Protruding Length Research Articles

A practical approach to determine the role of rockbolts in stoping gullies

A research project was carried out on a gold mine in the Vaal River region of South Africa (Witwatersrand Basin) to evaluate the effect of two particular aspects of rockbolt installation - the angle of inclination of the bolt relative to the orientation of the rock surface, and the protruding length of the bolt - on the mine's gully support system. A keyblock analysis approach indicated that these factors do not have an adverse impact on the stability of the strike gullies. This was confirmed by extensive empirical data collected from the case study mine. While safety is the primary concern, cost saving opportunities can be realized through reconsidering historically inherited support standards that are perceived to be correct and appropriate. The research described in this paper sets forth a practical approach, that is easy to implement and repeatable, to evaluate the role of rockbolts in stoping gullies.

Selection of design parameters of working coil for Al/Cu tubular Magnetic Pulse Welding

MPW produces a high Lorentz force for welding through the interaction of magnetic fields between the working coil and outer workpiece. Therefore, the design of the working coil is crucial in the MPW process. In particular, it is important to understand and estimate the distribution of Lorentz force on the outer tube and the stress on the working coil. These factors greatly impact the efficiency of energy delivery and the durability of the process. The purpose of this research was to analyze the effect of coil design parameters on the Lorentz force and stress. The ultimate objective was to optimize these design parameters specifically for welding tubular workpieces; for this, an electromagnetic-mechanical FE-model was developed. The design parameters considered in this study included the angle, radius, and protruding length. The Lorentz force and stress were calculated based on these parameters. Notably, the response surface method (RSM) and sequential quadratic programing (SQP) were utilized to develop a prediction model and optimize the design parameters, respectively. The findings revealed that the protruding length and angle are significant design parameters. Consequently, a working coil was manufactured using the optimized design parameters, leading to a successful Al/Cu joint. These results emphasize the indispensability of optimizing design parameters to achieve high-quality joints.

Integrating Wire Arc Additive Manufacturing into Selective Paste Intrusion for Reinforced Concrete Elements: Effect of Temperature on the Mechanical Performance

AbstractThis research aims to integrate the Wire Arc Additive Manufacturing (WAAM) process into the Selective Paste Intrusion (SPI) process to enable the production of reinforced concrete elements with complex geometries. However, the high temperatures generated during the steel melting process in WAAM can locally lead to a full stop of hydration which consequently is linked to a decrease of the mechanical properties of the concrete in the bonding zone around the reinforcing bar. This study aims to determine the maximum allowable temperature at which concrete retains sufficient hardening conditions which allows strength development when combining SPI with WAAM. In practical application, this temperature limit can directly be affected by e.g. the protruding length of the WAAM‐reinforcing bar above the SPI particle bed or external cooling strategies. As continuation of previous research, this study establishes a link between actual and targeted temperatures in the steel bar to allow the combination of WAAM and SPI processes. Temperature limits without compromising mechanical performance are investigated, and the need for and extent of additional cooling measures are evaluated. The results show that temperatures of the concrete in the fresh state can reach up to 70°C without weakening its mechanical performance.

Investigating the effect of surface protrusions on galloping energy harvesting

This Letter explores the potential effect of implementing different surface protrusions on galloping energy harvesters. Three types of protruded bluff bodies with rectangular, triangular, and elliptical metasurfaces are proposed, and four kinds of surface treatments are deployed to vary their protruded shape. Wind tunnel experiments reveal that adding the protrusions can obviously change the mode of oscillations, and only the backward protrusions can enhance the galloping response. Both the experiments and simulations show that elliptical surface protrusions have the greatest potential to enhance the galloping energy harvesting performance. Specifically, with a backward protruded length of 15 mm, the maximum output power in the experiments is measured to be 0.757 mW, which occurs at 5.1 m/s, and an optimal load resistance of 300 kΩ. In this case, the energy harvester outperforms its counterpart carrying a simple square prism by 157.48%.

