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A mathematical gas dynamic model for semiconductor devices is numerically analysed. The well‐known ballistic diode problem is taken as an example.

This paper aims to develop a dynamic performance model of three-shaft gas turbine for electricity generation and to study a multi-loop control strategy of three-shaft gas turbine for electricity generation.

In this paper, the dynamic performance model of the three-shaft gas turbine is established and developed. A novel approach, variable partial differential coefficient deviation linearization method is used to simulate the dynamic performance of the three-shaft gas turbine. Single-loop control system, feed-forward feedback control system and cascade system are assessed to control the engine during transient operation.

A novel approach, variable partial differential coefficient deviation linearization method is used to simulate the dynamic performance of the three-shaft gas turbine. According to the results shown, the cascade control system is most satisfactory due to its fastest response and the best stability and robustness.

The method of variable partial linearization is adopted to make the dynamic simulation of the model achieve higher precision, better steady state and less computation time. This paper provides a theoretical study for the multi-loop control system of a marine three-shaft gas turbine.

Dynamic separator is an equipment having a rotor and static vanes and is used to separate solids from gas-solids flow based on size. Particle separation in a dynamic separator happens due to complex interchanges between multiple forces exerted in the separation zone. Currently, there is only limited knowledge concerning the working principles of separation. This paper aims to systematically study a dynamic separator using numerical models to get insights into particle separation.

The Lagrangian–Eulerian formulation is used to simulate gas-solid flow. Multiple frames of reference using stage interpolation are used to account for rotation. Periodic symmetry in the equipment is exploited to create a simplified numerical model. The predictions from the numerical model are compared against available experimental data.

The numerical results indicate that only when particle collision is included, the separation efficiency trend from the experiment is matched by numerical predictions. Further, it is shown that at the same range of rotor speeds where numerical results predict increased separation efficiency, the solid pressure due to particle collision also reaches its maximum value. The gas flow and particle behavior in the separator are explained in detail.

The importance of particle collision in separation is interesting because traditionally, particle separation is assumed to be influenced by three forces, namely, centrifugal force, drag force and gravity. The numerical results, however, point to the contribution by particle collision, in addition to the above three forces.

To improve the load capacity and stability of gas foil journal bearings (GFJB), this paper aims to propose a novel GFJB with taper-grooved top foil.

A modified bump stiffness model is established considering rounding and friction. By considering the variation of clearance in the circumferential and axial direction, the static and dynamic characteristics of the novel bearing are calculated using the finite difference method, and perturbation method, respectively. The bearing performance under different groove parameters is studied and compared to the traditional bearings.

The results show that this novel GFJB can bring multi-extra local dynamic pressure and decrease the gas end leakage, which improves the static and dynamic properties. Moreover, as the increment of groove depth, the load capacity and direct stiffness are reinforced. There is an optimal groove width to maximize the load capacity, and the taper-groove is more beneficial to the improvement of bearing performance than other groove shapes. For the novel GFJB (Ng = 6, Hg = 10µm), the load capacity and direct stiffness increase by about 6.67 and 13.5 per cent, respectively. The stability threshold speed (STS) of a rotor supported by the novel bearings is also increased.

The performance of the presented novel GFJB is enhanced immensely compared to the traditional bearings, and the results are expected to be helpful to bearing designers, researchers and academicians concerned.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2019-0307.

The capability to predict and evaluate the motor pressure during each phase by means of a numerical analysis can significantly increase the efficiency of the preliminary design process with a reduction of both the motor development and operational costs. This paper aims to perform numerical simulation to analyze the ignition transient in solid rocket motor by solving Euler equation coupled with some semi-empirical correlations. These relations take into account the main phenomena affecting the ignition transient. Coupling relationships include the heat transfer of the gas to the propellant and erosive burning rate relationship.

The current research effort divides motor into series of control volumes along the port axis, and the variation of port area, burning surface and burning rate along the port are taken into account. A set of governing equations are then solved using explicit, time-dependent, predictor-corrector finite difference method. The numerical model helps to capture and embed shock wave associated with igniter flow within the solution. Second-order artificial viscosity dampens out the numerical oscillations due to sharp gradient within the flow field. The developed computer code predicts the start-up characteristics of motor. The study also provides comparison of simulation results with in-house experimental motor.

Simulations are performed with and without erosive burning to demonstrate that the flow model is a good physical approximation of motor. Numerical results calculated by this model without erosive burning are not in good agreement with experimental results. This minor discrepancy has motivated the inclusion of erosive burning in numerical model. The simulated results are then compared with the experimental data for head-end and rear-end pressure. The agreement between simulation and experiment is remarkable. In summary, major finding of this study is that unsteady quasi-one-dimensional gas dynamic model can capture the flow field in the motor during ignition transient effectively.

Unsteady quasi-one-dimensional gas dynamic model can capture the flow field in the motor during ignition transient effectively. However, in systems where two- and three-dimensional effects are pre-dominant, one would require to develop a more elaborate, multi-dimensional model which will allow for further understanding of the flow behavior and eventually lead to modeling of rocket motors with more complex geometries.

The close agreement between experimental and simulation results can be considered as forced to some degree, because the general mathematical model of erosive burning contains a free variable erosive burning exponent. However, in future, this variable can be established a priori by erosive burning tests.

The solid propellant ignition process consists of series of rapid events and must be completed in a fraction of a second. An understanding of the dynamics of ignition has become increasingly vital with the development of larger and more sophisticated solid propellant rocket motors. This research effort provides the simulation framework to predict and evaluate the motor pressure during each phase by means of a numerical analysis, thus significantly increasing the efficiency of the preliminary design process with a reduction of both the motor development and operational costs.

