How to summarize the work of the drawing review center
"20": read as [Ni] à n] It is a numeral; It can be composed of four histories, ~ two histories, ~ four styles, etc“ The radical of "20" is "Zhen"
Twenty
twenty Pinyin: Ni à n. Four strokes: AGHG, Cangjie: T, zhengma: EA, Sijiao: 44770
structure: single, code: 1700, location: 5605
interpretation: twenty four histories
< H2 > extended data
strokes of Chinese characters:
Related words: only three
1, 24 pile [Ni] à n s ì ī]
the cemetery of palace people in the Southern Song Dynasty
(2) twenty two histories à n è r sh ǐ]refers to 22 histories
3 à n s ì sh ǐ]
is the Twenty-Four Histories
homophone: read, read
1. Read Pinyin: Ni à N
definition:
1. Thinking, often thinking: thinking. Miss. Ideas (thoughts, ideas). Mourning. Nostalgia. Chanting
2. Intention, idea, view: idea. distracting thoughts. Faith
(2) pronouncing Pinyin: Ni à Ninterpretation: the same as "Nian". Read. Such as: study; Read poetry
just for personal point of view, don't spray if you don't like it, thank you.
< number >
twenty. Later, he wrote "Nian"
six months in March—— The book with his wife by Lin Juemin in Qing Dynasty
tianshaohe on the 22nd—— Yuan Hong's travels to Manjing in Ming Dynasty[ On the evolution of heaven by Huxley and Yan Fu
It is a closed container with neck, which is equivalent to a spring vibrator system. The air in the container is equivalent to the spring, and the inlet air is equivalent to the object connected with the spring. When the frequency of the incident sound wave is consistent with the natural frequency of the system, the air column at the neck of the resonator vibrates violently, and the friction damping between the air and the neck wall transforms the sound energy into heat energy. Its resonance frequency f0 (Hz) can be obtained from the following formula:
where V is the volume of the resonator cavity (m); L is the actual length of neck (m); R is the neck radius (m); C is the speed of sound (M / s)
the perforated plate sound absorption structure is composed of a certain depth of airtight cavity behind the perforated plate, which is a commonly used sound absorption structure, equivalent to the parallel combination of a single resonator. When the frequency of the incident sound wave is the same as the natural frequency of the system, the air in the perforated part vibrates violently, which strengthens the absorption effect and causes the absorption peak to appear, which makes the sound energy attenuate. The resonance frequency f0 (Hz) of the perforated plate is:
where C is the sound velocity (M / s); L is the thickness of perforated plate (m); R is the radius of the hole (m); H is the thickness of air layer behind the plate (m); P is perforation rate (ratio of pore area to total area). Usually, if the perforation rate is more than 20%, the perforated plate will not play the role of resonance absorption
the resonant absorption band of perforated plate is narrow, and the width of absorption peak can be widened by adding a layer of porous material or textile behind the perforated plate; At the same time, a wide absorption band can be obtained by using several kinds of perforated plates with resonance peaks connected with each other. If the aperture is reced to less than 1 mm, the thickness of the plate is less than 1 mm, and the perforation rate is 1-3%, the perforated plate and the cavity behind the plate can form a micro perforated plate sound absorption structure. Because it has larger sound resistance and smaller mass than perforated plate, it is higher than perforated plate in sound absorption coefficient and sound absorption bandwidth
the sound absorption structure of thin plate with air layer behind the thin plate becomes the resonance sound absorption structure of thin plate. When the sound wave is incident, the vibration of the system is excited, and the vibration energy is converted into heat energy e to the internal friction of the plate. When the frequency of the incident sound wave is consistent with the natural frequency of the system, resonance occurs, and an absorption peak appears at the resonance frequency. The resonance frequency f0 (Hz) is:
where m is the unit area density of the plate (kg / M); H is the thickness of air layer behind the plate (m); ρ Is the air density (kg / M); C is the speed of sound (M / s). It can be seen from the formula that when the unit area density or cavity depth of the plate is increased, the absorption peak moves to the low frequency. In order to increase the damping characteristics of the structure, the porous sound-absorbing material is placed along the keel in the cavity, and the felt or sponge strip is placed at the connection between the edge of the thin plate and the keel, which can improve the sound absorption coefficient and widen the sound absorption band