Osamu Kuwazuru

Computational fluid dynamics simulations on a Devonian spiriferid Paraspirifer bownockeri (Brachiopoda): Generating mechanism of passive feeding flows

A mechanism of generating passive feeding flow for the Devonian spiriferide brachiopod Paraspirifer bownockeri was theoretically elucidated through fluid dynamics simulations for flow around rigid shells. The RANS equations were used as a turbulence model, and the unsteady incompressible flow was solved using the finite volume method. Two directions of ventral and dorsal flows were investigated as typical cases where little exchange flow occurs inside the shells. The digital model of the shell was constructed using image processing of X-ray CT images of a shell replica made by molding a polycarbonate plate to a well-preserved fossil specimen of Paraspirifer. To examine the effect of flow velocity, three conditions of ambient flow velocity were adopted for both the ventral and dorsal flows. The pressure distribution along the gape showed that a relatively high pressure occurred around the sulcus in all simulated cases. This high pressure generated inflow from the sulcus and subsequent spiral internal flow, especially in fast ambient flows. This means that the sulcus generated the considerable pressure gradient around the gape passively and generated the stable intake of seawater and a spiral flow of water inside the shell for feeding. We conclude that the shell form of certain spiriferides could generate spiral flows so as to promote passive feeding, and the sulcus is interpreted as an important form for the passive intake of water.

Functional adaptation of spiriferide brachiopod morphology

It has been suggested that spiriferide morphologies have evolved to adapt to a variety of environmental conditions. Through a computational fluid dynamics approach, we examined how the spiriferide original form was optimized for a lotic condition, specifically addressing the functionalization of the Devonian spiriferide brachiopod Paraspirifer bownockeri to generate passive feeding flows. The results using four models, each of which differed in the development of the spiriferide shell depression, i.e. sulcus, showed that a deeper sulcus functions to create strong spiral flows so as to align on the feeding organ inside the shell. Among the sulcus‐developed models, only the mimic of the natural form could generate comparative slow flows with a stable inflow area. The fossil record of spiriferides shows a morphological trade‐off between the development of the sulcus and wing form. We concluded that spiriferide shells with such a morphological combination evolved to produce various feeding strategies, resulting in diversification.

Skin wrinkling morphology changes suddenly in the early 30s.

Does the morphology of wrinkles alter gradually with aging or suddenly at a certain age? On the basis of the theoretic wrinkle simulation of ideal skin, we have suggested that the wrinkle morphology suddenly changes from stratum corneum wrinkling to epidermis wrinkling; the former induces shallow fine furrows, and the latter induces deep prominent wrinkles. To examine the existence of drastic change in wrinkling morphology, we developed a new measurement system for facial skin wrinkling test.

Fabrication of Aluminum Foam-Filled Thin-Wall Steel Tube by Friction Welding and Its Compression Properties

Aluminum foam has received considerable attention in various fields and is expected to be used as an engineering material owing to its high energy absorption properties and light weight. To improve the mechanical properties of aluminum foam, combining it with dense tubes, such as aluminum foam-filled tubes, was considered necessary. In this study, an aluminum foam-filled steel tube, which consisted of ADC12 aluminum foam and a thin-wall steel tube, was successfully fabricated by friction welding. It was shown that a diffusion bonding layer with a thickness of approximately 10 μm was formed, indicating that strong bonding between the aluminum foam and the steel tube was realized. By the X-ray computed tomography observation of pore structures, the fabrication of an aluminum foam-filled tube with almost uniform pore structures over the entire specimen was confirmed. In addition, it was confirmed that the aluminum foam-filled steel tube exhibited mechanical properties superior to those of the ADC12 aluminum foam and steel tube. This is considered to be attributed to the combination of the aluminum foam and steel tube, which particularly prevents the brittle fracture and collapse of the ADC12 foam by the steel tube, along with the strong metal bonding between the aluminum foam and the steel tube.

Relationship between scapular position and structural strength of rib cage in quadruped animals

Determining scapular position is a major issue in reconstructing the skeletal systems of extinct quadruped archosaurs and mammals, because the proximal portion of the scapulae has no direct skeletal joint with the vertebrae or ribs. When quadrupeds stand or walk, their trunk is suspended between the forelimbs by the serratus muscles, which arises from the lateral sides of the “thoracic” ribs and inserts into the proximal portion of the costal surface of the scapula. Therefore, the “thoracic” ribs are subjected to a static or dynamic vertical compression between the lifting force from the muscle and the gravitational force from the vertebral column. To investigate the body support function of the ribs, we analyzed the mechanical strength of the ribs of extant tetrapods by the two‐dimensional finite element method, and compared the degree of strength through their craniocaudal scapular positions. The result of this simulation showed that the “thoracic” ribs of quadrupeds, to which the serratus muscles attach, have a relatively higher strength against compaction than the other ribs. In bipeds, however, we did not find a similar correlation between the strength of ribs and the serratus muscle. This implies that the location of robust ribs is associated with the arrangement of the serratus muscle, and provides a probable candidate for determination of the scapular position for extinct quadruped archosaurs and mammals. J. Morphol. 2009.

