Lin Hao's academic career

Lin Hao is a famous expert in hydraulic engineering and earthquake engineering in China, mainly engaged in seismic research of dams and nuclear power plants. 195 1 year, Lin Hao graduated from the Department of Civil Engineering of Tsinghua University, and then entered Harbin Institute of Technology and Dalian University of Technology for postgraduate studies in hydropower utilization. 198 1 became the first doctoral supervisor in China. 1997 was elected as an academician of China Academy of Sciences. Academician Lin Hao experienced the development of dam construction in China from the primary stage to the advanced stage. While solving practical problems, his research level gradually improved until he entered the advanced ranks in the world.

From the early days of the People's Republic of China to the 1960s, the first high tide of dam construction rose in China. Carrying forward the spirit of self-reliance and independent innovation, China has designed and built a number of dams, the height of which exceeds 100 meters, which makes China enter the ranks of dam construction in the modern world. 1956, the first hyperbolic arch dam project in China was built on Liuxi River in Guangdong. Well-known experts, led by chief engineer Pan, put forward the scheme of dam flood discharge by picking flow. This scheme can save a lot of engineering investment, keep the discharged water away from the dam foundation and ensure the safety of the dam foundation. It is more advanced than the dam crest turnover scheme abroad at that time. However, the impact of fluctuating vibration of water flow caused by jet flow on dam safety has become a huge challenge for the project.

With the support of domestic authoritative mechanics experts Professor Qian Lingxi and Professor Dai Zongxin, Academician Lin Hao, who graduated from the graduate class for only two years, bravely undertook the task of experimental research. Although everything starts from scratch, Academician Lin Hao and his research team are full of confidence. After unremitting efforts, they developed rubber model materials and built the first mechanical vibration table in China. At first, they successfully developed a sensor for measuring model vibration in China, put forward the model similarity law of arch dam vibration, initiated the measurement of fluctuating pressure on dam crest and the study of water flow fluctuation law, and designed an experimental device for dam vibration response caused by fluctuating vibration. In less than two years, the vibration test of the first arch dam model in China has finally been completed, which provides technical support for the realization of the dam crest pick-up scheme. The evaluation of books and periodicals in the former Soviet Union holds that "the model research is meticulous, the scientific level is high, and the measuring instruments are advanced".

65438-0958 According to the needs of the earth dam project in Maojiacun, Yili River, Yunnan Province, Academician Lin Hao led the first earthquake-resistant test of the earth dam model in China, and the research results were selected as foreign technical exchange materials by the Ministry of Water and Electricity. Academician Lin Hao also carried out the longitudinal bending seismic stability test of the first pier and dam model in China, and put forward the seismic response calculation model of arch dam and gravity dam. These works have laid a foundation for the seismic research of China dam.

At the end of 1970s, China entered the era of reform and opening up, and the dam construction in China entered a new climax. A large number of high dams from 100 m to 200 m have been built one after another, and the dam-building technology has reached a new height, and the dam seismic technology in China has gradually matured.

The research team led by Academician Lin Hao undertook the task of seismic safety evaluation of Baishan Arch Dam and Fengman Gravity Dam, the highest dams in China at that time. In the absence of equipment and funds, a new experimental technology-direct photography is proposed. The researchers designed, manufactured and made a light electromagnetic vibration table. The 9 th mode shapes and frequencies of Baishan arch dam and the 4 th mode shapes and frequencies of Fengman gravity dam are obtained with relatively simple equipment, which is intuitive and clear. At that time, Japan used electromagnetic excitation method for model test, and Britain used finite element method for dynamic analysis of arch dams. Only the 3-4 vibration modes and frequencies of arch dams and the 2-3 vibration modes and frequencies of gravity dams can be obtained. On this basis, Academician Lin Hao's team also developed a dynamic model failure test technology for simulating material gravity dams and arch dams, and simulated earthquake failure modes at various excitation levels, which won favorable comments in international exchanges. Academician Lin Hao and others also put forward the arch beam modal method for dynamic and static analysis of arch dams, which further improved the calculation efficiency and accuracy.

