Optimum Standoff Distance Research Articles

Comparison of the disintegration abilities of modulated and continuous water jets

This study investigated the erosion phenomena of a high-speed modulated water jet (MWJ) and a continuous water jet (CWJ) during jet–material interaction. The disintegration abilities of self-excited and continuous water jets were compared. The erosion abilities of the MWJ and CWJ for two levels of hydraulic powers (26 and 72 kW) on the aluminum alloy EN AW-6060 were tested. The CWJ was generated using a StoneAge 0.069″ nozzle with a circular orifice having a diameter of 1.75 mm, and the MWJ was generated by a nozzle with a rectangular orifice having dimensions of 1.5 mm × 1.5 mm. Owing to the asymmetrical MWJ profile, two different alignments of jet position (0° and 90°) with respect to the direction of nozzle travel were examined. A six-axis industrial robot equipped with both nozzles ensured the movement of the particular trajectory with a traverse speed of 1 mm/s. An optimal standoff distance was observed for all tested pressures of the given hydraulic powers with respect to the nozzle and material position. High-pressure flow diagnostic sensors were used to accurately adjust the hydraulic power of the tested operating conditions. A total of 29 samples with dimensions of 100 mm × 50 mm × 20 mm were investigated during experimental testing. Each erosion test was repeated three times. Subsequently, the eroded groove profiles were studied using a MicroProf FRT optical profilometer. Basic parameters such as average material groove depth, groove width, and material removal rate were statistically analyzed. The irregularities and specific surface characteristics of the eroded grooves were examined using scanning electron microscopy. It was observed that using MWJ, a four-times higher erosion rate of material removal can be achieved compared with standard CWJ using the same technological conditions. The details of the experiments are presented in this paper.

Erosion behavior of aluminum by an inclined cavitating jet

The erosion behavior of pure aluminum by an inclined cavitating jet in the acceleration period was experimentally investigated for potential applications in peening and cleaning. The mass loss and surface topography of the eroded specimens were investigated to unravel the erosion mechanism under inclined impingement with various feeding pressure. The cavitation cloud motion was numerically investigated in various erosion stages with two-phase CFD calculation. Results show that at the first optimum standoff distance of mass loss l1 close to the nozzle bottom, erosion occurs in two ring-like areas, whereas the erosion at the downstream second optimum standoff distance l2 appears as a single ring at inclined angles αi∈ [0∘, 15∘] and as separated crescent-shaped areas at αi = 30∘ and 45∘. The increasing αi induces a higher cumulative erosion ratio in the acceleration period at Pin = 15 MPa and 13 MPa, whereas the aggressive ability of inclined impingement is attenuated at Pin = 11 MPa due to the low cavitation intensity. An obvious transition from plastic deformation to erosion damage is found on the boundary of the main erosion area. Under the inclined impingement, the upper side of the main erosion area shows much more severe erosion damage than the lower side due to the blocking effect, where the upward spread of the cavitation clouds is blocked and their collapse primarily occurs in the erosion valley. The erosion develops with the a ring-shaped pattern at αi∈ [0∘, 5∘]. At higher inclined impingement angles αi∈ [15∘, 45∘], the erosion primarily develops along the surface normal direction in the part of the main erosion area closer to the nozzle exit.

Cement erosion process with recyclable sand particle water-jet impacts

Abstract Particle water-jet technology is an efficient method that increases the erosion rate of cement material. The full potential of the jet energy, the ability to cover the full cement surface, and avoidance of erosion of the side casing are vital issues that need to be solved. In this study, a full-scale testing apparatus was developed to perform ground tests of the cement erosion process with recycling particle water-jet impact. This device allows for the cement erosion rate to be reliably adjusted and measured. A two-way coupled Eulerian-Lagrangian Computational Fluid Dynamics (CFD) modelling approach was utilized to investigate the impact flow field and erosion characteristics of the particle liquid-solid jet. The operating parameters (particle concentration, particle velocity, particle diameter, and standoff distance) were determined to obtain the optimal erosion rate. Overall, the simulation results are in good agreement with the experimental results. Results demonstrate that the potential core in the free jet zone can maintain a high impact velocity of the particles, while the maximum pressure is distributed in the impact zone. After impact with the cement surface at a very high velocity, the rebound particle velocity considerably decreases. The measured average erosion rate increases when the particle concentration reaches a critical value of 8%, at which the average erosion rate increases to its maximum value. Both the maximum unit erosion rate and average erosion rate increase as the particle diameter increases. To improved erosion of the cement, the optimal standoff distance is 3 cm (about 5 times the nozzle diameter). Also, industrial tests were successfully performed to increase the erosion rate by 50.7% for cement compared to traditional erosion methods.