Length-Controllable Gold-Coated Silver Nanowire Probes for High AFM-TERS Scattering Activity.

Tip-enhanced Raman scattering (TERS) microscopy is an advanced technique for investigation at the nanoscale that provides topographic and chemical information simultaneously. The TERS probe plays a crucial role in the microscopic performance. In the recent past, the development of silver nanowire (AgNW) based TERS probes solved the main tip fabrication issues, such as low mechanical strength and reproducibility. However, this fabrication method still suffers from low control of the protruded length of the AgNW. In this work, a simple water-air interface electrocutting method is proposed to achieve wide controllability of the length. This water cutting method was combined with a succedent Au coating on the AgNW surface, and the probe achieved an up to 100× higher enhancement factor (EF) and a 2× smaller spatial resolution compared to pristine AgNW. Thanks to this excellent EF, the water-cut Au-coated AgNW probes were found to possess high TERS activity even in the nongap mode, enabling broad applications.

Comparison of ultrasound and dorsal tangential view for dorsal cortex screw penetration in volar plating of the distal radius.

We compared the accuracy of the fluoroscopic dorsal tangential view (DTV) and an ultrasound (US) examination in detecting dorsal screw penetration during volar distal radius plating. In six fresh cadaveric distal radii, seven periarticular locking screws in two rows for each plate were inserted according to the measured length using a depth gauge and then replaced with another that was 1 and 2 mm longer, respectively. The actual protruded length of each screw was determined using computed tomography (CT) images. The accuracy of US and DTV measurements was determined using the intraclass correlation coefficient (ICC), as both measurements were compared with CT measurements. The ICC of US and DTV was 0.96 and 0.75, respectively, for all screws. After excluding the data for proximal-row screws, the ICC of US remained unchanged at 0.96, and that of DTV improved to 0.86. The ICC of US was significantly higher than that of DTV (p < 0.01). US had a 100% detection rate for screw protrusion of more than 1.0 mm. US examination showed excellent consistency with CT measurements and its accuracy was not affected by screw location. US might thus be a practical tool for detecting dorsal cortex screw penetration during volar distal radius plating.

Influence of protection tube on thermocouple effect length

Thermocouples are often equipped with ceramic protection tubes. The existence of the tube changes the heat transfer of thermocouple wires. It will change the bead temperature, i.e., the measurement temperature. The one-dimensional axial heat transfer program for the thermocouple with the protection tube is developed. The accuracy of the program is validated by three-dimensional CFD simulations. The influence of the protection tube on the bead temperature and the effect length is studied with the one-dimensional program. The existence of the tube lowers the bead temperature. The smaller the wire protruding length from the tube, the larger the bead temperature drop. The effect of the tube thermal properties such as the thermal conductivity and emissivity on the thermocouple temperature is studied. The properties have strong effect on the tube temperature profile but their effect on the bead temperature is slight. An analytical method is developed to calculate the effect length of the thermocouple with the protection tube. The error of the method is less than 12% compared with the numerical result for the tested cases. The tube existence increases the effect length. Increasing the wire protruding length from the tube, the tube influence on the effect length decreases.

Sensitive pH measurement using EGFET pH-microsensor based on ZnO nanowire functionalized carbon-fibers

Herein, we report the fabrication of zinc oxide nanowire (ZnO NW) coated carbon fiber (CF) ultra-microelectrodes (UME). ZnO NWs were grown on commercial multifilament CFs through hydrothermal process in a teflon-lined autoclave at 90 °C for 4 h. X-ray diffraction (XRD), Raman and scanning electron microscopy characterizations showed that crystalline and well oriented NW structures were successfully obtained. The fabrication of the pH sensitive UME was carried out by a novel approach which allowed controlling the protruding length of the modified CF surface. The UME was then integrated with a metal-oxide-semiconductor field effect transistor (MOSFET) for the construction of an EGFET pH-microsensor. The present pH microsensor is expected to be useful for localized pH measurement in small volumes such single cell analysis.

