Study on the Optimal Design for Cavitation Reduction in the Vortex Suction Cup for Underwater Climbing Robot

In order to adhere to the wall stably in an underwater environment, a vortex suction cup that injects high-pressure water inside via two axisymmetrically side-distributed inlets to create a negative pressure area in the center is the necessary component for the underwater climbing robot (UCR). However, the suction force of this vortex suction cup is reduced and periodically unstable due to unstable cavitation. The aim of this paper is to propose a cavitation reduction optimization method for vortex suction cups and to verify the effectiveness of the optimization. Analyses of this vortex flow, including streamlines, pressure, and cavitation number fluctuations, were carried out by the introduced computational fluid dynamics (CFD) simulating methods based on the multiphase RNG k−ε model to study the periodic fluctuations of the suction force of the original suction cup and the optimized ones. Force measurement and vortex observation experiments were conducted to compare the suction force of the original vortex suction cup and the optimized suction cup, as well as the cavitation and pressure fluctuation phenomenon. Results of simulation and experiments prove the existence of the effect of vortex cavitation on the suction performance and verify the rationality of optimization as well.

Hydraulically Coupled Dielectric Elastomer Actuators for a Bioinspired Suction Cup

Suction cups of cephalopods show a preeminent performance when absorbing irregular or flat objects. In this paper, an octopi-inspired suction cup, driven by hydraulically coupled dielectric elastomer actuators (HCDEAs), is proposed, which is considered to be controlled easily and have compact structure. To investigate the performance of suction cups, experiments have been conducted to clarify the effect of the pre-stretch ratio and chamber angle on suction forces. It could be seen that both factors have a complicated influence on suction forces, and the best performance obtained was a reasonable combination of the pre-stretch ratio and chamber angle. Here, we achieved a maximum suction force of 175 mN with λp = 1.2, α = 23° under a DC voltage of 3500 V. To enhance the capacity and adaptation of the suction cup, flat objects of various types of materials were introduced as targets. Experimental results displayed that for tested materials, including a dry/wet acrylic plate, CD, ceramic wafer, and aluminum plate, the suction cup showed outstanding performance of absorbing and lifting the target without any damage or scratch to them. Our research may serve as a guide to the optimal design and provide insights into the performance of the HCDEAs-actuated suction cup.

Оцінка характеристик закапотованого гвинтовентилятора ТРДД з надвисоким сту-пенем двоконтурності

In many respects, the efficiency and economy of the aircraft are determined by the parameters and characteristics of the power plant. The analysis of trends in the world engine building shows that an increase in the bypass ratio can significantly increase the efficiency of engines. One of the possible technical solutions to ensure the high performance of the perspective engines with an ultra-high bypass ratio is the use of a ducted propeller or propfan. This solution allows you to reduce acoustic radiation. In addition, the main advantage of the ducted propfans is a certain increase in thrust for the same consumed power. When flowing around a ducted propfan, a significant suction force arises on the nose of the profiled ring, the projection of which on the direction of movement provides a positive thrust of the ring. The presence of a duct also leads to a decrease in the final loss of the propeller, which, in turn, leads to an increase in the efficiency of the engine. Ducted and unducted propfans with the same blade row are investigated to assess the characteristics of a ducted propfan. The researches were carried out by the method of numerical experiment. The object of the research is a propfan with an inlet diameter of 2.924 m and the number of blades of 14 for a turbofan engine with a bypass ratio of m = 30. To research the propfan characteristics, a cruising mode of operation was selected in the range of revolutions n = 1500 ... 1650 rpm. with Mach numbers at the input from M = 0.54 to M = 0.8. In this work, the calculation did not take into account the resistance force of the duct. For a qualitative assessment of the flow in the propfan, visualization of the flow lines in the ducted and unducted propfan was obtained. The analysis of the research results showed that for all modes of operation the ducted propfan has a thrust force higher than the unducted propfan. The increase in thrust load reaches 71 ... 76 %. Visualization of the flow lines when flowing around a ducted and unducted propfan showed that the presence of a duct improves the internal aerodynamics of the propfan.

Shape Effect of Polymetallic Nodules on Suction Forces and Flow Field During Seabed Hydraulic Collection

Turbulent suction pipe flow around a near-wall ellipsoid nodule, as basic research of polymetallic nodule hydraulic collection, is investigated numerically and experimentally in this paper. Seven ellipsoids with axe ratios (a/b) ranging from 1 to 2 are considered as nodule models to reveal the shape effect on the characteristics of suction forces and suction flow field. Methods of particle image velocimetry (PIV) and dye tracing were used to visualize the suction flow field. The results indicate that: (1) suction force coefficients increase with a/b; (2) the shape effect is more significant in the cases with smaller ratios of bottom clearance to semi-thickness of the ellipsoid (h/c); (3) the weak vortex shedding in suction flow results in small-amplitude fluctuations of time-history suction forces; (4) the detached-eddy simulation (DES) method based on shear stress transport (SST) model is validated to be accurate and feasible for predicting the suction forces and suction flow field. It is expected to provide references for the design of nodule pick-up devices and to help us further understand the mechanism of hydraulic collection.

