Effect of Angular Acceleration and Unbalance Force Orientation on the Backward Whirl in Cracked Rotors

2018 ◽  
Author(s):  
Fatima K. Alhammadi ◽  
Mohammad A. AL-Shudeifat ◽  
Oleg Shiryayev
Keyword(s):  
Experimental Testing ◽  
Crack Opening ◽  
Real Life ◽  
Angular Acceleration ◽  
Sharp Drop ◽  
Rotating Systems ◽  
Start Up ◽  
Backward Whirl ◽  
Unbalance Force ◽  
Vector Orientation

Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.

Breathing Crack Model Effect on Rotor's Postresonance Backward Whirl

2020 ◽  
Vol 15 (12) ◽  
Author(s):  
Tariq Alzarooni ◽  
Mohammad A. Al-Shudeifat ◽  
Oleg Shiryayev ◽  
C. Nataraj
Keyword(s):  
Linear Time ◽  
Crack Opening ◽  
Equations Of Motion ◽  
Angular Acceleration ◽  
Crack Model ◽  
Fe Model ◽  
Breathing Crack ◽  
Full Spectrum ◽  
Acceleration Rate ◽  
Backward Whirl

Abstract In this work, we investigate the appearance of postresonance backward whirl (Po-BW) using the model of a rotor with a breathing crack. This phenomenon could be employed as an indicator of crack and bearing damage in rotor systems that undergo recurrent passage through critical forward whirl rotational speed during startup and coast down operations. The finite element (FE) model is used to develop the linear-time-varying equations of motion of the considered accelerating cracked rotor. The whirl response is obtained by direct numerical integration. In addition, the effect of bearing anisotropy on Po-BW excitation is investigated. It is found that the appearance of Po-BW zones is significantly affected by the depth of the crack, angular acceleration rate, anisotropy of bearings, and the orientation of the unbalance force vector with respect to the crack opening direction. The full spectrum analysis (FSA) is also employed and found to be an efficient tool for identifying the Po-BW zones of rotational speeds in the whirl response.

Effect of Unbalance Force Vector Orientation on the Whirl Response of Cracked Rotors

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Mohammad A. AL-Shudeifat ◽  
Hanan Al Hosani ◽  
Adnan S. Saeed ◽  
Shadi Balawi
Keyword(s):  
Crack Opening ◽  
Equations Of Motion ◽  
Cracked Rotor ◽  
Force Vector ◽  
Rotor Systems ◽  
Free Case ◽  
Unbalance Force ◽  
Whirl Speed ◽  
Vector Orientation ◽  
Time Periodic

The combined effect of a crack with unbalanced force vector orientation in cracked rotor-bearing-disk systems on the values and locations of critical whirl amplitudes is numerically and experimentally investigated here for starting up operations. The time-periodic equations of motion of the cracked system are formulated according to the finite element (FE) time-varying stiffness matrix. The whirl response during the passage through the critical whirl speed zone is obtained via numerical simulation for different angles of the unbalance force vector. It is found that the variations in the angle of unbalance force vector with respect to the crack opening direction significantly alters the peak values of the critical whirl amplitudes and their corresponding critical whirl speeds. Consequently, the critical speeds of the cracked rotor are found to be either shifted to higher or lower values depending on the unbalance force vector orientation. In addition, the peak whirl amplitudes are found to exhibit significant elevation in some zones of unbalance force angles whereas significant reduction is observed in the remaining zones compared with the crack-free case. One of the important findings is that there exists a specific value of the unbalance force angle at which the critical whirl vibration is nearly eliminated in the cracked system compared with the crack-free case. These all significant numerical and experimental observations can be employed for crack damage detection in rotor systems.

