Nominal Design Research Articles

Influence of layer thickness variations on the structural behaviour of optimised fibre reinforced plastic parts

Fibre reinforced plastics (FRP) are considered as a modern high-tech material. The enormous lightweight potential, especially of carbon fibre reinforced plastics, accelerates its spreading in many industrial applications. However, as good as the lightweight potential of FRP is, as difficult is the optimal use in products because of its anisotropic material properties. Recently, methods considering the anisotropic material behavior during the product development process have been developed. These result in optimized nominal laminate layouts with defined laminate parameters like fibre orientation, ply thickness and ply stack-up order. Yet, during the manufacturing process, variations of these parameters, compared to the nominal design, occur. The variations result in asymmetric laminates, which causes couplings in the stiffness matrix and consequently undesired deformations. The effects of varying laminate design parameters have so far mainly been investigated with focus on manufacturing activities. However, to support the design engineer in considering the influence of varying laminate parameters on product behavior, this paper studies the effects on the structural behavior of optimized FRP-parts. The main novelty and contribution of the paper can be found in providing a new approach for the consideration of uncertainties in the ply thickness on FRP parts with optimized fibre layout. For this purpose, sensitivity analyses are performed with the aim of investigating the importance of the parameters on the structural behavior. With this knowledge, the product developer is able to distinguish between critical and non-critical laminate parameters and consider their variations in the product development process as early as possible.

Uncertainty analysis of sensitivity of MEMS microphone based on artificial neural network

Due to the uncertainties from manufacturing processes and material properties, MEMS (micro-electro-mechanical system) microphone may exhibit significant variations in their performance compared to the nominal design. The published analytical methods have obvious shortcoming, which cannot meet the needs of both accuracy and efficiency. In order to improve efficiency, the MC (Monte Carlo) simulation based on ANN (artificial neural network) is presented to analyze the uncertainty of sensitivity of polysilicon circular clamped diaphragm microphone. Using the PDS (probabilistic design system) of Ansys software and MC simulation to predict the qualified rate of microphone, the simulated results are 91.2% and 91.4% respectively. The qualified rate of manufactured microphones is 91.5%. In addition, the time-consuming of these two simulations are 10 minutes and about 3000 minutes. This paper also analyzes the change of sensitivity probability densities with the varieties of nominal parameters of diaphragm. The results show that the presented MC simulation with accuracy and high efficiency is an alternative to the traditional methods.

The role of overstrength on the seismic performance of asymmetric‐plan structures

SummaryUneven distribution of seismic demand in asymmetric‐plan structures is a critical concern in earthquake‐resistant design. Contemporary seismic design strategies that are based on linear elastic response, single load reduction factor, and uniform ductility demand throughout an asymmetric system generally lead to unsatisfactory performance in terms of realized ductilities and nonuniform damage distribution due to strong torsional coupling associated with asymmetric‐plan systems. In many cases, actual nonlinear behavior of the structure displays significant deviation from what is estimated by a linear elastic, force‐based seismic design approach. This study investigates the prediction of seismic demand distribution among structural members of a single‐story, torsionally stiff asymmetric‐plan system. The focus is on the effect of inherent unbalanced overstrength, resulting from current force‐based design practices, on the seismic response of code‐designed single‐story asymmetric structures. The results obtained are utilized to compile unsymmetrical response spectra and uniform ductility spectra, which are proposed as assessment and preliminary design tools for estimating the seismic performance of multistory asymmetric structures. A simple design strategy is further suggested for improving the inelastic torsional performance of asymmetric systems. Providing additional strength to stiff edge members over their nominal design strength demands leads to a more balanced ductility distribution. Finally, seismic responses of several asymmetric case study structures designed with the aid of the proposed strategy are assessed for validating their improved performance.

