Abstract in English:Abstract With the opening of the Northern Sea for international shipping routes, various vessels prefer to use this option to reach Europe as distance is significantly reduced if a ship is sailing through this route. In the same time, the demand to ensure ship safety rises as impact phenomenon between ship structures and ice causes numerous casualties. This work presented a numerical study with a concentration on contact between ship structures and levels. The double side skin of a chemical tanker was modelled with a shell element while a deformable characteristic was implemented on the ice as an indenter. Several target areas on the side structure were set as impact points based on its stiffener component. Different models of indenter were taken into account in order to observe structural responses and influences of external parameters, namely ice topology, while the described location parameters were taken as the ship's internal parameters. Impact force was presented with total energy, as well as the ratio between kinetic and internal energy. The deformation pattern was used as a verification of the collision process and its subsequent results. Finally, the behavior of the inner walls subjected to type indenters was observed as this component is the final component that maintains liquid cargo and resists an impact load.
Abstract in English:Abstract This paper presents effects of shear deformation on flutter instability of cantilever beam subject to a concentrated follower force. The discrete form of equation of motion is formulated based on the Lagrange. In the presented formulation, the beam is modeled using Timoshenko beam theory, and constant shear distribution through the thickness of the beam is considered. Consistent interpolation scheme is adopted to avoid the shear locking for thin beams. Consequently, convergence of the finite element simulation is enhanced. The effect of rotary inertial term is considered in the flutter study, which has significant influence on the beam behavior as the beam thickness increases. The axial degrees of freedom are taken into account in energy expressions, to improve the accuracy of the results. Results presented for different beam geometries. The numerical results show high efficiency and good convergence characteristic. The effect of concentrated mass on the flutter instability of beam is considered and results are presented for various locations and values of concentrated masses. Furthermore, the shear effects are highlighted in this study by comparing the results obtained from the Euler-Bernoulli with those obtained from the Timoshenko beam model.
Abstract in English:Abstract In this study, the dynamic instability of beams under tip follower forces are considered. The beam is modeled by using the geometrically exact, fully intrinsic beam equations which is subjected to an inclined tip follower force. Generalized differential quadrature method is employed to solve the governing equations. The effect of different parameters such as follower force inclination and magnitude, rotating speed, the distance between the beam center of gravity and elastic center, and cross-sectional properties on the instability boundary of beams are examined. Numerical results reveal that the critical load of the system can be influenced or in some cases be reversed by the combination of these parameters instead of considering these parameters separately. Moreover, it is shown that notwithstanding the simplicity of the equations and the method of solution, the results are very accurate and therefore the fully intrinsic equations and the method of solution is very useful for the dynamic solution of rotating and non-rotating beams.
Abstract in English:Abstract The floor pan is an important component that connects the front and rear segments of the automotive underbody structure. Global stiffness and NVH characteristics of BIW are highly dependent to shape, thickness and mass of the body panels and could be evaluated by modal characteristics of these panels. The feeling of solidness and comfort of passengers in an automotive is also dependent to the modal behavior of the underbody components as well as the floor pan. On the other hand, it is desired to reduce the total mass of the floor pan, in order to have a lighter vehicle with better fuel economy and emission standards. In this paper, the effect of geometrical parameters on natural frequency and total mass of the floor pan of a conventional B-Segment automotive body is investigated using finite element simulation. The finite element model is verified using an experimental test on the floor pan. Taguchi L 16 orthogonal array is used to design the numerical experiments. Subsequently, S/N ratio analysis is performed to evaluate the effect of each design variable on the output functions. The panel's thickness is determined to have the most contribution in affecting the natural frequency and weight using Analysis of Variance (ANOVA). The best combination of geometrical variables which leads to the trade-off results is then figured out by a new multi-criteria decision making (MCDM) method developed in this study. Accuracy of this method is verified by comparing the trade-off results with TOPSIS, as a conventional MCDM method.
Abstract in English:Abstract The purpose of this study is to obtain numerical estimations of seismic pressures in offshore areas considering the effect of seabed configurations and soil materials. To this end, the Boundary Element Method is used to irradiate waves, so that force densities can be obtained for each boundary element. From this hypothesis, Huygens´ Principle is implemented since the diffracted waves are constructed at the boundary from which they are radiated. Application of boundary conditions allows us to determine a system of integral equations of Fredholm type of second kind and zero order. Various models were analyzed, the first one is used to validate the proposed formulation. Other models of ideal seabed configurations are developed to estimate the seismic pressure profiles at several locations. The influence of P- and SV-wave incidence was also highlighted. In general terms, it was found that soil materials with high wave propagation velocities generate low pressure fields. The difference between the maximum pressure values obtained for a soil material with shear wave velocity of β = 3000 m/s is approximately 9 times lower than those obtained for a material with β = 90 m/s, for the P-wave incidence, and 2.5 times for the case of SV-waves. These results are relevant because the seabed material has direct implications on the field pressure obtained. A relevant finding is that the highest seismic wave pressure due to an offshore earthquake is almost always located at the seafloor.
