Head Design Research Articles

An Experimental and Numerical Study of Damage Due to Particle Impact on Sapphire Orifices Used in High-Pressure Water Jet Cutting

In the present study, the damage mechanisms that cause premature failure of sapphire water jet orifices were analyzed using a combined experimental and finite element modeling (FEM) approach. Depending on the operating behavior and local conditions, the service life of orifices for high-pressure water jet cutting often deviates considerably from the manufacturer’s specifications. Literature states a typical service life of 50 to 100 h, while in some cases, premature failure after a few hours or even minutes of operation can be observed. The focus of this paper is on the interaction of particles that impact the orifice surface but also the effect of faulty orifice assembly is taken into account. To estimate the risk of failure, the stress distribution in critical parts of the orifice were calculated via FEM, which is fed with experimental data. The modified Mohr failure criterion was then used to evaluate the stress distributions with respect to the possible failure of the orifice jewel. The results revealed that the risk of damage caused by excessive assembly preload forces is marginal. The stress caused by the impact of particles of different sizes is up to four orders of magnitude higher than the stress caused by assembly forces and is therefore identified as the main risk for orifices to fail prematurely. Experimental data shows mainly particles of calcium carbonate and iron–aluminum silicates, which are compounds that originate from the process water itself. It is demonstrated that particles are more critical than formerly assumed in the literature. This paper identifies particles with a diameter of more than 10 µm as critical when there are no other loads present. In operation, even particles as small as 2 µm in diameter can cause damage to the orifice jewel. To prevent premature orifice failure due to foreign particles, water filtration with a 2 µm mesh is recommended, while future research needs to focus on the interior cutting head design to prevent precipitation from the process water.

Performance Analysis of an Experimental Linear Encoder’s Reading Head under Different Mounting and Dynamic Conditions

The performance of an optical linear encoder is described and evaluated by certain parameters such as its resolution, accuracy and repeatability. The best encoder for a particular application, just like other sensors, is usually selected according these parameters. There are, however, many side effects that have a direct influence on the optimal operation of an encoder. In order to understand how to minimize these harmful effects, a deeper knowledge of an encoder’s performance and a method for determining these factors are necessary. The main aspects of an encoder’s accuracy, resolution and repeatability are briefly reviewed in this paper. Discussed and developed in previous work, the experimental reading head for a Moiré effect-based optical linear encoder is used for the experimental analysis of the influence of different reading head designs on an encoder’s performance under various mounting inaccuracies and dynamic conditions.

Evaluation of implant abutment screw head deformation in hexagonal and star designs after successive tightening and loosening.

Tightening and loosening of the prosthetic components of the implant are carried out with various screw designs. This study compared the rate of deformation of the abutment screw in two hexagonal and star screw head designs after consecutive tightening and loosening. In this study, two fixtures were mounted vertically in die stone blocks using a surveyor. Then the corresponding abutment (with a diameter of 4.5 mm and a gingival height of 2 mm; Dio-SM and Dio-UF system) was mounted on each fixture. In each fixture, six abutment screws from each manufacturer were used (12 abutment screws in total). The abutment screw head of the Dio-UF system is hexagonal, and the abutment screw head of the Dio-SM system is star-shaped. The samples were examined under a stereomicroscope (Nikon C-DS) at a magnification of×50. The image of each abutment screw head (6 abutment screws in each group) was prepared before the procedural steps and after 5, 10, and 15 times of tightening and loosening with 25-Ncm torque using a stereomicroscope. Then the differences in the surface areas of consecutive specimens (0, 5, 10, and 15 consecutive tightening and loosening rounds) between hexagonal and star-shaped abutment screws were calculated. The study results were reported via descriptive statistical methods (mean±standard deviation). Statistical analysis was performed using SPSS 24, and the significance level was defined at P<0.05. Increasing the number of tightening and loosening rounds increased the screw head surface area in both hexagonal and star shapes. At all stages, the changes in the star-shaped screw head were greater than in the hexagonal screw. These changes were statistically significant at all stages (P<0.05). In addition, there was a statistically significant difference between the area values and the number of tightening and loosening rounds separately in both screw types (P<0.001). Also, the surface areas of the head of both screws in all tightening and loosening rounds were significantly different (P<0.001). Increasing the number of tightening and loosening rounds increased the screw head surface area in both hexagonal and star-shaped geometrical forms. Also, the extent of area changes at all stages in star-shaped screw heads was greater than in hexagonal screws.