Rail wear inspection based on computer-aided design model and point cloud data

Railway transportation demands more efficient and accurate rail wear inspection systems to ensure the train operation safety. To obtain continuous three-dimensional data, a structured light rail wear inspection system is developed in this article, and the data processing method for aligning the point cloud from structured light scanning to the nominal computer-aided design model of the rail is investigated. For further data registration, the point cloud of the computer-aided design model is generated and the normal vectors of these points are calculated. In the coarse registration, conformal geometric algebra is applied to align the segmented point clouds by intuitive geometric calculations to those from the computer-aided design model. In the fine registration, the accurate alignment of the point clouds is implemented by the iterative closest point algorithm. The vertical and lateral wear amounts are obtained on the cross section by slicing the aligned three-dimensional point clouds data. Finally, the proposed system and method are validated by comparing the vertical wear amounts with the two-dimensional laser scanning and contact measurement results.

Sensitivity Analysis of a Two‐Lens System for Positioning Feedback

AbstractPrecise alignment of optical components is crucial for the assembly of optical system. Misaligned components (due to positioning tolerances) lead to a distorted wavefront that deviates from a desired wavefront given by an initial nominal design. Inferring the current poses of optical components solely from detector measurements is a difficult but necessary task in order to calculate corrections for feedback control without using external measurement devices. In this paper, we aim at deducing lens poses of a two‐lens system solely from wavefront measurements. The wavefront can be decomposed into a finite sequence of polynomials which are weighted by coefficients. Since pose deviations directly lead to deviations in the wavefront (and therefore in the wavefront coefficients), a sensitivity matrix can be established. The choice of lens poses and wavefront coefficients determines the sensitivity matrix which is often ill‐conditioned and may potentially suffer from rank loss. We conduct a sensitivity analysis and show how the sensitivity matrix can be utilized to generate a linear estimate of the optical component poses. This estimate can then be used to close the feedback loop. Validation is conducted by simulating an optical system consisting of a laser, two bi‐convex lenses, and a wavefront sensor.

Adaptive state‐feedback control with sensor failure compensation for asymptotic output tracking

SummaryThis paper addresses a new adaptive output tracking problem in the presence of uncertain plant dynamics and uncertain sensor failures. A new unified nominal state‐feedback control law is developed to deal with various sensor failures, which is directly constructed by state sensor outputs. Such a new state‐feedback compensation control law is able to ensure the desired plant‐model matching properties under different failure patterns. Based on the nominal compensation control design, a new adaptive compensation control scheme is proposed, which guarantees closed‐loop signal boundedness and asymptotic output tracking. The new adaptive compensation scheme not only expands the sensor failures types that the system could tolerate but also avoids some signal processing procedures that the traditional fault‐tolerant control techniques are forced to encounter. A complete stability analysis and a representative simulation study are conducted to evaluate the effectiveness of the proposed adaptive compensation control scheme.

Metrology Data-Based Simulation of Freeform Optics

This paper describes the approach to use measurement data to enhance the simulation model for designing freeform optics. Design for manufacturing of freeform optics is still challenging, since the classical tolerancing procedures cannot be applied. In the case of spherical optics manufacturing, tolerances are more or less isotropic, and this relationship is lost in case of freeform surfaces. Hence, an accurate performance prediction of the manufactured optics cannot be made. To make the modeling approach as accurate as possible, integration of measured surface data of fabricated freeform optics in the modeling environment is proposed. This approach enables performance prediction of the real manufactured freeform surfaces as well as optimization of the manufacturing process. In our case study this approach is used on the design of an Alvarez-optics manufactured using a microinjection molding (µIM) process. The parameters of the µIM process are optimized on the basis of simulation analysis resulting in optics, with a performance very close to the nominal design. Measurement of the freeform surfaces is conducted using a tactile surface measurement tool.

