| 1. |
- Persson, Peter, et al.
(författare)
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Byggande av lätta trähus i tätbebyggda städer
- 2020
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Ingår i: Bygg & Teknik. ; 3, s. 24-26
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Strävan efter ett hållbart byggande med miljövänliga material har bidragit till ett ökat intresse för trämaterial. Samtidigt förtätas städerna alltmer och mark nära kollektivtrafik behöver tas i anspråk. Eftersom lätta konstruktioner kan vara känsliga för vibrationer finns risk för att husen som byggs inte tillfredsställer kraven på en god inomhusmiljö med avseende på buller och vibrationer. Om det går att beräkna och förutsäga buller och vibrationsnivåer tidigt i designprocessen så finns det goda möjligheter att hitta tekniska lösningar som fungerar. Problemet idag är att beräkningsmodellerna är alltför komplicerade och kräver specialistkompetens. Vår ambition är att utveckla en användarvänlig, effektiv och rimligt säker modell för att prediktera vibrationer i lätta trähus nära spårbunden trafik.
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| 2. |
- Askari, Amir R., et al.
(författare)
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Free vibrations of bi-stable pressurized FG plate-type MEMS
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Recently, it has been shown that besides initially curved micro-plates, pressurized flat ones can also experience bi-stable behavior that enjoys many potential applications in designing high sensitive MEMS sensors [1]. In the sequence of ref. [1], the present work aims to investigate free vibrations of pressurized electrically actuated thin micro-plates made of FGM. To this end, the geometric nonlinear in-plane and out-of-plane governing equations of motion are obtained using the Hamilton principle and reduced to an initial value problem associated with the first transversal eigenmode of the structure through a multi-term Galerkin projection method. Having the reduced equation of motion, the eigenvalue equation governing the free vibrations of the micro-plate around its equilibrium configuration is then obtained. Afterward, the oscillatory behavior of pressurized plate-type MEMS is studied. It has been observed that the fundamental frequency of the system suddenly drops to zero when the micro-plate faces the limit points in its equilibrium path. The present findings are compared and successfully validated by 3D FE simulations carried out in COMSOL Multiphysics commercial software for a Silicon-Copper graded micro-plate with dimensions as same as the case studied in ref. [1], the power-law index is set to n=0.5, and the micro-plate is assumed to be subjected to 3kPa differential pressure in the opposite direction of the electrical attraction. References [1] A.R. Askari, "Bi-stability of pressurized electrically actuated flat micro-plates", Int. J. Solids Struct., 178-179, 167 - 179 (2019).
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| 3. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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A direct approach for three-dimensional elasto-static and elasto-dynamic solutions in curvilinear cylindrical coordinates with application to classical cylinder problems
- 2022
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with introducing a unique representation of the three-dimensional Navier's equations of motion in cylindrical coordinate system in an exact simplified form without any approximation, aiming at facilitating solution procedure for different 3-D elasto-static and elasto-dynamic problems in the future. A novel form of the 3-D elasticity equations of motion including the body forces in cylindrical coordinate system is derived in an uncoupled form in terms of the longitudinal (axial) displacement component and the 'r-theta' in-plane anti-symmetric rotation function instead of introducing any additional auxiliary unknown potential function. The other displacement components (i.e., circumferential and radial displacement components) are shown to be obtained from two independent equations in terms of the determined axial displacement and the aforementioned rotation component. The correctness, validity and easy implementation of the introduced elasticity approach for obtaining exact elasticity solutions for various 3-D elasto-static and elasto-dynamic problems are demonstrated through solving a number of known elasticity problems. Three-dimensional static and free vibrations of finitelength solid cylinders as well as thick-walled hollow cylindrical shells are analytically solved. Numerical comparative results and discussion are conducted. Excellent agreement between the obtained results and those reported in the literature is observed in all cases, confirming the validity of the proposed new approach.
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| 4. |
- Atashipour, Rasoul, 1983, et al.
(författare)
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On the complete solution of the three-dimensional solid space problems based on a novel curvilinear elasticity representation
- 2023
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 97
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Tidskriftsartikel (refereegranskat)abstract
- A solution scheme is presented for the three-dimensional elasticity theory in the curvilinear cylindrical coordinate, without introducing any new physically dubious potential function. Exact analytical solutions for the essential 3-D solid full- and half-space problems are developed based on the introduced elasticity approach. The Kelvin's classical problem of concentrated force acting in the interior of an infinite solid space, as well as the Boussinesq's half-space problem of concentrated force normal to the free surface of a semi-infinite 3-D solid are treated. Furthermore, the three-dimensional non-axisymmetric problem of semi-infinite solid space under concentrated tangential force on its surface (the so-called Cerruti's problem) is revisited. It is demonstrated that unlike most of the conventional solutions in the literature for the aforementioned problems, the present approach is capable of obtaining the complete solution without needing to combine with other approaches. Evidently, the completeness issue associated with any new method of potentials is not present for the established direct elasticity approach. At the end, an extension of the approach to a nonhomogeneous elastic media is presented and, as an application, the Boussinesq's problem for a nonhomogeneous half-space is solved analytically. The developed representation may serve as an efficient replacement of the original three-dimensional Navier's elasticity equations for solving different 3-D elastic problems in the future.
