Immersion Ratios Research Articles

Fluid-structure interaction analysis of an elastic surface-piercing propellers

In high-speed planing craft, surface-piercing propellers (SPPs) operate semi-submerged in a two-phase air-water environment, facing stress and displacement from variable forces. In this paper, the fluid-structure interaction (FSI) of the SPP is investigated at immersion ratios of 30 %, 50 %, 70 % and 90 %, under low and high advance coefficients. A coupling of Reynolds-averaged Navier–Stokes equations (RANS) and elasticity theory are used to simulate fluid dynamics and the blade deformation with the multi-physics computational fluid dynamics software STAR-CCM+. The analysis is performed after several rotations of the SPPs at five different positions. The results show that at the advance coefficient of 0.4, a higher immersion ratio increases torque, thrust, efficiency, maximum stress, and maximum displacement. When the advance coefficient is equal to one, the efficiency, maximum stress, and maximum displacement remain constant for the immersion ratio above 50 %. The maximum displacement occurs at the blade tip, while maximum stress is at the trailing edge root. Most blade deformations happen where the blade enters the water, aligns perpendicularly with the water surface, and exits. The two-phase flow around the blade increases its displacement.

Structural Quality Factor of Flo-TENG under Stochastic Wave Excitation.

Triboelectric nanogenerators (TENGs) have recently emerged as a promising technology for efficient water wave energy harvesting. However, there is a paucity of clear guidance regarding the optimal designs of TENGs and their shells to achieve efficient absorption and conversion of water wave energy in real random waves. Herein, from the perspective of wave-body interaction and energy transfer, this paper proposes a structural quality factor (Qunit) for the quantitative evaluation of both the motion of floating triboelectric nanogenerator (Flo-TENG) shells and their capability to absorb and convert water wave energy efficiently. The factor is further subdivided into the amplitude structural quality factor (Qacc), which characterizes shell motion amplitude, and the frequency structural quality factor (Qf), which describes shell motion frequency. This paper systematically investigates the impact of various shell parameters such as bow shapes, curvatures, inclinations, and immersion ratios on Qacc and Qf. The findings indicate that variations in shell shape result in distinct Qunit values along different axial directions of wave propagation. These variations directly influence energy absorption efficiency in these directions. These results provide fundamental guidance for the design of high-performance Flo-TENG shells and the selection of internal energy harvesting directions to enable more efficient energy conversion.

Effect of Hydrostatic and Hydrodynamic Pressures on the Stability of Landfill Veneer Covers with an Internal Seeper

The accumulated water in the drainage layer of the municipal solid waste landfill veneer cover system becomes the principal cause of the failure of landfill cover. In this study, seismic stability evaluation is carried out using the pseudostatic approach considering direct sliding and uplifted floating failures. The factors of safety against direct sliding failure (FSds) and uplifted floating failure (FSuf) are estimated considering hydrostatic and hydrodynamic pressures. Hydrodynamic pressures acting along the failure planes are computed using Westergaard’s theory. The different cases based on the height of accumulated seepage levels in the drainage layer (hw) are considered in the analysis. The angle of the sliding plane (ψ) for direct sliding failure and the failure ratio (Ω) for the uplifted floating failure are evaluated to determine the critical values of FSds and FSuf. It is observed that the immersion ratio (Ir) is the most important parameter that significantly affects the factor of safety against both failure modes (FSds and FSuf) under seismic loading. The results of the present study under static loading are compared with the available results in the literature. The effects of the slope angle (θ), the ratio of the thickness of the cover soil layer to the height of the landfill (h/H), the stability number (c/γsatH), the horizontal seismic acceleration coefficient (kh), and the ratio of vertical to horizontal seismic acceleration coefficients (kv/kh) on FSds and FSuf are presented for different values of immersion ratios (Ir). The magnitude and the direction of seismic inertia forces also govern the factor of safety values against both direct sliding and uplifted floating failure modes. The design charts are established to estimate the allowable thickness of the cover soil layer (h) for different values of immersion ratios by targeting the factors of safety, FSds and FSuf ≥ 1.15. This condition ensures the safety of the landfill veneer cover system against direct sliding and uplifted floating failures simultaneously.