Radiography study on osteotome sinus floor elevation with placed implant simultaneously with no graft augmentation

OBJECTIVE To investigate the change of endo-sinus bone height and bone volume in osteotome sinus floor elevation (OSFE) without bone graft but placing implants simultaneously by using cone beam computed tomography (CBCT) and three dimensional analysis, and to find the impacting factors on endo-sinus bone augmentation. METHODS OSFE was performed in 38 edentulous patients with missing teeth at posterior maxillary region, and 44 implants were placed and referred for OSFE using no graft materials. CBCT was performed pre-surgery and 9－68 months post-surgery when the patients encountered another implant surgery. The gained bone height at mesial, distal, buccal and palatal sites around the implant in sinus were measured, volumetric measurements of the endo-sinus gained bone volume (ESGBV) in the elevated region were calculated by Mimics software. Univariate analysis and multiple linear regression were performed to investigate the impacting factors on the gained bone height and ESGBV. Marginal bone loss was recorded according to the periapical radiography after implant restoration. RESULTS The mean residual bone height (RBH) pre-surgery was (3.41±1.23) mm, the mean protruded length (PL) into sinus of implant post-surgery was (3.41±1.28) mm, the mean endo-sinus gained bone height was (2.44±1.23) mm at distal sites, (2.88±1.20) mm at mesial sites, (2.83±1.22) mm at buccal sites and (2.96±1.16) mm at palatal sites, the mean endo-sinus gained bone height at distal sites was significantly lower than the other three sites (P < 0.05). The average endo-sinus gained bone height was (2.78±1.13) mm. The mean ESGBV was (122.15± 73.27) mm3. Univariate analysis showed the more RBH, the less bone height gained in sinus, which existed at buccal, lingual, mesial and distal sites (P < 0.001), and the more RBH, the smaller ESGBV gained (P=0.012). The ESGBV was significantly higher in the subjects whose bone generation period was more than 24 months than those whose bone generation period less than 24 months (P=0.034). The more PL, the more bone height and ESGBV gained (P=0.008). Multivariate analysis showed after adjusting factors of gender, age, smoking, width of sinus floor, thickness of sinus membrane pre-surgery, diameter and length of the implant, PL and bone generation period was positively correlated with mean endo-sinus gained bone height and ESGBV, while RBH negatively correlated with mean endo-sinus gained bone height. During the follow-up, the mean marginal bone loss was 0 (0－1.41) mm and all the implants loaded successfully. CONCLUSION OSFE without bone graft but with placed implant simultaneously can increase endo-sinus gained bone height and ESGBV. RBH, PL and bone generation period are the significant factors impacting endo-sinus bone augmentation.

Investigation of proposed countermeasures against coastal erosion and sediment invasion around half-buried floodway

ABSTRACTCountermeasures are investigated against coastal erosion and sediment invasion around a half-buried floodway through a series of small-scale physical model experimentations. Further, countermeasures are proposed to shorten the protruded length of the floodway across the shoreline to prevent interruption of longshore sediment transport and to excavate downdrift sediments at the mouth of the floodway to minimize the downdrift erosion as well as the sedimentation inside the floodway. Results of the study show that the shortened floodway is successful in mitigating downdrift erosion, while continuous downdrift excavation is proven to be significantly effective in reducing sedimentation inside the floodway when excavation is implemented with the same order-of-magnitude of the longshore sand transport rate. Attention must be paid, however, on the effect of wave randomness and floodway discharge during stormy waves as they further increase sedimentation inside the floodway apparently owing to onshore sediment movement enhanced by asymmetric horizontal acceleration and to a large skewness in the water particle velocity at the mouth of the floodway.

