Search Results (7,179)

This article theoretically investigates the interaction of a normal shock wave in a flow with chemical reactions under high-temperature conditions. The main novelty of the work is that the thermal effect of chemical reactions is modeled as a function of the temperature. A modified Rankine–Hugoniot model for a shock wave in a flow with chemical reactions has been developed. It is shown that for an exothermic reaction the pressure jump increases with increasing Arrhenius numbers. This is due to the additional energy introduced into the flow as heat is released during the chemical reaction. For endothermic reactions, the opposite trend is observed. The change in the speed of the adiabatic gas flow as it passes through a normal shock wave depending on the type of chemical reaction is clarified. The study provides comparisons between the results of the analytical and numerical solutions of the modified Hugoniot adiabatic equations. Full article

The mechanical and hydrodynamic characteristics of single-piece nets are key to the design and optimization of offshore aquaculture net cages. A numerical approach for offshore submerged aquaculture net materials based on the Morison equations and finite element is proposed, simulating the hydrodynamic characteristics of single-piece nets under varying parameters such as wire diameter, mesh size, and flow velocity, and simulating the impact of marine organism attachment on nets by modifying the drag coefficient. The simulation results of nets made from materials such as Copper–Zinc Alloy (Cu-Zn), Zinc–Aluminum Alloy (Zn-Al), Semi-Rigid Polyethylene Terephthalate (PET), and Ultra-High Molecular Weight Polyethylene (UHMWPE) are compared, which provides a theoretical basis for optimizing design parameters and selecting materials for nets based on force conditions and hydrodynamic characteristics. The simulation results indicate that the current force on the net is positively correlated with flow velocity; the maximum displacement of the net is also positively correlated with the flow rate. Compared to other materials, the Cu-Zn net is subjected to the greatest water flow force, while the UHMWPE net experiences the greatest displacement; the larger the diameter of the netting twine, the greater the current force on the net; the mesh size is inversely related to the current force on the net. With increasing drag coefficient, both the maximum displacement of the net and the current force experiences increase, and UHMWPE material nets are more sensitive to increases in the drag coefficient, which indicates a greater impact from the attachment of marine organisms. The density and elastic modulus of the netting material affect the rate of increase in force on the net. The research results can provide a basis for further research on material selection and design of deep-sea aquaculture nets. Full article

Freshwater shortages in coastal regions are intensifying due to rapid urbanisation, economic growth, and climate variability, particularly in deltaic areas where rivers meet the sea. This study evaluates the feasibility of implementing a Coastal Reservoir (CR) as an innovative solution to increase freshwater availability without relying on desalination. Using the Brisbane River Estuary (BRE), Australia, as a case study, the research examines critical factors such as freshwater inflow, seawater intrusion, and reservoir volume requirements. A three-dimensional hydrodynamic model (MIKE 3) was calibrated and validated using observed data from the 2008 and 2011 flow events. Simulation results indicate that a freshwater discharge of 150 m³/s during a spring-neap tidal cycle effectively pushes saline water out of the estuary. The CR can store 300 GL/year of freshwater with 92% reliability, meeting Southeast Queensland’s (SEQ) annual water demand of 440 GL during drought conditions combined with existing infrastructure. During its initial filling phase, the CR can flush 95% of saltwater within 240 days, using a steady inflow of 150 m³/s. The findings demonstrate the technical feasibility of CRs as a sustainable and practical water management strategy for mitigating freshwater shortages in BRE and other similar coastal regions. Full article

Geometrical optics stability analysis has proven effective in deriving analytical instability criteria for 3D flows in ideal hydrodynamics and magnetohydrodynamics, encompassing both compressible and incompressible fluids. The method models perturbations as high-frequency wavelets, evolving along fluid trajectories. Detecting local instabilities reduces to solving ODEs for the wave vector and amplitude of the wavelet envelope along streamlines, with coefficients derived from the background flow. While viscosity and diffusivity were traditionally regarded as stabilizing factors, recent extensions of the geometrical optics framework have revealed their destabilizing potential in visco-diffusive and multi-diffusive flows. This review highlights these advancements, with a focus on their application to the azimuthal magnetorotational instability in magnetohydrodynamics and the McIntyre instability in lenticular vortices and swirling differentially heated flows. It introduces new analytical instability criteria, applicable across a wide range of Prandtl, Schmidt, and magnetic Prandtl numbers, which still remains beyond the reach of numerical methods in many important physical and industrial applications. Full article

