Initial Compression Research Articles

X-ray free electron laser observation of ultrafast lattice behaviour under femtosecond laser-driven shock compression in iron

Over the past century, understanding the nature of shock compression of condensed matter has been a major topic. About 20 years ago, a femtosecond laser emerged as a new shock-driver. Unlike conventional shock waves, a femtosecond laser-driven shock wave creates unique microstructures in materials. Therefore, the properties of this shock wave may be different from those of conventional shock waves. However, the lattice behaviour under femtosecond laser-driven shock compression has never been elucidated. Here we report the ultrafast lattice behaviour in iron shocked by direct irradiation of a femtosecond laser pulse, diagnosed using X-ray free electron laser diffraction. We found that the initial compression state caused by the femtosecond laser-driven shock wave is the same as that caused by conventional shock waves. We also found, for the first time experimentally, the temporal deviation of peaks of stress and strain waves predicted theoretically. Furthermore, the existence of a plastic wave peak between the stress and strain wave peaks is a new finding that has not been predicted even theoretically. Our findings will open up new avenues for designing novel materials that combine strength and toughness in a trade-off relationship.

Primary Stability and Bone Contact Loading Evaluation of Suture and Screw based Coracoid Graft Fixation for Anterior Glenoid Bone Loss

Background: Reconstruction techniques for anterior glenoid bone loss have seen a trend from screws to suture-based fixations. However, comparative biomechanical data, including primary fixation and glenoid-graft contact pressure mapping, are limited. Hypothesis: Suture-based bone block cerclage (BBC) and suspensory suture button (SB) techniques provide similar primary fixation and cyclic stability to double-screw fixation but with higher contact loading at the bony interface. Study Design: Controlled laboratory study. Methods: In total, 60 cadaveric scapulae were prepared to simulate anterior glenoid bone loss with coracoid autograft reconstruction. Graft fixation was performed with 3 different techniques: (1) an interconnected all-suture BBC, (2) 2 SB suspensions, and (3) 2 screws. Initial compression was analyzed during primary fixation. Cyclic peak loading with 50 N and 100 N over 250 cycles at 1 Hz was performed with a constant valley load of 25 N. Optical recording and pressure foils allowed for spatial bone block tracking and contact pressure mapping at the glenoid-graft interface. Load-to-failure testing was performed at a rate of 1.5 mm/s with ultimate load and stiffness measured. Results: Initial graft compression was higher with screw fixation (141 ± 5 N) compared with suture-based fixations (P < .001), with BBC fixation providing significantly higher compression than SB fixation (116 ± 7 N vs. 91 ± 5 N; P < .001). Spatial bone block migration and ultimate failure load were similar between the BBC and screw groups. The SB group showed significantly increased bone block translation (3.1 ± 1.0 mm; P≤ .014) and rotation (2.5°± 1.4°; P≤ .025) and significantly lower ultimate failure load (180 ± 53 N) compared with the BBC (P = .046) and screw (P = .002) groups. Both suture-based fixations provided significantly increased graft-glenoid contact loading with higher pressure amplitudes (P≤ .032) and contact pressure after cyclic loading (+13%; SB: P = .007; BBC: P = .004) compared with screw fixation. Conclusion: Both SB and interconnected cerclage fixation improved dynamic contact loading compared with screw fixation in a biomechanical glenoid bone loss model. Cerclage fixation was biomechanically comparable with screw fixation but with a greater variability. SB fixation showed significantly lower primary fixation strength and greater bone block rotation and migration. Clinical Relevance: Suture-based bone block fixations improved graft-glenoid contact loading, but the overall clinical consequence on healing remains unclear.