Parametric Numerical Study on the Self-Propulsive Performance of The DARPA Suboff Submarine via the Body-Force Propeller Method

This study is based on previous works in a series of numerical studies on submarine hydrodynamics, which involved developing a computational fluid dynamics method to estimate the self-propulsive performance of underwater vehicles. Herein, the Defense Advanced Research Projects Agency SUBOFF submarine model was adopted as a benchmark. The computational modeling applied was based on the Reynolds-averaged Navier-Stokes turbulence model. A body-force propeller method was adopted to model the propulsion. The self-propulsive performance was verified via mesh refinement and validated by comparing the computational solutions with the results obtained from the experiments. The effect of the Reynolds number on the self-propulsive performance was investigated by varying the positions of the stern planes, while the free surface effect was determined by varying the Froude number (Fr) via the volume of fluid method. The computed Taylor wake fraction (w) and hull efficiency (ηH) depended on the Reynolds number as it decreased monotonically. The w and thrust deduction fraction (t) for the model of aft-fitted stern planes were approximately 3–7% and 8–10% higher than those of the baseline and fore-fitted stern planes, respectively. The differences in ηH between the models were insignificant. Regarding the free surface effects, the computations of w, t, and ηH generally decreased with Fr, thus exhibiting several humps and hollows. The computed upward suction force and pitching moment varied from negative to positive and vice versa, depending on Fr.

VACStent: Combining the benefits of endoscopic vacuum therapy and covered stents for upper gastrointestinal tract leakage

Background and study aims Endoscopic treatment has markedly improved the high morbidity and mortality in patients with upper gastrointestinal tract leakage. Most procedures employ either covered self-expanding metal stents (SEMS) or endoscopic vacuum therapy (EVT), both with good clinical success but also with concomitant significant shortcomings inherent in each technique. A newly developed device, the VACStent, combines the fully covered SEMS with a polyurethane sponge cylinder anchored on the outside. This allows endoluminal EVT while keeping the intestinal lumen patent. The benefit is prevention of stent migration because the suction force of the sponge-cylinder immobilizes the VACStent on the intestinal wall, while at the same time, the attached external vacuum pump suctions off any secretions and improves healing with negative-pressure wound treatment (NPWT). Patients and methods In this pilot study, the first patients to receive the VACStent were assessed. Outcomes included the applicability and stability of the VACStent system together with the clinical course. Results Three patients with different clinical courses were managed with the VACStent. The first patient suffered anastomotic leakage following subtotal esophagectomy and was successfully treated with two postoperative VACStents for 12 days. The second patient received a covered SEMS for 14 days for acute Boerhaave syndrome. Due to persistent leakage, management was converted to EVT. Seven days, later a VACStent was inserted to allow oral nutrition while the leak finally closed. In the third patient, a LINX Reflux Management System had to be removed for erosion, leaving the gastroesophageal junction (GEJ) with a full-thickness gap. After VACstent insertion, successful closure was achieved within 4 days. Conclusions These clinical cases demonstrate the applicability and efficacy of the VACstent in management of esophageal and anastomotic leakage. With its vacuum sponge, the stent fosters wound healing while the covered SEMS keeps the passage patent for nutrition.

Soft Hybrid Suction Cup Capable of Sticking to Various Objects and Environments

A universal suction cup that can stick to various objects expands the areas in which robots can work. However, the size, shape, and surface roughness of objects to which conventional suction cups can stick are limited. To overcome this challenge, we propose a new hybrid suction cup structure that uses the adhesive force of sticky gel and the suction force of negative pressure. In addition, a flexible and thin pneumatic balloon actuator with a check valve function is installed in the interior, enabling the controllable detachment from objects. The prototype has an outer diameter of 55 mm, a weight of 18.8 g, and generates an adsorption force of 80 N in the vertical direction and 60 N in the shear direction on porous walls where conventional suction cups struggle to adsorb. We confirmed that parts smaller than the suction cup and fragile potato chips are adsorbed by the prototype. Finally, the effectiveness of the proposed method is verified through experiments in which a drone with the prototypes can be attached to and detached from concrete walls and ceilings while flying; the possibility of adsorption to dusty and wet plates is discussed.

Subduction dynamics and rheology control on forearc and backarc subsidence: Numerical models and observations from the Mediterranean

<p>The dynamics of oceanic and continental subduction zones is linked to the rise and demise of forearc and backarc basins in the overriding plate. Subsidence and uplift rates of these distinct sedimentary basins are controlled by variations in plate convergence and subduction velocities and determined by lithospheric rheological structure and different lithospheric thicknesses.</p><p>In this study we conducted a series of high-resolution 2D numerical models applying the thermo-mechanical code 2DELVIS (Gerya and Yuen, 2007). The model, based on finite differences and marker-in-cell techniques, solves the mass, momentum, and energy conservation equations for incompressible media; assumes elasto-visco-plastic rheologies and involves erosion, sedimentation and hydration processes.</p><p>The models show the evolution of wedge-top basins lying on top of the accretionary wedge and retro-forearc basins in the continental overriding plate, separated by a forearc high. These forearc regions are affected by repeated compression and extension phases. Higher subsidence rates are recorded in the syncline structure of the retro-forearc basin when the slab dip angle is higher and the subduction interface is stronger and before the slab reaches the 660 km discontinuity. This implies the importance of the slab suction force as the main forcing factor creating up to 3-4 km negative dynamics topographic signals.</p><p>Extensional back-arc basins are either localized along inherited crustal or lithospheric weak zones at large distance from the forearc region or are initiated just above the hydrated mantle wedge. During trench retreat and slab roll-back the older volcanic arc area becomes part of the back-arc region. Back-arc subsidence is primarily governed by crustal and lithospheric thinning controlled by slab roll-back. Onset of continental subduction and soft collision is linked to the rapid uplift of the forearc basins; however, the back-arc region records ongoing extension. Finally, during hard collision the forarc and back-arc basins are ultimately under compression.</p><p>Our results are compared with the evolution of the Mediterranean and based on the reconstructed plate kinematics, subsidence and heat flow evolution we classify the Western and Eastern Alboran, Paola and Tyrrhenian, Transylvanian and Pannonian Basins to be genetically similar forearc–backarc basins, respectively.</p>