This study aims to study the gas film stiffness of the spiral groove dry gas seal.

The present study represents the first attempt to calculate gas film stiffness in consideration of the slipping effect by using the new test technology for dry gas seals. First, a theoretical model of modified generalized Reynolds equation is derived with slipping effect of a micro gap for spiral groove gas seal. Second, the test technology examines micro-scale gas film vibration and stationary ring vibration to determine gas film stiffness by establishing a dynamic test system.

An optimum value of the spiral angle and groove depth for improved gas film stiffness is clearly seen: the spiral angle is 1.34 rad (76.8º) and the groove depth is 1 × 10^–5 m. Moreover, it can be observed that optimal structural parameters can obtain higher gas film stiffness in the experiment. The average error between experiment and theory is less than 20%.

The present study represents the first attempt to calculate gas film stiffness in consideration of the slipping effect by using the new test technology for dry gas seals.

This paper aims to establish a multi-input equilibrium manifold expansion (EME) model for gas turbine (GT). It proposes that the extension of model input dimension is realized based on similarity theory and affine structure in the framework of single-input EME model. The study aims to expand the scope of application of the EME model so that it can be used for the control or fault diagnosis of GTs.

In this paper, the concepts of corrected equilibrium manifold expansion (CEME) model and multi-cell equilibrium manifold expansion (MEME) model are first proposed. This paper uses theoretical analysis and simulation experiments to demonstrate the effectiveness of the bilayer equilibrium manifold expansion (BEME) model, which is a combination of the CEME and the MEME models. Simulation experiments include confirmatory experiments and comparative experiments.

The paper provides a new sight into building a multiple-input EME (MI-EME) model for GTs. The proposed method can build an accurate and robust MI-EME model that has superior performance compared with widely used nonlinear models including Wiener model (WM), Hammerstein model (HM), Hammerstein–Wiener model (HWM) and nonlinear autoregressive with exogenous inputs (NARX) network model. In terms of accuracy, the maximum error percentage of the proposed model is just 1.309%, far less than WM, HM and HWM. In terms of the stability of model calculation, the range of the mean error percentage of the proposed model is just a quarter of that of NARX network model.

The paper fulfills the construction of a novel multi-input nonlinear model, which has laid a foundation for the follow-up research of model-based GT fault detection and isolation or GT control.

This paper aims to study the bearing performance with different cone angle errors, to study the effect law of manufacturing taper error on the properties of gas foil conical bearing (GFCB).

For the GFCB supported by separated bump foil strips, a nonlinear structure stiffness model considering Coulomb friction and arch characteristics was proposed. The finite element method and finite difference method were used to solve the Reynolds equation and the film thickness equation by coupling, and the properties of the GFCB were obtained. The effect of foil and bearing structure parameters on the static and dynamic performance under different taper error cases was analyzed. Moreover, a test on the air compressor supported by GFCBs was conducted to verify the practicability.

The taper error has a largely adverse effect on the load capacity of GFCB. When the taper error is −0.03°, the radial load capacity Fr and axial load capacity Fz decrease by 37.5 and 58.3%, respectively. The taper error decreases the direct stiffness and cross-coupled damping of GFCB, which will weaken the bearing stability. Moreover, the performance of GFCB is closely related to the foil and bearing parameters.

The taper error adversely affects the static and dynamic characteristics of GFCB, which should be concerned by bearing designers, researchers and academicians.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2020-0089/

This paper's aim is to propose a quasi‐steady numerical model of a solid rocket motor that includes the coupling of motor chamber gas dynamics with the composite solid propellant combustion.

The paper considers a model problem of steady‐state burning of a pure monopropellant coupled with a quasi‐steady gas dynamic model of the combustion chamber. In order to simulate the time evolution as the propellant burns back with time, the flow‐field in the chamber, the burning rate and the linear response function parameters are calculated for three port diameters of a simple cylindrical geometry.

It is shown that the pressure‐coupled linear response function remains approximately constant along the propellant surface but can change very strongly as the chamber pressure rises due to increase in the burn surface.

Only simplified motor geometry is considered but more realistic geometries can also be analyzed using a similar approach.

This study is the first step in building a comprehensive fully coupled model for numerical simulation of the internal flow‐fields of solid rocket motors. In addition, it demonstrates how to use the steady‐state results to calculate linearized pressure‐coupled response of the propellant.

To accurately predict transient flow in homogeneous gas‐liquid mixtures in rigid and quasi‐rigid pipes, two mathematical models based on the gas‐fluid mass ratio are presented. The fluid pressure and velocity are considered as two principal dependent variables and the gas‐fluid mass ratio is assumed to be constant. By application of the conservation of mass and momentum laws, non‐linear hyperbolic systems of two differential equations are obtained and integrated numerically by a finite difference conservative scheme. The fluid density is defined by an expression averaging the two‐component densities where a polytropic process of the gaseous phase is admitted. The rigid model is deduced by neglecting the liquid compressibility and the pipe wall elasticity against the gas deformability. The quasi‐rigid model takes into account these two parameters. The effect of fluid compressibility on transient pressure behaviour is then analysed and confronted to the pipe wall elasticity. Numerical solutions are compared with numerical results available in literature and experiment developed in the laboratory. The results show that the pressure wave propagation is significantly influenced by the gas‐fluid mass ratio and the elasticity of the pipe wall. They indicate that the pipe elasticity and liquid compressibility may be neglected for great values of gas‐fluid mass ratio but not for the smaller ones.