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engleski na srpski: The Side Force General field: Tehnika/inženjerstvo Detailed field: Aeronautika / avijacija / svemir
Izvorni tekst - engleski Skids and straight rolling tires are pretty easy. And, it turns out that yawed rolling tires aren't too difficult either. Rather than there being a breakout, slipping, or sliding threshold that acts like a light switch, the tire is always slipping to some degree relative to the ground - even when rolling straight ahead. To prove it to yourself, mark your car tire and the ground simultaneously with a chalk mark and roll slowly forward (straight) about 100 feet and barely brake. Then, roll backwards along the same path. The original marks will not line up.
A yawed rolling tire has a "continuum" of slip that doesn't act like a light switch anywhere. The average tire (at a constant vertical load, at least) acts like a lateral spring with yaw angle in that it can be reasonably well modeled as a linear function of yaw. So, the side force (again, at a constant vertical load) can be modeled as Fs = K times Fn times yaw angle, that is
This value isn't anywhere near universal, (it changes with tire, vertical load, surface condition, etc) but the kind of number we're talking about here for K is something like 0.06 /deg. A 4-degree yaw angle would give a side coefficient of about 0.24, providing essentially a 1/4 g. turn. Half as much yaw would give half the side force, etc. This generally will hold up to about 8-10 degrees before the linearity starts to break down (as does a lift coefficient curve near stall). Remember that vertical load affects the value of K as do a number of other variables.
This can be understood without too much trouble, and the code can be pictured in ones mind, as well. Nose/tail-wheel steering is done using rudder command. A side force on the nose/tail wheel can be calculated. Of course, this will yaw the vehicle. It must be considered that when the nose gear is turned and the nose yaws left or right, the main gear will acquire a yaw with respect to the direction of travel, and will itself impart a force to the airframe in the direction of yaw towards the center of the radius of motion while in the turn. This will turn and translate the vehicle until the new yaw vector is aligned with the actual direction of travel of the vehicle cg.
This sounds very simple, and for the most part it is, if this is all that needs to be modeled. However, it is possible to lock up the wheels and skid, or turn the wheel such that skidding takes place. Braking also figures into the equation. Just so that we are all on the same page, here are some definitions:
• Static friction: Any force applied to a stationary object must be greater than the static friction to overcome it and start it moving. The static friction force is the product of the normal force and the static friction coefficient, and acts in the runway plane opposite to the direction of the applied force.
• Dynamic (or sliding) friction: Any object that slides or skids with respect to another surface experiences sliding or dynamic friction between itself and the surface. The force exerted on the objects is equal and opposite, and it opposes the direction of travel. The magnitude is equal to the normal force times the dynamic (sliding) friction coefficient.
• Example:
• Suppose, for example, that we talk about a turned nose gear. We have three vectors of note:
Say that the aircraft is currently heading directly north, the wheel is turned right 15 degrees, but the actual wheel velocity vector is slightly less than that, say, 13 degrees (of course, the aircraft is in the process of turning, having already begun the turn at an earlier time). For completeness' sake, let's say that we have nearly instantaneously turned the wheel to its current position, and this is one reason why the wheel velocity vector has not caught up more closely to the wheel heading. The big question now is, now what? We ultimately want the forces (and thus the moments which can be determined) as they act on the body axis.
Here, there is an analogy with the aerodynamic forces, axes, etc.:
The wheel axis is analogous to the aircraft body axis.
The velocity vector of the wheel is analogous to stability axes.
The angle *from* the velocity vector of the wheel, *to* the wheel "X" axis is analogous to alpha. In our example, this is two degrees.
We can get the side force (Fs) using this relationship:
Fs = K * Fn * Yaw
Prevod - srpski Zanošenje i pravolinijsko kotrljanje pneumatika je prilično lako. Ispostavlja se da ni kotrljanje pneumatika sa zanošenjem u stranu nije naročito teško. Umesto da dođe do skretanja sa pravca, proklizavanja ili klizne granice koja deluje kao blaga skretnica, pneumatik uvek proklizava do određene tačke koja je relativna u odnosu na tlo – čak i kada je kotrljanje pravolinijsko. Kako biste to potvrdili, istovremeno obeležite pneumatik svog automobila i tlo kredom i pokrećite automobil lagano napred (pravolinijski) oko 100 stopa uz minimalno kočenje. Zatim ga vratite nazad istom trasom. Obeležena mesta se neće poklopiti.
