Large-amplitude flapping of an inverted flag in a uniform steady flow – a vortex-induced vibration

The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements by Kim et al. (J. Fluid Mech., vol. 736, 2013, R1) show that reversing the sheet’s orientation, with the flow impinging on its free edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted flag displays large-amplitude flapping over a finite band of flow speeds. The physical mechanisms giving rise to this flapping phenomenon are currently unknown. In this article, we use a combination of mathematical theory, scaling analysis and measurement to establish that this large-amplitude flapping motion is a vortex-induced vibration. Onset of flapping is shown mathematically to be due to divergence instability, verifying previous speculation based on a two-point measurement. Reducing the sheet’s aspect ratio (height/length) increases the critical flow speed for divergence and ultimately eliminates flapping. The flapping motion is associated with a separated flow – detailed measurements and scaling analysis show that it exhibits the required features of a vortex-induced vibration. Flapping is found to be periodic predominantly, with a transition to chaos as flow speed increases. Cessation of flapping occurs at higher speeds – increased damping reduces the flow speed range where flapping is observed, as required. These findings have implications for leaf motion and other biological processes, such as the dynamics of hair follicles, because they also can present an inverted-flag configuration

Flapping dynamics of an inverted flag

The dynamics of an inverted flag are investigated experimentally in order to find the conditions under which self-excited flapping can occur. In contrast to a typical flag with a fixed leading edge and a free trailing edge, the inverted flag of our study has a free leading edge and a fixed trailing edge. The behaviour of the inverted flag can be classified into three regimes based on its non-dimensional bending stiffness scaled by flow velocity and flag length. Two quasi-steady regimes, straight mode and fully deflected mode, are observed, and a limit-cycle flapping mode with large amplitude appears between the two quasi-steady regimes. Bistable states are found in both straight to flapping mode transition and flapping to deflected mode transition. The effect of mass ratio, relative magnitude of flag inertia and fluid inertia, on the non-dimensional bending stiffness range for flapping is negligible, unlike the instability of the typical flag. Because of the unsteady fluid force, a flapping sheet can produce elastic strain energy several times larger than a sheet of the deformed mode, improving the conversion of fluid kinetic energy to elastic strain energy. According to the analysis of the leading-edge vortex formation process, the time scale of optimal vortex formation correlates with efficient conversion to elastic strain energy during bending

Iron and Nickel spectral opacity calculations in conditions relevant for pulsating stellar envelopes and experiments

Seismology of stars is strongly developing. To address this question we have formed an international collaboration OPAC to perform specific experimental measurements, compare opacity calculations and improve the opacity calculations in the stellar codes [1]. We consider the following opacity codes: SCO, CASSANDRA, STA, OPAS, LEDCOP, OP, SCO-RCG. Their comparison has shown large differences for Fe and Ni in equivalent conditions of envelopes of type II supernova precursors, temperatures between 15 and 40 eV and densities of a few mg/cm3 [2, 3, 4]. LEDCOP, OPAS, SCO-RCG structure codes and STA give similar results and differ from OP ones for the lower temperatures and for spectral interval values [3]. In this work we discuss the role of Configuration Interaction (CI) and the influence of the number of used configurations. We present and include in the opacity code comparisons new HULLAC-v9 calculations [5, 6] that include full CI. To illustrate the importance of this effect we compare different CI approximations (modes) available in HULLAC-v9 [7]. These results are compared to previous predictions and to experimental data. Differences with OP results are discussed.Comment: 4 pages, 3 figures, conference Inertial Fusion Sciences and Applications, Bordeaux, 12th to 16th September 2011; EPJ web of Conferences 201

2020-06-19/20/21 DAILY UNM GLOBAL HEALTH COVID-19 BRIEFING

Executive Summary: NM Highlights: Dr. Scrase on-line briefing. NM cases. Campgrounds closed through July 4th. Otero prison reports. Navajo nation’s first police dies. Santa Fe cancels 4th July fireworks. Face coverings donated. NM infection rate drops. US Highlights: AZ Governor issues Exec Order. Economics, Workforce, Supply Chain, PPE: Epidemiology Highlights: Reopening hospitals metric. Comparison of mask effectiveness. Private practices suffer. Healthcare Policy Recommendations: Maternal mortality. Practice Guidelines: Recommendations on hepatobiliary surgery and neonate management. Drugs, Vaccines, Therapies, Clinical Trials: Animal studies generate new vaccine candidates and vaccine platform. 16 new clinical trials registered. Other Science: Respiratory secretions detected by trained dogs. MRI findings show brain lesions in non-survivors. Healthy blood vessels may protect children. Meta-analysis on pneumonia severity. Smoking and COVID-19 severity meta-analysis

