Curvilinear Path Research Articles

IGA Based Bi-Layer Fiber Angle Optimization Method for Variable Stiffness Composites

This paper presents a topology optimization method for variable stiffness composite panels with varying fiber orientation and curvilinear fiber path. Non-uniform rational B-Splines (NURBS) based Isogeometric analysis (IGA) is utilized for the numerical computation of the general minimum compliance problem. The sensitivity analysis of the structure compliance function for the density and bi-layer orientation is conducted. The bi-layer fiber paths in the design domain are generated using streamline method and updated by divided pieces reselection method after the optimization process. Several common examples are tested to demonstrate the effectiveness of the method. The results show that the proposed method can generate more manufacturable fiber paths than some typical topology optimization methods.

A Long Short-Term Memory Network for Vessel Reconstruction Based on Laser Doppler Flowmetry via a Steerable Needle

Hemorrhage is one risk of percutaneous intervention in the brain that can be life-threatening. Steerable needles can avoid blood vessels thanks to their ability to follow curvilinear paths, although knowledge of vessel pose is required. To achieve this, we present the deployment of laser Doppler flowmetry (LDF) sensors as an in-situ vessel detection method for steerable needles. Since the perfusion value from an LDF system does not provide positional information directly, we propose the use of a machine learning technique based on a Long Short-term Memory (LSTM) network to perform vessel reconstruction online. Firstly, the LSTM is used to predict the diameter and position of an approaching vessel based on successive measurements of a single LDF probe. Secondly, a “no-go” area is predicted based on the measurement from four LDF probes embedded within a steerable needle, which accounts for the full vessel pose. The network was trained using simulation data and tested on experimental data, with 75% diameter prediction accuracy and 0.27 mm positional Root Mean Square (RMS) Error for the single probe network, and 77% vessel volume overlap for the 4-probe setup.

Nonlinear flutter response of a composite plate applying curvilinear fiber paths

In the present study, nonlinear flutter and post-flutter behavior of a variable stiffness composite wing-like plate is investigated. The variable stiffness is obtained by varying fiber angles continuously according to a selected curvilinear fiber path function in the composite laminates. Flutter speed, limit cycle oscillations and bifurcation diagrams of the composite plate are explored for three different fiber path functions using the nonlinear structural model obtained based on the virtual work principle. The paper aims to exploit the ideal fiber paths with enhanced aeroelastic flutter and post-flutter properties for a composite plate in supersonic flow speed. First-order linear piston theory is applied to model the aerodynamics, and generalized differential quadrature is employed to solve the governing equations. Von Karman nonlinear strain theory is used to account for the geometric nonlinearities, and first-order shear deformation theory is employed to consider the transverse shear effects in the structural model. Time integration of the equation of motion is carried out using the Newmark average acceleration method. Different curvilinear fiber paths are introduced to enhance flutter instabilities and post-flutter behavior of the composite plate. Results demonstrate that the fiber orientation has a significant effect on the dynamic behavior of the plate and the asymmetric properties as well as the behavior of the limit cycle oscillation.

Efficiency of Commercial Egg Yolk-Free and Egg Yolk-Supplemented Tris-Based Extenders for Dromedary Camel Semen Cryopreservation

Simple SummaryThis study compared the efficiency of commercial egg yolk-free (AndroMed, OPTIXcell) and egg yolk-supplemented (Triladyl, Steridyl) Tris-based extenders for semen cryopreservation in dromedary camels. The camel-specific extender SHOTOR was used for reference. SHOTOR, Triladyl, Steridyl, AndroMed, and OPTIXcell can all be used for camel semen cryopreservation; however, SHOTOR and Triladyl provide the best post-thawing sperm quality.This study compared the efficiency of commercial egg yolk-free (AndroMed, OPTIXcell) and egg yolk-supplemented (Triladyl, Steridyl) Tris-based extenders for semen cryopreservation in seven adult dromedary camels. The camel-specific extender SHOTOR was used as control. The collected semen samples were evaluated and diluted with SHOTOR, Triladyl, Steridyl, AndroMed, or OPTIXcell. The diluted semen was gradually cooled and equilibrated for two hours before liquid nitrogen freezing. Semen was evaluated prior to freezing and after freeze-thawing cycles for motility, kinetics, vitality, abnormality, plasma membrane integrity, and DNA fragmentation using computer-assisted sperm analysis. In pre-freezing evaluation, progressive sperm motility was higher in SHOTOR-diluted samples (21.54 ± 1.83) than in samples diluted with Steridyl, OPTIXcell, or AndroMed (15.76 ± 1.80, 17.43 ± 1.10, and 13.27 ± 1.07, respectively). Moreover, Triladyl and SHOTOR resulted in significantly (p < 0.05) better sperm vitality and DNA integrity than all other diluents, but Triladyl resulted in a significantly (p < 0.05) better plasma membrane integrity (87.77 ± 0.31) than SHOTOR (85.48 ± 0.58). In the post-thawing evaluation, Triladyl led to significantly (p < 0.05) higher sperm motility (38.63 ± 0.81%; p < 0.05) when compared to SHOTOR, Steridyl or AndroMed (35.09 ± 1.341%, 34.4 ± 0.84%, and 31.99 ± 1.48%, respectively), with OPTIXcell being the least efficient (28.39 ± 0.86%). Progressive sperm motility was the highest when using Triladyl. Post-thawing curvilinear, straight line and average path sperm velocities were highest with Triladyl and lowest with AndroMed. Triladyl led to the highest linearity coefficient and straightness sperm coefficient, while SHOTOR to the highest DNA and plasma membrane integrity. OPTIXcell and AndroMed resulted in poor post-thawing sperm vitality, while Steridyl was less efficient than Triladyl. The highest rate of sperm abnormalities was recorded with OPTIXcell and the lowest with SHOTOR or Triladyl. In conclusion, SHOTOR, Triladyl, Steridyl, AndroMed, and OPTIXcell can all be used for camel semen cryopreservation; however, SHOTOR and Triladyl provided the best post-thawing sperm quality. Based on our findings, Triladyl is the best commercially available extender for dromedary camel semen cryopreservation to date.

Tendon-driven continuum robots with extensible sections—A model-based evaluation of path-following motions

Continuum robots are highly miniaturizable, exhibit non-linear shapes with several curves, and are flexible and compliant. In particular, concentric-tube and tendon-driven continuum robots can be designed on a small scale with diameters of below 10 mm. A small diameter-to-length ratio enables insertion of these robots through small entry points in order to reach hardly accessible regions by avoiding obstacles. This scenario can often be found in minimally invasive surgery and technical inspections. However, to reach the target region, a deployment along a narrow tortuous path is often required. Common tendon-driven continuum robots are intrinsically incapable of such deployment and concentric-tube continuum robots require special path conditions and intensive parameter optimization. Other proposed robot types, such as hyper-redundant and pneumatically actuated robots, exhibit less favorable diameter-to-length ratios and are thus not suitable for those tasks. Since the limiting factors are found in the design of continuum robots, we propose a novel tendon-driven continuum robot design, which features an additional degree of freedom in each robot section. The backbone is composed of straight, concentrically arranged tubes, each of which composes a section and is used to adapt its length. We present a three-section continuum robot prototype with a diameter of 7 mm, determine its follow-the-leader capabilities theoretically, and validate the results experimentally using model-based control. For our 165 mm long robot prototype, the repeatability is below 2.38 mm. The model accuracy reaches a median of 3.16% over 25 configurations with respect to robot length. The path-following error over five curvilinear paths results in median errors of 2.59% with respect to robot length.