Variable Loop Gain Using Excessive Regeneration Detection for a Delayed Wide-Area Control System

Excessive time delay in the implementation of a wide-area damping controller may lead to poor time-domain response or instability of an otherwise stable closed loop system. Careful monitoring of the controller output reveals the relative phase margin as it tends toward a vanishingly small value. Design and analysis of the excessive regeneration detector for system stability migration is presented. Details of degradation are followed by the description of a variable loop gain controller to ensure stability in the presence of significant delay, with nominal controller design developed using loop shaping theory. Linear and nonlinear stability of the system is assessed with the variable loop gain controller in place. Simulations of multiple disturbance environments and time delay conditions validate the developed theory using a detailed nonlinear model of the western North American power system. Finally, a GPS spoofing algorithm is employed to demonstrate the efficacy of the approach to a malicious phasor measurement unit attack.

Surrogate Modeling of Manufacturing Variation Effects on Unsteady Interactions in a Transonic Turbine

This effort develops a surrogate modeling approach for predicting the effects of manufacturing variations on performance and unsteady loading of a transonic turbine. Computational fluid dynamics (CFD) results from a set of 105 as-manufactured turbine blade geometries are used to train and validate the surrogate models. Blade geometry variation is characterized with point clouds gathered from a structured light, optical measurement system and as-measured CFD grids are generated through mesh morphing of the nominal design grid data. Principal component analysis (PCA) of the measured airfoil geometry variations is used to create a reduced basis of independent surrogate model parameters. It is shown that the surrogate model typically captures between 60% and 80% of the CFD predicted variance. Three new approaches are introduced to improve surrogate effectiveness. First, a zonal PCA approach is defined which investigates surrogate accuracy when limiting analysis to key regions of the airfoil. Second, a training point reduction strategy is proposed that is based on the k–d tree nearest neighbor search algorithm and reduces the required training points up to 38% while only having a small impact on accuracy. Finally, an alternate reduction approach uses k-means clustering to effectively select training points and reduces the required training points up to 66% with a small impact on accuracy.

Maximum likelihood geoacoustic inversion from surface generated noise

Noise generated at the surface from wind and breaking waves is incident upon the seabed at a wide range of angles and frequencies. The reflectivity of the seabed thus plays an important role in determining the vertical directionality of the noise field. It is therefore not surprising that from an information theory perspective, the noise field encodes a significant amount of information about the geoacoustic properties of the seabed that govern reflectivity, such as layering structure, sound speed, density, and attenuation. Using a physics-based ambient noise model, the Cramer-Rao lower bound (CRLB) can be computed, which specifies the lowest possible variance that an unbiased estimator can have. Existing estimators have primarily involved vertically beamforming the noise field to recover the vertical noise directionality and bottom loss, which is then processed to estimate geoacoustic seabed properties. The method described here takes a different approach by estimating the properties directly from the measured data (i.e., without beamforming). This presentation will show that maximizing the proposed likelihood function can perform better than beamforming-based techniques, and approaches the CRLB. Further, it remains unbiased in low signal-to-noise ratio conditions, is tolerant to array tilt, and can operate beyond the nominal array design frequency.Noise generated at the surface from wind and breaking waves is incident upon the seabed at a wide range of angles and frequencies. The reflectivity of the seabed thus plays an important role in determining the vertical directionality of the noise field. It is therefore not surprising that from an information theory perspective, the noise field encodes a significant amount of information about the geoacoustic properties of the seabed that govern reflectivity, such as layering structure, sound speed, density, and attenuation. Using a physics-based ambient noise model, the Cramer-Rao lower bound (CRLB) can be computed, which specifies the lowest possible variance that an unbiased estimator can have. Existing estimators have primarily involved vertically beamforming the noise field to recover the vertical noise directionality and bottom loss, which is then processed to estimate geoacoustic seabed properties. The method described here takes a different approach by estimating the properties directly from the me...

Probability of Failure of Sylgard-Mounted Optical Lenses in Head-Up Display During Thermal Cycle Testing

Lenses made from optical glass do not have a single characteristic strength. The strength of any optical glass is highly dependent on the area under stress and its surface finish. The nominal design strength of manufactured glass is typically in the 6.9–70 MPa range. This study presents an analysis of measured strain data and an approach to quantify the failure probability of optical lenses that are used in head-up display systems for aircraft applications when these lenses are subjected to accelerated thermal cycling. The thermal cycling produces thermal stress within the elastomerically mounted optical lens of the head-up display. We used a combination of experimental methods and finite element modeling to determine the thermal strain in the optical lens. The thermal strain values that were obtained using these methods were validated and were found to be in a cumulative distribution. This cumulative strain provides a quantitative estimate of the effects of thermal stress in the optical lens. We then determined the failure probability using Weibull parameters.

