Stroke Length Research Articles

Analysis of stroke rate (SR) and Stroke Length (SL) the Three Fastest Breaststroke Swimmers at the Tokyo Olympics 2021

Analysis of stroke rate (SR) and Stroke Length (SL) the Three Fastest Breaststroke Swimmers at the Tokyo Olympics 2021

Effects of Successive Annual Training on Young Swimmers’ Strength Asymmetries and Performance

This study aimed to compare changes in swimmers’ performance, biomechanical variables, and strength asymmetries within two successive training years. Eight competitive age-group swimmers (four males and four females; age: 14.8 ± 1.3 years) were tested before and after the same 12-week mesocycle period within two successive years (Year-1, Year-2). The swimmers were timed in 50, 200, and 400 m, and the stroke rate (SR), stroke length (SL), and stroke index (SI) were calculated. SI was calculated by the product of SL with swimming speed. Dryland shoulder isometric strength (ISO), hand grip isometric strength test (HG), and in-water maximum 30 s tethered swimming force (TF) were evaluated. The asymmetry index was calculated using ISO, HG, and TF tests as [(Fd − Fnd)/0.5 × (Fd + Fnd)] × 100, where Fd is strength in the dominant hand and Fnd is strength in the non-dominant hand. Performance time improved in 200 and 400 m, while the asymmetry indices calculated by the ISO, HG, and TF tests were similar after 12 weeks of training in both Year-1 and Year-2 (p = 0.01). Changes (Δ) in HG strength asymmetries correlated with Δ in 200 and 400 m in Year-2 (r = 0.78–0.87, p = 0.01). The asymmetry index does not change after two successive years of training but may be connected to performance changes in 200 and 400 m front crawl.

Emergent endovascular treatment versus medical treatment for acute large vessel occlusions with nondisabling symptoms.

The aim of this study is to analyze the effectiveness and safety of medical treatment (MT) versus endovascular treatment (EVT) in acute large vessel occlusion patients with mild nondisabling stroke symptoms. This study is a multicenter observational study in which data from patients at three stroke centers were prospectively obtained and retrospectively analyzed. Patients were included if they arrived for treatment within 6 h of stroke onset or last known well time and had a baseline National Institutes of Health Stroke Scale (NIHSS) score of ≤5. Primary outcome was modified Rankin Scale (mRS) score 0-2 at 90 days. Secondary outcomes included symptomatic intracranial hemorrhage (sICH), discharge NIHSS score, 90-day all-cause mortality and length of stay. Clinical outcomes were compared through a multivariable logistic regression after adjusting for age, treatment type admission and discharge NIHSS score, admission Alberta Stroke Program Early CT (ASPECT) score and length of stay. Of the 82 patients included in the study, 42 were in the EVT group and 40 were in the MT group. The groups were similar in age (MT:66, EVT:64 age; p = .62), gender (MT:55%, EVT:54.8%; male) admission NIHSS score (MT:2, EVT:3 points; p = .26), ASPECT score (MT:10, EVT:9; p = .15). While discharge NIHSS score was found to be statistically significant between the groups (MT:1, EVT:2; p = .04). There was no difference between the two groups in terms of 90-day mRS scores (MT:1, EVT:1, p = .86) and mortality rates (MT:4, EVT:4; p = .94). In unadjusted analysis, sICH rates were similar between the MT and EVT groups (MT 5%, EVT 7.1%, p = .52). Neurological intensive care unit length of stay (MT:5 days, EVT:2 days p < .001), inpatient clinic length of stay (MT:3, EVT:2 days p = .041), and total length of stay (MT:9 days, EVT:4 days p < .001) were significantly longer in the MT group. Our multicenter study demonstrated that MT with blood pressure augmentation and anticoagulation at hyperacute stage is an alternative option for emergency large vessel occlusion patients with nondisabling mild stroke symptoms.

