Longitudinal Propagation Velocity Research Articles

Influence of Interturn Contact Stress on the Quench Behavior of Insulated YBCO Pancake Magnets: A Study Based on Numerical Simulations

Insulated high temperature superconducting (HTS) magnets are still widely used in low field applications, such as HTS motors and generators. In this paper, a two-dimensional/three-dimensional (2D/3D) mixed electrothermal model and a homogeneous 3D electrothermal model are employed to study the influence of inter-turn contact stress on the minimum quench energy (MQE), longitudinal and transverse normal zone propagation velocity (NZPV) of insulated YBCO magnets for the temperature range 30 K – 60 K. This temperature range is of interest usually in applications, such as HTS motors, generators and transformers, because it allows the use of low cost cooling system. It is found that MQE increases significantly with increasing inter-turn contact stress. The inter-turn contact stress has small influence on the longitudinal NZPV of insulated YBCO pancake magnet. However, the transverse NZPV rises significantly with the increase of inter-turn contact stress. The transverse NZPV is nearly proportional to the inter-turn contact stress. The 3D homogeneous model gives results that are in agreement with those of 2D/3D mixed model, especially for the temperature range 45 K – 60 K; however, the MQE and transverse NZPV given by the two models are different for the temperature range 30 K – 45 K. That means for insulated HTS YBCO pancake magnets operating at the temperature range 45 K – 60 K, the 3D homogeneous electro-thermal model can be a good replacement of the 2D/3D mixed model to study the quench behavior, which can achieve better computational efficiency without significant loss of accuracy.

Investigation on the fire behaviour and propagation rule of fire overflow in the high-rise concave building structure

The concave building structure (CBS) featured with a partial sunken façade is prevalent in the high-rise residence and comprehensive buildings. The building is a 3/4 enclosed longitudinal shaft that creates a new channel for longitudinal fire propagation. The objective of the paper is to reveal the dynamic mechanism of fire propagation in CBS. A small-scale experiment and Fire Dynamics Simulator (FDS) were conducted to investigate the fire behaviour. The results show that CBS could enhance the longitudinal propagation velocity of the flame and smoke with a slender profile. It could reduce the heat loss and create a higher space temperature than no-concave building structure (NBS). The maximum temperature and smoke concentration extended from the external facade centre to two flanks with the building height increase. Raising the structure factor extended the flame length from 7.0 m to 8.6 m. It exhibited a typical three stages of entrainment velocity growth: rapid growth, medium growth and slow growth. The flame transferred from the external façade to the lateral façade when the heat release rate was 8–10 MW. The research is essential to distinguish the hazardous region and provide a basis for architectural design and personal safe evacuation in the CBS fire scenario.

Propagation velocity model of stress waves in larch wood (Larix gmelinii) three-dimensional space with different moisture contents

Based on the effects of stress wave propagation in larch (Larix gmelinii) wood, the propagation mechanism of stress wave was explored, and a theoretical model of the propagation velocity of stress waves in the three-dimensional space of wood was developed. The cross and longitudinal propagation velocities of stress wave were measured in larch wood under different moisture contents (46% to 87%, 56% to 96%, 20% to 62%, and 11% to 30%) in a laboratory setting. The relationships between the propagation velocity of stress waves and the direction angle or chord angle with different moisture contents were analyzed, and the three-dimensional regression models among four parameters were established. The analysis results indicated that under the same moisture content, stress wave velocity increased as the direction angle increased and decreased as chord angle increased, and the radial velocity was the largest. Under different moisture contents, stress wave velocity gradually decreased as moisture content increased, and the stress wave velocity was more noticeably affected by moisture content when moisture content was below the fiber saturation point (FSP, 30%). The nonlinear regression models of the direction angle, chord angle, moisture content, and the propagation velocity of stress wave fit the experiment data well (R2 ≥ 0.97).