Biomechanical implications of the fenestration structure after thoracic endovascular aortic repair

The inadequate landing zone during thoracic endovascular aortic repair (TEVAR) could be resolved by fenestration technology. The fenestration structure consists of a main endograft and a left subclavian artery (LSA) stent-graft. The purpose of this study is to assess the biomechanical implications of the protruding segment (PS) of the LSA stent-graft after TEVAR with in situ fenestration (ISF-TEVAR). The PS is characterized by the protruding length and centerline angle between the LSA and PS. An idealized three-dimensional geometric model of the human aorta was constructed as the reference benchmark. We designed nine postoperative aortic geometries with different protruding lengths (5, 10, 15 mm) and centerline angles (-20°, 0°, +20°). The blood was assumed to be non-Newtonian and the three-element Windkessel model was applied to reproduce physiological pressure waveforms. The interaction between the blood and vessel wall was captured by a two-way fluid-structure method. We also considered the impact of the fenestration structure on the vessel wall. Long protruding length (15 mm) and the retrograde angle (+20°) result in a markedly reduced LSA flow ratio (1.3%). There is a pressure difference between the inner and outer walls of the PS. The region around the PS is more prone to thrombosis. The flow stability and turbulence intensity of downstream blood of the PS gradually deteriorate. The largest deformed region moves from the aortic arch to the ascending aorta after ISF-TEVAR. The postoperative hemodynamics largely depends on the protruding length and angle of the LSA stent-graft. The configurations should be carefully controlled during ISF-TEVAR.

Accelerating sample preparation of graded thermoelectric materials using an automatic powder feeding system

In recent years, the development of techniques for the controlled preparation of functional graded materials (FGMs) has become a vigorous research field. In this study, to improve the efficiency and accuracy of sample preparations, an automated feeding system based on gravimetric principles for dry powder with three dosing feeders is designed and realized. The feeding rate and accuracy can be regulated by coordinating the protruded length L (mm) and rotational speed V (r/min) of the feeder stirrer. To demonstrate this automatic sample preparation system, the well-known thermoelectric material BixSb2−xTe3 (x = 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) is selected and prepared by the developed system, and the composition distribution of the functional graded material is characterized. Experimental results show that the BixSb2−xTe3 (x = 0.3–0.8) functionally graded material crystalizes in the rhombohedral phase after hot-pressing sintering and annealing and the prepared sample has a good gradient composition distribution. This verifies the reliability and accuracy of the feeding system. The concept of samples with a gradient component and application of the automatic powder feeding system could considerably accelerate the research and development of new materials.

SURVEY OF BUILDINGS WITH NATURAL VENTILATION AND BASIC ANALYSIS OF BUOYANCY DRIVEN VENTILATION

In recent times, the use of natural ventilation in office buildings, schools or public facilities has become popular. The purpose of natural ventilation is not only to reduce air conditioning usage and enhance comfort but also to facilitate the improvement in intellectual productivity. However, natural ventilation rate must be appropriate in order to achieve these results. Since natural ventilation rate is affected by changes in outside conditions, to execute natural ventilation control, it is necessary to adjust the opening area. Therefore, develop simulations that can help evaluate natural ventilation control. The main purpose of this study is to evaluate the performance evaluation of natural ventilation control in office buildings. In this study, we first surveyed the actual state of buildings with natural ventilation. In addition, following the survey, we examined the basic characteristics of the buoyancy driven ventilation using airflow network analysis. In the survey, the elements that affect the natural ventilation rate were identified. We surveyed the effective opening area of natural ventilation opening (αAi), natural ventilation path, and the movement of buildings that use natural ventilation. We found three things: 1) αAi is correlated with typical floor area, 2) about 85% of the naturally ventilated buildings have adopted the buoyancy driven ventilation, 3) there is a recent technique to separate the chimney for effective natural ventilation. The details of this survey are given in Chapter 3. We carried out three numerical analyses of natural ventilation rate and neutral pressure level due to change αAi. These analyses assumed ten-story buildings. 1) We calculated air changes per hour due to opening and closing of the entrance. There was not any significant effect on the natural ventilation rate of the second floor and more due to a sufficient increase in the neutral pressure level. 2) We suggested two methods to reduce the difference between the natural ventilation rates of each floor. First, we calculated air changes per hour due to a smaller αAi on the lower half of the floor. Second, we calculated air changes per hour due to separate chimneys into two, upper and lower, of the floor. According to these analyses, αAi of the lower half of the floor can be set to 50% of the αAi of the upper half of the floor or the chimney can be lowered up to sixth floor to reduce the difference between natural ventilation rates each floor. 3) We determined the neutral pressure level. In brief, there are three findings. First, αAi on all the floors should be same. Second, αAi on the lower half of the floor should be small. Finally, the chimney's protruding length set to be longer. Following these suggestions, one can determine neutral pressure level. Furthermore, we presented a graph for determining αAi to achieve appropriate natural ventilation rate, which is called “Isodose curve of air changes per hour.” Details of these analyses are given in Chapter 4. In future research, the proposed airflow network analysis method can be used to evaluated the performance of natural ventilation control in office buildings.

