Binqi Chen

During quadrotor load transport, the cable’s elasticity exacerbates load fluctuations, which may result in platform instability or a potential crash. This paper introduced a model of the connecting cable as a spring-damper system and established the dynamic model of the suspension system based on Newton’s law. Nonsingular fast terminal sliding mode control (NFTSMC) was employed for attitude, position, and anti-swing controller design. Adaptive controllers were integrated into altitude control to address uncertainties related to load mass and cable length. The inclusion of an anti-swing controller into the position control loop effectively dampens load oscillations while ensuring accurate position tracking. Numerical simulations demonstrated that the proposed controller outperforms both the energy-based controller and the conventional linear sliding mode controller.

The parallel expander ORC system is one of the solutions for providing an additional power output by improving the partial-load performance of an ORC. The parallel expander system corresponds to partial-load conditions by switching between various combinations of the expanders. During this process, the dynamic behavior occurs, which have not been characterized well in the open literature according to the best of the authors’ knowledge. In this study, we developed a dynamic modeling of an ORC system using dual expanders (DE-ORC) to study the dynamic responses during its mode changes. System components were simulated using an open-source library of ThermoCycle written in Modelica language. For each component, empirical parameters were implemented based on the experimental results. Furthermore, during the mode change that involved going from dual expander mode to singular expander mode, and to prevent the formation of the droplet in the expanders, a control strategy was proposed and simulated. The strategy involved lowering of the mass flow rate and then shifting the mode. Several timings between flow rate lowering and shifting the mode were analyzed, and the optimum shifting time was found to be in between 40 to 50 s.

Prediction of oscillating pressure is a key technology for cavity research. Nonlinear Acoustic Solver (NLAS) is applied to analyze aeroacoustics recently. A nonlinear numerical solver is combined with the Reynolds-averaged Navier-Stokes (RANS) method. RANS is applied to solving the flow field around a cavity, and average solution of initial turbulent statistics is obtained which contains the basic characteristics of the average flow field and statistic description of turbulence fluctuation. The source of acoustic generation is reconstructed, and the spreading of oscillating pressure is simulated precisely. According to the comparison of the cavity noise calculation and experimental results under Mach numbers 0.6, 0.85, and 1.35, it indicates that NLAS is capable to predict oscillating pressure of cavity flow from subsonic to supersonic with acceptable deviation. On this basis, the contribution to oscillating pressure suppression made by passive control such as rectangular fence (RF) and square tooth spoiler (STS) is investigated. It is found that these two passive control methods can lessen the total noise.

In the present study, CFD simulation with delayed detached eddy simulation (DDES) is performed to investigate an open cavity at Mach 0.85. A clean cavity and cavity with passive and active control methods, including sawtooth spoiler, flat-top spoiler, crossflow rod, and steady leading edge blowing, are analyzed. The results obtained from all the control methods are compared with clean cavity, and all the flow control methods show positive effect on the overall sound pressure level reduction with the decrement up to 8 dB. The effect of active control on sound pressure level in the cavity is much better than that of passive control, with the magnitude of tone noise decreasing by 20-30 dB. The main focus of this investigation is to test the noise suppression effect by passive and active control methods.