2020-06-29/30 DAILY UNM GLOBAL HEALTH COVID-19 BRIEFING

Executive Summary: NM Highlights: NM cases update. ABQ nursing home hit hard. UNM student family housing closure. White Sands National Park reopening. 52% of federal COVID-19 relief money for tribal communities. Bill signed to help NM taxpayers. US Highlights: Polarization of political elite response on Twitter. International Highlights: China’s military to use Ad5-nCoV vaccine in trials. Economics, Workforce, Supply Chain, PPE: Decontaminate N95 respirators using a microwave. Epidemiology Highlights: Mask-wearing prevents transmission. Face-masks associated with Italy’s declining epidemic. Healthcare Policy Recommendations: Social distancing reassessed? Lessons learned from previous pandemics. Digital tools against COVID-19. Investigating cultural and psychological factors to reduce spread. Practice Guidelines: Preserving couple relationships during COVID-19. Testing: No difference in viral load between symptomatic and asymptomatic individuals. A new fast point-of-care virus detection test. Few patient serum samples have virus RNA (at low viral load) and these are not associated with infectious disease. Symptoms and temperature reports are informative to screen health care workers. Drugs, Vaccines, Therapies, Clinical Trials: 37 new trials registered June 29-30. Other Science: Multisystem pediatric inflammatory syndrome. Hazardous postoperative outcomes. Childhood immunization in Africa. Citizen science and protein folding

2020-05-22 DAILY UNM GLOBAL HEALTH COVID-19 BRIEFING

Executive Summary: NM Highlights: 12 positive cases at NMSU. Short-term rentals restrictions. Dine-in reopening. US Highlights: Models to forecast COVID-19 deaths. Places of worship reopening. Contact tracing at University of Alabama. International Highlights: More deaths among poor. Mortality data in Italy. High death toll in Brazil. Global vaccines fall behind. Italy cases drop. Vaccines to go through India. Epidemiology Highlights: Children not pandemic drivers. Healthcare Policy Recommendations: Burnout of HCWs. NYC surgeons’ response. Foggy glasses tips. Practice Guidelines: Recommendations are provided on surgical strategies during COVID-19, management of hypertension, anesthesia practice, avoiding drug-induced cardiovascular impairments, arrhythmia management, elective surgery reboot, nutritional management, stroke care, neurointerventional surgery, blood management. Testing: Unregulated tests identified. Interpreting test results. Drugs, Vaccines, Therapies, Clinical Trials: Vaccine trials results. Vaccine moves to trials. Monoclonal antibody identified. Hydroxychloroquine no benefit. Adjuvant corticosteroid therapy. Old drugs may benefit. Vaccines inducing antibodies. Other Science: Mortality and CKD/liver disease. Transmission in pregnancy. Pathophysiology insights. Readmission characteristics. Sodium and severity. Simulated sunlight disinfects

2020-05-02/03 DAILY UNM GLOBAL HEALTH COVID-19 BRIEFING

Executive Summary: More NM cases. Free Shiprock testing. Prison release demands. 8 state parks reopen. Higher US deaths. NY PPE case dismissed. Orthopedic Tx down. European deaths down. UK mortality factors. People leaving large cities. Ending lockdown strategies. Public mask impact. Taiwan tracing. Homeless shelter prevalence. Homeless shelter outbreak. 50-state R0. COVID-19 decades later. US county tracking site. Hospital management model. COVID-19 behavioral transformation. Practice guidelines for: cardiology, IBD surgery, and rheumatic physical inactivity. Roche antibody test approved. Abbott antibody test EU-certified. Home anosmia assessment. CVD and ACE/ARBs. Tocilizumab early evidence. Tocilizumab systematic review. WHO vaccines trial. HCQ slower viral clearance. CBC predicts severity. Kidney disease meta-analysis. Innate/adaptive immunity timing. Combating misinformation. Mental health living reviews

2020-05-13 DAILY UNM GLOBAL HEALTH COVID-19 BRIEFING

Executive Summary: APS virtual graduation. NM Governor update. Free testing for all. NM 2020 census challenges. BCBS $1M COVID-19 donation. NM case count. Most tribes infected. Increased NM Medicaid enrollment. UNM revenue losses. UNM limited operations continue. No dine-in eating yet. Clothing store reopening measures. Aid package. Consumer prices tumble. Public guidance adherence survey. Healthcare resource prediction. Food insecurity. Supply system comparison. Pentagon PPE award. Ensemble mortality model. 4.4% French infections. Asymptomatic spread. Traffic infection correlation. Comorbid COPD/smoking mortality. Airplane transmission contained. CDC COVID-19 statistics. WHO: endemic virus risk. Iceland tracking app impact. WHO: prison management. Quality of life. Containment amongst HCWs. Emotional regulation. Literature overload coping. Exercise and well-being. Information sources. Distress among healthcare students. Expanding pharmacy role. Recommendations on sedation in mechanical ventilation. Long-acting antipsychotics usage. Comorbidities and mortality. Continuing clinical trials. Short interval re-testing. Pharynx gargle samples. BCG vaccination not protective. Plasmapheresis case series. Convalescent plasma safety. Neutralizing antibodies. 40 new trials. Acute kidney injury. Multiorgan and renal tropism. Intestinal cell infections. Cardiovascular disease risk link. Cutaneous manifestations. Underpowered studies