Space Envelope Research Articles

Efficient methods to build structural performance envelopes in characteristic load space

Performance envelopes provide a novel methodology that quantifies the load bearing capacity of a structure in a reduced dimension load space. The envelopes relate the complex loads acting on a structure to the corresponding structural failure constraints and may find many applications within the aircraft structural design process. Constructing envelopes for industrial problems is of particular interest, where the state-of-the-art implementation involves a point cloud meshing and surface modelling strategy. A main challenge in implementing envelopes within an engineering process is the large associated computational costs of construction. The contribution of this article is a robust and efficient strategy to reduce the computational costs of building a performance envelope. The paper presents a method to build the envelopes using a ray-scaling approach. The novel approach is validated by building 3-dimensional envelopes for a representative industrial problem (stiffened panels of AIRBUS’s XRF-1 wing). The results demonstrate a ∼ 42 % reduction in the computation costs compared to the preceding research. The improved construction efficiency makes the employment of envelopes more feasible for large industrial scale processes or when individual failure assessments are computationally expensive.

New Insights into the Stiffness and Strength of Flax Composites from Tsai’s Modulus and the Area of the Failure Envelope

There is a growing trend toward the use of natural fibers as reinforcing materials, with flax being a significant part of this market. The mechanical properties of these polymer composites, like those of synthetic fibers, are governed by parameters and material invariants. The challenge is to minimize these parameters, and to reveal these invariants to make stiffness and strength easily comparable with each other and with other composites, while avoiding excessive complexity. To this end, a simple methodology has been developed using the following parameters: Tsai’s modulus or the trace of the stiffness tensor and the area of the Omni Failure Envelope in stress space. Based on the analysis of significant published experimental data on flax composites, new insights were found. The trace-normalized longitudinal Young modulus is a material property that were found to be 0.77 for tension and 0.67 compression with a coefficient of variation of 5.6% and 15%, respectively. The area of the Omni Failure Envelopes and the strength are linearly related. The use of the proposed parameters and some invariants has been discussed and they are used to compare and rank them with each other and with other composites, including carbon, aramid, and glass fiber-reinforced polymer composites.

Manipulating winding numbers and multiple topological bound states via long-range coupling in chiral photonic lattices

The topological bound states are limited to one pair in traditional one-dimensional (1D) topological chiral models as the winding number can only take the value of 0 or 1. It was increased to 2 or 3 via long-range couplings (LRCs) that were restricted to second- or third-order in recent experimental or theoretical researches. How to generate larger winding number to manipulate more topological bound states remains a challenge. Here, we propose an effective method by introducing arbitrary Nth order LRC stronger than the sum of other order couplings. The resulting winding number has been computed by getting the winding loop's envelope in parameter space. The coupling-inverted 1D photonic topological insulators supporting up to three pairs of highly localized multiple topological bound states are realized by fabricating photonic lattices with multi-layer waveguide arrays. Furthermore, these topological bound states are closely spaced, offering a promising implementation approach of multimode topological lasers in gain media. Our work highlights the advantages of LRCs in manipulating the topological phases of matter. Published by the American Physical Society 2024

Stress-dependent instantaneous cohesion and friction angle for the Mohr–Coulomb criterion

The strength criterion of rock is essential for stability control and safety design of geotechnical engineering constructions. Due to its widespread adoption, the Mohr–Coulomb (M-C) criterion is prominent among strength criteria. However, the M-C criterion is constrained by three significant limitations: it fails to capture the nonlinear strength response, overlooks the critical state, and disregards σ2. This study introduces a novel Stress-dependent Instantaneous Friction angle and Cohesion (SIFC) model for the M-C criterion to represent the convex strength envelope of intact rock, covering the spectrum from non-critical to critical states. In pursuit of this objective, an innovative approach for calculating these instantaneous shear parameters at each corresponding σ3 is initially introduced. By examining the confining pressure dependency of the instantaneous friction angle and cohesion, the SIFC model is derived and introduced to the M-C criterion. The SIFC-enhanced M-C criterion, utilizing parameters obtained from triaxial tests under lower σ3, delineates the complete non-linear strength envelope in (σ1, σ3) space, covering brittle to ductile behavior. This criterion is then extended to polyaxial stress conditions. Validation through triaxial test data confirms that the SIFC-enhanced M-C criterion accurately reflects the strength characteristics of the tested rocks.