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| 5. |
- Folkow, Peter, 1968, et al.
(författare)
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Effects on buildings from blast induced vibrations – a numerical pre-study
- 2022
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Ingår i: 11th EFEE World Conference on Explosives and Blasting. - 9780955029073 ; :3.-Blast-Vibration-and-Seismology, s. 101-110
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Konferensbidrag (refereegranskat)abstract
- It is well known that blasting in rock may cause structural damage to nearby buildings. There are differences among most countries regarding legislation with respect to blast induced vibrations. Criticism has been raised against this unclear situation, and it is of importance to develop more reliable predictions on ground and structural vibrations. The present work has its origin based on the features within the Swedish Standard. These guidelines are related to distance and underground conditions, contrary to many other national standards which are based on frequency measures. There is a desire to update the Swedish Standard; either based on distance, frequency or some other measures. This pre-study considers numerical studies (2D FEM) for modelling blasting effects. The aim is to illustrate how various parameters (material, geometry, load) influence ground vibration phenomena as well as structural effects above-ground.
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| 6. |
- Folkow, Peter, 1968, et al.
(författare)
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Skadeverkan mot byggnad av markvibrationer från sprängning
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Vid sprängningsarbete uppstår en omgivningspåverkan i form av markvibrationer som kan ge upphov till skador hos närliggande byggnader och konstruktioner. I dagens svenska vibrationsstandard anges riktlinjer för tillåtna vibrationsvärden för att undvika skador på olika typer av byggnader och byggnadsmaterial. Dessa riktlinjer är i huvudsak baserade på arbete utfört under 1940 till 1960-talet och beror av faktorer såsom t.ex. avstånd och grundförhållanden. Det vetenskapliga stödet är dock svagt, och kritik har framförts att givna riktlinjer i flera fall bedöms vara alltför konservativa. Med anledning av detta finns det i branschen en önskan att modernisera den nationella standarden. För att kunna göra detta finns det dock ett behov av att bättre förstå den teoretiska bakgrunden till hur olika vibrationsfaktorer påverkar skadebilden i en byggnad samt vilken effekt olika typer av parametrar har på skaderisken. Denna förstudie behandlar modellering av markvibrationer från sprängning och dess inverkan på närliggande byggnader. Arbetet omfattar dels att studera vilka markvibrationer som genereras från sprängning (lastresponsen), och dels hur dessa vibrationer påverkar angränsande byggnader (strukturresponsen). I projektet studeras inverkan på skaderisken från olika parametrar kopplade till lastens, markens och byggnadens egenskaper. Ett ytterligare syfte med förstudien är att utifrån numerisk modellering närmare studera de riktlinjer för sprängningsinducerade vibrationer i byggnader som formuleras i Svensk Standard, samt i någon mån också relatera resultaten till standarder i andra länder. Projektet syftar således till att ge en djupare förståelse för kopplingen mellan mark- och strukturvibrationer, och hur detta i sin tur relaterar till skador i konstruktioner. Genom att belysa hur olika fenomen, och samspelet dem emellan, inverkar på skaderisken hos en vibrationsutsatt byggnad kan sådana modeller utgöra en viktig grundsten för en framtida revidering av Svensk Standard.
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| 7. |
- Jafarzadeh, Ata, 1992, et al.
(författare)
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Scattering of elastic SH waves by transversely isotropic sphere
- 2020
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Ingår i: Proceedings of the International Conference on Structural Dynamic , EURODYN. - Athens : EASD. - 2311-9020. ; 2, s. 2782-2797
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Konferensbidrag (refereegranskat)abstract
- The scattering by a transversely isotropic sphere in a three-dimensional, homoge-neous, isotropic and infinite elastic medium is considered. The problem is a scalar one andis phrased as a scattering problem for an incident SH elastic waves propagating in the direc-tion parallel to the axis of material symmetry. The elastodynamic equations inside the sphereare transformed to spherical coordinates and the displacement field is expanded in associatedLegendre functions in the polar coordinate and powers in the radial coordinate. This leadsto recursion relations for the expansion coefficients inside the sphere. Using the boundaryconditions on the surface of the sphere results in a system of equations for all the expansioncoefficients for the fields outside and inside the sphere. As a result, the transition (T) matrixelements are calculated and given explicitly for low frequencies.
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| 8. |
- Jafarzadeh, Ata, 1992, et al.