Mechanical and tribological assessment of PEEK and PEEK based polymer composites for artificial hip joints

Abstract Human hip failure remains a significant issue, and constructing artificial joints is imperative for affected individuals. This study examined the mechanical and wear behavior of polyether ether ketone (PEEK) polymers, including bare PEEK (BP), HA (Hydroxyapatite)-infused PEEK (HA-PEEK), and GO (Graphene oxide)-infused HA-PEEK (GO-HA-PEEK). The samples were prepared using compression molding, and wear characteristics were evaluated using a linear reciprocating tribo-tester against a stainless-steel counterface under a load 50 N, frequency 5 Hz, stroke length 20 mm, and time 30 min. The 10 % w/w HA inclusions slightly elevate the PEEK’s tensile strength from 29.85 ± 1.11 MPa (BP) to 34.23 ± 1.09 MPa, and the 0.5 % w/w GO with 10 % w/w HA encapsulations have significantly improved tensile properties (65.10 ± 1.12 MPa), which is 2.2 fold higher than the BP. However, the attained impact properties fall below the satisfactory level. Coefficient of friction and wear rate are significantly reduced. The wear rate reduced from 3.39 × 10−6 mm3 N−1 m−1 (BP) to 2.54 × 10−6 mm3 N−1 m−1 on HA-PEEK, and more than two times reduction (1.69 × 10−6 mm3 N−1 m−1) with 0.5 % w/w GO incorporating HA-PEEK. The results show that the reinforcements significantly reduced wear and improved the mechanical strength of PEEK polymers. Unlike BP and HA with lowered impact resistance, GO integrated HA-PEEK exhibited outstanding mechanical and wear performance. Therefore, HA and GO-infused PEEKs are suitable alternatives for hip repair applications.

A critical assessment of the onset strain of densification in the evaluation of energy absorption for additively manufactured cellular materials

Densification strain is an essential parameter in the characterization of energy absorption of additively manufactured cellular structures. In addition to its own merits as a metric that indicates usable stroke length for energy absorbers, it is central to the computation of energy absorbed by the structure. However, at least four different approaches have been used in the literature, each with its own limitations. In this work, a critical review of these approaches is first presented. While the maximum efficiency approach has been demonstrated to be optimal for cellular foams, this work shows how, for some additively manufactured cellular materials, it can fail to estimate densification strain accurately due to its sensitivity to instantaneous stress values in the plateau region. An alternative method is proposed in this work that leverages peak stress instead to determine the onset strain of densification and is shown to be consistently accurate across a range of cellular materials. The method is validated with the results from an experimental study of energy absorption in six different types of cellular structures across three relative densities, with identical geometries fabricated in two different base materials and processes: AlSi10Mg with Laser Powder Bed Fusion, and Nylon-12 with Selective Laser Sintering.

Outcomes in peripheral right ventricular device support: Comparing the dual lumen, single canula and femoral vein cannulation strategies for right ventricular support.

The Protek Duo (PtD) dual lumen, single cannula was developed as a percutaneous system for temporary mechanical support, inserted through the internal jugular vein (IJ) for both atrial inflow and pulmonary artery outflow. Outcomes of PtD compared to alternative Peripheral Right Ventricular Assist Device (pRVAD) methods are limited. A retrospective analysis was conducted of pRVAD recipients from January 2017 - February 2022 (n = 111). These were classified into PtD (n = 52) patients and Non-Protek [(N-PtD) (n = 59)] recipients undergoing cannulation of the IJ and femoral vein. Results were further stratified by indication for pRVAD support: cardiogenic etiologies of heart failure and progressive ARDS. No survival benefit was detected between PtD and N-PtD groups at 1-week (OR: 1.32, 95% CI: 0.49-3.56, p = 0.58) or 6-month (OR: 9.83, 95% CI: 0.37-1.84, p = 0.64) follow-up. There were no statistically significant differences in whether patients' mobility progressed to out-of-bed activity (p = 0.26) or ambulation (p = 0.38). No differences were noted in time to out-of-bed (p = 0.26) or time to ambulation (p = 0.36). On subgroup analysis of patients by indication for pRVAD cannulation, these results persisted; no difference was noted in mid-term mortality (Cardiogenic: p = 0.39; ARDS: p = 0.91), progression to out-of-bed (p = 0.59; p = 1.00), or ambulation (p = 0.51; p-0.68). Among secondary outcomes, PtD patients had an increased dialysis requirement (p = 0.02). There were no differences in ability to wean from RVAD (p = 0.06), tracheostomy (p = 0.88), major bleeding events (p = 0.57), stroke (p = 0.58), or hospital length of stay (p = 0.39). Outcomes with PtD are comparable to those of traditional pRVAD cannulation strategies. Of note, no mobility benefit was observed to the use of PtD across several metrics.