Fueling Spin-offs: Case Studies of University-based Technology Start-up Funding

2021 ◽  
Vol 22 (1) ◽  
pp. 29-40
Author(s):  
Julie Lenzer ◽  
Piotr Kulczakowicz
Keyword(s):  
Product Development ◽  
New Technologies ◽  
Early Stage ◽  
New Products ◽  
Academic Research ◽  
Real Life ◽  
Private Investment ◽  
Building Relationships ◽  
Start Up ◽  
Single Path

The new technologies born from academic research can be very promising, yet they are often very early stage. University spin-off companies are uniquely positioned to tackle the risks associated with new technologies emerging from academia by developing proofs of concept, functioning prototypes, and new products. While these enterprises start from a solid research and development foundation, they face their own unique set of challenges—they are strongly anchored in the scientific and technological expertise that is typically backed by intellectual property but often lack the business experience needed to develop and market products demanded by customers. University spin-offs have access to substantial non-dilutive funding that can be utilized for advancing product development. While the relentless pursuit of these funds builds a company's credibility and improves its position for negotiating future private investment, university spin-offs would greatly benefit from an early focus on complementing their technology teams with their business teams. These new enterprises should consider pursuing private investment in parallel to utilizing sources of non-dilutive funding. Timing of private investment is extremely important to maximize the value of the opportunity, and, therefore, building relationships with investors early on and getting ready for executing an investment round can greatly increase odds for success. While there is no single path to formulate, pursue, and adapt successful financing strategies, lessons can be learned from real-life cases of university spin-offs that continue their journeys towards ultimate success.

scholarly journals The Reaction to Fire Test for Fire Retardant and for Combustible Material

2016 ◽  
Vol 11 (2) ◽  
pp. 22-28
Author(s):  
Adelaida Fanfarová ◽  
Ladislav Mariš
Keyword(s):  
Fire Test ◽  
Experimental Testing ◽  
Combustion Process ◽  
Real Life ◽  
Fire Retardant ◽  
Specific Area ◽  
Combustible Material ◽  
Hemp Fiber ◽  
Research Article ◽  
Timber Construction

Abstract Currently the natural materials become popular building material for houses, buildings and recreational property. The risk of fires in residential timber construction or eco houses cannot be completely ruled out, therefore there is a need for proper and correct implementing preventive measures and application of all available solutions, which may reduce the risk of fire as far as possible, to slow down the combustion process, to protect the life of people, animals and also the building itself until arrival members of the Fire and Rescue Services. Fireproofing of combustible materials is a specific area of fire protection. For scientific research as well as for real-life practice, not only their structural and physical properties, but also fire-technical characteristics are really important. The present researchers mostly focus on fire-retardant treatment of wood that is why the authors of this contribution focused on a different combustible material. This research article presents the experimental testing and examination of the reaction to fire test of the selected thermal insulation of hemp fiber that was impregnated by the selected fire retardant in laboratory conditions.

scholarly journals Evaluati on of long-term start up costs impact on short-term price based operational optimization of a CCGT using MILP

2019 ◽  
Vol 137 ◽  
pp. 01012
Author(s):  
Sylwia Gotzman ◽  
Paweł Ziόłkowski ◽  
Janusz Badur
Keyword(s):  
Power Plants ◽  
Unit Commitment ◽  
Real Life ◽  
Mixed Integer ◽  
Unit Commitment Problem ◽  
Operational Optimization ◽  
Start Up ◽  
Commitment Problem ◽  
Electricity Spot Market

An increasing share of the weather-dependent RES generation in the power system leads to the growing importance of flexibility of conventional power plants. They were usually designed for base load operation and it is a challenge to determine the actual long-term cycling costs, which account for an increase in maintenance and overhaul expenditures, increased forced outage rates and shortened life expectancy of the plant and components. In this paper, the overall impact of start up costs is evaluated by formulating and solving price based unit commitment problem (PBUC). The electricity spot market is considered as a measure for remunerating flexibility. This approach is applied to a real-life case study based on the 70 MWe PGE Gorzόw CCGT power plant. Different operation modes are calculated and results are used to derive a mixed integer linear programming (MILP) model to optimize the operation of the plant. The developed mathematical model is implemented in Python within the frame of the PuLP library and solved using GUROBI. Results of the application of the method to a numerical example are presented.