Study on thermal-mechanical characteristics and crater wear of cemented carbide tools during the milling 508III steel

The water chamber head is made of 508III steel with high strength and hardness. The cemented carbide tool bears a large thermal-mechanical load during the cutting process, which leads to severe insert wear and damage as well as low tool life. Firstly, the milling experiments and finite element (FE) simulation were carried out to study the thermal-mechanical characteristics of tools. Secondly, the thermal-mechanical coupling simulation was carried out to explore the temperature field, strain, total deformation of the milling cutter, and the deformation and strain of the rake face of the milling insert respectively. Finally, the tool wear experiment was carried out, and the form, morphology, and energy spectrum of tool wear were analyzed, and the parameters of the crater wear were measured. The proposed crater wear rate was used as the characterization variable of tool wear, and the crater wear rate model was established to explore the wear evolution process of inserts preliminarily. The research results can provide theoretical support and experimental basis for the in-depth study of the tool failure mechanism and tool optimal design of the high-efficiency milling water chamber head.

Topology optimization of a heat-assisted magnetic recording write head to reduce transition curvature using a binary optimization algorithm utilizing the adjoint method

In this work, the possibility to reduce transition curvature in heat-assisted magnetic recording, using a conventional write head design, by shaping the recording field to counteract the circular profile of the heat pulse is investigated. Topology optimization of the head tip is performed in order to create the desired cross-track field profile for increasing distances from the write head tip. For the topology optimization, the adjoint method is utilized to calculate the necessary gradients and a binary optimization scheme is proposed. The optimizations are performed considering linearized material parameters reducing the computational complexity and the results are compared to optimizations incorporating the full non-linear material behavior. The optimized field profiles are evaluated for their influence on the read-back process. To do so, switching probability phase diagrams are calculated and the curvature parameter, the signal to noise ratio and the channel bit density are extracted. The presented results show that while transition curvature can be reduced by shaping the cross-track profile of the write field, this alone does not consequently lead to an improvement of the read back process. Therefore, completely new head designs, considering additional parameters have to be investigated.

The importance of maldistribution matching for thermal performance of compact heat exchangers

Compact heat exchangers have gained increased attention in recent years, particularly in demanding applications where high temperatures, high pressures, and/or high power densities are required. For decades, the heat exchanger (HX) community believes that flow maldistribution is a key factor for HX effectiveness, that is, reducing the degree of flow maldistribution (MALD) can help increase the HX effectiveness. Therefore, significant efforts have been devoted in the past to optimizing the header geometry to minimize flow maldistribution. This work was initially motivated by this, and the original goal was to figure out a HX header design with the lowest maldistribution. However, by systematically constructing a comprehensive maldistribution matrix, the analysis revealed that the HX effectiveness is not actually determined by the MALD, but instead dominated by the degree of maldistribution mismatch (MISM). This conclusion was also theoretically generalized, which indicated that matching of the local heat capacity rate is key for achieving maximum performance. The MISM provides a local means of tracking this information, while the MALD only provides a global approximation of the maldistribution itself. With this new perspective, flow maldistribution needs not necessarily be avoided, but instead matched between two fluid streams, to improve the HX performance. We demonstrated that by carefully designing the header geometry to match the velocity profiles of the two fluids in a 2 MW PCHE with molten salt and supercritical carbon dioxide (sCO2) as the heat transfer fluids, the HX could achieve a higher effectiveness even when the maldistribution increased. A technoeconomic study using a CSP system as an example revealed that the use of this new HX design paradigm could result in CSP capital cost savings as large as 16.6%.

Space-qualified, compact and lightweight pulsed DPSS UV laser for the MOMA instrument of the ExoMars mission

A space-qualified pulsed UV laser has been developed as an irradiation source for the Mars Organic Molecule Analyser (MOMA) instrument aboard the “Rosalind Franklin” rover of the ExoMars mission (ESA/Roscosmos). MOMA will search for signatures of extinct and/or extant life on Mars. Its advanced analytical capabilities arise from the combination of a pyrolysis gas chromatograph and an ion trap-based mass spectrometer. With the addition of a compact UV laser system enabling laser desorption/ionization mass spectrometry, MOMA can detect a wide variety of both volatile and non-volatile, organic and inorganic molecules within Martian soil samples of interest. The design of the MOMA Laser Head is based on a longitudinally diode-pumped, passively Q-switched Nd:Cr:YAG oscillator generating millijoule pulses with nanosecond pulse durations at a wavelength of 1064 nm. A subsequent two-stage frequency quadrupling converts the fundamental infrared emission of the oscillator into the deep UV at 266 nm. The Laser Head emits UV pulses with a duration of about 1.5 ns and an energy tunable between 12.5 and 125 µJ for optimum adaptation to varying ionization thresholds of different molecular species. The complex but highly compact opto-mechanical design, enclosed in a hermetically sealed housing, is realized within an envelope of 200 × 56 × 45 mm3 with a total mass of less than 220 g. In this paper, we present a comprehensive summary of our development efforts towards the delivery of the LH Flight Model, which has been integrated to the MOMA instrument and finally incorporated into the ExoMars rover.

Revealing the bonding mechanisms between deposit and substrate of the friction rolling additive manufactured hybrid aluminum alloys

Friction rolling additive manufacturing (FRAM) is an emerging solid-state additive manufacturing technology for high-strength aluminum alloys that are prone to produce solidification defects using fusion-based additive manufacturing method. However, the mechanisms responsible for good bonding between the FRAM interlayers remain unclear. This study successfully reveals such mechanisms for FRAM-produced hybrid AA2319 and AA6061 aluminum alloys using 3D X-ray computed tomography, electron backscatter diffraction, and transmission electron microscopy. Three findings concerning the quality of bonding between adjacent layers in FRAM were obtained. Firstly, material plastic flow and macroscopic migration behavior occurred simultaneously along the longitudinal and transverse directions at the interlayer, forming a macroscopic mechanically interlocking nonplanar interface. The convex thread at the tool head increased the material flow in the transverse direction, facilitating material mixing in the adjacent layer. Secondly, severe plastic deformation resulted in significant grain refinement on both sides of the interface. The average grain size reduction rates for the sides of AA2319 and AA6061 were 98.3% and 95.9%, respectively. Thirdly, direct contact with no obvious oxides resulted in complete metallurgical interface bonding. These findings can aid in the elucidation of the basic physical process of FRAM and provide guidance for process parameter optimization and tool head design in the future. • Mechanically interlocked non-planar interface was formed during the FRAM process. • Material flow occurred simultaneously along with the longitudinal and transverse directions at the interlayer. • Thread protrusion significantly increased the material flow in the transverse direction. • Severe plastic deformation resulted in significant grain size reduction for both sides of the interface. • It was experimentally proved that direct contact with no oxide was achieved at the interface, forming a complete metallurgical bonding.

ULO: An Underwater Light-Weight Object Detector for Edge Computing

Recent studies on underwater object detection have progressed with the development of deep-learning methods. Generally, the model performance increase is accompanied by an increase in computation. However, a significant fraction of remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs) operate in environments with limited power and computation resources, making large models inapplicable. In this paper, we propose a fast and compact object detector—namely, the Underwater Light-weight Object detector (ULO)—for several marine products, such as scallops, starfish, echinus, and holothurians. ULO achieves comparable results to YOLO-v3 with less than 7% of its computation. ULO is modified based on the YOLO Nano architecture, and some modern architectures are used to optimize it, such as the Ghost module and decoupled head design in detection. We propose an adaptive pre-processing module for the image degradation problem that is common in underwater images. The module is lightweight and simple to use, and ablation experiments verify its effectiveness. Moreover, ULO Tiny, a lite version of ULO, is proposed to achieve further computation reduction. Furthermore, we optimize the annotations of the URPC2019 dataset, and the modified annotations are more accurate in localization and classification. The refined annotations are available to the public for research use.

