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This study developed a discrete topology optimization procedure for the simultaneous design of ply orientation and thickness for carbon fiber reinforced plastic (CFRP)-laminated structures. A gradient-based discrete material and thickness optimization (DMTO) algorithm was developed by using casting-based explicit parameterization to suppress the intermediate void across the thickness of the laminate. A benchmark problem was first studied to compare the DMTO approach with the sequential three-phase design method using the free size, ply thickness, and stacking sequence of the laminates. Following this, the DMTO approach was applied to a practical design problem featuring a CFRP-laminated engine hood by minimizing overall compliance subject to volume-related and functional constraints under multiple load cases. To verify the optimized design, a prototype of the CFRP engine hood was created for experimental tests. The results showed that the simultaneous discrete topology optimization of ply orientation and thickness was an effective approach for the design of CFRP-laminated structures.

A novel bi-graded honeycomb was proposed by introducing both in-plane and out-of-plane thickness gradients into a regular honeycomb. The graded honeycombs were additively manufactured by fused deposition modeling (FDM) with polylactic acid (PLA) and then tested for axial crushing. Numerical simulation models were constructed through LS-DYNA and validated using experiment results. Based on the super folding element (SFE) method, theoretical models of the proposed bi-graded honeycombs were derived and the accuracy for crushing response was validated against the numerical results. Finally, an active learning based multi-objective optimization algorithm was used to seek the optimal design. The results showed that the bi-graded design for honeycomb structures could improve energy absorption capacity and decrease the peak crushing force in the Pareto frontier manner. The specific energy absorption of the optimal bi-graded honeycomb could be 45.6% higher than that of the regular honeycomb while the peak crushing force was controlled at the same level.

This paper describes the mix design of geopolymer-based ultra-high performance concrete (G-UHPC) with the compressive strength from 100 to 150 MPa. Projectile impact tests at two striking velocities of ~550 m/s and ~800 m/s were then performed to explore the impact resistance of G-UHPC targets. G-UHPC without the addition of fibres yielded better impact resistance than Ordinary Portland Cement (OPC) concrete regarding crater damage and crack propagation, but inferior performance on reducing depth of penetration (DOP). The addition of fibres in G-UHPC effectively helped reduced DOP, crater damage and crack propagation. Steel fibres with a length of 10 mm and a volumetric fraction of 2% were most effective in resisting projectile impact compared with other G-UHPC specimens. To further comprehend the projectile impact performance of G-UHPC, a calibrated Karagozian and Case Concrete (KCC) model accounting for the strain rate effect was successfully used for G-UHPC in projectile analysis. Numerical results including single element and full-scale quasi-static tests, deceleration-time histories of projectiles during penetration and DOP of G-UHPC targets were obtained to validate the numerical models. After that, trendlines were regressed to predict DOP of G-UHPC at two striking velocities of ~550 m/s and ~800 m/s. Perforation limits of G-UHPC were also proposed for the design of both safe and cost-effective protective structures against projectile impact, in which the perforation limits of G-UHPC were taken as 1.1 times of DOP.

In engineering practice, most design criteria require time-consuming functional evaluation. To tackle such design problems, multiobjective Bayesian optimization has been widely applied to generation of optimal Pareto solutions. However, improvement function-based expected improvement (EI) and the hypervolume improvement-based lower confidence bound (LCB) infill-criteria are frequently criticized for their high computational cost. To address this issue, this study proposes a novel approach for developing multiobjective LCB criteria on the basis of LCB improvement matrix. Specifically, three cheap yet efficient infill-criteria are suggested by introducing three different improvement functions (namely, hypervolume improvement, Euclidean distance and maximin distance) that assemble the improvement matrix to a scalar value, which is then maximized for adding solution points sequentially. All these criteria have closed-form expressions and can maintain the anticipated properties, thereby largely reducing computational efforts without either integration or expensive evaluation of hypervolume indicator. The efficiency of the proposed criteria is demonstrated through the ZDT and DTLZ tests with different numbers of design variables and different complexities of objectives. The testing results exhibit that the proposed criteria have faster convergence, and enable to generate satisfactory Pareto front with fairly low computational cost compared with other conventional criteria. Finally, the best performing criterion is further applied to real-life design problems of tailor rolled blank (TRB) thin-walled structures under impact loads, which demonstrates a strong search capability for with good distribution of Pareto points, potentially providing an effective means to engineering design with strong nonlinearity and sophistication.

This study develops a topology optimization approach for design of carbon fiber reinforced plastic (CFRP) laminated components with different failure criteria to reduce the risk of structural failure. The discrete material and thickness optimization (DMTO) method is adopted to parameterize the design variables of thickness and orientation of CFRP composites, which is driven by the Method of Moving Asymptote (MMA) algorithm. A large number of local constraints associated with the failure criteria are aggregated in terms of a p-norm function. Analytical sensitivities are derived with respect to the design variables. In this study, a battery hanging structure in electrical vehicle (EV) is exemplified; and a DMTO based design is prototyped and validated through the in-house experimental tests first. To prevent different failure modes, the Hashin, Hoffman and Tsai-Wu failure criteria are then imposed as the design constraints together with manufacturing requirements in the optimization. A comparative study is performed for the design with and without such failure criteria. The results demonstrate that the maximum failure index of the optimized structure with the Tsai-Wu failure criterion decreases the most by 40%; and follows by the Hashin and Hoffman criteria by 24% and 33%, respectively. Finally, the CFRP structure is also optimized to design a so-called double-double laminates for demonstrating the generality of the proposed method. The study is anticipated to gain in-depth understanding of how the failure criteria would affect the design of fiber reinforced composite structures to ensure structural integrity.

Water temperature is a significant environmental stressor that affects physiology and biochemical activities of bivalves. Here, temporal variations in physiological and biochemical parameters of Zhikong scallop, Chlamys farreri, under three water temperature treatments were investigated. For the first treatment, scallops were transferred from rearing temperature (15 degrees C, control temperature) to 5, 10, 20 and 25 degrees C, respectively. The second group of scallops was gradually acclimated to above experimental temperatures at a rate of 1-2 degrees C day(-1). The third group was transferred directly between 15 and 7 degrees C every 12h and for six times. Results showed that significantly higher oxygen consumption and ammonia-N excretion together with a significant lower ingestion rate was observed for the acute temperature change treatment compared to those in the equivalent gradual temperature variation treatment (P

The biomass and size fraction of phytoplankton in terms of chlorophyll a (Chl a) was measured during four cruises conducted in April, July, October 2013 and January 2014 in mariculture area, the Sanggou Bay, China. Results show that total Chl a levels in the surface seawater of the Sanggou Bay generally range from 0.10 to 20.46 μg/L, with an average value of 2.13 μg/L. Nano-phytoplankton was the most important size-fraction and accounted for about 65.1% of total Chl a. In order to evaluate the importance of the “protozoan trophic link” for energy transfer from the microbial loop to filter-feeding feeders, Zhikong scallop Chlamys farreri was then offered a natural planktonic community as potential prey. Results show that scallops obtained carbon source from natural plankton with the rate of 11 033.05 μg/(g·d). Protists (nanoflagellates and ciliates) were the dominant source of carbon retained by scallop (48.78%). The microbial loop provided 58.45% of the carbon source for farmed scallops. These results indicate that the microbial loop represent a valuable trophic resource in mariculture system of the Sanggou Bay.