Effect of Aeration Flow Rate on Improvement of Surface-Piercing Propellers Performance

The Surface-Piercing propeller blades move in and out of the water with each rotation to reduce the immersion depth from the free surface to the shaft axis . The main challenge facing surface piercing propellers, however, is their lower efficiency at lower advance velocity, compared to other propulsion systems. To improve the performance of the propeller, an aeration mechanism was used at low advance velocities so that air was blown to the surface behind the propeller. Experimental studies were carried out on a propeller model in the Hydrotech laboratory of the Iran University of Science and Technology, and the effect of the injected air velocity ratio was evaluated at different immersion ratios. Based on the results obtained, it was concluded that an increase in the injected air velocity ratio could only promote thrust enhancement under specific conditions. For immersion ratios of 0.85 and more, as well as advance coefficients of 0.6 and more, a change in the velocity ratio of the injected air could not lead to an improvement in thrust. The best performance was identified with an immersion ratio of 0.4 and an advance coefficient of 0.4, while thrust performance at below or above of this condition declined .

Flow characteristics comparison of PIV and numerical prediction results for an unmanned underwater vehicle positioned close to the free surface

In the present paper, flow characteristics of an Unmanned Underwater Vehicle (UUV) with a commonly used Myring profile were investigated numerically and experimentally using Computational Fluid Dynamics (CFD) and the Particle Image Velocimetry (PIV) technique under the influence of free surface. The 3-D and two-phase flow simulation generated using the Volume of Fluid (VOF) were carried out using the Large Eddy Simulation (LES) turbulence model for high accuracy in both near free-surface and almost uniform flow conditions. Due to the presence of the free-surface effect, dynamics and unsteady instantaneous flow characteristics such as force and moment coefficients, streamlines topology, and pressure values on the body surface along with vorticity structures were found to be very chaotic and have irregular motion in the wake while the followable variation trend of the time-averaged properties was obtained to show critical immersion ratio. The immersion ratios of 0.75≤ h/D≤3.50 were examined at Reynolds numbers Re = 2.0 × 104 and 4.0 × 104. Jet-like flow between the UUV body and the free surface of the water was detected at the immersion ratio of h/D = 0.75, which caused a substantial asymmetry in flow structures, resulting in highest drag and lift values. Increased surface disturbance at Re = 4.0 × 104 caused air introduction into via jet-like flow in h/D = 0.75, which caused positive lift. Hydrodynamic coefficients and isosurfaces shown that the free-surface effect decreased significantly up to h/D = 1.50 at constant Reynolds numbers. Further investigation of time-averaged velocity components, streamlines, vorticity and turbulence statistics revealed that h/D = 1.50 acted as a transitional immersion ratio as the flow structure changed significantly with Reynolds numbers. The utilized CFD approach yielded especially excellent agreement with the PIV measurements with the discrepancy which varies from 1% to 15% in near wake for streamwise velocity components to simulate the essential unmeasured flow features needed in the research and development process of UUVs when they move below the free surface.

Theoretical Investigation Applied to Scattering Water Waves by Rectangular Submerged Obstacles/and Submarine Trenches

A simple analytical model is presented in this work to investigate reflection coefficients due to the interactions of waves with rectangular submerged obstacles/and submarine trenches. Our intention in this work is to present a simple analytical model to simulate and study water-wave scattering by evaluating reflection coefficients. Further, our challenge is to present an analytical model that can easily investigate simultaneously the effects of rectangular submerged obstacles/and submarine trenches on wave scattering. Furthermore, reflection coefficients are investigated for different immersion ratios and relative lengths simultaneously for submarine trenches/and rectangular submerged obstacles. In addition, to ensure the validity of the presented model, our results are well compared with those of the literature. Finally, a comparison of reflection coefficients associated with the interactions of waves with rectangular submerged obstacles/and submarine trenches are presented to investigate the most efficient breakwater, and to highlight the importance of the presented model.

