Tolerance Research Articles

Rapid multi-criterial design of microwave components with robustness analysis by means of knowledge-based surrogates

Manufacturing tolerances and uncertainties concerning material parameters, e.g., operating conditions or substrate permittivity are detrimental to characteristics of microwave components. The knowledge of relations between acceptable parameter deviations (not leading to violation of design specifications) and the nominal performance (not considering uncertainties), and is therefore indispensable. This paper proposes a multi-objective optimization technique of microwave components with tolerance analysis. The goal is to identify a set of trade-off designs: nominal performance versus robustness (quantified by the maximum input tolerance values that allow for achieving 100-percent fabrication yield). Our approach exploits knowledge-driven regression predictors rendered using characteristic points (features) of the component’s response for a rapid evaluation of statistical performance figures, along with trust-region algorithm to enable low execution cost as well as convergence. The proposed methodology is verified with the use of three microstrip circuits, a broadband filter, and two branch-line couplers (a single- and a dual-band one). It is demonstrated that a Pareto set w.r.t. nominal performance and robustness objectives can be produced using only 40 to 60 EM simulations of the respective structure (per design). Reliability of the proposed algorithm is corroborated with the use of EM-based Monte Carlo simulation.

Uncertainty-oriented multi-scale topology optimization of coupled thermo-mechanical continuum structures

Multi-scale and multi-physical field topology optimization (TO) design has attracted large of attention, especially in aerospace and mechanical engineering, for the complex loadings and increasing performance requirements. Moreover, the unavoidable uncertainties, such as environment change, load variation, manufacturing tolerance, and elastic modulus fluctuation, exist in both macro- and micro-scale under coupled thermo-mechanical environment, which poses a significant danger for the safety of topological design of multi-scale structure in practical engineering. Therefore, a 2D multi-scale reliability-based topology optimization (MSRBTO) model is constructed to account for the uncertainty behavior of multi-physical TO problems, in which mechanical and thermal loadings are considered simultaneously. In addition, the solid isotropic material with penalization method is adopted at both macro- and micro-scales. Sensitivities of the compliance and temperature constraints with respect to the macro design variables, micro design variables, and random variables are derived simultaneously. Then, a single-loop method is introduced to address the MSRBTO problem to guarantee computational efficiency. Several numerical examples are solved by the developed MSRBTO method and traditional mono-scale RBTO method. The results show that the optimized results of the MSRBTO method show better performance than the mono-scale RBTO method, and the validity and effectiveness of the proposed method are validated.

Effect of basket/rail gap on temperature prediction in the TN-32 cask under storage and drying conditions

This paper investigates the effect of the variation in the gap width between the basket and rails on predicted temperatures in the TN-32 dry storage cask. Two-dimensional (2D) cross-section models of the TN-32 containing thirty-two spent nuclear fuel assemblies generating 30.5 kW of thermal energy are constructed. Storage and vacuum drying pressures, a range of basket/rail gap widths, and shifting of the basket from the cask center, are considered. The simulations include surface-to-surface radiation and gas conduction (including rarefaction), but do not consider natural convection due to the 2D assumption. Results show that the peak cladding temperature, TPC, increases as the gap width increases and as the pressure decreases to vacuum drying (rarefied) levels. As a result, analysis using the nominal unloaded design gap width may overpredict TPC by up to 40 °C under storage conditions and up to 75 °C under vacuum drying conditions. The sensitivity of TPC on pressure is found to decrease as the gap width decreases, and as the basket shifts from the cask center. This paper demonstrates that reducing the uncertainty in the basket/rail gap width by, for example, calculating predictable thermal expansion, and/or statistically quantifying unpredictable manufacturing tolerances and basket shifting, may significantly reduce the uncertainty of peak cladding temperature prediction.