Ultra-sharp and surfactant-free silver nanowire for scanning tunneling microscopy and tip-enhanced Raman spectroscopy.

Chemically-synthesized single-crystalline silver nanowire (AgNW) probes can combine the scanning tunneling microscopy (STM) technique with tip-enhanced Raman scattering spectroscopy (TERS) for complementary morphological and chemical information with nanoscale spatial resolution. However, its performance has been limited by the blunt nanowire tip geometry, the insulating surfactant layer coating AgNW surfaces, and the thermal-induced mechanical vibrations. Here, we report a reproducible fabrication method for the preparation of sharp-tip AgNW-based TERS probes. By removing the polyvinylpyrrolidone (PVP) surfactant molecules from the AgNW surfaces for stable electrical conductivity and controlling the protruding length with μm-level accuracy for improved mechanical stability, we demonstrate atomic-resolution STM imaging with the sharp-tip AgNW probe. Furthermore, the sharp-tip AgNW has an excellent TER enhancement (∼1.1 × 106), which is about 66 folds of that achieved by regular AgNWs. Our experiments demonstrate that AgNWs with clean interfaces and the proper tip geometry can provide reliable and reproducible STM and TER characterizations, which remove the hurdles preventing the implementation of AgNW in STM-based near-field optical applications for a broad community.

The connection between microscopic and macroscopic properties of ultra-high strength and ultra-high ductility cementitious composites (UHS-UHDCC)

There is an important connection between the microscopic and macroscopic properties of UHS-UHDCC with compressive strength (more than 160 MPa) and uniaxial tensile ductility (more than 6%). First, some microscopic properties were studied. For the fresh mortar matrix, the plastic viscosity within an optimal range is beneficial to achieve uniform fiber distribution. Compared with the fluorescence analysis, the backscattering analysis more truly displays the fiber distribution situation and cross section shapes of fibers. Based on the mesh size of three-dimensional grid formed by theoretically absolutely uniform distributed fibers, the river sand with an average particle size of 240 μm was selected as the aggregate. The addition of fibers slightly increases the porosity, the larger bubbles are not easy to be excreted due to the isolation of the fiber mesh. With the increasing of silica fume (SF) dosage and the decreasing of the water-binder ratio (w/b), the overall protruded length of fibers on fracture surface of tensile specimen reveals a decreasing trend, the hydration product attached to the fibers first increases and then decreases, and the decreasing accompanies a more severely scraped fiber surface, the fiber shedding changes from being no apparent to gradually increase. Increasing SF dosage or decreasing the w/b, the elastic modulus increases with different degrees, and the difference between the elastic modulus in interfacial transition zone (ITZ) of about 60 μm span and that of mortar matrix gets smaller and smaller. The elastic modulus in ITZ exhibits a gradient that first decreases and then increases. Further, the connection between microscopic and macroscopic (flexural、compressive、tensile) properties was analyzed. The highest fiber dispersion degree at mix proportion 0.4SF + W0.19 + PE and its suitable interfacial bonding strength together create the saturated multi-crack ductility of 6.53% and compressive strength of 163 MPa. When the strength growth benefitting from the increasing of interfacial bonding strength lowers than the strength loss due to the decreasing of the fiber dispersion degree, the ultimate tensile strength and the flexural strength of UHS-UHDCC decrease.

