Initial Compression Research Articles

Numerical Analysis of the Tunnel-Train-Air Interaction Problem in a Tunnel with a Double-Hat Oblique Hood

The tunnel-train-air interaction problem is investigated by using a numerical method able to provide relevant information about pressure fluctuations, aerodynamic drag characteristics and the “piston wind” effect. The method relies on a RNG k-ε two-equation turbulence model. It is shown that although reducing the oblique slope can alleviate the pressure gradient resulting from initial compression waves at the tunnel entrance, the pressure fluctuations in the tunnel are barely affected; however, a large reduction of micro-pressure wave amplitudes is found outside the tunnel. In comparison to the case where no tunnel hood is present, the amplitudes of micro-pressure waves at 40 m from the tunnel reach an acceptable range. The aerodynamic drag of the head and tail fluctuates greatly while that of the intermediate region undergoes only limited variations when the high-speed train passes through the double-hat oblique tunnel. It is shown that the effects of the oblique slope of the portal on the aerodynamic drag can almost be ignored while the train speed plays an important role.

Collision characteristics of the intermediate coupler of a rail vehicle

Suppose the intermediate coupler of a rail vehicle is unstable during the collision process and loses its connection and energy dissipation functions. In that case, it will significantly reduce the performance of the train crashworthiness function and increase the risk of train derailment. This paper aims to establish a refined finite element model (RFEM) that can simulate the buckling behaviour and investigate the bending resistance and buckling instability characteristics of the intermediate coupler, and the accuracy of the RFEM was verified by quoting the results of an existing intermediate coupler impact test. The results demonstrated that the proposed coupler modelling method could better simulate the energy absorption characteristics and unstable behaviour. Compared to the test results, the differences in the initial crushing force, maximum longitudinal compression displacement, minimum crushing force, and maximum crushing force were 6.5%, 1.3%, 3.6%, and 6.5%, respectively. Within the allowable range of parameters, the maximum bending force linearly increased with an increase in the initial longitudinal compression displacement. As the pitch or yaw angle increased, the longitudinal buckling load of the coupler linearly decreased and became more sensitive to the pitch angle. When pitch and yaw angles existed simultaneously, the longitudinal buckling load was further reduced.

A Unified Nonlinear Elastic Model for Rock Material

Under conditions of low or medium stress, rocks that are in the compression state exhibit perceivable nonlinear elastic characteristics. After a comprehensive review of the existing nonlinear elastic models of rocks and joints, we proposed a new unified nonlinear elastic model. This new model contains two parameters with clear definitions, namely, the initial elastic modulus Eni and the modulus change rate m. This model covers a variety of existing models, including the simple exponential model, BB model and two-part Hooke’s model, etc. Based on the RMT experimental system, a large number of uniaxial compression tests for dolomite, granite, limestone and sandstone were performed, and their nonlinear deformation stress‒strain curves were obtained and fit with the unified nonlinear elastic model. The results show that the rocks have obvious nonlinear elastic characteristics in their initial compression stage, and that the unified nonlinear elastic model is able to describe these phenomena rather well. In addition, an empirical formula for predicting the uniaxial compressive strength of the rock was constructed, corresponding to the unified nonlinear elastic model.

A novel arch lattice-shell of enlarged cross-section hoods for micro-pressure wave mitigation at exit of maglev tunnels

With technology development of 600 km/h high-speed maglev trains, how to effectively alleviate the transient pressure wave problem caused by such a high-speed maglev train passing through the tunnel is significantly of importance. In this paper, based on the three-dimensional, unsteady, compressible Navier-Stokes equations and k-epsilon turbulence model, a high-speed maglev train with a speed of 600 km/h was simulated to pass through a single-track tunnel with a cross-sectional area of 92 m2, and the numerical method used was validated by a moving model test. The propagation characteristics of pressure waves in the tunnel and the evolution properties of the initial compression wave were explored. A new enlarged cross-section hood with an arch lattice-shell was proposed. With helps of the semi-closed decompression domain formed by the outer wall of the inner arched plate and the inner wall of the enlarged cross-section tunnel hood, the novel hood can further dissipate the energy of the initial compression wave; thus, the pressure gradient at 140 m from the tunnel entrance and the micro-pressure wave amplitude at 20 m from the tunnel exit can reduce by 32.1 % and 35.6 % respectively, as compared with the existing enlarged cross-section tunnel hood. When compared to the tunnel without hoods, this novel hood can achieve 64.8 % and 74.3 % reduction at the same monitoring points.

