Impulsive Force Research Articles

A criterion for selecting the mass of the counterweight of the crank mechanism

A criterion for the equality of impulses of reaction forces along the axes in the main bearing of the crank mechanism is proposed, which allows to determine the mass of a single counterweight that provides the best balancing and, as a result, a reduction in vibrations, wear of the main bearing and mechanical losses. An assessment of the influence of the mass and location of the counterweight on the reaction forces in the mechanism was carried out, which confirmed the results of mathematical modeling. Keywords: piston pump, internal combustion engine, crank mechanism, balancing, counterweight, vibrations, wear vladamgenja@mail.ru, rodionov@ssau.ru

Effect of Femoral Head Material, Surgeon Experience, and Assembly Technique on Simulated Head-Neck Total Hip Arthroplasty Impaction Forces

BackgroundThere is no standard method for assembling the femoral head onto the femoral stem during total hip arthroplasty (THA). This study aimed to measure and record dynamic 3-dimensional (3D) THA head-neck assembly loads from residents, fellows, and attending surgeons, for metal and ceramic femoral heads. MethodsAn instrumented apparatus measured dynamic 3D forces applied through the femoral stem taper in vitro for 31 surgeons (11 attendings, 14 residents, 6 fellows) using their preferred technique (ie, number of hits or mallet strikes). Outcome variables included peak axial force, peak resultant force, impulse of the resultant force, loading rate of the resultant force, and off-axis angle. They were compared between femoral head material, surgeon experience level, and the number of hits per trial. ResultsAverage peak axial force was 6.92 ± 2.11kN for all surgeons. No significant differences were found between femoral head material. Attendings applied forces more “on-axis” as compared to both residents and fellows. Nine surgeons assembled the head with 1 hit, 3 with 2 hits, 14 with 3 hits, 2 with 4 hits, and 3 with ≥5 hits. The first hit of multihit trials was significantly lower than single-hit trials for all outcome measures except the off-axis angle. The last hit of multihit trials had a significantly lower impulse of resultant force than single-hit trials. ConclusionDifferences in applied 3D force-time curve dynamic characteristics were found between surgeon experience level and single and multihit trials. No significant differences were found between femoral head material.

PERIODIC MODES IN THE MODEL OF A MATHEMATICAL PENDULUM WITH IMPULSE EFFECT

The article is devoted to establishing the conditions for the existence of periodic regimes of the model of a mathematical pendulum with impulse effect. An important aspect is that such a system is subjected to the action of instantaneous forces at the moments when the moving point passes some fixed position. In addition, it is subjected to impulse action at unfixed moments of time, whereby its amount of movement is increased by a certain amount. The paper presents some theoretical aspects, as well as a description of the sequence of moments of time, which describes the mechanism of reducing the problem with impulse action at unfixed moments of time to the problem of finding fixed points of the interval within itself. The relevance and degree of research of the problem is revealed by comparing existing solutions to the problem and finding and adding new ones. Actually, this is the main task of this work. The resulting problem involves investigating the existence of conditions that ensure the existence of cycles to which periodic solutions correspond. In the work, a second-order differential equation with impulse action is investigated in a specific case with a fixed value of the position of the impulse action depending on the values of the parameters in the impulse action function. As a result, two cycles of period three were found. It is also demonstrated by verification that the given cycles form periodic solutions. The obtained results are recorded as detailed and informative as possible. In the work, a clear view of the points that guarantee the existence of periodic regimes in the system of the mathematical pendulum with impulse action is obtained and two graphs are given, that demonstrate the results of the experiment. It is illustrated in colors how the trajectories change after each action of impulse forces. Using a corollary from Sharkovsky's theorem, it is shown that if a function is continuous and has a periodic point of period three, then it has periodic points of any natural period. Therefore, in the system there are such periodic regimes in which the phase point undergoes impulse action exactly n times per period, where n is a natural number.

Is quadriceps strength associated with patellofemoral joint loading after anterior cruciate ligament reconstruction?

