Mesoscale Model Initialization of the Fourier Method for Mountain Waves

2008 ◽  
Vol 65 (8) ◽  
pp. 2749-2756 ◽  
Author(s):  
John Lindeman ◽  
Zafer Boybeyi ◽  
Dave Broutman ◽  
Jun Ma ◽  
Stephen D. Eckermann ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Wave Field ◽  
Froude Number ◽  
Mesoscale Model ◽  
Fourier Method ◽  
Lower Boundary ◽  
Mountain Waves ◽  
Lower Boundary Condition ◽  
Model Initialization ◽  
The Waves

Abstract A Fourier method is combined with a mesoscale model to simulate mountain waves. The mesoscale model describes the nonlinear low-level flow and predicts the emerging wave field above the mountain. This solution serves as the lower boundary condition for the Fourier method, which follows the waves upward to much higher altitudes and downward to the ground to examine parameterizations for the orography and the lower boundary condition. A high-drag case with a Froude number of ⅔ is presented.

Modified electromyography-assisted optimization approach for predicting lumbar spine loading while walking with backpack loads

2020 ◽  
Vol 234 (5) ◽  
pp. 527-533
Author(s):  
Simon SW Li ◽  
Daniel HK Chow
Keyword(s):  
Boundary Condition ◽  
Lumbar Spine ◽  
Maximal Voluntary Contraction ◽  
Lower Boundary ◽  
Voluntary Contraction ◽  
Optimization Approach ◽  
Compression Force ◽  
Lower Boundary Condition ◽  
Force Profile ◽  
Mean Square Difference

This study modified an electromyography-assisted optimization approach for predicting lumbar spine loading while walking with backpack loads. The modified-electromyography-assisted optimization approach eliminated the electromyography measurement at maximal voluntary contraction and adopted a linear electromyography–force relationship. Moreover, an optimal lower boundary condition for muscle gain was introduced to constrain the trunk muscle co-activation. Anthropometric information of 10 healthy young men as well as their kinematic, kinetic, and electromyography data obtained while walking with backpack loads were used as inputs in this study. A computational algorithm was used to find and analyse the sensitivity of the optimal lower boundary condition for achieving minimum deviation of the modified-electromyography-assisted optimization approach from the electromyography-assisted optimization approach for predicting lumbosacral joint compression force. Results validated that the modified-electromyography-assisted optimization approach (at optimal lower boundary condition of 0.92) predicted on average, a non-significant deviation in peak lumbosacral joint compression force of −18 N, a standard error of 9 N, and a root mean square difference in force profile of 73.8 N. The modified-electromyography-assisted optimization approach simplified the experimental process by eliminating the electromyography measurement at maximal voluntary contraction and provided comparable estimations for lumbosacral joint compression force that is also applicable to patients or individuals having difficulty in performing the maximal voluntary contraction activity.

scholarly journals Nonlinear Dynamic Characteristic Analysis of a Landing String in Deepwater Riserless Drilling

2018 ◽  
Vol 2018 ◽  
pp. 1-17
Author(s):  
Jun Liu ◽  
Hongliang Zhao ◽  
Simon X. Yang ◽  
Qingyou Liu ◽  
Guorong Wang
Keyword(s):  
Boundary Condition ◽  
Dynamic Model ◽  
Marine Environment ◽  
Lower Boundary ◽  
Dynamic Responses ◽  
Characteristic Analysis ◽  
Lower Boundary Condition ◽  
Response Characteristics ◽  
Proposed Model ◽  
Nonlinear Dynamic Characteristic

