An Analysis of the Effects Causing an Asymmetric Behavior of the Lateral Lubricating Films of External Spur Gear Machines

The torque efficiency and flow efficiency of positive displacement machines for fluid power applications are determined by the behavior of their internal lubricating interfaces. This aspect has motivated the development of tribological simulation tools for the analysis of these interfaces. The level of details these tools can provide allows explaining some counterintuitive aspects that occur in these interfaces. This paper focuses on a significant example, which is the high asymmetric behavior of the lubricating films occurring in pressure compensated external gear pumps. These units are often designed with a symmetric axial balancing compensation system. Notwithstanding, there are differences between the lateral gaps that can be explained only considering the mutual effects of the pressure development in the film and the material deformation. To study this problem, this paper utilizes the tool Multics-HYGESim developed by the authors’ research team. Two analyses are performed: the first one imposing axial symmetry in the behavior of the gap, which is the common assumption discussed in literature; the second one (referred to as “full configuration”), which holds the asymmetric behavior of the gap. An experimental set-up is used to validate the modeling assumptions based on the measurements of the drain leakage and volumetric efficiency. The main paper findings are on the uneven distribution of these leakages, which indicates an asymmetric behavior of the gap films in the unit.

Modeling multi-class disordered traffic flow subject to varying vehicle composition using the concept of traversable distance

Disordered traffic stream at the microscopic level can be described as a permeable medium. Each vehicle is considered to traverse through a series of lateral gaps created by other vehicles. We develop a multi-class traffic flow model that considers such viable and accessible gaps for individual vehicle classes to traverse downstream. The model accounts for the varying shares of different vehicle classes. The concept of traversable distance and modified equilibrium speed functions are used to model the interplay among multiple vehicle classes. Using a higher order finite volume approximation method, evolution for a two-class traffic stream is shown. This model replicates prominent empirical characteristics exhibited by multi-class disordered traffic such as overtaking and creeping. Varying shares of smaller vehicles affect queue formation and discharge characteristics, and have significant impacts on roadway capacity. The model also could compute dynamic class-specific travel times at different vehicular compositions more realistically.

Registration of Knee Kinematics with a Navigation System. A Validation Study

The specific navigation system used can be currently considered as a reliable instrument for measuring the kinematics of a TKA for HKA angle and medial and lateral gaps, but non for femoral translation and rotation.

Predictors of Malreduction in Zone II and III Fifth Metatarsal Fractures Fixed With an Intramedullary Screw

Background: Proper implant selection and placement is crucial during fixation of zone II and III fifth metatarsal fractures to avoid postoperative complications. This study examined the effects of screw parameters and placement on malreduction, delayed union, nonunion, and refracture rate. Methods: A retrospective review of zone II and proximal zone III fifth metatarsal fractures managed with intramedullary screw fixation was conducted. Comparisons were made between cortex distraction (gap) and ratios of screw length, diameter, and entry point. Further analysis was carried out between time to union and distraction in the lateral and plantar cortices. Results: The plantar and lateral gaps were both associated with the mean entry point ratio on the lateral and anteroposterior (AP) views ( P < .001 for both views). No association between the plantar and lateral gaps and the screw diameter ratio ( P = .393 for AP and P = .981 for lateral) or the screw length ratio ( P = .966 for AP and P = .740 for lateral) was identified. The ratio of postoperative to preoperative apex height on AP and lateral views was correlated with the presence of lateral and plantar fracture gaps ( P < .001). The presence of a plantar gap was associated with increased time to union ( P = .022). A majority of fractures showed radiographic union at 12 weeks (38/43). Only 5 of 38 patients had delayed union. There were no refractures or nonunions as per available records. Conclusion: Plantar or lateral fracture site distraction (gap) was not influenced by screw diameter ratio or screw length ratio. The entry point ratio had a significant effect on plantar and lateral gaps on postoperative radiographs, with lateral and inferior placement leading to fracture site distraction. Patients with a plantar gap did have an increased risk of delayed union. The results of this study emphasize the significance of the entry point when managing zone II and III fifth metatarsal base fractures. Level of Evidence: Level IV, case series.

Result of posteromedial capsule and superficial medial collateral ligament release on gap and alignment in total knee arthroplasty in varusknee deformity by computer assisted surgery measurement: a retrospective stud

Soft tissue release and gap balancing in total knee arthroplasty (TKA) are important issue and lack of conclusive result. We performed posteromedial capsule (PMC) and superficial medial collateral ligament (sMCL) release by preservation of anterior attachment of pes anserine. Gaps and alignment were recorded by computer assisted surgery measurement. Results: T: The mean correction of varus deformity after PMC release and sMCL release were 4.88 ± 2.82° and 3.39 ± 1.7 respectively with the mean FC after PMC and sMCL release correction of 5.57 ± 3.5 and 1.34 ± 2.9° respectively. The mean medial gap changes on full extension after PMC and sMCL release was 1.83 ± 1.39 and 1.67 ± 1.04 mm. respectively with the mean medial gaps at 90 degree flexion after PMC and sMCL release changes of 0.73 ± 0.9 and 5.14 ± 2.11 mm. respectively. The mean lateral gap changes on extension after PMC and sMCL release were -1.3 ± 1.83 and -1.1 ± 1.6 mm. respectively with the mean lateral gaps at 90 degree flexion after PMC and sMCL release changes of -0.19 ± 1.03 and 0.06 ± 1.75 mm. here were 21 patients (16 female and 5 male) with mean age of 68 (48-78) years. The mean body mass index was 28.49 (20.70 – 39.95) kg/m2. The mean preoperative hip-knee-ankle angle was varus 8.12 (3.5-16.0) degrees with mean flexion contracture of 11.3 (3.5-16.0) degrees. Sixteen knees were implanted with Fixed bearing knee prosthesis and five knees were implanted with Mobile bearing knee prosthesis (Table.1). We performed PMC release in all patients, and combined PMC and sMCL release in fourteen patients. The mean correction of varus deformity after PM release and sMCL release were 4.88 ± 2.82 and 3.39 ± 1.7 degrees respectively. While the mean correction of flexion contracture after PMC release and sMCL release were 5.57 ± 3.5 and 1.34 ± 2.9 degrees respectively (Fig.8). The mean medial gaps change on extension after PMC and sMCL release were 1.83 ± 1.39 and 1.67 ± 1.04 mm. respectively. The mean medial gaps change at 90 degree flexion after PMC and sMCL release were 0.73 ± 0.9 and 5.14 ± 2.11 mm. respectively (Fig.9). The mean lateral gaps change on extension after PMC and sMCL release were 1.3 ± 1.83 and -1.1 ± 1.6 mm. respectively. The mean lateral gaps change at 90 degree flexion after PMC and sMCL release were -0.19 ± 1.03 and 0.06 ± 1.75 mm. (Fig.9). There is no instability of knee after PMC and sMCL release. Materials and Methods: Twenty one patient had been operated on. TKA with computer assisted surgery was performed using PMC and sMCL release by preservation of anterior attachment of pes anserine. Alignment, medial and lateral gaps were measured by computer assisted surgery. The mean age was 68 (48-78) years with the mean preoperative hip-kneeankle angle of 8.12 (3.5-16.0) degrees and the mean flexion contracture (FC) of 11.3 (3.516.0) degrees. Conclusion: We believe that sMCL release with preservation of anterior attachment of pes anserinus in total knee arthroplasty has additional effect on varus knee correction after PMC release without creation of knee instability.

Evaluation of the Hydro—Mechanical Efficiency of External Gear Pumps

This paper proposes and describes a model for evaluating the hydro-mechanical efficiency of external gear machines. The model is built considering and evaluating the main friction losses in the machines, including the viscous friction losses at the tooth tip gap, at the bearing blocks-gears gaps, at the journal bearings, and the meshing loss. To calculate the shear stress at each gap interface, the geometry of the gap has to be known. For this reason, the actual position of the gears inside the pump casing and consequent radial pressure distribution are numerically calculated to evaluate the gap height at the tooth tips. Moreover, the variation of the tilt and reference height of the lateral gaps between the gears and the pump bushings are considered. The shear stresses within the lateral gaps are estimated, for different lateral heights and tilt values. At the journal bearings gaps, the half Sommerfeld solution has been applied. The meshing loss has been calculated according to the suggestion of the International Standards. The hydro-mechanical efficiency results are then discussed with reference to commercial pumps experimentally characterized by the authors in a previous work. The average percentage deviation from experimental data was around 2%, without considering the most critical operating conditions (high delivery pressure, low rotational speed). The limits of this approach are also explained. Finally, the role of each source of loss is discussed, considering different operating conditions and two values of fluid viscosity. Lateral gap losses and meshing loss are much more relevant in determining the hydro-mechanical efficiency variation in the pump’s operating range, especially at a low delivery pressure. Moreover, while lateral gap losses increase with the rotational speed, the meshing loss shows the opposite behavior. The tooth tip gap losses are never as relevant, but they increase at high pressure. The journal bearings losses become comparable with the lateral and meshing ones at high delivery pressure values. Considering the pumps analyzed and the operating range of delivery pressure values and rotational speed values, the meshing loss made the mechanical efficiency vary in a percentage range of ±7%, with lateral losses in the range of about the ±15%, when also considering the extreme operating points (low speed, high pressure; high speed, low pressure). The weight of the lateral losses slightly reduced when we analyzed the higher temperature results, while the meshing losses slightly increased.

KdV–Berger solution and local cluster effect of two-sided lateral gap continuum traffic flow model

This study proposes a new nonlane-based continuum model derived from a two-sided lateral gap-following theory using the relation between microscopic and macroscopic variables. The model considers the effect of lateral gaps of the leading vehicles available on both sides of the following vehicle in multilane scenario. Linear stability analysis is performed to establish the neutral stability condition for the stable traffic flow. Nonlinear analysis is carried out at neutral stability line to derive the KdV–Berger equation, which describes density wave propagation. For that, one of the traveling wave solutions is also obtained. Numerical simulation results show that the two-sided lateral gap in the model improves the stability of the traffic flow by suppressing the traffic jams even at high-density conditions. The results implies that the proposed model is successful in replicating the properties of actual traffic jams in nonlane-based traffic environment.

Changes of mediolateral soft tissue gaps in total knee arthroplasty after suturing medial extensor in navigation

Purpose: Aim is to investigate the changes of mediolateral soft tissue gaps in total knee arthroplasty (TKA) after suturing medial extensor. Methods and materials: We compared the differences of medial and lateral gap values that were shown by the computer navigation at 0°, 45°, 90°, and 120° knee flexion during patella in situ and during patella repaired by a towel clip on two constant sites. Fifty consecutive knees (43 patients) scheduled for TKA due to varus knee osteoarthritis, from February 2017 to May 2017, were enrolled in this prospective study. Results: The medial gaps with patella repaired were significantly lower ( p < 0.05) than the medial gaps with patella in situ at 45°, 90°, and 120° knee flexion. Differences in the medial gap were largest at 90, with the difference of 0.87 mm. Twenty-four of 50 cases (48%) showed medial gap differences of 1 mm or over, and 13 of 50 cases (26%) showed medial gap differences of 2 mm or over. The variation in the medial gap at 90° following patellar repair showed significant association (correlation coefficient = 0.78, p = 0.001) with the difference between medial and lateral gaps (medial gap − lateral gap) at 90° of patella in situ. At 90° knee flexion, when the medial and lateral gap difference in patella in situ was 1 mm or less, 73.5% (25/34) of the cases showed variation in the medial gap of less than 1 mm after patellar repair. Conclusion: During TKA, while measuring the medial gap with patella in situ, overestimation might occur, especially in the position of knee flexion. Thus, reevaluation using towel clips should be considered when the medial and lateral gap difference is 1 mm or larger when patella in situ during evaluation of the medial and lateral gaps at 90° knee flexion.