Pneumatik koji se kotrlja sa zanošenjem u stranu ima ”kontinuum” proklizavanja koje ni na kom mestu ne deluje kao blaga skretnica. Prosečan pneumatik (konstantnog vertikalnog opterećenja) deluje kao bočna opruga sa uglom obrtanja oko vertikalne ose tako da može da se može obrazovati linearna funkcija ugaone oscilacije. Dakle, bočna sila (ponovo, konstantnog vertikalnog opterećenja) može da se izrazi kao Fs = K puta Fn puta ugao obrtanja oko vertikalne ose, što znači
Ova vrednost nije ni približna univerzalnoj, (ona se menja sa pneumatikom, vertikalnim opterećenjem, uslovima podloge itd.) ali vrednost broja o kojoj se ovde govori za K je otprilike 0.06/stepen. Ugao obrtanja od 4 stepena dao bi bočni koeficijent od otprilike 0.24, uz skretanje od 1/4 g. Polovina ugaone oscilacije dala bi polovinu bočne sile, itd. To će se u principu podizati do oko 8-10 stepeni pre nego što linearnost počne da se prekida (kao i kriva koeficijenta potiska u blizini zaustavljanja). Ne zaboravite da vertikalno opterećenje utiče na vrednost K kao i broj drugih promenljivih.
Ovo se može razumeti bez većih problema a i slika se takođe može zamisliti. Upravljanje točkom nosa/repa vrši se komandom sa kormila. Bočna sila točka nosa/repa može da se izračuna. Naravno, to će skrenuti vozilo sa pravca. Mora se uzeti u obzir da kada se nosni pogon okrene i nos skrene sa pravca u levu ili desnu stranu, glavni pogon će izvršiti skretanje u pogledu na pravac kretanja i sam će primeniti silu na konstrukciju aviona u smeru skretanja ka centru poluprečnika kretanja prilikom skretanja. Ovo će okrenuti i pomeriti vozilo dok se novi obrtni vektor ne dovede u ravan sa stvarnim pravcem kretanja težišta aviona.
Ovo zvuči prilično jednostavno. Veći deo i jeste takav, ukoliko je ovo sve što treba modelirati. Ipak, moguće je blokirati točkove ili okrenuti točak tako da nastupi zanošenje.Kočenje se takođe javlja u jednačini. Kako ne bi bilo nejasnoća, evo nekih definicija:
• Statičko trenje: Bilo koja sila koja se primenjuje na nepokretan objekat mora biti veća od statičkog trenja kako bi se ono prevazišlo i pokrenulo. Sila statičkog trenja je proizvod normalne sile i koeficijenta statičkog trenja i deluje na površini piste nasuprot smeru primenjene sile.
• Dinamičko (ili klizno) trenje: Svaki objekat koji se kliza ili zanosi u odnosu na drugu površinu trpi klizno ili dinamičko trenje između sebe i te površine. Sila koja je primenjena na objekte je jednaka i suprotna i suprotstavlja se smeru kretanja. Apsolutna vrednost jednaka je proizvodu normalne sile i koeficijenta dinamičkog (kliznog) ‚trenja.
• Primer:
• Pretpostavimo, na primer, da se radi o okrenutom nosnom pogonu. Imamo tri vektora koje treba uzeti u obzir:
1) Obrtanje aviona oko vertikalne ose ...
2) Obrtanje točka oko vertikalne ose ...
3) Vektor brzine točka
Recimo da se avion trenutno kreće u pravcu severa, točak je okrenut u desnu stranu za 15 stepeni, ali je vektor stvarne brzine točka malo manji od toga, recimo, 13 stepeni (naravno, avion je u fazi skretanja, već je prethodno započeo proces skretanja). Radi potpunijeg obrazloženja, recimo da smo gotovo istog trenutka okrenuli točak u njegovu trenutnu poziciju i to je jedan razlog zbog koga vektor brzine točka nije bliži obrtanju točka oko vertikalne ose. Glavno pitanje koje se sada postavlja je šta sada? Na kraju nas interesuju sile (a samim tim i momenti koji se mogu odrediti) i njihovo dejstvo na osovinu avionske konstrukcije.