Around the new century, hydropower energy construction in China has entered a rapid stage, and a number of 300m dams close to and exceeding the world's top level have been and are under construction. The world dam building center has turned to China, and China ranks first in the world in dam number, dam height, dam scale and technical difficulty. These dams are built in the upper reaches of the Yangtze River and the Yellow River in China, and the designed seismic acceleration far exceeds the highest level in history, so the seismic safety of dams has become one of the key technical problems to be solved in the design. Before 1990s, the design seismic acceleration of dams built in China was generally less than 0. 15g~0. 16g. However, when Xiaowan Arch Dam (292m high) and Xiluodu Arch Dam (282m high) were completed around 2000, the design seismic acceleration had been increased to 0.308g and 0.312g respectively, while the design seismic acceleration of Dagangshan Arch Dam (2 10/0m high) which will be completed soon. Supported by the three key projects of the National Natural Science Foundation and the national key scientific and technological projects, the scientific research team led by Academician Lin Hao has made unremitting efforts to overcome technical difficulties.

The first thing to do is to reform the traditional calculation model, calculation method and evaluation system, including a series of complex technical problems such as foundation, reservoir water and the influence of transverse joints. In the existing foundation design, the massless foundation model is generally used to simulate the influence of foundation on the seismic response of arch dams, but this ignores the dissipation of vibration energy by infinite foundation. According to the actual seismic observation results of some arch dams in Switzerland, the massless model will give too conservative calculation results. Some researchers at home and abroad try to deal with this complex problem with boundary element method, infinite element method and transmission boundary method, but there are many problems such as heavy calculation workload, poor calculation stability and unsatisfactory calculation accuracy. Moreover, due to the complexity of calculation, the foundation can only be simplified into a uniform medium for treatment. But in fact, the foundation of arch dam is complex and uneven, which has an impact on the seismic safety of arch dam.

Academician Lin Hao believes that we can't stay in the original framework, and we must adopt new ideas and new methods to solve problems. Academician Lin Hao and others have discovered an effective calculation method-proportional boundary finite element method through continuous exploration. This method only needs to be discretized on the boundary of the calculation domain, which reduces the dimension of the problem by one dimension and saves a lot of calculation work. In particular, this method can conveniently deal with the anisotropy of foundation medium and the change of modulus of foundation medium along a certain law. Based on this, academician Lin Hao's team took the lead in studying the influence of complex heterogeneous foundation such as weak interlayer in foundation, discontinuous interface in foundation and the increase of foundation modulus along the depth on the seismic response of arch dam. Through the research, the understanding of seismic response of arch dam-foundation system is obviously deepened.

The dynamic interaction between arch dam and reservoir water is also a complex technical field. For many years, the simplified formula of Westergaard has been used to calculate the ground motion water pressure in dam seismic design. However, according to chopra's research, the compressibility of reservoir water and the absorption of hydrodynamic pressure wave by reservoir boundary are important factors to be considered. Chopra et al. use finite element method to solve the problem, which has a great discrete workload for the three-dimensional reservoir of arch dam. The calculation model and method he proposed are very complicated and complicated, and it is difficult to popularize and apply in practical projects. For this reason, many researchers have improved it and solved it by boundary element method, thus reducing the order of the problem to one dimension. However, the amount of work BEM spends on numerical calculation of the basic solution is almost enough to offset the amount of work saved by dimension reduction, and the final calculation matrix is asymmetric and full, which increases the difficulty of solving. Therefore, the boundary element method is basically only extended in the case of two-dimensional gravity dams.

The finite element method of proportional boundary proposed by Academician Lin Hao and others can easily solve these problems. It can not only deal with the problem of reservoir water compressibility and reservoir boundary absorption conveniently, but also discretize the three-dimensional arch dam-reservoir hydrodynamic interaction problem on the dam surface under the condition of prism reservoir, which greatly saves the calculation workload and is greatly convenient for popularization and application in engineering. Academician Lin Hao used this calculation model to study the influence of reservoir geometry of three-dimensional arch dam and two-dimensional gravity dam on dam-water coupling vibration, and expounded the influence of reservoir geometry change, the absorption of hydrodynamic pressure wave by reservoir boundary, the frequency response function of dam ground motion and the distribution law of hydrodynamic pressure along dam surface. The research level of dam-water coupled vibration is raised to a new height.

After cracks appear on the upstream surface of concrete dam, the influence of hydraulic fracturing on dam safety has been widely concerned. The calculation model established by academician Lin Hao and others by using the proportional boundary finite element method can conveniently and accurately calculate the influence of the variation law of water pressure in cracks on the stress intensity factor and fracture characteristics of cracks, so as to evaluate the stability of cracks under earthquake reasonably and properly.

