| 1. |
- Christensen, P. W., et al.
(författare)
-
Formulation and comparison of algorithms for frictional contact problems
- 1998
-
Ingår i: International Journal for Numerical Methods in Engineering. - : John Wiley & Sons. - 0029-5981 .- 1097-0207. ; 42:1, s. 145-173
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents two algorithms for solving the discrete, quasi-static, small-displacement, linear elastic, contact problem with Coulomb friction. The algorithms are adoptions of a Newton method for solving B-differentiable equations and an interior point method for solving smooth, constrained equations. For the application of the former method, the contact problem is formulated as a system of B-differentiable equations involving the projection operator onto sets with simple structure; for the application of the latter method, the contact problem is formulated as a system of smooth equations involving complementarity conditions and with the non-negativity of variables treated as constraints. The two algorithms are numerically tested for two-dimensional problems containing up to 100 contact nodes and up to 100 time increments. Results show that at the present stage of development, the Newton method is superior both in robustness and speed. Additional comparison is made with a commercial finite element code.
|
|
| 2. |
- Strömberg, Niclas, 1968-
(författare)
-
A Newton method for three-dimensional fretting problems
- 1999
-
Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 36:14, s. 2075-2090
-
Tidskriftsartikel (refereegranskat)abstract
- The present paper concerns the numerical treatment of fretting problems using a finite element analysis. The governing equations resulting from a formal finite element discretization of an elastic body with a potential contact surface are considered in a quasi-static setting. The constitutive equations of the potential contact surface are Signorini's contact conditions, Coulomb's law of friction and Archard's law of wear. Using a backward Euler time discretization and an approach based on projections, the governing equations are written as an augmented Lagrangian formulation which is implemented and solved using a Newton algorithm for three-dimensional fretting problems of didactic nature. Details concerning the implementation are provided.
|
|
| 3. |
- Strömberg, Niclas, 1968-
(författare)
-
An augmented Lagrangian method for fretting problems
- 1997
-
Ingår i: European journal of mechanics. A, Solids. - : Gauthier-Villars. - 0997-7538 .- 1873-7285. ; 16:4, s. 573-593
-
Tidskriftsartikel (refereegranskat)abstract
- The present work concerns the numerical treatment of fretting in the interface between a body and a rigid foundation. Starting from a variational formulation of a fretting model given in a framework of continuum thermodynamics, an augmented Lagrangian formulation is derived by introducing finite element discretizations in space and a finite difference discretization in time. The augmented Lagrangian formulation is implemented and solved by a Newton method for the two-dimensional case.
|
|
| 4. |
- Strömberg, Niclas, 1968-, et al.
(författare)
-
Derivation and analysis of a generalized standard model for contact, friction and wear
- 1996
-
Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 33:13, s. 1817-1836
-
Tidskriftsartikel (refereegranskat)abstract
- A model for mechanical contact including friction, wear and heat generation is proposed. By defining an internal state variable for the wear process, a generalized standard model for contact, friction and wear is derived from the principle of virtual power and the fundamental laws of thermodynamics. Within the frame of the generalized standard model some specific constitutive models are presented. For instance, a free energy corresponding to an extension of Signorini's unilateral contact conditions to include the wear process at the interface and having a linear tangential compliance between the relative tangential displacement and the tangential contact traction is suggested. Furthermore, a dual pseudo-potential with a friction and wear limit criterion in agreement with Coulomb's law of friction Archard's law of wear is given. In order to study existence and uniqueness questions, this pair of free energy and dual pseudo-potential is analysed in a one point elastic quasi-static contact problem with two degrees of freedom and thermal effects neglected. The so-called rate problem is solved.
|
|
| 5. |
|
|
| 6. |
- Strömberg, Niclas, 1968-
(författare)
-
Finite element treatment of two-dimensional thermoelastic wear problems
- 1999
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier. - 0045-7825 .- 1879-2138. ; 177:3-4, s. 441-455
-
Tidskriftsartikel (refereegranskat)abstract
- The present paper concerns the numerical treatment of thermoelastic wear problems. The governing equations of thermoelasticity coupled to Signorini contact, Coulomb's friction and Archard's wear are formulated as a system of discrete equations. This equation system is solved, using a Bouligand differentiable Newton method, for five problems of didactic nature.
|
|
| 7. |
- Runnemalm, Anna, et al.
