CONVEXITY OF THE FREE BOUNDARY FOR AN AXISYMMETRIC INCOMPRESSIBLE IMPINGING JET

This paper is devoted to the study of the shape of the free boundary for a threedimensional axisymmetric incompressible impinging jet.To be more precise,we will show that the free boundary is convex to the fluid,provided that the uneven ground is concave to the fluid.

Numerical Analysis of the Influence of the Impinging Distance on the Scouring Efficiency of Submerged Jets

Water jet technology is widely used in submerged buried pipes as a non-traditional trenching process,often invol-ving a complex sediment response.An important adjustable and influential engineering variable in this technol-ogy is represented by the impinging distance.In this study,the FLOW-3D software was used to simulate the jet scouring of sand beds in a submerged environment.In particular,four sets of experimental conditions were con-sidered to discern the relationship between the maximum scour depth and mass and the impinging distance.As shown by the results,a critical impinging distance h0 exists by which the static scour depth can be maximized;the scour mass ratio between dynamic and static conditions decreases as the impinging distance increases.Moreover,the profile contours are similar when the erosion parameter Ec is in the range 0.35<Ec<2.Empirical equations applicable for predicting the jet trenching contour under both dynamic and static scour modes are also provided in this study.

Numerical study of flow and thermal characteristics of pulsed impinging jet on a dimpled surface

This research comprehensively investigates the flow and thermal characteristics of a pulsating impinging jet over a dimpled surface.It analyzes the impact of key parameters(e.g.,inlet velocity pulsation functions,pulsation frequency,amplitude,dimple pitch,dimple depth,Reynolds number)on flow patterns and heat transfer.Validated computational fluid dynamics and the Re-normalization group turbulence model are employed to accurately simulate complex turbulent flow behavior.Local and average heat transfer coefficients are calculated and compared to steady impingement cases,revealing the potential benefits of pulsation for heat transfer enhancement.The study also examines how pulsation-induced flow modulation and thermal mixing affect heat transfer mechanisms.Results indicate that combining fluctuating flow with a dimpled surface can improve heat transfer rates.In summary,increasing pulsation amplitude consistently enhances heat transfer,while the effect of frequency varies between impinging and wall jet zones.

Posterior ankle impingement syndrome: A systematic fourstage approach

Posterior ankle impingement syndrome(PAIS) is a common injury in athletes engaging in repetitive plantarflexion, particularly ballet dancers and soccer players. Despite the increase in popularity of the posterior twoportal hindfoot approach, concerns with the technique remain, including; the technical difficulty, relatively steep learning curve, and difficulty performing simultaneous anterior ankle arthroscopy. The purpose of the current literature review is to provide comprehensive knowledge about PAIS, and to describe a systematic four-stage approach of the posterior two-portal arthroscopy. The etiology, clinical presentation, diagnostic strategies are first introduced followed by options in conservative and surgical management. A detailed systematic approach to posterior hindfoot arthroscopy is then described. This technique allows for systematic review of the anatomic structures and treatment of the bony and/or soft tissue lesions in four regions of interest in the hindfoot(superolateral, superomedial, inferomedial, and inferolateral). The review then discusses biological adjuncts and postoperative rehabilitation and ends with a discussion on the most recent clinical outcomes after posterior hindfoot arthroscopy for PAIS. Although clinical evidence suggests high success rates following posterior hindfoot arthroscopy in the short- and mid-term it may be limited in the pathology that can be addressed due to the technical skills required, but the systematic four-stage approach of the posterior two-portal arthroscopy may improve upon this problem.

