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Introduction to fluid mechanics
Published in Mike Tooley, Lloyd Dingle, Engineering Science, 2020
A body is considered unstable if a small displacement tends to cause a turning moment that displaces the body further from its equilibrium position. A body is considered to have neutral stability when it remains at rest in the position to which it was disturbed. With respect to boats, we are primarily concerned with the ability of the vessel to return to its equilibrium position after rolling (its lateral stability). When it rotates about its longitudinal axis, this type of built-in stability is important to avoid the boat capsizing! With aircraft, stability in pitch, that is stability about the lateral axis, and stability in yaw, that is stability about the vertical or normal axis, is also important. We will now consider the stability conditions for equilibrium of a boat.
Fluid Statics
Published in Ahlam I. Shalaby, Fluid Mechanics for Civil and Environmental Engineers, 2018
The rotational stability of a floating or neutrally buoyant/suspended body is determined by considering what happens when it is displaced from its position of stable equilibrium. Stability considerations are important for both floating or neutrally buoyant/suspended bodies because the centers of gravity and buoyancy do not necessarily coincide. Therefore, when a small rotation causes the two centers to move out of vertical alignment, it can result in either a restoring or overturning moment (couple). Furthermore, when a small rotation does not cause the two centers to move out of vertical alignment, it results in a zero moment (neutral stability). Thus, there are three positions/states of equilibrium with respect to rotational stability. A body is said to be in a position of stable equilibrium if, when displaced by a small rotation, it returns to its original position of stable equilibrium (due to a restoring moment). Conversely, a body is in a position of unstable equilibrium if, when displaced even slightly (i.e., a slight rotation), it moves to a new position of stable equilibrium (due to an overturning moment). Furthermore, a body is in a position of neutral stability if, when displaced by a small rotation, it will remain in static equilibrium in the new position of stable equilibrium (due to a zero moment).
Risk and Reliability
Published in Graeme Dandy, Trevor Daniell, Bernadette Foley, Robert Warner, Planning & Design of Engineering Systems, 2018
Graeme Dandy, Trevor Daniell, Bernadette Foley, Robert Warner
Note that the terms “resilience” and “resiliency” tend to be used interchangeably in the literature. From this point onwards, we will use the term resilience throughout. A more general definition of resilience is the ability of a system to recover from large perturbations without changing its basic structure (Fiksel, 2003). This definition is commonly applied to ecological (Holling, 1973) or socio-economic systems (Resilience Alliance, 2010). This is related to the concept of stability for mechanical systems. A system is said to be in a stable state if, when perturbed, it returns to that state.
Practical stability of fractional-order nonlinear fuzzy systems
Published in International Journal of General Systems, 2023
Mohamed Rhaima, Lassaad Mchiri, Nizar Hadj Taieb, Mohamed Ali Hammami, Abdellatif Ben Makhlouf
The study of the stability makes it possible to see the behavior and the quality of the solutions without solving the differential system. There are many types of stability: like asymptotic stability, Mittag–Leffler stability and practical stability. The stability of fractional-order systems takes much more attention (see Choi, Kang, and Koo 2014; Duarte-Mermoud et al. 2015; Leung et al. 2015; Y. Li, Chen, and Podlubny 2009; Liu et al. 2016; Deepika and Veeresha 2023; Popa 2023; J. Wang et al. 2023). The practical stability ensures the Mittag–Leffler stability of a ball containing the origin of the state space, the radius of the ball can be made arbitrarily small. Many researchers have studied the practical stability (see Ben Hamed, Haj Salem, and Hammami 2013; Ben Makhlouf and Hammami 2015; Ben Makhlouf, Hammami, and Sioud 2017; Ben Makhlouf 2022; Naifar, Ben Makhlouf, and Hammami 2018).
The effect of rollover protection systems and trailers on quad bike stability
Published in International Journal of Forest Engineering, 2020
Björn Edlund, Ola Lindroos, Tomas Nordfjell
A vehicle’s stability or propensity to roll is primarily a function of the vehicle’s track width and center of gravity (CoG). The vehicle will overturn when the CoG vector travels outside the quad bikes farthest point of contact with the ground. Static stability is a measure of a vehicle’s stationary stability and is defined as the angle at which the vehicle’s stationary tipping point is reached (the static tilt angle). In practice, other aspects also influence the maximum angle of an inclined slope that it is possible to drive along without over-turning. For instance, the dynamic force generated when passing over obstacles in the terrain as well as the centrifugal force when negotiating a curve have an important influence (Nordfjell 1998). The narrower the track width that a vehicle has, the more sensitive the vehicle is to obstacle height (Nordfjell 1998). Due to the quad bike’s narrow-track width and high CoG, obstacles with a height of as little as 100 mm can result in a rollover incident when riding on off-road terrain at typical speeds of perhaps 20 km/h and characteristic slopes of 12.5° (Hicks et al. 2018). However, even though dynamic forces have a significant influence on a vehicle’s stability, its static and dynamic stability are closely related. Indeed, vehicles with a low static stability have been shown to be closely associated with a higher risk of rollover incidents and the measurement of static stability through, e.g., static stability factor (SSF) is a common metric for measuring a vehicle's rollover propensity (Mengert et al. 1989; Grzebieta et al. 2015e).
Shifting role for human factors in an ‘unmanned’ era
Published in Theoretical Issues in Ergonomics Science, 2018
Karen M. Feigh, Matthew J. Miller, Raunak P. Bhattacharyya, Minyue (Lanssie) Ma, Samantha Krening, Yosef Razin
The increasingly prominent role of automation in engineered systems has and will continue to change many of the challenges that HFPs face in the design phase. In the short-term, the familiar challenge of mixed-initiative or collaborative systems will be dominant. Such systems are controlled alternatively by either a human or an automated system depending on the mission phase, or task. In some advanced systems, they are controlled dually with certain elements always remaining under the control of a minimum amount of automation. Examples of this include stability control in cars, and envelope protection systems in civilian aircraft.