Ovde postoji analogija sa aerodinamičkim silama, osovinama, itd.:
Osovina točka analogna je osovini avionske konstrukcije.
Vektor brzine točka analogan je osovinama koje utiču na stabilnost.
Ugao *od* vektora brzine točka *do* osovine točka ”X” analogan je veličini alfa. U našem primeru, to je dva stepena.
Možemo da dobijemo bočnu silu (Fs) pomoću sledeće veze:
Fs = K * Fn * Ugaona oscilacija
engleski na srpski: Historic Preservation General field: Tehnika/inženjerstvo Detailed field: Arhitektura
Izvorni tekst - engleski Historic Masonry and Concrete Construction
INTRODUCTION
The function of masonry units such as brick or stone is related to the thickness of a wall, the mortar, the bond, and the quality of workmanship. The relationship of all these materials determines the historic building's structural soundness as well as its appearance. While masonry is among the most durable of historic building materials, it is also the most susceptible to damage by improper maintenance or repair techniques and harsh or abrasive cleaning methods.
Stone is one of the more lasting of masonry building materials and has been used throughout the history of American building construction. In the 17th and 18th centuries, stone was often used only for decorative details, trimwork, foundations, and chimneys on brick buildings. Where stone was plentiful, however, it was used to construct even simple houses and outbuildings. Stonework on most buildings was roughly finished, but more elaborate stone structures often featured finely tooled or carved decorative surfaces. The kinds of stone most commonly encountered on historic buildings in the U.S. include various types of sandstone, limestone, marble, granite, slate, and fieldstone.
Brick varied considerably in size and quality. Before 1870, brick clays were pressed into molds and were often unevenly fired. The quality of brick depended on the type of clay available and the brick-making techniques; by the 1870s – with the perfection of an extrusion process – bricks became more uniform and durable.
Terra-cotta is also a kiln-dried clay product popular from the late 19th century until the 1930s. Brownstone terra-cotta was the earliest type used throughout the last half of the 19th century. It was hollow cast, glazed or unglazed, and was generally used in conjunction with brick to imitate brownstone. Fireproof terra-cotta was developed for use in high-rise buildings. Inexpensive, lightweight, and fireproof, these rough-finished hollow building blocks were well suited to span I-beams in floor, wall, and ceiling construction. Glazed architectural terra-cotta consists of hollow units hand cast in molds or carved in clay and heavily glazed and fired. The development of the steel-frame office building in the early 20th century and the eclectic taste of the time contributed to the widespread use of architectural terra-cotta.
Preservation of Structural Systems
INTRODUCTION
Structural systems in architecture are composed of structural elements (such as beams, piers, and trusses) and building materials (wood, steel, and masonry) that together form the walls, floors, and roofing of buildings.
If features of the structural system are exposed, such as load-bearing brick walls, cast iron columns, roof trusses, posts and beams, vigas, or stone foundation walls, they may be important in defining the building's overall historic character.
The types of structural systems found in America include, but certainly are not limited to, the following: wooden frame construction (17th century), balloon frame construction (19th century), load-bearing masonry construction (18th century), brick cavity wall construction (19th century), heavy timber post and beam industrial construction (19th century), fireproof iron construction (19th century), heavy masonry and steel construction (19th century), skeletal steel construction (19th century), and concrete slab and post construction (20th century).
Prevod - srpski Izvorni zidarski elementi i betonska konstrukcija
UVOD
Funkcija zidarskih elemenata kao što su opeka ili kamen, povezana je sa debljinom zida, malterom za zidanje, vezivnim materijalom i kvalitetom izrade. Odnos svih ovih materijala određuje konstruktivnu sigurnost istorijske zgrade kao i njen izgled. Iako su zidarski materijali među najtrajnijim materijalima istorijske zgrade, takođe su i najpodložniji oštećenjima izazvanim nepravilnim održavanjem ili načinima popravke i grubim metodama čišćenja i abrazivnim sredstvima.
