Search Results (218)

It is recognized that boats which intervene in dangerous situations are characterized by high maneuverability, have good governance properties, and must be equipped with high-speed propellers. This paper proposes a computerized analysis, using Computational Fluid Dynamics modeling, of a high-speed propeller, in open water, from the perspective of velocity and pressure manifested on the propeller blades. The use of numerical methods allows to determine the thrust forces on the propellers, to highlight the areas in the propeller blade where the maximum and minimum pressures occur, to identify the cavitation zone and to visualize the degree of turbulence of the fluid flow on the propeller blades in rotational motion. The analysis proves to be an efficient procedure in determining the characteristics of a high-speed propeller before deciding its production/manufacture. The Shear Stress Transport method was used for fluid turbulence analysis and the “Thrust–Propeller RPM” diagram and “Torque–propeller RPM” diagram finalized this study, the mentioned diagrams being the most important in choosing an efficient propeller for a given boat. Full article

Hydrodynamic cavitation is one of the most promising technologies for sustainable process intensification in the food, nutraceutical, and environmental sectors, due to its ability to generate highly localized and intense implosions. Venturi-type devices, known for their simplicity and efficiency, are widely used for non-thermal extraction, microbial inactivation, and cellular disruption. However, the effectiveness of cavitation critically depends on internal geometry—particularly the perimeter-to-area ratio (P/A), which influences both pressure gradient distribution and the density of nucleation sites. In this context, an innovative configuration based on the Reuleaux triangle is proposed, allowing for a significant increase in the P/A ratio compared to conventional circular-section devices. This theoretical study extends the Navier–Stokes and Rayleigh–Plesset models to describe bubble dynamics and assess the influence of geometric and rotational variants (VRAt) on the localization and intensity of cavitation collapse. The results suggest that optimized internal geometries can reduce treatment times, increase selectivity, and improve the overall energy efficiency of cavitation processes, offering strong potential for advanced and sustainable industrial applications. This work is entirely theoretical and is intended to support the future design and experimental validation of next-generation cavitating devices. Full article

To improve environmental sustainability and operational safety in maritime industries, the development of efficient methods for removing biofouling from submerged surfaces is critical. This study investigates the erosion mechanisms of cavitation jets as a non-contact, high-efficiency method for detaching marine organisms, including bacteria and larvae, from ship hulls and underwater infrastructure. Through erosion experiments on coated specimens, variations in jet morphology, and flow visualization using the Schlieren method, we examined how factors such as jet incident angle and nozzle configuration influence removal performance. The results reveal that erosion occurs not only at the direct jet impact zone but also in regions where cavitation bubbles exhibit intense motion, driven by pressure fluctuations and shock waves. Notably, single-hole jets with longer potential cores produced more concentrated erosion, while multi-jet interference enhanced bubble activity. These findings underscore the importance of understanding bubble distribution dynamics in the flow field and provide insight into optimizing cavitation jet configurations to expand the effective cleaning area while minimizing material damage. This study contributes to advancing biofouling removal technologies that promote safer and more sustainable maritime operations. Full article

This study investigates the performance of B-series marine propellers enhanced through geometric modifications, namely face camber ratio (FCR) and cupping percentage modifications, using a machine learning (ML)-driven optimization framework. A large dataset of over 7000 open-water propeller configurations is curated, incorporating variations in blade number, expanded area ratio (EAR), pitch-to-diameter ratio (P/D), FCR, and cupping percentage. A multi-layer artificial neural network (ANN) is trained to predict thrust, torque, and open-water efficiency (η_o) with a high coefficient of determination (R²), greater than 0.9999. The ANN is integrated into an optimization algorithm to identify optimal propeller designs for the KRISO Container Ship (KCS) using empirical constraints for cavitation and tip speed. Unlike prior studies that rely on boundary element method (BEM)-ML hybrids or multi-fidelity simulations, this study introduces a geometry-coupled analysis of FCR and cupping—parameters often treated independently—and applies empirical cavitation and acoustic (tip speed) limits to guide the design process. The results indicate that incorporating 1.0–1.5% cupping leads to a significant improvement in efficiency, up to 9.3% above the reference propeller, while maintaining cavitation safety margins and acoustic limits. Conversely, designs with non-zero FCR values (0.5–1.5%) show a modest efficiency penalty (up to 4.3%), although some configurations remain competitive when compensated by higher EAR, P/D, or blade count. The study confirms that the combination of cupping with optimized geometric parameters yields high-efficiency, cavitation-safe propellers. Furthermore, the ML-based framework demonstrates excellent potential for rapid, accurate, and scalable propeller design optimization that meets both performance and regulatory constraints. Full article