The landing string is an important component of deepwater riserless drilling systems. Determination of the dynamic characteristics of the landing string plays an essential role in its design for ensuring its safe operation. In this paper, a dynamic model is developed to investigate the dynamic response characteristics of a landing string, where a landing string in a marine environment is modeled as a flexible slender tube undergoing coupled transverse and axial motions. The heaving motion of the drilling platform is taken as the upper boundary condition and the motion of the drilling bit caused by the interaction between the rock and the bit as the lower boundary condition. A semiempirical Morison equation is used to simulate the effect of the load imposed by the marine environment. The dynamic model, which is nonlinearly coupled and multibody, is discretized by a finite element method and solved by the Newmark technique. Using the proposed model, the dynamic responses of the displacement, axial force, and moment in the landing string are investigated in detail to find out the influences of driving depth of surface catheter, platform motion, bit movement, and marine environment on the dynamical characteristics of the landing string.

scholarly journals Effects of Lower Boundary Conditions on the Stability of Radiative Shocks

2002 ◽  
Vol 19 (2) ◽  
pp. 282-292 ◽  
Author(s):  
Curtis J. Saxton
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Lower Boundary ◽  
Stationary Flow ◽  
Physical Models ◽  
Lower Boundary Condition ◽  
Stability Properties ◽  
Shock Region ◽  
Post Shock ◽  
The Stability

AbstractThermal instabilities can cause a radiative shock to oscillate, thereby modulating the emission from the post-shock region. The mode frequencies are approximately quantised in analogy to those of a vibrating pipe. The stability properties depend on the cooling processes, the electron–ion energy exchange, and the boundary conditions. This paper considers the effects of the lower boundary condition on the post-shock flow, both ideally and for some specific physical models. Specific cases include constant perturbed velocity, pressure, density, flow rate, or temperature at the lower boundary, and the situation with nonzero stationary flow velocity at the lower boundary. It is found that for cases with zero terminal stationary velocity, the stability properties are insensitive to the perturbed hydrodynamic variables at the lower boundary. The luminosity responses are generally dependent on the lower boundary condition.

The Influence of Turbulence Memory on Idealized Tornado Simulations

2020 ◽  
Vol 148 (12) ◽  
pp. 4875-4892
Author(s):  
Aaron Wang ◽  
Ying Pan ◽  
Paul M. Markowski
Keyword(s):  
Boundary Condition ◽  
Shear Stress ◽  
Stress Component ◽  
Lower Boundary ◽  
Surface Friction ◽  
Surface Shear Stress ◽  
Normal Surface ◽  
Shear Stress Component ◽  
Surface Shear ◽  
Lower Boundary Condition

AbstractSurface friction contributes to tornado formation and maintenance by enhancing the convergence of angular momentum. The traditional lower boundary condition in atmospheric models typically assumes an instant equilibrium between the unresolved stress and the resolved shear. This assumption ignores the physics that turbulent motions are generated and dissipated at finite rates—in effect, turbulence has a memory through its lifetime. In this work, a modified lower boundary condition is proposed to account for the effect of turbulence memory. Specifically, when an air parcel moves along a curved trajectory, a normal surface-shear-stress component arises owing to turbulence memory. In the accompanying large-eddy simulation (LES) of idealized tornadoes, the normal surface-shear-stress component is a source of additional dynamic instability, which provides an extra pathway for the development of turbulent motions. The influence of turbulence memory on the intensity of quasi-steady-state tornadoes remains negligible as long as assumptions employed by the modified lower boundary condition hold over a relatively large fraction of the flow region of interest. However, tornadoes in a transient state may be especially sensitive to turbulence memory.Significance StatementFriction between the wind and the ground can influence atmospheric phenomena in important ways. For example, surface friction can be a significant source of rotation in some thunderstorms, and it can also help to intensify rotation when rotation is already present. Unfortunately, the representation of friction’s effects in atmospheric simulations is especially error-prone in phenomena characterized by rapid temporal evolution or strong spatial variations. Our work explores a new framework for representing friction to include the effect of the so-called turbulence memory. The approach is tested in idealized tornado simulations, but it may be applied to a wide range of atmospheric vortices.