Design Evaluation Of Hydraulic Pumping Unit At Well Alf-04 Kawengan Field

The methods of lifting fluid from the well to the surface consists of natural wells method and artificial lift method. One type of artificial lifting is Hydraulic Pumping Unit (HPU) method. In this case, well ALF-04 as the HPU well in Kawengan field which faces lower actual production compare to its theoritic production calculation then decided need to be redesigned. The objectives of redesigned is to reach optimum flow rate of the well. Recently actual flow rate of this well is 309.2 bfpd, and then the result of IPR calculation by Vogel shows the Q max is 957.25 bfpd, it means this well production is still feasible to be optimized till approximately 765.8 bfpd. After redesign calculation , obtained pump setting depth 755 m, plunger size of 2.5 ", 120" stroke length, and speed of 6 spm, pump displacement 568.425 bpd. For the rod diameter was changing from 0.75 inch to 0.875 inch with total length 2395m , it greatly affects the maximum stress value of 22,774.03 psi, and also has an influence to the increasing of PPRL value of 8243.26 lb, and the MPRL value of 3000 lb.

Abstract Mo114: Assessing Diastolic Performance in Working Myocardial Slices from ZSF1 Rats

Diastolic dysfunction is a prevalent and therapeutically intractable feature of heart failure which arises from increased ventricular compliance and impaired relaxation. Properly assessing diastolic performance is challenging because it requires simultaneous in-vivo measurement of ventricular pressure and volume. Furthermore, identifying diastolic dysfunction may require the simultaneous application of a stress such as physical exertion. Herein, we demonstrate a preparation that recapitulates the complexity of diastole in working myocardial slices: a force-feedback system providing precision control of pacing frequency, preload, afterload, and a tunable stretch at the end of diastole that mimics late filling driven by atrial systole. We assess the diastolic performance (isovolumic relaxation, early and late filling characteristics) in working myocardial slices from a known model of diastolic dysfunction, ZSF1 Obese rats and their Lean control. We find that parameters relating to myocardial performance such as slice work, stroke length, and twitch force are the same between Lean and Obese animals but parameters of diastolic performance are altered in the Obese rats. Specifically, we observe a decreased separation between peak early and late filling with a reduced diastolic filling interval at the same pacing frequency while we do not observe a difference in isovolumic relaxation time. Taken together, these results indicate that while the work output of myocardium is preserved in ZSF1 Obese rats, a reduction in available filling time and early filling efficiency may indicate a reduced capacity maintain output at higher heart rates.

A Piecewise Particle Swarm Optimisation Modelling Method for Pneumatic Artificial Muscle Actuators

Pneumatic artificial muscles (PAMs) possess compliant properties desirable for certain applications such as prosthetics and robotic structures. However, this compliance along with their inherent nonlinear dynamics make them difficult to accurately model and as such accurately control under certain control architectures. Common approaches to this problem include measuring the actuator’s physical properties and approximating a model based on these parameters or using deep learning methods to train a model with the actuator’s behaviours. This paper introduces an optimisation-based modelling approach based on a particle swarm optimisation (PSO) algorithm using a mass–spring–damper approximation for the PAM, as well as a piecewise modelling method that accounts for nonlinear dynamics. The use of optimisation to estimate model parameters removes the need to measure physical properties, and the three-element approximation allows for fast model generation with low computational complexity and training data requirements. Through multiple tests comparing model behaviour with real PAM motion, the accuracy of these models is confirmed to be promising for future work. Dynamic nonlinearities are properly accounted for using the piecewise modelling method, including both hysteresis and disproportionate input/output relationship across the stroke length of the actuator. Compared with other PAM modelling techniques, this method has improved generation time, lower computational load requirements, and complexity and can be applied to actuators for which the phenomenological mass–spring–damper model is a good approximation.