Current concepts in management of femoroacetabular impingement

Femoroacetabular impingement(FAI)is an increasingly recognized condition,which is believed to contribute to degenerative changes of the hip.This correlation has led to a great deal of interested in diagnosis and treatment of FAI.FAI can be divided into two groups:cam and pincer type impingement.FAI can lead to chondral and labral pathologies,that if left untreated,can progress rapidly to osteoarthritis.The diagnosis of FAI involves a detailed history,physical exam,and radiographs of the pelvis.Surgical treatment is indicated in anatomic variants known to cause FAI.The primary goal of surgical treatment is to increase joint clearance and decrease destructive forces being transmitted through the joint.Treatment has been evolving rapidly over the past decade and includes three primary techniques:open surgical dislocation,mini-open,and arthroscopic surgery.Open surgical dislocation is a technique for dislocating the femoral head from the acetabulum with a low risk of avascular necrosis in orderto reshape the neck or acetabular rim to improve joint clearance.Mini-open treatment is performed using the distal portion of an anterior approach to the hip to visualize and to correct acetabular and femoral head and neck junction deformities.This does not involve frank dislocation.Recently,arthroscopic treatment has gained popularity.This however does have a steep learning curve and is best done by an experienced surgeon.Short-to mid-term results have shown relatively equal success with all techniques in patients with no or only mild evidence of degenerative changes.Additionally,all techniques have demonstrated low rates of complications.

Sports hernia and femoroacetabular impingement in athletes: A systematic review

AIM: To investigate the association between sports hernias and femoroacetabular impingement(FAI) in athletes.METHODS: Pub Med, MEDLINE, CINAHL, Embase, Cochrane Controlled Trials Register, and Google Scholar databases were electronically searched for articles relating to sports hernia, athletic pubalgia, groin pain, long-standing adductor-related groin pain, Gilmore groin, adductor pain syndrome, and FAI. The initial search identified 196 studies, of which only articles reporting on the association of sports hernia and FAI or laparoscopic treatment of sports hernia were selected for systematic review. Finally, 24 studies were reviewed to evaluate the prevalence of FAI in cases of sports hernia and examine treatment outcomes and evidence for a common underlying pathogenic mechanism.RESULTS: FAI has been reported in as few as 12% to as high as 94% of patients with sports hernias, athletic pubalgia or adductor-related groin pain. Cam-type impingement is proposed to lead to increased symphyseal motion with overload on the surrounding extra-articular structures and muscle, which can result in the development of sports hernia and athletic pubalgia. Laparoscopic repair of sports hernias, via either the transabdominal preperitoneal or extraperitoneal approach, has a high success rate and earlier recovery of full sports activity compared to open surgery or conservative treatment. For patients with FAI and sports hernia, the surgical management of both pathologies is more effective than sports pubalgia treatment or hip arthroscopy alone(89% vs 33% of cases). As sports hernias and FAI are typically treated by general and orthopedic surgeons, respectively, a multidisciplinary approach for diagnosis and treatment is recommended for optimal treatment of patients with these injuries.CONCLUSION: The restriction in range of motion due to FAI likely contributes to sports hernias; therefore, surgical treatment of both pathologies represents an optimal therapy.

Experimental Investigation on Flow and Heat Transfer of Jet Impingement inside a Semi-Confined Smooth Channel

Experimental investigation is conducted to investigate the flow and heat transfer performances of jet impingement cooling inside a semi-confined smooth channel.Effects of jet Reynolds number(varied from 10 000to 45000),orifice-to-target spacing(zn=1d—4d)and jet-to-jet pitches(xn=3d—5d,yn=3d—5d)on the convective heat transfer coefficient and discharge coefficient are revealed.For a single-row jets normal impingement,the impingement heat transfer is enhanced with the increase of impingement Reynolds number or the decrease of spanwise jet-to-jet pitch.The highest local heat transfer is achieved when zn/dis 2.For the double-row jets normal impingement,the laterally-averaged Nusselt number distributions in the vicinity of the first row jets impinging stagnation do not fit well with the single-row case.The highest local heat transfer is obtained when zn/dis 1.A smaller jetto-jet pitch generally results in a lower discharge coefficient.The discharge coefficient in the double-row case is decreased relative to the single-row case at the same impingement Reynolds number.