Single-polarization low loss Terahertz Hollow-Core Anti-Resonant Fiber with high Polarization Loss Ratio

We proposed a single-polarization low loss Terahertz (THz) Hollow-Core Anti-Resonant Fiber (HC-ARF) with 4-tube nested Semi-Elliptical Cladding Tubes (SECTs). Through adopting different wall-thicknesses of SECTs along two orthogonal directions, single-polarization and low loss performance can be simultaneously achieved by means of mode coupling between X-polarized Fundamental-Mode (FM) and dielectric mode of SECTs. By optimizing structural parameters, Polarization Loss Ratio (PLR) of X-polarized FM to Y-polarized FM reaches up to 156 at the frequency of 0.5 THz. As a result, only single Y-polarized FM can effectively propagate through the fiber with a low loss of 0.98 dB/m at 0.5 THz. Meanwhile, single Y-polarized region with PLR ≥ 20 covers the frequency range from 0.484 THz to 0.517 THz, i.e. frequency bandwidth of 33 GHz, thus a wide single polarization bandwidth can be obtained. To the best of our knowledge, the proposed THz HC-ARF has the highest PLR, low-loss and relatively wide bandwidth among currently reported THz HC-ARFs. In addition, this THz HC-ARF has been confirmed to have good manufacture tolerance and excellent SP frequency tunability.

Short dual-core GaAs photonic crystal fiber splitter with a broad bandwidth and ultrahigh extinction ratio.

Microstructured polarization beam splitters (PBSs) have attracted much interest in recent years. Here, a ring double-core photonic crystal fiber (PCB) PSB (PCB-PSB) with an ultrashort, broadband, and high extinction ratio (ER) was designed. The effects of the structural parameters on the properties were analyzed by the finite element method, which revealed that the optimal length of the PSB was 19.08877µm and the ER was -324.257d B. The operating bandwidth for an ER of less than -20d B is 440nm, and the wavelength range spans the full E+S+C+L+U band between 1,320 and 1,760nm. The fault and manufacturing tolerance of the PBS was demonstrated for structural errors of ±1%. Moreover, the influence of temperature on the performance of the PBS was determined and discussed. Our results show that a PBS has excellent potential in optical fiber sensing and optical fiber communications.

Uncertainty Quantification of Compressor Map Using the Monte Carlo Approach Accelerated by an Adjoint-Based Nonlinear Method

Precise and inexpensive uncertainty quantification (UQ) is crucial for robust optimization of compressor blades and to control manufacturing tolerances. This study looks into the suitability of MC−adj−nonlinear, a nonlinear adjoint-based approach, to precisely and rapidly assess the performance discrepancies of a transonic compressor blade section, arising from geometric alterations, and building upon previous research. In order to assess the practicality and illustrate the benefits of the adjoint-based nonlinear approach, its proficiency and precision are gauged against two other methodologies, the adjoint-based linear approach (MC−adj−linear) and the high-fidelity nonlinear Computational Fluid Dynamics (MC−CFD) method. The MC−adj−nonlinear methodology exhibits impressive generalization capabilities. The MC−adj−nonlinear method offers a great balance between precision and time efficiency, since it is more precise than the MC−adj−linear method in both design and near-stall conditions, yet requires approximately a thirtieth of the time of the MC−CFD method. Finally, the MC−adj−nonlinear method was utilized to conduct fast UQ analyses of the section at four distinct speeds to quantify the performance uncertainty for the compressor map. It is found that aerodynamic performance is more sensitive to geometric deviations at high speeds than at low speeds. The impact of the geometric deviations is generally detrimental to the mean efficiency.

3D printed circular nodal plate stacks for broadband vibration isolation

This paper introduces additively manufactured plate stack isolators capable of broadband vibration isolation over multiple frequency ranges. The isolator consists of axisymmetric stepped plates stacked in series and connected using compliant hinges. The monolithic design eliminates friction, leading to deeper stop bands and a potentially larger cycle life. A Kirchhoff–Love plate model predicts the frequency response. Additively manufactured polymer plate network isolators show that multiple band gaps can be achieved by model based tuning of plate geometries. A sensitivity study shows that additive manufacturing tolerance errors affect the width and center frequency of the band gap. Finally, the experimentally validated model predicts that metal isolators manufactured with Laser Powder-Bed fusion are capable of achieving low frequency band gaps and other design metrics of commercially available vibration isolators.