A mixed methods study on effectiveness and appropriateness of face shield use as COVID-19 PPE in middle income countries

BackgroundFace shields were widely used in 2020-2021 as facial personal protective equipment (PPE). Laboratory evidence about how protective face shields might be and whether real world user priorities and usage habits conflicted with best practice for maximum possible protection was lacking – especially in limited resource settings. MethodsRelative protective potential of 13 face shield designs were tested in a controlled laboratory setting. Community and health care workers were surveyed in middle income country cities (Brazil and Nigeria) about their preferences and perspectives on face shields as facial PPE. Priorities about facial PPE held by survey participants were compared with the implications of the laboratory-generated test results. ResultsNo face shield tested totally eliminated exposure. Head orientation and design features influenced the level of protection. Over 600 individuals were interviewed in Brazil and Nigeria (including 240 health care workers) in March-April 2021. Respondents commented on what influenced their preferred forms of facial PPE, how they tended to clean face shields, and their priorities in choosing a face cover product. Surveyed health care workers commonly bought personal protection equipment for use at work. ConclusionsAll face shields provided some protection but none gave high levels of protection against external droplet contamination. Respondents wanted facial PPE that considered good communication, secure fixture, good visibility, comfort, fashion, and has validated protectiveness.

High-fidelity eye, head, body, and world tracking with a wearable device

We describe the design and performance of a high-fidelity wearable head-, body-, and eye-tracking system that offers significant improvement over previous such devices. This device’s sensors include a binocular eye tracker, an RGB-D scene camera, a high-frame-rate scene camera, and two visual odometry sensors, for a total of ten cameras, which we synchronize and record from with a data rate of over 700 MB/s. The sensors are operated by a mini-PC optimized for fast data collection, and powered by a small battery pack. The device records a subject’s eye, head, and body positions, simultaneously with RGB and depth data from the subject’s visual environment, measured with high spatial and temporal resolution. The headset weighs only 1.4 kg, and the backpack with batteries 3.9 kg. The device can be comfortably worn by the subject, allowing a high degree of mobility. Together, this system overcomes many limitations of previous such systems, allowing high-fidelity characterization of the dynamics of natural vision.

Error analysis driven network modification for surgical tools detection in laparoscopic frames

AbstractIn minimally invasive laparoscopic surgery, accurate detection of the location and specific category of surgical tools assists the surgeon in making a correct objective judgment of the current surgical outcome and alerts to these possible adverse medical events. In this paper, an analyzing error method is proposed for revealing the specific sources of error in previous work. Then we confirm the main bottlenecks of the current methods with a high level of missing error and localization error. To reduce these errors, we render the backbone with a three‐dimensional attention mechanism and adopt a double‐headed detection head design to replace the single detection head. Moreover, we propose an enhanced multilayer perceptron called Mconv to enhance the localization branch of the double‐headed detection head. Our experiments evaluate our improved approach by our proposed error analysis method on a pubic dataset m2cai16‐tool‐locations, showing that our method yield remarkable detection accuracy than others.

Spherical Collimation Systems Radiation Fields Monte Carlo Calculation

Purpose: To determine the optimal parameters of the collimation system of the gamma therapeutic apparatus. Material and methods: collimation system parameters Monte Carlo simulation in Geant4 Software Package. Results: Simulation in the Geant4 software package is a reliable tool for solving such problems The good agreement between calculated and experimental data was achieved. The proposed system of spherical beam collimation using a source similar to GIK-9-3(4) (manufactured by Mayak), with a value of SSD=1000 mm, is capable of providing the required characteristics of the radiation field over the entire range of its sizes. It seems appropriate to consider the reduction of radiation leakage with the help of a jagged shape of the contacting surfaces of the collimator jaws, since the dose is mainly due to leakage through poorly connected collimator jaws, reduced to a negative angle. Conclusion: The performed calculation of the collimation system makes it possible to use the obtained results for the design of radiation heads of gamma therapeutic devices without additional scientific research. The paper also provides a detailed description of the libraries of physical processes used in Geant4, which allows the reader, if necessary, to repeat the experiment for his/her own needs.