Local stability of laser-welded stainless steel slender I-sections under combined loading

This paper presents a comprehensive experimental and numerical investigation into the local buckling behaviour of laser-welded stainless steel slender I-sections under combined compression and bending moment. A testing programme was firstly carried out, including initial local geometric imperfection measurements and eccentric compression tests on ten laser-welded stainless steel slender I-section stub column specimens. Following the testing programme, a numerical modelling programme was conducted. Finite element models were developed and validated against the test results, and then adopted to perform parametric studies to generate additional numerical data. The obtained test and numerical data were used to evaluate the applicability of the interaction curves in the European and American codes and the continuous strength method to laser-welded stainless steel slender I-sections under combined loading. The evaluation results generally show that the three sets of considered interaction curves offer adequate design accuracy for laser-welded stainless steel slender I-sections under combined compression and major-axis bending moment, but they yield unduly conservative and scattered resistance predictions for laser-welded stainless steel slender I-sections under minor-axis combined loading, owing principally to the conservative minor-axis bending end points. Finally, an improved design interaction curve for the minor-axis combined loading case was developed and shown to yield substantially more accurate and consistent resistance predictions for laser-welded stainless steel slender I-sections under minor-axis combined loading than the three considered design methods. The reliability of the new design interaction curve was confirmed based on a reliability study.

Dynamic Response and Numerical Simulation of Closed-Cell Al Foams.

The drop hammer impact test was carried out to investigate the dynamic response of closed-cell Al foams. A relatively reasonable method was also developed to evaluate the velocity sensitivity of cellular material. The typical impact load-displacement curve exhibited two stages containing the initial compression stage and the progressive crushing stage. Three compressive damage behaviors and four failure modes of closed-cell Al foams were revealed, while the effect of velocity on the impact properties and the energy absorption capacity of different specimens were investigated. The results showed that the specific energy absorption of the specimens increased with the increasing density of the specimen and the impact velocity. However, the specimens with higher specific energy absorption seemed not to indicate better cushioning performance due to the shorter crushing displacement. In addition, the uniaxial impact simulation of two-dimensional (2D) Voronoi-based foam specimens was conducted at higher impact velocities. The simulation results of impact properties and deformation behavior agreed reasonably well with the experimental results, exhibiting similar velocity insensitivity of peak loads and deformation morphologies during uniaxial impact.

Ravitch Surgery or Dynamic Compression Bracing for Pectus Carinatum: A Retrospective Cohort Study

BackgroundPectus carinatum is a pediatric condition that can be treated by dynamic compression system (DCS) bracing or surgery. Several publications on DCS bracing or surgery are available; however, they do not compare both treatments. MethodsOver a 10-year period, 738 patients with pectus carinatum were treated at the Amsterdam Pectus Center (Amsterdam, The Netherlands). This study describes this 10-year experience and the results of both treatments. ResultsOf the 631 patients who underwent DCS bracing treatment, 553 finished treatment, and 78 patients are still under treatment. A total of 73.8% (n = 408) of these patients finished treatment successfully, 13.6% (n = 75) experienced treatment failure, and 12.7% (n = 70) were lost to follow-up. The success rate decreased with an increasing pressure of initial compression (84.2%-67.3%). Marfan syndrome and Poland syndrome were associated with unfavorable results. Ravitch surgery was performed in 105 patients, with a success rate of 92.4%. Complications occurred in 32.4% of patients, and 6.7% of patients had complications for which surgery was needed. No relationship was found between osteotomy or sternal fixation and outcomes or complications. The Abramson procedure was performed in 2 patients. ConclusionsDCS bracing should be the treatment of choice in patients with pectus carinatum because of its noninvasiveness, good results, and lower complication rate compared with surgery. Besides pressure of initial correction, motivation is an important factor influencing outcomes, and compliance remains a major challenge in treating pectus carinatum using DCS bracing. Bracing patients before their growth spurt should be discouraged. Patients with a higher pressure of initial compression (>8.0-8.5 psi) and Marfan syndrome or Poland syndrome have poorer outcomes. In those patients, surgery may be considered.

WITHDRAWN: Shock wave implosion in water

Analytical modeling of the evolution of cylindrical and spherical shock waves (shocks) during an implosion in water is presented for an intermediate range of convergence, which is not described by the models of self-similar shock propagation far from and in the vicinity of the piston. The model is based on an analysis of the change in pressure and kinetic energy density, as well as on the corresponding fluxes of internal and kinetic energy densities behind the shock front. The model shows that the spatial evolution of the shock velocity strongly depends on the initial compression, the adiabatic index of water, and the geometry of convergence. The model also explains the transition to a rapid increase in the shock velocity at only a certain radius of the shock that is observed in experiments. The dependence of the threshold radius, where the shock implosion follows the power law (quasi self-similarity), on the initial compression is determined. It is stated that in the entire range of the shock radii the internal and kinetic energy density fluxes are equal, which is in agreement with known experimental data.

Experimental and Numerical Study of a Rebar-Prestressed Cylinder Concrete Pipe (RPCCP) under Internal Load.

In order to study the load-bearing failure characteristics of a RPCCP under internal load, a field prototype test was designed, and a finite element model was established. An internal load was applied up to 2.0 MPa step by step and the force variation law of each part was obtained. During the production of the RPCCP, by wrapping prestressed steel bars around the concrete core with a cylinder, the core was subjected to an initial precompression stress. In the loading process, the protective cover cracked first, from where the concrete core gradually changed from the initial compression state to a tension state, finally cracking from the inner and outer diameter. The stresses of the cylinder and steel bars increased steadily with the internal load and did not yield. The finite element calculation results were in good agreement with the test results, and the influence characteristics of the tension control stress of the steel bar and the concrete strength on the failure of the RPCCP under internal load were discussed. The results showed that the internal load of the protective cover was independent of the tension control stress, but decreases with a decrease in concrete strength, while the load corresponding to the concrete core entering plasticity is related to the tension control stress and the concrete strength, and the relationships were basically linear.

Interaction of multiple shocks in planar targets with a ramp-pulse ablation

Interaction of multiple shocks plays a critical role in setting up an adiabatic compression of megabar pressure in nanosecond timescale in inertial confinement fusion. In this paper, we present observations of dynamic behavior and interaction of multiple shocks in polystyrene (CH) planar targets driven by a single-ramp pulse of 2.5 ns at the SG-II laser facility with a specially designed velocity interferometer system for any reflector (VISAR). A maximum pressure of 7.65 Mbar and a mass density of 3.46 g/cm3 are measured, respectively. Radiation-hydrodynamic simulations reveal the interaction process of the multiple shocks and are in good agreement with the measurements. A theoretical model is proposed to invert the space-time history of the shock generation with the VISAR data. Moreover, an optimized double-slope ramp pulse is proposed for further compression experiments. The improved multiple-shock coalescence is expected to effectively enhance both density and velocity for an initial compression of the CH target.

Hybrid test and numerical study of beam-through frame enhanced by friction spring-based self-centering rocking core

Beam-through frames (BTFs) are gradually becoming popular as low-to-medium rise buildings in China because of their economic benefits and fast construction. However, BTFs are prone to soft-story failure mechanisms, especially under the ultimate stage. The self-centering rocking core (SRC), composed of a steel truss rocking core and a friction spring-based self-centering (SC) device, is introduced to improve the resilience of the BTF. Quasi-static tests and hybrid tests were conducted to investigate the seismic performance of the SC device and the SRC, respectively. Quasi-static tests demonstrate that the SC device has highly stable flag-shaped hysteretic behavior under two different loading protocols. Hybrid tests reveal that the system could realize the target seismic performance with an effectively controlled deformation pattern under both far-field (FF) and near-fault (NF) pulse-like ground motions. Based on the experimental results, the uniaxial material model of the SC device and the numerical model of the system were verified. Subsequently, a parametric study was performed to investigate the influence of two stiffness parameters (i.e., the ratio of the initial actual (experimental) compression stiffness to the initial theoretical compression stiffness (κ) and the ratio of the initial actual tension stiffness to the initial actual compression stiffness (ρ)) of the SC device on the seismic performance of the system. The incremental dynamic analysis (IDA) results show that the collapse capacity of the system increases first and then decreases with the increase in κ values and a larger ρ leads to a larger collapse capacity of the system. Besides, the influence of such stiffness parameters on the peak responses of the system under various seismic hazard levels was also investigated. The strategy employing the SRC could realize a uniform peak inter-story drift (PID) distribution of BTFs while the peak floor acceleration (PFA) tends to be concentrated on the upper floors.

Effect of Insertion Trajectory on the Compressive Performance of Intramedullary Devices for Subtalar Arthrodesis

Category: Hindfoot; Other Introduction/Purpose: Subtalar arthrodesis is a common procedure to treat hindfoot pathologies. Prior studies have evaluated the effect of screw trajectory on the initial compression of the subtalar joint. More recently, intramedullary (IM) devices using pseudoelastic NiTiNOL, developed for subtalar arthrodesis, can apply sustained dynamic compression (SDC). Headed screws' compression is achieved via the lag effect and is dependent upon its fixation in bone. The SDC device's compression is achieved by a manual mechanism; however, its fixation is dependent upon transverse screws. However, it is unknown how the trajectory of these devices in the subtalar joint alters compression. The aim of this study is to determine how the trajectory of both static compression screws and sustained dynamic compression devices affects joint compression. Methods: Based upon previously published methods, a synthetic talus and calcaneus were mechanically isolated in a custom fixture, and the compression measured via a load cell located in parallel to the subtalar construct. Static headed screws were inserted either in a parallel configuration across the posterior facet or in a diverging configuration across the posterior and anterior facets. A single IM SDC device was inserted across the posterior facet or the anterior facet and secured in the talus and calcaneus via transverse cortical screws. The resulting compression was measured in a thermal chamber at 37°C (n=8/group). Devices were inserted following the manufacturer's recommended instructions. Data was tested for normality using the Kolmogorov-Smirnov test. A one-way ANOVA was performed with a post-hoc Tukey test (α=0.05). All values are given as mean +- standard deviation. Results: The SDC device's compression was 398+-47N in the posterior facet and 417+-31N in the anterior facet (p=0.64). The screws' compression was 267+-31N in the parallel configuration and 269+-21N in the diverging configuration (p=0.99). The single SDC device, regardless of position, had significantly greater compression than the parallel or diverging headed screws configuration (p<0.01). Conclusion: The SDC device's compression is not affected by insertion trajectory, thus allowing for surgeon preference in anatomic placement. The SDC device is able to generate more compression than the headed screws, regardless of trajectory or screw configuration.

Microstructure, Mechanical Properties and Cross‐sectional Behaviour of Additively Manufactured Stainless Steel Cylindrical Shells

AbstractPowder bed fusion (PBF) is an additive manufacturing method that enables complex metallic components to be manufactured with high precision. The microstructure, mechanical properties and cross‐sectional behaviour of PBF additively manufactured stainless steel circular hollow sections are investigated through experiments in this paper, with a view to applications in construction. The experimental programme included tensile coupon tests, microstructural characterisation, initial geometric imperfection measurements and compression tests on PBF 316L stainless steel cylindrical shells with large diameter‐to‐thickness (D/t) ratios. Advanced measurement methods – 3D laser scanning and digital image correlation, were employed to measure the specimen geometries prior to testing and deformation fields during testing, respectively. The possible anisotropy in mechanical properties was examined through tensile coupon tests and correlated with the underlying microstructural and textural features. Compression tests were performed to investigate the resistance against local buckling of thin‐walled cylindrical shells produced by PBF. All cylindrical shells buckled below their yield loads with a chequerboard failure mode and revealed the anticipated trend of reducing capacity relative to the yield load with increasing local slenderness, reflecting the increasing susceptibility to local buckling.