Polymers are amongst the main candidate materials for load bearing tissue engineering scaffolds. Their effective and reliable clinical uses necessitate insightful analyses of the nonlinear characteristics, which has so far received little attention in literature. To better understand the failure characteristics of these porous structures, yielding behaviors of scaffolds made of a commercial photopolymer (RGD720) were studied using experiments and finite element method (FEM). The polymer exhibits substantial softening under uniaxial material test, but the extent of such softening behavior in a scaffold structure is compromised or even eliminated due to the internal non-uniformity of material yielding.

As a class of widely observed materials in nature, hierarchical micro structures maybe of superior mechanical properties. In this study, we incorporate the concept of hierarchy into honeycomb structures for enhancing their crashworthiness performance. Hierarchical honeycombs are constructed by replacing every vertex of a regular hexagonal network with a smaller hexagon topology and repeating this process for constructing fractal-appearing honeycombs with higher order of structural hierarchy. To examine the crashing characteristics the hierarchical honeycombs with the first-order and second-order structures were investigated under an out of the cross-sectional plane loading. A parametric study on structural variables (γ1, γ2) which are defined by γi = Li / L0 (L0 is the edge length of regular honeycomb cell, Li is the edge length of i-th order hexagon in hierarchical honeycombs) and oblique-wall angles θ which is defined by the angle of oblique-wall edge to the vertical direction are undertaken with three different densities. A comparison between regular honeycombs and hierarchical honeycombs was conducted. The results showed that the out-of-plane energy absorption of the first-order hierarchical honeycombs with 0.04 ≤ γ1 ≤ 0.2 and the second-order hierarchical honeycombs with 0.15 ≤ γ1 ≤ 0.2 and 0.04 ≤ γ2 ≤ 0.08, as well as the hierarchical honeycombs with oblique-wall angle θ from 30° to 50° have better overall performance. Further, it was found that the specific energy absorptions (SEA) of the first-order hierarchy with γ1 = 0.08 and the second-order hierarchy with γ1 = 0.20, γ2 = 0.06 were improved about 81.3% and 185.7%, respectively. Moreover, their corresponding peak forces (Pmax) do not increase much compared with the regular honeycomb under the same density, indicating that hierarchical honeycombs can be an ideal lightweight structure for designing crashworthy structures. Keywords: Structural hierarchy, Crashworthiness, Honeycombs, Fractal structures, Energy absorption

© 2016, Springer-Verlag Berlin Heidelberg. Light weight and crashworthiness signify two main challenges facing in vehicle industry, which often conflict with each other. In order to achieve light weight while improving crashworthiness, tailor rolled blank (TRB) has become one of the most potential lightweight technologies. To maximize the characteristics of TRB structures, structural optimization has been adopted extensively. Conventional optimization studies have mainly focused on a single loading case (SLC). In practice, however, engineering structures are often subjected to multiple loading cases (MLC), implying that the optimal design under a certain condition may no longer be an optimum under other loading cases. Furthermore, traditional deterministic optimization could become less meaningful or even unacceptable when uncertainties of design variables and noises of system parameters are present. To address these issues, a multi-objective and multi-case reliability-based design optimization (MOMCRBDO) was developed in this study to optimize the TRB hat-shaped structure. The radial basis function (RBF) metamodel was adopted to approximate the responses of objectives and constraints, the non-dominated sorting genetic algorithm II (NSGA-II), coupled with Monte Carlo Simulation (MCS), was employed to seek optimal reliability solutions. The optimal results show that the proposed method is not only capable of improving the reliability of Pareto solutions, but also enhancing the robustness under MLC.

© 2016, Springer-Verlag Berlin Heidelberg. Optimization for structural crashworthiness and energy absorption has become an important topic of research attributable to its proven benefits to public safety and social economy. This paper provides a comprehensive review of the important studies on design optimization for structural crashworthiness and energy absorption. First, the design criteria used in crashworthiness and energy absorption are reviewed and the surrogate modeling to evaluate these criteria is discussed. Second, multiobjective optimization, optimization under uncertainties and topology optimization are reviewed from concepts, algorithms to applications in relation to crashworthiness. Third, the crashworthy structures are summarized, from generically novel structural configurations to industrial applications. Finally, some conclusions and recommendations are provided to enable academia and industry to become more aware of the available capabilities and recent developments in design optimization for structural crashworthiness and energy absorption.

The effects of three temperatures (15°C, 20°C and 25°C) and four feed types (artificial feed, AF; sediment, SM; fish faeces, FF; and fish meat, FM) on the growth, carbon budget and nitrogen budget of the polychaete Perinereis aibuhitensis were evaluated over a 35 day period. The final body weight and specific growth rate (SGR) of P. aibuhitensis were significantly affected by temperature and feed types (T, F = 15.831, P = 0.000; Feed, F = 81.827, P = 0.000), but the interaction between these factors was not significant (F = 0.435, P = 0.848). The worms achieved the highest SGR in the AF group at 20°C. However, the SGR in the SM group was only half that of the other groups. The food conversion efficiency (FCE) was significantly lower at 25°C than at 15°C and 20°C (P

In this paper, the analytical formulas of mean crashing force for four different hexagonal tubes with multiple cells were first derived based on the Simplified Super Folding Element (SSFE) theory through several typical constituent elements: corner element, three-panel angular element I and three-panel angular element II. The numerical simulations of hexagonal multi-cell configurations were then correlated with the derived analytical solutions. Finally, both analytical formulas and finite element analysis (FEA) based surrogate models were employed to optimize the cross-sectional dimensions of the hexagonal tubes. From the optimization results, web-to-web (W2W) is the most efficient configuration in improving the crashing behavior, while corner-to-corner (C2C) is the worst of these four configurations. Importantly, the Pareto fronts obtained from the analytical formulas agree well with those from the FEA based surrogate models. As a result, analytical formulas could be recommended in crashworthiness optimization for the sake of computational efficiency.