Experimental characterisation of rotor noise in tandem configuration

This paper presents a comprehensive investigation into the noise radiation characteristics of two rotors in a tandem configuration. Through an extensive experimental campaign, the study explores the effect of the separation distance between two rotors on the noise directivity patterns, spectral characteristics and temporal features of the radiated noise under both hovering and edge-wise flight conditions. The directivity patterns of the overall sound pressure level obtained from the polar and side arrays demonstrate a dependence on the separation distance and advance ratio. Spectral characteristics elucidate the influence of separation distance on tonal and broadband energy content. While the high-frequency broadband noise increases for both hovering and edge-wise flight similarly, the low-frequency broadband energy strongly depends on the advance ratio and the rotor separation distance. The results reveal a distinct envelope in the design space, where the radiated broadband noise for tandem configurations can be minimized, offering potential insights for noise reduction strategies. Additionally, the wavelet analysis for tandem configurations reveals that the emitted noise at the first and second blade passing frequency is strongly intermittent with amplitude modulation, which shall be considered for annoyance perception.

An experimental methodology for the calibration of indoor building environment models using thermal point clouds and CFD simulation

ABSTRACT This paper presents an experimental methodology employing thermal point clouds (TPCs) of indoor spaces to develop and calibrate Computational Fluid Dynamics (CFD) models for simulating indoor building environments. TPCs, captured at various time intervals, provide geometry and surface temperatures of the space envelope are crucial for initial and final contrast parameters in model calibration. Segments from TPCs of interior surfaces serve as ground truth for calibrating theoretical CFD models. This involves adjusting boundary conditions to approximate real surface temperature distributions on selected walls. The innovative calibration approach incorporates automatic wall segmentation processes, enabling comparison between in-situ measured and simulated values. A case study assesses the similarity between real thermal orthoimages and CFD simulations, employing qualitative and quantitative analysis with a convergence criterion. Results validate the methodology, highlighting the need for further automation of manual processes.

Anisotropic ductile fracture of a stainless steel under biaxial loading: Experiments and predictions

The anisotropic ductile fracture behavior of a stainless steel is investigated using a combination of experiments and analysis. The material is SS-304L, an austenitic, low-carbon stainless steel, received in the form of tubes of 2.38 mm dia. and 0.15 mm thickness. The tubes are inflated under volume control in a custom apparatus. At the same time, the axial force on the tubes is kept proportional to the pressure induced by the inflation. This leads to quasi-proportional stress paths in the meridional-hoop engineering stress space. A total of 15 discrete paths are successfully tested. Stereo-type Digital Image Correlation is used to measure the strains. In every case, the tubes develop a series of instabilities before bursting. The failure is oriented along the meridional or the hoop direction of the tube, depending on which stress is greater. A mild plastic anisotropy is detected in these experiments. Hence these results are then used for calibrating the anisotropic yield criterion Yld2004-3D. This is introduced in a finite element model of the experiments, which includes a thickness imperfection designed to capture the two failure orientations observed in the experiments. The numerical model using the Yld2004-3D criterion reproduces the experiments well, e.g., it captures the experimental stress-strain and induced strain paths better than von Mises. It is then used to probe the conditions at the onset of fracture (hybrid method). It is found that most paths lead to essentially proportional loading during deformation. A significant anisotropy in the fracture behavior is detected, with the meridional-stress-dominated paths being able to develop much higher strains than the hoop-dominated ones. These results are then captured by the DF2016 ductile fracture criterion, modified to use the anisotropic yield criterion Yld91. The proposed criterion is flexible enough to represent the fracture anisotropy very well, without being unnecessarily complex. The fracture forming limit curve (i.e., the fracture envelope in strain space) predicted by the DF2016/Yld91 model is also found to be very close to the experiments. The results and findings of this work help establish a framework to reliably design components and processes when significant fracture anisotropy is expected.

Internal instability of cohesionless soils in upward and downward flow: an experimental verification of theory

Rigid-wall permeameter testing of two potentially unstable gradations established that the critical hydraulic gradient to trigger instability is smaller for upward flow than for downward flow. The experimental finding is explained with reference to the Skempton-Brogan stress reduction factor α in the finer fraction content of the soil. Theory uses the α-factor to define a hydro-mechanical envelope in gradient-stress space that is independent of flow direction, and the experimental results are found to be in good agreement with the theory. Testing with upward flow is recommended to determine the value of α for an internally unstable gradation because, in contrast to downward flow, there is no requirement for an outflow boundary.