Kamen je jedan od trajnijih materijala za zidanje zgrade i korišćen je kroz istoriju američke izgradnje. Kamen se u XVII i XVIII veku često koristio samo za dekorativne detalje, profilacije, temelje i dimnjake na zgradama od opeke. Ipak, tamo gde ga je bilo u izobilju, kamen je korišćen čak i za izgradnju jednostavnih kuća i pomoćnih objekata. Kamenorezački radovi na većini zgada bili su grubo završeni ali su složenije kamene konstrukcije često imale fino obrađene ili izrezbarene dekorativne površine. Vrste kamena koje se najčešće sreću na istorijskim zgradama u S.A.D.-u uključuju razne tipove peščara, krečnjaka, mermera, granita, škriljca i kamena nađenog na površini zemlje.
Opeka se znatno menjala po veličini i kvalitetu. Pre 1870. glina za opeku je presovana u kalupe i često bila neravnomerno pečena. Kvalitet opeke je zavisio od vrste gline koja je bila dostupna i od načina pravljenja opeke; do 1870-ih – sa usavršenim postupkom istiskivanja – opeke su postale jednoličnije i izdržljivije.
Terakota je takođe proizvod od veštački sušene gline, popularan od kraja XIX veka do 1930-ih. Terakota od mrkog peščara je najstarija vrsta koja se koristila u drugoj polovini XIX veka. Bila je livena šuplja, glazirana ili neglazirana i uglavnom se koristila zajedno sa opekom da bude nalik mrkom peščaru. Terakota otporna na vatru nastala je za upotrebu kod solitera. Jevtini, lagani i otporni na vatru, ovi grubo obrađeni, šuplji zidarski blokovi bili su veoma pogodni za obuhvatanje I-nosača u podu, zidu i tavanskoj konstrukciji. Glazirana arhitektonska terakota se sastoji od šupljih blokova, ručno livenih u kalupima ili izrezbarenih u glini i debelo glaziranih i pečenih. Razvoj poslovne zgrade sa čeličnim skeletom početkom XX veka i odabran ukus tog vremena doprineli su širokoj upotrebi terakote.
Očuvanje konstruktivnih sistema
UVOD
Konstruktivni sistemi u arhitekturi sastoje se od konstruktivnih elemenata (kao što su grede, stubovi i rešetkasti nosači) i građevinskih materijala (drveta, čelika i zidarskih materijala) koji zajedno obrazuju zidove, podove i krovni pokrivač zgrada.
Ukoliko su elementi konstruktivnog sistema izloženi, poput nosećih zidova od opeke, stubova od livenog gvožđa, krovnih rešetki, stubova i greda, krovnih gredica ili kamenih temeljnih zidova, onda mogu da budu značajni za definisanje celokupnog istorijskog karaktera zgrade.
Tipovi konstruktivnih sistema pronađenih u Americi obuhvataju, ali svakako nisu ograničeni na, sledeće: drvenu ramovsku konstrukciju (XVII vek), drvenu konstrukciju sa vertikalnim nosećim i pregradnim elementima (XIX vek), noseću zidanu konstrukciju (XVIII vek), konstrukciju od dvostrukog zida od opeke podeljenog praznim prostorom (XIX vek), konstrukciju od ogromnih stubova i greda industrijske drvene građe (XIX vek), gvozdenu konstrukciju otpornu na vatru (XIX vek), zidanu i čeličnu konstrukciju (XIX vek), čeličnu skeletnu konstrukciju (XIX vek) i konstrukciju od betonskih ploča i stubova (XX vek).
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Master's degree - Faculty of Philology, University of Belgrade
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Godine iskustva: 6. Registrovan/a na ProZ.com: Aug 2010.
engleski na srpski (University of Belgrade - Faculty of Philology) srpski na engleski (University of Belgrade - Faculty of Philology) srpski na engleski (Cambridge University (ESOL Examinations))
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