A brief overview of the School of Aerospace Engineering of Tsinghua University

Nanxiang GUAN,Bing WANG,Luming LI

School of Aerospace Engineering,Tsinghua University,Beijing 100084,China

KEYWORDS Aerospace engineering;Funding;Publication;Research activity;Student education

Abstract This article provides a brief overview of the teaching and research at the School of Aerospace Engineering(SAE)to celebrate the 80th anniversary of the establishment of aeronautics as a discipline at Tsinghua University.The evolution of the school,undergraduate/graduate students and faculty members,and research activities and achievements have been described.The research input including research funding and research projects are summarized,showing a diversity of funding sources and a significant growth in either sum total or spending per researcher.The achievements including publications and inter/national academic awards are also introduced.It can be seen that the level of academic publications has been growing over the past decades.In addition,four representative research achievements have been briefly described to show the scientific contributions of the school.

1.Introduction

The discipline of aviation and mechanics at Tsinghua University originated in the 1930s,with the aeronautical engineering research division being founded in 1934.This was the earliest one of its kind in China,and was later evolved into an institute in 1936.The Department of Aeronautical Engineering was established in 1938,and was reorganized as the School of Aeronautical Engineering in 1951.However,this school was separated from Tsinghua University due to adjustment of disciplines and departments of higher education all around China in 1952.1

To cultivate talents for space engineering,the Department of Engineering Mechanics(DEM)was set up in 1958.Forty years later in 1998,the Space Center was established.Two significant milestones of the Space Center are two launches of university satellites in 2000 and 2004.On May 18,2004,the School of Aerospace Engineering(SAE)was re-established,appointing Prof.Yongzhi Wang as the Dean,who was a member of the Chinese Academy of Engineering and the first chief designer of the Chinese manned space engineering program.

Fig.1 Hierarchical structure of the SAE.

At present,the SAE has two departments,the DEM and the Department of Aeronautical and Astronautical Engineering(DAAE),as shown in Fig.1.The Space Center is also managed by the SAE.The DEM has four institutes:Institute of Solid Mechanics,Institute of Fluid Mechanics,Institute of Biomechanics and Medical Engineering,and Institute of Engineering Thermophysics.The DAAE has six institutes:Institute of Engineering Dynamics,Institute of Aircraft and Spacecraft Design,Institute of Propulsion Engineering,Institute of Man-machine Environment Engineering,Institute of Space Information Techniques,and Center of Aero-engine.2To promote the development of cross-disciplinary research on aeronautical and astronautical science and technologies,the school has organized several joint-research centers across the departments of Tsinghua University and between the institutes in related fields.

Based on the advantages of research on mechanics and thermophysics,the school has gradually established a system of disciplines related to aerospace.

This article summarizes the current status of the SAE,introduces the undergraduate and graduate programs offered by the school,as well as research activities including funding and projects,publications and typical research achievements.

2.Students and faculty members

2.1.Undergraduate programs

The undergraduate programs offered by the SAE lasts four years,with each year having three semesters.Each year,the school enrolls approximately 130 students in the undergraduate programs including Mechanical Engineering,Power&Thermal Physics,and Aeronautics&Astronautics.The school currently has 516 undergraduate students,with the student teacher ratio being around 5:1.

The SAE now offers more than 80 undergraduate courses,with four courses being taught in English,and the school will continue to develop English or bilingual courses in the next ten years.To obtain the Bachelor’s degree,students are required to earn 171 credits,with 117 credits for specialty courses(86 credits for spring/autumn semester courses;15 credits for thesis completion;the others for practical training in summer semesters),44 credits for general courses,and 10 credits for non-specialty courses.

Further information on the under graduate programs offered by the SAE can be found in Ref.3.

2.2.Graduate programs

The SAE currently has 664 graduate students,70%of whom are doctoral students.The school now has had 13 international students,including 7 doctoral students and 6 graduate students,since it began to enroll international students three years ago.

The core courses offered for the doctoral students consist of three major modules:philosophy,mathematics,and specialty courses.The core courses offered for the master students consist mainly of three modules:philosophy,foreign languages,and specialty courses,and it generally takes one year to complete the master’s degree courses.

Further information on SAE graduate programs can be found in Ref.3.