Foam-filled thin-wall structures have exhibited considerable advantages in energy absorption with light weight and have been widely used as energy absorber in engineering. Unlike existing uniform or mono-gradient structures, this paper introduces a novel dual functionally graded structure with changing both foam density and wall thickness along the transverse direction, namely transverse functionally graded foam-filled and functionally graded wall thickness (FGF-FGT) structures. According to different combinations of gradient directions in foam density and wall thickness, four different patterns are considered here. Based on the established surrogate models, the surface plots of crashworthiness criteria indicate that the combination of gradient patterns and the gradient exponents have significant effect on overall crashing performances. The multiobjective particle swarm optimization (MOPSO) algorithm is then adopted to seek optimal gradients of wall thickness and foam density, aiming to simultaneously improve the specific energy absorption (SEA) and reduce the maximum force (Fmax). The optimization results indicate that the transverse FGF-FGT structures with ascending grading patterns in both FGF and FGT is superior to the uniform counterparts and other graded structures, providing the designer with the promising optima in a Pareto sense.

Smoothed finite element methods (SFEM) are formulated and used for multi-layered bio-material system.The selective ES/NS-FEM model overcomes volumetric locking in multi-layered bio-material system.ES-FEM are more accurate than conventional FEM and NS-FEM in compressible multi-layered bio-material systems. In general, the biologic system can be rather sophisticated and commonly present in hierarchical layers. Hence, the quadrilateral or brick elements are very difficult to precisely capture the anatomic details for mechanobiologic modeling. Further, the conventional finite element method (FEM) could possibly give poor solutions using triangular or tetrahedral elements due to its overly-stiff property. In addition, the biologic soft tissues are often considered as 'incompressible' materials, where conventional FEM could suffer from volumetric locking in numerical solution. For these reasons, smoothed finite element methods (SFEM) are proposed here to solve the multi-layered bio-systems for softening conventional FEM models.

Dissolved organic carbon (DOC) concentrations were measured in the Sanggou Bay (SGB) in northern China, in order to investigate the seasonal distribution, sources and sink of DOC in an integrated multi-trophic aquaculture (IMTA) system of fish, shellfish and seaweed. The sampling was conducted during April (spring), August (summer), October (autumn) and January (winter) of 2011–2012. Salinity, Chlorophyll a (Chl a) and DOC showed large spatial and seasonal variation during sampling period. DOC increased with increasing Chl a in spring, summer and autumn and decreased with increasing salinity in summer compared to other seasons. Maximum surface concentration of DOC ranged from 108.0 to 875.2 µM and minimum from 134.4 to 184.7 µM was found during summer and spring, respectively. Terrestrial input, phytoplankton and seaweed were the main sources of DOC in SGB. Shellfish farming area was enriched in organic matter as well as served to reduce DOC levels in the bay. As it was indicated that average annual removal of 42 % DOC occurred in the shellfish, the lowest occurred at an average 32 % in combined shellfish and seaweed culture area. Additionally, controlled experiment results showed that seaweed produced approximately 64.81 ± 40.86 µM day−1 and shellfish generated approximately 13.36 ± 6.07 µM day−1 and assimilated 17.07 ± 13.12 µM day−1 DOC in SGB. Accumulation of DOC at the bottom could be a result of long-term aquaculture activities in the bay. Integration of sea cucumber into IMTA system could be useful to mitigate the stockpile of organic matter at the bottom.

Picoplankton abundance and biomass in Sanggou Bay, China, were investigated in 4 successive seasons (April, August and October 2011, January 2012). Different distribution patterns of picoplankton abundance and biomass were observed according to season and culture areas (bivalves or macroalgae). Synechococcus, picoeukaryotes and heterotrophic prokaryotes exhibited higher abundance and biomass in warm seasons (summer and autumn) than in cold seasons (spring and winter). Over all 4 seasons, picoplankton abundance was higher in the bivalve culture area than in the macroalgae culture area. Among picoplankton, picoeukaryotes contributed most to the carbon standing stock in summer and autumn. In spring and winter, the heterotrophic component biomass exceeded that of the autotrophic picoplankton. Picoeukaryotes were an important contributor (21-27%) to total phytoplankton carbon biomass in spring to autumn. In spring, heterotrophic prokaryote biomass accounted for more than 56% of total phytoplankton biomass, and even exceeded phytoplankton biomass at some stations. As revealed by multiple stepwise regression analysis, physicochemical factors and protist grazing were the most important variables that controlled picoplankton distribution and variation. The reduction in grazing pressure, as well as phosphorus release by bivalves, is likely to explain the higher abundance of picoplankton in the bivalve culture area of Sanggou Bay.

Stable isotopic signatures of organic carbon (δ 13 C) and total nitrogen (δ 15 N) were measured on suspended particulates and sediments in order to understand the sources of organic matter (OM), water quality and flow of organic carbon and nitrogen among integrated multi- trophic aquaculture (IMTA) species, as well as to evaluate the role of IMTA practice in accumula- tion and assimilation of OM during wet and dry seasons. OM distribution and composition were studied during 2011 in Sanggou Bay (SGB) of northern China, a system that receives terrestrial and oceanic inputs, and which is used for IMTA ventures. Results showed that higher terrestrial input of OM occurs during the wet compared to the dry season in the SGB. OM in suspended par- ticulates (POM) showed marine- and terrestrial-derived signatures during the wet season, as revealed from their ranges in δ 13 C (�27.4 to �20.7‰) and δ 15 N (4.7 to 9.4‰). Sedimentary organic matter (SOM) showed signatures of marine-derived OM during both seasons, with ranges in δ 13 C and δ 15 N of �22.4 to �21.4‰ and 1.7 to 6.4‰, respectively. Shellfish and combined (shellfish, sea- weed) cultures in SGB have the potential to reduce OM received from the fish cages as well as from the seasonal inputs from rivers. Mixing with Yellow Sea water, combined with prevailing circulation, favours the dispersal, dilution and transformation of OM and maintains and improves water quality. Based on our results, and compared with previous studies, the water quality of the SGB is likely to be sustained by IMTA activities.

Integrated multi-trophic aquaculture (IMTA) involves the farming of species from different trophic positions or nutritional levels in the same system. In China, IMTA has been prac- ticed for many decades, with dozens of species farmed in close proximity to each other at the scale of whole coastal bays. Articles in this Theme Section present results from the MoST-China Project on 'Sustainability of Marine Ecosystem Production under Multi-stressors and Adaptive Manage- ment' (2011�2015). This project sought to understand the interactions between biogeochemical cycles and ecosystem function in the IMTA system of Sanggou Bay, China, which produces a total of >240 000 t of seafood each year from >30 species in approximately 100 km 2 of production space. Results include measurements of carbon, nitrogen flow and trophic relationships among cultured species; impacts of IMTA on benthic nutrient fluxes, reduced inorganic sulfur in sediments, distri- bution of dissolved inorganic selenium, and nutrient cycling; distribution and seasonal variation of picoplankton; and a model for kelp growth. Combined, the articles enable a complex understand- ing of the dynamics between IMTA and the environment in one of the most important coastal aquaculture production systems in the world.

Field observations were made from 2012 to 2014 at an integrated multi-trophic aquaculture (IMTA) site in Sanggou Bay (SGB), China, to characterize the nutrients associated with aquaculture activities, and to assess the effects of aquaculture on nutrient cycles in the bay. Dissolved inorganic and organic nutrient levels were measured in rivers, groundwater, and SGB. Seasonal variations in nutrient concentrations were detected in the rivers, particularly enrichment of dissolved inorganic nitrogen (DIN) and silicate (DSi). Nutrient concentrations showed considerable seasonal variation, with higher and significantly different concentrations occurring in autumn than in the other seasons. The composition and distribution of nutrients were also affected by the species being cultured. Dissolved organic nitrogen and phosphorus (DON and DOP) accounted for 27 to 87% of total dissolved nitrogen and 34 to 81% of total dissolved phosphorus, respectively. Phosphorus may be a potentially limiting nutrient for phytoplankton growth in summer. Nutrient budgets were developed based on a simple steady-state box model. These showed that bivalve aquaculture was the major source of PO43- (contributing 64% of total influx) and led to increased riverine fluxes of PO43-. The results indicated that substantial quantities of nitrogen and DSi accumulated in sediments or were transformed into other forms (e.g. phytoplankton cell composition or particles). Large quantities of DIN and PO43- were removed from the bay through harvesting of seaweeds and bivalves, which represented up to 64 and 81% of total outflux, respectively. The results show that aquaculture activities play the most important role in nutrient cycling in SGB.

Benthic nutrient fluxes in an integrated multi-trophic aquaculture (IMTA) bay— Sanggou Bay, China—were measured in June and September 2012. The benthic nutrient fluxes and total organic carbon (TOC) of sediment in this IMTA system were significantly lower than in monoculture bays. This was due to the efficient recycling of organic matter in the IMTA system, as revealed by historical data of annual production, dissolved inorganic nitrogen (DIN) concentra- tion in seawater and TOC in sediment. Benthic nutrient fluxes in the IMTA system were mainly controlled by seawater temperature, dissolved oxygen (DO) and nutrient concentrations, which were strongly related to aquaculture activities. In June, the early growth phase of cultured finfish and bivalves contributed little to biodeposition, and benthic nutrient fluxes tended to be from the sediment to the seawater and contributed to algal growth. In September, the active growth of finfish and bivalves resulted in high concentrations of nutrients in the seawater and TOC in the sediment; 64% of the nitrogen and 25% of the phosphorus metabolized by bivalves were trans- ferred from the seawater to the sediment.

Copyright © 2016 SAE International. A compiled method of the programmed load spectrum, which can simplify and accelerate the fatigue bench test of a car body, is proposed and its effectiveness is checked by the fatigue simulation. By using the multi-body dynamics model with a satisfactory accuracy, the virtual iteration is applied to cascade body loads from the wheel hubs. Based on the rain-flow counting method and statistics theory, the distributions of the body loads are analyzed, and then the programmed load spectrum is compiled and simplified. Through comparative study, the simulation results of random and programmed load spectrum are found to agree well with each other in terms of the damage distribution and fatigue life, which demonstrates the effectiveness of the presented method.

Although cultured algae and shellfish can be the dominant species in some localized coastal waters, research on the effect of large-scale mariculture on the carbonate system variations in these local waters is still lacking. We conducted five cruises from May to September and studied spatiotemporal variations in the seawater carbonate system in the semi-closed Sanggou Bay, which is famous for its large-scale mariculture. Our results showed that both kelp and bivalve farming induced significant spatiotemporal variations in the carbonate system within the bay. When cultured kelp reached its highest biomass in May, the maximum ΔDIC, ΔpCO2 and ΔpHT between the seawater from the kelp farming area and the non-farming outer bay area was −156 μmol kg−1, −102 μatm and 0.15 pH units, respectively. However, no significant effect of kelp farming on seawater total alkalinity (TA) was observed. Kelp farming also caused the carbonate system variations of seawater from the bivalve farming area. Assuming no kelp was farmed in May, the average pH and pCO2 would reduce by 0.12 pH units and increase by 179 μatm, respectively, in the bivalve farming area. Bivalve farming significantly reduced seawater TA, indicating that fast deposition of calcium carbonate occurred in the bivalve farming area. Although bivalve respiration released CO2 into seawater and elevated seawater pCO2 level and reduced seawater pHT, surprisingly, seawater dissolved inorganic carbon (DIC) reduced significantly in the bivalve farming area. These results indicated that bivalves fixed a larger amount of inorganic carbon by calcification than that released into seawater by respiration. Overall, large-scale kelp and bivalve farming are important biological drivers of variations in the carbonate system within the semi-enclosed Sanggou Bay. Altered carbonate systems by kelp farming may favour calcification of farmed bivalves and provide an essential refuge for these species during the future ocean acidification.

The original Holmquist-Johnson-Cook (HJC) model, which can only capture the compressive behaviour but not the tensile behaviour of brittle materials, is modified in this study. First, the Lode-angle function is introduced to the yield strength surface to consider the changes in the substantial shear strength between the tensile and compressive meridians. A hyperbolic function is used to describe the strain rate effect under dynamic tensile loading. An exponential model is introduced to express the tensile softening stage of brittle material and define the tensile damage variable. Then the modified HJC model is implemented in LS-DYNA via user subroutine UMAT. Further the modifications are validated by single element tests and rock mechanical laboratory experiments. The verification results show that the modified HJC model can effectively describe the tensile responses of brittle material under static and dynamic loading. Last, a comparison between a blasting-crater field test and the corresponding numerical prediction by the modified HJC model is carried out. The comparison results demonstrate that the shape and size of the crater predicted by the modified HJC model show a good agreement with the field test data. Therefore, the modified HJC model has the capacity to capture the tensile and compressive behaviours and damage evolution of brittle material.

