in literature, for certain alloys, in a specific range of cycles number, the S-N curves do not present any asymptote. So that, problems result in the assessment of the fatigue life. In these conditions, the concept of the fatigue limit has to be replaced by the fatigue strength at a fixed number of loading cycles. Temperature acquisitions during fatigue tests allow for a specific analysis that can support the researchers in understanding the complex processes that are involved in fatigue and their influence on fatigue life, even for aluminium alloys. In fact, the analysis of the surface temperature signal that was detected during a self-heating test provides a curve that is characterized by a distinct slope-change point at a specific stress value. Even though researchers have been investigating fatigue life characterisation and temperature variations for more than a decade, it is not clear what this point represents in terms of fatigue strength. The aim of the present paper is to find out a possible correlation between the thermal behaviour of AA5754-H111 undergoing self-heating testing procedure and fatigue strength at a specific loading cycles.

International audience; In this work, we experimentally evaluate the rendering of topology optimisation through the design of hollow structures manufactured using a 3D printing technique. The moving asymptote method is used as a mathematical optimisation strategy to virtually minimise the volume of 2D designs subject to hydrostatic pressure by half. Designs are converted to 3D models by extrusion in the building direction and printed using the Fused Deposition Modelling technique. Compression testing up to densification is performed and designs are evaluated. The results show that extrusion of the design in the building direction provides the best option to avoid mechanical anisotropy induced by processing. Depending on the type and extent of excluded regions, mechanical performance proves to be adapted to a wide range of designs and different types of mechanical anisotropies can be derived. Comparison with finite element results shows differences in behaviour related to mechanical instabilities that occur as a result of the lack of inter-filament cohesion and external frame unsoldering.

The paper presents an original method of determining the elements of the production cycle time by using the modified work sampling method applied to a textile factory. It is shown that the movement of the elements of time can be viewed as a process and in the mathematical sense can establish control limits of error of ± 3 SD. The mean time of the production cycle of the groups created by the number of pieces in the series – tpcu moving the hyperbolic function, which has the asymptote c, a function of the form tpcu = c + b/log n, where all groups of the production cycle in the mathematical sense do not act like strata but are function tpcu related to technology and deterministic factors of the production series.

New method for evaluation of the ideal growth performance in pigs has been proved in the experimental stable room of MZLU in ŠZP Žabčice. This method is based on the biological interpretation of the exponential growth function of Gompertz. This solution defines the dynamic of the animal’s phenotype by the body mass at the begin of the fattening (G0), by the animal's race standard body mass (Gli) which is equal to the value of the growth curve asymptote and by the value of the daily maximum body mass increase (dGmax) given by the genotype of the animal. This phenotype definition yields the possibility to define the exponential growth curve of the animal from birth until to the body mass maturity by the equation in which (t) represents the age of the animal:Gt = Gli.exp(-ln(Gli/G0).exp(-(e.dGmax/Gli).t)) [kg] (1)The value of the real daily body mass increase is than estimated by the best approximation of the experimental body mass values by the growth curve defined in the equation (1). The distribution of animals in three groups, according to the calculated daily maximum body mass increase: the thin growing animas, by default growing animals and the most growing animals, demonstrated the dynamic of the relation between the value of the daily maximum body mass increase (dGmax) and the body mass of the animals (Gt). In animals aged 37 days the clear correlation between the daily maximum body mass increase and the body mass reached:Y = 21.486x – 14.826 (R2 = 0.69); and Y = 28.609x2 – 45.21x + 23.868 (R2 = 0.70).In animals of the age 150 days the correlation is a little bit looser:Y = 54.316x +39.146 (R2 = 0.31); and Y = 8.203x2 + 35.192x + 50.241 (R2 = 0.31).The presented original methodology for evaluation of the animal’s individuality by means of the biological version of Gompertz exponential growth functions has been proved as a tool for direct evaluation of expression of the genotype body mass into its phenotype values, already during the experiment or the fattening process.