Evaluation and treatment of internal impingement of the shoulder in overhead athletes

One of the most common pathologic processes seen in overhead throwing athletes is posterior shoulderpain resulting from internal impingement. "Internal impingement" is a term used to describe a constellation of symptoms which result from the greater tuberosity of the humerus and the articular surface of the rotator cuff abutting the posterosuperior glenoid when the shoulder is in an abducted and externally rotated position. The pathophysiology in symptomatic internal impingement is multifactorial,involving physiologic shoulder remodeling,posterior capsular contracture,and scapular dyskinesis. Throwers with internal impingement may complain of shoulder stiffness or the need for a prolonged warm-up,decline in performance,or posterior shoulder pain. On physical examination,patients will demonstrate limited internal rotation and posterior shoulder pain with a posterior impingement test. Common imaging findings include the classic "Bennett lesion" on radiographs,as well as articular-sided partial rotator cuff tears and concomitant SLAP lesions. Mainstays of treatment include intense non-operative management focusing on rest and stretching protocols focusing on the posterior capsule. Operative management is variable depending on the exact pathology,but largely consists of rotator cuff debridement. Outcomes of operative treatment have been mixed,therefore intense non-operative treatment should remain the focus of treatment.

Transient heat transfer characteristics of air-array-jet impingement with different nozzle arrangements on high-tempera-ture flat plate in small jet-to-plate distance

Numerical studies on transient heat transfer characteristics of air-array-jet impingement with a small jet-to-plate distance and a large temperature difference between nozzles and plate were presented.The dimensionless jet-to-plate distance(H/D)was 0.2,and non-dimensional nozzle-to-nozzle spacing(S/D)was 3,4,5 and 6,respectively.It is found that the quenching time is shortened at a constant total mass flow at air jet inlet m·(m·=218.21 kg/h),and the heat transfer uniformity is deterio-rated as S/D increases.However,the adding reversed-flow nozzles can shorten the quenching time of the glass plate considerably with a modest change in the heat transfer uniformity.The results at variable m·are the same as those at a fixed m·.Furthermore,the parity and arrangement of nozzles are also discussed,It is found that an odd number of nozzles is more beneficial for transient heat transfer.Based on these results,an appropriate proposal for ultra-thin glass tempering process is presented.

Planar collisionless jet impingement on a specular reflective plate

This paper presents a fundamental gas-kinetic study on a high speed planar rarefied jet impinging on a flat plate of specular reflections. Based on previous collisionless planar free jet results, it is straightforward to obtain jet impingement flowfield solutions, and jet impingement for specular reflective plate surface properties. Several direct simulation Monte Carlo simulation results are provided and they validate these analytical solutions of rarefied planar jet flows. The results can find applications in many disciplines, such as materials processing, molecular beams, and space engineering.

Mucoid Degeneration of Posterior Cruciate Ligament Leads to Roof Impingement with Anterior Cruciate Ligament: Case Report

Mucoid degeneration of cruciate ligament is rare cause of knee pain, however there are some cases causing pain and restriction of extension. A 60-year-old man came to our clinic complaining of pain in knee joint on full range of extension about 3 months ago. The range of motion (ROM) was a flexion contracture of 5 degree and a further flexion of 140 degree with pain aggravation by forced extension. Magnetic resonance imaging of the knee joint showed thickened posterior cruciate ligament (PCL) mucoid degeneration. Arthroscopic treatment consists of PCL reduction-plasty by debridement of yellowish material in the PCL fiber and reduces the volume of the hypertrophied PCL. Immediately after surgery, patient gain the full ROM without any symptom of impingement. Enlarged PCL can make impingement in femoral notch with anterior cruciate ligament (ACL). Then, Partial debulking surgery of PCL is an effective treatment to pain relief and restore ROM of knee.