(författare)
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Scattering of elastic waves by a sphere with cubic anisotropy
- 2021
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Scattering of elastic waves in materials with inhomogeneities is a classical problem in physics and geophysics, and have applications in non-destructive testing, material characterization, medical ultrasound, etc. The classical analytical solution of the scattering by a single isotropic spherical obstacle provides a good approximation and a basis for more complicated problems and gives a deep understanding of the scattering phenomenon [1]. However, plenty of natural and synthetic materials, specifically the grains in a metal, are known to be anisotropic. Recently, the scattering of elastic waves by a circle with cubic anisotropy is studied in 2D by Bostrom [2, 3], and Jafarzadeh et al. [4] use the same method to study the 3D scattering problem for a transversely isotropic sphere. The present work is a continuation of these studies and investigates the 3D scattering by a sphere with cubic anisotropy. Consider the scattering of a single spherical obstacle with cubic anisotropy contained in a three-dimensional, homogeneous, isotropic and infinite elastic medium. In the isotropic surrounding the classical approach is used with the displacement field constructed as a superposition of incident and scattered waves, which are expanded in spherical vector wave functions. Inside the sphere the stress-strain relations are given in Cartesian coordinates for the cubic material and these are first transformed to spherical coordinates. These relations then become inhomogeneous in that they contain factors with trigonometric functions in both angular coordinates and the same becomes true also for the equations of motion. To proceed it is useful to expand the displacement into a series of vector spherical harmonics where each coefficient in turn is expanded into a power series in the radial coordinate. It follows from the equation of motion that the coefficients in the power series obey certain recursion relations, thus reducing the number of unknowns inside the sphere. Expressing also the stresses as a series in the vector spherical harmonics, the rest of the unknowns are determined by the continuity of the displacement and traction on the sphere boundary. As a result, the transition (T) matrix elements, relating the expansion coefficients of the scattered wave to those of the incident wave, are calculated. It is, in particular, possible to obtain explicit expressions for the leading order T matrix elements for low frequencies. References [1] V. Varadan, A. Lakhtakia, and V. Varadan, Field representations and introduction to scattering. North-Holland, Amsterdam, 1991. [2] A. Bostrom, "Scattering by an anisotropic circle," Wave Motion, vol. 57, pp. 239-244, 2015. [3] A. Bostrom, "Scattering of in-plane elastic waves by an anisotropic circle," The Quarterly Journal of Mechanics and Applied Mathematics, vol. 71, pp. 139-155, 2018. [4] A. Jafarzadeh, P. D. Folkow, and A. Bostrom, "Scattering of elastic sh waves by transversely isotropic sphere," in Proceedings of the International Conference on Structural Dynamic, EURODYN, vol. 2, pp. 2782-2797, 2020.
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| 9. |
- Jafarzadeh, Ata, 1992, et al.
(författare)
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Scattering of elastic waves by a sphere with cubic anisotropy with application to attenuation in polycrystalline materials
- 2023
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Ingår i: Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences. - 1471-2946 .- 1364-5021. ; 479:2272
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Tidskriftsartikel (refereegranskat)abstract
- Scattering of elastic waves by an anisotropic sphere with cubic symmetry inside an isotropic medium is studied. The waves in the isotropic surrounding are expanded in the spherical vector wave functions. Inside the sphere, the elastodynamic equations are first transformed to spherical coordinates and the displacement field is expanded in terms of the vector spherical harmonics in the angular directions and a power series in the radial direction. The governing equations inside the sphere give recursion relations among the expansion coefficients in the power series. The boundary conditions on the sphere then determine the expansion coefficients of the scattered wave. This determines the transition (T) matrix elements which are calculated explicitly to the leading order for low frequencies. Using the theory of Foldy, the T matrix elements of a single sphere are used to study attenuation and phase velocity of polycrystalline materials with cubic symmetry, explicitly for low frequencies and numerically for intermediate frequencies. Numerical comparisons of the present method with previously published results and recent finite element method (FEM) results show a good correspondence for low and intermediate frequencies. The present approach shows a better agreement with FEM for strongly anisotropic materials in comparison with other published methods.
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| 10. |
- Jafarzadeh, Ata, 1992, et al.
(författare)
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Scattering of elastic waves by a sphere with orthorhombic anisotropy and application to polycrystalline material characterization
- 2024
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Ingår i: Ultrasonics. - 0041-624X. ; 138
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Tidskriftsartikel (refereegranskat)abstract
- Scattering of elastic waves by an anisotropic sphere with orthorhombic symmetry inside an isotropic medium is studied and applied to characterization of polycrystalline materials with anisotropic grains. For a single sphere the waves in the isotropic surrounding are expanded in the spherical vector wave functions. Inside the sphere, the elastodynamic equations are first transformed to spherical coordinates and the displacement field is expanded in terms of the vector spherical harmonics in the angular directions and power series in the radial direction. The governing equations inside the sphere give recursion relations among the expansion coefficients in the power series. The boundary conditions on the sphere then determine the relation among the scattered wave expansion coefficients and those of the incident wave, expressed as the transition (T) matrix. For low frequencies the elements of the T matrix are obtained in explicit form. According to the theory of Foldy the T matrix elements of a single sphere are used to study attenuation and phase velocity of polycrystalline materials, explicitly for low frequencies. Comparisons of the present method with previously published results and recent FEM results show a good correspondence for low frequencies. The present approach shows a better agreement with FEM for strongly anisotropic materials in comparison with other published methods.
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