Compositional inhomogeneities in type-I and type-II superlattices for GaAsSbN-based solar cells: Effect of thermal annealing

GaAsSbN alloys is recognized as an effective candidate to incorporate in multijunction solar cell applications due to its advantages of being grown lattice-matched to GaAs and its capability to achieve bandgap around 1.0 eV. Recently, the use of superlattice (SL) structures that permit type–II (GaAsSb/GaAsN) and type-I (GaAsSbN/GaAs) alignments showed a strongly heightened luminescence and a significant EQE compared to their thicker quaternary bulk counterparts. In this work, the correlation between the compositional distribution and its optical properties in both SL structures before and after RTA treatment is analyzed. Firstly, while N is confined following the nominal design, Sb presents a strong segregation to the upper layers achieving similar compositional profiles along the growth direction even after the RTA. However, the SL type-II approach presents a higher interface quality and a much lower trend to cluster formation than SL type-I. Secondly, RTA gives place to an improvement of the interface roughness, together to a decrease of the area associated to clusters in both structures. The blueshift and the improvement of the PL intensity induced by annealing in both samples is more correlated to the decomposition of nitrogen pairs to isolated substitutional nitrogen than to the dissolution of Sb inhomogeneities. A different distribution of new substitutional N atoms around Sb clusters could explain the differences in the PL improvement of both SLs during the annealing. SL type-II approach is the best design to minimize cluster formation and to obtain more abrupt interfaces and mainly describe the optical enhancement compared to SL type-I structures.

Sequential approximate optimisation for statistical analysis and yield optimisation of circularly polarised antennas

The study addresses a problem of low-cost statistical analysis and yield optimisation of circularly polarised (CP) microstrip antennas. For the sake of computational efficiency, auxiliary response surface approximation models are utilised to establish a fast representation of the expensive full-wave electromagnetic (EM)-simulation antenna model. The surrogate permits feasible Monte Carlo (MC) analysis using a large number of random samples (necessary to maintain low variance of yield estimation). The sequential approximate optimisation is then utilised to carry out a robust design, where at each iteration, a new surrogate model is established in a relocated domain. The design objectives are set for the in-band axial ratio and impedance bandwidth. For illustration purposes, a planar CP antenna with two feed line stubs is considered. Accurate yield estimation is obtained at the cost of only a hundred of EM antenna simulations despite a large number of independent geometry parameters. Yield improvement from the initial value of 63.5% at the nominal design to 99% is achieved at the cost of 300 EM analyses. Comparison with conventional MC analysis is also provided demonstrating the accuracy of the presented approach.

Thermodynamic optimisation of a high-electrical efficiency integrated internal combustion engine – Organic Rankine cycle combined heat and power system