2.3.Faculty members

The SAE currently has 120 faculty members,including 105 teachers,of which 52 are professors,46 are associate professors,and 7 are assistant professors.4The age distribution of the faculty members is shown in Fig.2(a).The final education background of the faculty members is shown in Fig.2(b),with graduates from Tsinghua University,other universities,and overseas universities accounting for 60%,20%,and 20%,respectively.

2.4.Employment of students

The employment rates of our students at the year of graduation are shown in Fig.3.

In 2017,the SAE had 117 graduates(113 obtained the bachelor’s degree,and 4 obtained the certificate of completion),and the graduation rate is 96.6%.According to the statistics by the Ministry of Education,the employment rate of the undergraduates enrolled in 2013 is 97.62%(further study was also counted as employment).There were 19 students who went abroad for further study,accounting for 22.6%,of whom 13 went to American universities such as the Massachusetts Institute of Technology and the University of Pennsylvania;3 went to the University of Cambridge;2 went to the University of Tokyo.A total of 45 students were selected to further their study at domestic universities,accounting for 53.6%,of whom 44 chose to continue their study at Tsinghua University.

The employment rate of the SAE master students remains very high.For example,the employment rate of the graduate students in the 2017 was 94.62%,a slight decrease from the previous year.There are 35 master’s degree graduates in 2017,of whom 29 are contract employees;5 choose to continue their study.There are 58 doctoral degree graduates in 2017,of whom 33 are contract employees;19 choose to continue their study.

Fig.2 Basic data of faculty members.

Fig.3 Employment rates of graduates in the past five years.

3.Research activities

In the SAE,scientific research is very active.A number of scientific research indicators,proposed by the university,rank the SAE at the forefront compared to the other schools and departments of Tsinghua University.The school has made breakthroughs in research funding,projects,high-level papers,scientific and technological awards,and major scientific research platforms.This section cannot include all the details of the scientific research in the school,but only gives an overview of some key points such as funding,projects and publications.

3.1.Research funding4,5

Since its establishment in 2004,the SAE has been very active in the research and application in the field of aerospace.The total annual research funding of the school has been steadily increasing,as shown in Fig.4.In 2011,the research funding exceeded 100 million Yuan,which is over quadruple that given in 2004.Since then,the annual funding has been over 100 million Yuan each year.

3.2.Diversity of scientific research projects4,5

The number of newly signed research projects at SAE has been increasing each year,including the projects funded by the National Natural Science Foundation of China(NSFC),the Ministry of Education,the Ministry of Science and Technology,the National Development and Reform Commission,the Ministry of Industry and Information Technology,the China Aerospace Science and Technology Corporation,as well as collaborative projects and international cooperation projects.

Fig.4 Research funding(2004–2017).

For example,159 new projects were signed and the total funding for the projects reached 127 million Yuan in 2017,as shown in Fig.5.

Table 1 shows the number of newly granted projects by NSFC,which is an important index representing the level of devotion to fundamental research.In the past 5 years,the number of projects is generally close to 30 per year,and the research funds are around 25 million Yuan per year.

Fig.5 Composition of research funding in 2017(Unit:104 Yuan).

Table 1 Projects supported by NSFC since 2004.

3.3.Publications4,5

Since 2004,the number of papers published by the SAE faculty has been increasing each year.Fig.6 shows the papers indexed in Web of Science Database.Table 2 shows the number of SCI-indexed papers and that per capita.It can be seen that in recent years,the number of papers per capita maintains around 2.5.

Fig.7 shows the papers published over the last 5 years in the authoritative international journals including Nature,Science,Journal of Fluid Mechanics(JFM),AIAA Journal(AIAA),Journal of Mechanics and Physics of Solid(JMPS),and Journal of Guidance,Control and Dynamics(JGCD).

3.4.Other academic activities

The faculty members are active in many international academic organizations,including the executive member of International Union of Theoretical and Applied Mechanics(IUTAM),the executive chairman and Vice Chairman of the Organizing Committee of 2018 International Heat Transfer Conference,Co-director of International School of Space Optics UN,the American Institute of Aeronautics and Astronautics(AIAA)Fellow and Associate Fellow.

Fig.6 Papers indexed in Web of Science(2004–2017).

Fig.7 Publications in authoritative journals(2013–2017).

Approximately 20 professors serve as associate editors of international academic journals,including AIAA Journal,The Aeronautical Journal,Experimental Mechanics,IMA Journal of Applied Mathematics,Computer Modeling in Engineering&Sciences,International Journal of Fatigue,Heat Transfer Research,and Acta Mechanica Sinica.