Energetics and Basic Stroke Kinematics of Swimming With Different Styles of Wetsuits.

Lim, B, Villalobos, A, Mercer, JA, and Crocker, GH. Energetics and basic stroke kinematics of swimming with different styles of wetsuits. J Strength Cond Res XX(X): 000-000, 2024-This study investigated the physiological responses and basic stroke kinematics while wearing different styles of wetsuits during submaximal intensity front-crawl swimming. Fourteen subjects (6 men and 8 women) completed a swimming-graded exercise test to determine maximal aerobic capacity (V̇O2max) and four 4-minute submaximal front-crawl swims at a pace that elicited 80% of V̇O2max with different wetsuits: regular swimsuit (no wetsuit [NWS]), buoyancy shorts (BS), sleeveless wetsuit (SLW), and full-sleeve wetsuit (FSW). The rate of oxygen consumption (V̇O2), rate of carbon dioxide production (V̇CO2), minute ventilation (V̇E), heart rate (HR), respiratory exchange ratio, and cost of swimming (CS) were determined as the average for the last minute of each trial. The rating of perceived exertion was assessed after each swimming bout. In addition, stroke length and index were determined from swimming pace and stroke rate. V̇O2, V̇CO2, V̇E, HR, and CS differed significantly among wetsuit conditions (p < 0.01). Respiratory exchange ratio and rating of perceived exertion also varied by wetsuit conditions (p < 0.05). However, stroke rate, length, and index were not significantly different across wetsuit conditions (p > 0.05). No differences existed between SLW and FSW for any dependent variable (p > 0.05). Results from this study suggest that swimming at the same pace without a wetsuit is the least economical, and both SLW and FSW are most and equally economical without significant kinematic changes. In addition, BS could be beneficial during training and racing in terms of less physiological demands than a regular swimsuit but not as economical as the SLW or FSW.

Experimental study on the treatment of deep miscellaneous fill foundation in Xinjiang by vibrating rod compaction method

Currently, the treatment of miscellaneous fill foundations, composed of a mixture of domestic garbage, construction solid waste, and natural soil, presents a significant challenge in urban peripheral engineering construction. This paper discusses the application of vibrating rod compaction technology for foundation treatment in Xinjiang. It evaluates the effectiveness of cross-section vibrating rod compaction equipment in reinforcing fine-grained miscellaneous fill foundations. The study analyzes the impact of construction disturbances caused by the insertion of the vibrating rod, monitoring horizontal stresses at various depths. Both laboratory and field tests show significant improvements: soil dry density increased by 8% to 18%, porosity decreased by 10% to 23%, compression modulus increased by 22% to 246%, and compression coefficient decreased by 8% to 70%. Additionally, cohesion (C) and angle of friction (ɸ) saw increases ranging from 7 to 38% and 3% to 25%, respectively. Below a depth of 3 m, cone tip resistance exceeded 10 MPa, and sidewall friction resistance increased to over 100 kPa, surpassing pre-treatment values. The standard penetration test results doubled stroke length compared to pre-treatment, indicating a substantial improvement in foundation bearing capacity. Surface wave tests before and after treatment showed a 15% increase in wave velocity, reflecting a more compact soil structure. The vibrating rod compaction method is innovative, energy-efficient, environmentally friendly, and economically beneficial, holding great potential for future miscellaneous fill treatments.

Concomitant tricuspid valve surgery in patients with significant tricuspid regurgitation undergoing left ventricular assist device implantation: A systematic review and meta-analysis.