Standoff Distance in Ultrasonic Pulsating Water Jet.

The water hammer effect is the basis of technologies which is artificially responsible for the decay of continuous jets. A recently developed technique enhances the pressure fluctuations using an acoustic chamber, leading to enhanced erosion effects for various water volume flow rates. The optimum standoff distance for an ultrasonic enhanced water jet is not appropriately estimated using an inclined trajectory. The objective of this study is to comprehend the true nature of the interaction of the standoff distance following the stair trajectory and traverse speed of the nozzle on the erosion depth. Additionally, it also critically compares the new method (staircase trajectory) that obeys the variation in frequency of the impingements for defined volume flow rates with the inclined trajectory. In this study, at constant pressure (p = 70 MPa), the role of impingement distribution with the variation of traverse speed (v = 5–35 mm/s) along the centerline of the footprint was investigated. The maximum erosion depth corresponding to each traverse speed is observed at approximately same standoff distance (65 ± 5 mm) and decreases with the increment in traverse speed (h = 1042 and 47 µm at v = 5 and 35 mm/s, respectively). The results are attributed to the variation in the number of impingements per unit length. The surface and morphology analysis of the cross-section using SEM manifested the presence of erosion characteristics (micro-cracks, cavities, voids, and upheaved surface). By varying the water cluster, different impingement densities can be achieved that are suitable for technological operations such as surface peening, material disintegration, or surface roughening.

Erosion Characteristics and the Corresponding Self-Resonating Oscillations of Cavitating Jet on Oblique Surfaces

The erosion and the corresponding self-resonating oscillations of the cavitating jet were experimentally investigated on the oblique surfaces. To evaluate the intensities of erosion and self-resonating oscillations of the jet, mass loss, surface morphology of the eroded specimens, upstream fluctuating pressure and unsteady cavitation noise were obtained at a series of stand-off distance ratios l d / d t in the cases where the oblique angles are α = 0°, 5°, 15° and 30°. In the low l d / d t range, with the increase of α , the erosion gradually transforms from two isolated circular erosion rings at α = 0° into irregular oval shaped rings at α = 5° and separated horseshoe shaped rings at α = 15°. The self-resonating oscillations and cavitation were weak in this range because the dominating frequency f 0 is away from the design frequency of the organ-pipe nozzle, resulting in the depressed aggressive ability in the low l d / d t range. With increasing l d / d t , the cavitation is enhanced before the self-resonating oscillations achieving more energy. The spectral decomposition reveals the existence of an intermediate state at the optimum standoff distance, where the energy of self-resonating oscillations and the cavitation reach a balance to realize the severest erosion damage.

Effects of nozzle lip geometry on the cavitation erosion characteristics of self-excited cavitating waterjet

The cavitation erosion characteristics of self-excited cavitating waterjet produced by a nozzle with various lip geometries were investigated. The cavitation erosive intensity was estimated by the mass loss of pure aluminum specimens and the sound press level of under the optimum standoff distance. The power spectrum density of noise and the surface profiles of the specimens were studied to uncover the influencing mechanism. The variables of lip geometries include: straight length (L1/d = 0.15–0.75), expansion angles (0–40°), expansion length (L2/d = 0.5–3). It is shown that the nozzle lip geometry can produce a significant influence on the cavitation erosion characteristics. The cavitation erosive ability can be affected by the straight length based on the vena contracta and pressure fluctuation feedback. The expansion structure can influence the jet’s cavitation erosive characteristic from two different aspects: the jet’s structuring frequency and the periodic behavior of the cavitation cloud. Moreover, it is possible to define an optimal geometry under this condition where the erosion mass loss is at a relative maximum, that is straight length L1/d around 0.35, expansion angle 10°<θ<25°, length 1.0<L2/d<2.5.

