1,721,049 research outputs found
Coastal wetlands at risk: Learning from Venice and New Orleans
No full textCoastal regions have progressively become more vulnerable to intense hydrodynamic and atmospheric events, thus raising important questions about their fate in the century of global warming. A variety of natural and anthropogenic factors have contributed to this fragility: eustacy, isostasy, soil compaction, reduced sediment supply and reduced extension of natural defenses (barrier islands and coastal wetlands). With the aim to emphasize the crucial role played by the intense human manipulation of the environment, we provide a brief overview of the state of knowledge on this extremely complex problem, moving from two cases of special importance: Venice and New Orleans. We discuss similarities (causes of wetland degradation and related restoration problems) as well as differences (different economical scales involved in the restoration projects, different risk reduction ensured by wetland and natural defense restoration and, finally, cultural relevance of the environment to be preserved) between these two regions
Scaling strategies for Brinkman penalization in fluid topology optimization
Full text linkTopology optimization provides a rigorous framework for determining optimal flow-path designs in fluid mechanics. A popular technique is the density-based approach, which treats fluid-solid interfaces by considering the solid phase as a porous medium with low permeability. Mathematically, such a problem is governed by the Navier-Stokes equations combined with the Brinkman penalization. To consistently solve the optimization problem, this study examines the theoretical foundations of the method, focusing on dimensionless parameters such as the Reynolds number and a specific Darcy number, D a * . Through dimensional analysis, we derive scaling guidelines for the Brinkman penalization in relation to fluid properties and domain geometry. Numerical simulations show that incorrect scaling can yield nonphysical results, including excessive fluid penetration into solid regions, undermining the optimization. Our findings demonstrate that the invariance of the solution can be maintained by appropriately scaling D a * with the relative velocity in the porous region, ensuring accurate and reliable results in different scenarios. This work provides a systematic framework for parameter selection in fluid topology optimization, addressing key modeling and computational challenges. By emphasizing the importance of dimensional analysis, it contributes to a broader understanding of topology optimization, paving the way for its more robust and consistent application in fluid mechanics
Eco-morphodynamics of coastal wetlands
Full text linkWe survey the problem of the response of coastal wetlands to sea level rise. Two opposite views have traditionally been confronted. According to the former, on the geological time scale, coastal lagoons would be ‘ephemeral’ features. The latter view maintains that marshes would keep pace with relative sea level rise as, increasing the rate of the latter, the sedimentation rate would also increase. In any case, the timescale of morphodynamic evolution is of the order of centuries, which makes it not easily perceived. For example, in Venice, the diversion of the rivers debouching into the lagoon undertaken in the Renaissance has taken centuries to display its consequences (shift from depositional to erosional environment). This process accelerated in the last two centuries due to effects of the industrial revolution and of an enhanced sea level rise. Recent research has employed powerful computational techniques and advanced models of marsh vegetation. Zero-order modeling suggests that marsh equilibrium is possible, provided the rate of relative sea level rise does not exceed a threshold depending on the availability of minerogenic sediments, quantified through a loosely defined ambient sediment concentration. Analysis of the morphological interaction between adjacent morphological units suggests that the ‘equilibrium states’ identified by zero-order modeling correspond to marshes which either prograde or retreat, i.e., are not in equilibrium. Results suggest that available techniques, e.g., artificial replenishment of salt marshes or search for more productive halophytic species, will hardly allow Venice wetlands to keep up with a strong acceleration of sea level rise
Reply to Comment by Cao and Hu on Long waves in erodible channels and morphodynamic influence
No full text
Una famiglia nobiliare di Terraferma: i Martinengo da Barco, a cura di P. Lanzoni – S. Onger, Roccafranca, La Compagnia della Stampa Massetti Rodella, 2009, 200 p
No full textin “Civiltà bresciana” 1-2 (2009), p. 224-227:
Una famiglia nobiliare di Terraferma: i Martinengo da Barco, a cura di P. Lanzoni – S. Onger, Roccafranca, La Compagnia della Stampa Massetti Rodella, 2009, 200
- …