Significant tricuspid regurgitation (TR) is a predictor of right heart failure (RHF) and increased mortality following left ventricular assist device (LVAD) implantation, however the benefit of tricuspid valve surgery (TVS) at the time of LVAD implantation remains unclear. This study compares early and late mortality and RHF outcomes in patients with significant TR undergoing LVAD implantation with and without concomitant TVS. A systematic search of four electronic databases was conducted for studies comparing patients with moderate or severe TR undergoing LVAD implantation with or without concomitant TVS. Meta-analysis was performed for primary outcomes of early and late mortality and RHF. Secondary outcomes included rate of stroke, renal failure, hospital and ICU length of stay. An overall survival curve was constructed using aggregated, reconstructed individual patient data from Kaplan-Meier (KM) curves. Nine studies included 575 patients that underwent isolated LVAD and 308 patients whom received concomitant TVS. Both groups had similar rates of severe TR (46.5% vs. 45.6%). There was no significant difference seen in risk of early mortality (RR 0.90; 95% CI, 0.57-1.42; p = 0.64; I2 = 0%) or early RHF (RR 0.82; 95% CI, 0.66-1.19; p = 0.41; I2 = 57) and late outcomes remained comparable between both groups. The aggregated KM curve showed isolated LVAD to be associated with overall increased survival (HR 1.42; 95% CI, 1.05-1.93; p = 0.023). Undergoing concomitant TVS did not display increased benefit in terms of early or late mortality and RHF in patients with preoperative significant TR. Further data to evaluate the benefit of concomitant TVS stratified by TR severity or by other predictors of RHF will be beneficial.

Effects Of The Nozzle Exit Section Shape On The Velocity Field And Heat Transfer Of Impinging Synthetic Jets

"The versatility and effectiveness of synthetic impinging jets for cooling applications have pushed the scientific community to optimize the design of such devices investigating the effects of all the relevant flow parameters, such as the stroke length, the Reynolds number and the shape of the driving wave. The current work focuses on the influence of different nozzle exit section shapes on the flow field evolution and heat transfer behavior of synthetic jet. In work presented herein, the actuator consists of a loudspeaker oscillating inside a cavity provided with a nozzle that has a circular entry section and a variable-shape exit section with a fixed hydraulic diameter (equal to 20 mm). The exit section shapes investigated in the current work are the circular, the triangular, the square and rectangular one with aspect ratio equal to 2. Simultaneous synchronized two component particle image velocimetry and infrared thermography measurements are performed. Consistent results are found both in terms of flow fields as well as Nusselt patterns: small nozzle-to-plate distances exhibit less spreading of the jet combined with a less spreaded, although more intense, Nu pattern. Smaller nozzle-to-plate distances also reveal the shape of the nozzle in the thermal pattern: this behavior can be seen for every nozzle, and it is associated with the presence of a Nu peak in correspondence of every corner of the shape, where the three-lobe footprint of the triangular nozzle exit section shape is clearly visible. Larger nozzle-to-plate distances are associated with a higher spreading in the jet and a lower vertical velocity in the vicinity of the impinged plate. "

Oscillating flow around a circular cylindrical post confined between two parallel plates

This work is motivated by the interest in determining the effect of the micro-anatomy of the spinal subarachnoid space (SSAS) on the cerebrospinal fluid flow. To that aim, we model the nerve roots in the SSAS by circular posts of radius a, confined between two parallel plates separated by a distance 2h and subjected to an oscillatory flow of angular frequency ω. First, we analyze the asymptotic limit of small values of the dimensionless stroke length of the oscillatory flow, for a harmonic waveform, varying the aspect ratio of the post λ=h/a and the Womersley number Wo=(a2ω/ν)1/2. For low values of Wo, the time-averaged steady flow exhibits symmetric recirculating vortices attached to the wall of the post whose size decreases as Wo increases. However, for values of Wo larger than a critical one, Woc(λ), which depends on λ, a second, outer vortex is also formed. The dependence of Woc(λ) has been quantified in the range 0.5&amp;lt;λ&amp;lt;∞, showing a decrease in Woc with λ. The analysis has been corroborated experimentally for λ = 2, and varying Wo, the stroke length as well as the wave form of the oscillating flow. Imposing an anharmonic oscillating flow shows that the fort-and-aft symmetry of the steady flow is broken, with the formation of two vortices of different size when Wo&amp;lt;Woc and only one outer vortex in the systolic direction when Wo&amp;gt;Woc. Finally, the study is experimentally extended considering an array of equally spaced posts, separated a semi-distance d=2a aligned with the flow. Qualitatively, the steady flow patterns induced for ℓ=d/a=2 are similar to those for ℓ→∞, although the presence of the nearby posts confines the recirculating vortices and delays the flow transition, increasing Woc(λ).

