387 results about "Structural dynamics" patented technology

A floating wind turbine system with a tower structure that includes at least one stability arm extending therefrom and that is anchored to the sea floor with a rotatable position retention device that facilitates deep water installations. Variable buoyancy for the wind turbine system is provided by buoyancy chambers that are integral to the tower itself as well as the stability arm. Pumps are included for adjusting the buoyancy as an aid in system transport, installation, repair and removal. The wind turbine rotor is located downwind of the tower structure to allow the wind turbine to follow the wind direction without an active yaw drive system. The support tower and stability arm structure is designed to balance tension in the tether with buoyancy, gravity and wind forces in such a way that the top of the support tower leans downwind, providing a large clearance between the support tower and the rotor blade tips. This large clearance facilitates the use of articulated rotor hubs to reduced damaging structural dynamic loads. Major components of the turbine can be assembled at the shore and transported to an offshore installation site.

A floating wind turbine system with a tower structure that includes at least one stability arm extending therefrom and that is anchored to the sea floor with a rotatable position retention device that facilitates deep water installations. Variable buoyancy for the wind turbine system is provided by buoyancy chambers that are integral to the tower itself as well as the stability arm. Pumps are included for adjusting the buoyancy as an aid in system transport, installation, repair and removal. The wind turbine rotor is located downwind of the tower structure to allow the wind turbine to follow the wind direction without an active yaw drive system. The support tower and stability arm structure is designed to balance tension in the tether with buoyancy, gravity and wind forces in such a way that the top of the support tower leans downwind, providing a large clearance between the support tower and the rotor blade tips. This large clearance facilitates the use of articulated rotor hubs to reduced damaging structural dynamic loads. Major components of the turbine can be assembled at the shore and transported to an offshore installation site.

The invention discloses a model updating method based on strain modal shape correlation. The specific steps are as follows: step 1), establishing a finite element model of a structure and analyzing the finite element model; step 2), performing experimental design and analysis; step 3), extracting a finite element simulation strain mode; step 4), performing correlation analysis: adopting a model confidence factor, and analyzing the correlation between the finite element model and the strain modal shape of an experimental test; step 5), selecting a mode to be modified; step 6), selecting a parameter to be identified; step 7), constructing a modification target; and step 8), performing modified iteration. According to the model updating method based on the strain modal shape correlation provided by the invention, by selecting an appropriate unit type, the obtained finite element model of the structure provides a reference model for strain response calculation; by selecting an appropriate strain mode to be modified, parameters to be modified and an optimum design method, the modified finite element model can better reflect the strain response of the structure; and the accurate finite element model is beneficial to the subsequent structural dynamic optimization design based on the finite element model, and the development of structural health monitoring and structural response prediction and so on.

The invention discloses a structural finite-element parametric modeling method applicable to a grating-configuration rudder surface. According to the method, a mapping transformation method based on a finite element model and a parametric approach to achieving conversion from two-dimensional mesh parameterization division to three-dimensional appearance expansion are adopted. The method includes the steps of specifically conducting two-dimensional plane projection on the grating-configuration rudder surface, extracting characteristic parameters, and conducting two-dimensional parameterization division; building a mapping relation between a two-dimensional finite element mesh and a three-dimensional finite element mesh, designing a numbering rule for finite element mesh points, and achieving conversion from the two-dimensional mesh to the three-dimensional appearance expansion; by means of a high-level computer language program, implementing the structural finite-element parametric modeling procedures for the grating-configuration rudder surface. By using the method, in a conceptual design phase or a preliminary design phase, the structural modeling efficiency can be greatly increased, the costs of time and manpower are low, parameters of self-compiled programs can be adjusted quickly, analysis applicability is high, the obtained model is applicable to analytical calculation of structural vibration, structural dynamics and the like, and the method is applicable to grating-configuration rudder surfaces and grating-configuration airfoils.

