Impact of Hysteresis Heating of Railroad Bearing Thermoplastic Elastomer Suspension Pad on Railroad Bearing Thermal Management

It is a known fact that polymers and all other materials develop hysteresis heating due to the viscoelastic response or internal friction. The hysteresis or phase lag occurs when cyclic loading is applied leading to the dissipation of mechanical energy. The hysteresis heating is induced by the internal heat generation of the material, which occurs at the molecular level as it is being disturbed cyclically. Understanding the hysteresis heating of the railroad bearing elastomer suspension element during operation is essential to predict its dynamic response and structural integrity, as well as to predict the thermal behavior of the railroad bearing assembly. The main purpose of this ongoing study is to investigate the effect of the internal heat generation in the thermoplastic elastomer suspension element on the thermal behavior of the railroad bearing assembly. This paper presents an experimentally validated finite element thermal model that can be used to obtain temperature distribution maps of complete bearing assemblies in service conditions. The commercial software package ALGOR 20.3™ is used to conduct the thermal finite element analysis. Different internal heating scenarios are simulated with the purpose of determining the bearing suspension element and bearing assembly temperature distributions during normal and abnormal operation conditions. Preliminary results show that a combination of the ambient temperature, bearing temperature, and frequency of loading can produce elastomer pad temperature increases above ambient of up to 125°C when no thermal runway is present. The higher temperature increase occurs at higher loading frequencies such as 50 Hz, thus, allowing the internal heat generation to significantly impact the temperature distribution of the suspension pad. This paper provides several thermal maps depicting normal and abnormal operation conditions and discusses the overall thermal management of the railroad bearing assembly

Hysteresis Heating of Railroad Bearing Thermoplastic Elastomer Suspension Element

Thermoplastic elastomers (TPE’s) are increasingly being used in rail service in load damping applications. They are superior to traditional elastomers primarily in their ease of fabrication. Like traditional elastomers they offer benefits including reduction in noise emissions and improved wear resistance in metal components that are in contact with such parts in the railcar suspension system. However, viscoelastic materials, such as the railroad bearing thermoplastic elastomer suspension element (or elastomeric pad), are known to develop self-heating (hysteresis) under cyclic loading, which can lead to undesirable consequences. Quantifying the hysteresis heating of the pad during operation is therefore essential to predict its dynamic response and structural integrity, as well as, to predict and understand the heat transfer paths from bearings into the truck assembly and other contacting components. This study investigates the internal heat generation in the suspension pad and its impact on the complete bearing assembly dynamics and thermal profile. Specifically, this paper presents an experimentally validated finite element thermal model of the elastomeric pad and its internal heat generation. The steady-state and transient-state temperature profiles produced by hysteresis heating of the elastomer pad are developed through a series of experiments and finite element analysis. The hysteresis heating is induced by the internal heat generation, which is a function of the loss modulus, strain, and frequency. Based on previous experimental studies, estimations of internally generated heat were obtained. The calculations show that the internal heat generation is impacted by temperature and frequency. At higher frequencies, the internally generated heat is significantly greater compared to lower frequencies, and at higher temperatures, the internally generated heat is significantly less compared to lower temperatures. However, during service operation, exposure of the suspension pad to higher loading frequencies above 10 Hz is less likely to occur. Therefore, internal heat generation values that have a significant impact on the suspension pad steady-state temperature are less likely to be reached. The commercial software package ALGOR 20.3TM is used to conduct the thermal finite element analysis. Different internal heating scenarios are simulated with the purpose of obtaining the bearing suspension element temperature distribution during normal and abnormal conditions. The results presented in this paper can be used in the future to acquire temperature distribution maps of complete bearing assemblies in service conditions and enable a refined model for the evolution of bearing temperature during operation

Heat Generation in the Railroad Bearing Thermoplastic Elastomer Suspension Element

The main purpose of this ongoing study is to investigate the effect of heat generation within a railroad thermoplastic elastomer suspension element on the thermal behavior of the railroad bearing assembly. Specifically, the purpose of this project is to quantify the heat generated by cyclic loading of the elastomer suspension element as a function of load amplitude, loading frequency, and operating temperature. The contribution of the elastomer pad to the system energy balance is modeled using data from dynamic mechanical analysis (DMA) of the specific materials in use for that part. DMA is a technique that is commonly used to characterize material properties as a function of temperature, time, frequency, stress, atmosphere or a combination of these parameters. DMA tests were run on samples of pad material prepared by three different processes: injection molded coupons, transfer molded coupons, and parts machined from an actual pad. The results provided a full characterization of the elastic deformation (Energy Storage) and viscous dissipation (Energy Dissipation) behavior of the material as a function of loading frequency, and temperature. These results show that the commonly used thermoplastic elastomer does generate heat under cyclic loading, though the frequency which produces peak heat output is outside the range of common loading frequency in rail service. These results can be combined with a stress analysis and service load measurements to estimate internally generated heat and, thus, enable a refined model for the evolution of bearing temperature during operation

Cardiovascular magnetic resonance evaluation of aortic stenosis severity using single plane measurement of effective orifice area