Glucose-insulin-potassium improves left ventricular performances after aortic valve replacement: a secondary analysis of a randomized controlled trial

BackgroundPatients with left ventricular (LV) hypertrophy may suffer ischemia-reperfusion injuries at the time of cardiac surgery with impairment in left ventricular function. Using transesophageal echocardiography (TEE), we evaluated the impact of glucose-insulin potassium (GIK) on LV performances in patients undergoing valve replacement for aortic stenosis.MethodsIn this secondary analysis of a double-blind randomized trial, moderate-to-high risk patients were assigned to receive GIK (20 IU insulin with 10 mEq KCL in 50 ml glucose 40%) or saline over 60 min upon anesthetic induction. The primary outcomes were the early changes in 2-and 3-dimensional left ventricular ejection fraction (2D and 3D-LVEF), peak global longitudinal strain (PGLS) and transmitral flow propagation velocity (Vp).ResultsAt the end of GIK infusion, LV-FAC and 2D- and 3D-LVEF were unchanged whereas Vp (mean difference [MD + 7.9%, 95% confidence interval [CI] 3.2 to 12.5%; P < 0.001) increased compared with baseline values. After Placebo infusion, there was a decrease in LV-FAC (MD -2.9%, 95%CI − 4.8 to − 1.0%), 2D-LVEF (MD -2.0%, 95%CI − 2.8 to − 1.3%, 3D-LVEF (MD -3.0%, 95%CI − 4.0 to − 2.0%) and Vp (MD − 4.5 cm/s, 95%CI − 5.6 to − 3.3 cm/s).After cardiopulmonary bypass, GIK pretreatment was associated with preserved 2D and 3D-LVEF (+ 0.4%, 95% 95%CI − 0.8 to 1.7% and + 0.4%, 95%CI − 1.3 to 2.0%), and PGLS (− 0.9, 95%CI − 1.6 to − 0.2) as well as higher Vp (+ 5.1 cm/s, 95%CI 2.9 to 7.3), compared with baseline. In contrast, in the Placebo group, 2D-LVEF (− 2.2%, 95%CI − 3.4 to − 1.0), 3D-LVEF (− 6.0%, 95%CI − 7.8 to − 4.2), and Vp (− 7.6 cm/s, 95%CI − 9.4 to − 5.9), all decreased after bypass.ConclusionsAdministration of GIK before aortic cross-clamping resulted in better preservation of systolic and diastolic ventricular function in patients with LV hypertrophy undergoing aortic valve replacement.Trial registrationClinicalTrials.gov: NCT00788242, registered on November 10, 2008.

Quench Characteristics Comparison Between Solid Nitrogen and Conduction Cooled REBCO Coil Under Thermal Disturbance and Over Current Pulse

In power system application of high temperature superconducting (HTS) equipment, large amount of heat caused by thermal disturbance or over current during sudden electric interruptions will endanger the thermal stability of HTS devices. However, solid nitrogen (SN2) with large heat capacity can enhance the thermal stability of HTS magnets. In this paper, the quench characteristics of SN2 and conduction cooled REBCO coil under thermal disturbance and over current pulse has been investigated at 60 K. For the thermal disturbance experiment, the minimum quench energy, longitudinal and transverse normal zone propagation velocities in SN2, and conduction cooled system are compared and discussed. The strain response property of the coil from quench to complete cooled down after power off during the quench process has also been preliminarily discussed. What is more, the accumulated peak voltage and strain of the coil during the over current pulse test has been studied. These results show that SN2 can help to enhance the thermal stability of REBCO coil under thermal disturbance and over current pulse.