The invention provides a binocular photogrammetry method of large flexible structure vibration displacement, and belongs to the technical field of flexible structure dynamic analysis and measurement. The binocular photogrammetry method of large flexible structure vibration displacement aims to solve the problem that the existing contact measurement impacts performance of a flexible structure. Firstly, industrial cameras are demarcated; then, shock excitation is conducted on the flexible structure to be tested, all the industrial cameras are controlled to be triggered synchronously through a single-chip microcomputer, and shooting of vibration displacement is conducted on the point to be tested of the flexible structure to be tested; next, images obtained by shooting of all the industrial cameras are dealt with, pixel coordinates of the point to be tested are obtained through an angular point detection algorithm, object space coordinates of the point to be tested at each point of time are obtained through a binocular three-dimensional reconstruction technology, and thus the vibration displacement curve of the flexible structure to be tested is obtained. The binocular photogrammetry method of large flexible structure vibration displacement is applied to measuring vibration displacement of the flexible structure.

The invention provides a coaxial rigid rotor coupling pneumatic elastic response analysis method, and belongs to a helicopter kinetic analysis technology. The method is characterized in that according to the operation and control characteristics of a coaxial rigid rotor helicopter, a balance equation optimization solution method is built, and an optimization solution is found according to the given target and constraint conditions. According to the characteristic of complicated coaxial rigid rotor flow field environment, a rotor flow field is calculated by using a computational fluid dynamic method based on an Euler / N-S equation; and then, the coupling pneumatic elastic response is calculated by using a computational fluid dynamic / computational structural dynamic loose coupling analysis method. The coaxial rigid rotor coupling pneumatic elastic analysis method has the advantage that when the analysis method is used, balance operation and control parameters, blade response, rotor loads and the like of the coaxial rigid rotor helicopter can be calculated. The method has good analysis precision and engineering applicability; the relying of the development process on the test can be reduced; and the design period and the development cost can be greatly reduced.

The invention discloses a synchronous monitoring system for multi-field parameters of a wind turbine. The system comprises a test bench, a wind turbine generator set, a flow field monitoring subsystem, a dynamic parameter monitoring subsystem of a rotating body structure, a dynamic parameter monitoring subsystem of a non-rotating body structure, a generator output parameter monitoring subsystem and a trigger integrated control subsystem. The flow field monitoring subsystem injects smoke into the air flow inlet end of the test bench, and the simultaneous correlation monitoring of blade tip flow fields and tip vibration displacement is achieved. The dynamic parameter monitoring subsystem of the rotating body structure collects acceleration signals and strain signals of blades of the wind turbine and conducts conversion. The dynamic parameter monitoring subsystem of the non-rotating structure achieves conversion of the acceleration signals or the strain signals of the fixed position on the wind turbine. The trigger integrated control subsystem achieves operation time sequence control of all the subsystems. By the adoption of the synchronous monitoring system, simultaneous monitoring of the wind turbine flow field parameters, the structural dynamic parameters and the generator output parameters can be achieved, and the test system support is provided for the correlation analysis among the various field parameters.

Disclosed is a structural dynamics design method of the rotor of an aerial engine. Based on the characteristics of the working status of a high propulsion ratio aerial engine, the structural dynamics design method of the rotor of the aerial engine presents the concept of thermal modal to adapt to structural dynamics design of the rotor of the aerial engine under variable working conditions. The structural dynamics design method of the rotor of the aerial engine is characterized by optimizing the parameters of the rotor and bearings, enabling the thermal modal of a rotor system to avoid the modal of the rotor under the absolute rigidity of the bearings, meanwhile, giving play to the effects of a damper and enabling the rotor system to meet the requirements of vibration standards in the thermal modal. The structural dynamics design method of the rotor of the aerial engine comprises taking the margin between the modal of the rotor with elastic bearings and the modal of the rotor under the absolute rigidity of the bearings as optimized parameters, meanwhile giving play to the damping effects of the damper to meet the dynamics requirements of the rotor system. The structural dynamics design method of the rotor of the aerial engine changes the traditional design concept of design first and checking calculation later and performs active design of the dynamics characteristics of the rotor to achieve circulating design, thereby improving the working efficiency and having significant engineering practical value.

