Front Wall Research Articles

Enclosure fire extinguishment with water mist and nitrogen as affected by fire size, obstruction and ventilation

Fire tests were conducted to evaluate the efficacy of incorporating nitrogen to enhance water mist's fire-extinguishing capability in an obstructed, naturally-ventilated 1.22 × 0.61 × 1.22 m high enclosure. Water mist and nitrogen were applied from the enclosure ceiling in the respective ranges of 0.35–3.89 lpm and 0.113–0.283 m3/min, with median droplet sizes ranging from 16 to 35 μm. The obstruction was facilitated with horizontal baffles with various vertical spacings to force the transport of water mist and nitrogen to follow an alternating path to a 76- or 152-mm heptane pan fire sitting on the enclosure floor. The enclosure ventilation was provided with a 0.23 × 0.15 m high base opening centered on the enclosure's front wall, together with a 0.33 × 0.05 m high opening centered on the enclosure's front wall or on the enclosure's back wall at the respective elevations of 0.36 m and 0.81 m above the enclosure floor, or with the presence of these two elevated openings. The tests showed that incorporating nitrogen in the water mist application did improve water mist’ fire-extinguishing capability in the enclosure. However, the improvement was highly affected by the fire size, obstruction and ventilation conditions.

Changes in vestibular-related responses to combined noisy galvanic vestibular stimulation and cerebellar transcranial direct current stimulation.

Vestibular nuclei and cerebellar function comprise vestibular neural networks that control vestibular-related responses. However, the vestibular-related responses to simultaneous stimulation of these regions are unclear. This study aimed to examine whether the combination of noisy galvanic vestibular stimulation (nGVS) and cerebellar transcranial direct current stimulation (ctDCS) using a complex transcranial electrical stimulation device alters vestibular-dominant standing stability and vestibulo-ocular reflex (VOR) function. The center of foot pressure (COP) sway and VOR of participants (28 healthy, young adults) were assessed under four conditions of transcranial electrical stimulation using nGVS and ctDCS. The COP was calculated with the participant standing on a soft-foam surface with eyes closed using a force plate to evaluate body sway. VOR measurements were collected via passive head movements and fixation on a target projected onto the front wall using a video head impulse test (vHIT). VOR gain was calculated in six directions using a semicircular canal structure based on the ratio of eye movement to head movement. The nGVS + ctDCS and nGVS + sham ctDCS conditions decreased COP sway compared to the sham nGVS + ctDCS and sham nGVS + sham ctDCS conditions. No significant differences were observed in the main effect of stimulation or the interaction of stimulation and direction on the vHIT parameters. The results of this study suggest that postural stability may be independently affected by nGVS. Our findings contribute to the basic neurological foundation for the clinical application of neurorehabilitation using transcranial electrical stimulation of the vestibular system.

Cyclic behavior of masonry walls retrofitted with post-installed twisted bars or bonded rebars

The damage observed after the recent earthquakes showed that the most common failures for masonry buildings involve out-of-plane mechanisms associated to the ineffective connection between walls. For this reason, retrofitting techniques aiming to achieve a box-like behavior are of great interest. This paper presents the results of an experimental study conducted to investigate two different retrofitting solutions used to improve the structural connection between orthogonal walls: a mechanical connection by means of twisted bars and a fastening solution with rebars and injection mortar. Two full-scale T-shaped masonry specimens were realized in solid clay brick, with a “weak” connection between the front and the back wall. The specimens were tested in unreinforced and strengthened configurations, considering different retrofitting layouts. An out-of-plane load was applied on the front wall, together with a vertical prestress to simulate the gravity load coming from the floors and walls above. Each specimen was tested in three consecutive runs: a monotonic one on the unreinforced masonry, a first cyclic run with the wall intersection reinforced with twisted bars, and a second cyclic run on the wall retrofitted with rebars and injection mortar, after the removal of the twisted bars. The twisted bar solution resulted in a significant increase of the dissipative capacity of the wall despite the number of adopted bars, while, in the case of rebars and adhesive, a higher resistance was achieved together with a perfect box-like behavior.