Deformation Behavior Estimation of Aluminum Foam by X-ray CT Image-based Finite Element Analysis

Aluminum foam is a lightweight material owing to the existence of a large number of internal pores. The compressive properties and deformation behavior of aluminum foam are considered to be directly affected by the shape and distribution of these pores. In this study, we performed image-based finite element (FE) analyses of aluminum foam using X-ray computed tomography (CT) images and investigated the possibility of predicting its deformation behavior by comparing the results of FE analyses with those of actual compressive tests. We found that it was possible to create an analytic model reflecting the three-dimensional (3D) pore structure using image-based modeling based on X-ray CT images. The stress distribution obtained from image-based FE analysis correctly indicates the layer where deformation first occurs as observed in actual compressive tests. Also, by calculating the mean stress of each plane perpendicular to the direction of compression based on the stress distribution obtained from image-based FE analysis, it was found that deformation begins in the layer containing the plane with maximum stress. It was thus possible to estimate the layer where deformation begins during the compression of aluminum foam.

Fabrication of Aluminum Tubes Filled with Aluminum Alloy Foam by Friction Welding

Aluminum foam is usually used as the core of composite materials by combining it with dense materials, such as in Al foam core sandwich panels and Al-foam-filled tubes, owing to its low tensile and bending strengths. In this study, all-Al foam-filled tubes consisting of ADC12 Al-Si-Cu die-cast aluminum alloy foam and a dense A1050 commercially pure Al tube with metal bonding were fabricated by friction welding. First, it was found that the ADC12 precursor was firmly bonded throughout the inner wall of the A1050 tube without a gap between the precursor and the tube by friction welding. No deformation of the tube or foaming of the precursor was observed during the friction welding. Next, it was shown that by heat treatment of an ADC12-precursor-bonded A1050 tube, gases generated by the decomposition of the blowing agent expand the softened ADC12 to produce the ADC12 foam interior of the dense A1050 tube. A holding time during the foaming process of approximately tH = 8.5 min with a holding temperature of 948 K was found to be suitable for obtaining a sound ADC12-foam-filled A1050 tube with sufficient foaming, almost uniform pore structures over the entire specimen, and no deformation and minimum reduction in the thickness of the tube.

Functionally Graded Aluminum Foam Fabricated by Friction Powder Sintering Process with Traversing Tool

Functionally graded aluminum foam (FG Al foam) is a new class of Al foam in which the pore structure varies over the foam, resulting in corresponding variations in the mechanical properties of the foam. In this study, FG Al foam plates were fabricated by a friction powder sintering (FPS) process with a traversing tool that is based on a previously developed sintering and dissolution process. The variation of the mechanical properties was realized by setting the volume fraction φ of NaCl in the mixture to 60, 70, and 80%. Long FG Al foam plates were fabricated with a length equal to the tool traversing length with φ varying in the tool traversing direction. From x-ray computed tomography observation, it was shown that the density of the Al foam decreased with increasing φ. In contrast, almost uniform pore structures were obtained in each area. According to the results of compression tests on each area, the plateau stress and energy absorption tended to decrease with increasing φ. Therefore, it was shown that FG Al foam plates with varying mechanical properties can be fabricated by the FPS process with the traversing tool.

Swimming capability of the remopleuridid trilobite Hypodicranotus striatus: hydrodynamic functions of the exoskeleton and the long, forked hypostome.

The sophisticated hydrodynamic performance achieved by the exoskeleton and the long, forked hypostome of the remopleuridid trilobite Hypodicranotus striatus was demonstrated using image-based modelling and computational fluid dynamics simulation techniques. To understand the function of the long, forked hypostome, we examined two types of exoskeletal models, one with and one without the hypostome. We simulated the flow structures around the exoskeletal models under several ambient flow velocities to evaluate the shapes of the streamlines, the values of the drag and lift forces and the relevant coefficients acting on the models. The simulation results showed that the long, forked hypostome prevents the formation of a ventral vortex; thus, it stabilises the flow structure under all of the ambient velocities tested. Moreover, the hypostome functions to create positive lift, with stable lift coefficients observed under a wide range of velocities, and to reduce the drag coefficient as velocity increases. These results imply that the hypostome can reduce viscous drag with a modest lift force, which is an essential requirement for actively swimming animals. We conclude that the long, forked hypostome evolved to provide an active and stable swimming system, and we therefore hypothesise that Hypodicranotus exoskeletal morphology resulted from the adaptation to be a high-performance swimmer.

Theoretical approach to the functional optimisation of spiriferide brachiopod shell: Optimum morphology of sulcus.

Evidence suggests that biological forms that provide physiological and autecological functions have evolved to adapt to environmental conditions and to optimise requisite morpho-functions. We examined whether shell morphology is functionally optimised to generate passive feeding flow in the Devonian spiriferide brachiopod Paraspirifer bownockeri. This study was based on quantitative results from a computational fluid dynamics simulation and the Lagrangian multiplier method. We estimated the optimum development of the ventral median shell depression, which is called the sulcus, by minimising the pressure difference along the gape. This estimation was made under the constraint that the number of spiral flow rotations must be greater than one, which is effective for spiriferide feeding because of its alignment with the spiral lophophore. During mathematical optimisation, the equation resulted in a suitable flow velocity of approximately 0.1m/s. At this velocity, the pressure difference was minimised, regardless of sulcus development. The constraint equation showed that the number of spiral flow rotations increased with sulcus development. The optimal solution was similar to the original sulcus form of Paraspirifer under an ambient flow of approximately 0.1m/s. This result suggests that the variation of shell outline in spiriferids could provide a variety of preferential conditions for ambient flow and that the flow intensity could be adjusted by sulcus development to generate a robust passive feeding flow along the spiral feeding organs.