<p>Abstract</p> <p>Background</p> <p>Transthoracic echocardiography (TTE) is the standard method for the evaluation of the severity of aortic stenosis (AS). Valve effective orifice area (EOA) measured by the continuity equation is one of the most frequently used stenotic indices. However, TTE measurement of aortic valve EOA is not feasible or not reliable in a significant proportion of patients. Cardiovascular magnetic resonance (CMR) has emerged as a non-invasive alternative to evaluate EOA using velocity measurements. The objectives of this study were: 1) to validate a new CMR method using jet shear layer detection (JSLD) based on acoustical source term (AST) concept to estimate the valve EOA; 2) to introduce a simplified JSLD method not requiring vorticity field derivation.</p> <p>Methods and results</p> <p>We performed an in vitro study where EOA was measured by CMR in 4 fixed stenoses (EOA = 0.48, 1.00, 1.38 and 2.11 cm²) under the same steady flow conditions (4-20 L/min). The in vivo study included eight (8) healthy subjects and 37 patients with mild to severe AS (0.72 cm²≤ EOA ≤ 1.71 cm²). All subjects underwent TTE and CMR examinations. EOA was determinated by TTE with the use of continuity equation method (TTE_CONT). For CMR estimation of EOA, we used 3 methods: 1) Continuity equation (CMR_CONT); 2) Shear layer detection (CMR_JSLD), which was computed from the velocity field of a single CMR velocity profile at the peak systolic phase; 3) Single plane velocity truncation (CMR_SPVT), which is a simplified version of CMR_JSLDmethod. There was a good agreement between the EOAs obtained in vitro by the different CMR methods and the EOA predicted from the potential flow theory. In the in vivo study, there was good correlation and concordance between the EOA measured by the TTE_CONTmethod versus those measured by each of the CMR methods: CMR_CONT(r = 0.88), CMR_JSLD(r = 0.93) and CMR_SPVT(r = 0.93). The intra- and inter- observer variability of EOA measurements was 5 ± 5% and 9 ± 5% for TTE_CONT, 2 ± 1% and 7 ± 5% for CMR_CONT, 7 ± 5% and 8 ± 7% for CMR_JSLD, 1 ± 2% and 3 ± 2% for CMR_SPVT. When repeating image acquisition, reproducibility of measurements was 10 ± 8% and 12 ± 5% for TTE_CONT, 9 ± 9% and 8 ± 8% for CMR_CONT, 6 ± 5% and 7 ± 4% for CMR_JSLDand 3 ± 2% and 2 ± 2% for CMR_SPVT.</p> <p>Conclusion</p> <p>There was an excellent agreement between the EOA estimated by the CMR_JSLDor CMR_SPVTmethods and: 1) the theoretical EOA in vitro, and 2) the TTE_CONTEOA in vivo. The CMR_SPVTmethod was superior to the TTE and other CMR methods in terms of measurement variability. The novel CMR-based methods proposed in this study may be helpful to corroborate stenosis severity in patients for whom Doppler-echocardiography exam is inconclusive.</p

Effects of wind power spectrum analysis over resource assessment

Based on the Van der Hoven's seminal work, wind power industry has adopted the 10 minutes mean time as the proper sampling to estimate resource assessment. However, research within the literature questions the generalization of the 10 minutes as a standard measure of minima dispersion due to the particular geographic characteristics where the measurements took place. In this work the power spectrum of a high-frequency wind speed time series is analyzed and its influence over the resource assessment in the region of La Ventosa, Oaxaca, Mexico. Power spectrum analysis from a monthly, seasonal, and annual time series results show a defined synoptic-scale, diurnal, and semi-diurnal variations, which changes in amplitude throughout the year.To study the influence of power spectrum in wind resource assessment were estimated and compared the capacity factors of a typical 2MW wind turbine against measured wind speed with 1, 5, 10, 60, and 360 minutes mean times, we found that a maximum difference of 1.4 %. Resource assessment was also estimated using reanalysis data and WRF results, finding similar to high-resolution estimations, highlighting bias-corrected WRF performance, offering reliable results to model power performance after a statistical correction

Liver-specific insulin receptor isoform A expression enhances hepatic glucose uptake and ameliorates liver steatosis in a mouse model of diet-induced obesity

Among the main complications associated with obesity are insulin resistance and altered glucose and lipid metabolism within the liver. It has previously been described that insulin receptor isoform A (IRA) favors glucose uptake and glycogen storage in hepatocytes compared with isoform B (IRB), improving glucose homeostasis in mice lacking liver insulin receptor. Thus, we hypothesized that IRA could also improve glucose and lipid metabolism in a mouse model of high-fatdiet-induced obesity. We addressed the role of insulin receptor isoforms in glucose and lipid metabolism in vivo. We expressed IRA or IRB specifically in the liver by using adeno-associated viruses (AAVs) in a mouse model of diet-induced insulin resistance and obesity. IRA, but not IRB, expression induced increased glucose uptake in the liver and muscle, improving insulin tolerance. Regarding lipid metabolism, we found that AAV-mediated IRA expression also ameliorated hepatic steatosis by decreasing the expression of Fasn, Pgc1a, Acaca and Dgat2 and increasing Scd-1 expression. Taken together, our results further unravel the role of insulin receptor isoforms in hepatic glucose and lipid metabolism in an insulin-resistant scenario. Our data strongly suggest that IRA is more efficient than IRB at favoring hepatic glucose uptake, improving insulin tolerance and ameliorating hepatic steatosis. Therefore, we conclude that a gene therapy approach for hepatic IRA expression could be a safe and promising tool for the regulation of hepatic glucose consumption and lipid metabolism, two key processes in the development of non-alcoholic fatty liver disease associated with obesity