Non-destructive testing of full-length bonded rock bolts based on HHT signal analysis

Full-length bonded rock bolts are commonly used in mining, tunneling and slope engineering because of their simple design and resistance to corrosion. However, the length of a rock bolt and grouting quality do not often meet the required design standards in practice because of the concealment and complexity of bolt construction. Non-destructive testing is preferred when testing a rock bolt's quality because of the convenience, low cost and wide detection range. In this paper, a signal analysis method for the non-destructive sound wave testing of full-length bonded rock bolts is presented, which is based on the Hilbert-Huang transform (HHT). First, we introduce the HHT analysis method to calculate the bolt length and identify defect locations based on sound wave reflection test signals, which includes decomposing the test signal via empirical mode decomposition (EMD), selecting the intrinsic mode functions (IMF) using the Pearson Correlation Index (PCI) and calculating the instantaneous phase and frequency via the Hilbert transform (HT). Second, six model tests are conducted using different grouting defects and bolt protruding lengths to verify the effectiveness of the HHT analysis method. Lastly, the influence of the bolt protruding length on the test signal, identification of multiple reflections from defects, bolt end and protruding end, and mode mixing from EMD are discussed. The HHT analysis method can identify the bolt length and grouting defect locations from signals that contain noise at multiple reflected interfaces. The reflection from the long protruding end creates an irregular test signal with many frequency peaks on the spectrum. The reflections from defects barely change the original signal because they are low energy, which cannot be adequately resolved using existing methods. The HHT analysis method can identify reflections from the long protruding end of the bolt and multiple reflections from grouting defects based on mutations in the instantaneous frequency, which makes weak reflections more noticeable. The mode mixing phenomenon is observed in several tests, but this does not markedly affect the identification results due to the simple medium in bolt tests. The mode mixing can be reduced by ensemble EMD (EEMD) or complete ensemble EMD with adaptive noise (CEEMDAN), which are powerful tools to used analyze the test signal in a complex medium and may play an important role in future studies. The HHT bolt signal analysis method is a self-adaptive and automatic process, which can be programed as analysis software and will make bolt tests more convenient in practice.

Radiographic Outcomes of Osteosynthesis Using Proximal Femoral Nail Antirotation (PFNA) System in Intertrochanteric Femoral Fracture: Has PFNA II Solved All the Problems?

PurposeWe evaluated the geometric discrepancies between the proximal femur in Koreans and two types of proximal femoral nail using plain radiographs.Materials and MethodsA total of 100 consecutive patients (38 treated with proximal femoral nail antirotation [PFNA], 62 PFNA II) with intertrochanteric fracture were retrospectively identified. The minimum follow up period was 32 months. The geometric analysis of the proximal femur was performed using preoperative true hip antero-posterior radiographs of the unaffected side, and the data were compared with the PFNA and PFNA II dimensions. Postoperative assessments were performed using postoperative radiographs for the proximal protruding length of nail tip, quality of reduction, implant position and the presence of lateral cortical impingement.ResultsThe geometric dimensions of the proximal femur were different between the two proximal femoral nail types. No impingement was detected in patients treated with PFNA II, whereas 13 cases of lateral impingement were observed in patients treated with PFNA. A significant association was observed between the short proximal femur and the presence of lateral cortical impingement (P=0.032) and between impingement and intraoperative reduction loss (P=0.012). Proximal protrusion of the nail tip was seen in 71 patients and no difference was observed between two groups.ConclusionOur study demonstrates that the flat lateral surface of PFNA II can avoid lateral cortical impingement, which provide better fixation for intertrochanteric fracture. However, there was still a problem associated with longer proximal end of PFNA II compared with the proximal femoral length in Korean.