OptEnvelope: A target point guided method for growth-coupled production using knockouts.

Finding the best knockout strategy for coupling biomass growth and production of a target metabolite using a mathematic model of metabolism is a challenge in biotechnology. In this research, a three-step method named OptEnvelope is presented based on finding minimal set of active reactions for a target point in the feasible solution space (envelope) using a mixed-integer linear programming formula. The method initially finds the reduced desirable solution space envelope in the product versus biomass plot by removing all inactive reactions. Then, with reinsertion of the deleted reactions, OptEnvelope attempts to reduce the number of knockouts so that the desirable production envelope is preserved. Additionally, OptEnvelope searches for envelopes with higher minimum production rates or fewer knockouts by evaluating different target points within the desired solution space. It is possible to limit the maximal number of knockouts. The method was implemented on metabolic models of E. coli and S. cerevisiae to test the method benchmarking the capability of these industrial microbes for overproduction of acetate and glycerol under aerobic conditions and succinate and ethanol under anaerobic conditions. The results illustrate that OptEnvelope is capable to find multiple strong coupled envelopes located in the desired solution space because of its novel target point oriented strategy of envelope search. The results indicate that E. coli is more appropriate to produce acetate and succinate while S. cerevisiae is a better host for glycerol production. Gene deletions for some of the proposed reaction knockouts have been previously reported to increase the production of these metabolites in experiments. Both organisms are suitable for ethanol production, however, more knockouts for the adaptation of E. coli are required. OptEnvelope is available at https://github.com/lv-csbg/optEnvelope.

Numerical generation of omnistrain failure envelopes

Traditional failure criteria for composites are usually formulated in material coordinates and depend on all three inplane stresses, hence failure evaluation depends on the ply angle. The omnistrain failure envelope describes the most critical failure envelope in strain space irrespective of ply orientation. This independence of ply orientation leads to an isotropic failure criterion that depends only on the principal strains. Omnistrain envelopes greatly simplify the task of design and optimisation of composite laminates. This paper proposes a numerical technique to generate omnistrain failure envelopes for different composite failure criteria. The failure index, describing how far a point in strain space is from the failure boundary, is used to describe the failure surface. Assuming convexity of the failure surface, a set of points is generated on the surface, and the convex hull algorithm is used to generate a polygonal approximation of the failure surface. Representing strains in terms of principal strains and the angle between the principal and material coordinates, allows us to eliminate the angle analytically by considering the worst case condition. The omnistrain envelope is thus directly generated from the approximate three-dimensional failure surface. The proposed algorithm does not require analytic expressions of the failure surface. An adaptive algorithm is proposed to generate the omnistrain envelope with relatively small number of points. As demonstration of the proposed algorithm, the omnistrain envelopes for various composite materials are generated for a number of composite failure criteria. The omnistrain envelopes generated for the Tsai-Wu criteria accurately match to existing analytic expressions.

Deep learning-based conductive particle inspection for TFT-LCDs inspired by parametric space envelope

Deep learning-based conductive particle inspection for TFT-LCDs inspired by parametric space envelope

A low-dimensional energy model to distinguish strength and stability in a jammed column

A low-dimensional “phase space” energy model is presented that outlines contributions to relative strength and stability of two jammed granular+fluid columns: one of small, fine, nearly monodisperse grains and one of larger, coarse, more polydisperse grains. Both granular (dry) structure and pore-fluid (wet) structure contributions to the strength and stability are determined by experimental parameters obtained for bulk measurements from previously published studies. Physical quantities that are controlled by granular-dominant parameters or controlled by fluid-dominant parameters can be fit to sigmoid functions that produce a phase space envelope of strength and stability for a particular column. The novel model presented here replicates this phase space envelope by defining a single granular temperature based on the sigmoid fits. The model demonstrates the overall role that granular temperature plays in both the relative strength and stability of the system in a manner that allows the two characteristics to be distinguished.

