A finite difference/boundary integral procedure to determine theacoustic reflected pressure from a fluid-loaded bi-laminated plate isdescribed. The bi-laminate is composed of a piezoelectric layer andan elastic layer ...A finite difference/boundary integral procedure to determine theacoustic reflected pressure from a fluid-loaded bi-laminated plate isdescribed. The bi-laminate is composed of a piezoelectric layer andan elastic layer in contact with the fluid, and is held by anacoustically hard baffle. In the numerical model, the fluid pressureat fluid/solid interface is replaced by a continuum of point sourcesweighted by the normal acceleration of the elastic plate, and thegoverning equation system is solved in the solid domain.展开更多
America's first documented wooden covered bridge was erected at Philadelphia,Pennsylvania in 1805.Hundreds were constructed within two decades and at least 10,000 by the later 1800s.As settlers moved West,broad ri...America's first documented wooden covered bridge was erected at Philadelphia,Pennsylvania in 1805.Hundreds were constructed within two decades and at least 10,000 by the later 1800s.As settlers moved West,broad rivers were crossed with inventive structures incorporating timber trusses ingeniously developed by carpenters.Called covered bridges because of the roof and siding needed to protect the timber trusses,they became ubiquitous features on the American landscape.Over the past two centuries,most covered bridges were lost to flood,ice,arson,lightening,decay,as well as"progress,"replaced by"modern"iron,concrete,and steel spans.Of some 700 covered bridges remaining,many are mere replicas of their original forms no longer supported by timber trusses.Genuine historic bridges remain largely from the last half of the 1800s while civic boosterism has led to claims of earlier dates with often questionable authenticity.This essay presents three wooden covered bridges constructed in the 1820s along a 10-mile stretch of the Wallkill River in New Paltz,New York.Of the three,only Perrine's Bridge,constructed first in 1821 and covered in 1822,is still standing with intact Burr timber trusses.Perrine's is an iconic structure with exceptional heritage value because of authentic re-building and restoration in 1834,1846,1917,and 1968.Using documentary records,this essay establishes an accurate intertwined chronology for the three bridges,detailing nineteenth century building practices and contentious mid-twentieth century struggles pitting preservationists wanting authentic restoration against those wanting removal.展开更多
基金the National Natural Science Foundation of China (No.10172039).
文摘A finite difference/boundary integral procedure to determine theacoustic reflected pressure from a fluid-loaded bi-laminated plate isdescribed. The bi-laminate is composed of a piezoelectric layer andan elastic layer in contact with the fluid, and is held by anacoustically hard baffle. In the numerical model, the fluid pressureat fluid/solid interface is replaced by a continuum of point sourcesweighted by the normal acceleration of the elastic plate, and thegoverning equation system is solved in the solid domain.
文摘America's first documented wooden covered bridge was erected at Philadelphia,Pennsylvania in 1805.Hundreds were constructed within two decades and at least 10,000 by the later 1800s.As settlers moved West,broad rivers were crossed with inventive structures incorporating timber trusses ingeniously developed by carpenters.Called covered bridges because of the roof and siding needed to protect the timber trusses,they became ubiquitous features on the American landscape.Over the past two centuries,most covered bridges were lost to flood,ice,arson,lightening,decay,as well as"progress,"replaced by"modern"iron,concrete,and steel spans.Of some 700 covered bridges remaining,many are mere replicas of their original forms no longer supported by timber trusses.Genuine historic bridges remain largely from the last half of the 1800s while civic boosterism has led to claims of earlier dates with often questionable authenticity.This essay presents three wooden covered bridges constructed in the 1820s along a 10-mile stretch of the Wallkill River in New Paltz,New York.Of the three,only Perrine's Bridge,constructed first in 1821 and covered in 1822,is still standing with intact Burr timber trusses.Perrine's is an iconic structure with exceptional heritage value because of authentic re-building and restoration in 1834,1846,1917,and 1968.Using documentary records,this essay establishes an accurate intertwined chronology for the three bridges,detailing nineteenth century building practices and contentious mid-twentieth century struggles pitting preservationists wanting authentic restoration against those wanting removal.