Design of vehicle frontal structures signifies an important topic of studies on protection of pedestrian lower extremity. Conventional optimization has been largely focused on continuous variable problems without involving complexity of human model. Nevertheless, design of frontal structures is commonly discrete from a manufacturing perspective and the responses of the lower extremity of pedestrian are highly nonlinear in nature. For this reason, this study aimed to develop a multiobjective discrete optimization (MODO) algorithm for design of frontal structures involving a pedestrian model. In the proposed MODO method, the order preference by similarity to ideal solution (TOPSIS) was coupled with the entropy algorithm to develop a multiple attribute decision making (MADM) model for converting multiple conflicting objectives into a unified single cost function. The presented optimization procedure is iterated using the successive orthogonal experiment to deal with a large number of design variables and design levels. In this study, the proposed method was first verified by two benchmark examples; and then was applied to a more sophisticated real-life design case of vehicle frontal structure to better protect pedestrian lower extremity from impacting injury. The finite element model was validated via experimental tests first and the optimized design was then prototyped for the further physical tests. The results showed that the algorithm is able to achieve an optimal design in a fairly efficient manner. The proposed algorithm exhibits considerable potential to solve other complex engineering design problems.

© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. This study proposes a non-deterministic robust topology optimization of ply orientation for multiple fiber-reinforced plastic (FRP) materials, such as carbon fiber–reinforced plastic (CFRP) and glass fiber–reinforced plastic (GFRP) composites, under loading uncertainties with both random magnitude and random direction. The robust topology optimization is considered here to minimize the fluctuation of structural performance induced by load uncertainty, in which a joint cost function is formulated to address both the mean and standard deviation of compliance. The sensitivities of the cost function are derived with respect to the design variables in a non-deterministic context. The discrete material optimization (DMO) technique is extended here to accommodate robust topology optimization for FRP composites. To improve the computational efficiency, the DMO approach is revised to reduce the number of design variables by decoupling the selection of FRP materials and fiber orientations. In this study, four material design examples are presented to demonstrate the effectiveness of the proposed methods. The robust topology optimization results exhibit that the composite structures with the proper ply orientations are of more stable performance when the load fluctuates.

© 2018 Elsevier Ltd Bio-inspired engineering design has drawn considerable attention in the recent years for its great structural and mechanical features. This study aimed to explore the energy absorption characteristics of a novel bionic-bamboo tube (BBT) structure subjected to axial crushing. The tubes with six different cross-sectional configurations were devised with inspiration of bamboo microstructure. The effects of rib shape and rib number were analyzed by using the finite element code LS-DYNA. The numerical results indicated that the BBT structures with the rib shape of “X” and the rib number of six exhibited the best crashworthiness. To further improve the energy absorption capabilities of these BBT structures, the multiobjective optimization was employed with respect to design variables of configurational structure, such as the rib angle of the “X” shaped cross-section, center distance and rib thickness. The response surface method (RSM) and multiobjective particle swarm optimization (MOPSO) algorithm were adopted to maximize specific energy absorption (SEA) while minimizing peak crushing force (PCF). The optimization results demonstrated that compared to the baseline design, the SEA value of the optimized BBT structure was further increased by 6.84% without sacrificing in peak crushing force.

Physiological and biochemical responses in bivalves exposed to pollutants have proved a valuable tool to assess the health of organisms in aquatic ecosystems. The single and combined effects of mercury (Hg2+, 2 and 10 μg/L) and benzo[a]pyrene (BaP, 3 μg/L) on physiological and biochemical biomarkers in Manila clam, Ruditapes philippinarum were evaluated. Results showed that significant higher oxygen consumption (OR) and ammonia-N excretion rates (NR) together with significant lower ingestion rates (IR) were observed for the 10 μg/L Hg2+ or 3 μg/L BaP treatments compared to controls (P

The currents of the northern shelf of the Yellow Sea are investigated using observations of current and hydrography and numerical current model results. The Regional Ocean Model System (ROMS) with a horizontal resolution about 1km is implemented for the Yellow Sea and the Bohai Sea, and the results are produced for the year 2014 and 2015. Observations from bottom moored ADCP profilers and CTD on the northern shelf of the Yellow Sea are used for validation of the model. The comparison of current time series and bottom temperature evolution show good agreement between model and observation. Barotropic tides are the dominant current component throughout the year on the shelf and consistently mixing the water column in the shallower parts. A thermal front and associated jet exists during the summer creating a robust current structure on the western part of the shelf. The winds in the region are changing constantly creating episodic currents in the upper part of the sea lasting from hours to a couple of days. publishedVersion

Thin-walled structures have been widely used as energy-absorbing components, which can be probably subjected to multiple loading conditions in real life, such as axial crushing and lateral bending. Most of the existing literature solely focuses on the pure axial crushing or lateral bending. In this paper, a novel tailored-property multi-cell tubular structure is proposed, where the material's ultimate strength at the corner region is increased to accommodate both the axial crushing and lateral bending conditions. Finite element (FE) models were developed and validated through experimental results. The FE models were used to investigate the crashworthiness performances of the tailored-property multi-cell tubes under axial crushing and lateral bending. Under both axial crushing and lateral bending, it was found that the tailored-property multi-cell tubes exhibited noticeable advantages over the corresponding traditional tubes. The tailoring ratio and thickness had a significant influence on the crashworthiness performance of the tailored-property multi-cell tubes. Moreover, the well-designed tailored-property multi-cell tubes could exhibit the progressive deformation mode under axial crushing. Furthermore, a theoretical model for the tailored-property multi-cell tubes under axial crushing was developed based on the Superfolding Element (SFE) Method. The results showed that the theoretical solutions were in good agreement with the finite element analysis results. The findings of this paper have the potential for energy absorption applications under different loading conditions.

Open holes and cutouts have been widely used in composite structures for various engineering purposes. However, perforation could largely alter the structural responses and crashing behavior, thereby creating significant challenge in composite design. This study carried out a parametric study and design optimization on the perforation parameters for the perforated carbon fiber reinforced plastic (CFRP) square tubes to improve the structural crashworthiness. First, a finite element model was established for perforated square tube through experimental validation. Second, the support vector regression (SVR) surrogate models of the crashworthiness indices were established with respect to the perforation design variables following a parametric study. It was found that the radius of the hole had the most significant effect on crashworthiness performance of the CFRP tube, followed by the height-to-length ratio and the offset-to-width ratio of the hole. Finally, the multiobjective optimization was performed to optimize the perforated parameters by integrating the surrogate modeling technique and multiobjective grey wolf optimizer (MOGWO). The optimal design enabled to enhance 100.47% in the specific energy absorption ( S E A ) (specifically from 29.61 J/g to 59.36 J/g) only with a minor sacrifice of 4.62% in the first peak load ( F m a x ) (from 81.22 kN to 84.97 kN).