The aim of this work is to define a general method for the optimization of composite patch repairing. Fracture mechanics theory shows that the stress intensity factor tends towards an asymptotic limit K∞.This limit is given by Rose’s formula and is a function of the thicknesses and mechanical properties of the cracked plate, the composite patch and the adhesive. The proposed approach consists in considering this limit as an objective function that needs to be minimized. In deed lowering this asymptote will reduce the values of the stress intensity factor hence optimize the repair. However to be effective this robust design must satisfy the stiffness ratio criteria. The resolution of this double objective optimization problem with Matlab program allowed us determine the appropriate geometric and mechanical properties that allow the optimum design; that is the selection of the adhesive, the patch and their respective thicknesses.

A anti-slug control requires operation around an open-loop unstable operating point. One solution is to design a robust controller based on a mechanistic model. An alternative and more robust approach is to identify an unstable model of the system based on input–output data. We used a closed-loop step test to identify an unstable linear model. From this, we obtained a second order IMC (Internal Model Control) controller that can be implemented as a PIDF controller. From the asymptotes of the proposed IMC controller, we also derive a simple tuning for PI-controller. Next, we considered two types of robust H ∞ controller (mixed-sensitivity and loop-shaping). The proposed model identification and control solutions were verified experimentally on two different test rigs. We found that the robustness and performance of the IMC (PIDF) controller is comparable with the H ∞ controllers. However, the proposed IMC (PIDF) controller is easier to tune compared to H ∞ control.

This article provides a unified look at MOSFET model parameter extraction methods that rely on the application of successive differential and integral operators, their ratios, and various other combinations thereof. Some of the most representative extraction procedures are assessed by comparatively examining their ability to extract basic model parameters from synthetic MOSFET transfer characteristics, generated by an ad hoc minimalist four-parameter model. The model used, comprised of a single polylogarithm function of gate voltage, approximately describes in a very concise manner the essential features of MOSFET drain current continuously from depletion to strong inversion. The exponential-like low voltage and monomial-like high voltage asymptotes of this simple model are conveniently used to analyze and compare the different extraction schemes that are founded on successive differentiation or integration. In addition to providing a combined view useful for comparative methodological appraisal, the present unified analysis facilitates visualizing and exploring other potentially promising extraction strategies beyond the straightforward use of successive differential and integral operators and their ratios. We include examples of parameter extraction from measured transfer characteristics of real experimental MOSFETs to comparatively illustrate the actual numerical implementation of typical successive differential and integral operator-based procedures.

Large-span prestressed concrete bridges are sensitive to concrete creep which has a profound effect on bridge safety and serviceability. In this study, 3D computational simulations based on different concrete creep and shrinkage models are employed to investigate the long-term deformation of a prestressed concrete bridge. An improved rate-type algorithm powered by the continuous spectrum method and exponential algorithm is utilised to enhance the computational accuracy and efficiency. The asymptotic behaviours of the deflection and shortening at the main cantilever tip are captured. Compared to deflection, the asymptotic slope of the shortening curve is more systematically correlated with the asymptotic trend of creep models containing logarithmic time functions and this close correlation can be established at a relatively young age after construction. Thus, it can be used to realistically predict long-term deformation, as well as approximate the governing parameters in the compliance functions. Sensitivity studies based on Latin hypercube sampling are employed to explore the scatter band of the deflection and shortening due to material randomness, prestress fluctuation and environmental variations. Its effect on the correlation between deformation and creep asymptote is comprehensively examined. Furthermore, the influence of individual tendons on the deflection is probed based on the sensitivity investigation.

Interference effects between the dominant waves created by the bow and the stern of a monohull ship, of length L , that advances at constant speed V along a straight path in calm water of uniform finite depth D are considered. The largest waves due to constructive interference result in an apparent wake angle ψ max that can differ greatly from the cusp or asymptote angles associated with the wave pattern of a ship when interference effects are ignored, as in Kelvin’s classical analysis. Thus, wave interference has a very large effect on the wave signature of a ship in shallow water and cannot be ignored. Water-depth effects on the wake angle ψ max are found to be insignificant for water depths d L ≡ D / L greater than d deep L ≈ 0.89 or for Froude numbers F ≡ V / g L greater than F deep ≈ 0.5 / d L . Furthermore, the water depth d L has only a relatively small influence on the wake angle ψ max for 1.5 F , and the deep-water approximation ψ max ≈ 0.14 / F 2 can then be used.