ObjectiveTo test whether quadriceps strength is associated with measures of patellofemoral (PF) joint loading during running and hopping in people after an anterior cruciate ligament reconstruction (ACLR). DesignCross-sectional study. SettingBiomechanics laboratory. ParticipantsSixty-five participants (24 women; 41 men) 1–2 years post-ACLR. Main outcome measuresPeak isometric quadriceps strength for the surgical limb was measured using a dynamometer. Motion analysis and ground reaction force data were combined with musculoskeletal modelling to measure PF joint loading variables for the reconstructed knee (peak knee flexion angle; peak/impulse of the PF joint contact force; time to peak PF joint contact force) during the stance phase of running and during the landing phase of a standardised forward hop. Linear regression analysis (adjusting for age and sex) assessed the association between quadriceps strength and PF joint loading variables. ResultsTwo significant, albeit modest, associations were revealed. Quadriceps strength was associated with the time to peak PF joint contact force during running (β = −0.001; 95%CI -0.002 to −0.000; R2 = 0.179) and the impulse of the PF joint contact force during hopping (β = 0.014; 95%CI 0.003 to 0.024; R2 = 0.159). ConclusionsA strong link between quadriceps strength and PF joint loading was not evident in people 1–2 years post-ACLR.

Hydrodynamic Diversity of Jets Mediated by Giant and Non-Giant Axon Systems in Brief Squid.

Neural input is critical for establishing behavioral output, but understanding how neuromuscular signals give rise to behaviors remains a challenge. In squid, locomotion through jet propulsion underlies many key behaviors, and the jet is mediated by two parallel neural pathways, the giant and non-giant axon systems. Much work has been done on the impact of these two systems on jet kinematics, such as mantle muscle contraction and pressure-derived jet speed at the funnel aperture. However, little is known about any influence these neural pathways may have on the hydrodynamics of the jet after it leaves the squid and transfers momentum to the surrounding fluid for the animal to swim. To gain a more comprehensive view of squid jet propulsion, we made simultaneous measurements of neural activity, pressure inside the mantle cavity, and wake structure. By computing impulse and time-averaged forces from the wake structures of jets associated with giant or non-giant axon activity, we show that the influence of neural pathways on jet kinematics could extend to hydrodynamic impulse and force production. Specifically, the giant axon system produced jets with, on average, greater impulse magnitude than those of the non-giant system. However, non-giant impulse could exceed that of the giant system, evident by the graded range of its output in contrast to the stereotyped nature of the giant system. Our results suggest that the non-giant system offers flexibility in hydrodynamic output, while recruitment of giant axon activity can provide a reliable boost when necessary.

Experimental study on failure mode and failure mechanism of multi-box girder bridge under attack of tsunami

Comprehensive and intensive understanding to the failure process and failure mechanism of girder bridges is extremely crucial for anti-tsunami design of coastal bridges. The scaled down model of the multi-box girder bridge was manufactured and physical experiments were conducted in the dam-break flume to investigate the failure mode and failure mechanism. Results show that the superstructure can fail in three modes: HM (horizontal movement), HMR (horizontal movement with rotation) and HMRD (horizontal movement with rotation and dropping). And the two variables, namely the exceedance duration and the exceedance impulse, are proposed to analyze the possible failure mode and failure mechanism of the superstructure. The analysis conclusions obtained by the proposed method agree with the failure modes observed in the physical experiments. It is found that transverse horizontal movement of the superstructure always takes precedence over rotation and flow upward. With the increase of incoming tsunami bore height, the risk of failure increases; with the increase of the initial downstream water depth, the exceedance duration and exceedance impulse of horizontal force decreases firstly and then increases, the exceedance duration and exceedance impulse of vertical force and overturning moment increase.

