33 0

자동차 충돌안전도를 고려한 등가정하중법 기반의 구조최적설계

Title
자동차 충돌안전도를 고려한 등가정하중법 기반의 구조최적설계
Other Titles
Structural Optimization for Automobile Crashworthiness Based on the Equivalent Static Loads Method
Author
이영명
Alternative Author(s)
Lee, Youngmyung
Advisor(s)
박경진
Issue Date
2017-02
Publisher
한양대학교
Degree
Doctor
Abstract
충돌안전도는 구조물이 승객을 보호하는 능력이다. 각국의 정부 및 보험회사는 충돌안전도에 대한 다양한 평가방법을 제정하였다. 일반적으로 구조물의 변형된 형상, 변형에너지, 전달되는 하중뿐만 아니라 인체부위에서 발생하는 가속도 응답을 대상으로 충돌안전도를 평가한다. 이에 산업은 제품설계에 유한요소법을 이용하여 충돌안전도를 고려한 구조최적설계를 하고 있다. 그러나 충돌해석은 시간영역에서 강체운동 및 유연체운동을 포함할 뿐만 아니라 기하비선형, 재료비선형, 접촉비선형을 수반한다. 이러한 충돌문제는 민감도 해석이 어려워 비선형 동적 응답 구조최적설계의 적용이 어렵다. 따라서 이러한 난점을 극복할 수 있는 구조최적설계 방법이 필요하다. 등가정하중법은 비선형 동적 응답 구조최적설계 방법으로 외부루프(충돌해석)와 내부루프(선형 정적 응답 구조최적설계)를 반복하는 설계주기를 통해 최적해를 산출한다. 따라서 충돌문제의 특징을 내부루프에서 반영하는 것이 필요하다. 본 연구에서는 등가정하중법을 기반으로 자동차 충돌안전도를 고려하는 전략 및 방법을 제안한다. 충돌문제의 수렴성을 향상시키기 위해 이동제한전략을 적용하였다. 충돌해석의 불침투조건을 내부루프에서 간접적으로 고려하기 위해 변위제한조건을 이용하였다. 경계조건이 없는 구조물에 관성제거법을 이용하여 내부루프의 강성행렬에 발생하는 특이를 방지하였다. 준정적시험인 천장강도시험에서 자동차를 누르는 강체벽의 힘을 고려할 수 있는 강제변위법을 제안하였다. 위상최적설계에서 낮은 상대밀도의 요소를 삭제하는 갱신방법을 제안하였으며 하이브리드 셀룰러 오토마타와 비교하여 약 1/5 수준의 해석만으로 유사한 위상을 도출하였다. 또한 등가정하중으로 산출한 머리모형 충돌해석의 변위장으로 유한차분법을 이용해 가속도 응답을 산출하였으며 필터로 잡음을 제거한 후 머리상해지수를 고려하였다. 제안한 방법은 실제적인 대형 충돌문제의 충돌안전도를 고려하여 검증하였다. 정면충돌시험에서 크래쉬 매니지먼트 시스템의 전면 부 침입에 대한 제한조건을 만족하였다. 측면충돌시험에서 B-필라 침입에 대한 승객의 생존공간을 확보하는 구조최적설계를 효과적으로 수행하였다. 천장강도시험에서 자동차를 누르는 강체벽의 힘에 저항하는 최적화에 있어 구조물의 반력을 향상시켰다. 측면충돌시험과 천장강도시험을 동시에 고려하여 B-필라 보강재의 개념을 도출한 후 치수 및 형상최적설계로 상세설계를 수행했다. 머리상해지수를 제한조건으로 자동차 천장 내장재의 치수최적설계 수행하였으며 머리상해지수를 최소화하는 자동차 후드 보강재의 개념을 도출하였다. 모든 예제는 규정에서 정한 충돌안전도를 만족하면서 동시에 질량을 절감하였으며, 충돌안전도를 향상시킬 수 있는 위상을 도출할 수 있었다. 제안한 방법은 대형 충돌문제의 충돌안전도를 대상으로 적은 해석으로 최적해를 도출해 우수성과 유용성을 증명하였다. 제안한 전략과 방법론은 고려한 등가정하중법 기반의 구조최적설계 방법은 산업의 실제적 수준의 복잡한 문제에 적용이 가능함을 보였다. |Crashworthiness is the ability of the structure to protect passengers. Globally, governments and insurance companies have proposed various evaluation methods for crashworthiness. Crashworthiness is evaluated not only based on the structural responses, such as the deformed shape of the structure, strain energy, and transmitted force, but also based on the acceleration and reaction force response of test dummy parts, such as the head and chest, in a crash test event. Automotive industries have researched the crashworthiness for the product design using a structural optimization that is based on the finite element method. The crash analysis is a highly nonlinear phenomenon which includes rigid body motion and flexible body motion as well as large geometrical nonlinearity, material nonlinearity, and contact nonlinearity in the time domain. Thus, it has been difficult to implement a nonlinear dynamic response structural optimization based on the sensitivity method for the crashworthiness problem. To overcome these difficulties, a novel structural optimization method is required. The equivalent static loads method (ESLM) is a nonlinear dynamic response structural optimization method that repeatedly performs the outer loop of crash analysis and the inner loop of linear static structural optimization to find the optimum solution. The characteristics of the crash problem should be considered in the inner loop optimization process. This research proposes a strategy and method on the ESLM for the automobile crashworthiness application. The convergence efficiency is improved on an industrial scale crashworthiness problem, when the move limit strategy is applied. The impenetrability condition in the crash analysis is converted to displacement constraints in the inner loop. The inertia relief method is applied to avoid singularity of the linear stiffness matrix that has no boundary conditions. Using the characteristics of the quasi-static roof crush test, the reaction force of the structure that resists the rigid wall is considered using the enforced displacement method. In topology optimization, the update design method is proposed by eliminating the element that has a lower relative density. This method could generate a similar material layout result using 1/5 level of the number of the crash analyses, compared to the hybrid cellular automata (HCA) method as in the case of a typical cantilever plate problem. The safety index, HIC (Head Injury Criterion) is calculated using the finite difference method in the inner loop. The proposed methods are validated through various automobile crashworthiness cases, of which the finite element models are in an industrial scale crashworthiness problem. In the frontal crash event, the intrusion is considerably reduced by satisfying the intrusion distance constraint. In the side impact crash test, the survival space of the occupant is secured by optimizing the B-pillar design with regard to the intrusion constraint. In the roof crush test, the reaction force of the structure is improved at the critical intrusion limit. The requirements of the side impact crash test and the roof crush test are simultaneously considered to find the conceptual design of B-pillar reinforcement and additional detailed design is carried out using size and shape optimizations. The size optimization for the roof interior of the vehicle is carried out by considering the HIC as a constraint and the topology optimization for the vehicle hood is carried to minimize the HIC. In all the examples, the regulation requirements for the crashworthiness is satisfied while the mass is reduced, and the optimal material layout that enhances the crashworthiness is derived. The proposed method could generate an optimum solution in terms of major crashworthiness of a crash problem with less crash analysis. The case study results demonstrate the efficiency and the effectiveness of the proposed ESLM method and prove that the method can be applied to sophisticated practical industrial problems.