Methods for calculating aerodynamics inside high-speed railway tunnel lining cracks and predicating stress intensity factors

PurposeThis study aims to propose a series of numerical and surrogate models to investigate the aerodynamic pressure inside cracks in high-speed railway tunnel linings and to predict the stress intensity factors (SIFs) at the crack tip.Design/methodology/approachA computational fluid dynamics (CFD) model is used to calculate the aerodynamic pressure exerted on two cracked surfaces. The simulation uses the viscous unsteady κ-ε turbulence model. Using this CFD model, the spatial and temporal distribution of aerodynamic pressure inside longitudinal, oblique and circumferential cracks are analyzed. The mechanism behind the pressure variation in tunnel lining cracks is revealed by the air density field. Furthermore, a response surface model (RSM) is proposed to predict the maximum SIF at the crack tip of circumferential cracks and analyze its influential parameters.FindingsThe initial compression wave amplifies and oscillates in cracks in tunnel linings, resulting from an increase in air density at the crack front. The maximum pressure in the circumferential crack is 2.27 and 1.76 times higher than that in the longitudinal and oblique cracks, respectively. The RSM accurately predicts the SIF at the crack tip of circumferential cracks. The SIF at the crack tip is most affected by variations in train velocities, followed by the depth and length of the cracks.Originality/valueThe mechanism behind the variation of aerodynamic pressure in tunnel lining cracks is revealed. In addition, a reliable surrogate model is proposed to predict the mechanical response of the crack tip under aerodynamic pressures.

Wireless point-of-care ultrasound in a multiplace hyperbaric chamberWireless point-of-care ultrasound in a multiplace hyperbaric chamber

Background: Electronic devices remain highly restricted from use during hyperbaric oxygen treatment (HBO2) due to risk of fire in a pressurized, oxygen-rich environment. Over recent decades, point-of-care ultrasound (POCUS) has established utility in most clinical environments except hyperbaric chambers, where only heavily-modified POCUS devices have been used.This study evaluated proof-of-concept, safety, and performance of a wireless off-the-shelf handheld POCUS device in the hyperbaric environment. Materials and Methods: The GE Vscan Air was initially tested in a Class C chamber with 100% nitrogen to up to 4.0 ATA and monitored. Second, the Vscan was paired with an encased Apple iPad, tested previously for hyperbaric use, and both were pressurized to 2.4 ATA in a Class A chamber (21% oxygen) and evaluated. Similarly, it was then tested at 2.8 ATA and also paired wirelessly with an iPad outside the chamber. Device temperature, image quality, functionality, and wireless connection were tested continuously. Results: The GE Vscan Air automatically shut off due to power button depression during initial compression; thus the power button was punctured with an 18-gauge needle to equalize gas pressure. Thereafter, the system performed well throughout all tests without degradation in function or image quality. The device did not overheat nor reach temperatures concerning for fire hazard. Further, wireless connection to out-of-chamber devices was maintained. Conclusions: Our results suggest that the GE Vscan Air can be used with minor modification in a multiplace hyperbaric chamber. Wireless functionality allows for pairing with a screen and device outside the chamber.

Research on Design and Optimization of Large Metal Bipolar Plate Sealing for Proton Exchange Membrane Fuel Cells

The sealing system, as the most important load-bearing component, is a critical part of the stack assembly in a proton exchange membrane fuel cell (PEMFC). Currently, flat or single-peak sealing gaskets are commonly used for large metal bipolar plate sealing, which can easily cause problems such as significant internal stress and distortion displacement. In order to solve this problem, an innovative double-peak sealing gasket structure is proposed. Based on the Mooney–Rivlin constitutive model, the impact of the sealing material hardness, friction coefficient, and compression ratio on the sealing performance are investigated. Meanwhile, the double-peak seal is fabricated and assembled into a single fuel cell for testing. The results show that the sealing performance of a double-peak sealing gasket with extended wings has been optimized, and the maximum contact pressure on the upper and lower contact surfaces is 1.2 MPa and 0.67 MPa, respectively, which is greater than the given air pressure of 0.1 MPa. And the sealing effect is optimal with a 45 Shore A hardness rubber, a friction coefficient of 0.05, and an initial compression ratio of 35%. The simulation and experimental sealing performance of the sealing gasket under different compression ratios remain similar.