The Münchberg Gneiss Complex (Central European Variscides, Germany) is separated by a deep-seated lineamentary fault zone, the Franconian Lineamentary Fault Zone, from its Mesozoic foreland. The study area offers insight into a great variety of landforms created by fluvial and mass wasting processes together with their bedrocks, covering the full range from unmetamorphosed sediments to high-grade regionally metamorphic rocks. It renders the region an ideal place to conduct a study of compositional and numerical geomorphology and their landscape-forming indices and parameters. The landforms under consideration are sculpted out of the bedrocks (erosional landforms) and overlain by depositional landforms which are discussed by means of numerical landform indices (LFIs), all of which are coined for the first time in the current paper. They are designed to be suitable for applied geosciences such as extractive/economic geology as well as environmental geology. The erosional landform series are subdivided into three categories: (1) The landscape roughness indices, e.g., VeSi_val (vertical sinuosity—valley of landform series) and the VaSlAn_alti (variation in slope angle altitude), which are used for a first order classification of landscapes into relief generations. The second order classification LFIs are devoted to the material properties of the landforms’ bedrocks, such as the rock strength (VeSi_lith) and the bedrock anisotropy (VaSlAn_norm). The third order scheme describes the hydrography as to its vertical changes by the inclination of the talweg and the different types of knickpoints (IncTal_lith/grad) and horizontal sinuosity (HoSi_lith/grad). The study area is subjected to a tripartite zonation into the headwater zone, synonymous with the paleoplain which undergoes some dissection at its edge, the step-fault plain representative of the track zone which undergoes widespread fluvial piracy, and the foreland plains which act as an intermediate sedimentary trap named the deposition zone. The area can be described in space and time with these landform indices reflecting fluvial and mass wasting processes operative in four different stages (around 17 Ma, 6 to 4 Ma, <1.7 Ma, and <0.4 Ma). The various groups of LFIs are a function of landscape maturity (pre-mature, mature, and super-mature). The depositional landforms are numerically defined in the same way and only differ from each other by their subscripts. Their set of LFIs is a mirror image of the composition of depositional landforms in relation to their grain size. The leading part of the acronym, such as QuantSan_heav and QuantGrav_lith, refers to the process of quantification, the second part to the grain size, such as sand and gravel, and the subscript to the material, such as heavy minerals or lithological fragments. The three numerical indices applicable to depositional landforms are a direct measurement of the hydrodynamic and gravity-driven conditions of the fluvial and mass wasting processes using granulometry, grain morphology, and situmetry (clast orientation). Together with the previous compositional indices, the latter directly translate into the provenance analysis which can be used for environmental analyses and as a tool for mineral exploration. It creates a network between numerical geomorphology, geomorphometry, and the E&E issue disciplines (economic/extractive geology vs. environmental geology). The linguistics of the LFIs adopted in this publication are designed so as to be open for individual amendments by the reader. An easy adaptation to different landform suites worldwide, irrespective of their climatic conditions, geodynamic setting, and age of formation, is feasible due to the use of a software and a database available on a global basis. Full article

In this study, we report the synthesis of amphiphilic hyperbranched poly[(2-dimethylaminoethyl methacrylate)-co-(benzyl methacrylate)] statistical copolymers with two different stoichiometric compositions using the reversible addition–fragmentation chain transfer polymerization (RAFT) technique. The selection of monomers was made to incorporate a pH and thermoresponsive polyelectrolyte (DMAEMA) component and a hydrophobic component (BzMA) to achieve amphiphilicity and study the effects of architecture and environmental factors on the behavior of the novel branched copolymers. Molecular characterization was performed through size exclusion chromatography (SEC) and spectroscopic characterization techniques (¹H-NMR and FT-IR). The self-assembly behavior of the hyperbranched copolymers in aqueous media, in response to variations in pH, temperature, and ionic strength, was studied using dynamic light scattering (DLS), electrophoretic light scattering (ELS), and fluorescence spectroscopy (FS). Finally, the efficacy of the two novel copolymers to encapsulate curcumin (CUR), a hydrophobic, polyphenolic drug with proven anti-inflammatory and fluorescence properties, was established. Its encapsulation was evaluated through DLS, UV–Vis, and fluorescence measurements, investigating the change of hydrodynamic radius of the produced mixed copolymer–CUR nanoparticles in each case and their fluorescence emission properties. Full article

