The valve-controlled hydraulic cylinder system (VCHCS) is commonly used for actuators such as manipulators in deep-sea equipment, whose working performance is crucial to subsea tasks. Affected by the ambient pressure introduced by the pressure compensator, the viscosity of the hydraulic oil increases significantly. On this basis, the viscosity changes further when flowing in the slender pipeline, making the pipeline pressure loss substantially increase and subsequently affecting the working performance of the deep-sea VCHCS. Aiming at this issue, a detailed nonlinear mathematical model of the deep-sea VCHCS is established, in which the viscosity-pressure characteristics of the hydraulic oil is considered to take the viscosity changes in the pipeline into account. Besides, the hydrodynamic effects are also included in the model. Then the corresponding numerical simulation model of the deep-sea VCHCS is established, and its working performance at different depths is simulated and analyzed. When the depth is 11km, the extension and retraction movements are delayed by 52.50% and 43.12% respectively. The root cause of the delay is then analyzed and discussed. Finally, the parameters that affect the working performance are studied, and suggestions to reduce or eliminate the delay phenomenon are given. The results can provide theoretical support for the performance optimization of the deep-sea VCHCS.

The high ambient pressure in deep-sea conditions greatly increases the viscosity of hydraulic oil and then the pipeline pressure loss in deep-sea hydraulic systems. Large pipeline pressure loss can lead to a further change of viscosity on the basis of the viscosity increase caused by the ambient pressure when the hydraulic oil flows through the pipeline. Therefore, the classic Poiseuille’s law can no longer accurately calculate the pipeline pressure loss in deep-sea conditions since it treats the viscosity as a constant. In this paper, based on laminar flow theory and the viscosity-pressure characteristics of hydraulic oil, a novel equation for pipeline pressure loss is proposed, in which the viscosity change when flowing through the pipeline is taken into account. A CFD (Computational Fluid Dynamics) model of a pipeline in the deep-sea hydraulic system has been established, and CFD simulations have been conducted to verify the correctness of the proposed equation for pipeline pressure loss. Theoretical analysis shows that the proposed novel equation for pipeline pressure loss is equivalent to the classic Poiseuille’s law when the pipeline pressure loss or the viscosity change is low. The research results in this paper can provide theoretical support for work efficiency optimization, load capacity improvement, and precise control of deep-sea operation equipment or deep-sea hydraulic systems.

The prediction of coal fusion characteristics and determination of slagging behaviour are of great significance to the operation of thermal power plants. The traditional method needs a long time to measure coal ash fusion temperatures (AFTs) by heating the coal ash cone. The purpose of this work is to predict the coal AFTs directly from coal rather than coal ash using Laser-Induced Breakdown Spectroscopy (LIBS). On the premise that ash content, volatile matter, fixed carbon and moisture are known on the air-dry base state, these four parameters are added into the model as generalized spectral (GS) variables to improve the accuracy of coal AFT prediction, in which the R² of softening temperature (ST) and hemisphere temperature (HT) reached 0.9958 and 0.9856, the root-mean-square of cross-validation (RMSECV) reached 4.88 °C and 9.11 °C, and the root-mean-square of prediction (RMSEP) reached 8.15 °C and 11.3 °C, respectively. The trend relationships between the AFTs and the intensities (or ratio) of the spectral lines corresponding to individual elements of the LIBS spectrum were analysed. Then the variation trend of coal AFTs with specific element content (or ratio) is deduced qualitatively. We demonstrated that the model and scheme developed in this work can be applied in a real-time guiding role in the actual production process of the power plant.