The effects of stress ratio on high-cycle fatigue (HCF) and very-high-cycle fatigue (VHCF) behavior of a Ti-6Al-4V alloy were systematically investigated in this paper. Fatigue tests with ultrasonic frequency (20 kHz) were performed on specimens of a bimodal Ti-6Al-4V alloy with stress ratios of -1, -0.5, -0.1, 0.1 and 0.5. Three types of crack initiation mode were observed on the fracture surfaces of the specimens that failed in the HCF and the VHCF regimes, which were explicitly classified as surface-without-facets, surface-with-facets and interior-with-facets. With the increase of stress ratio from 1 to 0.5, the number of specimens for surface-without-facets decreased, that for surface-with-facets increased, and that for interior-with-facets increased first and then decreased. For the failure types of surface-with-facets and interior-with-facets, the fatigue strength decreased sharply in the VHCF regime, and the S-N curve switched from an asymptote shape to a duplex shape. Then, a new model based on Poisson defect distribution was proposed to describe the effects of stress ratio on the occurrence of different failure types, i.e., the competition of alternative failure types. The observations also showed that there is a rough area at the crack initiation region for interior initiation cases, and the values of the stress intensity factor range for the rough area are within a small range, with the mean value being close to the threshold for the crack starting to grow in vacuum environment of the alloy. The estimated value of plastic zone size at the periphery of rough area is close to the average diameter of the primary cc grains of the alloy. (C) 2014 Elsevier B.V. All rights reserved.

We study the nanoscale terraced topographies that arise when a solid surface is bombarded with a broad ion beam that has a relatively high angle of incidence θ. We find that the surface is not completely flat between the regions in which the surface slope changes rapidly with position: Instead, small-amplitude ripples propagate along the surface. Our analytical work on these ripples yields their propagation velocity as well as the scaling behavior of their amplitude. Our simulations establish that the surfaces exhibit interrupted coarsening, i.e., the characteristic width and height of the surface disturbance grow for a time but ultimately asymptote to finite values as the fully terraced state develops. In addition, as θ is reduced, the surface can undergo a transition from a terraced morphology that changes little with time as it propagates over the surface to an unterraced state that appears to exhibit spatiotemporal chaos. For different ranges of the parameters, our equation of motion produces unterraced topographies that are remarkably similar to those seen in various experiments, including pyramidal structures that are elongated along the projected beam direction and isolated lenticular depressions.

Asphalt concrete behavior is heavily dependent on temperature and loading rate. Hence, the material is typically tested at a range of temperatures and loading frequencies to capture its properties. Results are then used to develop a master curve exhibiting material behavior at the full spectrum of loading frequencies. An abbreviated testing protocol, under AASHTO PP 61-13, proposes a practical approach for development of this master curve. In this practice, the low temperature asymptote of the master curve is dominated by the limiting maximum modulus estimated through the Hirsch model. In this study, the dynamic modulus (DM) testing coupled with impact resonance (IR) test was used to evaluate the effect of this limiting maximum modulus on construction of the asphalt concrete master curve. Three different asphalt mixtures prepared with the same gradation and binder content, but different grades of stiffness were tested. The DM testing was performed at multiple temperatures and loading frequencies. The IR tests were conducted on the same specimens at the same temperatures. Two sigmoid functions (MEPDG and Richards models), and three shift factors (Arrhenius, Williams–Landel–Ferry, and polynomial) were utilized in the analysis. Richards sigmoid function coupled with polynomial shift factor provided the best fitting accuracy to the measured data. It was observed that the limiting maximum modulus obtained from experimental data was underpredicted by that obtained from the Hirsch model. The results indicated potential benefits of the IR test as a complementary testing tool to the abbreviated DM testing protocol to reliably characterize asphalt concrete.