As a core component in renewable energy systems for grid regulation, hydropower units are increasingly exposed to flow conditions that elevate the risk of cavitation and erosion, posing significant challenges to the safe operation of flow-passage components. In this study, model testing and computational fluid dynamics (CFD) simulations are employed to investigate the hydraulic performance and cavitation behavior of a bulb turbine operating under rated head conditions and varying cavitation numbers. The analysis focuses on how changes in cavitation intensity affect flow characteristics and efficiency within the runner region. The results show that as the cavitation number approaches its critical value, the generation, growth, and collapse of vapor cavities increasingly disturb the main flow, causing a marked drop in blade hydraulic performance and overall turbine efficiency. Cavitation predominantly occurs on the blade’s suction side near the trailing edge rim and in the clearance zone near the hub, with bubble coverage expanding as the cavitation number decreases. A periodic inverse correlation between surface pressure and the cavitation area is observed, reflecting the strongly unsteady nature of cavitating flows. Furthermore, lower cavitation numbers lead to intensified pressure pulsations, aggravating flow unsteadiness and raising the risk of vibration. Full article

Additively manufactured (AM) parts have been applied in many areas with the risk of cavitation erosion (CE), and pores are common defects in AM metals. However, the role of pores in CE is still unclear, and a systematic investigation is needed. In this study, 316L stainless steel was selected as a model material and produced using laser powder bed fusion; the porosity was 6.4%. The morphological evolution of various pores during CE was investigated via electron backscatter diffraction and scanning electron microscopy. It was found that material removal easily occurred around large polygonal pores. The critical size for large polygonal pores was estimated to be between 13 and 20 μm. For narrow pores, concavity first appeared around the pores during CE, and then the narrow pores closed. Small spherical pores with sizes of 3–9 μm showed strong resistance to CE, and no damage occurred within the 60 min CE period. The main reason that different pores played different roles in CE was analyzed. Finally, factors for improving the CE resistance of AM metals were suggested. The research results are helpful for understanding the CE behaviors of AM metals and porous materials. Full article

Micro-nano bubbles (MNBs) are tiny bubbles with diameters ranging from 200 nm to 30 µm. They possess unique physicochemical properties such as a large specific surface area, slow rising velocity, high gas dissolution rate, high mass transfer efficiency, and strong interfacial zeta potential. These properties endow MNBs with great potential in various fields, including water treatment, enhanced oil recovery, medical and health care, and agriculture. This paper systematically reviews the physicochemical properties, generation methods, and applications of micro-nano bubbles. The main production methods include the mechanical stirring, pressurized dissolved gas release, ultrasonic cavitation, venturi injection, electrolysis, etc. The principles, advantages and disadvantages, and optimization strategies of these methods are comprehensively analyzed. In terms of applications, the mechanisms and typical cases of MNBs in enhanced oil recovery, water treatment, mineral flotation, medical drug delivery, and crop yield enhancement are thoroughly discussed. Extensive research has shown that MNB technology is highly efficient, energy-saving, and environmentally friendly. However, improving bubble stability, generation efficiency, and large-scale application remain key directions for future research. Full article

Outboard Dynamic-inlet Waterjets (ODW) are axisymmetric units, powered by a self-contained pump, that, by processing a uniform undisturbed streamtube, can operate more efficiently than conventional marine propulsors. This feature also provides methodological convenience, enabling accurate numerical investigations of the system alone using 2D axisymmetric models. Leveraging this property, the present study bridges the gap on the design principles required to tailor ODW geometries across multiple operating conditions. Reynolds-Averaged Navier Stokes (RANS) equations are solved, including turbulence and cavitation models, to draw the propulsor’s characteristic maps and identify two relevant operating points, set by the combination of a specified pump rotational regime with an advancing velocity. Simulations for these in- and off-design conditions are systematically performed over a database of 512 randomly sampled geometric variants. The corresponding results show that optimised shapes improving the inlet Pressure Recovery (PR) and nacelle drag at cruise conditions result in beneficial outcomes also at take-off operations, where lip cavitation may occur. Thus, analysing together the off-design PR and the cruise net force underscores their conflicting behaviour. In fact, while nacelles shortened by $12\%$ can reduce overall drag and enhance nominal net thrust by $2\%$, designs featuring a $34\%$ wider capture area improve off-design PR by over $1.5\%$, albeit at the cost of compromised propulsive efficiency under any operating range. Full article