Novel measurement techniques for oil consumption and spark plug temperature measurement to support engine components development in terms of wear and in situ monitoring

Large engines will continue to play a major role in the transportation sector, especially in shipping. In the energy sector, they are essential due to increasingly complex networks and operating strategies. These two sectors are set up for a renewable world through their use of large engines operated with alternative, preferably carbon-free fuels. Intensive research will remain necessary to make these engines even more climate-friendly, to further increase their lifetime and to reduce production, operating and maintenance costs. This research will be supported by the development and deployment of novel key technologies. This paper describes two of these technologies that have been developed at the Large Engines Competence Center: a temperature measurement spark plug and a system for measuring engine oil consumption. Both technologies have in common that they should help engines to run more efficiently, cleaner and with less wear. Spark plug wear impacts engine reliability and maintenance costs. Likewise, wear of the piston assembly and its tribological system is of great importance. This paper provides insight into the development of both technologies and the first instance of their simultaneous application on an engine test bench. It also reveals how spark plug temperature, oil consumption and emissions parameters correlate with each other. The results of an extensive running-in program and endurance runs are presented, and the influence of the manufacturing tolerance of the piston rings on wear and lubricating oil consumption is shown.

Robust Design of Aero Engine Structures: Using the Weighted Product Method

Total loss of quality in products or processes Reduction is the objective of robust design. Strong Design is an effective approach that aims to simultaneously decrease product costs and enhance quality while also significantly reducing development time. Strength is defined as a skill Raw material, operating conditions, process equipment, environmental conditions, and human Expected variation in factors Tolerant manufacturing process. Robust design is the design of products, devices, and manufacturing equipment so that their performance and functionality are insensitive to multiple variations, such as manufacturing and assembly tolerances, ambient use conditions, or degradation over time. Therefore, there is not strong design sensitivity – meaning that variation in the product will have minimal influence. In essence, robust design means minimizing the impact of variation on a product. One or more due to unforeseen circumstances Input variables or assumptions are rigorous although modified, their output and predictions are accurate A model is considered robust if. The alternatives being considered are related to specific aircraft features: the aerodynamic characteristic (C1), maximum takeoff weight (C2), armament (C3), and avionics (C4). The evaluation options are Ao, F-16, Su-35, and Mig-35. Based on the evaluation results, Ao obtained the top rank, while Mig-35 received the lowest rank.The value of the dataset for Robust Design of Aero Engine in Weighted product method shows that it results in Ao and top ranking

Estimation of the error field due to winding manufacturing and assembly tolerances of the DTT SC magnet system

The Divertor Tokamak Test facility (DTT) currently under construction in Frascati, Italy, is an experimental fusion reactor part of the EUROfusion roadmap to fusion energy. Due to their non-ideal winding distribution and assembly and manufacturing tolerances, real magnets are responsible for what is referred to as Error Fields (EFs). In some cases, EFs above a certain level can be unacceptable for achieving the sought performance of the fusion reaction and the implementation of dedicated in-vessel correction coils may become a necessary requirement. This work describes an approach to verify the magnet winding disposition by computing the EFs caused by the non-ideal shape of the DTT superconducting (SC) magnets. The results here presented are a contribution to the other activities aimed at deriving and verifying the requirements for the in-vessel correction coils.

