Optimal parameters of dynamic vibration absorber for linear damped rotary systems subjected to harmonic excitation

Dynamic vibration absorber (DVA) is a simple and effective device for vibration absorption used in many practical applications. Determination of suitable parameters for DVA is of significant importance to achieve high vibration reduction effectiveness. This paper presents a method to find the optimal parameters of a DVA attached to a linear damped rotary system excited by harmonic torque. To this end, a closed-form formula for the optimum tuning parameter is derived using the fixed-point theory based on an assumption that the damped rotary systems are lightly or moderately damped. The optimal damping ratio of DVA is found by solving a set of non-linear equations established by the Chebyshev's min-max criterion. The performance of the proposed optimal DVA is compared with that obtained by existing optimal solution in literature. It is shown that the proposed optimal parameters allow to obtain superior vibration suppression compared to existing optimal formula. Extended simulations are carried out to examine the performance of the optimally designed DVA and the sensitivity of the optimum parameters. The simulation results show that the improvement of the vibration performance on damped rotary system can be as much as 90% by using DVA

Rheological properties of emulsion of crude oil and water

In the paper the rheological properties of crude oil of White Tiger oil-field (Vietnam) and its emulsion with sea-water, including measurement results and analytical approximation formulae for wide range of pressure, temperature and water concentration, are presented. As it is known, the crude oil of White Tiger oil-field is a high-paraffin and high-viscous oil. At the low temperature (T ≤ 40°C) it behaves as non-Newtonian fluid of Bingham-Shvedov group. Therefore, beside the effective viscosity, the effective dynamic shear stress is also measured and approximated. The rheological properties of crude oil and emulsion of crude oil and water are also measured and approximated for the case when the mixture contains 0.1% chemical reagent ES-3363

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Vibration Characteristics of Tapered Roller Bearings with Roller Diameter error

This study investigates the vibration characteristics of tapered roller bearings with the presence of error in roller diameter. A general model for tapered roller bearing with five degree-of-freedom was adopted with taking into account the error in roller diameter. Then, the effect of one single errored roller and multiple errored rollers on the vibration behaviour of tapered roller bearing was investigated. Simulation results confirmed that the bearing vibration frequencies are equal to cage rotational frequency in the case of axial preloading, and multiple of cage rotational frequency in the case of combined loadings, irrespective of the error magnitude, the number or position of errored rollers, which, however, significantly affect the vibration amplitude of bearing

Vibration Characteristics of Tapered Roller Bearings with Roller Diameter error

This study investigates the vibration characteristics of tapered roller bearings with the presence of error in roller diameter. A general model for tapered roller bearing with five degree-of-freedom was adopted with taking into account the error in roller diameter. Then, the effect of one single errored roller and multiple errored rollers on the vibration behaviour of tapered roller bearing was investigated. Simulation results confirmed that the bearing vibration frequencies are equal to cage rotational frequency in the case of axial preloading, and multiple of cage rotational frequency in the case of combined loadings, irrespective of the error magnitude, the number or position of errored rollers, which, however, significantly affect the vibration amplitude of bearing

The Load Distribution of the Main Shaft Bearing Considering Combined Load and Misalignment in a Floating Direct-Drive Wind Turbine

The main shaft tapered double-inner ring bearing (TDIRB) of floating direct-drive wind turbine system (FDDWT) is one of the most critical components in FDDWT, and its failure accounts for a large proportion of wind turbine malfunctions and faults. Over the past decades, a significant number of methods have been proposed to calculate the contact load distribution along the roller length in TDIRB, since the contact load distribution of roller is the key factor of fatigue life of TDIRB. Most of methods, however, neglected the misalignment of inner ring with respect to outer ring and friction force. In this paper, with the help of comprehensive and accurate quasi-static mathematical method, the contact load distribution of internal loads in TDIRB are analysed by considering the effects of combined loads, angular misalignment and friction force at different wind speeds for FDDWT. The simulation results show that the amount of combined load has an apparent effect on the contact load distribution along the TDIRB raceways and flanges in both rows. Furthermore, the slight change of tilted misalignment has a great influence on the contact load distribution. In addition, the slight angular misalignment easily produces noncontact zone for the bearing raceway in both rows, which is significantly disadvantage for the external load uniform transmitting to each roller

The Load Distribution of the Main Shaft Bearing Considering Combined Load and Misalignment in a Floating Direct-Drive Wind Turbine