Modeling Variation in Multi-Station Compliant Assembly Using Parametric Space Envelope

Abstract Compliant parts have different characteristics from rigid parts and are used frequently in industries. One of the biggest challenges facing by industries is geometric variation management of these compliant parts which can directly impact product quality and functionality. Existing rigid body-based variation modeling approaches are not suitable for compliant assembly while finite element analysis-based methods have the disadvantages of requiring heavy computation efforts and detailed design information which is unavailable during preliminary design phase. Hence, this paper proposes a novel geometric variation propagation model of multi-station compliant assembly based on parametric space envelope. Three sources of variation: location-led positional variation, assembly deformation-induced variation, and station transition caused variation are analyzed. In this study, geometric variations are modeled indirectly through control points of constructed variation tool. Compared with existing methods where geometric variation is modeled by tracking key feature points on the manufacturing part, the proposed approach brings unique benefits. It can deal with arbitrary complex compliant part, and it provides a unified modeling framework for different types of variation. The method is illustrated and verified through a two-station three parts case study on a multi-station compliant panel assembly. The proposed method provides industries with a new way to manage geometric variation from compliant assembly.

DSM launches color and mechanical properties prediction tool powered by AI

On January 31 2023, DSM Engineering Materials announced the launch of Lucidiris™, a tool to help customers reduce their time to market when developing colors of high-performance materials for a variety of applications. Besides predicting color and mechanical properties, it can predict the envelope of potential color space within critical mechanical properties and prescribe recipes for targeted color properties. Lucidiris™ has been developed for several high-performance material grades and will be extended, including recycled-based and repurposed materials.

PREDIÇÃO DA DISTRIBUIÇÃO GEOGRÁFICA E CONSERVAÇÃO DAS PALMEIRAS AMAZÔNICAS Astrocaryum acaule MART. E Astrocaryum aculeatum MART.

ABSTRACT Astrocaryum aculeatum Mart. Moreover, Astrocaryum acaule Mart. are palm trees with ecological and extractive importance in the Amazon. These are hearty species that have been associated with archaeological sites and thrive in the presence of humans in certain areas. This work aimed to verify the effect of global climate change on the potential geographic distribution of A. acaule and A. aculeatum in the current period and future climate scenarios using ecological niche modeling in Brazilian phytogeographic domains. The modeling was based on 19 bioclimatic variables obtained from the Worldclim website and four algorithms (Climate space model, Envelope Score, Niche Mosaic, and Environmental Distance). Additionally, the Environmental Distance algorithm showed greater similarity regarding species distribution with potential occurrence in the five Brazilian domains (Amazon, Pantanal, Caatinga, Cerrado, and Atlantic Forest). The dispersion patterns were very similar between the two Astrocaryum palms though A. aculeatum was more sensitive to climatic variations. A. acaule may be more resilient to changes, as demonstrated by being able to recolonize in the southern portion of the Amazon in future scenarios in the year 2070. The modeling helped to delimit potential areas for A. aculeatum and A. acaule, indicating the need for the conservation of the species in more sensitive regions.

Projeções futuras e modelagem ecológica para a distribuição de plantas alimentícias não convencionais

ABSTRACT The importance of non-conventional food plants has been evidenced due to their great potential for phenotypic plasticity, resilience and resistance to permanence in inhospitable places. This study aimed to evaluate the natural distribution of two of these species (Eryngium foetidum and Fridericia chica) in the present period (2009-2019) and the projection for two future climate scenarios (RCP 4.5 - “less pessimistic” and RCP 8.5 - “more pessimistic”) in two-time intervals (2020-2050 and 2051-2070), in the six Brazilian phytogeographic domains. Nineteen bioclimatic variables obtained from the WorldClim database and four algorithm models were tested: Climate Space Model, Envelope Score, Niche Mosaic and Environmental Distance. The Environmental Distance algorithm presented the best discrimination of the models adjusted for the two species. From the projections, it is possible to perceive that the species are severely affected in the phytogeographic domains of the Amazon, Pantanal and Pampa, becoming practically extinct in the RCP 8.5 scenario, for the period of 2051-2070.

Basic Design and Progress of the Spliced Joint for CFETR TF Coil

High-performance superconducting joints are essential for the continuous and stable operation of superconducting magnet systems to generate stable magnetic fields, because the local heating from resistive losses can cause the superconductor to enter an unstable regime and result in quench. The China fusion engineering test reactor has five internal joints for each toroidal field coil. To provide a lower heat load of the joints to the cryogenic system, the direct current (dc) resistance of the internal joint connection must be below 0.3 nΩ. At the same time, the structure of the joint jacket should be convenient for winding. The internal joints must fit a space envelope equivalent to the original conductor cross section and must have enough structural strength and a low pressure drop. In the basic design, two trial joints were manufactured and tested at ASIPP. This article provides a description of the design, simulation, and manufacturing process of the trial joint, and finally obtained the test results with electrical resistances of 0.057 and 0.076 nΩ.