The invention provides a continuous character gesture track recognizing method based on a structural dynamic time domain wrapping algorithm (STDW) for solving the problems in the prior art. Through the automatic cutting problem of continuous gesture tracks, extraction of angular point new characteristics, the recognition of the STDW and the processing between character gesture tracks, natural, real-time and accurate recognition on continuous character gesture tracks is achieved. Compared with the prior art, the interaction mode is more natural, the constraint of users is smaller, and the requirement of man-machine interaction is met. Compared with the traditional situation that multiple gesture actions are more diversified in type, under the condition that accuracy and real-time performance are considered at the same time, the recognition effect of an original algorithm is improved by means of the STDW formed by combining a character gesture track structure and a dynamic time wrapping algorithm, the recognition rate is increased, and the method is high in accuracy and good in man-machine interaction experience and can meet the requirement for real-time performance.

The invention provides a bridge dynamic load testing method based on neural network technology, which includes conducting statistic analysis on a large amount of existing bridge testing results, determining dynamic load response affecting parameters of a bridge structure, using the affecting parameters as an input layer to construct a neural network model, and deducing structural dynamic load response predicted value; and conducting dynamic load actual measurement on the bridge under single vehicle speed, conducting reliability inspection on neural network theoretical derivation value by using actual measurement value, obtaining dynamic response verified through the actual measurement and characteristics of the bridge structure, and judging actual states and safety performance of the bridge structure according to the dynamic response and the characteristics of the bridge. Due to the fact that the bridge dynamic load testing method combines advantages of a conventional dynamic load testing method and the neural network technology is used to optimize a testing process, bridge dynamic load testing estimation conducted by means of the method greatly reduces structural damage caused by conventional dynamic load testing and improves analysis efficiency and operability on the basis of being capable of guaranteeing accurate and reliable testing results.

The invention relates to a time frequency domain time varying structure modal parameter identification method based on a time varying common demominator model and belongs to the technical field of structural dynamics. Firstly, structural dynamics response signals measured and obtained by aircraft or spacecraft structures with the time varying characteristics under the work situations are analyzed in a time frequency mode to obtain a time relative power spectral function of non-parametric evaluation corresponding to time varying structures. Then, the time varying common demominator model is used as a parametric model of the time varying structural dynamics to evaluate to-be-evaluated parameters of the time varying common demominator model through a least squares methods of the time domain. Finally, the evaluated to-be-evaluated parameters of the time varying common demominator model is utilized to calculate the model frequency and the model damping ratio corresponding to the time varying common demominator model. The time frequency domain time varying structure modal parameter identification method based on the time varying common demominator model is suitable for model parameters recognition of time varying structure in the field of aircraft and spacecraft engineering application and has the advantages of being simple and convenient to use. Furthermore, users are low in participation degree.

The invention relates to the technical field of calculation, simulation and estimation of dynamic stress of a bearing structure of a high-speed tracked vehicle, in particular to a method for simulating and calculating dynamic stress of a vehicle body structure of the high-speed tracked vehicle. The method comprises two implementation steps of constructing a finished high-speed tracked vehicle system rigid-flexible coupling model based on a modal comprehensive method and calculating the dynamic stress of the vehicle body structure based on a modal stress recovering method. An integrated rigid body suspension system model, a propelling system model and a high-speed tracked vehicle rigid-flexible coupling complex dynamics model with a vehicle body structure finite element model are built by adopting a modal comprehensive technology, and the characteristics of the coupling dynamics between the vehicle system dynamics and the structure dynamics are accurately reflected. The method can obtain structural edge load at a designing and development stage of the high-speed tracked vehicle and simultaneously obtain structure dynamic stress, and provides effective means for design and improvement of a system structure of the high-speed tracked vehicle.

The invention relates to a method for identifying a time-varying structure modal frequency based on a time frequency distribution map. The method comprises the following steps of: 1, acquiring structural dynamic response signals of an identified structure and setting sampling time and sampling frequency; 2, performing time frequency transformation on each response signal to obtain a time frequency distribution coefficient and drawing the time frequency distribution map; 3, writing the time frequency distribution coefficient into a corresponding energy distribution form and rearranging the coefficient as a column vector; 4, determining a time frequency distribution region corresponding to the response containing each-order time-varying modal frequency for identification according to the time frequency distribution map of each response; 5, extracting parts with the highest energy time frequency distribution corresponding to the each-order time-varying modal frequency from the time frequency distribution map by using proper time frequency window functions respectively; 6, estimating the each-order time-varying modal frequency by using a weighting nonlinear least square method; and 7, performing error analysis on the identification result. The method has the advantages of clear physical significance, simple and convenient use, high applicability and high anti-interference capability.

The invention discloses a bridge rapid test and evaluation method based on temperature change. Structural dynamic response of the bridge structure under different temperature conditions is acquired through sensors arranged on the bridge; and the basic dynamic characteristic parameters of the bridge structure under different temperature conditions are identified by using a dynamic signal analysis method and substituted in the mapping relationship between the vibration mode scaling factor and the external temperature conditions and the dynamic parameters to obtain the vibration mode scaling factor of the bridge structure and the displacement flexibility matrix deep parameters under different temperature conditions so as to predict deformation of the structure under any static load and perform damage identification and long-term structural performance study. The disadvantages that the conventional impact vibration test requires an artificial excitation device and requires to close the traffic can be overcome, and the disadvantages that the present environmental vibration test method cannot effectively support bridge structure safety evaluation can also be overcome so that the method has the advantages of less test time without closing the traffic, high accuracy and high anti-noise capacity.

The invention discloses a control method and a system for suppressing boom vibration. The method includes the following steps: receiving current boom gesture and current velocity vectors and the current gesture includes the length vectors and the angle vectors, determining mass matrix and stiffness matrix corresponding to the current gesture according to the current gesture, plugging the mass matrix and the stiffness matrix into a structural kinetic equation of the boom, conducting active vibration control according to the structural kinetic equation, figuring out feedback gain vectors, and controlling the hydraulic pressure exerted on the boom according to the feedback gain vectors and the current velocity vectors to suppress the boom vibration. With the technical scheme, the feedback gain vectors under the current gesture can be obtained through variable gesture modeling, the hydraulic pressure can be controlled through the feedback of the feedback gain vectors and a velocity sensor, and the boom vibration can be effectively suppressed.

The invention provides a tunnel structure damage identification device based on a vibration response test. A vibration pulse signal is excited by a pulse excitation device, structural vibration response is collected by a high-precision acceleration sensor, and an extraction structure transmits function information to identify the tunnel structure damage (namely, change of structural dynamic properties); the damage identification device mainly comprises acceleration sensors, the pulse excitation device, a central control computer, a signal collector, a horizontal telescopic arm and a matched circuit; an operator controls the development length of the horizontal telescopic arm through an operation instruction to determine a detection range. The acceleration sensors on both ends of the horizontal telescopic arm are fixed on the surface of the structure, the pulse excitation device is controlled to apply pulse excitation on the structure to collect the acceleration response of the structure, and the central control computer is used for carrying out the structure damage identification through tunnel structure damage identification system software.

The invention relates to a non-contact type structural dynamic response measurement method for a wind tunnel test. The method includes the following steps that: A, a wind tunnel test model is built, and the parameters of a high-speed camera are debugged; B. a binocular system is calibrated; C, a continuously adaptive mean shift algorithm is adopted to realize a target dynamic tracking task; and D, a multi-structure space three-dimensional dynamic displacement is automatically measured and stored.

The invention discloses an output-only linear time-varying structure modal parameter identification method and belongs to the technical field of structural dynamics. Firstly, a cost function of a least squares support vector machine vector time-varying autoregressive model is deduced; secondly, a function space is built by means of a Wendland compactly supported radial basis function; a regular factor is determined through the non-parameter method based on Gamma testing, and a basis function width reduction coefficient is given on the basis of actual experiences; a time-varying autoregressive model order is determined according to the Bayesian information criterion and the Akaike information criterion; a function space order is determined according to the ratio of residual sum of squares to sequence sum of squares; finally, the matrix expression of the least squares support vector machine vector time-varying autoregressive model is solved according to the cost function, modal frequency of a system is solved according to a time freezing method, and linear time-varying structure modal parameter identification is finished. The method can improve calculation efficiency, improves system robustness, and is widely used in linear time-varying structure modal identification in structural dynamic engineering application.