Laser-driven ramp-compression experiments on the national ignition facility

This report details the analyses and related uncertainties in measuring longitudinal-stress–density paths in indirect laser-driven ramp equation-of-state (EOS) experiments [Smith et al., Nat. Astron. 2(6), 452–458 (2018); Smith et al., Nature 511(7509), 330–333 (2014); Fratanduono et al., Science 372(6546), 1063–1068 (2021); and Fratanduono et al., Phys. Rev. Lett. 124(1), 015701 (2020)]. Experiments were conducted at the National Ignition Facility (NIF) located at the Lawrence Livermore National Laboratory. The NIF can deliver up to 2 MJ of laser energy over 30 ns and provide the necessary laser power and control to ramp compress materials to TPa pressures (1 TPa = 10 × 106 atmospheres). These data provide low-temperature solid-state EOS data relevant to the extreme conditions found in the deep interiors of giant planets. In these experiments, multi-stepped samples with thicknesses in the range of 40–120 µm experience an initial shock compression followed by a time-dependent ramp compression to peak pressure. Interface velocity measurements from each thickness combine to place a constraint on the Lagrangian sound speed as a function of particle velocity, which in turn allows for the determination of a continuous stress–density path to high levels of compressibility. In this report, we present a detailed description of the experimental techniques and measurement uncertainties and describe how these uncertainties combine to place a final uncertainty in both stress and density. We address the effects of time-dependent deformation and the sensitivity of ramp EOS techniques to the onset of phase transformations.

Dynamic characteristics of sandwich panels with novel improved star-shaped honeycomb

This study proposes a novel sandwich panel with an improved star-shaped honeycomb (SP-ISH) by replacing sharp corners with cubic struts and lengthening inclined ribs of traditional honeycomb. To more effectively analyze its special dynamic characteristics, the bending Poisson’s ratio was derived and effective engineering constants were obtained through asymptotic analysis of the energy functional stored in periodic unit cells. Based on this analysis, a two-dimensional equivalent downscaling model (2D-EDM) was developed to investigate the free vibration of SP-ISH under various boundary conditions, and the influence of initial deformation on free vibration was also discussed. The frequency-domain and time-domain analyses were employed to identify the resonance characteristics of the SP-ISH under harmonic loading. Our findings demonstrate that 2D-EDM can accurately predict the free and forced vibration of SP-ISH and improve computational efficiency by reducing DOFs. The results indicate that the maximum resonance response was obtained by applying excitation at the center of the sandwich panel. Additionally, under cyclic loading, a sharp change in local stress amplitude was observed in the facesheet-core interface region. Compared with traditional star-shaped honeycomb, the incorporation of extended ribs and added struts could significantly reduce the maximum resonance amplitude by 3.8%. Notably, the natural frequencies of SP-ISH were affected by initial compression (up to a 40.6% reduction) and tensile deformation (up to a 26.4% increase).

Push-pull mechanics of E-cadherin ectodomains in biomimetic adhesions

E-cadherin plays a central role in cell-cell adhesion. The ectodomains of wild-type cadherins form a crystalline-like two-dimensional lattice in cell-cell interfaces mediated by both trans (apposed cell) and cis (same cell) interactions. In addition to these extracellular forces, adhesive strength is further regulated by cytosolic phenomena involving α and β catenin-mediated interactions between cadherin and the actin cytoskeleton. Cell-cell adhesion can be further strengthened under tension through mechanisms that have not been definitively characterized in molecular detail. Here we quantitatively determine the role of the cadherin ectodomain in mechanosensing. To this end, we devise an E-cadherin-coated emulsion system, in which droplet surface tension is balanced by protein binding strength to give rise to stable areas of adhesion. To reach the honeycomb/cohesive limit, an initial emulsion compression by centrifugation facilitates E-cadherin trans binding, whereas a high protein surface concentration enables the cis-enhanced stabilization of the interface. We observe an abrupt concentration dependence on recruitment into adhesions of constant crystalline density, reminiscent of a first-order phase transition. Removing the lateral cis interaction with a “cis mutant” shifts this transition to higher surface densities leading to denser, yet weaker adhesions. In both proteins, the stabilization of progressively larger areas of deformation is consistent with single-molecule experiments that show a force-dependent lifetime enhancement in the cadherin ectodomain, which may be attributed to the “X-dimer” bond.