Julian Huxley and the quantification of relative growth

In 1932, Julian Huxley introduced biologists around the world to a simple method for fitting two-parameter power equations, $$ Y\, = \,b \times \, X^{k} $$, to bivariate observations that follow a curvilinear path on the arithmetic (= linear) scale. The method entails fitting a straight line to logarithmic transformations of the data and then (at least implicitly) back-transforming the resulting equation to the arithmetic domain. This general approach continues to be in wide use by students of biological allometry despite its several limitations and shortcomings. For example, Huxley’s allometric method requires that the bivariate data of interest follow the path of a straight line in log domain (i.e., that the data be loglinear). However, many datasets that are otherwise suitable for allometric analysis do not meet the requirement for loglinearity and consequently are beyond the scope of Huxley’s method. Such data can usually be examined in the untransformed state by nonlinear regression, and the regression approach enables investigators to fit models with different functional form and random error. Moreover, by combining nonlinear regression with a categorical variable, investigators can compare sets of observations that follow curvilinear paths on the arithmetic scale. The regression protocol is illustrated by re-examining data for relative growth by the internal hinge ligament in a bivalve mollusk and by the elongated snout in garfish (Actinopterygii). The methodology promoted by Huxley has played a major role in development of the field of biological allometry, but the procedure has been superseded by nonlinear regression.

Intelligent Path Recognition against Image Noises for Vision Guidance of Automated Guided Vehicles in a Complex Workspace

Applying computer vision to mobile robot navigation has been studied more than twodecades. The most challenging problems for a vision-based AGV running in a complex workspaceinvolve the non-uniform illumination, sight-line occlusion or stripe damage, which inevitably resultin incomplete or deformed path images as well as many fake artifacts. Neither the fixed thresholdmethods nor the iterative optimal threshold methods can obtain a suitable threshold for the pathimages acquired on all conditions. It is still an open question to estimate the model parameters ofguide paths accurately by distinguishing the actual path pixels from the under- or oversegmentationerror points. Hence, an intelligent path recognition approach based on KPCA–BPNNand IPSO–BTGWP is proposed here, in order to resist the interferences from the complexworkspace. Firstly, curvilinear paths were recognized from their straight counterparts by means of apath classifier based on KPCA–BPNN. Secondly, an approximation method based on BTGWP wasdeveloped for replacing the curve with a series of piecewise lines (a polyline path). Thirdly, a robustpath estimation method based on IPSO was proposed to figure out the path parameters from a set ofpath pixels surrounded by noise points. Experimental results showed that our approach caneffectively improve the accuracy and reliability of a low-cost vision-guidance system for AGVs in acomplex workspace.

Tracks impacted field area simulation using kinematics and geometry for different equipment and operation scenarios

The intensity of the traffic caused by the farm equipment in mechanised agriculture generates track impacted areas which aggravate the soil compaction in the fields. A developed R simulation program evaluated the track impacted area and operational time of the equipment during bale aggregation along with harvesting and baling using kinematics and geometrical principles. Distance travelled by equipment and their respective track widths (footprint) determined the track impacted areas under different scenarios. Tracks impacted areas simulated for automatic bale picker (ABP) with several bales/trip (8–23 bales/trip) and areas (1–259 ha) were compared with a control method, using a tractor that can handle 1 and 2 bales/trip. The logistics simulation used the developed more realistic curvilinear method (circular turning paths developed for the harvester, baler, tractor, and ABP) and compared with simpler Euclidean paths. Overall, the impacted areas by the curvilinear method were 1.06–1.29 times the Euclidean for bale aggregation but were not statistically different ( p ≥ 0.49). Results indicated that the baler followed by harvester produced the least impacted area and ABP the most. Developed prediction models determined the curvilinear track path from Euclidean distances, impacted area from the field area, bales/trip, and biomass yield for different operations, as well as overall operational time fitted well to the results (0.95 ≤ R 2 ≤ 0.99). A small ABP of 8 bales/trip (which is also capable of 11 bales/trip) was recommended based on efficient bale aggregation and least impacted area.