Proteins have the ability to form foam, which is a system consisting of a gas phase dispersed within a continuous phase, either liquid or solid. In certain types of food, the incorporation of gas is important for maintaining quality and sensory attributes. However, foam is a thermodynamically unstable system, and its stabilization is a highly researched area. In recent years, there has been growing interest in the application of ultrasound not only to improve foaming properties, but also to alter physicochemical and structural characteristics of proteins, making it an environmentally friendly and versatile technology. Ultrasound can enhance formation and stability by inducing conformational changes through the cavitation phenomenon. However, the benefits of this technology depend on the inherent characteristics of the proteins and the conditions applied during its use, such as frequency, time, amplitude, energy, protein concentration, volume, and medium conditions. This review aims to explore how ultrasound influences the physicochemical properties, induces structural modifications, and consequently enhances functional characteristics such as foaming capacity. Full article

Background/Objectives: This study tested a method for evaluating the internal fit of indirect resin-based composite (RBC) restorations, as well as the influence of different combinations of impression and die materials on the reproducibility of the topography of teeth prepared for indirect RBC restoration. Methods: Bovine incisors received flattened and cavitated areas at the cervical and middle thirds of the buccal surface, respectively. The samples were randomly assigned to two groups according to the material used for impression taking (n = 5): irreversible hydrocolloid and polyvinyl siloxane (PVS). Die replicas were obtained with Type IV gypsum or elastomeric material. RBC restorations were fabricated through an indirect technique (test) and a direct-indirect technique as the control. The internal fit of restorations was assessed by measuring the cementation line thickness with a digital caliper (simulated cementation protocol with ultra-light PVS) and validated using scanning electron microscopy (SEM). Surface topography (Sa, Sq, and Sz) was analyzed via optical profilometry, and wettability was assessed through the water contact angle method. The data were analyzed using t-test, ANOVA, and Pearson correlation tests (α = 5%). Results: The simulated cementation resulted in internal gap values positively correlated to the values from SEM (R² = 0.958; p = 0.0102). The internal gap of restorations was not significantly correlated with the discrepancies between the topography of the die and tooth substrate (p ≥ 0.067). The combination of irreversible hydrocolloid and gypsum resulted in restorations with the lowest cementation line thickness, although in terms of roughness, this combination was the only one that resulted in significant differences from the control (p ≤ 0.028). The internal mean gap values of restorations were significantly correlated to the cumulative wettability difference of materials used during impression taking, fabrication of die replica, and restoration build-up (R² = 0.981; p = 0.003). Conclusions: The reproducibility of topographical characteristics of the tooth in the die replica did not affect the internal adaptation of indirect RBC restorations, whereas surface wettability of materials presented a more relevant effect on the overall gap formation. The simulated cementation technique tested in the study shows potential as a simpler, cost-effective, and non-destructive method for evaluating the adaptation of indirect RBC restorations. Full article

A syndrome called “Kiwifruit Decline Syndrome” (KiDS) affects kiwifruit in several Mediterranean areas, causing growth arrest and wilt that rapidly progress to desiccation, scarce root growth, absence of fibrous roots, brown soft-rotting areas, and cortical detachment from the central cylinder. The origin is considered multifactorial, and a correlation with hydraulic conductance impairment caused by a high vapor pressure deficit (VPD) and temperature was detected. In this work, over-tree micro-sprinkler irrigation and shading nets were tested to protect leaves from overheating and locally decrease VPD. Leaf gas exchanges, leaf temperature, stem water potential, stem growth, root starch content, root xylem vessel diameter, density, and vulnerability to cavitation were assessed. A positive effect of over-tree irrigation associated with shading was observed: lower leaf temperature, higher stem water potential, stomatal conductance, and photosynthesis were detected; moreover, root starch content was higher in the summer. Narrow xylem vessel diameters were observed, indicating a long-term adaptation to rising VPD for lower vulnerability to cavitation, in all plants, but higher diameter, lower density, and higher vulnerability index indicated lower plant water stress under over-tree irrigation associated with shading. These results indicate that microclimate control by proper agronomic management can protect kiwifruit from climate stress, decreasing the risk of KiDS onset. Full article