(författare)
-
Sound intensity measurements of an open organ pipe
- 1997
-
Ingår i: ISMA 97 conference. - : Institute of Acoustics. - 1901656047
-
Konferensbidrag (refereegranskat)abstract
- What part of an open organ pipe emits most of the sound and what is the spatial sound distribution for the harmonic tones? The sound intensity from a blown open organ pipe, tuned to C4 at 260 Hz, is measured in an anechoic room using a 3D sound intensity probe. The measurements are performed both in the vertical and in the horizontal plane in front of the pipe. The two dimensional sound intensity vector field for different harmonic tones are studied. The study focuses on the active mean intensity field and the results point out the main sources of acoustic power and their contribution to the far field. Pipes made of different material and tooled in different ways are compared. Interference phenomena between sources are also visualised. First it can be noted that the top and the mouth are the main sound radiators compared to the walls. They are of about the same strength for the first four harmonics. For the fifth and sixth harmonics the top is the main sound radiator. For odd numbered harmonic tones the mouth and the top emit sound in phase and for even numbers, out of phase. The material choice and tooling method affect the sound spectra.
|
|
| 8. |
|
|
| 9. |
- Tinnsten, Mats, et al.
(författare)
-
Optimization of acoustic response
- 1999
-
Ingår i: Structural Optimization. - 0934-4373. ; 18:1, s. 36-47
-
Tidskriftsartikel (refereegranskat)abstract
- The expression 'acoustic optimization' can be applied to numerous different disciplines within the field of acoustics. From seismic waves, sound in the atmosphere through bioacoustic, psychoacoustics, and room and theater acoustics over shock and vibration in mechanical structures. This paper deals with the latter. Sound generated by vibrating structures is often called noise which is to be minimized. However, not all vibrating structures produce noise, for example the violin is also a vibrating structure that in most people's opinion produces sound called music. In the case of the violin, great effort is made not to minimize but to optimize the sound, i.e. to get the 'right' sound out of the structure. Acoustic optimization within this discipline involves automatic changes of structural design variables to obtain minimum or specified sound in specified regions inside or outside the structure. Examples of problem formulations and some theoretical considerations in the field of acoustic optimization in connection with vibrating mechanical structures will be pointed out. Four simple test cases are included as numerical examples of the method proposed.
|
|
| 10. |
- Berbyuk, Viktor, 1953, et al.
(författare)
-
Internal torques of human upper extremity during its optimal motion in vertical plane
- 1997
-
Ingår i: The Tenth Biomechanics Seminar. - 1100-2247. ; 10, s. 66-83
-
Konferensbidrag (refereegranskat)abstract
- In the paper a number of optimal control problems for the motion of the human upper extremity (HUE), for different types of working tasks, are considered. The performance index used in these problems is the integral over the duration of the working task of the sum of the square of the controlling stimuli acting at the joints of the human arm. Under some conditions this performance index can be used for evaluation of the muscles' energy expenditure during human movements. The HUE is simulated by a plane multibody system of rigid masses. The system comprises the three elements with mass and rotatory inertia modelled the upper arm, the forearm and the hand. The controlled motions of the mechanical system are described in terms of joint angles and Cartesian coordinates of the shoulder joint, through the application of Lagrange's equations. The main aim of the study is an investigation of the interaction between the gravity forces and the internal torques acting at the joints during goal-directed extremal motions of the HUE. The analysis of the internal torques, energetic and viscoelastic characteristics of the shoulder, the elbow and the wrist joints for the exstremal controlled motions of the human arm under the external load acting on the hand has been done.
|
|