Optimization of parameters of the OWC wave energy converter device using MLP and XGBoost models

In the present work, we have studied the performance of a breakwater-integrated quarter-circle-shaped front wall OWC device under the influence of irregular incident waves. Firstly, the boundary value problem associated with the hydrodynamics of OWC device is handled for solution using the dual boundary element method (BEM). To examine the complex relationships between all input features and the target variable in a time-efficient manner, supervised machine learning models are developed. Here, two different models: (i) multilayer perceptron (MLP) model based on an artificial neural network, and (ii) a tree ensemble model, namely the XGBoost model are developed. The submergence depth of the front wall of the OWC device, chamber length, rotational speed, and diameter of the turbine blade are considered as input attributes, and the average annual power generated by the OWC device is considered as the output attribute. The MLP model is employed to optimize these input parameters, leveraging the insights provided by the XGBoost model to maximize the annual average power generation. From the dual BEM based numerical results, and using the Latin hypercube sampling technique, 3750 samples were generated to train, validate, and test the machine learning models. Using the XGBoost model with the support of accumulated local effect plots, we find four specific regions of the input space in which the annual average power extraction will be maximum. Hereafter, an extended input database is generated with twenty equally spaced levels for each parameter and the dataset is passed through the developed MLP model to find the optimized values of the parameters of the OWC device which maximizes the power generation. It is obtained that the maximum power generation is attained for y0/h=−0.65, r/h=3, 2.8≤D≤3 and 70≤N≤80∪105≤N≤116.

GENERALIZED HISTOSTRUCTURAL AND MORPHOMETRIC CHARACTERISTICS OF THE FRONTAL SINUS OF HUMAN IN HEALTH

The aim of our study is to determine the histo-topographic and morphometric features of the structural components of the mucous membrane of the human frontal sinus on different walls. Materials and methods: to achieve the goal, we used a set of methods for morphological studies including the method of serial semi-thin sections, histochemical studies, and the morphometric method. The thickest mucous membrane on the lower wall has an average epithelium thickness of 51.45±1.59 μm on the left and 50.78±1.64 μm on the right. On the left, the lamina propria thickness is 42.49±5.34 μm, and on the right, it is 43.03±2.22 μm. The submucosal base has a thickness of 423.67±21.33 μm on the left and 426.45±16.77 μm on the right, which is four times higher than the average thickness of the back wall and septum (p<0.05). The average diameter of the lumen of the resistive and capacitive links of the hemomicrocirculatory channel is the largest in the mucous membrane of the front wall of the human frontal sinus (respectively, 11.16±0.37 μm on the left and 11.34±0.31 μm on the right (p<0.05); 7, 63±0.08 μm on the left and 7.57±0.09 μm on the right), the smallest is in the mucous membrane of the back wall (respectively, 6.96±0.19 μm on the left and 6.56±0.35 μm on the right; 8.82±0.16 μm on the left and 9.02±0.43 μm on the right (p<0.05)). Exchangeable hemomicrovessels with the smallest diameter had a measurement of 3.89±0.08 μm on the left and 4.19±0.02 μm on the right (р<0.05) within the specified area. The study revealed the largest capillaries in the mucosal lining of the lower wall, which measured 4.88±0.07 μm on the left and 4.73±0.12 μm on the right (p<0.05). Furthermore, complex alveolar-tubular glands were evident in the submucosal base of the mucosal lining in all walls of the designated sinus. It has been found that the glands on the lower wall have the largest diameter of the terminal sections, whereas those on the septum have the smallest. On the left, the glands on the lower wall have a diameter of 30.42±2.36 μm, while those on the septum have a diameter of 25.42±1.68 μm. On the right, the corresponding measurements are 31.01±1.34 μm and 25.89±1.38 μm (p<0.05). In conclusion, this study highlights the distinct differences in gland diameter and type among different sections of the organ. The glands on the front and back comprised a mixture of protein and mucous types, while two types were identified on the lower wall and septum. The statistical processing of the obtained histo-topographic, histological, histochemical, and morphometric data significantly enhances the comprehension of the microscopic structure of the mucous membrane in the frontal sinus. These findings can be important in modern morphology and otorhinolaryngology.