Erosion characteristics and mechanism of the self-resonating cavitating jet impacting aluminum specimens under the confining pressure conditions

In order to study the effects of the confining pressure on the erosion characteristics of the self-resonating cavitating jet under wellbore and deep-water conditions, experiments are conducted on aluminum specimens impinged by the organ pipe cavitation nozzle and the conical nozzle with the confining pressure in the range 0 MPa–10.0 MPa. Meanwhile, through the numerical simulation of the collapsing process of the cavitation bubble and the noise test, the cavitation erosion mechanism is analyzed. The experimental results show that the optimal standoff distance and the confining pressure can be obtained for the maximum erosion quantities, and the optimal standoff distance is 5 to 7 times greater than the equivalent nozzle outlet diameter and the confining pressure is about 2.0 MPa. Under the same conditions, the erosion caused by the cavitation nozzle is up to 2 times larger than that caused by the conical nozzle. According to the numerical simulation and the noise test, the cavitation erosion on the aluminum specimens is mostly caused by mechanical forces due to the high-frequency pressure pulse generated during the collapse of cavitation bubbles, while just a small part is caused by micro-jets.

Study on the rock‐breaking effect of water jets generated by self‐rotatory multinozzle drilling bit

AbstractUnderground radial drilling technique is a novel hydraulic stimulation technology, which is one of the important ways to realize precise, intelligent, and efficient extraction of the gas resources. There are many factors influencing the hole‐forming effect by water jet, such as nozzle arrangement and so on. Recently, the self‐rotatory multinozzle drilling bit is frequently used to improve the rock‐breaking effect of water jets. In this paper, to study the effects of inclination angle of forward nozzles and standoff distance, the ANSYS FLUENT combined with RNG turbulence model was adopted to analyze the multinozzle jets flow field. The results indicate that the components of axial velocity and tangential velocity of forward nozzle jets are different with inclination angles of forward nozzles. Moreover, there exists an optimal standoff distance of multinozzle drilling bit for rock breaking. Besides, the drilling test was conducted using the self‐developed drilling simulation system to investigate the effect of inclination angle, radial angle, standoff distance, and jet pressure on the rock‐breaking effect of water jet. Based on the rotating characteristic of rotary jet, the asymmetric inclined linear nozzle arrangement was proposed for the multinozzle drilling bit. And the results also show that the drilling bit with three forward nozzles has larger rock‐breaking zone in terms of jetted hole diameter. Besides, the depth of jetted hole decreased, while the hole diameter increased with the inclination angle of forward nozzle.

The Effect of Stand - Off Distance on the Mechanical Properties of TIG Butt Joints of 316 Stainless Steel

The objective of this study is to investigate and determine the effect of the stand-off distance (distance between the welded plates) on the mechanical properties of the Tungsten Inert Gas (TIG) welded joints. Butt TIG welding was performed for 316 stainless steel (SS) by using different pre welding stand-off distances with fixing the other parameters (thickness of welded plates, voltage, current, groove shape, and scanning speed). The influence of the stand-off distance parameter was examined by using tensile test, hardness test in the three different regions (base metal, heat effected zone, and molten zone), non-destructive testing (including visual inspection, liquid pentrant and X – ray) and microscopic examinations. Results show that the stand-off distance is one of the most important geometrical parameters of the Butt welded joints to end by good mechanical properties. It is found that the optimum stand-off distance was about 1 mm (shows the highest hardness results), but still there were some defects in some spots in the molten metal zone which caused a decrease in the hardness values in these locations. The 2 mm stand-off distance shows reasonable results, and the worst case was recorded for the 0 mm stand-off distance condition. Generally the hardness values of the heat affected zone in all conditions were the highest when compared to both metal welding zone and the base metal zone.

