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Prediction of the clearance between the components of a rotor and casing of a gas turbine is generally based on the two-dimensional (2D) finite-element analysis of the overall layout, the three-dimensional (3D) finite-element analysis of the local parts, and the deformation of the gas turbine components caused by other, unimportant 3D effects, such as cold-build clearances and ovalization. Using this, the variation of clearance, the minimum clearance, and the contact evaluation between the components with respect to the operation time are evaluated. Detailed 3D modeling of the overall shape for transient thermal-structural analysis for the prediction of clearances between components under the operating conditions of gas turbines with complex components, including both axisymmetric and non-axisymmetric shapes, is not economical in terms of computational time and cost. To address this problem, it is efficient to perform finite-element analysis by means of 2D modeling based on the crosssectional information of the gas turbine components. At this moment, the 2D finite-element modeling for the axisymmetric and non-axisymmetric structures of the gas turbine is important for predicting the correct and accurate deformation. In this paper, we show that 2D modeling can obtain results similar to those of 3D finite-element analysis for the original shape. The proposed 2D finite-element modeling method for rotor and support of a gas turbine that includes both axisymmetric and non-axisymmetric shapes will enable rapid and effective prediction of the components' behavior.

© The Author(s) 2019. Hermetic digital scroll compressor has been widely used as a small-scale organic Rankine cycle application in the heating, ventilation, and air conditioning systems. A clunking noise issue is recently found in an air conditioning outdoor unit, and the main cause of the noise is experimentally identified to be the impact of the scrolls in the compressor unit during the switching process. The semi-active control methods are thus designed to greatly reduce the noise level by using additional valves to adjust the pressure changing rate within the modulation chamber. The response time for the impact of the scrolls can then be controlled by the added valves. The additional release valve with a smaller diameter pipe parallel to the main valve is tested firstly for its performance. Slower flow rate is produced and the pipe can extend the response time and decrease the speed of the impact process by reducing the pressure changing rate. The use of a discharge valve is also tested for controlling the pressure changing rate inside the chamber. The discharge valve with an opposite effect to the release valve is found useful for solving the noise issue. Both noise and vibration results confirm that the impact noise in the frequency range of interest can be reduced by using the proposed semi-active control methods.

The development of flexible and sensitive three-axis pressure sensors is of great interest for various wearable applications, such as electronic skin, soft robotics, and health monitoring. This study aims to propose a highly sensitive and flexible pressure sensor that can measure three-axis pressure based on conductive microstructured carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) elastomer with a simple and large-scale fabrication method that uses a polymer wet etching process. The randomly exposed CNTs on the surface using PDMS wet etching improve the sensitivity of the pressure sensors. The fabricated sensors exhibit a high sensitivity of 1.39 kPa−1 for a pressure range of 250 Pa, excellent limit of detection capability of 1.26 Pa, fast response time of within 52 ms, and high reliability of over 10,000 times of pressure loading/unloading. As an application, the pressure sensors are demonstrated using electronic skin on human fingers for the detection of the pressure levels and pattern recognition of distributed pressure. Moreover, to measure the three-axis pressure, pressurization tests are conducted using artificial fingers, demonstrating that the fabricated sensor can successfully measure the pressures applied along the three axes.

This paper investigates the whistle noise issue of ducted air-conditioning units under high discharge pressure operating conditions. The high-frequency whistle noise source is identified within the pipe system through onsite experiments. Commonly used mufflers for vehicle engines and industrial ducts are found not suitable for air-conditioning pipe systems due to the high fluid velocity that goes through. A dedicated pipe muffler is then designed, and several design configurations are theoretically and experimentally tested. The muffler with the perforated inlet penetration pipe is found to have the best noise attenuation performance at high frequencies without sacrificing its noise reduction performance at low frequencies. The noise measurement results of the whole unit in both the anechoic room and on site confirm that the high-frequency whistle noise can be eliminated and the designed muffler can overall reduce the noise level and improve its sound quality metric-tonality level (TNR).

The effect of non-conductive films (NCF) and under-bump metallization (UBM) materials on the electromigration (EM) failure mechanism of Sn-Ag microbumps was investigated under stress conditions at current densities ranging from 0.5~1.3 × 105 A/cm2 at 150°C. In the case of NCF microbumps, the EM failure mechanism were almost similar to that involving Cu/Ni/Sn-Ag microbumps with NCF and non-NCF. However, the NCF applications increased EM lifetime for the Cu/Ni/Sn-Ag microbumps. In the case of Ni and Cu UBM microbumps, the EM failure mechanism varied between Sn-Ag microbumps with Ni UBM and Cu UBM. No EM-induced failure was observed in Cu UBM microbump. However, EM-induced voids were found on the cathode side of the Al trace in the Ni UBM microbump. The three-dimensional (3-D) finite element method was used to simulate the current density and temperature distributions of the microbumps. The results showed that the Joule heating of the Ni UBM microbump was higher than that of the Cu UBM microbump. Thus, the increased Joule heating due to thicker Ni UBM resulted in a negative effect on the EM failure time. Therefore, the Cu UBM microbumps are expected to display enhanced EM resistance.