Upaya Meningkatkan Mobilitas Fisik Dengan Latihan Mobilisasi Dini Pada Pasien Post Sectio Caesarea Di RSUD Sleman D.I Yogyakarta

Background: Sectio Caesarea is a method of giving birth to a fetus by making an incision in the uterine wall through the front wall of the abdomen (Amru Sofian, 2013). Giving birth by cesarean can drain more energy on the body and the recovery process takes longer. To speed up the recovery process, early mobilization exercises are needed. However, there are several factors that prevent mothers from doing early mobilization For this reason, it is important that efforts to increase early mobilization are carried out in order to speed up the healing process. Objective: To describe the description of nursing care in post sectio caesarea patients in practicing early mobilization. Research Methods: This study uses a literature review method in a journal that discusses early mobilization in post sectio caesarea mothers. Research Results: The results of the research from the literature review that the authors obtained through 10 journals, namely the mobilization efforts of post-SC postpartum mothers in carrying out early mobilization are influenced by pain in the surgical wound, knowledge/experience, motivation and beliefs. These results are relevant to the case managed by the author, namely Mrs. K was reluctant to do early mobilization because of pain and fear. Conclusion: From the results of the literature study above, it can be concluded that early mobilization of post sectio caesarea mothers can be improved by implementing pain management nursing, motivation, education and support from families and health workers

Smíšený adenoneuroendokrinní karcinom žaludku – kazuistika

Neuroendocrine tumours represent a heterogeneous group of neoplasia arising from different anatomical locations, with approximately 50% of gastrointestinal origin. Main parameters in the evaluation of each case include tumour morphology, mitotic cell count, and Ki-67 index. Mixed adeno-neuroendocrine carcinomas (MANECs) are rare aggressive neoplasms consisting of both adenocarcinomatous and neuroendocrine cells, each component constituting at least 30% of the lesion. Our case represents 77-year-old polymorbid patient who, due to signs of acute bleeding in the upper gastrointestinal tract with anaemic syndrome, underwent a gastroscopic examination for melena with the finding of an ulcer lesion on the front wall of the stomach at the junction of the body and the antrum. The control gastroscopic examinations with biopsies, at first only signs of chronic gastritis with Helicobacter pylori positivity were histologically proven, then fragments of high-grade tubular to tubulovillous adenoma and structures of moderately differentiated tubular adenocarcinoma were found. Histological analysis of the gastric resection showed mixed adeno-neuroendocrine carcinoma with lymphangioinvasion.

Analysis of clinical efficacy and safety of hand-sewn anastomosis for the digestive tract with Da Vinci robot in rectal cancer surgery

PurposeThe study aimed to analyze the clinical efficacy and safety of hand-sewn anastomosis for the digestive tract with Da Vinci robot in rectal cancer surgery.MethodsA retrospective study was conducted to collect the clinical data from 27 patients who underwent Da Vinci robotic rectal cancer radical surgery in the department of gastrointestinal surgery at the Second Affiliated Hospital of Dalian Medical University from August 2019 to February 2022. All patients received a manual suture for digestive tract reconstruction. After the posterior wall was sutured, the anterior wall was sutured continuously. Finally, a prilling thread was used to sew the junction of the front and rear walls. Perioperative indexes and complications were recorded.ResultsAll 27 patients successfully underwent the operation. Neither conversion to laparotomy nor perioperative death occurred. The operation time and intraoperative blood loss were 183.6 ± 44.8 min and 54.8 ± 34.4 ml, respectively. A total of 15.3 ± 7.8 lymph nodes were harvested. The pain score 24 h after operation was 1.3 ± 1.3. The time out of bed, the time to exhaust, and the time to eat were 15.6 ± 2.9 h, 2.2 ± 0.8 days, and 2.1 ± 0.6 days, respectively. A total of 4 patients (14.8%) developed complications after the operation. Grade B anastomotic leakage gradually resolved after drainage and antibiotic therapy in 1 case. A patient with grade C anastomotic leakage received a second operation for ileostomy. One patient with postoperative pneumonia recovered after anti-infective treatment. Another patient with intraperitoneal hemorrhage improved after symptomatic treatment with blood transfusion and hemostasis. The postoperative hospitalization time and total hospitalization costs were 8.9 ± 4.4 days and 89,236.1 ± 13,527.9 yuan, respectively.ConclusionsManual suture with Da Vinci robotic surgery system is safe and feasible for reconstructing the digestive tract in rectal cancer surgery.

Optimization of secondary air operation parameters of waste incineration boiler based on response surface methodology

To reduce the NOx emission concentration of waste incineration boilers and improve the thermal efficiency of incinerators, the combustion process of a 600 t/d incineration boiler was numerically investigated. First, the influences of the secondary air injection angle, velocity and temperature on the NOx concentration at the waste incineration boiler outlet and the thermal efficiency of the incinerator were analyzed through a single factor simulation test. Then, coupling optimization of key operating parameters, including the secondary air injection angle, velocity and temperature, was conducted via the response surface design method to obtain the specific functional relationships between outlet NOx concentration, incinerator thermal efficiency, front wall secondary air injection angle, rear wall secondary air velocity and secondary air temperature, as well as the optimal operating parameters for the boiler. The results showed that when the secondary air injection angle of the front wall ranges from 68°∼80° and the secondary air injection angle of the back wall is 67°, the minimum NOx concentration is 142.23 mg/m3, and the maximum thermal efficiency of the incinerator reaches 85.51 %. When the secondary air velocity at the front wall is 42 m/s and the secondary air velocity at the back wall ranges from 42 ∼ 66 m/s, the NOx concentration at the outlet is the lowest at 140.05 mg/m3, and the thermal efficiency of the incinerator is the highest at 85.63 %. When the secondary air temperature ranges from 297.16 ∼ 309.16 K, the NOx concentration at the outlet is the lowest at 155.45 mg/m3, and the thermal efficiency of the incinerator is the highest at 84.64 %. The secondary air injection angle, velocity and temperature impose significant effects on the NOx concentration at the outlet and thermal efficiency of the incinerator. The optimal parameters, as determined in the multifactor simulation test, include a 77° secondary air injection angle of the front wall, 69 m/s secondary air velocity at the back wall, and 297.15 K secondary air temperature. Under these conditions, the NOx concentration at the outlet is 134.98 mg/m3, and the thermal efficiency of the incinerator reaches 86.11 %. This study has important guiding significance for reducing pollution and improving the efficiency of waste incineration boilers.

3D structure of H ii regions in the star-forming complex S254-S258

ABSTRACT The S254-258 star-forming complex is a place of massive star formation where five OB-stars have created H ii regions, visible as optical nebulae, and disrupted the parental molecular gas. In this work, we study the 3D structure of these H ii regions using optical spectroscopy and tunable-filter photometry with the 6- and 1-m telescopes of the Special Astrophysical Observatory of the Russian Academy of Sciences. We construct maps of the optical extinction and find that the H ii emission is attenuated by neutral material with 2 ≤ AV ≤ 5 mag. The typical electron density in S255, and S257 is ≈100 cm−3, with enhancements up to 200 cm−3 in their borders, and up to 400 cm−3 toward the dense molecular cloud between them, where active star formation is taking place. We show that either a model of a clumpy dense neutral shell, where UV photons penetrate through and ionize the gas, or a stellar wind, can explain the shell-like structure of the ionized gas. S255 is surrounded by neutral material from all sides, but S257 is situated on the border of a molecular cloud and does not have dense front and rear walls. The compact H ii regions S256 and S258 are deeply embedded in the molecular clouds.