Buckling Load Maximization of Curvilinearly Stiffened Tow-Steered Laminates

Under certain loading conditions, curvilinearly stiffened panels are seen to have better structural performance while being lighter in mass when compared to panels with straight stiffeners. A curvilinearly stiffened tow-steered composite laminate could be manufactured by fastening or bonding metallic curvilinear stiffeners to the composite panel. In this paper, such panels are computationally evaluated for their benefit in improving the panel buckling load. Initially, a parallel processing-based optimization framework to design tow-steered composite laminates with metallic curvilinear stiffeners is presented, where the objective is to maximize the buckling load with only a structural mass constraint and no stress constraint. The results show that the curvilinear stiffeners and curvilinear fiber paths in the composite laminated skin can lead to more than a 75% increase in the panel buckling load as compared to the use of equidistant straight stiffeners and straight fibers. Subsequently, a multiobjective optimization is conducted with the objectives to maximize the buckling load while minimizing the mass of the panels. It is seen that the improvement in the buckling load, by using curvilinear stiffeners and curvilinear fibers over equidistant straight stiffeners and straight fibers, depends upon the prescribed structural mass constraint.

Flutter improvement of a thin walled wing-engine system by applying curvilinear fiber path

In the present study, the aeroelastic behavior of a wing-engine system modeled as composite Thin Walled Beam (TWB) with curvilinear fiber path is investigated. The variable stiffness is acquired by constructing laminates of TWB with curvilinear fibers having prescribed paths. In order to account the effect of chordwise and spanwise locations, mass, and thrust force of engine on the aeroelastic characteristics of TWB, the novel governing equations of motion are obtained using Hamilton's variational principle. The paper aims to exploit desirable fiber paths with improved aeroelastic properties for different wing-engine configuration. Ritz based solution methodology is employed to solve the equations with coupled incompressible unsteady aerodynamic model based on Wagner's function. Numerical simulation results which conform to previously published literatures are presented for validation purposes. Although different curvilinear fiber paths can be introduced to enhance flutter instabilities for each wing-engine configurations, there exists an ideal placement of engine on the wing considering only the engine mass, and the engine mass and thrust force, simultaneously. A comprehensive insight is provided over the effect of parameters such as the lamination fiber path and the effect of engine positions with different mass and thrust values on the flutter speed and frequency.

Programming curvilinear paths of flat inflatables.

Inflatable structures offer a path for light deployable structures in medicine, architecture, and aerospace. In this study, we address the challenge of programming the shape of thin sheets of high-stretching modulus cut and sealed along their edges. Internal pressure induces the inflation of the structure into a deployed shape that maximizes its volume. We focus on the shape and nonlinear mechanics of inflated rings and more generally, of any sealed curvilinear path. We rationalize the stress state of the sheet and infer the counterintuitive increase of curvature observed on inflation. In addition to the change of curvature, wrinkles patterns are observed in the region under compression in agreement with our minimal model. We finally develop a simple numerical tool to solve the inverse problem of programming any 2-dimensional (2D) curve on inflation and illustrate the application potential by moving an object along an intricate target path with a simple pressure input.

Who Responds Creatively to Role Conflict? Evidence for a Curvilinear Relationship Mediated by Cognitive Adjustment at Work and Moderated by Mindfulness

This study aims to clarify to what extent, how and under what conditions role conflict is positively related to employee creativity. Drawing on activation theory and conservation of resources theory, we hypothesized an inverted U-shaped relationship between role conflict and creativity in which the relationship is stronger and positive at intermediate levels of role conflict. Additionally, we predicted that this curvilinear path would be mediated by cognitive adjustment at work and moderated by mindfulness. To test our hypotheses, we conducted two independent studies—a cross-sectional study with 123 employees from an Italian firm and a time-lagged research with 320 employees from various UK firms. Consistent with our predictions, polynomial regression analysis results provided evidence for an inverted U-shaped relationship between role conflict and creativity and for the mediating role of cognitive adjustment at work. Moreover, when mindfulness was high (versus low), intermediate levels of role conflict were associated with increased cognitive adjustment at work and creativity. Our findings enhance current understanding of the conditions under which different levels of role conflict boost or impair creativity at work and offer new insights into how employee can maintain an optimal level of creativity despite conflicting role demands. This is the first study to document a non-linear and indirect relationship between role conflict and employee creativity, as well as to identify mindfulness as a boundary condition shaping the creativity-enhancing effects of role conflict.

