Improved Mu Method with Mixed Perturbation to Dynamic Pressure

2011 ◽  
Vol 101-102 ◽  
pp. 606-609
Author(s):  
Ying Song Gu ◽  
Zhi Chun Yang
Keyword(s):  
Frequency Domain ◽  
Dynamic Pressure ◽  
Equation Of Motion ◽  
Solution Technique ◽  
Test Cases ◽  
Pressure Perturbation ◽  
Improved Method ◽  
Sample Test ◽  
Mu Method ◽  
Real Complex

Mu method is a flutter solution technique based on frequency domain mu-analysis, which directly applies perturbation to dynamic pressure in aeroelastic equation of motion. In a previous study, the dynamic pressure perturbation was modeled as a purely real uncertainty, which could not guarantee the continuity of mu. To improve the continuity of mu, a small amount of complex perturbation is added to the dynamic pressure in addition to the real perturbation. Thus the mu method is improved with this mixed real/complex perturbation. Formulations and algorithm of the improved method are presented and validated with sample test cases. It is demonstrated that the improved mu method is more feasible and conservative than the original mu method due to the mixed perturbation.

MBTDD: MODEL BASED TEST DRIVEN DEVELOPMENT

2012 ◽  
Vol 22 (08) ◽  
pp. 1085-1102 ◽  
Author(s):  
ALIREZA SADEGHI ◽  
SEYED-HASSAN MIRIAN-HOSSEINABADI
Keyword(s):  
Human Resource Management ◽  
Human Resource ◽  
Systems Development ◽  
Test Cases ◽  
Use Case ◽  
Improved Method ◽  
Test Driven Development ◽  
Writing Test ◽  
Model Based ◽  
Model Based Testing

Test Driven Development (TDD), as a quality promotion approach, suffers from some shortages that discourage its usage. One of the most challenging shortcomings of TDD is the low level of granularity and abstraction. This may lead to production of software that is not acceptable by the end users. Additionally, exploiting of TDD is not applicable in the enterprise systems development. To overcome this defect, we have merged TDD with Model Based Testing (MBT) and suggested a framework named Model Based Test Driven Development (MBTDD). According to TDD, writing test cases comes before programming, and based on our improved method of TDD, modeling precedes writing test cases. To validate the applicability of the proposed framework, we have implemented a use case of Human Resource Management (HRM) system by means of MBTDD. The empirical results of using MBTTD show that our proposed method overwhelms existing deficiencies of TDD.

The Cavitation-Induced Pressure Fluctuations in a Mixed-Flow Pump under Impeller Inflow Distortion

Machines ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 326
Author(s):  
Huiyan Zhang ◽  
Fan Meng ◽  
Yunhao Zheng ◽  
Yanjun Li
Keyword(s):  
Frequency Domain ◽  
Pressure Fluctuation ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Mixed Flow ◽  
Guide Vanes ◽  
Time Frequency ◽  
Critical Cavitation ◽  
Flow Pump

To reduce cavitation-induced pressure fluctuations in a mixed-flow pump under impeller inflow distortion, the dynamic pressure signal at different monitoring points of a mixed-flow pump with a dustpan-shaped inlet conduit under normal and critical cavitation conditions was collected using high-precision digital pressure sensors. Firstly, the nonuniformity of the impeller inflow caused by inlet conduit shape was characterized by the time–frequency-domain spectra and statistical characteristics of pressure fluctuation at four monitoring points (P4–P7) circumferentially distributed at the outlet of the inlet conduit. Then, the cavity distribution on the blade surface was captured by a stroboscope. Lastly, the characteristics of cavitation-induced pressure fluctuation were obtained by analyzing the time–frequency-domain spectra and statistical characteristic values of dynamic pressure signals at the impeller inlet (P1), guide vanes inlet (P2), and guide vanes outlet (P3). The results show that the flow distribution of impeller inflow is asymmetric. The pav values at P4 and P6 were the smallest and largest, respectively. Compared with normal conditions, the impeller inlet pressure is lower under critical cavitation conditions, which leads to low pav, pp-p and a main frequency amplitude at P1. In addition, the cavity covered the whole suction side under H = 13.6 m and 15.5 m, which led the pp-p and dominant frequency amplitude of pressure fluctuation at P2 and P3 under critical cavitation to be higher than that under normal conditions.

Dynamic Tilt Correction Using Direct Rotational Motion Measurements

2020 ◽  
Vol 91 (5) ◽  
pp. 2872-2880 ◽  
Author(s):  
Felix Bernauer ◽  
Joachim Wassermann ◽  
Heiner Igel
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Ground Deformation ◽  
Time Domain Method ◽  
Caldera Collapse ◽  
Frequency Domain Method ◽  
Test Cases ◽  
Ground Acceleration ◽  
Data Set ◽  
Domain Method

Abstract Inertial sensors like seismometers or accelerometers are sensitive to tilt motions. In general, from pure acceleration measurements, it is not possible to separate the tilt acceleration from the translational ground acceleration. This can lead to severe misinterpretation of seismograms. Here, we present three different methods that can help solving this problem by correcting translational records for dynamic tilt induced by ground deformation with direct measurements of rotational motions: (1) a simple time-domain method, (2) a frequency-domain method proposed by Crawford and Webb (2000) using a coherence-weighted transfer function between rotation and acceleration, and (3) an adapted frequency-domain method that corrects only those parts of the spectrum with coherence between translational acceleration and rotation angle higher than 0.5. These three methods are discussed in three different experimental settings: (1) a reproducible and precisely known laboratory test using a high-precision tilt table, (2) a synthetic test with a simulated volcanic very-long-period event, and (3) a real data set recorded during the 2018 Mt. Kīlauea caldera collapse. All the three test cases show severe influence of tilt motion on the acceleration measurements. The time-domain method and the adapted frequency-domain method show very similar performance in all three test cases. Those two methods are able to remove the tilt component reliably from the acceleration record.

Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver

2003 ◽  
Vol 125 (1) ◽  
pp. 25-32 ◽  
Author(s):  
W. Ning ◽  
Y. S. Li ◽  
R. G. Wells
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Test Data ◽  
Computational Efficiency ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Flow Solver ◽  
Time Marching

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.

A simple method to include vertical resolution in a river model, and results from an implementation

2005 ◽  
Vol 36 (2) ◽  
pp. 163-174 ◽  
Author(s):  
Flemming Jakobsen ◽  
Kim Wium Olesen ◽  
Mads Madsen
Keyword(s):  
Velocity Profile ◽  
Solution Technique ◽  
Test Cases ◽  
Vertical Resolution ◽  
Simple Method ◽  
One Dimensional ◽  
Accelerated Flow ◽  
Bed Friction ◽  
Logarithmic Velocity Profile ◽  
Good Agreement

A simple method to include vertical resolution in a one-dimensional river model is outlined. The equations on which the method is based are the width-averaged continuity, momentum and transport equations. Some details are given on how to formulate the bed friction in a river model with vertical resolution. The equations are transformed to be in sigma coordinates. The numerical techniques, which make maximum use of an already implemented numerical solution technique in an existing river model, are described. The method is used to implement vertical resolution in the existing river model, MIKE 11. The implementation is tested on the following cases: logarithmic velocity profile, wind driven velocity profile, rapid accelerated flow, lock exchange and finally wind-forced entrainment. All test cases showed good agreement.

An Improved Component-Mode Synthesis Method to Predict Vibration of Rotating Spindles and Its Application to Position Errors of Hard Disk Drives

2005 ◽  
Vol 128 (5) ◽  
pp. 568-575 ◽  
Author(s):  
Takehiko Eguchi ◽  
Teruhiro Nakamiya
Keyword(s):  
Mathematical Model ◽  
Natural Frequencies ◽  
Hard Disk ◽  
Equation Of Motion ◽  
Component Mode Synthesis ◽  
Mode Shapes ◽  
Air Bearings ◽  
Improved Method ◽  
Stationary Part ◽  
Improved Model

This paper describes an accurate mathematical model that can predict forced vibration of a rotating spindle system with a flexible stationary part. In particular, we demonstrate this new formulation on a hard disk drive (HDD) spindle to predict its position error signal (PES). This improved method is a nontrivial extension of the mathematical model by Shen and his fellow researchers, as the improved method allows the flexible stationary part to comprise multiple substructures. When applied to HDD vibration, the improved model consists not only a rotating hub, multiple rotating disks, a stationary base, and bearings (as in Shen’s model) but also an independent flexible carriage part. Moreover, the carriage part is connected to the stationary base with pivot bearings and to the disks with air bearings at the head sliders mounted on the far end of the carriage. To build the improved mathematical model, we use finite element analysis (FEA) to model the complicated geometry of the rotating hub, the stationary base and the flexible carriage. With the mode shapes, natural frequencies, and modal damping ratios obtained from FEA, we use the principle of virtual work and component-mode synthesis to derive an equation of motion. Naturally, the stiffness and damping matrices of the equation of motion depend on properties of the pivot and air bearings as well as the natural frequencies and mode shapes of the flexible base, the flexible carriage, the hub, and the disks. Under this formulation, we define PES resulting from spindle vibration as the product of the relative displacement between the head element and the disk surface and the error rejection transfer function. To verify the improved model, we measured the frequency response functions using impact hammer tests for a real HDD that had a fluid-dynamic bearing spindle, two disks, and three heads. The experimental results agreed very well with the simulation results not only in natural frequencies but also in gain and phase.

Predicting Bladerow Interactions Using a Multistage Time-Linearized Navier-Stokes Solver

2002 ◽  
Author(s):  
W. Ning ◽  
Y. S. Li ◽  
R. G. Wells
Keyword(s):  
Unsteady Flow ◽  
Frequency Domain ◽  
Test Data ◽  
Computational Efficiency ◽  
Unsteady Flows ◽  
Navier Stokes ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Flow Solver ◽  
Time Marching

A multistage frequency domain (time-linearized/nonlinear harmonic) Navier-Stokes unsteady flow solver has been developed for predicting unsteady flows induced by bladerow interactions. In this paper, the time-linearized option of the solver has been used to analyze unsteady flows in a subsonic turbine test stage and the DLR transonic counter-rotating shrouded propfan. The numerical accuracy and computational efficiency of the time-linearized viscous methods have been demonstrated by comparing predictions with test data and nonlinear time-marching solutions for these two test cases. It is concluded that the development of efficient frequency domain approaches enables unsteady flow predictions to be used in the design cycles to tackle aeromechanics problems.

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