© 2019 Elsevier Ltd The human masticatory system has received significant attention in the areas of biomechanics due to its sophisticated co-activation of a group of masticatory muscles which contribute to the fundamental oral functions. However, determination of each muscular force remains fairly challenging in vivo; the conventional data available may be inapplicable to patients who experience major oral interventions such as maxillofacial reconstruction, in which the resultant unsymmetrical anatomical structure invokes a more complex stomatognathic functioning system. Therefore, this study aimed to (1)establish an inverse identification procedure by incorporating the sequential Kriging optimization (SKO)algorithm, coupled with the patient-specific finite element analysis (FEA)in silico and occlusal force measurements at different time points over a course of rehabilitation in vivo; and (2)evaluate muscular functionality for a patient with mandibular reconstruction using a fibula free flap (FFF)procedure. The results from this study proved the hypothesis that the proposed method is of certain statistical advantage of utilizing occlusal force measurements, compared to the traditionally adopted optimality criteria approaches that are basically driven by minimizing the energy consumption of muscle systems engaged. Therefore, it is speculated that mastication may not be optimally controlled, in particular for maxillofacially reconstructed patients. For the abnormal muscular system in the patient with orofacial reconstruction, the study shows that in general, the magnitude of muscle forces fluctuates over the 28-month rehabilitation period regardless of the decreasing trend of the maximum muscular capacity. Such finding implies that the reduction of the masticatory muscle activities on the resection side might lead to non-physiological oral biomechanical responses, which can change the muscular activities for stabilizing the reconstructed mandible.

© 2017 Informa UK Limited, trading as Taylor & Francis Group. To reduce the scatter of fatigue life for welded structures, a robust optimization method is presented in this study based on a dual surrogate modelling and multi-objective particle swam optimization algorithm. Considering the perturbations of material parameters and environment variables, the mean and standard deviation of fatigue life are fitted using dual surrogate modelling and selected as the objective function to be minimized. As an example, a welded box girder is presented to reduce the standard deviation of fatigue life. A set of non-dominated solutions is produced through a multi-objective particle swam optimization algorithm. A cognitive approach is used to select the optimum solution from the Pareto sets. As a comparative study, traditional single objective optimizations are also presented in this study. The results reduced the standard deviation of the fatigue life by about 16.5%, which indicated that the procedure improved the robustness of the fatigue life.

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

© 1965-2012 IEEE. An analytical method for calculating the no-load magnetic field of external rotor permanent magnet brushless direct current motor (PMBLDCM) used as in-wheel motor of electric vehicle in the stator static coordinate and the rotor motion coordinate is presented in this paper. First, the analytic formulas of slotless permanent magnetic field in both coordinate systems are derived, respectively. Then, the complex relative permeance of external rotor PMBLDCM in both coordinate systems is calculated. Finally, the analytical solution of the no-load magnetic field in both coordinate systems is derived by applying the magnetic potential multiplied by the complex relative permeance. In this paper, a 46-pole-51-slot external rotor PMBLDCM is taken as an example, and the accuracy of the proposed analytical model is verified by the finite-element results. Based on the analytical model, the influences of the stator slotting effect on the no-load magnetic field of the external rotor and the inner stator are analyzed. The spatial order characteristics and frequency characteristics of the no-load magnetic field of the external rotor PMBLDCM in both coordinate systems are revealed, respectively.

The Changjiang (Yangtze River) Estuary plays an important role in the land-ocean interactions of East Asia, particularly in regard to the fate of land-derived materials and their impact on marine ecosystems in the Northwest Pacific Ocean. The 12 papers included in this special issue describe results from the MEcoPAM Study, an IMBER-China project, which occurred in 2011-2015. This project used a multi-disciplinary approach to understand ecosystem function of the Changjiang Estuary in response to multiple stressors (i.e. combined external forcings). The results presented here show that human activities in the watersheds have greatly changed the flux and variation of dissolved and particulate materials from the river. Further interactions between the Changjiang Watersheds and the East China Sea can dramatically modify the pathways of biogeochemistry and food web dynamics of the estuary and adjacent coastal environment at seasonal and inter-annual scales. (C) 2015 Elsevier B.V. All rights reserved.

This editorial article introduces the research progress of IMBER-China Study on “Sustainability of Marine Ecosystem Production under Multi-stressors and Adaptive Management” (MEcoPAM), funded by the Ministry of Science and Technology of China (MoST-China No. 2011CB409800). There are 12 research articles in this Special Issue of Deep-Sea Research II on the “East China Sea”, which provide the reader with snapshots of “Impact of Multi-stressors on the Structure and Function of Marine Ecosystems”, one of research foci of MEcoPAM in the period of 2011–2015.

The duration of embryonic development and the numbers of offspring and body lengths at sexual maturity of the biofouling amphipod Caprella acanthogaster at different temperatures were studied. Embryonic development was divided into nine stages: fertilized egg, cleavage stage, morula, blastula, gastrula, limb-bud stage, heart-beat stage, fully developed juveniles, and hatching juveniles. The duration of embryonic development was 196 h at 14 °C and 117 h at 20 °C. Temperature had a significant influence on maturation time and body length at sexual maturity ( P P > 0.05). Mean body lengths of juveniles, mean body lengths at sexual maturity, and maturation times at 14 °C were: 1.52 ± 0.17 mm, 10.14 ± 1.24 mm, and 33.20 ± 3.27 days, respectively; and at 20 °C, they were: 1.37 ± 0.07 mm, 6.66 ± 0.75 mm, and 18.17 ± 2.56 days. The number of offspring ( EO ) was positively correlated with the body length ( BL ). At 14 °C, the relationship was: EO = 7.74 BL − 39.66 ( R 2 = 0.75) and, at 20 °C, it was: EO = 13.69 BL − 78.15 ( R 2 = 0.77). Statement of relevance We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.