Femoroacetabular impingement with chronic acetabular rim fracture- 3D computed tomography, 3D magnetic resonance imaging and arthroscopic correlation

Femoroacetabular impingement is uncommonly associated with a large rim fragment of bone along the superolateral acetabulum. We report an unusual case of femoroacetabular impingement(FAI) with chronic acetabular rim fracture. Radiographic, 3D computed tomography, 3D magnetic resonance imaging and arthroscopy correlation is presented with discussion of relative advantages and disadvantages of various modalities in the context of FAI.

Impingement capability of high-pressure submerged water jet: Numerical prediction and experimental verification

At jet pressures ranging from 80 to 120 MPa, submerged water jets are investigated by numerical simulation and experiment. Numerical simulation enables a systematic analysis of major flow parameters such as jet velocity, turbulent kinetic energy as well as void fraction of cavitation. Experiments facilitate an objective assessment of surface morphology, micro hardness and surface roughness of the impinged samples. A comparison is implemented between submerged and non-submerged water jets. The results show that submerged water jet is characterized by low velocity magnitudes relative to non-submerged water jet at the same jet pressure. Shear effect serves as a key factor underlying the inception of cavitation in submerged water jet stream. Predicted annular shape of cavity zone is substantiated by local height distributions associated with experimentally obtained footprints. As jet pressure increases, joint contribution of jet kinetic energy and cavitation is demonstrated. While for non-submerged water jet, impingement force stems exclusively from flow velocity.

Corrections in alpha angle following two different operative approaches for CAM-type femoral acetabular impingement-Ganz surgical hip dislocation vs anterior mini-open

BACKGROUND Femoroacetabular impingement(FAI)is a predisposing factor for secondary osteoarthritis of the hip joint.The two extensively described impingement mechanisms of FAI are CAM and Pincer-type.Initially managed conservatively,operative intervention should be offered to the persistently symptomatic patient.The measurement of the alpha angle is considered a standard method of assessing the severity of pathology in Cam-type FAI on pre-operative plain radiographs.The radiological correction of the alpha angle has not been previously compared between different surgical approaches.We hypothesize that there is no difference in alpha angle correction between Ganz surgical hip dislocation and the anterior mini-open approach.AIM To compare the magnitude of alpha angle correction achieved by using the Ganz surgical hip dislocation and the anterior mini-open approach.METHODS This is a retrospective study assessing seventy-nine patients identified in a 5-year period.These patients had preoperative radiographic evidence of FAI and underwent surgery by a single surgeon at our institution,a tertiary care center.Patients with missing radiographic documentation,radiographs with insufficient quality which then precluded accurate measurement of the angleα,a diagnosed congenital condition,isolated type II pathology(Pincer),and history of prior surgery were excluded from the study.Either the Ganz surgical hip dislocation or the anterior mini open approach was used.Postoperative radiographic evaluation of the alpha angle between the two surgical methods was done and corrected for age and gender using two-sample t-tests and Chi-square analyses.RESULTS A total of 79 patients met the inclusion and exclusion criteria.Forty-seven males(mean age of 35.3,range 16-53)and 32 females(mean age 36.7,range 16-60)were enrolled.Forty-seven patients underwent the anterior mini-open approach,and 32 underwent the Ganz surgical hip dislocation.There were no significant differences in age between the two surgical groups or in pre-and post-operative alpha angles based on patient gender.The mean pre-operative alpha angle for the Ganz surgical hip dislocation group was 88.0 degrees(SD 12.3)and 99.4 degrees(SD 7.2)for the anterior mini-open group.Mean post-operative angles were 49.9 degrees(SD 4.3)for the Ganz surgical hip dislocation and 43.8(SD 4.3)degrees for the anterior mini-open group.There was a statistically significant difference in patient’s pre-operative and post-operative angles(P=0.000)with both surgical approaches.CONCLUSION Statistically significant decreases in alpha angle were noted for both surgical techniques,with larger decreases seen in the anterior mini-open group.