Effect of the sliding-rolling ratio on the force chain properties of granular flow lubrication interfaces

PurposeTo further understand the granular flow lubrication mechanism in metal contact pairs, the effect of sliding-rolling ratio on the force chain properties was investigated.Design/methodology/approachThe parallel inter-plate model of the granular flow lubrication was established with discrete element method. Then, the correlation law between sliding-rolling ratio and force chain evolution properties was calculated and analyzed with PFC2D software platform.FindingsNumerical calculation results show that the dynamic fluctuation property of force chain is existed, and the shock frequency of it is increased with the increase of sliding-rolling ratio. The same evolution law is also occurred for the bearing rate of strong force chain in the initial expansion and final compression phases, and the opposite phenomena is obtained for the overall expansion phase. Moreover, the directivity of strong force chain is changed by the sliding-rolling ratio. With the increase of sliding-rolling ratio, the directivity of strong force chain is first tended to y-axis, and then inclined to the x-axis in the whole phases. The basic reason is that a clamping up and downward movement impact for the neighbor particles are the essence of the above phenomenon.Originality/valueThe main contribution of this work is to lay a theory foundation of interfacial lubrication mechanism with granular flow.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2023-0133/

Liquid-gas heat transfer characteristics of near isothermal compressed air energy storage based on Spray Injection

Isothermal compressed air energy storage (I-CAES) could achieve high roundtrip efficiency (RTE) with low carbon emissions. Heat transfer enhancement is the key to achieve I-CAES, thus the liquid-gas heat transfer characteristics of near I-CAES system based on spray injection was analyzed in this paper. The liquid-gas heat transfer model and thermodynamic model were established and the effects of design variables on heat transfer rate and energy efficiency were analyzed. The results showed that spray injection can produce considerable heat transfer capacity and effectively suppress air temperature change, but spray injection at initial compression stage will not bring much heat transfer enhancement. Increasing spray flow rate shifts the dominant heat transfer contribution from water bulk to spray heat transfer and increases total heat transfer rate and RTE, however the increase effect of spray injection is more obvious in small-scale CAES. Low water flow rate and large working cylinder volume are recommended to achieve slow compression and expansion processes with enough liquid-gas heat transfer duration, realizing near I-CAES with high RTE. High air storage pressure increases heat transfer rate, but deviates CAES from isothermal system, resulting in low RTE. This research will provide scientific basis for heat transfer enhancement, system design and performance optimization of I-CAES.

Experimental investigation of impact resistance and compression behavior of CF/PEEK laminates after hot‐press fusion repair with different stacking sequences

AbstractUnidirectional fiber‐reinforced composite laminates have limited resistance to out‐of‐plane impact and are prone to structural integrity damage during service due to low‐velocity impact (LVI). In this study, the hot‐press fusion method was employed to repair the impact‐damaged unidirectional carbon fiber‐reinforced poly‐ether‐ether‐ketone (CF/PEEK) thermoplastic composites. No delamination or matrix cracking induced by impact was observed in the repaired specimens, as confirmed by ultrasonic scanning and digital microscope. In addition, the hot pressing treatment enables the fibers to be covered again by the resin matrix, which eliminates fiber pull‐out and fiber/matrix debonding. Afterward, typical responses of CF/PEEK composite laminates to re‐impact and post‐repair compression are presented in a comprehensive and detailed manner, and compared with the initial impact response and compression after impact (CAI) behavior. The effects of three impact energies and two stacking sequences are considered. The results indicate that quasi‐isotropic laminates are more susceptible to localized fracture damage upon re‐impact as the impact energy increases, due to initial fiber breakage, compared to orthotropic laminates. The hot‐press treatment enhances the compression residual strength of the specimen by 20%–30% compared to its state before repair. These studies offer technical insights into the application of the hot‐press fusion method to enhance the mechanical properties of composite laminates post impact damage.

Proof-of-Principle Experiment on the Dynamic Shell Formation for Inertial Confinement Fusion.