Experimental determination of a probabilistic failure envelope for carbon fiber reinforced polymers under combined compression–shear loads

The compressive strength of fiber reinforced composites is sensitive to material imperfections. Material imperfections are spread in the volume in an apparently random manner in the form of fiber misalignment, resulting in non-deterministic strength in compression dominated load cases. The main factors dictating failure under compression dominated loads are the fiber misalignment and the nonlinear material behavior. To enable reliable failure prediction, a quantification of the strength uncertainty is required. Therefore, the current investigation considers different experimental aspects of the problem such as measurements of the fiber misalignment and the material characterization. To implement combined compression–shear loading, a newly in-house developed combined loading fixture was used. A statistically significant number of specimens was tested under aforementioned load cases. Macroscopic images of the failed specimens and a micrograph of the fracture surface are shown to provide evidence of microbuckling failure mode under combined compression–shear loads. Using the experimental strain measurements, a probabilistic failure envelope in strain space is presented. Results of the axial compression load case are interpreted in the context of the notion of the effective misalignment angle using an analytical model. A failure envelope in stress space is derived using an analytical solution for the combined compression–shear load cases and the effective global misalignment angle calculated from the measurements. Applied far field stresses of different load cases are compared, and a visual depiction of the strain localization phenomenon leading to microbuckling failure using digital image correlation is presented.

Phase Portrait Trajectory of a Three Degree-of-Freedom Vehicular Dynamic Model

Abstract This article formulates a front-wheel-drive three degree-of-freedom (3DOF) four-wheel planar vehicle model with the Magic Formula tire model. The state variables' evolutions of the model, i.e., trajectories of the model under acceleration and deacceleration conditions, are analyzed. The process of evolution is divided into desirable and undesirable phases based on the response characteristics of the vehicle to the driver input during the process. The trajectories are categorized as unsaturated trajectories and saturated trajectories by the existence of saturated tires during these phases. The response of state variables to driver input under acceleration conditions during undesirable phases are zero or even opposite, while the response of undesirable phases under the deacceleration condition is partially positive. Besides, the existing yaw rate safety envelope is recalibrated by using a longitudinal and lateral tire force coupling model. A more accurate yaw rate safety envelope is obtained from the given driver input. Furthermore, a longitudinal speed safety envelope is proposed according to the relationships among slip angle, yaw rate, and longitudinal speed. These safety envelopes are determined by driver input, tire properties, and grip condition. After overlaying yaw rate and longitudinal speed safety envelopes in the state space, the feasibility of using the safety envelope as trajectory classification criteria is discussed.

Propagation properties of circularly symmetric Airy beam modulated by spectral asymmetric envelope

An asymmetric envelope function for modulating the spectrum of circular Airy beam is proposed in this work. The propagation properties of the modified circular Airy beam are investigated in both theory and experiment. The three parameters of the asymmetric hyperbolic secant function can be used to adjust the ratio of the high frequency components to the low frequency components in Fourier space, and thus tuning the propagation properties of this modified circular Airy beam. The results demonstrate that the focal position is affected mainly by the high frequency components. The maximum focal intensity will not be enhanced continuously by increasing the proportion of the high frequency components. It depends on the ratio of the high frequency components to the low frequency components when the center frequency is determined. Therefore, using an asymmetric envelope in Fourier space is much more reasonable than using the high pass filtering or symmetric Gaussian envelope. The FWHM decreases significantly with the increase of center frequency. When the parameters are chosen appropriately, the size of focal spot will be reduced significantly, the maximum focal intensity, especially the abruptly autofocusing property will be enhanced greatly and the focal position can remain almost the same as the focal position of the common circular Airy beam. The maximum focal intensity of the proposed beam is 3.4 times that of the common circular Airy beam and the abruptly autofocusing property of the proposed beam is much better than that of the beam using the symmetric Gaussian envelope. The phase-only encoding method in Fourier space is used to generate the proposed beam in experiment. The experimental results are in reasonable agreement with the simulation results. It indicates that the modified beam can be generated conveniently by using the same method as that used to generate the common circular Airy beam.