Ultimate Load of Different Types of Reinforced Self-Compacting Concrete Columns Attacked by Sulphate

In this study, the effects of the partial immersion of sulphate attack on the ultimate load capacity of reinforced self-compacting concrete (SCC) columns and the sulphate attack resistance improvement using silica fume, steel fibres, and the combination of silica fume and steel fibres were assessed. Twelve short circular self-compacting reinforced concrete columns (0.150 m in diameter and 0.7 m long) were cast and divided into groups according to (1) the three acid-attack groups. The first group was tested without an acid attack (control). The second group was tested after 1 month of exposure to 2% acid. The final group was tested after 1 month of exposure to 4% acid and was then (2) subdivided according to the type of casted concrete. The first group was cast with SCC. The second group was cast with SCC and silica fume (0.1% of the cement weight). The third group was cast with SCC and 1% volume fraction steel fibres. The fourth group was cast with SCC silica fume and 1% volume fraction steel fibre. All columns were tested by axial loading. The ultimate load was increased by 42% with silica fume, 190% with steel fibres, and 238% with silica fume and steel fibres. Exposure to 2% and 4% acid reduced the ultimate loads of the columns casted with SCC by 23% and 47%, the columns casted with SCC and silica fume by 34% and 37%, the columns casted with SCC and steel fibres by 69% and 78%, and the columns casted with SCC, silica fume, and steel fibres by 72% and 79%, respectively. Based on the results, using silica fumes improved sulphate resistance, and using steel fibres enhanced sulphate resistance at an acceptable ratio. Furthermore, the mix with silica fume and steel fibres improved sulphate resistance at a good ratio. We encountered several problems in this study. The partial immersion of sulphate affected the strain in both concrete and steel. Future studies using different immersion ratios are recommended. Doi: 10.28991/CEJ-2022-08-10-04 Full Text: PDF

CFD를 이용한 덕트 프로펠러의 자유수면 영향도 연구

The influence of free surface for the ducted propeller was investigated based on the numerical simulation in this paper. The ducted propeller consists of a duct with 19A section and the KA4-70 propeller. The immersion ratio was defined as the non-dimensional value between the distance from propeller axis to free surface and diameter of propeller. In this study, 4 immersion ratios were considered as 0.75, 1, 1.25, and 1.5, and the results from each condition were compared to those of fully immersed condition, respectively. As the immersion ratio is decreased, the total thrust and torque of the ducted propeller tend to be decreased, in particular, the portion of thrust reduction on the duct was greater than that of the propeller. It was observed that the pressure on duct is asymmetrically distributed due to the effect of free surface, on the contrary, it is axis-symmetrical in fully immersed condition. And the free surface behind the ducted propeller system is observed in the shape of “V”. As the immersion ratio decreases, the difference between crest and though of free surface was increased.

Analysis of Attack Angle Effect on Flow Characteristics Around Torpedo-Like Geometry Placed Near the Free-Surface via CFD

In this study, the flow characteristics of torpedo-like geometry placed near the free-surface at various angles of attack were investigated numerically. The study was carried out at the Reynolds number of Re=4x104 between immersion ratios of 0.75≤h/D≤3.5 and angles of attack α=0°,4°, 8°, and 12°. Large Eddy Simulation (LES) turbulence model was used along with the Volume of Fluid (VOF) multiphase model to investigate the effects of free-surface. Wake region had an asymmetrical structure near the free-surface as a result of the interaction. A jet-like flow region was observed between the geometry and the free-surface at lower immersion ratios due to the restriction of the flow area. This flow region had a downward movement towards the lower pressure wake region. The drag coefficient, CD, values were increased with the decrease of immersion ratio. At angles of attack α=8° and 12°, the flow separation occurring near the nose caused an additional restriction in the flow area and directed the jet-like flow toward free-surface. Variation of Froude numbers (Fr) depending on the immersion ratio is examined, and it is found that Fr number and corresponding drag coefficient have higher values for the lower immersion ratio. The free-surface effect was found negligible at h/D≥2.5 for all cases.