Robust Design of Aero Engine Structures Using the Weighted Product Method

Total loss of quality in products or processes Reduction is the objective of robust design. Strong Design is to reduce product cost and quality to improve, the development time at the same time it is also a very powerful method of reduction. Strength is defined as a skill Raw materials, operating conditions, process equipment, environmental conditions, and human Expected variation in factors Tolerant manufacturing process. Research significance: Robust design is the design of products, devices, and manufacturing equipment so that their performance and functionality are insensitive to multiple variations, such as manufacturing and assembly tolerances, ambient use conditions, or degradation over time. Therefore, there is not strong design sensitivity – meaning that variation in the product will have minimal influence. In essence, robust design means minimizing the impact of variation on a product. One or more due to unforeseen circumstances Input variables or assumptions are rigorous although modified, their output and predictions are accurate A model is considered robust if Methology: Alternative: “The aerodynamic characteristic (C1), the maximum takeoff weight (C2), Armament (C3), Avionics (C4).” Evaluation Option: Ao, F-16, Su-35, Mig-35. Result: “from the result it is seen that Ao and is got the first rank whereas is the Mig-35 got is having the lowest rank”. Conclusion: The value of the dataset for Robust Design of Aero Engine in Weighted product method shows that it results in Ao and top ranking

Autonomous Resonant Frequency Tuner for a 6.78MHz Inductive Coupling Wireless Power Transfer System to Stably Maximize Repeater Current

Recently, the resonant inductive coupling wireless power transfer (RIC-WPT) technique is being widely used to charge small IoT devices dispersed in a wide area, e. g., an office desk and warehouse rack. In this application, the repeater is utilized to expand the chargeable area without an additional AC power source. The repeater comprises a LC resonator commonly with a high-quality factor to induce large current in the repeater coil. However, this causes the problem that the repeater performance is highly susceptible to the variation in its resonant frequency due to the manufacturing tolerance of coil inductance and resonant capacitance as well as the variation of the magnetic coupling between the transmitter and repeater coils. To solve this problem, a previous study has proposed a concept of the autonomous resonant frequency tuning circuit to stably maximize repeater coil current, although this study implemented a part of this control system as a practical circuit. This paper aims to develop a complete autonomous resonant frequency tuning circuit that implements the aforementioned concept. The proposed circuit adjusts the resonant frequencies of the transmitter and repeater by utilizing the Automatic Tuning Assist Circuits. These frequencies are optimized using the infrared wireless signal communication from the transmitter to the repeater. Along with the operating principle of the proposed circuit, this study presents detailed circuit design as well as the experimental results, which verified the stable autonomous maximization of the repeater coil current against the variation in the resonant frequency of the repeater resonator.

Repeatability in fan sound ratings: Challenges faced in a certification program

The Air Movement and Control Association International (AMCA International) maintains a certified ratings program for published air and sound performance for fans. Sound test results can come from AMCA 300 reverberant room testing but are also accepted from manufacturers’ accredited labs using other international test standards covering in-duct, enveloping surface, and sound intensity test methods. Observed repeatability between these test methods and labs will be discussed. AMCA 301 covers sound calculation methods, including extrapolation to non-tested sizes and speeds. Requirements and practical recommendations for this conversion will be discussed. Surveillance for the program comes through periodic check tests on manufacturers’ products. The check test process provides an overall view of measurement and calculation variance, as well as inevitable manufacturing tolerances and their impact on sound. Finally, the results of round robin testing conducted on centrifugal, tube axial, and vane axial fans at various accredited sound labs will be reviewed.

Expedited surrogate-based quantification of engineering tolerances using a modified polynomial regression

Statistical analysis is frequently used to determine how manufacturing tolerances or operating condition uncertainties affect system performance. Surrogate is one of the accelerating ways in engineering tolerance quantification to analyze uncertainty with an acceptable computational burden rather than costly traditional methods such as Monte Carlo simulation. Compared with more complicated surrogates such as the Gaussian process, or Radial Basis Function (RBF), the Polynomial Regression (PR) provides simpler formulations yet acceptable outcomes. However, PR with the common least-squares method needs to be more accurate and flexible for approximating nonlinear and nonconvex models. In this study, a new approach is proposed to enhance the accuracy and approximation power of PR in dealing with uncertainty quantification in engineering tolerances. For this purpose, first, by computing the differences between training sample points and a reference point (e.g., nominal design), we employ certain linear and exponential basis functions to transform an original variable design into new transformed variables. A second adjustment is made to calculate the bias between the true simulation model and the surrogate’s approximated response. To demonstrate the effectiveness of the proposed PR approach, we provide comparison results between conventional and proposed surrogates employing four practical problems with geometric fabrication tolerances such as three-bar truss design, welded beam design, and trajectory planning of two-link and three-link (two and three degrees of freedom) robot manipulator. The obtained results prove the preference of the proposed approach over conventional PR by improving the approximation accuracy of the model with significantly lower prediction errors.