3.5.National and international awards/honors4,5

From 2004 to 2017,the faculty members from the SAE have gained 13 national awards for scientific research or technological invention,as shown in Table 3.It can be seen that the research outputs are competitive among the top-ranked universities in China.

Besides the national awards,some faculty members have obtained international academic honors and awards.For example,Prof.Shouwen YU was awarded the PioneeringNational Leader Award of IFEES(The International Federation of Engineering Education Societies)for his outstanding contribution to engineering education in 2012.Prof.Zengyuan GUO won the Outstanding Achievement Award granted by the Asian Thermal Science Society in 2017.Prof.Wei Yang was awarded the Warner Koiter Medal by the American Society of Mechanical Engineering(ASME)to commend his contribution to the field of solid mechanics in 2017.Associate Prof.Yihui ZHANG was voted one of MIT Technology Review’s 35 Innovators Under 35(MIT TR35)in 2016.

Table 3 National awards.

Table 2 Annual SCI-indexed papers(2004–2017).

In addition,some invention patents authored by the faculty members have won golden awards at international exhibitions such as the International Exhibition of Inventions of Nuremberg and International Exhibition of Inventions of Geneva.

Fig.9 NS-1(model figure).

4.Representative research achievements

The SAE has obtained many influential achievements in both fundamental and applied research.Here,we introduce four of our representative research achievements,including Design of Micro/Nanosatellites,Discovery and Modelling of Superlubricity,Mechanically-guided Assembly Approach,and Thermomass Theory and Its Applications.

4.1.Design of micro/nanosatellites

On June 28,2000,a micro-satellite—Space Tsinghua-1,as shown in Fig.8,weighing 50 kilograms and having a volume of 0.77 cubic meters,was successfully sent into space and entered the700 km sun-synchronous orbit.The microsatellite carried the payloads such as CCD cameras,data storage and forwarding communications,and radio signal processing and transmission equipment.On the morning of June 29,2000,the ‘‘Tsinghua-1” ground station successfully captured the signal sent from space,and then the minimum system test,as well as testing of software upload,altitude control,signal transmission and reception,camera load,and GPS receiver,was successfully performed.

Fig.8 Space Tsinghua-1.

On April 19,2004,the satellite ‘‘NS-1” with a weight of approximately 25 kilograms and a volume of approximately 0.04 cubic meters was successfully launched,as shown in Fig.9.Through the space station of the Aerospace Center,the SAE completed all the measurement and control experiments of the satellite independently.The ‘‘NS-1” nanosatellite and ground station is a successful innovation that has reached the international advanced level.As an experimental satellite,the main tasks of this satellite include tests on micro-satellite orbit retention and orbit change,CMOS camera imaging for ground test,satellite program uploading and software testing.After it entered the intended orbit,it has been monitored and controlled by the ‘‘NS-1” nanosatellite ground station developed by Tsinghua University,and on-orbit experiments are also conducted by the school.

On September 4,2014,a smart communication experimental satellite with a weight of 131.2 kg,a flight orbit altitude of 780 km,and a mission assessment life of one year,as shown in Fig.10,was launched at the Jiuquan Satellite Launch Center,and successfully entered the intended orbit.This satellite is mainly used for tests on satellite multimedia communication.After the satellite entered the intended orbit,a large number of on-orbit tests were conducted,realizing the communication between hand-held satellite terminals,communication between hand-held satellite terminals and mobile phones,internet data transmission,and electromagnetic spectrum monitoring and positioning.

4.2.Discovery and modelling of superlubricity

The research group of Prof.Quanshui ZHENG discovered the sliding behaviors of van der Waals(vdW)layered media and established a mechanical model for the behaviors.

