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Comparison of two possible approaches to inverse laplace transform applied to wave problems
Adámek, V. ; Valeš, František ; Červ, Jan
This paper concerns the investigation of non-stationary wave phenomena in a thin elastic disc under radial impact by means of analytical methods. When the method of integral transforms is used for solving the system of PDEs describing a wave problem solved, one has to overcome the problem of inverse transform. This work focuses on two possible approaches to the inverse Laplace transform. Using the existing analytical solution of the problem, the classic method making use of the residue theorem and the method based on the numerical inverse Laplace transform are compared. Advantages and disadvantages of both approaches, mainly from computational point of view, are discussed and demonstrated.
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Enigma of submerged fence skin friction sensor
Tesař, Václav
The problem with the known “sublayer fence” skin friction sensor is the disturbance caused by the fence protruding above the surface. Author comes with the solution preventing the premature transition into turbulence or even flow separation. In his original version of thesensor the fence is submerged slightly below the surface. Detailed investigations revealed the pressure difference output to be dependent on creation of two recirculation regions. An attempt tofacilitate the recirculation, quite surprisingly, has led to the merging of the vortices and total disappearance of a useful output signal.
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Early Defect Detection of Acetabular Implants
Kytýř, Daniel ; Jiroušek, Ondřej ; Zlámal, Petr ; Doktor, Tomáš ; Jandejsek, I.
The paper is focused on possibilities of modern X-ray detectors and micro-focus X-ray source for investigation of early degradation processes of acetabular implants. To simulate the most adverse activity (downstairs walking) a hip joint simulator was developed. The experimental setup was designed for cyclic loading of polyethylene acetabular cup implanted into the human pelvic bone and fixed by commercial polymethyl methacrylate bone cement. To predict the bone degradation numerical analysis of detailed three-dimensional model of the acetabular cup and the cement mantle implanted in a bone block was performed. Using large area flat panel detector and microfocus X-ray source it is possible to investigate micro-damage propagation and detect early defect in the bone-implant interface.
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Stress wave propagation in the Institute of Thermomechanics
Okrouhlík, Miloslav
The paper is devoted to a survey of old, recent and contemporary stress wave propagation tasks having been studied in the Institute of Thermomechanics (IT) within the period of the last sixty years. Scientific deeds as well as people who deserve admirations for achieving them are mentioned.achieving them are mentioned. Problems and employed analytical and numerical methods are shortly listed.
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Finite element contact-impact algorithm in explicit transient analysis
Gabriel, Dušan ; Kopačka, Ján ; Plešek, Jiří ; Ulbin, M.
This work addresses three issues in computational modelling of contact-impact problems: i) overviews a contact algorithm proposed by these authors, ii) local search treatment based on the modification of the Nelder-Mead simplex method, iii) discusses an algorithmic aspects of contact algorithm in conjunction with the explicit time integration scheme. The talk closes with the presentation of several numerical examples including the longitudinal impact of two thick plates, for which analytical solution is available.
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Sedimentation of dilute suspension in intermediate region
Vlasák, Pavel ; Chára, Zdeněk
The present paper describes the results of experimental investigation of the continuous sedimentation of a dilute model of fine-grained suspension in the intermediate region of settlement. The effects of particle size (glass beads of average diameter 150–850 μm), concentration, and inclination of the vessel axis on particle fall velocity were evaluated. It was confirmed that the local relative particle-liquid velocity has a practically constant value across the vessel cross-section. The settling pattern is strongly affected even by a very gentle slope of the vessel axis, which causes an asymmetrical absolute velocity profile and significant increase of the local concentration and absolute fall velocity of particles near the upward-facing wall of the vessel.
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