The main shaft tapered double-inner ring bearing (TDIRB) of floating direct-drive wind turbine system (FDDWT) is one of the most critical components in FDDWT, and its failure accounts for a large proportion of wind turbine malfunctions and faults. Over the past decades, a significant number of methods have been proposed to calculate the contact load distribution along the roller length in TDIRB, since the contact load distribution of roller is the key factor of fatigue life of TDIRB. Most of methods, however, neglected the misalignment of inner ring with respect to outer ring and friction force. In this paper, with the help of comprehensive and accurate quasi-static mathematical method, the contact load distribution of internal loads in TDIRB are analysed by considering the effects of combined loads, angular misalignment and friction force at different wind speeds for FDDWT. The simulation results show that the amount of combined load has an apparent effect on the contact load distribution along the TDIRB raceways and flanges in both rows. Furthermore, the slight change of tilted misalignment has a great influence on the contact load distribution. In addition, the slight angular misalignment easily produces noncontact zone for the bearing raceway in both rows, which is significantly disadvantage for the external load uniform transmitting to each roller

Badanie zapewnienia rozwoju przepływu w przybrzeżnych marginalnych pól naftowych w Wietnamie: Studium przypadku pola naftowego Ca Ngu Vang

Over the last few years, PetroVietnam has discovered and exploited several marginal oil fields such as Ca Ngu Vang, Te Giac Trang, Hai Su Den, Hai Su Trang, etc. however the reserves are modest. Test results received during drilling exploratory wells within these fields indicated that the maximum total daily production rate from the wells could promisingly range to about 20,000 barrels of oil per day (BOPD). Unfortunately, the optimum development of these offshore oil fields still offers numerous challenges to oil engineers due to the limitations of equipment and technology. Oil production activities worldwide show that if the daily production of an offshore oilfield is less than 20,000 BOPD, a connection of the marginal fields to their nearest larger oil field should be taken into consideration in order to efficaciously recover more crude oil. Often, this method of production requires a long subsea pipeline system. Besides, the transportation of the fluids from these fields to the processing platform will undergo several serious problems caused by the deposition of wax. All these matters should be handled to guarantee the performance of transportation. A number of models using PIPESIM, PIPEPHRASE and OLGA have been applied to design and examine the operations of the subsea pipeline in different working conditions. Results of the simulations proposed the use of passive insulation to economically eliminate wax deposition and recommended proper pipeline shutdown operations to minimize several problems related to flow assurance issues in the region of interest.W ciągu ostatnich kilku lat w Vietnamie odkryto i eksploatowano kilka marginalnych pól naftowych, takich jak Ca Ngu Vang, Te Giac Trang, Hai Su Den, Hai Su Trang, itd.… Jednak zasoby są skromne. Wyniki testów otrzymane podczas wiercenia odwiertów poszukiwawczych na tych polach wykazały, że maksymalny całkowity dzienny poziom wydobycia z odwiertów może potencjalnie sięgać około 20 000 baryłek ropy dziennie (BOPD). Niestety, optymalny rozwój tych przybrzeżnych pól naftowych nadal stwarza liczne wyzwania dla inżynierów naftowych ze względu na ograniczenia sprzętu i technologii. Działalność wydobywcza ropy naftowej na całym świecie pokazuje, że jeśli dzienna produkcja morskiego pola naftowego jest mniejsza niż 20 000 BOPD, należy wziąć pod uwagę połączenie pól marginalnych z ich najbliższym większym polem naftowym, aby efektywnie odzyskać więcej ropy. Często ta metoda produkcji wymaga długiego systemu rurociągów podmorskich. Poza tym transport płynów z tych pól na platformę obróbkową będzie wiązał się z kilkoma poważnymi problemami spowodowanymi osadzaniem się wosku. Wszystkie te sprawy powinny być załatwione, aby zagwarantować wykonanie transportu. Szereg modeli wykorzystujących PIPESIM, PIPEPHRASE i OLGA zostało zastosowanych do projektowania i badania działania rurociągu podmorskiego w różnych warunkach pracy. W wynikach symulacji zaproponowano zastosowanie izolacji pasywnej w celu ekonomicznego wyeliminowania osadzania się wosku oraz zalecono prawidłowe operacje wyłączania rurociągu, aby zminimalizować kilka problemów związanych z kwestiami zapewnienia przepływu w obszarze zainteresowania