Measurement of fiber reinforced composite engineering constants with laser ultrasonic

In this paper, a noncontact laser ultrasonic method is proposed to determine the engineering constants of fiber reinforced composite. The method is based on the measurements of the transverse wave velocities as well as the longitudinal wave velocities. In the experiment, the unidirectional carbon fiber reinforced bismaleimide resin matrix composite is measured and the sample is equivalent to a transversely isotropic material. Two longitudinal wave propagation velocities and three transverse wave propagation velocities in two specific directions are measured, respectively. On this basis, all five independent elastic constants can be obtained according to the Christoffel equation. In the finite element analysis, the model of laser induced ultrasonic in the composites is established. The pulsed laser is equivalent to the surface load and the relationship between the physical parameters of the laser and the load is established by the correction coefficient. The numerical results match well with experimental measurements, which show that the method presented in this paper can achieve an accurate measurement of the elastic constants of fiber reinforced composite.

The influence of temperature on the speed of sound of cortical bone phantom: a metrological view

This paper presents an experimental study to estimate the group velocity of ultrasound longitudinal propagation in a cortical bone phantom for the temperature range of 19 °C to 37 °C, and respective measurement uncertainty estimates. The group velocity was measured using the pulse/echo method. The uncertainty model was proposed based on the BIPM JCGM:100 – Guide of the Expression of Uncertainty in Measurements. The velocity results show a tendency to decrease linearly as the temperature increases, considering the uncertainty estimated.

Saline-Induced Coronary Hyperemia: Mechanisms and Effects on Left Ventricular Function.

During thermodilution-based assessment of volumetric coronary blood flow, we observed that intracoronary infusion of saline increased coronary flow. This study aims to quantify the extent and unravel the mechanisms of saline-induced hyperemia. Thirty-three patients were studied; in 24 patients, intracoronary Doppler flow velocity measurements were performed at rest, after intracoronary adenosine, and during increasing infusion rates of saline at room temperature through a dedicated catheter with 4 lateral side holes. In 9 patients, global longitudinal strain and flow propagation velocity were assessed by transthoracic echocardiography during a prolonged intracoronary saline infusion. Taking adenosine-induced maximal hyperemia as reference, intracoronary infusion of saline at rates of 5, 10, 15, and 20 mL/min induced 6%, 46%, 111%, and 112% of maximal hyperemia, respectively. There was a close agreement of maximal saline- and adenosine-induced coronary flow reserve (intraclass correlation coefficient, 0.922; P<0.001). The same infusion rates given through 1 end hole (n=6) or in the contralateral artery (n=6) did not induce a significant increase in flow velocity. Intracoronary saline given on top of an intravenous infusion of adenosine did not further increase flow. Intracoronary saline infusion did not affect blood pressure, systolic, or diastolic left ventricular function. Heart rate decreased by 15% during saline infusion (P=0.021). Intracoronary infusion of saline at room temperature through a dedicated catheter for coronary thermodilution induces steady-state maximal hyperemia at a flow rate ≥15 mL/min. These findings open new possibilities to measure maximal absolute coronary blood flow and minimal microcirculatory resistance.

Analysis of the quench propagation along Nb3Sn Rutherford cables with the THELMA code. Part I: Geometric and thermal models

The paper describes the new lumped thermal model recently implemented in THELMA code for the coupled electromagnetic–thermal analysis of superconducting cables. A new geometrical model is also presented, which describes the Rutherford cables used for the accelerator magnets. A first validation of these models has been given by the analysis of the quench longitudinal propagation velocity in the Nb3Sn prototype coil SMC3, built and tested in the frame of the EUCARD project for the development of high field magnets for LHC machine. This paper shows in detail the models, while their application to the quench propagation analysis is presented in a companion paper.

Diabetic gastroparesis alters the biomagnetic signature of the gastric slow wave.