Water temperature can be a significant environmental stressor that affects the physiological and biochemical responses of mollusks. Yesso scallop, Patinopecten yessoensis, is influenced by water temperature fluctuations caused by the Northern Yellow Sea Cold Water Mass. Here, the effects of acute seawater temperature change, gradual temperature change, and fluctuating temperature on the physiological and enzymatic activities in Yesso scallop were studied. Scallops were transferred directly from rearing temperature (15 degrees C) to 5, 10, or 20 degrees C for the acute water temperature change treatment. Scallops in the gradual water temperature change treatment were acclimated to different temperatures (5, 10, and 20 degrees C) by increasing or decreasing seawater temperature progressively (1-2 degrees C/day). The results showed that oxygen consumption and ammonia-N excretion rates in the 20 degrees C-acute water temperature change treatment were significantly higher than those in the gradual treatment (one-way ANOVA, P < 0.01). However, scallop ingestion rate decreased significantly in response to an acute water temperature decrease from 15 to 5 degrees C, compared with equivalent groups exposed to a gradual temperature drop (one-way ANOVA, P < 0.01). Moreover, hepatopancreatic superoxide dismutase (SOD), catalase (CAT), acid phosphatase (ACP), and lysozyme (LSZ) activities reached their highest levels in the 20 degrees C-acute treatment after 12 h. Malondialdehyde (MDA) content increased significantly following the acute water temperature changes and reached the highest level in 10 degrees C-acute treatment after 72 h. Heat shock protein70 gene (Hsp70) expression levels also increased significantly when water temperature was increased rapidly from 15 to 20 degrees C or decreased rapidly from 15 to 10 degrees C (P < 0.01). In the fluctuation treatment, seawater temperature was altered every 12 h for a total of six fluctuations. Scallops were transferred directly from 15 to 7 degrees C (first fluctuation), moved from 7 to 15 degrees C for the next 12 h (second fluctuation), and then transferred from 15 to 7 degrees C again (third fluctuation) and so on. As results, significant increases in SOD and CAT activities and MDA content, and decreases in ACP and LSZ activities were observed (one-way ANOVA, P < 0.01). Significantly upregulated Hsp70 expression was also found in hemocytes, gills, and the adductor muscle of scallops in the fluctuating temperature treatment (one-way ANOVA, P < 0.01). In conclusion, acute water temperature changes and fluctuations impacted the physiological and enzymatic activities of Yesso scallops and upregulated Hsp70 expression. (C) 2015 Elsevier B.V. All rights reserved.

Seasonal distribution of dissolved nutrients (, , , , ) was measured in the Sanggou Bay (SGB), China. In order to understand the impact of rivers and of the Yellow Sea (YS) and the role of integrated multi-trophic aquaculture (IMTA) in nutrient reduction and dynamics. Seasonal surveys were conducted in spring (April), summer (August), autumn (October) and winter (January) in 2011–2012 along 19 stations covering culture areas. The summer was highly impacted by excess water discharge and aquaculture activities than benthic sediments source; however other seasons were mostly influenced by the YS. Results showed that nutrients were vertically mixed and IMTA helped in reducing the elevated nutrient concentration generated by water discharge and the mixing process. The N/P ratio indicated phosphate as a limiting nutrient. Historical values of nutrient data showed that the concentration of , and increased while decreased with slightly higher uptake rate of in the bay during the last decade. A simple mass...

Multi-cell structures have been extensively studied for their outstanding performance as potential energy absorbers. Unlike existing multi-cell tubes with a uniform thickness (UT), this paper introduces a functionally graded thickness (FGT) to multi-cell tubes under dynamic impact, which can be fabricated by an extrusion process. A numerical model is first established using the nonlinear finite element analysis code LS-DYNA and validated with experimental data. Based on a numerical study, the thickness gradient parameters in different regions have considerable effects on the crashworthiness of the FGT multi-cell tubes. Moreover, the FGT multi-cell tubes are able to absorb more energy while yielding a similar level of peak impact force to the UT multi-cell tubes. Finally, multiobjective optimizations of the UT and FGT multi-cell tubes are then performed to determine the optimal gradient parameters that simultaneously improve the specific energy absorption (SEA) and reduce the maximum impact force. In these optimizations, the multiobjective particle optimization (MOPSO) algorithm and response surface (RS) surrogate modeling technique are adopted. The optimization results demonstrate that the FGT multi-cell tubes produce more competent Pareto solutions than the conventional UT counterparts; similar gradients in the outer walls and stronger internal ribs are recommended for the FGT multi-cell tubes because of their improved interactions.

Multi-cell tubes have been drawn increasing attention for their excellent energy-absorbing ability. However, the effect of cell number and oblique loads on crashing behaviors has seldom been studied to date. In this paper, a group of multi-cell tubes with different cell numbers were comprehensively investigated under both axial and oblique loads. The finite element models were first established and then validated by experimental tests. The simulation results showed that the increase in cell number can be beneficial to the energy absorption ( EA ) but detrimental due to increase in peak force ( F max ) under axial load. When the oblique loads were taken into account, the tubes could undergo global bending, which is an inefficient deformation mode. By applying complex proportional assessment (COPRAS) method, the 7×7 tube was selected as the best based on multi-criteria under multiple loading angles. Then the Kriging modeling technique and multiobjective particle optimization (MOPSO) algorithm were integrated to address the optimization problems, where EA and F max were taken as objectives and tube sizes as design variables. The results demonstrated that different loading angles have different requirements on cell allocation and optimizations of multiple load cases (MLC) can yield better solutions in a weighted average fashion, whereas the optimization for separate single load cases (SLC) could result in inferior performance under other load cases.

A dissolved inorganic carbon (DIC) budget was constructed for Sanggou Bay, Shandong, China. This was based on field data on sea-air flux, primary production, river runoff, advection flux, etc. during four cruises from April 2013 to January 2014, and these data were combined with those taken from the literature related to sediment remineralization, annual river discharge, etc. Results showed that Sanggou Bay acted as a net importer of DIC. The DIC flux exchanged across the sea-air interface was the largest contribution to the net DIC input of this bay, comprising 59.3% of the total DIC net input. Other inputs, in order of importance, were sediment remineralization (18.1%), horizontal advection (16.7%), submarine groundwater discharge (4.2%) and river runoff (1.7%). Seaweeds ( Saccharina japonica and Gracilaria lemaneiformis ) as well as phytoplankton were greatly involved in the carbon biogeochemical cycle and acted to update inflowing DIC. The total amount of DIC sequestration caused by photosynthesis was about 1.36 × 10 5 t. Although forms of the scallop ( Chlamys farreri ) and oyster ( Crassostrea gigas ) absorb a certain amount of DIC into their shells, the DIC released from respiration and calcification processes counterbalance this sequestration. In terms of the bay scale, Sanggou Bay acted as a net DIC sink with an annual mean uptake of DIC estimated at 1.39 × 10 5 t. These findings provided powerful support for revealing the role of Sanggou Bay in the carbon cycle. Statement of relevance This study is relevant for understanding the effect of mariculture on the marine carbon cycle.