The Biophysical Modeling of the Hemodynamic in the Human Organism

2020 ◽  
Vol 7 (11) ◽  
pp. 494-502
Author(s):  
Janos Vincze ◽  
Gabriella Vincze-Tiszay ◽  
Julianna Szakacs
Keyword(s):  
Blood Flow ◽  
Vascular System ◽  
Experimental Testing ◽  
Real Life ◽  
Pathological Process ◽  
Human Organism ◽  
Main Function ◽  
Biophysical Modeling ◽  
Circulatory Apparatus ◽  
Cardio Vascular

The circulatory apparatus has as a main function the constant maintaining of the internal environment in all the regions of the organism. The blood is a liquid tissue, being formed of a fundamental substance – plasma and blood cells. Heart is the central organ of the cardiovascular apparatus. The heart muscles have numerous biophysical properties. The cardiac muscle is never tired unless it suffered a pathological process. During the diastole, blood is aspired in the heart and during the systole it is pushed in the big and small circulation. The blood amount pushed from the heart in the vascular system in a certain time represents the blood flow. The biophysical methods are next: we administer a certain substance amount, then its passing speed will depend on its concentration; to apply the calorimetric principles for the measurement of the gastric blood flow; the diagnostic of a chronic peripheral arteriopathy we use the calorimetric method is based on measuring the heat being introduced in a certain amount of water which has known temperature; one of the most often used methods for the evaluation of the use of radioisotopes in the cardio-vascular system is the compartment method. Any attempt to apply biophysics to the life systems involves three stages. First we observe the phenomena and formulate a biophysical description in the form of equations; after to solve the equations. Finally we return to the real life system and interpret this solution in terms of reality, this interpretation may requiew experimental testing.

The relational capital of micro-enterprises run by women: the startup phase

VINE ◽  
2015 ◽  
Vol 45 (2) ◽  
pp. 172-197 ◽  
Author(s):  
Paola Paoloni ◽  
John Dumay
Keyword(s):  
Real Life ◽  
Personal Characteristics ◽  
Work And Family ◽  
Relational Capital ◽  
Female Entrepreneurs ◽  
Content Type ◽  
Study Approach ◽  
Start Up ◽  
Current Events ◽  
Micro Enterprises

Purpose – The purpose of this paper is to investigate how relational capital contributes to the startup phase of women-owned micro-enterprises. The motivation for the study stems from the fact that micro-enterprises are key drivers of economic growth and that woman entrepreneurs are key developers of these businesses. Design/methodology/approach – To gather data for our study, a qualitative research methodology was adopted using a case study approach based on examining current events of real life in depth (Yin, 2009). Nine cases of micro-enterprises run by women are analysed, focusing on the management of the start-up phase to investigate the nature and role of the relationships that are activated by the entrepreneurs. Findings – The paper develops the CAOS model of micro-entrepreneurship, examining the personal characteristics of the female entrepreneur (C); the environment in which the micro-enterprise operates (A); organizational and managerial aspects (O); and the motivations for starting a new business (S). Using this model, the authors’ are able to link these factors and classify different types of connections, it is possible to identify the kind of existing relations. From the analysis, it was found that a predominant use of networks characterized by informal and permanent relations, supporting the need to reconcile work and family and to involve relatives and friends in the network. This emphasizes the lack of strategy in the female-run micro-enterprises. Originality/value – Given that female entrepreneurship is regarded as central to the development and welfare of economies, the deepening of knowledge of how women entrepreneurs manage the start-up of her business can contribute to improving the effectiveness policies aimed at promoting the participation of female entrepreneurs in the economy.

scholarly journals A Review on Computational Fluid Dynamics Applications in the Design and Optimization of Crossflow Hydro Turbines