Pump station engineering is extensively utilized in water supply and drainage, as well as agricultural irrigation. Due to its geographical advantages and significant comprehensive benefits, the construction of pumping stations in coastal areas has gained substantial attention in recent years. Adverse flow conditions caused by various factors negatively affect the inlet flow regime of pumps, becoming a key factor that restricts the operating life and further development of pump station systems. Optimizing the flow regime in the forebay is crucial for enhancing overall engineering quality, minimizing pump performance degradation, and reducing the risks of cavitation and vibration. This study investigates the flow characteristics of the forebay by combining the Navier–Stokes equations and the $k-\epsilon$ RNG turbulence model. The analysis focuses on the internal flow field, transverse flow before the inlet channel, and the uniformity of flow velocity distribution after the inlet channel. Numerical simulations are validated through physical model tests. We examine the flow characteristics in the forebay, analyze the causes of internal flow disorder, and propose a reasonable and practical rectification scheme for the forebay. Additionally, we elucidate the mechanism of flow state optimization through partition walls. The findings indicate that with the optimal partition wall length, the average elimination rate of transverse flow velocity before the pump station inlet channel reached 48.3%, and the uniformity of flow velocity distribution after the inlet increased by 3.24%. These research findings contribute to mitigating cavitation and vibration in water pump units, providing theoretical support for the safe operation of coastal pumping stations. Full article

Copper and its alloys are widely used in marine environments due to their excellent corrosion resistance and thermal conductivity. Cold spray technology can avoid the thermal damage to the underlying material and is suitable for the manufacturing and repair of parts. In this study, Cu coatings were prepared on 304 stainless steel substrates by high-pressure cold spray technology, and the effects of cold spray parameters on the microstructure, mechanical properties, and cavitation resistance were investigated. The coatings (Cu-N₂1, Cu-N₂2, and Cu-He) were prepared using distinct cold spray parameters: Cu-N₂1 and Cu-N₂2 employed nitrogen gas at 5 MPa/800 °C with different nozzle geometries, while Cu-He utilized helium gas at 3 MPa/600 °C. The results show that the porosity of the Cu coating prepared by cold spray technology is less than 0.1%. The coating treated with helium gas exhibits a higher bonding strength (81.3 MPa), whereas the coating treated with nitrogen demonstrates greater strain hardening (130–136 HV_0.1). XRD results show that no phase change or oxidation occurred for coatings under all cold spraying conditions. After the cavitation test, the mass loss of the Cu coating is significantly less than that of the as-cast copper. The Cu coating surface first develops holes, and with the increase in cavitation time, the hole area begins to increase. However, with prolonged cavitation exposure, the surface of as-cast copper has a large area of holes, and with the increase in cavitation time, the hole growth rate is faster. These observations indicate the cavitation resistance of the Cu coating prepared by cold spray is more than 10 times higher than that of the as-cast copper. This study highlights the potential application of cold spray technology in the preparation of high-performance anti-cavitation copper coatings. Full article

Cavitation is a critical phenomenon in hydraulic systems, particularly in gear pumps, where it can significantly affect performance and reliability. This study uses numerical simulations with the Full Cavitation Model and k-ε turbulence model to investigate the thermodynamic effects of cavitation in gear pump lubricating oil at varying temperatures. It focuses on the formation and evolution of cavitation vortex structures in the outlet bridge area. The simulations reveal significant heat exchange between liquid and vapor phases, causing a local temperature drop and a reduction in saturated vapor pressure, which suppresses cavitation development. As temperature increases, this effect diminishes due to the lower density of the hydraulic oil. Full article

The enzymatic hydrolysis of lignocellulosic biomass is often hindered by lignin, which acts as a physical barrier and promotes non-productive enzyme adsorption. This study evaluated the potential of soybean protein in powdered and cavitated forms, along with lactonic sophorolipid biosurfactant (LSLB), to enhance sugar yields from cellulignin derived from sugarcane bagasse, a residue with a high lignin content. A Box–Behnken design was used to investigate the effects of enzyme loading (10–20 FPU/g cellulignin), soybean protein powder (10–30% w/w of dried cellulignin), and LSLB concentration (25–250 mg/L) on glucose and xylose yields. Hydrodynamic cavitation was employed to produce soluble soybean protein, achieving a solubility yield of 44.4% w/w in 10 min. The cavitated protein was compared with powdered protein to assess its impact on enzymatic hydrolysis efficiency. The results showed that hydrodynamic cavitation reduced the required SBP dosage while maintaining sugar yields, allowing 10% w/w of dried cellulignin cavitated SBP to achieve glucose and xylose yields comparable to 25% w/w of dried cellulignin non-cavitated SBP. Specifically, glucose yield increased by 24.92% (from 34.1% ± 1.01 to 42.6% ± 1.4), and xylose yield by 30.86% (from 32.4% ± 0.53 to 42.4% ± 2.21) compared to the no-additive condition. These improvements were linked to enhanced solubility, increased surface area, and reduced particle size in the cavitated protein. This study highlights hydrodynamic cavitation as a novel approach for modifying soybean protein structure to optimize enzymatic hydrolysis in lignocellulosic bioconversion. Full article