Clavicle Hook Depth and Impingement Syndrome—A Cause-Effect Relationship

Background: Clavicular hook plates are effective fixation devices for lateral end clavicle fractures and acromioclavicular joint dislocations and have been extensively used in the last decade. Although this plate achieves a high percentage of union, there are concerns about sub-acromial osteolysis and impingement of supraspinatus tendon. Objective: To show that impingement of supraspinatus tendon can be prevented by measuring the depth between acromion and supraspinatus tendon posteriorly and using hook plates of appropriate depth. Materials and Methods: We performed a prospective study on 25 patients with lateral end clavicle fractures and acromio clavicular joint disruptions by measuring the depth between posterior border of acromion and the superior border of supraspinatus at the point of application of hook plate. Fixation is then done by appropriate sized hook plate. Results: None of the patients had impingement of supraspinatus tendon. Five patients developed subacromial osteolysis which did not have any impact on shoulder function. Conclusion: There is a variation in anatomy of the acromion in different ethnic groups. Hence uniform sized hook plate will be inappropriate. A smaller hook depth is needed in south Asian population to prevent impingement.

3-D NUMERICAL COMPUTATION OF JET ARRAY IMPINGEMENT WITH INITIAL CROSSFLOW

The 3-D numerical computation of the flow and temperature fields for jet array impingement with initial crossflow investigates the effects of the jet-to-surface spacing, the impinging hole arrangement and the jet-to-crossflow mass flux ratio on heat transfer characteristics. The study shows that: (1) under the different jet-to-surface spacing, the impingement cooling with inline arrangement is better than that with staggered arrangement for a given jet-to-crossflow mass flux ratio;( 2 ) the value of jet-to-surface spacing impacts a complicated effect on the flow and heat transfer for jet array impingement; (3) as the ratio of crossflow-to-jet mass flux ratio increases, the cooling effectiveness on monotonous decrease for both inline and staggered arrangements at the same jet-to-surface spacing.

Posterior ankle impingement–an underdiagnosed cause of ankle pain in pediatric patients

BACKGROUND Posterior ankle impingement syndrome(PAIS)is a cause of ankle pain due to pinching of bony or soft tissue structures in the hindfoot.The diagnosis is primarily made based on detailed history and accurate clinical examination.The delay in its diagnosis has not yet been described in the pediatric and adolescent population.AIM To identify and characterize misdiagnosed cases of PAIS in pediatric and adolescent patients.METHODS This descriptive prospective study at a tertiary children’s hospital included patients≤18 years who underwent posterior ankle arthroscopy after presenting with chronic posterior ankle pain after being diagnosed with PAIS.Collected data included:Demographics,prior diagnoses and treatments,providers seen,time to diagnosis from presentation,and prior imaging obtained.Visual Analogue Scale(VAS)for pain and American Orthopedic Foot Ankle Society(AOFAS)ankle-hindfoot scores were noted at initial presentation and follow-up.RESULTS 35 patients(46 ankles)with average age of 13 years had an average 19 mo(range 0-60 mo)delay in diagnosis from initial presentation.25(71%)patients had previously seen multiple medical providers and were given multiple other diagnoses.All 46(100%)ankles had tenderness to palpation over the posterior ankle joint.Radiographs were reported normal in 31/42(72%)exams.In 32 ankles who underwent MRI,the most common findings included os trigonum(47%)/Stieda process(47%).Conservative treatment had already been attempted in all patients.Ankle impingement pathology was confirmed during arthroscopy in 46(100%)ankles.At an average follow-up of 13.1 mo,there was an improvement of VAS(pre-op 7.0 to post-op 1.2)and AOFAS scores(pre-op 65.1 to post-op 94).CONCLUSION This is the first study which shows that PAIS is a clinically misdiagnosed cause of posterior ankle pain in pediatric and adolescent population;an increased awareness about this diagnosis is needed amongst providers treating young patients.

