The Omega-model with two bankruptcy rates

2021 ◽  
pp. 1-37
Author(s):  
Esther Frostig ◽  
Adva Keren-Pinhasik
Keyword(s):  
Omega Model

$\sigma$ - $\omega$ model and compressible bag model

1999 ◽  
Vol 7 (2) ◽  
pp. 305-311
Author(s):  
S. Kagiyama ◽  
A. Nakamura ◽  
T. Otofuji
Keyword(s):  
Bag Model ◽  
Omega Model

Modification of the MPC Omega Model to Predict Primary and Tertiary Creep

2019 ◽  
Author(s):  
Mohammad Shafinul Haque
Keyword(s):  
Creep Deformation ◽  
Work Hardening ◽  
Primary Creep ◽  
Deformation Curve ◽  
Tertiary Creep ◽  
Suitable Model ◽  
Hyperbolic Tangent ◽  
Natural Logarithm ◽  
Wide Range ◽  
Omega Model

Abstract The MPC Omega model has become popular in recent years for the prediction of creep deformation. Successful predictions of the tertiary creep for a wide range of materials are available. The Omega model relates the strain as a linear function of the natural logarithm of strain-rate. It is assumed that the primary creep is a short-lived phenomenon and can be neglected. The Omega model is unable to predict the primary creep deformation. Often primary creep is a long-lived phenomenon and cannot be neglected. A mathematical modification can be performed to incorporate the primary creep curve in the Omega model. A common approach is by adding a work hardening function to the original constitutive model. Approaches using power, or exponential, or logarithmic work-hardening function are available. However, it is difficult to discern which function is the best for accurate prediction. In this study, the Omega model is modified to predict the primary and tertiary creep deformation curve by adding a hyperbolic tangent work hardening function. A metamodel incorporating the four modified Omega sub-models (power, exponential, logarithmic and hyperbolic tangent) is developed. The metamodel enables the determination of the most suitable model for a given material and avoids the force fit of a preselected model. Short, medium, and long-term creep deformation data for alloy P91 (pipe) and G91 (plate) at two isotherms of 600°C and 650°C are used to calibrate the metamodel. The data include five stress levels ranging from 70 to 160 MPa including creep life from 233 to 1.1 × 105 hrs. A detail calibration process is provided. A numerical analysis is performed to compare the four submodels. It is observed that the selection of the most suitable function depends on the loading condition and material properties. Based on the analysis, a recommendation to select the suitable work-hardening function to predict the primary and tertiary creep deformation curve is presented.

scholarly journals Parameterization of Vegetation Scattering Albedo in the Tau-Omega Model for Soil Moisture Retrieval on Croplands

2020 ◽  
Vol 12 (18) ◽  
pp. 2939
Author(s):  
Chang-Hwan Park ◽  
Thomas Jagdhuber ◽  
Andreas Colliander ◽  
Johan Lee ◽  
Aaron Berg ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Radiative Transfer ◽  
Data Assimilation ◽  
Brightness Temperature ◽  
Microwave Remote Sensing ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Time Varying ◽  
Vegetation Fraction ◽  
Omega Model

An accurate radiative transfer model (RTM) is essential for the retrieval of soil moisture (SM) from microwave remote sensing data, such as the passive microwave measurements from the Soil Moisture Active Passive (SMAP) mission. This mission delivers soil moisture products based upon L-band brightness temperature data, via retrieval algorithms for surface and root-zone soil moisture, the latter is retrieved using data assimilation and model support. We found that the RTM based on the tau-omega (τ-ω) model can suffer from significant errors over croplands in the simulation of brightness temperature (Tb) (in average between −9.4K and +12.0K for single channel algorithm (SCA); −8K and +9.7K for dual-channel algorithm (DCA)) if the vegetation scattering albedo (omega) is set constant and temporal variations are not considered. In order to reduce this uncertainty, we propose a time-varying parameterization of omega for the widely established zeroth order radiative transfer τ-ω model. The main assumption is that omega can be expressed by a functional relationship between vegetation optical depth (tau) and the Green Vegetation Fraction (GVF). Assuming allometry in the tau-omega relationship, a power-law function was established and it is supported by correlating measurements of tau and GVF. With this relationship, both tau and omega increase during the development of vegetation. The application of the proposed time-varying vegetation scattering albedo results in a consistent improvement for the unbiased root mean square error of 16% for SCA and 15% for DCA. The reduction for positive and negative biases was 45% and 5% for SCA and 26% and 12% for DCA, respectively. This indicates that vegetation dynamics within croplands are better represented by a time-varying single scattering albedo. Based on these results, we anticipate that the time-varying omega within the tau-omega model will help to mitigate potential estimation errors in the current SMAP soil moisture products (SCA and DCA). Furthermore, the improved tau-omega model might serve as a more accurate observation operator for SMAP data assimilation in weather and climate prediction model.

THE PERTURBED COMPOUND POISSON GAMMA OMEGA MODEL WITH A BARRIER DIVIDEND STRATEGY

2018 ◽  
Vol 106 (2) ◽  
pp. 279-296
Author(s):  
Zhongqin Gao ◽  
Jingmin He ◽  
Bingbing Wang
Keyword(s):  
Compound Poisson ◽  
Omega Model

Local Smooth Solutions of the Incompressible k - ω $k\mbox{-}\omega $ Model

2016 ◽  
Vol 146 (1) ◽  
pp. 1-16 ◽  
Author(s):  
Julien Mathiaud ◽  
Xavier Roynard
Keyword(s):  
Smooth Solutions ◽  
Omega Model

Creep Parameters Determination by Omega Model to Norton Bailey Law by Regression Analysis for Austenitic Steel SS-304

2021 ◽  
Vol 324 ◽  
pp. 188-197
Author(s):  
Mohsin Sattar ◽  
A. Rahim Othman ◽  
Shahrul Kamaruddin ◽  
Mohammad Azad Alam ◽  
Mohammad Azeem
Keyword(s):  
Regression Analysis ◽  
Creep Behavior ◽  
Creep Deformation ◽  
Complete Analysis ◽  
Mechanical Equipment ◽  
Strain Rates ◽  
Secondary Creep ◽  
Creep Data ◽  
Ss 304 ◽  
Omega Model

In the material’s creep failure analysis, the difficulty of assessing the applied thermo-mechanical boundary conditions makes it critically important. Numerous creep laws have been established over the years to predict the creep deformation, damage evolution and rupture of the materials subjected to creep phenomena. The omega model developed by the American Petroleum Institute and Material Properties Council is one of the most commonly used creep material models for numerical analysis over the years. It is good in defining the fitness of mechanical equipment for service engineering evaluation to ensure the reliable service life of the equipment. The Omega model, however, is not readily accessible and specifically incorporated for creep evaluation in FEA software codes and creep data is always scarce for the complete analysis. Therefore, extrapolation of creep behavior was performed by fitting various types of creep models with a limited amount of creep data and then simulating them, beyond the available data points. In conjunction with the Norton Bailey model, based on API-579/ASME FFS-1 standards, a curve fitting technique was employed called regression analysis. From the MPC project omega model, different creep strain rates were obtained based on material, stress and temperature-dependent data. In addition, as the strain rates increased exponentially with the increase in stresses, regression analysis was used for predicting creep parameters, that can curve fit the data into the embedded Norton Bailey model. The uncertainties in extrapolations and material constants has highlighted to necessitate conservative safety factors for design requirement. In this case study, FEA creep assessment was performed on the material SS-304 dog bone specimen, considered as a material coupon to predict time-dependent plastic deformation along with creep behavior at elevated temperatures and under constant stresses. The results indicated that the specimen underwent secondary creep deformation for most of the period.

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