Dense granular flow through a flat-bottomed silo: Comparison of the DEM and continuum models with experiments

The gravity flow of granular materials through a flat-bottomed rectangular silo is examined using experiments, the discrete element method (DEM), and continuum models. The flow is bounded by four flat frictional side walls, and the mass flow rate is controlled by an exit slot. The velocity and wall stresses are measured simultaneously in a steady fully developed zone which occurs far from the upper free surface and the exit slot, and they are compared with predictions of the DEM and the continuum models. The scaled velocities measured adjacent to the front face are in excellent agreement with the DEM. The centreline velocity is predicted to within 5%–30% by the DEM for larger widths. The normal and shear stresses measured at the mid-plane of one of the walls agree to within 5%–20% for the DEM. The DEM results are less sensitive to the spring stiffness kn, but are more sensitive to the interparticle coefficient of friction μp. There are larger discrepancies in the predictions of the continuum models when the effect of the front and rear walls are not included. The approximate inclusion of the latter improves the prediction of the shear stress and the slip velocity.

Aeroacoustic investigation of transonic flow behavior in M219 deep cavity with passive flow control configurations

This study aims to investigate the effect of front and aft wall modifications and their combinations on the sound pressure level response of the deep configuration of the M219 cavity at transonic speed. Experimental results for the baseline geometry of the cavity were validated with the high-fidelity lattice Boltzmann method computational fluid dynamics solver, SIMULIA PowerFLOW®. In this study, inclined and parallel cuts were applied to the front and aft walls of the M219 cavity to determine their efficiency in reducing the overall sound pressure level (OASPL). The most effective configurations on reducing OASPL at the front and aft walls were combined to form mixed configurations. All front wall and aft wall configurations as well as mixed configurations were validated through grid independence studies. Simulations showed that modifications to the aft wall were more effective in reducing noise than modifications to the front wall. The spectral analysis of pressure oscillations provided information about the broadband and tonal pressure responses of the mixed configurations. The findings showed that the mixed configurations were effective in reducing the frequency and amplitude of the Rossiter modes. The most successful configurations on noise reduction also showed a decrease in the drag coefficient and the average static pressure distribution along the cavity.

Ventilated silencer based on layered Helmholtz resonators

This study investigates the performance of a multilayer sound-attenuating metamaterial with ventilation capabilities. The design incorporates arrays of Helmholtz resonators embedded within the wall structure. Each cell of the barrier's front wall is a Euclidean polygon, triangular, square, or hexagonal, housing a parallel array of resonators interconnected via an axial ventilation duct. The sound attenuation performance of these barriers is meticulously examined using the lumped parameter theory and the transfer matrix method (TMM), complemented by finite element (FE) simulations. The results indicate that sound attenuation in the audible frequency range (300–2000 Hz) can be significantly enhanced by employing multiple layers of resonators, each layer assigned a unique peak resonance frequency. Despite the design's inherent trade-offs between barrier thickness, ventilation capacity, operational frequency range, and overall sound attenuation, its structural simplicity and straightforward theoretical performance estimation methods make it a promising candidate for applications requiring a specific attenuation spectrum. The sound-blocking performance of the design is further validated through impedance tube experiments, which show a reasonable agreement with the numerical predictions, thereby affirming the efficacy of the proposed design. The performance of multilayer design is also compared with the similar ventilated barriers proposed in the recent studies.

