Hydrodynamics of Moonpool-Type Floaters: A Theoretical and a CFD Formulation

Moonpool-type floaters were initially proposed for applications such as artificial islands or as protecting barriers around a small area enabling work at the inner surface to be carried out in relatively calm water. In recent years, a growing interest on such structures has been noted, especially in relation to their use as heaving wave energy converters or as oscillating water column (OWC) devices for the extraction of energy from waves. Furthermore, in the offshore marine industry, several types of vessels are frequently constructed with moonpools. The present paper deals with the hydrodynamics of bottomless cylindrical bodies having vertical symmetry axis and floating in a water of finite depth. Two computation methods were implemented and compared: a theoretical approach solving analytically the corresponding diffraction problem around the moonpool floater and a computational fluid dynamics (CFD) solver, which considers the viscous effects near the sharp edges of the body (vortex shedding) as non-negligible. Two different moonpool-type configurations were examined, and some interesting phenomena were discussed concerning the viscous effects and irregularities caused by the resonance of the confined fluid.

A physical investigation of dimensional and mechanical characteristics of 3D printed nut and bolt for industrial applications

Purpose A nut bolt joint is a primary device that connects mechanical components. The vibrations cause bolted joints to self-loosen. Created by motors and engines, leading to machine failure, and there may be severe safety issues. All the safety issues and self-loosen are directly and indirectly the functions of the accuracy and precision of the fabricated nut and bolt. Recent advancements in three-dimensional (3D) printing technologies now allow for the production of intricate components. These may be used technologies such as 3D printed bolts to create fasteners. This paper aims to investigate dimensional precision, surface properties, mechanical properties and scanning electron microscope (SEM) of the component fabricated using a multi-jet 3D printer. Design/methodology/approach Multi-jet-based 3D printed nut-bolt is evaluated in this paper. More specifically, liquid polymer-based nut-bolt is fabricated in sections 1, 2 and 3 of the base plate. Five nuts and bolts are fabricated in these three sections. Findings Dimensional inquiry (bolt dimension, general dimensions’ density and surface roughness) and mechanical testing (shear strength of nut and bolt) were carried out throughout the study. According to the ISO 2768 requirements for the General Tolerances Grade, the nut and bolt’s dimensional examination (variation in bolt dimension, general dimensions) is within the tolerance grades. As a result, the multi-jet 3D printing (MJP)-based 3D printer described above may be used for commercial production. In terms of mechanical qualities, when the component placement moves from Sections 1 to 3, the density of the manufactured part decreases by 0.292% (percent) and the shear strength of the nut and bolt decreases by 30%. According to the SEM examination, the density of the River markings, sharp edges, holes and sharp edges increased from Sections 1 to 3, which supports the findings mentioned above. Originality/value Hence, this work enlightens the aspects causing time lag during the 3D printing in MJP. It causes variation in the dimensional deviation, surface properties and mechanical properties of the fabricated part, which needs to be explored.

Instance Segmentation in Very High Resolution Remote Sensing Imagery Based on Hard-to-Segment Instance Learning and Boundary Shape Analysis

Although great success has been achieved in instance segmentation, accurate segmentation of instances remains difficult, especially at object edges. This problem is more prominent for instance segmentation in remote sensing imagery due to the diverse scales, variable illumination, smaller objects, and complex backgrounds. We find that most current instance segmentation networks do not consider the segmentation difficulty of different instances and different regions within the instance. In this paper, we study this problem and propose an ensemble method to segment instances from remote sensing images, considering the enhancement of hard-to-segment instances and instance edges. First, we apply a pixel-level Dice metric that reliably describes the segmentation quality of each instance to achieve online hard instance learning. Instances with low Dice values are studied with emphasis. Second, we generate a penalty map based on the analysis of boundary shapes to not only enhance the edges of objects but also discriminatively strengthen the edges of different shapes. That is, different areas of an object, such as internal areas, flat edges, and sharp edges, are distinguished and discriminatively weighed. Finally, the hard-to-segment instance learning and the shape-penalty map are integrated for precise instance segmentation. To evaluate the effectiveness and generalization ability of the proposed method, we train with the classic instance segmentation network Mask R-CNN and conduct experiments on two different types of remote sensing datasets: the iSAID-Reduce100 and the JKGW_WHU datasets, which have extremely different feature distributions and spatial resolutions. The comprehensive experimental results show that the proposed method improved the segmentation results by 2.78% and 1.77% in mask AP on the iSAID-Reduce100 and JKGW_WHU datasets, respectively. We also test other state-of-the-art (SOTA) methods that focus on inaccurate edges. Experiments demonstrate that our method outperforms these methods.