Crashworthiness is the ability of the structure to protect passengers. Globally, governments and insurance companies have proposed various evaluation methods for crashworthiness. Crashworthiness is evaluated not only based on the structural responses, such as the deformed shape of the structure, strain energy, and transmitted force, but also based on the acceleration and reaction force response of test dummy parts, such as the head and chest, in a crash test event. Automotive industries have researched the crashworthiness for the product design using a structural optimization that is based on the finite element method. The crash analysis is a highly nonlinear phenomenon which includes rigid body motion and flexible body motion as well as large geometrical nonlinearity, material nonlinearity, and contact nonlinearity in the time domain. Thus, it has been difficult to implement a nonlinear dynamic response structural optimization based on the sensitivity method for the crashworthiness problem. To overcome these difficulties, a novel structural optimization method is required. The equivalent static loads method (ESLM) is a nonlinear dynamic response structural optimization method that repeatedly performs the outer loop of crash analysis and the inner loop of linear static structural optimization to find the optimum solution. The characteristics of the crash problem should be considered in the inner loop optimization process. This research proposes a strategy and method on the ESLM for the automobile crashworthiness application. The convergence efficiency is improved on an industrial scale crashworthiness problem, when the move limit strategy is applied. The impenetrability condition in the crash analysis is converted to displacement constraints in the inner loop. The inertia relief method is applied to avoid singularity of the linear stiffness matrix that has no boundary conditions. Using the characteristics of the quasi-static roof crush test, the reaction force of the structure that resists the rigid wall is considered using the enforced displacement method. In topology optimization, the update design method is proposed by eliminating the element that has a lower relative density. This method could generate a similar material layout result using 1/5 level of the number of the crash analyses, compared to the hybrid cellular automata (HCA) method as in the case of a typical cantilever plate problem. The safety index, HIC (Head Injury Criterion) is calculated using the finite difference method in the inner loop. The proposed methods are validated through various automobile crashworthiness cases, of which the finite element models are in an industrial scale crashworthiness problem. In the frontal crash event, the intrusion is considerably reduced by satisfying the intrusion distance constraint. In the side impact crash test, the survival space of the occupant is secured by optimizing the B-pillar design with regard to the intrusion constraint. In the roof crush test, the reaction force of the structure is improved at the critical intrusion limit. The requirements of the side impact crash test and the roof crush test are simultaneously considered to find the conceptual design of B-pillar reinforcement and additional detailed design is carried out using size and shape optimizations. The size optimization for the roof interior of the vehicle is carried out by considering the HIC as a constraint and the topology optimization for the vehicle hood is carried to minimize the HIC. In all the examples, the regulation requirements for the crashworthiness is satisfied while the mass is reduced, and the optimal material layout that enhances the crashworthiness is derived. The proposed method could generate an optimum solution in terms of major crashworthiness of a crash problem with less crash analysis. The case study results demonstrate the efficiency and the effectiveness of the proposed ESLM method and prove that the method can be applied to sophisticated practical industrial problems.
URI
http://dcollection.hanyang.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000099132https://repository.hanyang.ac.kr/handle/20.500.11754/124814
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > MECHANICAL ENGINEERING(기계공학과) > Theses (Ph.D.)
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE