Minimum Weight Design Research Articles

공액경사법을 이용한 LPG 운반선 화물창 내부구조물 중량최소화 설계

Since the cargo tank of LPG carriers is made of expensive low-temperature steel that can maintain its function even at -50oC, the reduction of cargo tank materials has been a major concern for shipyards to improve price competitiveness. The purpose of this study is to minimize the weight of the web frames and stringers that form the interior of the cargo tank of the LPG carriers. A total of 92 design variables including 6 shape-related design variables were selected for the minimum weight design. In order to reduce the time required for the optimization process, the conjugate gradient method, which is a gradient-based optimization technique, was adopted. In addition, for the structural analysis, the cargo tank located at the second position in the bow was selected as the structural analysis target, and in order to improve the reliability of the analysis, a boundary condition considering the deformation of the entire ship for each loading condition was applied to the partial model. As a result of the study, it was confirmed that the error rate did not exceed the maximum 3% by comparing the maximum stress value generated in all internal structures for the entire model structure analysis and the partial model one. A total of 92 dimensions with the minimum objective function were determined, and the weight was reduced by about 39 tons per cargo tank.

Experimental Analysis and Finite Element Modeling of S-Core Sandwich Panel Composites Drop Impact Response

Sandwich panel composites have several applications in material technology. The sandwich panel composite material is constructed of stainless steel-316 for the top and bottom plates, aluminum 1050A-0 for the core, and DP-8405 acrylic adhesive for the binding element. The impact behavior of S-core composite sandwich panels was examined using low-velocity drop impact tests and finite element models. Finite element models have been created to characterize the influence of composite element bending behavior on variations. The specific flexural modulus and strength of composite S-core sandwich structures are equivalent to those found in the literature for core structures. As a result, the minimum weight design served as a guideline for producing weight and density-efficient hybrid composite sandwich panels. The energy absorbed in the test findings rose between 15.15% and 30% as the core thickness grew and between 3.571% and 41.34% as the core arrays changed. Impact load-bearing capability increases with varied core heights and array designs.

Compression properties of glued laminated timber and tensile properties of gluelam lamellas from oil palm wood

ABSTRACT When oil palm lumber is considered for load-bearing products such as glued laminated timber (GLT), defined strength and stiffness values are required. In this investigation, combined GLT from oil palm wood is tested in compression parallel and perpendicular and glulam lamellas in tension parallel to the vascular bundles. Strength and Young´s modulus in compression and tension parallel increase with the density by power law relationship. In contrast to dicotyle­dons, the strength in construction size exceeds that of small, defect-free test specimens (compression strength perpendicular), are in the same range (tensile and bending strength parallel) or only a little below (compression strength parallel). The specimen size does not influence the strength. The ratio of fc,0 : fm : ft,0 is 1.2 : 0.8 … 1.7 … 2.6 : 1 and fc,0 : fc,90 = 2.7 … 13.0 … 32.6 : 1 for ρ = 200 … 400 … 600 kg/m³; the ratio of Ec,0 : Em : Et,0 is 1.2 : 1.3 : 1 for ρ = 400 kg/m³. Ashby´s performance indices for minimum weight design rise with the density; the strength-density performance indices are comparable or only slightly lower than that for structural size softwood, whereas the modulus-density performance indices are much lower. The challenge in use of oil palm wood for load-bearing construction products is the low stiffness.

Experimental and theoretical study on the response of the X-frame CFRP sandwich beam under the local impulsive loading

The impact resistance of the carbon fibre reinforced X-frame sandwich beam and its foam reinforced structure was investigated experimentally and theoretically. To simulate the blast loading on the composite sandwich beams, the aluminum foam projectiles were utilised to impact the composite specimens. Under the local impulsive loads of the different intensities, the core shear failure, core crushing and skin fracture of the sandwich beams were observed by using a high-speed camera. A theoretical model for the dynamic response of the fibre-reinforced composite sandwich beam under the impact loads was constructed. Three phases, namely the local compression, the propagation of global bending/shearing wave and global stretching were considered in this theory. The theoretical model can provide the reasonable deflection history and failure modes of the sandwich beam compared with the experimental and simulated results. The impact pressure between the foam projectile and the beam were obtained by the theoretical and numerical predictions. The results indicated that the decreasing of the structural density can reduce the transmitted impulse. The optimal design charts were constructed by introducing the normalised variables based on the theoretical model. The minimum weight design revealed that the composite sandwich beams with low-density cores generally had the better specific impact resistance, while the foam-filled sandwich beams with the higher density had the outperformed impact resistance at the low impulse. It is expected that the theoretical model can provide a useful reference for predicting the impact resistance of the fibre-reinforced composite sandwich structures.

Investigation of temperature effect on the optimal weight design of steel truss bridges using Cuckoo Search Algorithm

In this article, the optimum weight design of steel truss bridges is carried out by considering the effect of temperature. One of the most significant issues such structures may encounter throughout their service life is the extreme temperature changes that can occur for various reasons. If a steel bridge is designed without considering this unfavorable scenario that might arise in the future, significant damage could happen in terms of the usability limit state, and it might even collapse by exceeding its carrying capacity before reaching its service life. Therefore, this study aims to conduct weight optimizations of steel truss bridges, considering the effect of temperature. Thus, it has been revealed how high-temperature variations alter material properties and affect the overall optimum weight of the structure. For this purpose, the minimum-weight designs of three planar steel truss bridges previously analyzed by other researchers have been re-evaluated using the Cuckoo Search Algorithm. The main program containing the flow steps of the algorithm based on the finite element method is coded in MATLAB. Stress and displacement limit values are used as constraints in solving the problems. The optimum weight results for each structure in the case of temperature effect not being considered are relatively similar. Thus, it has been demonstrated that the Cuckoo Search Algorithm can optimize such problems by comparing its results with similar studies in the literature. Then, the analyses are renewed by incorporating the temperature effect using this proven method. When the findings of both cases are examined, it is observed that the optimum weight values for all structures under the influence of temperature increase. This is due to the decrease in the material's modulus of elasticity because of the high-temperature change. In this case, the cross-section is insufficient owing to the loss of rigidity, and larger profiles are needed. The structure's weight tends to increase depending on the severity of the temperature. Also, numerical simulations of the structures under the same conditions are carried out with SAP2000 software to supplement the design optimization analyses detailed above and enrich the research content.

Optimization of key joints

Key-joints are used in many drives and rotating elements in engineering practice. Nowadays decreasing the dead-weight of the structures is more and more important (in vehicle industry, aircrafts, etc.). This paper shows an optimization process for minimum weight design of key-joints. For the solution of the optimization problem a 3D grapho-analytical optimization process is used, based on the Kuhn–Tucker optimality criterium. During the graphic part of the process, three dimensional diagrams show the behaviour of the objective function and of the design constraints, which makes easy to read the optimum solution from the diagram. The final optimum solution is given in a table numerically too. For better demonstration, the finite element analysis of the three dimensional CAD model of the optimal joint is shown.

Experimental and FEM investigation of bending behaviors of S-core sandwich panel composites

Sandwich panel composites have numerous applications in material technology. The sandwich panel composite structure’s mechanical behavior and performance are determined by the material properties and geometry of the relevant components. The top and bottom sheets of the designed sandwich panel composite material are made of stainless steel-316, the core material is aluminum 1050A-0, and the binding element is DP-8405 acrylic adhesive. Three-point bending tests and finite element models were utilized to investigate the bending behavior of S-core composite sandwich panels. Finite element models have been developed to characterize the effect of composite element bending behavior on variations. The specific flexural modulus and strength of composite S-core sandwich structures can be compared to core structures in the literature in general. As a consequence, the minimum weight design was used as a guideline to produce weight and density-efficient hybrid composite sandwich panels. The load-carrying capacity of the composite panel increased as the wall thickness of the S-shaped core increased when the damage loads were examined in the variations. It has been ascertained that as the core height increases, the load-carrying capacity of the composite panel decreases.

An efficient LightGBM-based differential evolution method for nonlinear inelastic truss optimization

A metaheuristic-based structural optimization method, whilst being popularly adopted due to its advantages in by-passing gradient function calculations, requires the use of time-consuming advanced analyses for constraint evaluation. To overcome this drawback, the present paper proposes a robust (machine learning-based) optimization method that combines the light gradient boosting machine (LightGBM) with the efficient p-best differential evolution (EpDE) method. In essence, the LightGBM classification model is constructed to assess the constraint (safety and integrity) satisfaction of structures. An efficient framework using a so-called safety parameter is proposed to prevent inaccurate predictions of the LightGBM model. The EpDE processes the optimization procedures on the constructed classification LightGBM model. This enables an enhanced machine learning-based optimization technique that not only maintains the sufficiently accurate optimal design of structures but also significantly reduces the required computing efforts, as compared to standard optimization schemes. Various examples of steel structure designs (i.e., two of which have been provided herein) have been successfully performed by the proposed approach. These illustrate the accuracy and robustness of the proposed method, where good comparisons with reference algorithms (including standard DE with “DE/rand/1” mutational strategy, Jaya, Rao-1 and CaDE) are evidenced. The statistical values collected present the accuracy and reliability of the proposed method in obtaining the minimum total weight designs with substantial (some 60%) reduction of computing efforts required to furnish optimal results.

