Abstract

So far, the day-ahead scheduling research of photovoltaic (PV)-based battery swapping stations (BSSs) has not fully considered the uncertainties of swapping demand and PV output. To address this issue, a day-ahead economic scheduling method based on chance-constrained programming and probabilistic sequence operation is proposed in this paper. First of all, a BSS day-ahead scheduling model with chance constraints as swapping demand satisfaction and the confidence level of the minimum cost is established. The confidence level of chance constraints is set by BSS operators. Then, probabilistic sequences of stochastic variables are constructed, and the quantitative index to measure the day-ahead scheduling risk of BSS is proposed based on sequence operation. Thereafter, the feasible solution space is determined based on the battery controllable load margin, and then the fast optimization method for the BSS day-ahead scheduling model is developed by combining the feasible solution space and genetic algorithm (GA). Finally, the validity and applicability of the proposed method is verified in the case study.

Abstract

Natural gas hydrate formation induced by the leakage of methane was observed in field investigation. The appearance of cold seep might be an indication of natural gas hydrate reservoir. In this study, CH4 hydrate formation in porous media with continuous gas flow was firstly investigated using magnetic resonance imaging. Three flow rates (0.2, 0.4, 0.6 mL/min) were experimentally conducted and the results indicated that the gas flow rate plays a crucial role in the hydrate formation. A high flow rate could reduce the CH4 displacement and hydrate formation time, however, more water was brought out from the sediment during displacement process, finally leading to a low hydrate saturation. It is suggested that for cold seep where gas bubble gushes violently, the hydrate reservoir may not be abundant. Our work can provide some insights of the mechanism of hydrate formation induced by cold seep, making contributions to future cold seep field investigation.

Abstract

During the process of natural gas hydrate exploitation, the cementation state of the stratum changes due to the decomposition of skeleton hydrate. Fine sand in the reservoir will migrate to the wellbore with the fluid, which is the so-called sand production phenomenon. Sand production will bring great harm to hydrate exploitation. In this paper, a set of macroscopic visualized sand production vessel is designed, which can observe the migration of sand in the sediment layer under different working conditions, and the factors influencing the sand production characteristics are obtained by measuring the amount and the size of sand production. It is found that fine sand will invade and block the gravel layer driven by water and it is accompanied by the collapse and subsidence of the sand layer. Fluid velocity and initial hydrate saturation are important factors affecting the characteristics of sand production. In addition, it is of certain guiding significance to select the appropriate median diameter ratio of sand to gravel for sand control in the actual exploitation process.

Abstract

This paper is aimed at analyzing the influence of fluctuation by gas load in the integrated electrical and natural-gas system (IENGS). To address this issue, an affine method is proposed to calculate energy flow in IENGS considering uncertainties. In the distribution network, the power flow is solved by affine arithmetic based on forward-backward sweep method after obtaining the solutions of coupling units in the gas system. A numerical test, in which an IENGS is made up by a 13-bus distribution network and a 7-node gas system, shows the correctness and effectiveness of the proposed method. The results draw the conclusion that the fluctuation of gas load leads to the fluctuation of the whole IENGS.

Abstract

Mooring lines are significant components for floating offshore wind turbines (FOWTs). Unlike offshore floating platforms, whose mooring systems are just for station-keeping, mooring lines for FOWTs are not only for station-keeping but may also have an effect on the global performance of FOWT and vice versa. Previous studies have reported mooring line damages under different operating conditions and questions have been raised about the reasons for those failures. To tackle this issue, this paper aims at studying the major contributing factors on FOWT mooring line tension. Potential influences on the mooring line fairlead tension have been grouped into forces and displacements. Using these forces and displacements as the input in an Artificial neural network (ANN) and the most loaded mooring line fairlead tension as the output, ANN was trained to investigate the significance of inputs to the mooring line tension. Under the operating condition, results from ANN showed that mooring line fairlead tension is heave motion dominated while blade root bending moment contributed first on mooring line tension in terms of forces.

Abstract

An energy management strategy based on double deep Q-learning algorithm is proposed for a SeriesParallel Hybrid Bus. The models of powertrain configuration and its main components are first established. Subsequently, a rule-based energy management strategy will be proposed. The China typical urban driving cycle (CTUDC) is used to evaluate the fuel economy performance of the two strategies studied in this paper. The simulation result indicates that the energy management strategy based on reinforcement learning decreased the fuel consumption by 7.3% per 100km compared to rulebased strategy.

Abstract

The small-scale skid-mounted natural gas liquefaction plant can recover natural gas economically and conveniently without pipeline transportation. The mixed refrigerant liquefaction process is widely used in small plants currently. However, the liquefaction process is very energy–intensive. In this paper, We simulated the propane precooled mixed refrigerant liquefaction process and found that increasing the pressure and lowering the feed gas temperature can reduce the liquefaction energy consumption. Moreover, parameters such as refrigerant composition, flow rate, and heat exchangers outlet temperature are also related to energy consumption. The genetic algorithm (GA) was used to optimize the process, and the minimum specific energy consumption of liquefaction process ?????? was 0.3821kW·h/kg, which was 37.9% lower than the base case. In addition, the results also suggest that when the C4H10 mass fraction exceeds 35%, the compressor inlet has liquid phase component. When the CH4 and N2 components are less than 20%, the cryogenic heat exchanger has insufficient heat exchange capacity.

Abstract

Hydrate formation and wax precipitation can occur simultaneously due to the high pressure and low temperature conditions in subsea pipelines, leading to complicated flow assurance issues. In this study, we provided direct measurements of hydrate induction time with different wax contents by using a high pressure autoclave equipped with an online viscometer. It was found that the presence of wax can significantly increase the hydrate induction time for the diesel oil systems. The petroleum samples from an operational well and real wax deposits from the pigging process were also mixed and used to represent in the field and real hydrate formation conditions. The hydrate induction time of field fluids showed that the presence of wax deposition could weaken the inhibiting effect of wax on hydrate nucleation by causing a reduction in the amount of wax adsorbed at the water/oil interface.

Abstract

Optimization of building design has the promise to substantially reduce building energy consumption. Though typically considered in early design, we demonstrate in this paper that optimal re-design of building layouts has the potential to reduce energy use throughout the lifetime of a building and as occupant dynamics evolve over time. We introduce novel methods for (1) inferring occupant activities and schedules based on plug load sensor data, and (2) clustering occupants by activity patterns to create optimal layouts that take advantage of controllable HVAC and lighting systems. Combining data from a real small office building with the Department of Energy’s small office reference building, we demonstrate that this near zero-cost occupant re-alignment strategy can save 3.3% in annual energy consumption.

Abstract

In response to some serious issues like the energy crisis and environmental problems associated with the conventional compression refrigeration system, thermal air-conditioning systems were therefore developed to overcome the mentioned problems. A completely novel integrated adsorption and absorption (AD-AB) refrigeration system driven by low-grade temperature heat sources is proposed in this investigation. This novel cycle focuses on the inherent characteristics of the adsorption and absorption phenomena. The innovation here is that the generator of the absorption cycle becomes the evaporator of the adsorption cycle. Therefore, the generation and evaporating pressure are associated with the heat source temperature. Moreover, the adsorber in the adsorption system replaces the condenser in the standard absorption system. Thus, the generation pressure is associated with the heat source temperature and can be adjusted according to the solution concentration and generation temperature.