Organic Rankine cycle (ORC) engines are suitable for heat recovery from internal combustion engines (ICE) for the purpose of secondary power generation in combined heat and power (CHP) systems. However, trade-offs must be considered between ICE and ORC engine performance in such integrated solutions. The ICE design and operational characteristics influence its own performance, along with the exhaust-gas conditions available as heat source to the ORC engine, impacting ORC design and performance, while the heat-recovery heat exchanger (ORC evaporator) will affect the ICE operation. In this paper, an integrated ICE-ORC CHP whole-system optimisation framework is presented. This differs from other efforts in that we develop and apply a fully-integrated ICE-ORC CHP optimisation framework, considering the design and operation of both the ICE and ORC engines simultaneously within the combined system, to optimise the overall system performance. A dynamic ICE model is developed and validated, along with a steady-state model of subcritical recuperative ORC engines. Both naturally aspirated and turbocharged ICEs are considered, of two different sizes/capacities. Nine substances (covering low-GWP refrigerants and hydrocarbons) are investigated as potential ORC working fluids. The integrated ICE-ORC CHP system is optimised for either maximum total power output, or minimum fuel consumption. Results highlight that by optimising the complete integrated ICE-ORC CHP system simultaneously, the total power output increases by up to 30% in comparison to a nominal system design. In the integrated CHP system, the ICE power output is slightly lower than that obtained for optimal standalone ICE application, as the exhaust-gas temperature increases to promote the bottoming ORC engine performance, whose power increases by 7%. The ORC power output achieved accounts for up to 15% of the total power generated by the integrated system, increasing the system efficiency by up to 11%. When only power optimisation is performed, the specific fuel consumption increases, highlighting that high-power output comes at the cost of higher fuel consumption. In contrast, when specific fuel consumption is used as the objective function (minimised), fuel consumption drops by up to 17%, thereby significantly reducing the operating fuel costs. This study proves that by taking a holistic approach to whole-system ICE-ORC CHP design and operation optimisation, more power can be generated efficiently, with a lower fuel consumption. The findings are relevant to ICE and ORC manufacturers, integrators and installers, since it informs component design, system integration and operation decisions.

Impact of demand controlled ventilation on system performance and energy use

Demand-controlled-ventilation (DCV) refers to a ventilation system with controlled air flow rate based on indoor air quality. DCV operates at reduced air flow rates during most of the operation time. Therefore, less energy is required for fan operation, compared to a constant-air-volume (CAV) ventilation system.Typically, DCV has a two-layer control with variable-air-volume (VAV) valves, and a fan speed control to maintain a constant-static-pressure in the duct system based on a pressure set point.However, this nominal design based fan pressure setpoint is higher than required when all VAV-valves are closed to a certain extent. Therefore, advanced pressure-reset (PR) control - resetting the pressure set point - potentially reduces fan energy use even further.This paper assesses the impact of fan control on both fan energy use and ventilation performance in DCV system of a densely occupied office. Results of a simulation model and realistic measurement setup are compared. The PR control, using air flow rate and VAV-valve position measurements as feedback, causes significantly reduction on fan energy use. These reductions compared to conventional DCV and CAV respectively, are approximately 10% and 72% in case of high occupancy and 50% and 93% in case of low occupancy. Largely, DCV with PR control is strongly considered, especially when occupancy is often expected to deviate significantly from the nominal conditions. Moreover, both simulations and measurements show that there is a clear trade-off between air flow rate deficit and fan energy use, when the fan energy use is lower, the air flow rate deficit is higher and vice versa. Furthermore, the results show that VAV-valve accuracy, characteristics and its lower operational limit hamper the ventilation system in achieving the predicted performance as in the simulation.

Design of asymmetrical directional couplers on ridge and strip SOI technology with high-dimensional variation tolerance.

The supermode analysis of asymmetrical directional couplers (ADC) based on SOI technology for strip and ridge structures at 1550nm is herein reported, targeting to reduce ADC device fabrication requirements. The reported analysis based on supermodes permits us to assess the sensitivity of the ADC coupling efficiency by calculating the index difference between even and odd supermodes. Optimum designs have been found for 100 and 400nm gaps, respectively, capable of converting and (de) multiplexing both TE0 and TE1 modes taking into account the width, gap, height, and slab thickness variations produced with respect to the nominal design.

