scholarly journals Drag cancellation by added-mass pumping

2016 ◽  
Vol 798 ◽  
Author(s):  
F. Giorgio-Serchi ◽  
G. D. Weymouth

A submerged body subject to a sudden shape change experiences large forces due to the variation of added-mass energy. While this phenomenon has been studied for single actuation events, application to sustained propulsion requires the study of periodic shape change. We do so in this work by investigating a spring–mass oscillator submerged in quiescent fluid subject to periodic changes in its volume. We develop an analytical model to investigate the relationship between added-mass variation and viscous damping, and demonstrate its range of application with fully coupled fluid–solid Navier–Stokes simulations at large Stokes number. Our results demonstrate that the recovery of added-mass kinetic energy can be used to completely cancel the viscous damping of the fluid, driving the onset of sustained oscillations with amplitudes as large as four times the average body radius $r_{0}$. A quasi-linear relationship is found to link the terminal amplitude of the oscillations $X$ to the extent of size change $a$, with $X/a$ peaking at values from 4 to 4.75 depending on the details of the shape-change kinematics. In addition, it is found that pumping in the frequency range of $1-a/2r_{0}<{\it\omega}^{2}/{\it\omega}_{n}^{2}<1+a/2r_{0}$, with ${\it\omega}/{\it\omega}_{n}$ being the ratio between frequency of actuation and natural frequency, is required for sustained oscillations. The results of this analysis shed light on the role of added-mass recovery in the context of shape-changing bodies and biologically inspired underwater vehicles.

Author(s):  
Hideo Hayashi ◽  
Yoshikazu Hirai ◽  
John T. Penniston

Spectrin is a membrane associated protein most of which properties have been tentatively elucidated. A main role of the protein has been assumed to give a supporting structure to inside of the membrane. As reported previously, however, the isolated spectrin molecule underwent self assemble to form such as fibrous, meshwork, dispersed or aggregated arrangements depending upon the buffer suspended and was suggested to play an active role in the membrane conformational changes. In this study, the role of spectrin and actin was examined in terms of the molecular arrangements on the erythrocyte membrane surface with correlation to the functional states of the ghosts.Human erythrocyte ghosts were prepared from either freshly drawn or stocked bank blood by the method of Dodge et al with a slight modification as described before. Anti-spectrin antibody was raised against rabbit by injection of purified spectrin and partially purified.


2021 ◽  
Vol 918 ◽  
Author(s):  
D. Paniccia ◽  
G. Graziani ◽  
C. Lugni ◽  
R. Piva

Abstract


Author(s):  
A. Y. T. Leung ◽  
B. Ravindra ◽  
A. K. Mallik ◽  
C. W. Chan

Abstract Numerical simulations of the response of a harmonically excited mass on an isolator with a cubic, hard, non-linear restoring force and combined Coulomb and viscous damping are presented. For a base-excited system, the inclusion of a Coulomb damper with a suitable break-loose frequency can suppress the secondary resonances and chaotic motion. However, for a force-excited system, the introduction of Coulomb damping does not alter the bifurcation structure. Transmissibility indices have been defined for the solution obtained by numerical integration and the role of the subharmonic resonances and chaotic motion on the performance of the system is pointed out.


2021 ◽  
Vol 33 (8) ◽  
pp. 085120
Author(s):  
Zhicheng Wang ◽  
Dixia Fan ◽  
Michael S. Triantafyllou

2021 ◽  
Author(s):  
◽  
Marie Bell

<p>This thesis presents the voices of 17 pioneers of the organisation parents' Centre, founded in Wellington, New Zealand, in 1952. They reflect on Parents' Centre's contribution to the welfare and happiness of young children and their parents, and the challenges and satisfactions for them as 'movers and shakers' of an entrenched system. The pioneers, 13 women and 3 men, were a group of professionals and parents educated in the progressive tradition who worked as volunteers to found and develop the organisation. They challenged the well-established and generally respected views of the policymakers of the 1950s about the management of childbirth and parent education for young children. They believed that the education and care of the child from birth to three needed to be brought into line with the progressive principles and practices which had been gaining ground in the schools and pre-schools of New Zealand since the 1920s and which emphasised holistic development, especially the psychological aspects. Using Bronfenbrenner's ecological systems theory I set the study within the social climate of the 1950s to assess the contribution the changing times made to the success of the organisation. I identified the social and economic forces which brought change both in the institutions of society and within every day family life, particularly for young children and their parents. As researcher, I added my voice to their reflections while also playing the role of analyst. The study used an oral history method to record the stories of the participants from a contemporary perspective. My involvement in the organisation over 50 years gave me insider knowledge and a rapport with the people interviewed. Using a loosely structured interview I adopted a collegial method of data gathering. A second interview, two years after the first, informed the pioneers about my use of the interview material and gave opportunities for critical comments on my analysis. It became apparent that under the leadership of Helen Brew, parents' Centre was able to influence change. Analyses of the background of the pioneers and of the educationalists who influenced them in training, career and parenthood show that key influences on the pioneers were lecturers at Wellington and Christchurch Training Colleges and Victoria University of Wellington. The liberal thrust of these educational institutions reinforced similar philosophical elements in the child rearing practices experienced by the pioneers. Overall, the pioneers expressed satisfaction with the philosophies and practice they advocated at that time, their achievements within Parent's Centre, and pride in founding a consumer organisation effective for New Zealand conditions. They saw Parents' Centre as having helped to shape change. This study documents the strategies used by Parents' Centre to spread its message to parents, policy makers and the general public. At the end of the study the pioneers were in agreement that the change in the role of women, particularly as equal breadwinners with men, presented a challenge to the consumer and voluntary aspects of the organisation of Parents' Centre today. Some felt the organisation had lost its radical nature and was at risk of losing the consumer voice. Nonetheless, all the pioneers felt that Parents' Centre still had a part to play in providing effective ante-natal education 'by parents for parents' and a continuing role in working for change in the services in accordance with the needs of parents and children under three.</p>


2021 ◽  
Vol 7 (1(37)) ◽  
pp. 9-22
Author(s):  
E.G. Yakubovsky

This article proposes an algorithm to describe the motion of a body in the atmosphere using the added mass. Attached mass is the property of a medium to form additional mass, as I assume with a relativistic denominator at the speed of sound instead of the speed of light. Newton’s second law for added mass assumes two terms with the same speed, one is relativistic at the speed of light, and the other is attached mass with a relativistic denominator at the speed of sound. The use of a relativistic denominator with the speed of sound is a new idea that allows, according to well-known formulas with added mass, which is valid at low speeds of a body, to describe


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