Gastroparesis is characterized by delayed gastric emptying without mechanical obstruction, but remains difficult to diagnose and distinguish from other gastrointestinal (GI) disorders. Gastroparesis affects the gastric slow wave, but non-invasive assessment has been limited to the electrogastrogram (EGG), which reliably characterizes temporal dynamics but does not provide spatial information. We measured gastric slow wave parameters from the EGG and magnetogastrogram (MGG) in patients with gastroparesis and in healthy controls. In addition to dominant frequency (DF) and percentage power distribution (PPD), we measured the propagation velocity from MGG spatiotemporal patterns and the percentage of slow wave coupling (%SWC) from EGG. No significant difference in DF was found between patients and controls. Gastroparesis patients had lower percentages of normogastric frequencies (60 ± 6% vs 78 ± 4%, p < 0.05), and higher brady (9 ± 2% vs 2 ± 1%, p < 0.05) and tachygastric (31 ± 2% vs 19 ± 1%, p < 0.05) frequency content postprandial, indicative of uncoupling. Propagation patterns were substantially different in patients and longitudinal propagation velocity was retrograde at 4.3 ± 2.9 mm/s vs anterograde at 7.4 ± 1.0 mm/s for controls (p < 0.01). No difference was found in %SWC from EGG. Gastric slow wave parameters obtained from MGG recordings distinguish gastroparesis patients from controls. Assessment of slow wave propagation may prove critical to characterization of underlying disease processes. Future studies should determine pathologic indicators from MGG associated with other functional gastric disorders, and whether multichannel EGG with appropriate signal processing also reveals pathology.

Quench Analysis of High-Current-Density Nb3Sn Conductors in Racetrack Coil Configuration

The luminosity upgrade of the large hadron collider (HL-LHC) requires the development of new type of superconducting cables based on advanced Nb 3 Sn strands. In the framework of the FP7 European project EUCARD, the cables foreseen for the HL-LHC project have been tested recently in a simplified racetrack coil configuration, the so-called Short Model Coil (SMC). In 2013-2014, two SMCs wound with 40-strand (RRP 108/127) cables, with different heat treatment processes, reached during training at 1.9 K a current and peak magnetic field of 15.9 kA, 13.9 T, and 14.3 kA, 12.7 T, respectively. Using the measured signals from the voltage taps, the behavior of the quenches is analyzed in terms of transverse and longitudinal propagation velocity and hot-spot temperature. These measurements are compared with both analytical and numerical calculations from adiabatic models. The coherence of the results from the presented independent methods helps in estimating the relevance of the material properties and the adiabatic assumption for impregnated Nb 3 Sn conductor modeling.

Variation of Quench Propagation Velocities in YBCO Cables

We show by modelling that the quench propagation velocity is not constant in HTS coils but it changes during the quench. Due to the large temperature margin between the operation and the current sharing temperatures, the normal zone does not propagate with the temperature front. This means that the temperature will rise in a considerably larger volume when compared to the quenched volume. Thus, the evolution of the temperature distribution below current sharing temperature T c s after the quench onset affects the normal zone propagation velocity in HTS more than in LTS coils. This can be seen as an acceleration of the quench propagation velocities while the quench evolves when margin to T c s is high. In this paper, we scrutinize quench propagation in a stack of YBCO cables with an in-house finite element method software which solves the heat diffusion equation. We compute the longitudinal and transverse normal zone propagation velocities at various distances from the hot spot to demonstrate the distance-variation of these velocities. According to the results in our particular simulation case, the longitudinal normal zone propagation velocity is 30 % higher far away from the quench origin compared to its immediate vicinity when T op=4.2 K and T c s =15 K.

Study of Quench Behavior of ReBCO Impregnated Pancake Coil with a 75-μm-thick Copper Stabilizer Under Conduction-cooled Conditions

Recently, high performance ReBa2Cu3Ox (ReBCO) coated conductor, such as those with over 500 A per 1cm in width at 77K, have become commercially available. The quench detection of ReBCO pancake coils under conduction-cooled conditions is an important issue for the safe operation of superconducting applications. Although experimental data on the quench characteristics of ReBCO coated conductors have been reported, there is no sufficient database available regarding ReBCO impregnated pancake coils.In this work, a ReBCO impregnated pancake coil was fabricated using ReBCO coated conductors laminated with a 75-μm-thick copper stabilizer. The inner diameter of the ReBCO coil was 50mm, and the outer diameter was approximately 73mm. The measured longitudinal normal-zone propagation velocities (NZPV) in the ReBCO coil were 3–27mm/s at 50–20K. It was also confirmed that the ReBCO coil was shut down from 100 A to 240 A by a balance voltage detection at 40–100mV under conduction-cooled conditions without degradation.

Integrated analysis of quench propagation in a system of magnetically coupled superconducting coils

We demonstrate in this paper how to use direct modeling of heat transfer and circuital equations based on “packaged” simulation tools to produce a model suitable for the study of quench propagation in a system of magnetically coupled solenoids protected without an external dump resistor. Our application example is a system of three, layer-wound and bath-cooled coils, all using a NbTi conductor. The same model can be easily adapted to study coils with different topologies, geometry and conductors. We demonstrate the use of the model by parametric analysis of physical parameters in the system, showing under which conditions a quench-back due to inductive coupling is triggered. The results, and in particular longitudinal and transverse propagation velocities, are consistent with expected analytical scalings. The advantage of the model is that it provides self-consistent results, i.e. based on first principles rather than assumptions on quench propagation, and it gives access to local details that are not intuitive, nor easily measurable.

The experimental research and analysis on the quench propagation of YBCO coated conductor and coil

Quench propagation characteristics of YBCO tapes and coils were studied in this paper. Quench propagation in each test was initiated by a NiCr wire heater mounted on the sample tape and coil. Quench propagation velocity was measured through voltage taps and temperature sensors across different zones of the tapes and coil. Voltage taps and temperature sensors are arranged in longitudinal and radial direction of the coil. The thermal stability margin, the longitudinal quench propagation velocity for the tape and coil, radial quench propagation velocity for coil and the minimum propagation current were measured. In this study, we investigated the relationship between heat inputs and normal zone propagation velocities and the impact of operating currents on normal zone propagation velocities. We also compared the longitudinal quench propagation velocity and the radial quench propagation velocity. Furthermore, we performed numerical simulations by using a computer program based on a one-dimensional heat flow equation model for YBCO tape. The temperature longitudinal distributions of YBCO tape were simulated. The simulation results also prove the relation between heat input and normal zone propagation velocities and agree with the experimental results.

Characterization and Classification of Rocks with Lamb Modes

The nondestructive investigation by ultrasound has become a fundamental tool for characterizing rocks. We applied this technique for characterizing samples of rocks. The later had been members of the following three big families of geogical classification: magmatic rocks, metamorphic rocks, sedimentary rocks. The method usually used is based on the measurement of ultrasound parameters, i.e. the longitudinal and transversal propagation velocities. The measurement of these parameters allows to determine the mechanical properties of each rock. These studies do not allow to find the three big axes of the rocks. In this work we show for each rock his corresponding ultrasonic signature by the use of his experimentally determined Lamb dispersion curves. The obtained results put in evidence that the descending slope of the Lamb modes is a reliable and efficient criterion for classifying rocks by ultrasound. This is an adequate solution for a good classification of rocks. It gives a high precision, it is reliable and quick and last not least cheap.

ГЕОДИНАМІКА

The influence of mineral composition and structure-texture features on elastic properties of rocks of the Ukrainian Shield at different pressure and temperatures has been research. Statistically grounded cross-correlation dependences longitudinal and transversal waves propagation velocity from mineral composition at different depths were obtained.