Fig.10 Overall view of smart communication satellite.

vdW layered media constitute a large class of materials.Typical examples are graphite and multi-walled carbon nanotubes that are made of multilayers of graphene.vdW media have strong intralayer chemical bonds and weak interlayer vdW forces,which give rise to many unique and extreme mechanical properties including high anisotropy and ultra low interlayer shear resistance.Since 2000,the team has led pioneering and in-depth theoretical and experimental studies on structural superlubricity and continuum mechanics models for vdW media,and has obtained the achievement as follows:

(1)Discovery of structural superlubricity.The dream of achieving ‘‘zero” friction at solid interfaces is a longpursued goal of scientists.It was predicted in 1990 that incommensurate interfaces could host nearly zero friction,named as structural superlubrictiy,however,only at nanoscale under ultrahigh vacuum condition and at a low sliding speed.In 2012,Prof.Zheng’s team reported the first observation of micrometer-scale superlubricity at ambient conditions and speeds of up to 25 m/s(Fig.11).6The discovery has been recognized as a break-through advancement by the leading experts in the field,and has attracted enormous research interests.The success of the experiment is contributed to another discovery by the team--self-retraction motion of graphite crystal(Fig.12),7where vdW interaction was revealed as the driving force.8Based on this unique phenomenon,the team designed novel experimental tools to study structural superlubricity and measure the cohesive energy of the vdW media.The team was also the first to conduct mechanistic studies on the self-retraction motion driven by the vdW force.

(2)Continuum mechanics models:The team revealed that the novel elastic buckling behaviors of vdW layered media stem from the extremely high anisotropy in elastic constants,which can reasonably explain some anomalous experimental observations reported in Science in 1997 and 1999).9The team found that graphite has the highest elastic anisotropy among all hexagonal crystals,and single walled carbon nanotube bundles have even higher elastic anisotropy.10The team developed the first mechanical model for single walled carbon nanotubes,taking into account all elastic constants,elastic anisotropy,and size effect(Fig.13).11A multi-beam shear model was proposed to explain the anomalous vibrational behaviors of graphene-multilayer beams,see Fig.14.12In Fig.14,MD is Molecular Dynamics,MBSM is Multibeam Shear Model,EBM is Euler–Bernoulli beam Model,f is resonant frequencies and n is layer number.And a model for strength and toughness design of vdW layered media was proposed based on their microstructures and interlayer cross-links.13

Fig.12 Self-retraction motion of graphite crystal.7

Their research has greatly advanced the progress of solid mechanics and relevant interdisciplinary fields,and provides theoretical insights for the practical design of highperformance micro/nano structural materials with ultra-low friction and wear.

Eight representative papers of the team have been SCI-cited 592 times,including Science,Nature and Review of Modern Physics.The team members have been invited to give plenary keynote talks over 10 times.Their work has been positively commented by many prominent researchers including Nobel Laureates A.K.GEIM and K.S.NOVOSELOV,and famous scholars home and abroad such as Academy Members Ted B.BELYTSCHKO,Huajian GAO,Joost W.M.FRENKEN,Wei YANG,and Jianbin LUO.Their research is also the first to win special funding from the National Basic Research Program of China(973 Program).

4.3.Mechanically-guided assembly approach

Fig.11 Superlubricity and incommensurate.6

Fig.13 Mechanical model for single walled carbon nanotubes.11

Assoc.Prof.Yihui ZHANG from the SAE has made pioneering contributions to the development of a brand-new approach for assembly of complex 3D mesostructures through mechanically-guided deterministic buckling of 2D micro/nanomaterials.14–19This approach is characterized by its applicability not only to a diversity of materials(e.g.,semiconductor,polymer,metal,and many other high-performance materials),but also to a broad range of length scales(e.g.,from nanometer to centimeter scales).To understand the underlying relations between the 3D buckling configurations and fabrication parameters,his group developed the analytic mechanics models of post-buckling in ribbon-shaped mesostructures as the guidelines for material/geometry designs.20,21When combined with strategically designed release sequences and 2D precursors,this approach allows access to the reconfigurable 3D mesostructures that can be switched between different stable states.22Their work provides a new route for fabrication of advanced 3D micro/nanodevice systems,which allows transformation of virtually any type of existing 2D microsystem technology into a 3D configuration(Fig.15).23For example,the group has proposed novel designs to enable tunable Radio Frequency(RF)devices,concealable electromagnetic devices,highly-integrated 3D softelectronics,and self-propelled micro-robots.16,23–25

Their research has been published in many top journals(e.g.,Science,and Nature/Science sister journals),of which three papers were featured as cover articles in Science,Nature Materials,and Nature Reviews Materials.Eight representative papers of Zhang’s group have been cited over 400 times in ISI Web of Science,as of June 2018.Three of these papers were selected as ‘‘ESI Highly Cited Paper” in ISI Web of Science.Their work has already stimulated specific interests and many fundamental/applied research projects in this area,as evidenced by a number of famous research groups in the world(from seven different countries)who followed this area and carried out further studies.In recognition of his academic accomplishments,Zhang was selected by MIT Technology Review as one of the 35 innovators under 35(TR35),and was marked as one of the eight ‘‘pioneers” in the annual list in 2016.He was also invited to deliver one of the five plenary lectures at the 11th International Conference ‘‘Shell Structures:Theory and Applications”(held every four years),and several keynote/invited lectures at major international conferences(e.g.,ASCE-EMI,SES and IMECE symposia).