Minimum weight design of CNT/fiber reinforced laminates subject to a frequency constraint by optimal distribution of reinforcements across the thickness

Present work involves minimization of the weight of a three-phase, glass and carbon nanotubes (CNT) reinforced angle-ply laminate, subject to a fundamental frequency constraint. Design variables include the optimal (nonuniform) distributions of the fibers and the CNTs across the laminate thickness, the stacking sequence, ply angles and ply thicknesses. In order to assess the effect of different design variables on weight minimization, a sequence of five different optimization problems is solved with an increasing number of design variables. The present approach has the advantage of comparing and assessing the effectiveness of different sets of design variables on the design efficiency and identifying the ones which are more effective in minimizing the weight. Design efficiency is defined as the ratio of the weight of the optimal laminate to the weight of a plate which is not reinforced, but subject to the same frequency constraint. It is observed that fiber and CNT reinforcements are used most effectively if placed close to or in the outer layers. It is also observed that CNT reinforcement affects the optimal values of the ply angles due to the fact that the directional properties of the fibers become less pronounced as the matrix is reinforced by CNTs.

Optimum design of steel frames with sizing and orientation design variables using a reformulated evolution strategy

Sizing optimization of steel frame structures has been traditionally conducted based on fixed orientations of structural members. However, it seems more expedient to search for an optimum design where orientations of column members are considered as design variables together with sizing of all members for the minimum weight design of a steel frame. In order to solve the resulting optimization problem effectively, a reformulated evolution strategy (ES) algorithm is proposed and employed in the present study. The numerical investigations are carried out using three test problems regarding the optimum design of steel space frames. In each test problem, a frame is first designed for the minimum weight considering sizing design variables only, where initial orientations of the column members are kept unchanged. Next, sizing and orientation design variables are considered simultaneously for minimizing the weight of the same frame. The results obtained in the foregoing two cases are compared and the associated optimal layouts for the column orientations are depicted. The study reveals that the optimal selection of column orientations has a significant influence on the minimum weight design of steel frames.

Minimum Weight Design of Transversely Stiffened Plate Girder Using Genetic Algorithm

Fundamental advantage of using transversely stiffened plate girders (TSPG) rather than plane web plate girders is in achieving increased strength and stiffness of the web panel. As these girders are made of steel plates, they can be custom designed to suit consumer's requirements. Weight minimization of TSPG by satisfying strength and serviceability conditions, further enables in achieving higher strength to weight ratios. The utilisation of these girders in the building sector in India is growing, and optimising these girders can lead to more cost-effective and structurally sound designs. No significant research has been carried out in the field of optimization of plate girders based on specifications according to IS 800 (2007): General Construction in Steel - Code of Practice (Bureau of Indian Standards). Therefore, in the present study, the main goal is to develop a formulation for optimum weight design of TSPG using genetic algorithm (GA) with weight minimization as objective function. The breadth of flange (bf), thickness of flange (t_f), depth of web (d), thickness of web (t_w), breadth of stiffener (b_s), thickness of stiffener (t_s) and spacing between stiffeners(c) are adopted as the design variables. The optimum girder weight is compared with weight obtained through conventional design using IS 800 (2007). The results demonstrate that conventional design overestimates the girder weight by about 30% on an average and therefore the developed formulation helps in attaining economical girder weight. The viability of the GA formulation is verified by comparing the optimized results with existing experimental and numerical data from literature. Parametric studies are also carried out to understand the behaviour of design variables. Results from these studies show that deeper web reduces flange thickness but requires thicker web in order to ensure ample shear capacity and to prevent shear buckling.

Minimum weight design of reinforced concrete beams utilizing grey wolf and backtracking search optimization algorithms

In this study, optimal weight design of a reinforced concrete beam subjected to various loading conditions is investigated. The purpose of the optimization is to attain the minimum weight design of the reinforced concrete beam under distributed and two-point loads. The design problem is handled under three different design load cases. The two-point loads are affected on beam-to-beam connection nodes of reinforced concrete beams. Thus, while the magnitudes of distributed load and two-points load are remained constant, the distances between two-points loads are taken as 2m, 3m and 4m, respectively. The width and height of the rectangular cross-section of the concrete beam, and the diameters of the longitudinal and confinement steel rebars are treated as design variables of the optimum design problem. The design constraints of the optimization problem consist of the geometric constraints and necessities of the Turkish Requirements for Design and Construction of Reinforced Concrete Structures (TS500), and Turkish Building Earthquake Code (TBEC). As two novel metaheuristics, grey wolf (GW) and backtracking search (BS) optimization algorithms are selected as optimizers. Both algorithms are independently operated five times for three different design problems. Thus, the obtained results are examined statistically to compare in accordance with algorithmic performances. The optimal findings from optimization algorithms show that the GW algorithm is a little bit more robust on the exploitation phase, while the BS algorithm is stronger on the exploration phase. Moreover, it can be deducted from optimal beam designs that the GW algorithm is more viable to minimize reinforced concrete beam design.

고유진동수 제한을 갖는 골조구조의 GA 기반 최적설계 시스템

Normal strategy of structure optimization procedure has been minimum cost or weight design. Minimum weight design satisfying an allowable stress has been used for the ship and offshore structure, but minimum cost design could be used for the case of high human cost. Natural frequency analysis and forced vibration one have been used for the strength estimation of marine structures. For the case of high precision experiment facilities in marine field, the structure has normally enough margin in allowable stress aspect and sometimes needs high natural frequency of structure to obtain very high precise experiment results. It is not easy to obtain a structure design with high natural frequency, since the natural frequency depend on the stiffness to mass ratio of the structure and increase of structural stiffness ordinary accompanies the increase of mass. It is further difficult at the grillage structure design using the profiles, because the properties of profiles are not continuous but discrete, and resource of profiles are limited at the design of grillage structure. In this paper, the grillage structure design system under the constraint of high natural frequency is introduced. The design system adopted genetic algorithm to realize optimization procedure and can be used at the design of the experimental facilities of marine field such as a towing carriage, PMM, test frame, measuring frame and rotating arm.

Three-point bending behaviors of the foam-filled CFRP X-core sandwich panel: Experimental investigation and analytical modelling

To enhance the energy absorption capacity of the sandwich structures, the foam filled composite X-core sandwich panels were fabricated by a hot-press molding technology. The bending behaviors of the empty and hybrid composite sandwich panels were investigated by the three-point bending tests. Analytical models and finite element models were developed to characterize the bending behaviors and the interaction effect between the foams and composite members. Generally, the specific bending modulus and strength of composite X-core sandwich structures are comparable to that of the competing cellular structures. The theoretical expressions can provide useful predictions of the bending stiffness and initial failure load, whilst the numerical models had a higher accuracy. A failure mechanism map was constructed to highlight the effect of geometry parameters on the failure modes. A minimum weight design was employed to provide a guideline for obtaining the weight-efficient hybrid composite sandwich panels.

Optimum Design of Aft-swept Composite Wings for Aeroelastic Characteristics with Structural Damping

The present paper deals with the aeroelastic characteristics of aft-swept composite plate wings with structural damping. Based on the complex modulus approach, a minimum weight design of cantilevered laminated plates with a sweep-back angle under the flutter and divergence speed constraints is conducted by using a differential evolution in which lamination parameters are used as design variables.

A Dynamic Programming Approach to the Design of Composite Aircraft Wings

A light and reliable aircraft has been the major goal of aircraft designers. It is imperative to design the aircraft wing skins as efficiently as possible since the wing skins comprise more than fifty percent of the structural weight of the aircraft wing. The aircraft wing skin consists of many different types of material and thickness configurations at various locations. Selecting a thickness for each location is perhaps the most significant design task. In this paper, we formulate discrete mathematical programming models to determine the optimal thicknesses for three different criteria: maximize reliability, minimize weight, and achieve a trade-off between maximizing reliability and minimizing weight. These three model formulations are generalized discrete resource-allocation problems, which lend themselves well to the dynamic programming approach. Consequently, we use the dynamic programming method to solve these model formulations. To illustrate our approach, an example is solved in which dynamic programming yields a minimum weight design as well as a trade-off curve for weight versus reliability for an aircraft wing with thirty locations (or panels) and fourteen thickness choices for each location.

Failure analysis of brazed sandwich structures with square honeycomb-corrugation hybrid cores under three-point bending

In this work, the bending stiffness, initial failure load, initial failure modes and minimum mass design of square honeycomb-corrugation hybrid core sandwich structures (SHCH) subjected to bending were explored by a combined theoretical analysis, experimental testing, and numerical prediction method. Samples were fabricated by brazing process and measured under three-point bending. To theoretically obtain the initial failure mechanism map, six different initial failure modes were taken into account, which agree well with associated experimental data and numerical results. It is found that honeycomb filler not only changed the failure mode of corrugated core sandwiches but also enhanced dramatically its bending resistance. Then the minimum weight design is achieved as a function of load index, and the effect of key factors, including honeycomb relative density, loading platen width, material parameters, and inclination angle are quantified. Furthermore, the mechanical performances of SHCHs are compared with the competing structures.

Optimality criteria-based minimum-weight design method for modular building systems subjected to generalised stiffness constraints: A comparative study

Recently, modular building construction has gained massive momentum as it continues to help many cities around the globe to tackle the ongoing housing crisis and the pressing demand for healthcare facilities during the pandemic. As a relatively new structural solution, there is a need to study modular buildings' optimal design. In this regard, previous studies focused only on employing optimisation techniques at the member level to enhance the structural capacity of steel beams in modular building systems (MBS). This paper explores the applicability and effectiveness of an optimality criteria (OC)-based minimum-weight design method in reducing self-weight of MBS while maintaining their overall lateral stiffness measured by natural frequency. This is achieved by pursuing an innovative optimisation investigation involving a three-storey, standalone MBS with hinged inter-module joints, together with a comparative moment-resisting frame (MRF) benchmark structure with two different beam-column connection rigidities. Continuous-valued sizing optimisation of two structural systems under a single frequency constraint is achieved through a novel, numerically stable, iterative OC algorithm. The latter is developed from frequency-related OC formulated rigorously through the Lagrange multiplier approach. The discrete minimum-weight design is supported by a mapping strategy designed to round the continuous optimum to the most economical standard steel sections. Pertinent numerical results show that the proposed method can achieve significant steel savings for the adopted MBS without compromising its modal stiffnesses. Further, it is found that the MRF structure with semi-rigid connections can meet the same target frequencies with slightly smaller steel tonnages. It is envisioned that this study will pave the way towards achieving more resilient and cost-effective modular units and tall modular buildings that further support the building industry in meeting its goals of construction efficiency and sustainability.

Compact Steam Bottoming Cycles: Minimum Weight Design Optimization and Transient Response of Once-Through Steam Generators

Compactness and weight minimization are key aspects for successful and widespread implementation of waste heat recovery steam cycles in off-shore oil and gas platforms due to the site weight and volume footprint constraints. The power plant off-shore must be designed for flexibility in its operations to provide varying power demands across multiple time scales. Reliability of the heat and power production units is crucial. Within a case study in an off-shore platform in the Norwegian Continental Shelf, this article conducts design optimization of compact and low-weight steam cycles for power production from gas turbine exhaust and transient analysis of the core of heat recovery steam generators (HRSGs) via dynamic modeling and simulation, considering once-through steam generators (OTSGs) for the HRSGs. A method for simultaneous thermodynamic and heat exchanger geometry optimization design for bottoming cycles is applied, with the main objective being weight minimization and compactness of the cycle heat exchangers. Ten different optimal minimum weight bottoming cycle designs are provided by selecting ten different manufacturable tubes. The resulting bottoming cycle designs are compared in terms of weight, OTSG core weight distribution, heat transfer area, and footprint. The resulting bottoming cycle weight varies from 48.4 to ca. 87.10 ton for designs sensible for off-shore applications, and from 95.8 to 178.9 ton when selecting outer tube diameters typical of onshore applications. Smaller outer tube diameter selection in OTSG bundles is a key driver for low-weight and compact steam cycle designs. Three different designs representing light, normal, and heavy OTSG designs are compared by dynamic trajectory and response time analysis under transient scenarios by means of dynamic modeling and simulation. More compact and lighter designs respond faster to changes in the gas turbine (GT) operation upstream the OTSG. The results in this analysis indicate the need for feedforward control. Feedback control alone is probably not a good option due to the high OTSG open loop stabilization time and large sensitivity to GT exhaust gas variations. More compact and low-weight designs based on the OTSG can reduce potential challenges in controlling and stabilizing bottoming cycles for power production.

Minimum Weight Design of Pitched Roof Steel Frames.(Dept.C)

The optimum elastic design of p itched roof frames has been studied. An iterative method which uses Taylor's first order series expansion to express the various required constraints is employed. The function of the problem is linear in the design variables, which enables the simp lex line ar programming algorithm to be used to solve the problem, An example of rectangular hall has been investigated. The hall is cove red by pitched roof frames with different sp ans, spacing and slop es. Stress and deflection limitations are taken into consideration and the optimum cross-sectional area of the various members of the structure has been obtained. Design charts to determine the minimum weight of p itched roof frames, with different sp ans, spacing and slopes, covering a rectangular hall are given.