MODEL UPDATE WITH THE OBSERVER/KALMAN FILTER AND GENETIC ALGORITHM APPROACH

The discrete time Observer/Kalman model identification technique is implemented in order to identify the structure pulse response. The model updating procedure based on the finite element model pulse response of the test structure and the genetic algorithm is developed. The objective function evaluates the difference between the system and the model pulse responses. The modal assurance criteria implementation is considered. The model reduction in order to match the model degrees of freedom (dofs) and the test structure dofs involved in the experiment is discussed. A case study on the frame test structure is provided

Experimental investigation of the added mass of the cantilever beam partially submerged in water

U radu se numerički i eksperimentalno analizira fenomen dodane (virtualne) mase konstrukcije uronjene u tekućinu. Standardni model dodane modalne mase se analizira usporedo s prividno dodanom lokalnom masom koja se određuje korištenjem vektora pseudo-ostatka sile. U određivanju lokalno dodane virtualne mase koristi se konstrukcija modelirana metodom konačnih elemenata. Procedura zahtijeva popravljeni model konačnih elemenata na temelju eksperimenta kao i redukciju modela. Način primjene popravke i redukcije modela u analizi lokalno dodane virtualne mase su prikazani u radu te je diskutirana njihova uloga. Postupak je primijenjen na konzolu djelomično uronjenu u vodu. Eksperimentalna modalna analiza izvršena je na konzoli u zraku te na istoj konzoli djelomično uronjenoj u vodu. Ova analiza daje dva seta modalnih parametara, a uzrok njihove razlike je dodana masa koja je prezentirana i objašnjena u ovom radu. Rezultati dobiveni na ovaj način mogu se koristiti u daljim istraživanjima kao polazna točka u simulacijama.The phenomena of added (virtual) mass of submerged structures are analyzed numerically and experimentally in this paper. The classical concept of modal added mass is analyzed in parallel with local added mass that is evaluated using pseudo-residual force vector. A finite element structure model is used to determine the local added mass. The model update and the model reduction techniques are necessary, and their respective roles are described and applied in determining the local added mass. The procedure is implemented to the cantilever beam partially submerged into water. Experimental modal analysis is performed on a cantilever beam in the air and on the same beam partially submerged in the water. This results in two sets of modal parameters, and the cause of their differences is presented and explained by the added mass. The results obtained in this way can be used as benchmark for further study and comparison with other simulations

Experimental Vibration Testing and Nondestructive Testing

An overview of the Vibration and Experimental Modal Analysis (EMA) and system identification method and possible applications in non-destructive testing (NDT) is provided. The system identification in time, frequency and scale-time domain methods are presented. The illustrative examples of stiffness, mass and damping identification are provided. The theoretical and experimental basis of for mechanical system condition assessment is given. Displayed NDT method is based on the residual force vector and dynamic properties of the system. Theoretically, the method is applicable to any structure that can be accurately modeled using the finite element method and whose frequencies and mode shapes can be reliably obtained. To confirm the method numerically, it is applied to the numerical model of story frame, where the damage was simulated for three different cases: change in mass, change in stiffness and both change in mass and change in stiffness simultaneously. The practical, experimental, validity of the method is demonstrated by applying it to the free-free beam. It is shown that the practical application of the method requires additional actions, without which the method can be difficult to implement. This is a model update with which it is possible to achieve reliable modal parameters and the model reduction is used with which enables the equality of degrees of freedom between numerical and experimental model to be obtained

Some dilemmas in energy approach to vibration and stability analysis of pressurized and rotating toroidal shells

In this paper some dilemmas related to the application of the Rayleigh – Ritz method (RRM) in conjunction with the Fourier series for vibration and stability analysis of pressurized and rotating toroidal shells are elucidated. The physical meaning of the strain and kinetic energy terms of different order of displacements in the energy balance equation are explained. Only the second order terms remain in the variation of equation of motion. In the RRM, a symmetric Coriolis mass matrix is obtained as a result of using the energy approach. In FEM, the matrix equation of motion is complex and the Coriolis mass matrix is antisymmetric. It is shown that by transferring the equation of motion from the complex into the real domain, its size is doubled and the total Coriolis matrix becomes symmetric. The influence of using the Green–Lagrange non–linear strains and the engineering strains on vibration and buckling of a toroidal shell is contrasted. It is observed that differences in the dynamic analysis, due to the two different non–linear strain formulations, is quite small. On the contrary, in buckling analysis the engineering strains give considerably higher value of the critical load

An Identification of the unbalanced magnetic pull in generator at excitation and the hydropower machine model validation

A mechanical vibration inverse analysis has been performed on 150MW hydro-power machine in order to identify unbalanced magnetic pull. FEM model of the machine is developed according to design data. The System Equivalent Reduction Expansion Process is involved in model validation during the power-machine experimental run. The unbalanced magnetic pull in the generator is calculated from the verified model and monitored data

Optimization of metal sandwich plates with corrugated core

This paper intends to lay out a possible approach to optimizing the metal-metal sandwich plates with corrugated cores based on a number of assumptions and for certain selected cases. The objective functions and constraints are derived based on standard requirements of minimum weight and satisfaction of static, structural, and design constraints. The intention of the approach and optimization model presented here is to be able to define the optimum geometry (design) of the sandwich plate for given conditions. With an additional module also developed by the authors, one can design the tool (profiled rolls) that will generate the ‘optimal’ geometry of the corrugated core. In this sense, the approach is actually one of product development based on optimization. More particularly, starting from case-specific given load and optimality conditions one can numerically derive the optimized shape and dimensions of the sandwich and sequentially numerically derive the corresponding production tool geometry, thereby completing the optimized product development

An Identification of the unbalanced magnetic pull in generator at excitation and the hydropower machine model validation

A mechanical vibration inverse analysis has been performed on 150MW hydro-power machine in order to identify unbalanced magnetic pull. FEM model of the machine is developed according to design data. The System Equivalent Reduction Expansion Process is involved in model validation during the power-machine experimental run. The unbalanced magnetic pull in the generator is calculated from the verified model and monitored data

Fluid Structure Interaction Using Modal Superposition and Lagrangian CFD

This study investigates the impact of fluid loads on the elastic deformation and dynamic response of linear structures. A weakly coupled modal solver is presented, which involves the solution of a dynamic equation of motion with external loads. The mode superposition method is used to find the dynamic response, utilizing predetermined mode shapes and natural frequencies associated with the structure. These essential parameters are pre-calculated and provided as input for the simulation. Integration of the weakly coupled modal solver is accomplished with the Lagrangian Differencing Dynamics (LDD) method. This method can directly use surface mesh as boundary conditions, so it is much more convenient than other meshless CFD methods. It employs Lagrangian finite differences, utilizing a strong formulation of the Navier–Stokes equations to model an incompressible free-surface flow. The elastic deformation of the structure, induced by fluid forces obtained from the flow solver, is computed within the modal coupling algorithm through direct numerical integration. Subsequently, this deformation is introduced into the flow solver to account for changes in geometry, resulting in updated flow pressure and velocity fields. The flow particles and vertices of the structure are advected in Lagrangian coordinates, resulting in Lagrangian–Lagrangian coupling in spaces with weak or explicit coupling in time. The two-way coupling between fluid and structure is successfully validated through various FSI benchmark cases. The efficiency of the LDD method is highlighted as it operates directly on surface meshes, streamlining the simulation setup. Direct coupling of structural deformation eliminates the conventional step of mapping fluid results onto the structural mesh and vice versa