Cavitation intensity and erosion pattern of a self-excited cavitating jet

Abstract The self-excited water jet technology is widely used in submerged conditions, while its performance is restricted under high confining pressure. To improve its erosive capability, the cavitation intensity and the erosion pattern of a self-excited cavitating jet (SECJ) were investigated through mass loss and the microscopic images of the eroded specimens. The experiment was carried out in a certain range of cavitation numbers (σ = 0.05 ∼ 0.15), within which the SECJ can achieve strong oscillation. The results showed that, the cavitation intensity peaked at two optimum standoff distances under different cavitation numbers. The first one barely changed, while the second one decreased monotonously with increasing cavitation numbers. The selection of the optimum standoff distance was investigated for the jet to perform better erosion effect. Three typical erosion patterns containing several erosion rings were distinguished, of which different characteristics such as large erosion area or deep erosion valley could be achieved by adjusting the standoff distance. The variation of the erosion patterns under different conditions was preliminarily explained using an impingement model. The obtained results demonstrated that the SECJ could produce strong erosion under high confining pressure, and be effectively applied for material removal with low power consumption in submerged fields like deep-sea mining or ship hull cleaning.

Splat analysis of plasma sprayed (Al + Ni + h(BN)) homogenized mixture for improvement of abradable resistance on aero-engine inner casing surface

In the past few years, there is a global need for engine manufacturers to give high performance and long durable engines by using good quality of materials. Previously, engine manufacturers have applied protective coatings to increase the life and performance of the aero engine. Today, a wide variety of parameters in environmental and material design challenges together with the component design of engines demanded towards the economic protective coating processes. In an aero engine, the protection against wear inside the inner surface casing is a great challenge. Present work is focused on the study of improvement of abradable resistance on aero-engine inner case materials by using a plasma spraying technique. Different wt% of (Al + Ni+(h)BN) homogenized powder mixture and sodium silicate as an inorganic binder is used for spraying. The surface property analysis of plasma sprayed coating has been characterized using, optical microscopy, scanning electron microscopy, X-Ray diffraction and Vicker hardness tester. It was found that the coating using (Al + Ni+(h)BN) homogenized powder is successful in finding optimum stand-off distance which can increase the life span of the aero-engine casing.

Study of the rock-breaking and drilling performance of a self-rotatory water-jet bit in water-jet drilling and its influential factors

ABSTRACT Water-jet drilling (WJD) is an effective method for stimulating, exploring, and developing oil and gas resources. The self-rotatory water-jet bit (SRWJB) is a type of potentially efficient bit applied in WJD. In this study, the three-dimension drilling model of the SRWJB is established, and the numerical simulation of this model is conducted based on the sliding mesh model combined with RNG turbulence model. The numerical simulation method was validated using experimental results. To improve the drilling performance, the effects of the standoff distance, bit rotation speed, and nozzle layout parameters on the SRWJB drilling capability were investigated. The results show that there exists an optimal standoff distance for the single water jet under the condition of maximum removal volume, that is 15 mm in this experiment. A high rotation speed will make the streamline bend and decrease the jet convergence, which weakens the jet rock-breaking capacity. To achieve a high rock-breaking performance, the design considerations of the SRWJB are as follows: (1) There is an optimal rock-breaking rotation speed for SRWJB by comprehensively considering the jet deflection, moving speed and impact times, such as 200 rpm for the 12 MPa; and the optimal rotation speed increases with the increase of jet pressure. (2) The nozzle arrangement angles should be near 10° to weaken the water cushioning effect. (3) There is an optimal combination of distribution radii for the middle nozzles and lateral nozzles for effectively drilling a large and round borehole. This work will provide a reference for the optimal design of an SRWJB and its application in drilling.

Investigation of sandstone erosion by continuous and pulsed water jets

The study compares the sandstone erosion manifestations (depth, width, and volume of the removed material) caused by continuous and pulsed water jets (WJs) with a frequency f = 20 kHz and 40 kHz. The WJ head follows an inclined trajectory at an angle of 45° to the horizontal surface. The starting point of the head was positioned 5 mm above the sandstone surface. The traverse speed of the head was varied from v = 0.25 mm/s to 1 mm/s. The structural changes and plastic deformation caused by the mechanical effect of the continuous and pulsed WJs were analysed using SEM and optical profilometer. The results showed that an optimal standoff distance was responsible for the maximum erosion effect under both continuous and pulsed regimes. The PWJ at f= 40 kHz showed better erosion performance in terms of depth (6.8 mm), width (6.83 mm) and volume removed (27.31 mm3) as compared to PWJ at f = 20 kHz and CWJ. The microstructural topography at varying standoff distance (z = 10 mm to 45 mm) showed erosion features such as micro-pits, cracks, perforated holes responsible for different erosion stages. On-line monitoring via means of acoustic emission was measured to evaluate the erosion phenomenon on the sandstone surface during the impact of the PWJ and CWJ. The correlation between the acoustic emission results and the erosion parameters showed the progression of the erosion process under different technological conditions.