Optimization Design of Deep-Coalbed Methane Deliquification in the Linxing Block, China

The production of deep-coalbed methane (CBM) wells undergoes four stages sequentially: drainage depressurization, unstable gas production, stable gas production, and gas production decline. Upon entering the stable production stage, the recovery rate of deep CBM wells is constrained by bottom hole flowing pressure (BHFP). Reducing BHFP can further optimize CBM productivity, significantly increasing the production and recovery rate of CBM wells. This paper optimizes the deliquification process for deep CBM in the Linxing Block. By analyzing the production of deep CBM wells, an improved sucker rod pump deliquification process is proposed, and a method considering the flow in the tubing, annulus, and reservoir is established. Using the production data of Well GK-25D in the Linxing CBM field as an example, an optimized design of the improved rod pump deliquification process was undertaken, with design parameters including the depth of the sucker rod pump, the stroke length, and stroke rate. The results show that the improved process significantly lowers the pressure at the coalbed, enhancing CBM well production by 12.24%. The improved sucker rod pump process enriches deliquification technology for deep CBM, offering a new approach for its development and helping to maximize CBM well productivity.

Acute effects of dryland muscular endurance and maximum strength training on sprint swimming performance in young swimmers

ABSTRACT The study examined acute effects of dryland muscular endurance (ME) and maximum strength (MS) sessions on performance, physiological, and biomechanical variables during a subsequent sprint swimming session. Twenty-seven swimmers (16.5 ± 2.6 yrs) completed three experimental conditions including: i) ME, 55% of 1-repetition maximum, ii) MS, 90% of 1-repetition maximum, and iii) control (CON, no dry-land). Twenty minutes following ME, MS and CON sessions swimmers performed a 10-s tethered swimming sprint, four by 50-m (4 × 50-m), and a 100-m front crawl sprints. Performance time, blood lactate, heart rate (HR), stroke rate (SR), stroke length (SL), stroke index (SI), and stroke efficiency (ηF) were measured during 4 × 50-m and 100-m. Hand grip strength (HG), and shoulder muscles isometric strength (ISO) were measured after each session. Mean 4 × 50-m time increased in ME compared to CON by 1.7 ± 2.7% (p = 0.01), while 100-m time was similar among conditions (p > 0.05). ISO was lower after dry-land training in all conditions (p = 0.01). Tethered force, HG, HR, SR, SL, SI, and ηF were no different between conditions (p > 0.05). Dryland ME session decrease swimming performance; however, ME and MS sessions did not affect technical ability during a subsequent maximum intensity swimming.

Changes in Young Swimmers' In-Water Force, Performance, Kinematics, and Anthropometrics over a Full Competitive Season.

The aim of the present study was to analyze changes in young swimmers' in-water force, performance, kinematics, and anthropometrics during one full competitive season. Twenty-five swimmers (11 girls and 14 boys, 12.04 ± 0.16 years) were assessed over four distinct time points throughout a competitive season. The in-water force of both hands (D, dominant; ND, non-dominant) was retrieved during two bouts of 25 m front crawl allowing the estimation of the symmetry index. The velocity (v25) was calculated from the time to complete the 25 m and considered the performance outcome, while the stroke rate, stroke length, and the stroke index were used as kinematic variables. For anthropometric variables, body mass, stature, arm span and the hand surface area were measured. The in-water force (16-24%) and performance (8%) improved over the competitive season with significant changes in the first macrocycle. The stroke index was the only kinematic variable that changed between M1 and M4 (12.7%), accompanied by a higher asymmetric motion later in the season. A time effect was found in the stature (p < 0.001, ηp 2 = 0.71), the arm span (p < 0.001, ηp 2 = 0.79), and the hand surface area (D = p < 0.001, ηp 2 = 0.63; ND = p < 0.001, ηp 2 = 0.666). Swimming performance showed associations with in-water force, stroke efficiency and anthropometric features in all time points of the season. Thus, the natural anthropometric growth experienced over the season may translate into a more efficient swimming pattern with greater in-water forces that can enhance performance.