Biomechanics of landing in injured and uninjured chickens and the role of meloxicam

Birds use their legs and wings when transitioning from aerial to ground locomotion during landing. To improve our understanding of the effects of footpad dermatitis (FPD) and keel bone fracture (KBF) upon landing biomechanics in laying hens, we measured ground-reaction forces generated by hens (n=37) as they landed on force plates (Bertec Corporation, Columbus, OH) from a 30 cm drop or 170 cm jump in a single-blinded placebo-controlled trial using a cross-over design where birds received an anti-inflammatory (meloxicam, 5 mg/kg body mass) or placebo treatment beforehand. We used generalized linear mixed models to test for effects of health status, treatment and their interaction on landing velocity (m/s), maximum resultant force (N), and impulse (force integrated with respect to time [N s]). Birds with FPD and KBF tended to show divergent alterations to their landing biomechanics when landing from a 30 cm drop, with a higher landing velocity and maximum force in KBF compared to FPD birds, potentially indicative of efforts to either reduce the use of their wings or impacts on inflamed footpads. In contrast, at 170 cm jumps fewer differences between birds of different health statuses were observed likely due to laying hens being poor flyers already at their maximum power output. Our results indicate that orthopedic injuries, apart from being welfare issues on their own, may have subtle influences on bird mobility through altered landing biomechanics that should be considered.

Asymmetries of kinematics and kinetics in female and male sprinting.

This study examined asymmetries in spatiotemporal (e.g. step length and frequency) and kinetic variables during maximal speed sprinting and aimed to determine differences in the asymmetries between female and male sprinters, and to examine relationships between magnitudes of asymmetries and sprint performance. Thirty-two female and 32 male sprinters, who were of comparable performance levels, performed 60-m sprints. Spatiotemporal and ground reaction force variables during maximal speed phase were measured using a long force platform system. The asymmetry was calculated as a difference between values obtained from right and left sides divided by the mean of the two sides. The magnitudes of asymmetries in step length (4.60% vs. 3.08%), step frequency (4.70% vs. 3.11%), stance time (3.81% vs. 2.12%), vertical impulse (8.41% vs. 5.30%) and braking mean force (13.32% vs. 8.55%) for male sprinters were greater than those for female sprinters. No significant correlation was found between maximal running speed and magnitudes of asymmetries for female or male sprinters. The results demonstrate that the magnitudes of asymmetries in step length, step frequency, stance time, vertical impulse and braking mean force during sprinting could be greater in male sprinters. Moreover, no magnitude of asymmetries could be associated with sprint performance for female and male sprinters. Although it is likely beneficial to be aware that there are greater asymmetries in male sprinting during the maximal speed phase compared to female sprinting as a baseline, the magnitudes of asymmetries can be individually different regardless of performance level.

Joint and Limb Loading during Gait in Adults with ACL Reconstruction: Comparison between Single-Step and Cumulative Load Metrics.

Individuals with anterior cruciate ligament reconstruction (ACLR) generally exhibit limb underloading behaviors during walking, but most research focuses on per-step comparisons. Cumulative loading metrics offer unique insight into joint loading as magnitude, duration, and total steps are considered, but few studies have evaluated if cumulative loads are altered post-ACLR. Here, we evaluated if underloading behaviors are apparent in ACLR limbs when using cumulative load metrics and how load metrics change in response to walking speed modifications. Treadmill walking biomechanics were evaluated in 21 participants with ACLR at three speeds (self-selected (SS); 120% SS and 80% SS). Cumulative loads per step and per kilometer were calculated using knee flexion and adduction moment (KFM and KAM) and vertical ground reaction force (GRF) impulses. Traditional magnitude metrics for KFM, KAM, and GRF were also calculated. The ACLR limb displayed smaller KFM and GRF in early and late stances, but larger KFM and GRF during midstance compared with the contralateral limb ( P < 0.01). Only GRF cumulative loads (per step and per kilometer) were reduced in the ACLR limb ( P < 0.01). In response to speed modifications, load magnitudes generally increased with speed. Conversely, cumulative load metrics (per step and per kilometer) decreased at faster speeds and increased at slow speeds ( P < 0.01). Patients with ACLR underload their knee in the sagittal plane per step, but cumulatively over the course of many steps/distance, this underloading phenomenon was not apparent. Furthermore, cumulative load increased at slower speeds, opposite to what is identified with traditional single-step metrics. Assessing cumulative load metrics may offer additional insight into how load outcomes may be impacted in injured populations or in response to gait modifications.

Re-shaping pruning improves the dynamic response of centuries-old olive trees to branch-shaker vibrations application.

The Mediterranean basin is home to centuries-old large olive trees; high-vigor cultivars are widespread, with training forms poorly adapted to mechanical harvesting by trunk/branch shakers. The significant quantity of leaves, the considerable tree height, and the presence of multiple dichotomous hanging branches reduce the transmission of vibrations applied by the branch-shaker machines. Thus, re-shaping pruning may improve the performance of this modern mechanical harvesting method by focusing on removing both the hanging branches and those forming dichotomies. The goal of this study was to evaluate the dynamic responses of large-sized olive trees to pruning (or not) through various field tests under different excitation forces. We hypothesized that more rational pruning could significantly increase vibration transmissions. To assess the transmission of vibrations, tests were conducted before and after the pruning on representative trees. Tri-axial accelerometers packed in a small titanium housing were used. Trees were assessed before and after the re-shaping pruning. This study reports the first data about the dynamic behavior of centuries-old tree skeletons, in the context of very large-sized olive trees, while taking into account the effects of two different vibrations application modes: a realistic one represented by the system vibration head-tree, originated when the gripper of a shaking machine wrapped and fastened the main branch of the olive trees, and a more speculative one, represented by a single impulse of a short-duration force originated by a hammer. After pruning, spectral density increased 10 fold in the tertiary branches of pruned trees (ranging 1.0-10 m s-2) compared to that of not-pruned ones (ranging 0.1-1.0 m s-2) at frequency >50 Hz under vibration excitation. Moreover, vibrational decay times (120-150 ms) and amplitude (>10-1 m s-2) were higher under single-impulse excitation. A more rational pruning applied to ancient large-sized olive trees significantly increased the vibration transmission under both impulse and vibratory excitation forces, without affected their typical "look". Moreover, these insights are helpful in turn in achieving maximum fruit-removal efficiency. These insights could be applied to various horticultural conditions which would improve the economic sustainability of monumental olive trees, a key portion of the Mediterranean landscape and cultural heritage.

On the potential of pupil size as a metric of physical fatigue during a repeated handle push/pull task

Force output and muscle activity represent the gold standards for measuring physical fatigue. This study explores using ocular metrics for tracking changes in physical fatigue during the completion of a repeated handle push/pull task. Participants completed this task over three trials, and pupil size was recorded by means of a head-mounted eye-tracker. Blink frequency was also measured. Force impulse and maximum peak force were used as ground-truth measures of physical fatigue. As expected, a reduction in peak force and impulse was observed over time as participants became more fatigued. More interestingly, pupil size was also found to decrease from trial 1 through trial 3. No changes in blink rate were found with increasing physical fatigue. While exploratory in nature, these findings add to the sparse literature exploring the use of ocular metrics in Ergonomics. They also advance the use of pupil size as a possible future alternative for physical fatigue detection.

A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

BackgroundThe ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown. Research questionDo foot-strike patterns during 18° uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces? MethodsThis study was based on a data subset from previous publications, analysing uphill walking on an 18° ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 ± 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests. ResultsFC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses. SignificanceIn terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.

Comparative Analysis of Movements of Curved Ultrasonic Instruments

The paper presents a theoretical analysis of vibrations of a curvilinear rod in the form of a loop of low rigidity formed from a quarter of a circle with a constant radius, limited by an angle π/2 &lt; γ &lt; π and two rectilinear rods. It is indicated that in the practice of ultrasonic technology, some types of structures are known in which elastic elements are used as resonators, waveguides, oscillation transformers and instruments for influencing the processed materials. Their use makes it possible to obtain an additional impulse of force in the working area by using the potential energy caused by the action of the elastic properties of such elements. However, insufficient attention has been paid to the theoretical justification of the use of elastic elements in ultrasonic systems. In this regard, the present work is devoted to the theoretical substantiation of the use of an elastic tool made of a thin rod having the shape of a loop. The diagram and calculation of displacements of the free end of a curved rod under the action of forces directed along the longitudinal axis are given in the paper. It is shown that elastic displacements are caused by a curved shape in the form of an arc of a circle of a curved rod. For comparison, calculation schemes of two types of curved rod with an attached rod are given. In the first case, the free ends of the rectilinear rods, directed vertically downwards, make elastic movements along two coordinates. In the second case, the ends of rectilinear rods directed at a certain angle to the vertical axis and converging at the bottom point due to the symmetry of their location, make vertical movements only along one coordinate. The considered shape of the curved rod can be successfully used as a tool for performing technological tasks in the ultrasonic method of processing holes in brittle materials, spot welding, etc. Such a scheme, in contrast to the traditional ultrasonic treatment scheme based on the use of rectilinear rods, makes it possible to increase the magnitude of the vibration amplitude of the instrument due to elastic displacements of the curved section of the rod of low rigidity. The proposed form will increase the intensity of tool vibrations and increase process productivity and processing accuracy. The resulting calculation formula shows that the amount of elastic displacements of curved rods is affected by the cross-sectional stiffness and the radius of curvature of the curved part, as well as the angle of inclination of the rectilinear rod. The theoretical calculation is supplemented by a comparative experimental study of the Chladni forms for both schemes obtained on the sheet surface using abrasive particles.

Influence of Axial Load and Transverse Impact Velocity on the Behavior of Concrete Shear Walls Reinforced with GFRP Bars

A three-dimensional numerical model was established to investigate the impact resistance of concrete shear walls reinforced with fiber-reinforced polymer (FRP) bars, considering the strain rate effect of FRP reinforcement and concrete materials. After validating the numerical model, the failure mechanism of concrete shear walls reinforced with glass fiber–reinforced polymer (GFRP) bars under impact load was studied. The influence of impact velocity and axial load ratio on the impact resistance of GFRP-reinforced concrete shear walls was discussed. The results showed that GFRP-reinforced concrete walls have similar behavior to conventional reinforced concrete walls under impact loadings. The former experienced more considerable deformation due to the lower elastic modulus of GFRP bars. The peak and residual displacement at the center of the wall increased linearly with the impact energy. In addition, the peak value, plateau value, impulse, and duration of impact force grew linearly with respect to impact velocity. The proportion of energy absorbed by concrete increased in the cases of larger impact velocity. From the perspective of the internal force envelope along the wall height, the dangerous sections under impact were located at both ends of the wall under axial load. The peak value of the internal force improved with an increase of the axial load ratio. When the axial load ratio was between 0.3 and 0.4, the impact force of the wall reached the largest, and the minimum deformation occurs, indicating the best impact resistance of the shear walls. As the axial load ratio increased from 0.1 to 0.5, the total energy consumption increased from 68% to 89%, among which the external force work is 57 times that of the 0.1 axial load ratio, aggravating the failure of walls.

Design and Development of Flapping Wing UAV

Flapping wing air vehicles are unmanned miniature aircraft’s that draw inspiration from birds, bats and insects. They utilize continuous flapping wing motion to generate aerodynamic forces and moments. The fluid structure interaction analysis of biological and artificial flapping flyers is extremely complicated thus an efficient unsteady aerodynamic model is required in such time consuming problems as optimal flapping wing simulation. This project deals with designing a flapping wing air vehicle which includes applying inertial impulsive force to UAV in such a way that the flapping wing air vehicle reaches almost constant flight speed after removing the initial impulsive forces. The flow dynamics are different of the flapping wing air vehicles with that of the fixed wing UAV and this project deals with the utilization of the flapping wing in the UAV to overcome the challenges faced by a fixed wing UAV like maneuverability in remote areas, sound produced and identification during mission. Structural and aerodynamic characteristics of a bird in flight offer benefits over typical propeller or rotor driven unmanned air vehicle (UAV). Hence this study deals with the designing of an flapping wing UAV to overcome these drawbacks of fixed wing UAV.

Experimental and optimization analysis of a multiple unidirectional single-particle damper

The particle damper is an efficient passive control device, which has been the focus of extensive research. It has certain applications in the fields of machinery, aviation, and aerospace, and is currently being investigated in the field of civil engineering. The current theoretical model of the particle damper is based on observations of the vibration phenomena of particles and a controlled structure, which cannot directly reveal its damping mechanism. In this paper, a multiple unidirectional single-particle damper (MUSPD) is discussed. Its mechanical model is established, and the corresponding numerical simulation method is proposed. Both the rationality and feasibility of the numerical simulation method are verified using a shaking table test. Secondly, based on the analysis of the damping mechanism of the MUSPD, the collision force between a particle and the controlled structure is equivalent to an impulse force; hence, an equivalent mechanical model for the MUSPD is established which is solved analytically in the frequency-time domain. Next, based on the equivalent mechanical model, a performance optimization method for the MUSPD under dynamic load is proposed. Finally, the accuracy of the equivalent mechanical model and the performance optimization method, along with the effectiveness of the latter, are verified by numerical simulation of the MUSPD. The results indicate that the MUSPD has a fine damping effect, and its numerical simulation method is reasonable and effective. The equivalent mechanical model of the MUSPD can directly represent its damping mechanism and has high accuracy, and the performance optimization method is both reasonable and feasible.

Biomechanical induction of mild brain trauma in larval zebrafish: effects on visual startle reflex habituation.

A mild traumatic brain injury is a neurological disturbance of transient or/and chronic nature after a direct blow of the head/neck or exposure of the body to impulsive biomechanical forces, indirectly affecting the brain. The neuropathological events leading to the clinical signs, symptoms and functional disturbances are still elusive due to a lack of sensitive brain-screening tools. Animal models offer the potential to study neural pathomechanisms in close detail. We recently proposed a non-invasive protocol for inducing concussion-like symptoms in larval zebrafish via exposure to rapid linearly accelerating-decelerating body motion. By mean of auditory 'startle reflex habituation' assessments-an established neurophysiological health index-we probed acute and chronic effects that mirror human concussion patterns. This study aimed at expanding our previous work by assessing the ensuing effects with visual-as opposed to auditory-'startle reflex habituation' quantifications, by using the same methodology. We observed that immediately after impact exposure, the fish showed impaired sensory reactivity and smaller decay constant, possibly mirroring acute signs of confusion or loss of consciousness in humans. By 30-min post-injury, the fish display temporary signs of visual hypersensitivity, manifested as increased visuomotor reactivity and a relatively enlarged decay constant, putatively reflecting human post-concussive sign of visual hypersensitivity. In the following 5-24 h, the exposed fish progressively develop chronic signs of CNS dysfunction, in the form of low startle responsivity. However, the preserved decay constant suggests that neuroplastic changes may occur to restore CNS functioning after undergoing the 'concussive procedure'. The observed findings expand our previous work providing further behavioural evidence for the model. Limitations that still require addressment are discussed, advancing further behavioural and microscopic analyses that would be necessary for the validation of the model in its putative relatability with human concussion.

Searching in Justification for the Intensification of Upward-Kicking in Dolphin Swimming

Abstract Scientific opinions about the importance of dolphin upward leg movements for swimming performance are still divided. Research on the efficiency of propulsion, similarly generated by a relatively larger the monofin surface, showed that quality of the upward movement phase is a measure of swimming performance. Therefore, the forces generated as a result of upward and downward kicks in butterfly swimming were analysed. The ability of the swimmers to kinaesthetically control of the upward dolphin kicking was also researched. Ten international level butterfly swimmers (mean 18,2±1,4 years) took part in the research. They performed three trials on 25m distance, at maximum speed using the monofin device (The plate of standard monofin was removed and two strain gauges were affixed in the middle, between the toe). They randomly swam: 1) butterfly stroke (BS), 2) dolphin-kicking only (LK) and 3) swam being focused on activation of upward-kicking (AUK). Time dependent signals of the force sagging the fin in reaction to the water resistance were registered. The impulses of force sagging the fin in each stroke were lower in upbeat than in downbeat. The lowest difference was in AUK trial. First, Wilks's test and then Duncan’s post hoc tests for each of the trial showed (at p≤0,05) that: downward impulses for LK was significantly higher than for BS. Upward impulses did not differ between the trials. Downward times for AUK, the same as total trial times, was significantly longer than for BS and for LK Upward times for AUK was significantly longer than for BS. The results demonstrated, that butterfly arms action leads to intensification of both kicking phases. The swimmers were well skilled for kinaesthetic controlling of the dolphin upbeat. They did not obtain the equal proportion between propulsion effect of both kicking phases, but it has been suggested, that this level of skill mastering is out of the human motor abilities. Opportunities for conscious controlling of the efficiency of the upward movement are seen in the modification of the time structure of this phase. These results could be used for improving the leg-kicking performance in butterfly swimming, as well as after stars and turns.