Collaborative Robust Design Optimization of Blade Geometry and Manufacturing Tolerance for a Transonic Centrifugal Impeller

Abstract Turbomachinery components are inevitably subjected to various sources of manufacturing errors. The resultant variations in blade geometry eventually lead to performance degradation. This is especially true for transonic centrifugal compressor impellers where the complex interaction between the geometric variations and shock waves may amplify such degradation. However, relevant studies on uncertainty quantification or robust design optimization of centrifugal impellers are quite rare. The mechanisms of how the realistic manufacturing errors influence the impeller aerodynamic performance are not clear. In addition, most existing studies have considered a fixed level of manufacturing tolerance applied to the impeller blade surface, which neglects the combined effect of blade geometry and manufacturing tolerance on impeller performance. In this study, a collaborative robust design optimization was performed for a transonic centrifugal impeller considering realistic manufacturing errors. The realistic manufacturing error field was first modeled based on the measurements of 92 centrifugal impellers. With a combination of computational fluid dynamics simulation and the non-intrusive polynomial chaos method, the influence of manufacturing errors on impeller performance and flow field variations was quantified. To save computational costs for the uncertainty quantification, a dual dimensionality reduction method was proposed to reduce the dimensionality of uncertainties. Finally, blade angles and the manufacturing tolerance of the impeller were collaboratively optimized to enhance the impeller performance robustness against manufacturing errors. The results show that the impeller aerodynamic performance exhibited a downward trend in the presence of manufacturing errors. The flow mechanisms responsible for this trend were mainly associated with increased intensity of the shock waves near the inducer blade tip. Such shock waves were significantly alleviated by reducing impeller inlet blade angles without the loss of pressure rise capability. Consequently, the impeller performance robustness against manufacturing errors was enhanced with the standard deviation of polytropic efficiency being reduced by 35% at a lower anticipated manufacturing cost due to increased tolerance allowance.

Leakage Characteristics of Proportional Directional Valve

This paper deals with the analysis of leakage characteristics of the proportional directional valve. These characteristics distinguish a real directional valve from an ideal one. The ideal directional valve is characterized by zero leakage due to its perfect geometry. The investigated element is the three-position four-way proportional directional valve with zero spool lap and feedback from the spool position. The spool position is measured by the inductive position sensor and processed by external electronics. Internal leakage occurs due to axial and radial clearances between the spool and the sleeve. The magnitude of axial clearances that occur at throttle edges and their effect on the directional valve leakage is the subject of research. The blocked-line pressure sensitivity curve, the leakage flow curve and the center flow curve are determined by experiment. Individual characteristics are determined for different working fluid temperatures and different supply pressures. The flow through internal leaks in the center position of the valve spool is determined by analytical calculations. The flow through internal leaks is also simulated using the Ansys Fluent software. Subsequently, the geometry of the flow simulation model is modified to take into account manufacturing tolerances. From simulation results, the effect of the manufacturing tolerance magnitude on the internal leakage of the directional valve is evaluated. Finally, simulated dependencies are compared with experimentally determined characteristics.