Mechanical Performance of High-Density Polyethylene (HDPE) Composites Containing Quarry Dust Filler

An innovative thermoplastic composite was produced using quarry dust which is an industrial waste from quarry industries. The quarry dust was added into high-density polyethylene (HDPE) using melt blending technique in an internal mixer at different mixing loading ratios. The quarry dust filled HDPE (QD-HDPE) composites were then characterized in terms of morphological and mechanical properties. Analysis on processing torque to produce QD-HDPE composites was conducted and the results showed that the optimum quarry dust loading in HDPE composites is at 30wt%. The results from mechanical test such as ultimate tensile strength (UTS), E-modulus, elongation at break, and flexural strength justify this. Scanning Electron Microscopy (SEM) analysis shows that quarry dust had a rough surface with sharp edges and it can be successfully added into HDPE matrix as a filler. In conclusion, performance of the HDPE composites is enhanced by the incorporation of quarry dust. This indicates that quarry dust is a potential filler to be used in thermoplastic composite industries in order to reduce the production cost and relax the pollution problems.

Study of the properties of the ovarian fluid of the Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1833) during freezing

The process of freezing the ovarian fluid of the Russian sturgeon (Acipenser gueldenstaedtii Brandt, 1833) was analyzed. With gradual cooling from 22°C to -196°C at a rate of 10° per minute, the process of freezing, formation and change of ice microparticles was observed. The ovarian liquid was glazed at -5°C and only at -70°. With the microparticles of ice began to form. From that moment, up to the temperature of liquid nitrogen (-196°C), the microparticles were crushed into smaller ones. The high content of intracellular water in the ovarian fluid of female Russian sturgeon contributes to the formation of the bulk of microparticles of ice, which is confirmed by their shape. These particles, which have sharp edges, are able to damage the thin shells of eggs during deep freezing.

The influence of joint geometry of toneholes with the main bore of wind musical instruments on their frequency characteristics

The article discusses the influence of geometric parameters (the presence and magnitude of the radius of curvature) at the junction of the toneholes with the main bore of the air column on the frequency characteristics of woodwind musical instruments. A theoretical calculation of the eigenfrequencies of an air column with one tonehole in the case of sharp edges has been carried out. The resonance frequencies were also found using computer simulation in the COMSOL Multiphysics 5.5 program for the case of sharp edges and joints with a radius of curvature. An empirical dependence of the frequency of the main tone of the air column on the radius of curvature of the edges of the tonehole is obtained. All simulation were carried out for two models: excluding and including viscous drag and thermal exchange losses.

Isolation of the singular part of the electromagnetic field scatteredby objects with sharp edges and conic points

In this article we propose a method for overcoming a number of problems that may arise when solving scattering problems on objects of complex structure. This approach can be used for mathematical and numerical modeling of waveguide, emitting and scattering systems of various complexity.

Features of the extraction of foreign bodies from the lower urinary tract

BACKGROUND:Foreign bodies introduced by patients into the bladder and urethra are relatively rare in clinical practice. As a result, there is insufficient information in the scientific literature regarding methods of extracting foreign bodies from the urinary tract. AIM:determination of the optimal methods for extracting foreign bodies from the urethra and bladder. MATERIALS AND METHODS:Foreign bodies of the lower urinary tract were removed in 21 patients: 15 (71.4%) men and 6 (28.6%) women. Foreign bodies were found in the urethra in 7 (33.3%) patients and in the bladder in 14 (66.7%) patients. Removal of foreign bodies from the urethra and bladder was performed endoscopically or during open surgery. RESULTS:Removal of stabbing, cutting and glass objects from the urinary tract in 9 patients was performed during open surgery. Foreign bodies with even smooth edges were removed in 12 patients under urethrocystoscopic control. At the same time, in two patients, coagulated suppositories were first fragmented in the bladder cavity, and then removed in parts. Cystolithotripsy was performed in one patient with a suppository inlaid with calculus before fragmentation. CONCLUSIONS:Foreign bodies with sharp edges or made of glass are safer to be removed from the lower urinary tract during open surgery. Foreign bodies with a smooth and even surface are optimally removed endoscopically. Long and bulky foreign objects that can be fragmented in the bladder cavity are best removed in parts. When foreign bodies are encrusted with large calculi, cystolithotripsy should be performed before their endoscopic extraction.