A regulation on the sulfur emissions of ships sailing in global sea areas has been enforced since 1 January 2020. In this new regulation, ships are required to use low-sulfur fuel oils or to install an after-treatment equipment, such as a scrubber. Open and hybrid scrubbers wash the exhaust gas using seawater and then discharge the wash water overboard. According to the regulation promulgated by the International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC), the wash water must have a pH of 6.5 or higher at 4 m from the discharge point. Wash water is generally acidic, with a pH of 2.5–3.5, whereas seawater is alkaline, with a pH of approximately 8.2. The wash water is dispersed after being discharged overboard through a nozzle, and its pH is restored through dilution with the surrounding seawater. In this study, the pH was calculated by using a theoretical chemical reaction model, and then the dispersion of wash water was analyzed using CFD simulation. This study describes the process of selecting the appropriate turbulent Schmidt number in a wide range of nozzle diameters. Finally, the appropriate nozzle diameter was determined based on the initial pH of the discharged scrubber wash.

In this paper, an experimental study on two-phase flow pressure drop of refrigerant FC-72 is carried out in a microchannel. The microchannel has a width and depth of 0.45 and 0.2 mm respectively, and comprises 15 parallel channels with a length of 60 mm. The experiment is conducted under the condition of mass flux of 100.3–458.0 kg/m²s and heat flux of 3.2–49.0 kW/m². This study analyzed the pressure drop characteristics for two-phase flow by using a separated flow model. To predict the frictional pressure drop, two-phase frictional multiplier obtained from experiments is compared with the existing correlations. The experimental results show that two-phase frictional multipliers rely heavily on the vapor quality. Fractional pressure drop increases as the vapor quality increases. However, the rate of increase in the high vapor quality region decreases as the vapor quality increases. Based on pressure drop characteristics obtained from the experiments, a new correlation is proposed to predict the frictional pressure drop. Two-phase multiplier is modified with the dimensionless parameters such as Reynolds number, Weber number, and Martinelli parameter. The newly developed correlation predicts the experimental results well within a mean absolute error of 8.0%.

This paper deals with the PID control synthesis with robust (H_∞) loop shaping framework to manage MIMO reverse osmosis (RO) desalination plants. This new method takes advantage of the robust controller which has a fixed low order of conventional PID scheme guaranteeing robust stability and performance under large parametric uncertainties, external disturbances, and sensor noises. The coprime factor uncertainty description in H_∞ loop shaping methodology can cover a wide variety of uncertainties over all frequencies for the RO plants. The test results demonstrate that the achieved controller has high stability margin, showing disturbance and noise attenuation abilities. Furthermore, most interactions between control channels have been decoupled in the complete control system. The presented control approach can help reduce membrane cleaning, save energy, and reduce product water costs for the RO plants. Note that weather changes increase unstableness in RO plants but the water treatment facilities are only dimensioned for PID control. In addition, this study addresses control robustness as well as performance of a RO system against uncertainties, disturbances, and noises. Finally, the present control method can be utilized for efficiently controlling water quality (including quantity) and managing water facility of the RO desalination plants.

Experimental research is performed on two-phase flow boiling heat transfer in micro-channels. FC-72 is used as the working fluid. In order to analyze the heat transfer mechanism during two-phase flow boiling, the dimensionless parameters, e.g., boiling number and convection number, are used, and the effect of these parameters on the heat transfer can be confirmed during flow boiling in the micro-channel. In addition, the transition criterion from bubbly/slug flow to annular flow is proposed from the modified Weber number. Based on the boiling heat transfer mechanism obtained from the experiments, a new correlation is proposed to predict the heat transfer coefficient. The new correlation predicts well the experimental results within a mean absolute error of 5.2%.

This article considers key theoretical and practical issues that arise in the robust control synthesis for dynamic positioning. A dynamically positioned vessel maintains its position (fixed location or predetermined track) by means of active thrusters and propellers. The concise kinematics and vessel dynamics are presented using three degrees of freedom model for describing the horizontal motions. Then, the mixed H_∞ and µ-synthesis framework has been employed to deal with perturbed model under external disturbances as well as measurement noises. To avoid excessive control energy for dynamic positioning system, the high frequency waves have been filtered using simple weighting functions. Using optimal Hankel-norm model approximation, the resulting full-order controller has been significantly reduced to make it easy to implement the practical works. Next, the simulation results in both frequency and time domains are presented to demonstrate the effectiveness of the robust control algorithms using the appropriate weighting functions. Finally, it is found that the proposed dynamic positioning system provides good maneuverability and robustness over a wide range of operating conditions, even under parametric variations and sea disturbances with sensor noises.