This paper focuses on a model order reduction (MOR) for large-scale rotordynamic systems by using finite element discretization. Typical rotor-bearing systems consist of a rotor, built-on parts, and a support system. These systems require careful consideration in their dynamic analysis modeling because they include unsymmetrical stiffness, localized nonproportional damping, and frequency-dependent gyroscopic effects. Because of this complex geometry, the finite element model under consideration may have a very large number of degrees of freedom. Thus, the repeated dynamic analyses used to investigate the critical speeds, stability, and unbalanced response are computationally very expensive to complete within a practical design cycle. In this study, we demonstrate that a Krylov subspace-based MOR via moment matching significantly speeds up the rotordynamic analyses needed to check the whirling frequencies and critical speeds of large rotor systems. This approach is very efficient, because it is possible to repeat the dynamic simulation with the help of a reduced system by changing the operating rotational speed, which can be preserved as a parameter in the process of model reduction. Two examples of rotordynamic systems show that the suggested MOR provides a significant reduction in computational cost for a Campbell diagram analysis, while maintaining accuracy comparable to that of the original systems.

A high-shock 2000 g accelerometer with suspended piezoresistive sensing bridges has been designed, fabricated, and tested. Structural size of the accelerometer has been obtained through an optimal design process. Four resistors are electrically connected to form a Wheatstone bridge circuit. A sensitivity of 25.5 μV/g has been measured from the fabricated accelerometer with a nonlinearity of 0.2% in an acceleration range within 2000 g. The real-time response of the fabricated accelerometers accurately follows the reference accelerometer. The newly fabricated accelerometer has survived an over-shock condition of 4667 g.

In recent times, turbomolecular pumps (TMPs) have been used frequently to generate and maintain high and clean vacuum. Because of the high-speed rotation of the rotor, its structural safety should be treated as the first design concern. This paper presents the structural analysis and optimization of rotor blades of a TMP. To increase the numerical efficiency in the finite element modeling and analysis, the P-method provided in Pro/ENGINEER was used for simulation. The structural responses for several types of rotor blades were investigated, and the effects of the blade angle, blade length, and round size are thoroughly studied for each type of TMP blade. In addition, structural optimization to reduce and even the maximum stress at each stage of the TMP by changing the size of rounds between the blade and the hub was performed very successfully by using the P-method.

The effects of primary flow molecular weight on the ejector performance in a generic rocket-based combined-cycle engine are examined by using steady-state, one-dimensional compressible flow equations. Ejector performance in terms of specific impulse, bypass ratio, thrust, and thrust augmentation factor are presented for three primary fluids with molecular weights of 2, 18, and 29, covering a range of primary rocket stagnation conditions, ejector geometries, and freestream conditions.

A robust optimal design of shape and size is formulated for vibratory microgyroscopes that can reduce the effect of variations from uncertainties in microelectromechanical systems fabrication. The important objective in the design of vibratory microgyroscopes is to reduce the difference between the resonance frequencies of the vertical (detecting) and lateral (driving) modes in order to attain high mechanical detecting sensitivity. The deterministic optimization for this goal results in good performance but is sensitive to fabrication errors. The basic idea of the present formulation is to obtain robustness of the objective function by minimizing the gradient of the objective function with respect to uncertain variables through a proper selection of shapes and sizes. The beam width, length and thickness of vibratory microgyroscopes are adopted as design variables and are simultaneously regarded as uncertain variables in the optimization problems. A robustness check using a newly defined yield through the Monte Carlo simulation has shown that the robust optimal design obtained has generated twice the number of acceptable designs than the deterministic optimum. The important point is that the formulation of minimizing the maximum sensitivity of the objective function requires no statistical information on the uncertainties and yet achieves robustness.

Atomic-based-combined-cycle (ABCC) engine combines an air-breathing ramjet engine with an atomic reactor to increase the mission-averaged specific impulse and thereby increasing the dry-mass ratio. ABCC engine is similar to RBCC engine except that energy needed for the propulsive power is derived from nuclear reaction rather than chemical combustion used in the RBCC engine. The potential performance improvement of an ABCC engine over a RBCC engine comes from two factors. Firstly, the energy density of nuclear reaction is several order of magnitudes higher than the chemical combustion. Secondly, hydrogen can produce much higher nozzle exit velocity because of its small molecular weight. A one-dimensional, transient numerical model was used to analyze a generic RBCC engine and it is used as a baseline to evaluate an imaginary ABCC engine performance. A nuclear reactor is treated as a black box energy source that replaces the role of the primary rocket and the chemical combustion chamber in a RBCC engine. The performance of a generic ABCC engine along a flight path (q0 =10 (exp 3) lbf per square ft) shows that the mission averaged-specific impulse is about twice larger than RBCC engine and the dry mass-ratio is about 50% larger. Results of the present ABCC engine performance are based on the assumptions that the flow passage of working fluids is identical to that of RBCC engine and that a nuclear reactor is treated as an energy black box. Preliminary heat transfer calculation shows that the rate of heat transfer to the working fluids is within the limit of turbulent convective heat transfer regimes. The flow passage of realistic ABCC engine must be known for a better prediction of ABCC engine performance. Also, critical heat transfer calculations must be performed for the ejector mode and ramjet mode operations. This is possible only when the details of a reactor configuration are available.