Can Principal Component Analysis Be Used to Explore the Relationship of Rowing Kinematics and Force Production in Elite Rowers during a Step Test? A Pilot Study

Investigating the relationship between the movement patterns of multiple limb segments during the rowing stroke on the resulting force production in elite rowers can provide foundational insight into optimal technique. It can also highlight potential mechanisms of injury and performance improvement. The purpose of this study was to conduct a kinematic analysis of the rowing stroke together with force production during a step test in elite national-team heavyweight men to evaluate the fundamental patterns that contribute to expert performance. Twelve elite heavyweight male rowers performed a step test on a row-perfect sliding ergometer [5 × 1 min with 1 min rest at set stroke rates (20, 24, 28, 32, 36)]. Joint angle displacement and velocity of the hip, knee and elbow were measured with electrogoniometers, and force was measured with a tension/compression force transducer in line with the handle. To explore interactions between kinematic patterns and stroke performance variables, joint angular velocities of the hip, knee and elbow were entered into principal component analysis (PCA) and separate ANCOVAs were run for each performance variable (peak force, impulse, split time) with dependent variables, and the kinematic loading scores (Kpc,ls) as covariates with athlete/stroke rate as fixed factors. The results suggested that rowers’ kinematic patterns respond differently across varying stroke rates. The first seven PCs accounted for 79.5% (PC1 [26.4%], PC2 [14.6%], PC3 [11.3%], PC4 [8.4%], PC5 [7.5%], PC6 [6.5%], PC7 [4.8%]) of the variances in the signal. The PCs contributing significantly (p ≤ 0.05) to performance metrics based on PC loading scores from an ANCOVA were (PC1, PC2, PC6) for split time, (PC3, PC4, PC5, PC6) for impulse, and (PC1, PC6, PC7) for peak force. The significant PCs for each performance measure were used to reconstruct the kinematic patterns for split time, impulse and peak force separately. Overall, PCA was able to differentiate between rowers and stroke rates, and revealed features of the rowing-stroke technique correlated with measures of performance that may highlight meaningful technique-optimization strategies. PCA could be used to provide insight into differences in kinematic strategies that could result in suboptimal performance, potential asymmetries or to determine how well a desired technique change has been accomplished by group and/or individual athletes.

A dynamic model for simulating vibration response of ball bearings with extended outer race defects for precise spall size estimation

A dynamic model for a ball bearing with an extended outer race defect has been proposed in this paper with an aim of precise fault size estimation. Both the varying stiffness and impact force excitation mechanisms have been incorporated. Besides, the continuously changing contact film damping and, the load zone and the resulting load distribution, are taken into account to accurately obtain the vibration response curve. The impulse force train due to impacts near the entry and the exit edges are also modelled and studied along with other important dynamic characteristics of the rotor bearing system under different operating conditions and defect parameters. The effects of different defect depth and its location, radial load, and shaft speed have been investigated. The theoretical findings were successfully validated using experimental results. The simulated results agree well with the actual vibration response of the defective bearing. Defects of five different sizes were diagnosed in light of the proposed method. A very good resemblance between the actual and the estimated values were achieved with a maximum error of 4.88%, corresponding to the smallest defect.