Study of extrudability and standoff distance effect during nanoclay-enabled direct printing

Nanoclay-enabled self-supporting printing has been emerging as a promising filament-based extrusion fabrication approach for different biomedical and engineering applications including tissue engineering. With the addition of nanoclay powders, liquid build materials may exhibit solid-like behavior upon extrusion and can be directly printed in air into complex three-dimensional structures. The objective of this study is to investigate the effect of nanoclay on the extrudability of N-isopropylacrylamide (NIPAAm) and the effect of standoff distance on the print quality during nanoclay-enabled direct printing. It is found that the addition of nanoclay can significantly improve the NIPAAm extrudability and effectively eliminate die swelling in material extrusion. In addition, with the increase of standoff distance, deposited filaments change from over-deposited to well-defined to stretched to broken, the filament width decreases, and the print fidelity deteriorates. A mathematical model is further proposed to determine the optimal standoff distance to achieve better print fidelity during nanoclay-enabled direct printing. Based on the extrudability and standoff distance knowledge from this study, NIPAAm–Laponite nanoclay and NIPAAm–Laponite nanoclay–graphene oxide nanocomposite hydrogel precursors are successfully printed into a three-layered one-dimensional responsive pattern, demonstrating the good extrudability and print quality during nanoclay-enabled printing under optimal printing conditions.

Investigation of Impact Loads Caused by Ultrasonic Cavitation Bubbles in Small Gaps

Ultrasonic cavitation shows a great potential in various industrial applications such as sonochemistry, food processing, ultrasonic cleaning, and surface treatments. These applications have the advantages of high temperatures or high pressure due to the collapse of cavitation bubbles. In surface treatments, the collapse of bubbles occurs near workpiece surfaces and creates micro-jets which lead to high impact forces. As one of these surface treatment processes, ultrasonic cavitation peening requires a small gap between the vibration source and the treated surface to obtain the maximum impact force. Due to these small gaps, the growth and collapse of cavitation bubbles are affected, which result in the changes of impact forces. Therefore, the investigation of the impact loads caused by ultrasonic cavitation bubbles in small gaps is the focus of this contribution. A theoretical model taking into consideration bubble interactions is utilized to estimate the optimal standoff distance at which the largest impact forces occur. Then, experimental investigations are carried out. A piezoelectric sensor with a titanium alloy cover is used to record the number of impacts and their amplitudes. The recorded signals are then processed in time and frequency domains. The experimental results show that large impact loads are generated when the gap width is in the range of 0.5–0.8 mm. It is also found that the maximum working efficiency occurs in this range.

Hybrid laser/arc welding of thick high-strength steel in different configurations

In this investigation, hybrid laser/arc welding (HLAW) was employed to join 8-mm-thick high-strength quenched and tempered steel (HSQTS) plates in the butt- and T-joint configurations. The influences of welding parameters, such as laser power, welding speed, stand-off distance (SD) between the arc of gas metal arc welding, and the laser heat source on the weld quality and mechanical properties of joints, were studied to obtain non-porous and crack-free fully-penetrated welds. The weld microstructure, cross-section, and mechanical properties were evaluated by an optical microscope, and microhardness and tensile tests. In addition, a finite element model was developed to investigate the thermal history and molten pool geometry of the HLAW process to join the HSQTS. The numerical study demonstrated that the SD had a paramount role in good synergy between the heat sources and the stability of the keyhole. For the butt-joint configuration, the results showed that, at a higher welding speed (35 mm/s) and optimum SD between the arc and laser, a fully-penetrated sound weld could be achieved. A non-porous weld in the T-joint configuration was obtained at a lower welding speed (10 mm/s). Microstructural evaluations indicated that the formation of residual austenite and the continuous network of martensitic structure along the grain boundary through the heat affected zone were the primary reasons of the softening behavior of this area. This was confirmed by the sharp hardness reduction and failure behavior of the tensile coupons in this area.