Analytical and Numerical Investigations Applied to Study the Reflections and Transmissions of a Rectangular Breakwater Placed at the Bottom of a Wave Tank

The purpose of the work presented in this paper is to study the reflection and transmission coefficients resulting from the interactions of regular waves with a rectangular breakwater sited at the bottom of a tank. The present investigation is devoted to the analysis of the reflection and transmission coefficients within the framework of linearized potential flow theory using two methods, a numerical method based on the improved version of the meshless singular boundary method, and the analytical approach within the plane wave model. The numerical method is first validated by studying the accuracy of the numerical computations with respect to the number of boundary nodes and the location of the vertical boundaries of the computational domain, for different immersion ratios (h/d) and different relative lengths (w/d) of the obstacle. To assess the limitations of the analytical approach, a comparison analysis is carried out between the analytical and numerical results. To improve the calculations and the effectiveness of the analytical model, slight adjustments are made to the analytical procedure, which is termed here the corrected analytical plane wave model. Finally, the effects of the immersion ratio (h/d) and the relative length (w/d) of the obstacle on the reflection and transmission coefficients are computed using the three methods, and discussed for several wave and structural conditions.

Performance improvement of surface piercing propeller at low advance coefficients by aeration

Surface piercing propeller (SPP) is a type of super-cavitating propellers which with ventilation on the blades have suitable performance at water-air interface. These propellers provide perfect ventilation behind the blade, which effectively controls cavitation/aeriation and improves trust performance at operational condition. Even if at high speeds the SPPs have higher efficiency compared to the conventional propellers and water jets, the main challenge is their lower efficiency than other propulsion systems, at a lower speed which can affects the starting phase of high-speed crafts. In fact, there is a lack of research in studies on these propellers which concern the improvement of their performance at low speed. In the present studies, an aeration mechanism is investigated so that air is injected upstream in order to improve performance of the propeller. The design of the experiment (DOE) is carried out on a SPP model to perform performance tests in open water conditions using the SPP flow loop mechanism at Hydrotech (Institute of Applied Hydrodynamics and Marine Technologies, Iran University of Science and Technology). The effects of the horizontal distances (α) and vertical distances (β) between the ventilation point and the location of the propeller are presented in the form of non-dimensional ventilation immersion ratios β/α. For different propeller immersion ratios, ventilation immersion ratios and advance coefficients, the thrust coefficient for different cases was measured and compared to unventilated conditions. The achievements of the present research are different performance curves about thrust coefficient which illustrate a good correlation between propeller performance and aeration at different propeller immersion ratios. The maximum thrust coefficient improvement is around 100% which can achieve at I=0.25, β/α=0.05 and J=0.4. As propeller immersion ratio I increases, region with improved performance shifts towards higher values of advance coefficient J.

Influence of the transom immersion to ship resistance components at low and medium speeds

The transom stern offered some advantages over the traditional rounded cruiser stern reducing the resistance of a ship. This can only be achieved if the transom stern is carefully designed with suitable transom immersion ratio. In this study, the influence of different transom area immersion ratios on the resistance components was investigated for a semi-displacement hull and a full displacement hull. The base hull was based on NPL hull form and KCS hull form for a semi-displacement and full-displacement hull respectively. The transom immersion ratios for the NPL hull were varied at a ratio of 0.5, 0.7, 0.8 and 1.0. The resistance of each of the NPL hull form was simulated at Froude number 0.3 up to 0.6. The transom immersion ratios for the KCS hull were varied at a ratio of 0.05, 0.1, 0.15 and 0.3. The resistance of each of the KCS hull form was simulated at Froude number 0.195, 0.23, 0.26 and 0.28. The transoms of both hulls were modified or varied systematically to study the influence of the transom shape or immersion on the total and wave resistance components. The investigation was carried out using a CFD software named SHIPFLOW 6.3 based on RANSE solver. These results on the NPL hull shows that the larger the transom immersion, the higher the resistance will be for a semi-displacement vessel. The increased resistance is contributed by additional frictional and wave resistance components. The results for the KCS hull seems to contradict with the results obtained from the NPL hull. The larger and deeper transom for the case of KCS hull form sometimes can be beneficial at higher Froude number.