Flow around clustered cylinders is widely encountered in engineering applications such as wind energy systems, pipeline transport, and marine engineering. To investigate the hydrodynamic performance and vortex dynamics of multiple cylinders under forced vibration at low Reynolds numbers, with a focus on understanding the interference characteristics in various configurations, this study is based on a self-developed radial basis function iso-surface ghost cell computing platform, which improves the implicit iso-surface interface representation method to track the moving boundaries of multiple cylinders, and employs a self-constructed CPU/GPU heterogeneous parallel acceleration technique for efficient numerical simulations. This study systematically investigates the interference characteristics of multiple cylinder configurations across various parameter domains, including spacing ratios, geometric arrangements, and oscillation modes. A quantitative analysis of key parameters, such as aerodynamic coefficients, dimensionless frequency characteristics, and vorticity field evolution, is performed. This study reveals that, for a dual-cylinder system, there exists a critical gap ratio between X/D = 2.5 and 3, which leads to an increase in the lift and drag coefficients of both cylinders, a reduction in the vortex shedding periodicity, and a disruption of the wake structure. For a three-cylinder system, the lift and drag coefficients of the two upstream cylinders decrease with increasing spacing. On the other hand, this increased spacing results in a rise in the drag of the downstream cylinder. In the case of a four-cylinder system, the drag coefficients of the cylinders located on either side of the flow direction are relatively high. A significant increase in the lift coefficient occurs when the spacing ratio is less than 2.0, while the drag coefficient of the downstream cylinder is minimized. The findings establish a comprehensive theoretical framework for the optimal configuration design and structural optimization of multicylinder systems, while also providing practical guidelines for engineering applications. Full article

The stability of deep-sea aquaculture equipment under extreme sea conditions such as typhoons directly affects the safety and operational reliability of the aquaculture platform, which in turn affects the economic benefits of fish farming. Therefore, it is particularly important to systematically analyze the hydrodynamic response of aquaculture facilities using numerical methods. This paper employs the hydrodynamic analysis software AQWA, integrating the boundary element method of three-dimensional potential flow theory with the Morison equation, to conduct hydrodynamic research on a flip-type aquaculture platform. The calculations include the platform’s amplitude response operators (RAOs), added mass, as well as motion responses and mooring line tensions under extreme sea conditions. The results indicate that the platform’s sway, surge, and heave motions are highly sensitive to wave frequency in the low-frequency range, with a significant resonance phenomenon occurring at a wave frequency of 0.84 Hz. The main wind and wave responses of the platform manifest as surge and roll motions. To address this issue, it is recommended to add additional anchor chains on the short sides of the platform to effectively reduce the amplitude of surge and roll motions. Furthermore, under extreme sea conditions when the platform faces the windward waves on the short side, its motion response frequency is lower than when facing the windward waves on the long side, but the difference in response amplitude between the two conditions is small. Full article

With the urgent demand for net-zero emissions, renewable energy is taking the lead and wind power is becoming increasingly important. Among the most promising sources, offshore wind energy located in deep water has gained significant attention. This review focuses on the experimental methods, simulation approaches, and wake characteristics of floating offshore wind turbines (FOWTs). The hydrodynamics and aerodynamics of FOWTs are not isolated and they interact with each other. Under the environmental load and mooring force, the floating platform has six degrees of freedom motions, which bring the changes in the relative wind speed to the turbine rotor, and furthermore, to the turbine aerodynamics. Then, the platform’s movements lead to a complex FOWT wake evolution, including wake recovery acceleration, velocity deficit fluctuations, wake deformation and wake meandering. In scale FOWT tests, it is challenging to simultaneously satisfy Reynolds number and Froude number similarity, resulting in gaps between scale model experiments and field measurements. Recently, progress has been made in scale model experiments; furthermore, a “Hardware in the loop” technique has been developed as an effective solution to the above contradiction. In numerical simulations, the coupling of hydrodynamics and aerodynamics is the concern and a typical numerical simulation of multi-body and multi-physical coupling is reviewed in this paper. Furthermore, recent advancements have been made in the analysis of wake characteristics, such as the application of instability theory and modal decomposition techniques in the study of FOWT wake evolution. These studies have revealed the formation of vortex rings and leapfrogging behavior in adjacent helical vortices, which deepens the understanding of the FOWT wake. Overall, this paper provides a comprehensive review of recent research on FOWT wake dynamics. Full article