In the dynamic-shell (DS) concept [V. N. Goncharov et al., Novel Hot-Spot Ignition Designs for Inertial Confinement Fusion with Liquid-Deuterium-Tritium Spheres, Phys. Rev. Lett. 125, 065001 (2020).PRLTAO0031-900710.1103/PhysRevLett.125.065001] for laser-driven inertial confinement fusion the deuterium-tritium fuel is initially in the form of a homogeneous liquid inside a wetted-foam spherical shell. This fuel is ignited using a conventional implosion, which is preceded by a initial compression of the fuel followed by its expansion and dynamic formation of a high-density fuel shell with a low-density interior. This Letter reports on a scaled-down, proof-of-principle experiment on the OMEGA laser demonstrating, for the first time, the feasibility of DS formation. A shell is formed by convergent shocks launched by laser pulses at the edge of a plasma sphere, with the plasma itself formed as a result of laser-driven compression and relaxation of a surrogate plastic-foam ball target. Three x-ray diagnostics, namely, 1D spatially resolved self-emission streaked imaging, 2D self-emission framed imaging, and backlighting radiography, have shown good agreement with the predicted evolution of the DS and its stability to low Legendre mode perturbations introduced by laser irradiation and target asymmetries.

Measuring microscale mechanical properties of PVdF binder phase and the binder-particle interface using micromechanical testing

In this study, we developed a robust methodology for extracting the mechanical properties of individual components in complex systems such as Li-ion battery electrodes and provided quantitative values that can be used as input for modelling and lifetime estimation of Li-ion batteries. We employed micromechanical testing techniques, including micropillar compression, microcantilever bending, and nanoindentation, to measure the mechanical properties of the PVdF binder phase in the active layer. We discovered that nanoindentation tends to overestimate the modulus due to uncertainty associated with the test volume and initial large compression strains, while the micropillar compression technique provides more accurate modulus data with a narrower spread. Additionally, the yield stress of the binder phase can be evaluated using micropillar compression. Our obtained modulus values were in the range of 2.5–4.4 GPa, and the yield stress was in the range of 162–270 MPa. By microcantilever bending tests, we determined that the binder–particle interface often fails before the binder itself, suggesting that the interface significantly influences the failure mechanics. Overall, our results indicate that the microcantilever bending tests provide moduli estimates that agree with those obtained from micropillar compression tests. We also qualitatively examined the binder-particle and binder-current collector interfaces, further emphasising the significance of our methodology and the obtained quantitative values.

A Laboratory Study of Use of Crumb Rubber as Partial Replacement of Fine Aggregate in Concrete

Abstract: The aim of this study is to analyse the effect of addition of crumb rubber on the various properties of concrete. The crumb rubber is used as replacement over aggregates in the concrete mix. Crumb rubber is prepared from the scraps of tyres. In this study aggregates are replaced by 0%, 30%, 40%, 60%, 100% crumb rubber. The rubberized concrete is tested for slump and compression strength. It is found that the slump of rubberized concrete increases first but as the amount of rubber is increased the slump starts decreasing. It is observed that initial compression strength of rubberized concrete reduced significantly but the final strength is found to be more than that of ordinary concrete. Waste tyres cause tremendous pressure and ecological issues for the entire tyre industry when accumulated in cultivated land or combusted. Crumb rubber (&lt;5 mm) grinded from waste tyres was introduced to substitute for natural fine aggregate in concrete and effectively solves the consumption challenge. This paper reviews the performance of concrete with crumb rubber as fine aggregate, providing evidence for crumb rubber concrete (CRC) materials design and application. Crumb rubber is characterized with light specific gravity, hydrophobicity and air entrapment in comparison with natural fine aggregate, inducing significant reduction in workability of fresh CRC and exhibiting poor bonding performance with cementitious matrix. By summarizing the compressive/tensile strength, elastic modulus and fracture behaviour of CRC at various rubber content, prediction models of strength reduction factors are proposed. The main reasons for strength deterioration are weak interface transition zone (ITZ) performance and non-uniform distribution of rubber particles. Water/chloride permeability, electrical/carbonation resistance and drying shrinkage of CRC are discussed for durability performance of CRC. Physical/chemical pre-treatments of rubber could alleviate the hydrophobicity and improve the mechanical and durability performance of transition zones between rubber and cement paste. Accordingly, scopes concerning the recycling of crumb rubber and its performance optimization are expected in future studies.