Energy efficiency improvement and emission reduction potential of domestic gas burners through re-orientating the angle and position of burner holes: Experimental and numerical study

The trend towards enhancing the thermal performance of domestic cooking burners necessitates developing a new design for such devices. With this picture in mind, this paper numerically and experimentally investigates the effect of burner head design configurations on the energy efficiency and CO emission of domestic gas burners. The results of a three-dimensional steady-state computational fluid dynamics (CFD) model is validated with the experimental data according to Volunteers in Technical Assistance (VITA) standard in cold start, hot start, and Simmer condition for two types of burners. Having the model validated, a step-by-step approach has been undertaken to improve the design of these reference cases, resulted in a total number of nine burner configurations analysed in this research. This is followed by determining the influence of introduced geometries on the thermal efficiency of burners. Based on the insights from the numerical model, the most efficient burner exhibits 3.3–22.2% higher thermal efficiency and 20.2–32.6% lower CO emission—depending on the gas flow rate—relative to the conventional burners. The optimised design can be implemented into existing burners with relatively little need for reconstruction. • Experimental and numerical study of natural gas combustion in domestic gas burners. • Experimental setup is designed to measure the thermal efficiency of typical burners. • A three-dimensional steady-state turbulent model is developed for numerical study. • Intense mixing induced by secondary effect improved the efficiency by 3.3–22.2%. • Optimum burner configuration lowered the carbon monoxide emission by 20.2–32.6%.

Development of a High-Reliability Vacuum Arc Thruster System

Current vacuum arc thruster systems show insufficient reliability in the low-power () operation mode, which is required for CubeSat propulsion systems. Typically, the failure of the whole thruster system is caused by the failure of the arc ignition system. The reasons for this are deposition of a conducting coating on the insulator surface and geometry changes of the cathode. In this work, a highly reliable vacuum arc thruster system for electric propulsion of small satellite systems (for example, CubeSats) is presented. It is able to reach more than 10 million pulses while keeping the trigger voltage below 3 kV, which is one order of magnitude higher than those of previously published results. The system includes a novel thruster head design in combination with a newly developed power supply system. It was tested with a variable pulse frequency from 1 to 5 Hz. The thruster uses a single titanium cathode in combination with a dual-anode design and can be easily extended with a magnetic nozzle. The combination of the geometry and the power supply creates a system that deals with the aforementioned failure mechanisms. Several long-term tests were performed to demonstrate the system’s functionality. Moreover, erosion measurements and a failure analysis were conducted.

Numerical Study of Factors Affecting Particle Suction Efficiency of Pick-Up Head of a Regenerative Air Vacuum Sweeper

The influence of variable operational conditions affects the performance of particle collection and separation of a regenerative air vacuum sweeper. Therefore, the purpose of this paper was to numerically investigate the factors affecting the particle suction efficiency of the pick-up head. Using computational fluid dynamics (CFD), a model of an integrated pick-up head was developed based on the particle suction process to evaluate the particle removal performance. The realizable k-ε and discrete particle models were utilized to study the gas flow field and solid particle trajectories. The particle structure, sweeping speed, secondary airflow, pressure drop, and distance between the particle suction port and the road surface, as factors that affect the particle removal efficiency, were investigated. The results indicate that the particle suction efficiency increases with decreasing sweeper speed. Furthermore, the particle overall removal efficiency increased with a reduction in the distance between the suction port and the road surface as well as the control of the secondary airflow in the system. By increasing the airflow rate at the suction port, high efficiencies were achieved at a high sweeper speed and high particle densities. At a sweeper speed of 6–10 km/h, the results showed that the secondary airflow recirculation varied between 60 to 80 %, while the high-pressure drop ranged from 2200 to 2400 Pa, and the particle suction efficiency recorded was 95%. The numerical analysis results provide a better understanding of the particle suction process and hence could lead to an improvement in the design of the pick-up head.

Design and fabrication of multi cutting hack saw machine

The growth of Indian manufacturing sector depends largely on its productivity &amp; quality. Productivity depends up on many factors one of the major factors being manufacturing efficiency with which the operation/activities are carried out in the organization. productivity can be improved by reducing the total machining time, combinating the operations etc. In the case of mass production where variety of jobs is less and quantity to be produced is huge, it is very essential to produce the job faster rate. This is not possible if we carry out the production by using general purpose machines. The best way to improve the production rate (productivity) along with quality is by the use of special purpose machine. Usefulness and performance of the existing radial cutter machine will be increased by designing and manufacturing of multi cutter head attachment. This paper details with design and development of multi cutter head for cycle time optimization of the component.

Influence of implant parameters on biomechanical stability of TMJ replacement: A finite element analysis.

The articular disc reduces the stress distribution from the mandible to fossa. In total temporomandibular joint (TMJ) replacement, the implant is required to reduce the stress on fossa implant. Current studies lack standard and optimized parameters for the cylindrical dome on Christensen TMJ implant collar. This study briefed a novel TMJ implant head design and investigates the biomechanical behaviour by considering the articular disc. The radius of the head was varied with the height of the cylinder height to obtain the design of the experiment and the stress distribution was compared with an intact mandible-articular disc model by considering the viscoelastic property of the TMJ disc. The model was simulated at three different angles: 20°, 0° and -20° in the mediolateral direction to simulate the manducation. FEA analysis showed high stresses at the circular heads, and high strength is achieved with increased implant cylinder length and diameter. The results also showed a stress reduction of 50% on the fossa from the mandible. Hence, the newly designed head and suggested modifications may be used as a reference for further clinical improvement of Christensen TMJ as well as other TMJ implants.

Minute workers and large soldiers in the subterranean ant Carebara perpusilla: Musculoskeletal consequences of Haller's rule in the thorax

Many organismal traits vary with body size, often reflecting trade-offs in the face of size-dependent constraints. For example, Haller's rule, the allometric pattern whereby smaller organisms have proportionally larger brains, can have carry-on effects on head design as the brain competes for space with other structures. Ant species with polymorphic worker castes are interesting cases for helping us understand these allometric effects. Here, we examine the effects of miniaturization on the ant power core, the mesosoma (thorax), with particular attention to how the scaling of nervous system structures affects the skeletomuscular elements involved with load bearing and locomotion. Using X-ray computed microtomography (microCT), we studied the thorax of Carebara perpusilla, an African ant species that has minute workers (1.5 mm-long) and larger soldiers (3.0 mm-long), allowing strong intraspecific comparisons. We find that the thoracic nervous system is relatively larger in minute workers, similar to Haller's rule, with consequences on the skeletomuscular organisation. Minute workers have relatively smaller petiole muscles and indirect head muscles, but relatively larger external trochanter muscles and direct head muscles. We link these allometric trade-offs to miniaturization and division of labor, and discuss how thorax design underlies the success of minute ants.

Complications of Conventional Sinus Augmentation Techniques Versus Modified Osteotome Techniques in Dental Implant Surgery: A 3-Year Retrospective Clinical Study.

Sinus Augmentation has proven to be a predictable and popular approach to overcome bone volume deficiency in the posterior maxilla for patients seeking dental implants. The most common surgical methods utilized for maxillary sinus augmentations are the lateral window approach and crestal osteotome technique, which may cause many complications like sinus membrane tear, bleeding, sinusitis, etc. the purpose of this study is to compare complications rates of different sinus lift techniques in dental implant surgery. To assess the intraoperative and postoperative complications between the conventional direct or indirect method with alternative sinus lift techniques using Modified Crestal and Lateral (CAS & LAS KIT) ®method (Osstem/Hiossen). This is a retrospective study where in all the sinus lift cases done during 3year duration in the center data was collected and analyzed a total of 61 sinus lift procedure was done and all the data is tabulated and analyzed. Results show of the total 61 cases 25 (40%) male patients and 36(59%)female patients traditional techniques like summers osteotome and conventional direct or indirect method had 7 cases (33.3%-37.5%) complication rates compared to Modified Lateral osteotome had 2 complications (14.2%) & Modified Crestal osteotome had only 3 case(3.7%) infections, wound dehiscence, membrane tear etc. Modified Crestal & Lateral Osteotome (CAS KIT & LAS KIT) ® technique does reduce the incidence of complications like sinus membrane tear compared to conventional Direct and Indirect techniques, because of stopper system used in hydraulic lift and the special design of drill head of these instruments.