Oscillating water column (OWC) wave energy converters (WECs) are very popular types of wave energy converters due to their practical implementations, their versatility in deployment in different marine environments, and their high reliability in wave energy conversion. In development, different forms of OWCs have been proposed and advanced, such as fixed OWCs (on the shoreline, on breakwaters, or bottom standing) and floating OWCs (the spar and the backward-bent duct buoy, BBDB). In reality, a special type of OWC, the cylindrical OWC, is the simplest OWC in terms of its structural design and possible analytical/numerical solutions. However, such a simple OWC has not seen any practical applications because a cylindrical OWC is inefficient in wave energy absorption when compared to other types of OWC WECs. To study the simplest cylindric OWC, an experiment was carried out in a wave tank, and the relevant results are presented in this paper, with the aims of (i) analyzing the experimental data and exploring why such an OWC is inefficient in terms of wave energy absorption; (ii) providing experimental data for those who want experimental data to validate their numerical models; and (iii) establishing a baseline model so that comparisons can be made for improvements to the simple cylindrical OWC. As an example, an innovative solution was applied to the simple OWC such that its hydrodynamics and energy extraction performance can be significantly improved (the corresponding results will be presented in a separate paper). Full article

While submissions of microfluidic-based medical devices to the Food and Drug Administration (FDA) have increased in recent years, leakage remains a common but difficult failure mode to detect in microfluidic systems. Here, we have developed a sensitive tool to measure and verify leakages ranging from 0.1% to 10% in leakage detection systems, which can then be used to detect leak in microfluidic devices. Our methodology includes an analytical model that applies hydrodynamic resistance using different fluid-contacting elements (e.g., tubing, junctions, and connectors) to tune the leakage rate based on the application-specific acceptance criteria. We then used three polymer-based microfluidic systems to target leakage rates of approximately 0.1, 1.0, and 10%. The experimental uncertainties in Polyether Ether Ketone (PEEK) tubing were 23.08%, 13.64%, and 1.16%, respectively, while the PEEK-Coated Fused Silica (PEEKsil) tubing system had errors of 0.00%, 0.72%, and 1.59%, respectively, relative to the theoretical values for the same target leak rates. The commonly used commercial grade Cyclic Olefin Copolymer (COC) microfluidic chips produced errors of 7.69% and 5.05%, respectively, for target leakage rates of 0.24% and 1.88%. We anticipate that the proposed bench test method can be useful for device developers as a verification tool for leakage detection systems before assessing flow-mediated leakage failure modes in microfluidic medical devices. Full article

When an ice-class propeller is operating in an ice-covered environment, as some ice blocks slide along the ship hull in front of the propeller blades, the inflow ahead of the propeller will become non-uniform. Consequently, the excitation force applied to the blades will increase and massive cavitation bubbles will be generated. In this paper, a hybrid Reynolds-Averaged Navier–Stokes/Large Eddy Simulation method and Schnerr–Sauer cavitation model are used to investigate the hydrodynamics, excitation force, cavitation evolution and flow field characteristics of the propeller in ice blockage conditions. The results show that the numerical method adopted has a relatively high accuracy and the hydrodynamic error is controlled within 3.0%. At low cavitation numbers, although the blockage distance decreases, the cavitation phenomenon is still severe and the hydrodynamic coefficients hardly increase accordingly. Ice blockage causes a sharp increase in cavitation. When the distance is 0.15 times the diameter, the cavitation area amounts to 20% of the propeller blades. As the advance coefficient grows, the total cavitation area diminishes, while the cavitation area of the blade behind ice does not decrease, resulting in an increment in excitation force. Ice blockage also causes backflow in the wake. At this time, the largest backflow appears at the tip of the blade behind the ice. The higher the advance coefficient, the more significant the high-pressure area of the pressure side and the greater the pressure difference, causing the excitation force to rise sharply. This work offers a positive theoretical basis for the anti-cavitation design and excitation force suppression of propellers operating in icy regions. Full article

