Control of small turbojet engines is challenging due to the small number of sensors and actuators. In these engines, typically the spool speed and exhaust gas temperature are the measured variables and the fuel flow is the only manipulated variable. However, the thrust command must be achieved and the engine’s structural and operational limitations must be safeguarded. In this research, a minimum selector control structure with a saturation function is presented for controlling small turbojet engines. One control loop is considered to control the spool speed and another loop is used to manage the exhaust gas temperature. The output of the control loops is the fuel flow rate and the minimum value is selected between them. To prevent the compressor surge and combustor blow-out during engine acceleration/deceleration, a fuel flow rate saturation is defined. Due to the switching structure of the proposed controller and existence of the saturation function, stability analysis is a critical issue. Therefore, a methodology is presented to analyse the stability of the proposed structure. In simulation study, a nonlinear thermodynamic model that matches more than 90% with the test data is used and the response of the proposed controller is compared with a proportional integral (PI) controller. In a comprehensive scenario, the throttle degree varies from 75% to 100%. Using the PI controller, some outputs have some overshoot and the exhaust gas temperature exceeds the corresponding constraint by 40K. While the proposed minimum selector controller, in addition to accurately fulfilling the thrust command, fully protects the limitations governing engine variables.

Traditionally, land subsidence resulting from groundwater over-pumping has often been described by the theory of consolidation. The mechanism of land subsidence due to the dehydration of clay minerals has not been well addressed. Therefore, this study develops a smectite dehydration model to describe the effect of the release of water from the smectite interlayer upon land subsidence. Using a thermodynamic solid-solution model and laboratory studies of clay-water systems, a complete description of the dehydration relationships among the swelling pressure, basal spacing and mw/mc in a Na-smectite water system at 25°C under variable pressure conditions was derived. Accordingly, the evaluation model of the ‘hydration state of smectite’, and the ‘solid-solution model of smectite dehydration’ were formulated rigorously. These two models were applied to quantify the effects of smectite dehydration on the accumulated land subsidence in the Yun Lin offshore industrial infrastructure complex and in the Tai-Shi area. The result reveals that smectite dehydration is of importance in assessing and predicting land subsidence in a shallow sedimentary basin.

Arctic landfast sea ice (LFSI) represents an important quasi-stationary coastal zone. Its evolution is determined by the regional climate and bathymetry. This study investigated the seasonal cycle and interannual variations of LFSI along the northwest coast of Kotelny Island. Initial freezing, rapid ice formation, stable and decay stages were identified in the seasonal cycle based on application of the visual inspection approach (VIA) to MODIS/Envisat imagery and results from a thermodynamic snow/ice model. The modeled annual maximum ice thickness in 1995–2014 was 2.02 ± 0.12 m showing a trend of −0.13 m decade−1. Shortened ice season length (−22 d decade−1) from model results associated with substantial spring (2.3°C decade−1) and fall (1.9°C decade−1) warming. LFSI break-up resulted from combined fracturing and melting, and the local spatiotemporal patterns of break-up were associated with the irregular bathymetry. Melting dominated the LFSI break-up in the nearshore sheltered area, and the ice thickness decreased to an average of 0.50 m before the LFSI disappeared. For the LFSI adjacent to drift ice, fracturing was the dominant process and the average ice thickness was 1.56 m at the occurrence of the fracturing. The LFSI stages detected by VIA were supported by the model results.