庇のある実大モデル空間が覆われ感に与える影響

Presently, semi-outdoor spaces with eaves are used as lounge spaces for waiting, resting, eating, and drinking with other people. Although previously eaves had been used for their original purposes, such as blocking the rain, they began to be used for new attractive aims with different functions in recent years. Human activity in semi-outdoor spaces with eaves has activated; in addition, the spaces have become new attractions in cities. However, the relationship between the physical environment and psychological effects weren't be considered quantitatively. In this study, the impact on the feeling of being covered in full-scale model of outdoor spaces with eaves was demonstrated quantitatively by conducting real space experiments by changing the height and size of the eaves. Experiments in full-scale model space were simulated using three levels of height and five or seven lengths of eaves. As a result, it was confirmed that the shape of the eaves with different heights and sizes affected the feelings of being covered, and the human sense of space was changed by the height and protruding length of the eaves. Specifically, the results were summarized in the following three points: 1) When the height and length of the protruding eaves are a variable, feelings of being covered can be quantitatively expressed by the ME method. 2) The feelings of being covered were reduced as the height of the eaves increased. The gradient of the decrease was substantially constant when the lengths of the eaves were different. 3) The sense of being covered increased as the protruding length of the eaves increased. As the heights of the eaves are low, the gradient of increase in the feelings of being covered becomes larger. With consideration given to the spatial characteristics of the eaves, it is necessary to conduct effective space design.

Thermomechanical analysis of the formation of hot cracks in remote laser welded aluminium fillet welds

Remote laser welding of high strength aluminum alloys is still a field of extensive research due to the hot cracking phenomena. Recent research activities have been focused on center-line hot cracks in welds that are located close to the edge of the material. To avoid this type of crack from occurring, a fillet weld joint design could be utilized. However, within the fillet welds there are still transverse hot cracks present on a microscopic scale. This paper presents a thermomechanical analysis of the formation of transverse hot cracks in EN AW-6082 alloy fillet welds. In order to calculate the local deformation near the mush zone, a welding simulation based on the finite element method was created. The simulation was able to depict different settings for the welding speed, laser power, beam position, protruding length of the lower sheet, and the sheet thickness. For this purpose, an automated method for heat source calibration was developed based on image processing of polish of cross sections of different weld seams. As a result, it was possible to investigate the influencing factors on the formation of local strain and strain rate during the hot crack sensitive temperature range. It was found that the welding speed and laser power significantly increased the strain rate, but had no effect on the strain. In addition, it was determined that the position of the laser beam caused a major difference in the formation of strain and strain rate if weld seams changed from partial penetration to full penetration. Full penetration welds had lower strain and strain rate. The protruding length of the lower sheet and the sheet thickness had a minor impact on strain and strain rate. By linking the computerized results of strain and strain rate with data obtained from experiments on the hot crack susceptibility, a hot cracking criteria based on strain rate was found.

Experimental and numerical investigation of air entrainment into a louvred funnel

In the present study, experiments as well as numerical computations based on finite volume method have been carried out to investigate the entrainment of ambient air into a laboratory-scale louvred funnel, which are mostly used in naval warships and cargo ships to suppress infrared emissions. Conservation equations for mass, momentum and energy are solved in a three-dimensional domain by employing eddy viscosity based two equation k−ɛ turbulence model with log-law wall functions. Reynolds number, louvred opening area as well as nozzle protruding length are varied in the range of 3250≤Re≤6600, 116.7≤AL/Dnz2≤584, and 0<Lp/Dnz<12, respectively. It is observed that the mass suction increases with the Reynolds number, louvred opening area and nozzle protruding length. The louvred opening-area is the most important parameter in the entrainment process and then, the nozzle protruding length is the second most affecting parameter on air suction. Experiments using hot nozzle fluid are conducted to establish the fact that hotter fluid will always entrain more surrounding air compared to the cold nozzle fluid because of buoyancy. It is also observed that the computed and experimental values of mass entrainment rates agree well with each other.