This study investigated the influence of parameters such as pH condition, polyelectrolyte concentration, polymer ratio, and order of addition of the commercial polyelectrolytes chitosan and iota-carrageenan (ι-carrageenan) on the formation of polymeric nanoparticles in suspension (coacervates). A preliminary purification step of the polymers was essential for obtaining stable nanoparticles with small sizes as impurities, particularly metal ions that interfere with complexation, are removed by dialysis. Microparticles (13.5 μm in dry diameter) are obtained when aliquots of chitosan solution are poured into the ι-carrageenan solution. In general, an excess of chitosan results in the formation of agglomerated particles. The addition of an aliquot of ι-carrageenan solution (30 mL at 0.6 mg/mL and pH 4.0) to the chitosan solution (6.0 mL at 0.3 mg/mL and pH 4.0) leads to dispersed nanoparticles with a hydrodynamic radius of 278 ± 5 nm, a zeta potential of −31 ± 3 mV, and an average dry diameter of 45 ± 11 nm. The hydrodynamic radius increases as the pH rises. The partial deprotonation of ι-carrageenan chains enhances the interaction with water molecules, causing the particles to swell. These findings contribute to the fundamental understanding of polyelectrolyte complexation processes in aqueous suspension and provide insights for developing stable nanomaterials for potential practical applications. Full article

Cilostazol (CIL), a BCS class II antiplatelet aggregation and vasodilator agent, is used for cerebrovascular diseases to minimize blood–brain barrier dysfunction, white matter-lesion formation, and motor deficits. The current work aimed to develop and optimize cilostazol-loaded spanlastics (CIL-SPA) for nose-to-brain delivery to overcome the low solubility and absorption, the first pass-metabolism, and the adverse effects. The optimal CIL-SPA formulation was loaded into Phytagel^® (SPA-PG), Poloxamer-407 (SPA-P407), and chitosan (SPA-CS) gel bases and characterized in terms of colloidal properties, encapsulation efficiency (EE%), mucoadhesive properties, and biopharmaceutical aspects. The developed in situ gelling formulations showed a <300 nm average hydrodynamic diameter, <0.5 polydispersity index, and >|±30| mV zeta potential with a high EE% (>99%). All formulations met the droplet size-distribution criteria of nasal requirements (<200 µm), and all formulations showed adequate mucoadhesion properties. Both the BBB-PAMPA and horizontal permeability study through an artificial membrane revealed that all formulations had higher CIL flux and cumulative permeability at in vitro nose-to-brain conditions compared to the initial CIL. The in vitro drug-release study showed that all formulations released ca. 100% of CIL after 2 h. Therefore, the developed formulations could be promising for improving the low bioavailability of CIL through nose-to-brain delivery. Full article

Hydropower stations and dams play a crucial role in water management, ecology, and energy. To meet the requirements of underwater dam defect detection, this study develops a streamlined underwater vehicle design and operational framework inspired by bionic principles. A parametric modeling approach was employed to propose the vehicle’s streamlined configuration. Using CFD simulations, hydrodynamic coefficients were calculated and validated through towing experiments in a pool. The hydrodynamic stability of the vehicle was assessed and verified through these analyses. Additionally, various configurations were generated using a free deformation method. An optimization function was established with resistance and stability as the objectives, and the optimal result was derived based on the function’s calculation outcomes. The study designed a high-metacentric underwater vehicle, inspired by the seahorse’s shape, and introduced a novel stability evaluation method. Simulations were conducted to analyze the vehicle’s variable attack angle, drift angle, pitching, and rotational motion at a forward three-throttle speed. The results demonstrate that the vehicle achieves static stability in both the horizontal and vertical planes, as well as dynamic stability in the vertical plane, but exhibits limited dynamic stability in the horizontal plane. After optimizing the original configuration, the forward resistance was reduced by 2.15%, while the horizontal plane dynamic stability criterion C_H was improved by 35.29%. Full article