Monitoring the technical state of load-bearing structures of the Luzhniki Stadium during reconstruction

Introduction. The paper presents the methods of reinforcing brick-and-stone structures, as well as monitoring of their strain capacity during the reconstruction of the Grand Sports Arena of Luzhniki Olympic Complex. The authors paid special attention to the methods for ensuring the preservation of front wall made of ceramic hollow stones.Aim. To ensure the reliability and stability of the wall of the Grand Sports Arena during the stadium reconstruction, in particular during the dismantling of the framework and stands.Materials and methods. The authors calculated the strain capacity (vertical deviation) of the framework of the stands at its dismantling stage and the wall stability, taking into account the framework fastening with rolled steel braces. The wall section taken for calculation at the first stage of dismantling stands consisted of several spans of 6 meters each. An extreme wind action was considered as the main stress factor that has the most severe impact on the front wall strain.Results. The calculations showed that the wind load on the system “front wall + 1 span of the stand framework” increases tensile and compressive stresses in the load-bearing elements by no more than 5–7% compared to the system “front wall + 2 spans of the stand framework”. Based on the calculations performed, only one span of the stand framework adjacent to the front wall was decided to retain. Monitoring of the structures strain confirmed the reliability and efficiency of the adopted solutions to strengthen the retained structures.Conclusion. Due to R&D support for the design and reconstruction of the Luzhniki Grand Sports Arena, complex issues arising in the process of reconstruction were efficiently solved. The principles of the Arena reconstruction can be applied to other similar facilities.

Почему Иона бодрствует? Интерпретация раннехристианского саркофага из Британского музея в современном искусствознании

Although the sarcophagus No. 1957, 1011.1 is investigated in detail, to this day there are many questions in its study. In addition to the main problems facing the researcher in the study of early monuments the item has a unique iconographic solution: unlike other objects of this kind (3rd c.), the prophet Jonah, reproduced on the front wall, is represented awake. The authors put forward a number of hypotheses explaining this feature, but none of them is comprehensive. These aspects justify the choice of the monument as an object of study.A review of texts (2nd-4th cc.) and objects (3rd-5th cc.) showed that, probably, the Old Testament prophet is not literally represented in the relief, but rather an allegorical transmission of the theology of bodily Resurrection is presented. Although the early texts were only trying to comprehend the relationship between the image (εἰκών) and the Prototype (ἀρχέτυπον), nevertheless, perhaps understanding the images at that time could be more complicated and led to the formation of the theology of the image.

Retrofit of a 600 MW Down-Fired Pulverized-Coal Furnace for Low NOx Emission

Aiming at solving the problem of high NOx emissions of a down-fired boiler, a new combustion system has been proposed by means of the numerical simulation using Ansys Fluent. The coal-lean stream (tertiary air), which was originally mixed with a separated overfired air (SOFA) stream on the front and rear walls of the upper furnace, was relocated to the lower zone of the furnace after retrofit. The secondary-air slots were transformed into a new annular port type, which was injected into the furnace with a down-tilt angle to increase the residence time of the coal stream. Furthermore, the effect of secondary air distribution and velocity of coal stream on performance was studied. After retrofitting the combustion system, the NO emissions were effectively controlled, decreasing from 906 mg Nm−3 to 576 mg Nm−3, but the carbon content of fly ash increased from 2.46% to 5.78%. Aiming at decreasing the carbon content of fly ash, the effect of coal/primary air velocity on the arch was studied. Less carbon content in fly ash can be observed for the lower arch airflow velocity. The results showed that the NO emissions can be controlled below 595 mg Nm−3, and the carbon content of fly ash was reduced to 3.39% when the velocity was decreased to 18 m s−1.

IMPLEMENTATION OF ROOT CAUSE ANALYSIS METHOD TO INVESTIGATE FAILURE OF FRONT WALL TUBE BOILER

Root cause analysis is a method that observes all of the possible causes that make the system or components fail. This research is implemented such a method to investigate the failed front wall tube on the boiler. The purpose of this research is to find out the main cause of failure on the front wall tube to avoid a similar problem in the future. Considering all aspects that have the potential to be the main cause of failure, therefore, many tests and examinations are done, including visual tests, fractography, metallography, chemical analysis, hardness test, SEM, and EDS analysis. Examination result on the fracture surface shows two bulges on a tube and some longitudinal cracks spread on bulges outside the surface area. At the same time, the thick scale is also found on the inside surface of these bulges. Moreover, microstructure and hardness changes are also found in this area. From the analysis of all test result that obtained it is concluded that the main cause of failure is the presence of scales which reduce heat transfer so that local overheating occurred. Consequently, its tensile strength in this area is decreased, and finally, the tube could not support operational pressure and deformed to make a bulge.