Abstract in English:Abstract Micro-buckling of unidirectional fiber-reinforced composites is investigated in this paper by means of an explicit representation of a geometrically imperfect fiber within the context of kinematical and material non-linear behavior. Two types of fiber imperfections are considered: a helicoidal shape, identified as 3D imperfection; and a sinusoidal plane shape (2D imperfection). Both imperfection models are characterized by a maximum misalignment angle of the fiber with respect to the ideal or perfect configuration, as is usually considered in this field. A total of 816 cases were computed in terms of imperfection type (either 2D or 3D), fiber volume fraction, fiber arrangement (square or hexagonal array), orientation for 2D models, matrix yield stress, and misalignment angle. Two load cases, with constrained and unconstrained transverse strain, were considered. Assuming periodic boundary conditions, homogenization was carried out to obtain macroscopic stresses. Numerical results are compared with an analytical model available in the literature. The results show a high imperfection-sensitivity for small misalignment angles; on the other hand, the type of imperfection and the fiber arrangement do not have a large influence on the results. In addition, it was found that this problem is governed by fiber volume fraction and matrix yield stress only for small imperfections, whereas for large misalignment angles, a change in fiber volume fraction produces small changes in micro-buckling stress.
Abstract in English:Abstract The beginnings and ends of guardrail designs have the function of providing adequate anchorage for the rest of the system. They should also demonstrate crashworthy performance and should not pose any hazard for errant vehicles. In Europe, the ends of guardrail systems traditionally have incorporated turned down end terminals. Due to its low cost, Turkey also adopted turned down guardrail end terminal, and the majority of these designs are 12 meters long. Accident statistics clearly demonstrate that this particular end terminal poses safety risks for impacting vehicles. However, crash tests performed on the system showed that it worked satisfactorily for cars impacting at 80 kph. In this study, a detailed finite element analysis was performed on a 12 m long turned down guardrail end treatment to fully evaluate its crashworthiness. Data obtained from previously performed TT 2.1.80 and TT 4.2.80 crash tests were used to verify the fidelity of finite element models used in the study. Further simulations performed in accordance with EN1317 part 7 at 100 kph demonstrated unacceptable performance for the end terminal. Results of the study are summarized and recommendations are presented.
Abstract in English:Abstract This study compares ball, bar-clip and bar-ball attachment systems for implant-retained mandibular overdentures with three implants. The first implant is placed in the middle of the mandible and the other two are imbedded in the first premolar regions. Linear elastic finite element analysis is used for design analysis. Three dimensional geometry of the mandible is generated from computed tomography. Other parts are modeled using SolidWorks software. The foodstuff is positioned at the right first molar, representing the most frequent masticating situation. To obtain accurate mesh-independent results, finite element models are solved using several mesh grids. They are then validated by means of a detailed convergence analysis. The results demonstrate that the highest von-Mises stress in the bone is always located around the neck of the implant, at its upper threads. Ball and bar-ball attachments transfer the highest and lowest stresses to the bone surrounding the implants, respectively. The lowest stresses in the cortical and cancellous bones are due to bar-ball attachment. Yet, the overdenture gets its maximum movement for this arrangement. Consequently, the use of bar-ball attachment is only recommended for the cases in which stress transferred to peri-implant bone is more important than overdenture stability. Among the three treatment designs, ball attachment seems to exhibit the lowest lateral and overall displacements and hence, better overdenture stability.
Abstract in English:Abstract This paper presents an experimental investigation on the axial crushing of coiled expanded metal tubes subjected to quasi-static compressive loading. The investigation aims at comparing the energy absorption characteristics between tubes fabricated with coiled expanded metal meshes and solid plates. Then, a series of quasi-static axial crushing tests were performed to obtain the structural performance on coiled tubes, and then compare these with round and square solid tubes. Coiled tubes were fabricated using circular and square geometries, as well as various cell orientations. The results showed that cell orientation enhance the energy absorption response of the coiled tubes. Regarding these responses in comparison to those of solid tubes, the results showed that for coiled and solid tubes with the same weight, the energy absorption capacity of the former is much lesser than the latter.
Abstract in English:Abstract In the present paper, buckling analysis of functionally graded rectangular micro-plates, on the basis of strain gradient theory with one length scale parameter is studied. Considering the Kirchhoff plate theory and the principle of minimum total potential energy, governing equations of micro-plate subjected to in-plane loads are extracted. In accordance with functionally graded distribution of material properties through the thickness, higher order governing equation of sixth order is derived. Consequently, the stability equation is solved analytically for simply supported micro-plates and the effects of material properties, micro-structure parameters, dimensions and loading conditions are expounded on the critical buckling load. Developing the strain gradient theory for buckling analysis of micro-plates made of functionally graded material is a significant novelty of the presented study.