In the traditional design, the arch dam is regarded as a whole structure to calculate the seismic response, but in fact, the arch dam is built in blocks. The earthquake damage experience of Baikema arch dam in the United States under strong earthquake shows that during strong earthquake, the transverse joints of arch dam will open, the tensile stress of arch will be released and the seismic stress of arch dam will be greatly adjusted. The transverse joint calculation model established by academician Lin Hao on the basis of non-smooth equations is more accurate and convergent than the existing models at home and abroad. The transverse joints of arch dams are connected by keyways, but the existing calculation models at home and abroad generally simplify the transverse joints into flat joints for calculation. Academician Lin Hao and others studied the rationality of this simplification and found that the structural form of transverse joint keyway has an influence on the change law of transverse joint opening and the change of seismic stress of arch dam.

In domestic and foreign codes and standards, the quasi-static analysis method or Newmark rigid slider method is generally used to analyze the stability of potential sliding bodies of dam foundation and abutment under earthquake, which is difficult to reflect the transient and reciprocating deformation characteristics of sliding bodies under earthquake. Therefore, Academician Lin Hao improved the contact judgment algorithm of the three-dimensional DDA model and realized the seismic dynamic stability analysis of the three-dimensional wedge-shaped sliding body. The results show that there are essential differences between dynamic stability and quasi-static stability, and the deviation between them increases with the increase of earthquake excitation acceleration. The research results were invited to be published as a keynote report at the 5th World Dam Engineering Conference held in Lisbon, Portugal in 2007.

The research work of academician Lin Hao and others has also developed the numerical simulation method of earthquake damage and failure process of concrete dams and the calculation model and method of earthquake risk.

Academician Lin Hao's team comprehensively developed and improved the calculation model of seismic action of arch dams and gravity dams, which made China's dam seismic technology enter the world's advanced ranks, and its research results won the first prize of scientific and technological progress of the Ministry of Education.

The seismic damage of concrete dams is mainly manifested as dynamic damage and fracture, and the dynamic strength and deformation characteristics of concrete have become the controlling factors of dam seismic damage, but this is a weak link in the current seismic research of concrete dams. The dynamic characteristic of concrete is its speed sensitivity. Under the action of different dynamic loads such as earthquake, impact and explosion, the dynamic characteristics of concrete have also changed greatly with the great change of loading rate. Since 1950s and 1960s, due to military needs, the research on dynamic characteristics of concrete has been greatly developed internationally. However, this kind of research mainly focuses on the characteristics of nuclear explosion: monotonous loading, small specimen and mainly compressive strength, so its application in seismic design has its limitations. Academician Lin Hao and others took the lead in obtaining the dynamic strength and deformation law of concrete under the conditions of variable amplitude and cyclic load by studying more than 2,000 specimens, which reflected the characteristics of earthquake load. Through research, it is further found that environmental factors such as temperature and humidity and initial static load amplitude affect the speed sensitivity of concrete. By observing and analyzing the fracture characteristics of specimens under different strain rates, a new understanding of the rate-sensitive mechanism of concrete is obtained. These research results are published in famous magazines such as ACI Materials Magazine and Concrete Research Magazine. , and was invited to independently write a chapter in the book Cement, Concrete and Composite Materials: Processing, Properties and Applications to introduce the research results.

As an important clean energy, nuclear power is developing vigorously in China. The seismic adaptability evaluation of nuclear power plant foundation determines the safety of seismic design of nuclear island structure and equipment, and is an important constraint factor for site selection. Academician Lin Hao is responsible for evaluating the seismic adaptability of the foundations of many nuclear power plants in China. Strongly weathered xenoliths were found during the foundation excavation of No.3 and No.4 nuclear islands in Hongyanhe Nuclear Power Station, Liaoning Province, and the uneven characteristics of the foundation were prominent. This complicated basic geological condition of nuclear island is the first time in China nuclear power construction. There is no similar experience in the world, so it is quite difficult to deal with it. The calculation model proposed by Academician Lin Hao provides a scientific basis for the evaluation of seismic adaptability of complex foundation of nuclear power plant, saves a lot of engineering investment and ensures the construction progress as planned. On this basis, the adaptive range of site foundation parameters for the standard design of PWR nuclear power units independently developed by China is further clarified, which accelerates the process of nuclear power autonomy in China. The influence of parameter uncertainty on the seismic response of nuclear power structures and equipment is also an important content of seismic adaptability evaluation of nuclear power plant foundation. Academician Lin Hao developed and improved the probabilistic statistical calculation model of ground motion, uncertainty of foundation and material characteristics, which made the evaluation of seismic adaptability of foundation closer to reality, more reasonable and more scientific.

Academician Lin Hao also led students to deepen the research on proportional boundary finite element, an efficient and accurate numerical simulation method, and further developed its application in new fields such as electromagnetism, geometry and other parameters, which won high praise in international exchanges.