Digital Signal Processing in the Frequency Domain of Audio Involves Various Steps and Techniques

Digital signal processing (DSP) in the frequency domain of audio encompasses a range of steps and techniques. These processes are employed to analyze, manipulate, and enhance audio signals in the digital domain. The key steps involved in DSP for audio in the frequency domain include initial conversion, frequency analysis, encoding, compression, inverse conversion, filtering, enhancement, and sound control. Each step contributes to the overall processing and improvement of audio signals, enabling efficient transmission, noise reduction, and quality enhancement in various audio applications.

Development and experimental validation of a dynamic numerical model for human articular cartilage.

The purpose of this study was to create a preliminary set of experimentally validated Finite Element Analysis (FEA) models, in order to predict the dynamic mechanical behaviour of human articular cartilage (AC). Current models consider static loading with limited independent experimental validation, while the models for this study assess dynamic loading of AC, with direct comparison and validation to physical testing. Three different FEA models of AC were constructed, which considered both linear elastic and hyperelastic models; Neo-Hookean and Ogden. Models were validated using the data collected from compression testing of human femoral heads across 0-1.7 MPa (quasi-static tests and dynamic mechanical analysis). The linear elastic model was inadequate, with a 10-fold over prediction of the displacement dynamic amplitude. The Neo-Hookean model accurately predicted the dynamic amplitude but failed to predict the initial compression of the cartilage, with a 10 times overprediction. The Ogden model provided the best results, with both the initial compression lying within one standard deviation of that observed in the validation data set, and the dynamic amplitude of the same order of magnitude. In conclusion, this study has found that the fast dynamic response of human AC is best represented by a third order Ogden model.

An ex vivo preliminary investigation into the impact of parameters on tissue welding strength in small intestine mucosa-mucosa end-to-end anastomosis.

Background: Tissue welding is an electrosurgical technique that can fuse tissue for small intestine anastomosis. However, limited knowledge exists on its application in mucosa-mucosa end-to-end anastomosis. This study investigates the effects of initial compression pressure, out-put power, and duration time on anastomosis strength ex vivo in mucosa-mucosa end-to-end anastomosis. Methods: Ex vivo porcine bowel segments were used to create 140 mucosa-mucosa end-to-end fusions. Different experimental parameters were employed for fusion, including initial com-pression pressure (50kPa-400kPa), output power (90W, 110W, and 140W), and fusion time (5, 10, 15, 20s). The fusion quality was measured by burst pressure and optical microscopes. Results: The best fusion quality was achieved with an initial compressive pressure between 200 and 250kPa, an output power of 140W, and a fusion time of 15s. However, an increase in output power and duration time resulted in a wider range of thermal damage. There was no significant difference between the burst pressure at 15 and 20s (p > 0.05). However, a substantial increase in thermal damage was observed with longer fusion times of 15 and 20s (p < 0.05). Conclusion: The best fusion quality for mucosa-mucosa end-to-end anastomosis ex vivo is achieved when the initial compressive pressure is between 200 and 250kPa, the output power is approximately 140W, and the fusion time is approximately 15s. These findings can serve as a valuable theoretical foundation and technical guidance for conducting animal experiments in vivo and subsequent tissue regeneration.

Pressure amplification effect of initial compression waves in circumferential cracks of high-speed railway tunnel linings