Incorporating baryon-driven contraction of dark matter halos in rotation curve fits

The condensation of baryons within a dark matter (DM) halo during galaxy formation should result in some contraction of the halo as the combined system settles into equilibrium. We quantify this effect on the cuspy primordial halos predicted by DM-only simulations for the baryon distributions observed in the galaxies of the SPARC database. We find that the DM halos of high surface brightness galaxies (with Σeff ≳ 100 L⊙ pc−2 at 3.6 μm) experience strong contraction. Halos become more cuspy as a result of compression: the inner DM density slope increases with the baryonic surface mass density. We iteratively fit rotation curves to find the balance between initial halo parameters (constrained by abundance matching), compression, and stellar mass-to-light ratio. The resulting fits often require lower stellar masses than expected for stellar populations, particularly in galaxies with bulges: stellar mass must be reduced to make room for the DM it compresses. This trade off between dark and luminous mass is reminiscent of the cusp-core problem in dwarf galaxies, but occurs in more massive systems: the present-epoch DM halos cannot follow from cuspy primordial halos unless (1) the stellar mass-to-light ratios are systematically smaller than expected from standard stellar population synthesis models, and/or (2) there is a net outward mass redistribution from the initial cusp, even in massive galaxies widely considered to be immune from such effects.

Influence of high-speed maglev train speed on tunnel aerodynamic effects

When a high-speed maglev train enters a tunnel, the pressure around it rises and changes quickly. This may lead to serious damage of the train and tunnel structures. With increases of train speed, up to 600 km/h, this issue will become worse. In this study, the three-dimensional, compressible, unsteady, k - ϵ two-equation turbulence model and sliding grid technologies were used to study the effect of train speed on the pressure waves induced by a maglev train passing through a tunnel. The numerical simulation method used was validated against results from moving model tests and semi-empirical formulations. The maglev train modelled was specified to pass through a 2 km tunnel with speeds in the range from 400 km/h to 600 km/h. The surface pressure distribution of the train and tunnel were found and are discussed. The transient pressures on the maglev train and tunnel surface are shown to have a significant relationship with the train speed. Generally, the maxima of the train surface pressures follow the power law relationship with an exponent of 2.35 to the train speed, while for the tunnel surface pressure, an exponent of 2.46 is obtained. The gradient of the initial compression wave at the tunnel entrance follows a power law relationship with an exponent of 3.51 to the train speed, while at the exit this rises to an exponent of 4.99. The amplitude of the micro-pressure wave follows a power law relationship with an exponent of 5.00 to the train speed. Having such data will provide essential support for the design of both the maglev train and tunnel. • Influence on tunnel aerodynamic effects induced by a high-speed maglev train passing through a tunnel has been studied. • Interesting sub-reflection waves induced by train motion in tunnel meeting reflection waves from portals are observed. • Power-law exponents of the relationship between train speed and pressure amplitude are higher than those in previous studies. • Amplitudes of micro-pressure waves follow the power law relationship with an approximate exponent of 5.00 to the train speed.

186. The effect of cement augmentation and anti-osteoporotic medication on secondary fracture risk in osteoporotic compression fractures

186. The effect of cement augmentation and anti-osteoporotic medication on secondary fracture risk in osteoporotic compression fractures

A novel concrete-filled auxetic tube composite structure: Design and compressive characteristic study

Concrete-filled stainless steel tube (CFSST) members take advantage of the high strength and the outstanding corrosion resistance to act as an important role in civil engineering structures. However, the steel tube could not provide the perfect confinement effect for the core concrete during the initial elastic compression stage because Poisson’s ratio of the concrete is smaller than that of the stainless steel tube (SST). In this paper, a novel concrete-filled auxetic stainless steel tube (CFASST) composite structure was designed and manufactured to actively restrain the concrete, making the best use of the desirable deformation characteristics of auxetic tubular structures. The axial compressive performance of these CFASST members and their control factors were investigated experimentally and numerically. Test results were discussed in detail which included failure modes, load versus displacement curves and strain analysis. Finally, parametric analyses were conducted to further study the effects of different parameters (Poisson’s ratio, thickness of the stainless tube) on the CFSST composite structure under axial compression. It was found that CFASST composite structures possess an unusual deformation mode and an improved confinement effect.