4.4.Thermomass theory and its applications The Thermomass theory was developed by Prof.Zengyuan GUO’s group from the SAE.In 2013,their research entitled Key Scientific Problems of Thermomass Theory was granted a subversive major project funded by the NSFC,which is the third subversive project in NSFC history.The concept of entransy and its applications in energy systems was awarded TOP 10 Research Fronts by Thomson Reuters in 2014.Based on the concept of thermomass defined by the mass-energy relation according to Einstein’s special relativity,the phonon gas in the dielectrics is a weighty compressible fluid.This means that heat is of the dual nature of energy and mass,that is,heat acts as energy during its conversion with other forms of energy,while heat acts as mass during its motion because,unlike other kinds of energy form,heat is conserved during the irreversible transport process.

When the heat flux in the device is so large that the inertial force of the phonon gas cannot be neglected,the Fourier’s law breaks down even under steady state conditions.The momentum conservation equation for the weighty phonon gas is then established as in fluid mechanics,which is just the general heat conduction law and will degenerate to three non-Fourier’s models under different simplified conditions.The general relation between the heat flux and temperature gradient can be deduced from phonon Boltzmann equations with the concept of thermomass,which is very close to the general heat conduction law.A more general macroscopic heat conduction law for nanosystems is presented based on the phonon gas dynamics in a porous medium,where the Darcy’s term represents the volume resistance,and the Brinkman term represents the surface resistance.Size reduction leads to the increase of relative importance of the Brinkman term,and consequently to the decreases of thermal conductivity of nanomaterials.An explicit expression for the size dependent thermal conductivity of silicon nanosystems is obtained,which agrees well with the experimental results for both nanowires and nano films.

Fig.14 A multi-beam shear model of graphene-multilayer beams.12

Based on analogy among heat conduction,electric conduction and fluid flow in the porous medium,a new quantity,thermomass potentialenergy,is introduced.Its simplified expression is the entransy,which is not conserved during heat transfer processes due to its dissipation.Entransy dissipation is the measure of irreversibility of the heat transfer process not related to the conversion from heat to work.For the simple heat transfer system,the entransy dissipation-based thermal resistance,rather than the entropy generation rate,should be taken as the criterion to optimize the heat transfer process or simplify heat transfer systems in the sense of energy saving.For complex heat transfer systems,we need to use the entransy balance equation as the overall system constraints to analyze or optimize the thermal performance of systems as a whole.

In summary,the thermomass theory includes the subversive innovations as follows:(A)contrary to the traditional concept that heat is a form of energy,heat should be of the dual nature of energy and mass;(B)subverting the assertion of the authority of heat transfer,Joseph Fourier that heat phenomena cannot be connected with dynamic theories,heat conduction can be described using the fluid dynamics method based on the thermomass concept;(C)overthrowing the prevailing viewpoint that the minimum entropy leads to the best heat transfer performance,entransy dissipation should be the optimization criterion of heat transfer process.

Fig.15 Schematic illustration of steps for fabricating 3D mesostructures by the mechanically-guided assembly method.23

5.Conclusive remarks

This paper has given a brief introduction to the SAE of Tsinghua University,including its current resources,students and faculty members,and teaching and research activities.The school has made an impressive development over the last 80 years.In the assessment of the school disciplines organized by The Ministry of Education of China,the discipline of Mechanics and the discipline of Energy&Power Engineering have both gained A+,and the discipline of Aeronautical and Astronautical Science and Technology has been ranked top.It is believed that the SAE will achieve even greater success in the future.

Acknowledgements

Prof.Ziniu WU put forward many constructive suggestions for the writing of this article;Ms.Yue ZENG and Ruxia MA helped to collect data;Profs.Quanshui ZHENG,Zengyuan GUO,Xing ZHANG,Yihui ZHANG,and Changqing JIANG proofread Section 4 of this article.