State of the art review on mix design and mechanical properties of warm mix asphalt

Warm mix asphalt (WMA) is a high-speed emerging technology of producing asphalt mixture at lower temperature with equivalent performance of hot mix asphalt (HMA). It offers benefits such as energy savings, compaction aid for stiffer mixes, reduces emission, and reduces asphalt binder aging during production. This paper is an overview of mix design concept, mix design properties and mechanical properties (moisture-induced damage, rutting resistance and fatigue life) of WMA and same was compared with the properties of control HMA mixtures. Review indicates that mix design concept of WMA is similar to that of control HMA and possesses better mix design properties. Regarding mechanical properties, WMA mixtures were found more prone to moisture-induced damage, rutting and fatigue than control HMA mixtures due to lower production temperature but similar or better resistance were noticed with the use of modified and higher grade binders, addition of anti-stripping agents (ASA) and hydrated lime (HL), use of open graded mix and inclusion of recycled asphalt pavement (RAP). Further, the effect of nominal maximum aggregate size (NMAS) and design gyration (Ndesign) on mix design, NMAS and aggregate type and its water absorption on moisture-induced damage, NMAS, wheel load, test temperature, air voids, and binder grade on rutting, and NMAS, air voids, and stress or strain levels on fatigue properties of asphalt mixtures were analysed. Results indicated that NMAS had the significant effect on moisture-induced damage, rutting resistance and fatigue life of WMA mixtures. WMA mixtures made with aggregates of higher water absorption values were more prone to moisture-induced damage and even fail to meet minimum (tensile strength ratio) TSR requirements. Results also indicated that WMA mixtures made with modified and higher grade binder grade were high rut resistant. WMA mixtures tested at high stress or strain levels shows higher fatigue damage compared to WMA mixtures tested at lower stress or strain levels.

Design of optical systems that maximize as-built performance using tolerance/compensator-informed optimization.

We describe an approach that enables the design of optical systems for optimal performance when built, i.e., when user-selected tolerances and compensators are taken into account. The approach does not require significant raytracing or computing time beyond what is used to optimize the nominal design. The approach uses nodal aberration theory to describe the effects of decentered optics; double Zernike polynomials to describe and quantify system performance; and an analytic approach to determining the necessary compensation and residual wavefront error due to a tolerance. We design a triplet using this approach and compare its Monte-Carlo-modeled as-built performance to that of a conventionally-optimized design which optimizes only nominal performance. We also describe several extensions to the theory.

Study on Effects of Heat Loss and Channel Deformation on Thermal-Hydraulic Performance of Semicircular Straight Channel Printed Circuit Heat Exchangers

Effective and robust high-temperature heat transport systems are essential for the successful deployment of advanced high temperature reactors. The printed circuit heat exchanger (PCHE) is a strong potential candidate for the intermediate or secondary loop of high temperature gas-cooled reactors (HTGRs) due to their high power density and compactness. For high-temperature PCHE applications, the heat loss, which is difficult to be insulated completely, could lead to the degradation of heat exchanger performance. This paper describes an analytical methodology to evaluate the thermal-hydraulic performance of PCHEs from experimental data, accounting for extraneous heat losses. Experimental heat exchanger effectiveness results, evaluated without accounting for heat loss, exhibited significant data scatter while the data were in good agreement with the ε-NTU method once the heat loss was accounted for. The deformation of PCHEs would occur during the diffusion-bonding fabrication process or high temperature operations due to the thermal deformation. Computational assessment of the PCHE performance test data conducted at the Ohio State University showed that the deformation of flow channels caused increase of pressure loss of the heat exchanger. The computational fluid dynamics (CFD) simulation results based on the nominal design parameters underestimated the pressure loss of the heat exchanger compared to the experimental data. Image analysis for the flow channel inlet and outlet was conducted to examine the effect of channel deformation on the heat exchanger performance. The CFD analysis based on the equivalent channel diameter obtained from the image analysis resulted in a better prediction of PCHE pressure loss.

Thermal Aware Test Scheduling for NTV Circuit

Although the near threshold voltage (NTV) design has achieved energy efficiency, certain challenges remain regarding its application. In this paper, we describe the analysis of thermally induced reliability concern in test process. In an NTV environment, the thermal dependency of a circuit delay is changed, and a difference in thermal constraints from that in a nominal voltage design exists. In addition, we propose a new test scheduling method for NTV circuits that alleviates the thermal constraints in system-on-chip test processes. Our simulation results show that the test time could be reduced while minimizing the reliability loss.