The invention relates to an in-plane-control-based active vibration control method for a wrinkled film. On the basis of the analysis on the influence on dynamic characteristics of a film structure bya wrinkle form, a dynamic model of a wrinkled film is established; according to a modal superposition method, a space vector based on a natural mode of vibration is obtained and dynamic models of thewrinkled film under different loads are established; condensation polymerization is carried out on the dynamic models according to contributions to system vibration deformation by all orders of modes,so that a control-oriented film structural dynamic model is established; and with a model reference adaptive controller, a PID-MRAC control method based on in-plane-control multi-model switching is proposed. According to the method provided by the invention, no actuator needs to be pasted on the surface of the film; the out-of-plane vibration of the film is suppressed effectively; the characteristics of the film are not affected; the high stability of the film structure is ensured; and compared with the conventional PID control method, the in-plane-control-based active vibration control method enables the vibration time to be shortened by about 39.7%.

Disclosed is a structural dynamic design method for a high-pressure rotor of an aircraft engine. The relationship between high-pressure rotor model design parameters and rotor vibration characteristics is determined, so that the design method and criterions are provided for dynamic design of the high-pressure rotor, and the method is of great guiding significance to the design of the high-pressure rotor of the aircraft engine. The method includes: establishing a dynamic model and a dynamic equation of the high-pressure rotor to obtain a nondimensionalization characteristic equation; introducing an equivalent critical speed, and determining a two-order critical speed range of a high-pressure rotor system according to the equivalent critical speed; changing a conventional equilibrium amount configuration method by configuring residual disequilibrium amount phases; configuring a ratio of rotor pole rotation inertia to mass center rotation inertia in design according to a specific design objective; establishing configuration criterions for a rotor bearing stiffness ratio. A conventional design process is changed, structural dynamic active design of the high-pressure rotor is realized, the design process is optimized beneficially, design cycle is shortened, and the method has important construction value.

The invention discloses a zero (micro) gravity suspension method and device with a zero-frequency vibration isolation characteristic and relates to the technical field of zero gravity or micro gravity environmental simulation in the outer space. The problems of space ground simulation, low-frequency and ultralow frequency vibration isolation and the like are solved. The series of suspension devices can be each substantially seen as being formed by connecting a vertical spring and a vertical spring which support gravity support through a connecting rod and a suspended object. According to the basic principle, support force which is equal to the magnitude of the gravity and opposite to the direction of the gravity is provided through geometric nonlinearity arrangement of a spring connecting rod mechanism, so that the resultant force acted on the suspended object within the device design range is zero, and thus the suspended object is in the suspension state. The zero (micro) gravity suspension device can be used for space zero and micro gravity environments including ground simulation experiments such as spacecraft docking, large space flexible structure dynamics performance tests and astronaut training. Through the suspension characteristics of the zero (micro) gravity suspension method device, the problems of low-frequency and ultralow frequency vibration isolation can be solved effectively, and the defect that through a traditional vibration isolation theory, system resonance is difficult to be avoided is overcome.

The invention discloses a hardware-in-loop testing platform used for a wind power generation electric variable-pitch system, which comprises a platform master control system, a load simulation converter cabinet, a load motor and a human-computer interaction module, wherein the platform master control system comprises an upper computer and a lower computer, and the load simulation converter cabinet comprises a multiaxial servo driver; and the human-computer interaction module is connected with the upper machine. The platform master control system comprises a fan master control system, a variable-pitch control system, an aerodynamic module, a structural dynamic module and a load torque simulation module, and the variable-pitch control system is communicated with the fan master control system through a CAN (Controller Area Network) bus. The testing platform can effectively test the response characteristics of the electric variable-pitch system under wind speed stimulation, the debugging and maintaining cost of the variable-pitch system of a wind turbine generator is reduced, the development time cycle is greatly shortened, and the testing efficiency is increased.

Apparatus and method for analyzing data collected from a physical structure for purposes of damage detection or structural health monitoring. The invention attempts to detect signs of nonlinear distortion, which is known to result from most forms of structural damage. The invention uses generic models that can be adjusted to fit arbitrary data to explore the relationship between data sets collected from different locations on or near the physical structure and to capture and detect nonlinearity with those models when it exists in the structural dynamics.