Damage and Risk Assessment for Single-Layer Reticulated Domes Subject to Explosive Blast Loads

In order to provide a better understanding of the dynamic behavior of single-layer reticulated domes subjected to explosive blast loads, a number of analyses are carried out on structures with different standoff distances ([Formula: see text]), explosive weights ([Formula: see text]), rise–span ratios ([Formula: see text] and other parameters. An equation for a structural damage factor is proposed to evaluate structural damage quantitatively. The damage states for single-layer reticulated domes are defined based on their structural dynamic performance and corresponding damage factors. Structural reliabilities for different standoff distances are obtained using the Monte-Carlo Analysis. A typical protective measure is bollards which are used to help ensure a minimum standoff distance. To illustrate the cost-effectiveness of such a protective measure, structural damage states and various losses, including direct and indirect economic loss and maimed and fatality loss, are considered for assessing the risk reduction, costs and benefits. It was found that the bollards significantly reduce the likelihood of structural progressive collapse or severe damage, and the optimal standoff distance can be determined.

Experimental Investigation on Surface Quality Processed by Self-Excited Oscillation Pulsed Waterjet Peening

High-speed waterjet peening technology has attracted a lot of interest and is now being widely studied due to its great ability to strengthen metal surfaces. In order to further improve the mechanical properties of metals, self-excited oscillation pulsed waterjets (SOPWs) were used for surface peening with an experimental investigation focused on the surface topography and properties. By impinging the aluminum alloy (5052) specimens with SOPWs issuing from an organ-pipe oscillation nozzle, the hardness and roughness at various inlet pressures and stand-off distances were measured and analyzed, as well as the residual stress. Under the condition of optimum stand-off distances, the microscopic appearances of peened specimens obtained by SEM were displayed and analyzed. Results show that self-excited oscillation pulsed waterjet peening (SOPWP) is capable of improving the surface quality. More specifically, compared with an untreated surface, the hardness and residual stress of the peened surfaces were increased by 61.69% and 148%, respectively. There exists an optimal stand-off distance and operating pressure for creating the highest surface quality. SOPWP can produce almost the same enhancement effect as shot peening and lead to a lower surface roughness. Although such an approach is empirical and qualitative in nature, this procedure also generated information of value in guiding future theoretical and experimental work on the application of SOPWP in the industry practice.

Effects of the geometry of impinging surface on the pressure oscillations of self-resonating pulsed waterjet

A preliminary experimental investigation was performed with a focus on the axial pressure oscillations of self-resonating pulsed waterjet under different impinging surfaces. Five target plates of different impinging surfaces were impinged by self-resonating pulsed waterjets at various standoff distances and under four inlet pressures. It was found that the geometry of impinging surface significantly affects the pressure oscillation peak and amplitude of self-resonating pulsed waterjet, and the influences largely depend on the inlet pressure. Both the pressure oscillation peak and the amplitude increase to their maximum and then drop with increasing standoff distance, which is regardless of the geometry of impinging surface. But the geometry influences the values of the optimum standoff distance and the oscillation peak and amplitude. Compared with the trend of pressure oscillation peak against standoff distance, the oscillation amplitude can be more obviously changed by the impinging surface. Moreover, an assumption that the geometry affects the pressure oscillation peak by the rebound waterjets and hydroacoustic waves has been proposed based on related literature. Further study should be conducted to clarify the relations between the axial pressure oscillation and the geometry of impinging surface.

Simulation of thermal stress effects in submerged continuous water jets on the optimal standoff distance during rock breaking

Although many hypotheses of rock breaking of water jets have been proposed, effects of thermal stresses on the jet-based rock breaking hasn't been systematically analyzed yet. A fluid-solid coupling analysis module in ANSYS was employed in the article to reveal the effects of thermal stresses on the water-jet rock breaking and prove the existence of the optimal standoff distance. It is found that the trend of the temperature is in accordance with the existence of the optimal standoff distance. The coupling effect of the temperature and pressure fields can enlarge the breaking area of water jets. The effects of thermal stresses on soft rock with the low elastic modulus are minor, and no optimal value exists, with regard to the standoff distance. Nevertheless, as for hard rock such as granite, the optimal standoff distance is about ten times the nozzle diameter and the value will decrease with the increase of jet time. The findings of this research can offer a novel research starting point and method for the effective application of high-pressure water jets to cut metal and rock.