Crash components in automobiles are probably subjected to multiple loading conditions in real life, such as axial crushing and lateral bending. Unlike most of the existing work that solely focuses on the pure axial crushing or lateral bending, this paper attempts to accommodate both by proposing a novel structure, namely foam-filled thin-wall tube with functionally lateral graded thickness (FLGT). From numerical study of FLGT structures, they are found to exhibit noticeable advantage over the corresponding traditional uniform thickness (UT) structures with the same weight under both axial crushing and lateral bending. Moreover, the gradient governing the varying thickness shows significant influence on the crashworthiness performance of FLGT. To seek for the optimal gradient, a multi-objective optimization is carried out using multi-objective particle swarm optimization (MOPSO) algorithm, where response surface models are established to formulate the objectives functions, i.e. specific energy absorption (SEA) and peak impact force ( F peak ). The optimization results show that the foam-filled structure with FLGT can produce more promising Pareto solutions than traditional UT counterparts. Therefore, the FLGT structure could have potential applications subjected to different loading conditions.

As a relatively new component with a higher efficiency of material utilization, functionally graded thickness (FGT) structure with desired varying wall thickness has been becoming more and more attractive. In order to sufficiently understand the crashworthiness of FGT under lateral impact, firstly, the finite element (FE) models of thin-walled columns with uniform thickness (UT) and FGT under lateral loading are established and validated by experimental results. It is exhibited that the FE simulations are in good agreement with experimental tests. Then, the crashworthiness of UT tube and the corresponding FGT tube is compared, and the results reveal that the FGT tube can absorb more energy but generate larger force than UT tube under the same weight. Further, parametric analyses show the gradient exponent, wall thickness range, the tube diameter and yielding stress have significant effects on the crashworthiness of FGT tubes. Finally, a multiobjective particle swarm optimization (MOPSO) method is used to optimally seek for those design parameters, where surrogate modeling methods are adopted to formulate the specific energy absorption (SEA) and peak crushing force functions. The results yielded from the optimization demonstrate that the FGT tube is superior to its uniform thickness counterpart in overall crashing behavior under lateral impact. Therefore, FGT tubes are recommended as potential absorbers of crashing energy under lateral loading.

Ascidians are globally important members of marine fouling communities. We meas- ured in situ biodeposition rates of Ciona intestinalis and Styela clava, common biofoulers of aqua- culture infrastructure, in Sanggou Bay, northern China, during September. Ascidian numbers were recorded within a scallop Chlamys farreri farming zone to assess biodeposit loading. Both ascidians were most abundant on lantern nets and scallop shells in August and September. The average densities of C. intestinalis and S. clava in the farming zone in September were approxi- mately 329 and 22 ind. m −2 , respectively, and their biodeposition rates were 32.1 and 121.2 mg dry material ind. �1 d �1 , respectively. Total daily biodeposit production by ascidians in September within the scallop farming zone may amount to 13.24 g m �2 , with daily organic matter, C, N, and P biodeposition rates of 1.88, 0.94, 0.11, and 0.98 × 10 �2 g m �2 , respectively. The predicted daily biodeposit production by C. intestinalis and S. clava within the scallop farming zone in the bay during September was 105.9 t dry material, 7.52 t C, 0.86 t N, and 0.078 t P. By comparison, drop- off to the sea floor was approximately 143.0 t of dry matter for an entire growing season, which would be a relatively small input if averaged on a daily basis. However, some of the drop-off is expected to occur as a short-duration pulse of material (e.g. during cleaning), which may be rela- tively important in terms of benthic effects. The results suggest that the biodeposition processes and drop-off of C. intestinalis and S. clava may play an important role in coupling material fluxes from the water column to the seabed.

In calibrating model parameters, it is important to include the model discrepancy term in order to capture missing physics in simulation, which can result from numerical, measurement, and modeling errors. Ignoring the discrepancy may lead to biased calibration parameters and predictions, even with an increasing number of observations. In this paper, a simple yet efficient calibration method is proposed based on sensitivity information when the simulation model has a model error and/or numerical error but only a small number of observations are available. The sensitivity-based calibration method captures the trend of observation data by matching the slope of simulation predictions and observations at different designs and then utilizing a constant value to compensate for the model discrepancy. The sensitivity-based calibration is compared with the conventional least squares calibration method and Bayesian calibration method in terms of parameter estimation and model prediction accuracies. A cantilever beam example, as well as a honeycomb tube crush example, is used to illustrate the calibration process of these three methods. It turned out that the sensitivity-based method has a similar performance with the Bayesian calibration method and performs much better than the conventional method in parameter estimation and prediction accuracy.

© 2017, The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany. Many studies on energy absorbers have been focused on tapered tubes because they have significant advantages in crashworthiness and provide a desired constant load-deflection response. However, few studies have been reported on tapered tubes with nonlinearlyvariable diameters along the longitudinal direction. This paper presents thin-walled Functionally graded tapered tube (FGTT) with a diameter varying nonlinearly subject to axial (0°) and oblique (10°, 20°, 30°) impacts. To explore the advantages of FGTT, conventional Straight/Conical circular tube (SCT/CCT) with the same mass are compared; and FGTTs with a gradient exponent n > 1 are found to be preferable to others in terms of energy absorption capacity under small impact angles. Then, crashworthiness analyses of different crushing distances are conducted and it is found that under a large impact angle (e.g. 20°, 30°), FGTT with a short crushing distance (e.g. 40 mm) have a higher mean crashing force than long crushing distance (e.g. 120 mm), especially for n > 1. In addition, the effect of geometric parameters, such as the gradient exponent n and diameter range ΔD between top (incident) and bottom (distal) diameters of FGTTs, are also studied and it is found that the FGTT with ΔD = 40 mm and n > 1 exhibits better crashworthiness than the others under small impact angles (0°, 10°). This paper demonstrates that such FGTT structures have a certain potential to be an energy absorber.

Multicell tubal structures have generated increasing interest in engineering design for their excellent energy-absorbing characteristics when crushed through severe plastic deformation. To make more efficient use of the material, topology optimization was introduced to design multicell tubes under normal crushing. The design problem was formulated to maximize the energy absorption while constraining the structural mass. In this research, the presence or absence of inner walls were taken as design variables. To deal with such a highly nonlinear problem, a heuristic design methodology was proposed based on a modified artificial bee colony (ABC) algorithm, in which a constraint-driven mechanism was introduced to determine adjacent food sources for scout bees and neighborhood sources for employed and onlooker bees. The fitness function was customized according to the violation or the satisfaction of the constraints. This modified ABC algorithm was first verified by a square tube with seven design variables and then applied to four other examples with more design variables. The results demonstrated that the proposed heuristic algorithm is capable of handling the topology optimization of multicell tubes under out-of-plane crushing. They also confirmed that the optimized topological designs tend to allocate the material at the corners and around the outer walls. Moreover, the modified ABC algorithm was found to perform better than a genetic algorithm (GA) and traditional ABC in terms of best, worst, and average designs and the probability of obtaining the true optimal topological configuration.