Stability and Quench Behavior of $\hbox{YBa}_{2} \hbox{Cu}_{3}\hbox{O}_{7 - x}$ Coated Conductor at 4.2 K, Self-Field

YBa2Cu3O7- x (YBCO) coated conductors (CCs) are now capable of carrying very high transport critical current density Jc over a broad range of magnetic field and temperature space, and as a result, they are receiving significant interest for a wide range of applications. While many of these applications take advantage of the high-temperature performance of YBCO CCs, because the YBCO CC is typically produced on a high-strength substrate and carries very high Jc at very high magnetic field, there is now growing interest in using YBCO CCs at 4.2 K to generate very high magnetic fields. The transition from high-field conductor to high-field superconducting magnet, however, requires that some challenging issues be addressed. One of the most important challenges remaining is to better understand the stability and quench behavior at 4.2 K, so that an effective quench protection system can be developed. Here, we report on measurements of the stability and quench behavior of short YBCO CC at 4.2 K by inducing a quench via a heat pulse from a heater mounted on the conductor surface. Through gradually increasing heater pulse amplitude, the transition from stable to unstable (i.e., recovery to quench) is observed through voltage and temperature measurements. Using these data, the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) are determined. It is found that, for the same fraction of critical current (I/Ic), YBCO CCs have similar MQE and NZPV as Ag-alloy-clad Bi2Sr2CaCu2Ox wires and significantly higher MQE and lower NZPV than those of MgB2 round wires of similar Ic (4.2 K). Furthermore, the voltage and temperature versus time data are correlated to better understand the quench onset behavior at 4.2 K. It is determined that a normal temperature gradient exists from the CC surface to the YBCO layer within the conductor, as well as a directly measured longitudinal temperature gradient. After the heater pulse has ended but while the transport current continues, the temperature gradient along the length becomes dominant. Nevertheless, voltage and temperature measurements remain problematic for quench detection in large magnets because of the slow longitudinal propagation velocity. Thus, new approaches to quench detection and/or protection of high-field YBCO magnets are needed.

Relation Between Transverse and Longitudinal Normal Zone Propagation Velocities in Impregnated ${\rm MgB}_{2}$ Windings

The transverse normal zone propagation velocity, v t, in impregnated magnets controls the 3D normal zone expansion during a quench. It is dominated by the thermal conductivities of the conductor insulation and the impregnation material. The longitudinal propagation velocity v l is mainly determined by the heat generation, critical surface of the superconductor and thermal conduction along the conductor. It has been generally assumed that the ratio v t/v l is proportional to the square root of the ratios of the corresponding effective heat conductivities. In this paper we study computationally the validity of this approach for an MgB2 wire surrounded by an epoxy layer. We take into account the finite n-value of the composite conductor in our finite element method (FEM) models. We computed v l with Whetstone-Roos formula and 1D and 2D FEM models. The 2D model was also used to compute v t. In addition to this, minimum quench energies given by the 1D and 2D FEM models were compared.

Estudo comparativo da velocidade e atenuação ultra-sônica na avaliação da consolidação óssea

OBJETIVO: O objetivo deste trabalho foi comparar a velocidade e atenuação ultra-sônica, na avaliação in vitro da consolidação óssea. MÉTODO: Foram empregados no estudo 17 carneiros, com massa corporal média de 37 kg, divididos entre grupos controle e três experimentais, conforme o período de observação pós-operatória de 30, 60 e 90 dias. As osteotomias foram realizadas nas tíbias direitas dos animais, ficando as esquerdas como controle. O processo de consolidação foi acompanhado por meio de avaliação radiográfica a cada duas semanas. Ao fim do período de observação estipulado para cada grupo, os animais sofreram eutanásia e as tíbias foram removidas para a análise ultra-sonométrica in vitro. Foram medidos e correlacionados a velocidade de propagação transversal e longitudinal do ultra-som e a atenuação do ultra-som (BUA) transversal na região da osteotomia. RESULTADOS: A velocidade de propagação do ultra-som (transversal e longitudinal, in vitro) aumentou com o avançar da consolidação, sendo as diferenças significantes em relação ao grupo controle e entre a maioria dos grupos experimentais. Já a BUA diminuiu, sendo parte das diferenças significantes entre os grupos. CONCLUSÃO: O método de avaliação da consolidação pelos parâmetros da ultra-sonometria é factível, com resultados confiáveis e precisos para medir a consolidação óssea.