Chatter stability analysis for milling with single-delay and multi-delay using combined high-order full-discretization method

Regenerative chatter limits the surface finish and machining efficiency of the products. The demand for milling stability prediction and chatter suppression has been increasing. This paper presents a combined high-order full-discretization method (CHFDM) to analyze the milling stability of the system with single-delay and then extends it to calculate the stability lobe diagram (SLD) of milling with multi-delay. Firstly, the dynamic model of the milling with single-delay is represented by delay differential equation (DDE). Both the free vibration process and the forced vibration process are considered in the calculating process. The state transition matrix of the milling system is obtained by directly constructing the mapping relationship between the dynamic responses for current and previous periods. The comparisons between the CHFDM and the benchmark methods are carried out from the aspect of the rate of convergence and computational time. It is indicated that the CHFDM is applicable for obtaining the stability boundary of milling with both large and small radial immersion ratios accurately. Meanwhile, the computational efficiency of the CHFDM is verified to be good through comparison. Then, the CHFDM is extended to obtain the SLD of milling with multi-delay. The effectiveness of the extended CHFDM is validated by comparing it with two existing methods. The comparison results indicate that the CHFDM can be extended to obtain the SLD of milling with multi-delay reliably and efficiently.

Numerical investigation of the immersion ratio effects on ventilation phenomenon and also the performance of a surface piercing propeller

Surface Piercing Propellers (SPP) show high efficiency at high advance speeds. Regarding operational conditions, this kind of propellers generate an air layer when entering the water due to the rotation of the propeller; this phenomenon is called ventilation. The ventilation phenomenon divided into some mechanism with respect to air cavity length on the propeller surface; among them are partially ventilation mechanism and fully ventilation mechanism which has great importance. In this study, using numerical simulation, we have investigated ventilation patterns and also the performance of a five-blade SPP propeller (SPP 5.74) at immersion ratio of 33, 40, 50and 70% respectively. We used Sliding Mesh Technique for modeling. Also, we applied the volume of fluid method to simulate the open surface pattern. To validate numerical results, the four-blade propeller, 841-B was simulated, and then the results of thrust and torque coefficients compared with Olofsson experimental results and validated accordingly. The findings indicate that the maximum value for thrust and torque coefficient would occur at immersion ratio of 70% and the maximum propeller efficiency occurs at immersion ratio of 33% and advance coefficient of 1.1; Moreover, the critical advance coefficient (at the partially and the fully ventilation boundary) increases by a reduction in immersion ratio, so that critical advance coefficients are 0.6 and 0.76, respectively at immersion ratios of 70 and 33%. Meanwhile, as advance coefficient increases, length of ventilation zone will decrease, and consequently the propeller will be laid on partial ventilation zone.

Experimental study of immersion ratio and shaft inclination angle in the performance of a surface-piercing propeller

Abstract. Surface-piercing propellers have been widely used in light and high-speed vessels because of their superior performance. Experimental study of these propellers is one of the most reliable and accurate ways which can provide details about the performance and effect of different design parameters on the performance of the surface-piercing propellers. In this research, a five-blade surface-piercing propeller was tested in the free surface water tunnel of Babol Noshirvani University of Technology in order to expand the available experimental data and database for future engineering designs. The effects of immersion ratio and shaft inclination angle on the propeller's efficiency and hydrodynamic coefficients were examined. A free surface water tunnel and a calibrated dynamometer with the measurability of the thrust forces and the torque of a propeller were used for this purpose. Comparing the obtained results with the existing semi-experimental equations shows that the equations presented in various geometric conditions are not accurate enough, and developing the existing database is necessary. The details of the obtained results showed that the hydrodynamic coefficients of the thrust and torque increased by increasing the immersion ratio, but the coefficient of hydrodynamic thrust and efficiency reduced. The results also indicated that the coefficient of torque increased by increasing the shaft inclination angle. The highest efficiency of the propeller was achieved in the range of 40 %–50 % immersion ratios at all angles of shaft inclination. For all immersion ratios, the maximum and minimum efficiencies were obtained at 0 and 15 shaft inclination angles, respectively. The best efficiency of the propeller was at 50 % immersion ratio and zero shaft inclination angle.