SLENDER COLUMN STRENGTH OF INNOVATIVE CONCRETE FILLED STEEL TUBE COLUMNS WITH HIGH‐PERFORMANCE BUILDING MATERIALS

AbstractThis paper presents a comprehensive experimental and numerical study on the load‐carrying behaviour of innovative high performance materials steel‐concrete composite columns: Namely concrete‐filled steel tube columns with solid steel core (CFSTCSC) and concrete‐filled double steel tube columns (CFDST). The experimental results exemplify the basic load‐carrying behaviour. In addition to that, the application range of high‐strength materials is evaluated in relation to the slenderness. Finally, the influence of geometric imperfections on the load‐carrying behavior is investigated based on the manufacturing tolerances of such multi‐component cross‐sections.

Experimental investigation of the effect of sectional airfoil profile deviation on propeller noise

The geometry of the sectional airfoil has a determinative impact on the aeroacoustic characteristics of propellers. However, there are always slight deviations in the practical profiles due to manufacturing tolerance, wear loss, and limitations of processing techniques, which can potentially introduce uncertainties to aeroacoustic measurements. To this end, a systematic investigation is conducted on a benchmark propeller with a diameter of 217.2 mm and several of its variants in an anechoic wind tunnel. The variants are redesigned by modifying the sectional airfoil shapes with varying finite trailing-edge thicknesses. High-accuracy computer numerical control machining is employed to ensure the subtle geometrical differences between the blades. Force measurements indicate that the aerodynamic performances are insensitive to the slight variations of the sectional geometry, as expected. As for the acoustic performance, both the tonal and broadband noise are slightly affected when the axial flow speed is lower than 5 m/s. By contrast, a discernible noise reduction above 3 dB can be achieved due to the finite trailing-edge thickness. The noise source features are also investigated using a wavelet-based beamforming method, confirming that the noise reduction is caused by the weakened trailing-edge noise around the tip. This study is beneficial for the quantification of uncertainties in propeller noise measurements. It also suggests that adjusting trailing-edge thickness might be an useful approach in reducing propeller noise in practical applications.

V-Band Fully Metallic Geodesic Luneburg Lens Antenna

Antennas in emerging millimeter-wave (mm-wave) applications are often required to have low losses and produce a steerable directive beam. These properties are achievable with fully metallic geodesic Luneburg lens antennas. In this communication, we report the first experimental verification of a geodesic Luneburg lens antenna in the V-band. The designed lens antenna is fed with 13 waveguides providing beam switching capability in a 110° range. The lens is implemented in the parallel plate waveguide (PPW) technology. The antenna is manufactured in two pieces, and a tolerance analysis indicates that gaps between the pieces can cause a severe performance degradation. Based on this tolerance analysis, two measures are taken to alleviate the manufacturing tolerances for the prototype. First, electromagnetic band gap (EGB) structures are placed around the feeding waveguides. Second, the electrical contact between the two pieces is improved in critical regions. Two prototypes are manufactured, one without and one with the extra measures implemented. The measured radiation patterns of the prototype without these measures have high side lobes and low realized gain compared with the simulation. The measurements of the robust version of the prototype agree well with the simulations and demonstrate the applicability of geodesic Luneburg lens antennas for applications in the V-band.

Experimental analysis and preliminary model of non-conventional lip seals

The paper describes the tests carried out to determine the applicability of a simple means for reducing friction force in linear pneumatic actuators. The idea is based on the use of commercial lip seals mounted in the direction opposite to that used in conventional systems. Two different non-conventional installations were tested using commercial spring-energized seals consisting of two different materials: virgin PTFE and graphite-filled PTFE. Tests assessed the effect of bore manufacturing tolerances with nominal bore diameters of 50.0 mm and 50.2 mm. Performance was evaluated in terms of leakage flow rate and friction force, comparing the proposed installation with conventionally mounted seals. Friction coefficient and stiffness of the two seal materials were measured on a seal segment mounted on a pin-on-disk tribometer featuring a special pin design. Tests were carried out by loading the seal segment against a portion of the cylinder barrel in reciprocating motion. Stiffness and friction coefficient measurements served as the basis for developing a preliminary lumped parameter model of the lip seal which was used to analyze lip deflections, exchanged forces and leakage flow rate between seal and barrel.