Spalling of concrete blocks from tunnel linings is a severe defect in high-speed railway tunnels (HSRTs). The amplified initial compression wave (ICW) in circumferential cracks induced by high-speed trains may be the main cause of crack propagation and concrete block formation. To investigate the aerodynamic amplification effect of the ICW in circumferential cracks, tunnel-crack models are established and solved based on the unsteady viscous k–ε turbulence method. A scaled indoor experiment is carried out to verify the reliability of the calculation method. The characteristics of amplified pressure and corresponding mechanisms are analyzed and revealed. Three influential parameters, including the crack width, crack depth, and train velocity, are analyzed and discussed in detail. The main conclusions are as follows: (1) the maximum amplified pressure in a typical circumferential crack is 5.68 times that of the ICW. (2) The maximum power spectrum density (PSD) of the aerodynamic pressure at the crack tip is 91.04 times that at the crack mouth. The crack tip suffers most from the aerodynamic impact of the fluctuating component of pressure waves, whereas the crack mouth is most susceptible to the average component. (3) The train velocity is the most influential parameter on the maximum pressure at the crack tip, followed by the crack depth. The power function with an exponent of 2.3087 is applicable for evaluating the relationship between the maximum pressure and train velocities. (4) The train velocity and crack depth are most influential parameters to the maximum PSD. The relationship between the maximum PSD and the crack widths, crack depths, and train velocities can be reasonably described by the power function. (5) The mechanism of pressure amplification is as follows: first, the superposition of the internal energy possessed by air molecules near crack surfaces. Second, the increase in the internal energy of air near the crack tip because of the gradually narrowing space. The results of our research may be applicable in analyzing the cracking behavior of tunnel lining cracks and preventing the spalling of concrete blocks in HSRTs.

A suction method to mitigate pressure waves induced by high-speed maglev trains passing through tunnels

When a high-speed maglev train travels through a tunnel, sudden pressure changes are generated in the tunnel, which have a negative impact on the comfort of passengers and the service life of equipment. Moreover, a strong micro-pressure wave is radiated, causing environmental noise at the tunnel exit. Using the unsteady compressible Reynolds-averaged Navier–Stokes equations based on the shear stress transport k-ω turbulence model, this study investigates the effectiveness of suction (deployed on the tunnel wall) to mitigate the pressure waves and compares the results obtained under different suction velocities. The results show that when the suction is actuated, a low-pressure region is generated near the suction slots, which can trim down the initial compression wave and the high-pressure region in front of the train. Moreover, the instantaneous train surface pressure, tunnel surface pressure and micro-pressure wave have a significant relationship with the suction velocity. For instance, compared to the no suction case, the suction-actuated case with the suction velocity of 50 m/s contributes to an amplitude reduction of 10.44% and 30.61% for the first and second sudden pressure changes, respectively, at train surface measuring point H1 (at the nose of the train); an amplitude reduction of more than 14% for the sudden pressure change at tunnel surface measuring point T17 (at the middle of the tunnel); and an amplitude reduction of 12.44% for the micro-pressure wave at measuring point M2 (outside the tunnel and 20 m from the tunnel exit). These indicate that the suction technique can be employed to alleviate the tunnel aerodynamic effect. Also, the results obtained under different suction velocities can serve as a guide for the design of suction actuators.

P-040 MERY'S SIGN IN LARGE INGUINO-VESICAL HERNIAS – A CASE REPORT AND REVIEW

Abstract Inguinal bladder hernia (IBH) is a variety of inguinal hernia rarely found: the urinary bladder is involved in no more than 5% of all groin hernias. Usually asymptomatic and occuring in men aged over 50 years, it can be incidentally encountered during hernia repair. Herein we report a case of a 68 years-old obese patient with a large symptomatic IBH, containing almost whole urinary bladder and successfully treated via open hernia repair using a properitoneal mesh technique, as described by Celdran. This entity of hernia should be suspected when inguinoscrotal hernia is associated with urinary symptoms. We evoke this specific clinical sign: Mery's sign, that implies two-stage micturition, i.e. initial manual compression of hernia is followed by bladder voiding. We emphasize the importance of preoperative diagnosis in order to reduce inadvertent lesions of the bladder or ureters during hernia surgery. Diagnosis is based on ultrasound, CT, cystography, but we also stress the idea of preoperative cystoscopy. Also, uretheral catheterization is an important aspect in diagnosis – intraoperative bladder filling/insufflation with saline fluid/methylene blue. Also it is important to emphasize that postoperative diagnosis can be exerted on bladder injury and leakage occuring after surgery in at least 10%, as literature reports. Treatment of IBH is based on reducing the bladder to its native position and hernia cure: open, laparoscopic or robotic approach.