Rapid Prototyping of Variable Angle-Tow Composites

The recent development of new manufacturing techniques of composite structures, e.g., additive manufacturing (AM) techniques, allows for going beyond the classical design rules, thus leading the designer to find innovative and more efficient solutions like the variable angle-tow (VAT) composites. VAT composites allow taking advantage from the benefits related to the curvilinear fibre path in the most effective way, though their utilisation unavoidably implies an increased complexity of the design process. In fact, VAT composites are characterised by a large number of design variables involved at different scales. Accordingly, a dedicated multi-scale optimisation approach able to integrate both mechanical and technological requirements (to ensure the manufacturability of the solution) must be developed. In this work, the multi-scale two-level (MS2L) optimisation strategy for VAT laminates is used, for the first time, to design a VAT laminate by taking into account the manufacturing requirements related to the fused filament fabrication (FFF) and continuous filament fabrication (CFF) processes. To show the effectiveness of the MS2L strategy in terms of manufacturability of the optimised solutions, a prototype of the VAT plate is realised by developing an ad hoc CAD model interfaced with the CFF machine. The realised prototype matches very well the optimum fibre path resulting from the MS2L strategy and the importance of including technological constraints within the design process is highlighted.

Effects of embedded perforation geometry on the free vibration of tow-steered variable stiffness composite laminated panels

The free vibration characteristics of the variable stiffness composite laminated plates containing embedded cutout of desired shapes is investigated. The circular, elliptical and quadrilateral perforation geometries are taken into account. In order to provide a strongly flexible calculation tool, an isogeometric analysis formulation based on the non-uniform rational B-splines (NURBS) along with the Nitsche technique is developed based on the first order shear deformation plate theory. The effects of change in the mechanical properties of tow steered laminates throughout the geometry due to fibers following prescribed curvilinear paths are taken into account in the integration procedures. The accuracy and reliability of the calculations is shown through some representative comparisons. The effects of change in the cutout geometry, location and orientation in conjunction with the curvilinear fiber placement are studied.

Computational assessment of nonlinear fracture resistance parameters for cracked fuselage panel under biaxial loading

This study focused on the numerical analysis of a cracked fuselage panel of an airplane on the basis of new nonlinear fracture mechanics parameters and concepts. Through finite element analysis (FEA) of the fragment of the fuselage panel with central crack, the governing parameters of the elastic–plastic crack-tip stress field (i.e., In-integral and the plastic stress intensity factor) were determined as a function of the crack length and biaxial loading conditions. Elastic–plastic FEAs of the cracked fuselage panel were performed by considering the accumulated damages in the fracture process zone at the crack tip via special cohesive elements. The curvilinear crack path in the fuselage panel under biaxial loading was predicted on the basis of strain energy density and cohesive zone concepts.

Aeroelastic panel flutter optimization of tow-steered variable stiffness composite laminated plates using isogeometric analysis

The optimization of linear flutter behavior of the thin plates made from tow-steered fiber-reinforced laminates is investigated. In the tow-steered variable stiffness composite laminates, the fiber reinforcements are assumed to follow prescribed curvilinear path orientations according to a linear function of geometry longitude. The effect of location-dependent fiber reinforcements is taken into account in the integration procedures. A stream is considered to travel over the panel area in different heading directions. The flutter response of the laminated panel is then improved by adjusting the fiber placement properties through applying a genetic algorithm optimization procedure. The isogeometric analysis method based on the cubic nonuniform rational B-splines is developed. The accuracy and reliability of the optimization process is shown through some representative comparisons. The effect of changes in the flow direction, panel edge constraints, and layup characteristics are inspected.

