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Wave-Powered Reverse Osmosis (WPRO) represents a promising convergence of ocean energy harvesting and advanced Reverse Osmosis (RO) desalination techniques. The significant fluctuations in pressures and flow rates within the integrated WPRO system present a critical challenge, necessitating an accurate transient model for effective performance estimation. This study presents a two-dimensional transient model based on pressure-correction algorithm to simulate channel flow with membrane boundary conditions under varying inlet conditions. The coupled dynamics of pressure, velocity, and salt concentration are addressed iteratively by decoupling and updating each term separately. The model investigates the performance of RO systems under different input conditions, including constant, sinusoidal, and irregular flow. The results indicate that constant input with higher pressure and lower flow rate achieves a better Recovery Ratio (RR). It is emphasized that for WPRO systems, a fair comparison requires choosing the same average power or pressure when evaluating different inputs. Under equivalent input power, sinusoidal waves result in a lower RR compared to constant inputs due to reduced average pressure. Conversely, under equivalent inlet pressure and flow rate, sinusoidal waves achieve a higher RR than constant inputs due to the phase difference between pressuredriven permeate velocity and diffusion-driven Concentration Polarization (CP). Specifically, sinusoidal inputs with higher frequency and higher amplitude display a higher RR. Additionally, irregular input yields a higher RR than constant inputs, as mean pressure and power can be maintained at levels comparable to those of constant input. The model’s adaptability to diverse flow regimes — from steady to sinusoidal and irregular fluctuations — highlights its potential as a critical tool for optimizing RO desalination processes powered by renewable ocean energy. 

Abstract Ocean wave-powered reverse osmosis (RO) desalination is an emerging field of study that combines the utilization of ocean energy and RO desalination techniques. However, due to the significant fluctuations in pressure and flow rate within the hydraulic system, an accurate transient model is necessary to estimate its performance accurately and effectively. This paper presents a two-dimensional transient model based on the pressure-correction algorithm to simulate the channel flow with porous walls and time-dependent inlet conditions. The coupled pressure, velocity, and salt concentration problem is solved iteratively by decoupling each term and updating them separately. The model is validated by comparing the results with analytical film theory which estimates the formation of the concentration polarization layer under constant inlet conditions. The performance of the RO systems, especially the concentration polarization phenomenon at the member surface, is investigated using different input conditions, including constant flow condition and sinusoidal flow condition. The salt concentration and permeate flux at the membrane boundary are studied to understand the effect of the dynamic inputs. Results show that the system can reach a higher maximum wall concentration and higher average recovery ratio in sinusoidal signal compared with the constant input. The model’s adaptability to different flow regimes, from steady to sinusoidal, underscores its potential as a valuable tool in optimizing RO desalination powered by ocean wave energy. 

Abstract Technologies to enhance the survivability of wave energy converters (WECs) in harsh ocean environment and reduce the difficulty and cost of deployment and operation are important. Traditional two-body point absorber with a rigid Power Take-off (PTO) may result in two essential problems on the deployment and operation. This study proposes a novel a two-body self-reactive point absorber with a flexible tether drive PTO. This flexible PTO design can avoid the request of supporting structures on the WEC to constrain the motion and harvest energy from multiple degree of freedoms (DOFs) motion without requirement of a taut mooring. System dynamics considering 4-DOF with the proposed flexible PTO system are formulated. A scaled prototype is designed, fabricated, and tested in a wave tank. Results show that the proposed flexible PTO can greatly increase the power absorption and add a reactive peak in the frequency domain. This study reveals that the proposed PTO is desirable for the two-body point absorber and thus holding the advantages of fast and easy deployment with slack mooring and good survivability under large wave conditions. 

Abstract Agriculture provides a large amount of the world’s fish supply. Remote ocean farms need electric power, but most of them are not covered by the electric power grid. Ocean wave energy has the potential to provide power and enable fully autonomous farms. However, the lack of solid mounting structure makes it very challenging to harvest ocean power efficiently; the small-scale application makes high-efficiency conversion hard to achieve. To address these issues, we proposed a self-reactive ocean wave converter (WEC) and winch-based Power Take-Off (PTO) to enable a decent capture width ratio (CWR) and high power conversion efficiency. Two flaps are installed on a fish feed buoy and can move along linear guides. Ocean wave in both heave and surge directions drive the flaps to move and hence both wave potential energy and wave kinetic energy are harvested. The motion is transmitted by a winch to rotation motion to drive an electric generator, and power is harvested. Dynamic modeling is done by considering the harvester structure, the added mass, the damping, and the excitation force from ocean wave. The proposed WEC is simulated in ANSYS AQWA with excitations from regular wave and results in a gross CWR of 13%. A 1:3.5 scaled-down PTO is designed and prototyped. Bench-top experiment with Instron is done and the results show that the mechanical efficiency can reach up to 83% and has potential for real applications.