Unsteady RANS simulation of a surface piercing propeller in oblique flow

Conventional propellers might undergo severe cavitation at high speeds and this phenomenon not only affects the efficiency of the propeller, but also may result in serious damages in propulsion system. Due to their special geometries, surface piercing propellers (SPPs) overcome this problem and achieve high efficiencies in high speeds. Therefore, SPPs are one of the popular propulsors for high-speed crafts. The present research is aimed to pursue SPP's performance in the off-design conditions. URANS method was used to study the performance of the 841-B SPP (a case with some available experimental results; Olofsson, 1996) in several immersion ratios (I=33%, 50%, 75% and 100%) and maneuvering conditions (incident angles of 0°, 10° and 20°). The free surface was simulated using VOF method. Off-design conditions might exert extra or less forces and torques on the propeller's blade. In the present research for 841-B SPP, it was found that a maneuver condition would increase the thrust and torque coefficient for some cases. The sliding mesh technique was utilized to simulate the 841-B SPP performance, which unlike the multiple reference frame (MRF) technique, this technique allows to capture the blades hit on the water surface in transient mode simulations.

Stability prediction for milling process with multiple delays using an improved semi‐discretization method

AbstractMilling chatter leads to a poor surface finish, premature tool wear, and potential damage to the machine or tool. Thus, it is desirable to predict and avoid the onset of this instability. Considering that the stability of milling with variable pitch cutter or tool runout case is characterized by multiple delays, in this paper, an improved semi‐discretization method is proposed to predict the stability lobes for milling processes with multiple delays. Taking the variable pitch milling, for example, a comparisonwith prior methods is conducted to verify the accuracy and efficiency of the proposed approach for the stability prediction both in low and high radial immersion ratios. In addition, the rate of convergence of the proposed method is also evaluated. The results show that the proposed method has high computational efficiency. Copyright © 2015 John Wiley & Sons, Ltd.

Stability Prediction in High-Speed Milling Process Considering the Milling Force Coefficients Dependent on the Spindle Speed

In order to further research the chatter vibration in high-speed milling, in this paper, a new regenerative chatter vibration model, considering the effect of milling force coefficients dependent on the spindle speed (MFCDSS) on the stability of high-speed milling process is proposed, and then milling stability lobe diagram is obtained, based on full-discretization method (FDM). The variable tendency of the stability of milling system is analyzed by comparisons in case of different radial immersion ratios in low-speed and high-speed milling regions, respectively. It is found that great stability predicting differences occur, especially in high-speed region when the MFCDSS is considered. This model can further supplement the theory of stability of high-speed milling process, it has certain engineering guidance significance in the selection of high-speed milling parameters.

Stability Prediction and Dynamics Analysis of Milling with Variable Pitch Cutter in Low Radial Immersion

By disrupting the regenerative effect, milling cutters with variable-pitch are usually used to improve stability. Since high interrupted cutting processes, such as low radial immersion case, will result in more nonlinear phenomena and some consequent differences of stability chart, in this paper, an improved semi-discretization algorithm is utilized to predict the stability lobes for variable-pitch milling under low radial immersion ratios, the focus of the current manuscript is to investigate the stability trend caused by tool geometries. In addition, the chart differences in the cases of low and high radial immersion milling are also discussed by comparisons. Under certain combinations of parameters, some phenomena, like bunch of isolated island and flip bifurcation region are described, and some influences of tool geometries on stability trends are shown and explained.

EIS Study on the Deterioration Process of Organic Coatings under Immersion and Different Cyclic Wet-Dry Ratios

Under immersed and we-dry cyclic conditions, the deterioration processes of the organic coating on carbon steel surface have been comparatively studied using electrochemical techniques. The wet-dry cycles were carried out by exposure to 4 h immersion and 4h dryness (4-4h cycles) and 12h immersion and 12h dryness (12-12h cycles) conditions, respectively. The immersion condition was carry out in a 3.5% NaCl solution and drying at 298K and 50% RH. According to the EIS characteristics, the entire deterioration processes under above three mentioned conditions can be divided into three main stages, consisting of the medium penetration, corrosion initiation and corrosion extension. Comparing with the immersed, the 4-4h wet-dry cycles greatly accelerated the entire deterioration process; especially during the corrosion initiation and the corrosion extension periods, leading the paint system lose its anti-corrosive performance in a short period. However, the 12-12h wet-dry cycles decelerated the entire deterioration process, prolonging the coatings anticorrosive ability. The acceleration mechanism of the coatings and underlying metal corrosion under wet-dry cycles was discussed based on the above results.