A finite element-based adaptive energy response function method for 2D curvilinear progressive fracture

An adaptive arbitrary-order curvilinear progressive 2D crack growth algorithm is presented. The method is automated such that the full crack path from inception to failure is computed with multiple finite element analyses. During each simulation step, a hypercomplex finite element method (ZFEM) program computes arbitrary order derivatives of strain energy with respect to self-similar and perpendicular crack extensions. These derivatives are used to construct a family of surrogate models as trial functions, each of which is a Taylor series function of strain energy versus crack growth direction. An adaptive algorithm automatically selects the trial function that most accurately models the existing crack path to extrapolate a forward progressing curvilinear crack path. The length of each crack growth increment is limited to maintain the advancing path and its consequential strain energy increase within desired tolerances. Numerical examples up to sixth order are presented and compared against experiments. The high-order simulations complete the crack growth analysis with fewer, longer progressive fracture steps than traditional first-order simulations of similar accuracy.

Auditory Display for Telerobotic Transnasal Surgery Using a Continuum Robot

Tubular continuum robots can follow complex curvilinear paths to reach restricted areas within the body. Using teleoperation, these robots can help minimize incisions and reduce trauma. However, drawbacks include the lack of haptic feedback and a limited view of the situs, often due to camera occlusion. This work presents novel auditory display to enhance interaction with such continuum robots to increase accuracy and path-following efficiency and reduce cognitive workload. We recreate a typical use case with a test environment that simulates a transnasal intervention through the sphenoidal sinus including a simulated continuum robot. Distance information is mapped to changes in a real-time audio synthesizer using sung voice to provide navigation cues. User studies with novice participants and clinicians were performed to evaluate the effects of auditory display on accuracy, task time, path following efficiency, subjective workload, and usability. When using auditory display, participants exhibit significant increase in accuracy, efficiency, and task time compared to visual-only display. Auditory display reduced subjective workload and raised usefulness and satisfaction ratings. The addition of auditory display for augmenting interaction with a teleoperated continuum robot has shown to benefit performance as well as usability. The method could benefit other scenarios in navigated surgery to increase accuracy and reduce workload.

Collaborative design of fiber path and shape for complex composite shells based on isogeometric analysis

Composite shells with complex geometry are widely used in aerospace structures. Due to the complexity of geometry and curvilinear fiber path, the analysis and optimization based on finite element analysis (FEA) for complex variable-stiffness (VS) shells is extremely time-consuming. By comparing with FEA, isogeometric analysis (IGA) exhibits higher prediction efficiency of buckling load. In this work, the formula of geometric stiffness matrix for complex VS shells is derived for the first time based on degenerated shell method using IGA, which is the basis of performing linear buckling analysis. Then, a new variable curvature quasi-linear function (VCQLF) to describe curvilinear fiber path is proposed, which can further expand the design space of VS shells. After that, two frameworks for shape optimization of complex shells are put forward and then compared, and it is found that the one based on LOFT function can provide representative control variables of shape and effectively reduces the number of design variables for complex shells. Finally, a novel collaborative optimization framework of fiber path and shell shape using IGA is established. By comparison of traditional methods, it is demonstrated that the proposed framework can greatly improve the efficiency of optimization and fully explore the buckling load of complex VS shells.

A general framework for solving inverse dynamics problems in multi-axis motion control

An inverse dynamics compensation (IDC) scheme for the execution of curvilinear paths by multi-axis motion controllers is proposed. For a path specified by a parametric curve r(ξ), the IDC scheme computes a real-time path correction Δr(ξ) that (theoretically) eliminates path deviations incurred by the inertia and damping of the machine axes. To exploit the linear time-invariant nature of the dynamic equations, the correction term is computed as a function of elapsed time t, and the corresponding curve parameter values ξ are only determined as the final step of the IDC scheme, through a real-time interpolator algorithm. It is shown that, in general, the correction term for P, PI, and PID controllers consists of derivative, natural, and integral terms (the integrand of the latter involving only the path r(ξ), and not its derivatives). The use of lead segments to minimize transient effects associated with the initial conditions is also discussed, and the performance of the method is illustrated by simulation results. The IDC scheme is expressed in terms of a linear differential operator formalism to provide a clear, general, and systematic development, amenable to further adaptations and extensions.