Optimization of the chamber of OWC to improve hydrodynamic performance

Nearly 71% of Earth's surface area is occupied by the ocean, which is abundant in energy, with wave energy being one of its essential components. As a result, the investigation of wave energy generation devices is a crucial matter. This paper analyzes the performance of the oscillating water column (OWC) wave energy conversion device under the influence of unidirectional regular waves and optimizes the OWC device accordingly. The impact of different structural dimensions on the first-stage conversion efficiency of the OWC device is determined. Moreover, to evaluate the performance of the OWC device in real sea conditions, the wave climate at Sanmen Gorge is employed as the experimental parameter. The study examines the performance and characteristic response of the OWC device regarding the air chamber width, thickness of the front wall, and draught of the front wall. The findings reveal that the width of the OWC air chamber and the draught of the front wall significantly affect the OWC performance. Decreasing the width of the air chamber results in a stable horizontal plane, eliminating the occurrence of standing wave phenomena. As the draft of the front wall increases, the reflection coefficient of the air chamber gradually increases, and it becomes difficult for the wave to penetrate into the air chamber section. The Latin hypercube design experiment method was used to select experimental points and establish quadratic polynomial response functions. The OWC device was optimized based on multi-island genetic algorithm. The simulation and fault tolerant optimization methods presented in this paper can be widely used to improve system performance.

Wave power extraction from slanted oscillating water columns in the presence of an array of arbitrary trenches

This paper investigates the impact of arbitrary bottom topography on the efficiency of a slanted oscillating water column device located in near-shore areas. The device incorporates a turbine positioned at its opening, which harnesses the oscillation of the fluid at the free surface, created by recurrent incident waves, to propel an air volume in a uni-direction. To analyze the wave power absorption capability of the system, an eigenfunction expansion and a boundary element model based on linear water wave theory are employed. The notion is to use the anticipated amplification of scattered and reflected wave fields resulting from the existence of a sloping wall to improve the wave power absorption caused by the walls' wave reflections. The accuracy of the current study's numerical results is ratified by conducting a comparative study using the available data given by other researchers. The study demonstrates that multiple efficiencies occur in the case of the long-wave region as compared to the short-wave region. Additionally, both the shape and magnitude of the efficiency curves are influenced by the slanted design of the device's front wall and the number of trenches.

Analysis of molten metal fluid flow mechanisms in variable polarity plasma arc welding of aluminum alloys

The stability and quality of welding in variable polarity plasma arc welding are determined by the directional fluid flow within the molten pool. In this study, the particle tracking method was employed to obtain flow traces and velocity of the molten metal on the walls of the keyhole using a high-speed camera system. Additionally, a confocal laser scanning microscope was utilized to capture the 3D morphology of the keyhole, while the flow channels were obtained through sectioning. By correlating the flow traces and velocity with the 3D keyhole morphology, the experimental results revealed the presence of saddle points on both the front and rear walls of the keyhole. The front saddle point represents the region where the flow velocity in the depth direction is minimum, causing the keyhole front side to converge upward and downward. The depth and volume of fluid flow to the keyhole sidewall are determined by this front saddle point. On the other hand, the rear saddle point is located at the center of the molten pool, marking the entry and exit sides of the keyhole rear wall where the melting metal eventually reaches. The location of the post-settlement point will affect the weld state. During the welding process, the double saddle points of the molten pool remain dynamically stable, and their position is influenced by shear force, gravity, arc pressure, keyhole morphology, and flow channels. These findings contribute to controlling the process characteristics necessary for stable welding of the keyhole in the molten pool.