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Hamisi Ally Mrope ◽  
Yusufu Abeid Chande Jande ◽  
Thomas T. Kivevele
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Experimental Testing ◽  
Real Life ◽  
Cfd Modeling ◽  
Speed Ratio ◽  
Design And Optimization ◽  
Life Tests ◽  
Clear Idea ◽  
Hydro Turbines

In recent years, advances in using computational fluid dynamics (CFD) software have greatly increased due to its great potential to save time in the design process compared to experimental testing for data acquisition. Additionally, in real-life tests, a limited number of quantities are measured at a time, while in a CFD analysis all desired quantities can be measured at once, and with a high resolution in space and time. This article reviews the advances made regarding CFD modeling and simulation for the design and optimization of crossflow hydro turbines (CFTs). The performance of these turbines depends on various parameters like the number of blades, tip speed ratio, type of airfoil, blade pitch, chord length and twist, and its distribution along the blade span. Technical aspects of the model design, which include boundary conditions, solution of the governing equations of the water flow through CFTS, and the assumptions made during the simulations are thoroughly described. From the review, a clear idea on the suitability of the accuracy CFD applications in the design and optimization of crossflow hydro turbines has been provided. Therefore, this gives an insight that CFD is a useful and effective tool suitable for the design and optimization of CFTs.

Let's Get Physical! Optimizing Nashville CWWTP Primary Influent Baffles with CFD and Physical Modeling

2020 ◽  
Author(s):  
Eric Mayhaus ◽  
◽  
John Barnett ◽  
Keyword(s):  
Physical Modeling ◽  
Construction Projects ◽  
Real Life ◽  
Scale Model ◽  
Cfd Modeling ◽  
Start Up ◽  
Plant Operations ◽  
Operations And Maintenance ◽  
Computational Fluid Dynamics Cfd ◽  
First Time

For most construction projects in the water/wastewater field, the first time the design can be validated and shown to actually work is after construction and start-up. It’s not too often that there is an opportunity to prove modeling with real-world results BEFORE improvements are constructed. What better way to see design translate from paper to real-life performance than to build a scale model and run multiple flow trials? This paper presents a case study for the design of primary settling tanks (PST) influent baffles at the Nashville Central WWTP (CWWTP by utilizing hydraulic computational fluid dynamics (CFD) modeling and validating results with physical modeling. Physical model results helped gain the plant operations and maintenance (O&M) trust in validating the design and provide the best solution for improvements.

Leak Detection Assessment of a Through Wall Crack in a Circumferential Weld

2017 ◽  
Author(s):  
Peter Gill ◽  
Colin Madew ◽  
Steve Booth
Keyword(s):  
Finite Element ◽  
Thermal Field ◽  
Crack Opening ◽  
Leak Detection ◽  
Defect Size ◽  
Element Analysis ◽  
Thermal Fields ◽  
Start Up ◽  
Tensile Data ◽  
Fit For Purpose

A leak detection assessment at a circumferential weld has been carried out to support a Leak-before-Break argument. This was performed using detailed finite element analysis (FEA) of the component to determine limiting defect sizes and crack opening areas. Leak rates of CO2 were then calculated and were found to be at an acceptable level. The loading on the component were complex, including thermal, pressure and weld residual stresses. The thermal field originated from both a steady state operating condition and hold point during start up plant state. Computational Fluid Dynamics (CFD) was used to generate the thermal fields for this component and the crack was postulated to occur at the region of highest opening stress along the weld. In addition to the thermal field, the weld was also subjected to a residual stress, which was applied in the model via a novel application method that is described in the paper. The FEA incorporated temperature dependent Ramberg-Osgood stress strain data that was generated from tensile data. For the limiting defect size calculation, lower bound material properties were used, and for the crack opening area, mean properties were used. Various crack sizes were considered and J-integrals were calculated and compared against the material toughness of the weld. This enabled the calculation of a limiting defect size, and crack opening area, so that a leakage rate could then be calculated. Contour independence was observed for the J-integral evaluation giving confidence that the finite element meshes were fit for purpose.

Sign in / Sign up

Export Citation Format

Share Document