Combined effects of local curvature and elasticity of an isothermal wall for jet impingement cooling under magnetic field effects

The aim of this study is to examine the effects of local curvature and elastic wall effects of an isothermal hot wall for the purpose of jet impingement cooling performance.Finite element method was used with ALE.Different important parametric effects such as Re number(between 100 and 700),Ha number(between 0 and 20),elasticity(between 104 and 109),curvature of the surface(elliptic,radius ratio between 1 and 0.25) and nanoparticle volume fraction(between 0 and 0.05) on the cooling performance were investigated numerically.The results showed that the average Nu number enhances for higher Hartmann number,higher values of elastic modulus of partly flexible wall and higher nanoparticle volume fraction.When the magnetic field is imposed at the highest strength,there is an increase of3.85% in the average Nu for the curved elastic wall whereas it is 89.22% for the hot part above it,which is due to the vortex suppression effects.Nanoparticle inclusion in the base fluid improves the heat transfer rate by about 27.6% in the absence of magnetic field whereas it is 20.5% under the effects of magnetic field at Ha=20.Curvature effects become important for higher Re numbers and at Re=700,there is 14.11% variation in the average Nu between the cases with the lowest and highest radius ratio.The elastic wall effects on the heat transfer are reduced with the increased curvature of the bottom wall.

Effect of Oscillating Jet Velocity on the Jet Impingement Cooling of an Isothermal Surface

Numerical investigation of the unsteady two-dimensional slot jet impingement cooling of a horizontal heat source is carried out in the present article. The jet velocity is assumed to be in the laminar flow regime and it has a periodic variation with the flow time. The solution is started with zero initial velocity components and constant initial temperature, which is same as the jet temperature. After few periods of oscillation the flow and heat transfer process become periodic. The performance of the jet impingement cooling is evaluated by calculation of friction coefficient and Nusselt number. Parametric study is carried out and the results are presented to show the effects of the periodic jet velocity on the heat and fluid flow. The results indicate that the average Nusselt number and the average friction coefficient are oscillating following the jet velocity oscillation with a small phase shift at small periods. The simulation results show that the combination of Re =200 with the period of the jet velocity between 1.5 sec and 2.0 sec and high amplitude (0.25 m/s to 0.3 m/s) gives average friction coefficient and Nusselt number higher than the respective steady-state values.

Femoroacetabular impingement is more common in military veterans with end-stage hip osteoarthritis than civilian patients: a retrospective case control study

Background: The purpose of this study was to compare the frequency of femoroacetabular impingement(FAI) between matched groups of military veterans and civilian patients with end-stage hip osteoarthritis(OA).Methods: Patients who underwent a primary total hip arthroplasty(THA) between January 1, 2015 and December 31, 2015 at a single Veteran’s Affairs Hospital were identified. Veterans were then matched 1:2 with civilian patients from our prospective outcome registry. The alpha angle and lateral center-edge angle(LCEA) were measured by a single evaluator. Independent t-tests were used to compare joint angles, and Fisher exact tests were used to compare the prevalence of cam(alpha angle ≥60°), pincer(LCEA ≥40°), or mixed-type pathologies.Results: Twenty-one veterans were matched 1:2 with civilian patients. The mean alpha angle did not significantly differ between groups(P=0.33) nor did the prevalence of cam deformities(P=0.79). The LCEAs were significantly greater in veterans than in civilians(P=0.04), and veterans also demonstrated a significantly greater prevalence of pincer and mixed-type deformities than civilians(P=0.025 and P=0.004, respectively).Conclusions: These results suggest that FAI is perhaps a more common mechanism in the progression of OA in a veteran population than in a civilian population, as pincer and mixed-type deformities were significantly more common among veterans than civilians. The forces borne by the hip during military training exceed normal physiologic conditions. In addition, the time between symptom onset and surgical correction may be 10–12 months longer for active military personnel than for civilians. The combination of increased physical demands and a protracted time to treatment highlights the need for better recognition of FAI in military members. Future studies are necessary to determine whether earlier intervention may prevent or delay the progression to end-stage OA and the need for total hip arthroplasty.