A Consistent Time-Split Numerical Scheme Applied to the Nonhydrostatic Compressible Equations*

2007 ◽  
Vol 135 (1) ◽  
pp. 20-36 ◽  
Author(s):  
Almut Gassmann ◽  
Hans-Joachim Herzog
Keyword(s):  
Boundary Condition ◽  
Lower Boundary ◽  
Fast Mode ◽  
Time Step ◽  
Lower Boundary Condition ◽  
The One ◽  
Consistent Treatment ◽  
Short Time ◽  
The Given ◽  
Upper Boundary

Abstract The primary interest of the paper is to apply a two-time-level split explicit time scheme developed by one of the authors to the Lokal-Modell (LM) of the German Weather Service (DWD). This model belongs to the operational NWP system at DWD, which makes it particularly interesting for this study. To better understand the implementation of this time scheme in a compressible nonhydrostatic model type, and so in the LM, a linear analysis is presented demonstrating how the equations are to be split up into fast- and slow-mode parts. For the fast-mode part, this analysis demonstrates how the connected short time-step scheme is necessary for a consistent treatment of gravity modes on the one side and a sufficient damping of acoustic modes on the other side. An extended linear stability analysis for the new splitting scheme follows then to establish its application in a full model. An advantage of the given time scheme is that any forward-in-time and stable advection scheme can be linked with the reformulated fast-mode equation part. A Runge–Kutta third-order-in-time and second-order-in-space scheme (RK3/2) has been applied to the horizontal advection, and the vertical advection terms are treated implicitly. A new consistent lower boundary condition and a radiative upper boundary condition are taken into account. Steady airflow simulations over an isolated mountain (Schär test) and the successful incorporation of the Klemp–Durran–Bougeault radiative upper boundary condition in the vertically implicit fast-mode scheme confirm the given approach as necessary and effective for the application of the time scheme.

Wellhead Fatigue Analysis Method: The Effect of Variation of Lower Boundary Conditions in Global Riser Load Analysis

2012 ◽  
Author(s):  
Lorents Reinås ◽  
Massimiliano Russo ◽  
Guttorm Grytøyr
Keyword(s):  
Boundary Condition ◽  
Boundary Conditions ◽  
Lower Boundary ◽  
Fatigue Analysis ◽  
Analysis Model ◽  
Lower Boundary Condition ◽  
Analysis Methodology ◽  
Well Integrity ◽  
Context Modelling ◽  
Load Analysis

Subsea wellhead mechanical fatigue can potentially result in a gross structural failure of barrier elements in the upper part of the well, potentially resulting in loss of well control. Several major E&P operators have acknowledged the importance of wellhead fatigue and are participating in the JIP “Structural Well Integrity”. It is within the scope of this JIP to develop a recommended practice for wellhead fatigue analysis methodology. The analysis methodology currently being investigated by the JIP is a decoupled approach, with modifications of the lower boundary to account for the stiffness of the conductor, soil and template interface. A detailed local wellhead model is used to generate the lower boundary condition for a decoupled global riser load analysis model. This lower boundary condition definition is intended to capture the overall non-linear stiffness of a site specific well in order to achieve best possible global riser loads estimate. In this article the effect of varying the lower boundary conditions on a global load estimate is studied. Global load estimates are generated from a typical North Sea case and various lower boundary conditions are introduced as the only change to the global riser model. A fixed lower boundary condition is used as a reference and load estimates generated from riser models with various lower boundary conditions are compared. The different lower boundary conditions selected for comparison in this study has been derived from the following cases: 1. Fixed at WH 2. As per ISO 13624-2 3. As per JIP “Structural Well Integrity” -Current 4. As per JIP “Structural Well Integrity” -Modified Comparing the analysis results gives indications that the lower boundary condition modelling approach affect global riser load estimate. The fixed lower end boundary conditions did not yielded the most conservative load history in a fatigue context. Modelling well specific flexibility at the riser lower end increased the total number of wellhead fatigue load cycles. This finding support the current approach suggested by the works of the JIP “Structural Well Integrity”. Ensuring that riser load results are still conservative places a higher importance on precise local modelling of the well system.

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