A realist evaluation to identify targets to improve the organization of compression therapy for deep venous thrombosis- and chronic venous disease patients.

BackgroundAlthough compression therapy is well established for patients with deep venous thrombosis (DVT) and chronic venous disease (CVD), considerable variation exists in its organization in clinical practice which may impact patient outcomes. The current study aims to deepen our understanding of the main drivers of the complex care organization for compression therapy and to identify targets for improvement.MethodsThis realist evaluation includes a mixed-method design consisting of semi-structured interviews with patients and health care professionals involved in compression therapy (n = 30), stakeholder meetings (n = 2) and surveys (n = 114). Data were collected to create the content of context-mechanism-outcome-configurations (CMOcs) important in compression therapy. Based on these CMOcs, targets for improvement to optimize the organization of compression care were identified.ResultsWe identified overarching context factors and mechanisms targeting four optimal outcomes for the organization of compression therapy: selecting initial compression therapy types that support patient’s self-reliance (1), evidence based selection of elastic compression stocking type and class (2), patient-based selection of assistive devices (3), individualizing treatment duration for DVT patients (4a) and providing follow-up for CVD patients (4b). We found that increasing health care professionals’ knowledge of compression therapy, the availability of unambiguous protocols and guidelines, increasing patient involvement (and if applicable their informal care giver) in the decision making process, the accessible availability of resources, and increasing interdisciplinary consultation enhanced desirable outcomes. These targets triggered mechanisms such as increased health care professionals’ willingness, confidence and motivation to provide patient-based care and increased patients’ self-confidence and self-efficacy.ConclusionsThis study provides a detailed insight into what needs to be in place to optimize compression care and identified five main targets for improvement.

Standard compression rate test method and its application for rockfill materials

To explore the standard compression rate test method’s suitability for rockfill and to solve the problem that rockfill is too large for the laboratory standard test, the similar grading method was used to scale down the rockfill. This was used to simulate five kinds of rockfill with different solid phase volume ratios of skeleton and gap-filling particles (7:3, 6:4, 5:5, 4:6, 3:7, respectively). The density property, maximum compression rate and the strength property tests were carried out on the five fill materials using a self-designed test device. The test results showed that the loose packing density, initial compression density, compact density and California bearing ratio of rockfill increase and then decrease with a decrease of the solid phase volume ratio between skeleton and gap-filling particles. The compressibility and crushing rate of the filler stone decreased with the decrease of the solid phase volume ratio of the skeleton to the gap-filling particles. The maximum compression rate of the filler is determined by the laboratory compression test, and the compaction can be measured according to the compression rate, for a known paving area.

In Situ Thickness Measurements During Cycling of Li-Ion Pouch Cells with Silicon Negative Electrodes

Cell expansion and contraction are major concerns for battery pack and module developers. This work is an effort to understand the behavior of cell expansion due to formation, lithiation and cycling, with measurements made by a system that uses a Linear Variable Differential Transformer (LVDT) sensor. For a NCM622-Silicon cell, impact of factors such as initial compression pressure and calendaring of electrodes on cell expansion were explored. Reversible expansion during charge/discharge in a cycle is a function of cell capacity and reversible expansion can be reduced with increasing initial compression. Irreversible expansion during cycling grows linearly with the number of cycles and can also be reduced with initial compression of the cell. With initial compression of 45 psi, measurements showed 3% cell expansion during formation, 4% reversible expansion in a charge/discharge cycle with C/5 rate, and 12% irreversible expansion over 220 cycles. From the data, a hypothesis was developed suggesting that SEI growth and plastic deformation of the silicon particles could be the main causes for irreversible expansion of the cells with silicon electrodes, with the assumption that cells show less than 20% capacity fade over life.