A Method for Straightening Distorted Giga-Cast Large Thin-Walled Components.

Giga-casting, a revolutionary approach for manufacturing large, single-piece car body components from aluminium, has emerged as a potential game-changer in the automotive industry. However, these large, thin-walled castings are prone to distortions during solidification and heat treatment processes. Straightening these distortions is crucial to ensure structural integrity, facilitate downstream assembly, and maintain aesthetic qualities. This paper proposes a novel method for straightening giga-cast components using a multi-pin straightening machine. The machine's versatility stems from its ability to adapt to various geometries through multiple strategically controlled straightening pins. This paper introduces the concept of a "straightening stroke decision algorithm" to achieve precise straightening and overcome the challenges of complex shapes. This algorithm determines the stroke length for each pin, combining a polynomial model representing the global stiffness of the component with a machine learning model that captures the stiffness changes arising from the current geometry. The effectiveness of the proposed approach is evaluated through comprehensive numerical experiments using finite element analyses. The straightening performance is assessed for the straightening algorithm with different machine learning models (deep neural network and XGBoost) and compared to a traditional optimisation method. The proposed surrogate models decided the straightening strokes so that the maximum remaining distortion became 0.02% of the largest dimension of each target geometry. The results of the numerical experiment showed that the proposed straightening method is suitable for straightening distortion in large thin-walled components.

Numerical Investigation of In-Cylinder Combustion Behaviors in a Medium-Speed Diesel Engine

Abstract This study aims to advance understanding of in-cylinder combustion processes in medium-speed diesel engines, which are extensively employed in heavy-duty applications where electrification proves inefficient yet remains insufficiently examined in the literature. By modeling a four-stroke engine with dimensions of 210 mm bore and 310 mm stroke, operating at 900 rpm under full load, this research identifies distinct combustion characteristics that differentiate medium-speed engines from their high-speed counterparts. Key findings illustrate that super turbocharging in medium-speed engines enhances the combustion of the fuel–air mixture under elevated temperatures and pressures. Moreover, an increased stroke length promotes gas velocity and turbulence, facilitating fuel atomization and mixing. Notably, rapid fuel ignition occurs near the nozzle due to the high temperature of compressed air, reducing the ignition delay. As a result, the premixed combustion stage nearly disappears, with diffusion combustion dominating, especially pronounced with long-duration injection, a characteristic of medium-speed engines. The study also reveals a more uniform but elevated distribution of nitrogen oxide emissions in medium-speed engines, attributed to prolonged high-temperature conditions that both facilitate their formation. Early stages of diffusion combustion show high concentrations of incomplete combustion products. However, as the combustion process progresses, the conditions favor the complete oxidation of these products at high temperatures, resulting in decreased carbon-based pollutions. In addition, the larger combustion chamber and enhanced turbulence characteristic of medium-speed engines support efficient fuel and air mixing without necessitating the swirl effect required by high-speed engines, diminishing the dependence on wall impingement dynamics for air utilization. Consequently, efficiency optimization strategies for medium-speed engines, emphasizing adjustable injection parameters, encounter fewer constraints than those inherent to the spatial limitations of high-speed engines.

An Experimental Study of the Influence of Cold Head Displacement Speed on Single-Stage Gifford-McMahon Cryocooler System Performance

In positive displacement cryocooler systems, the cooling performance is generally driven by the interaction between the compressor’s displacement and the cold head’s displacement. An experimental investigation explored the relationship between performance and cold end displacement speed for a single-stage gas-driven GM-type cold head operated at different frequencies. As loss mechanisms can be frequency related, the investigation also compared varying the cold end displacement by changing stroke length instead of changing operating frequency. Results showing these relationships are presented, and their impact on seal wear and variable-speed operation are discussed.