The invention relates to a method for testing the steering performance of a tracked vehicle. The method comprises the following steps of testing parameters related to the performance of the vehicle in an actual steering test through a testing system, obtaining changes of kinematic parameters and dynamic parameters in the steering process of the tracked vehicle, verifying the reasonability and accuracy of an established steering kinematic and dynamic model of the tracked vehicle, the reasonability of a steering radius correction coefficient formula and the reasonability of a steering angular speed correction coefficient formula, checking the variation range of a steering radius correction coefficient and the variation range of a steering angular speed correction coefficient under general ground conditions, analyzing and verifying the influences of various factors on tractive force and braking force of tracks on the two sides of the tracked vehicle, and examining the variation trend of the kinematic parameters and the variation trend of the dynamic parameters. The various steering parameters generated during steering are obtained at the same time, coupling characteristics between vehicle system dynamics and structural dynamics are accurately reflected, and effective measures are provided for the system structure design, demonstration and improvement on the tracked vehicle.

The invention relates to a flight flutter model, and the model comprises an elastic model, a power system, a flight control system, a taking-off and landing system, and a data collection system. The elastic model, the power system, the flight control system, the taking-off and landing system and the data collection system form a flutter model which can fly in the air. The model simulates the structural dynamic characteristics of an airplane, can accurately reflect the rigid motion characteristics of the airplane, can verify the conventional flutter characteristics, rigid and elastic coupling flutter characteristics and aeroservoelastic stability. The model is high in safety, is wide in application range, and is low in cost.

The invention discloses a random vibration analysis and calculation method of free body multi-point correlated pulsating pressures. The method comprises the steps that firstly, a finite element discrete model of free body structure dynamics is established; secondly, modal analysis of a free body is conducted; thirdly, a dynamic equation of rigid body motion and elastic motion of a free body structure is established; fourthly, corresponding modal of the pulsating pressures participates in the calculation of coefficients; fifthly, the random vibration power spectral density response calculation is conducted on the rigid body response, the elastic response and the coupling response under the pulsing pressure effect; sixthly, root mean square equivalent response of the whole structure is calculated. The random vibration analysis and calculation method has the advantages that the proposed method is fast in calculation speed, easy to expand and large in computation scale and the like, meanwhile considering the influence of the rigid body modal and the elastic modal, the response characteristic of an aircraft reentering a flying process is more accurately simulated, and the fast vibration response can be solved for the fine finite element model of an aircraft structure.

The invention relates to a structural dynamics analysis method and system for an inflatable reentry vehicle considering nonlinear influences, and belongs to the field of areospacecraft reentry and return. According to the structural dynamics analysis method and system for the inflatable reentry vehicle considering nonlinear influences, characteristics of statics, modality and thermal modality of the inflatable reentry vehicle under influences of different inflation pressures, film thicknesses, hypersonic flow field pressures, temperatures and other nonlinear factors can be accurately described. Calculation methods of fluid-solid unidirectional coupling and thermo-solid unidirectional coupling are successfully introduced into a nonlinear structural dynamic simulation module, combined with an actual trajectory of the inflatable reentry vehicle, and an influence rule of changes of internal inflatable gas parameters on characteristics of statics, modality and thermal modality of the inflatable reentry vehicle is truly expressed. The structural dynamics analysis method and system for the inflatable reentry vehicle considering nonlinear influences have the advantages that the problem ofthe existing study on structural dynamics of inflatable reentry vehicle that the consideration of flow field non-linear and material none-linear is insufficient will be hopefully solved, and valuablereferences can be provided to shape-preserving design and structural safety design of the inflatable reentry vehicle.

The invention discloses an oil-drive variable-pitch quad-rotor unmanned aerial vehicle which comprises a power-transmission system, a rotor-operation system and a rack system. Both the rotor-operation system and the power-transmission system are fixed to the rack system. The oil-drive variable-pitch quad-rotor unmanned aerial vehicle mainly solves the problems that a conventional electric multi-rotor vehicle is poor in wind resistance and the like, the load is small, and the flight time is short and the problems that purchasing, using and maintaining cost is high and the use and maintenance technical doorsill is high due to complexity of the mechanical structure, the structural dynamic characteristic, the flight dynamic characteristic, the aerodynamic characteristic and a flight control system of a conventional helicopter.

The invention belongs to the field of aircraft structural dynamics, and relates to a method for analyzing influences of wing deformation and vibration on aircraft transfer alignment. The method is characterized by including the following steps: (1) building a full-aircraft structure dynamical model, (2) building a full-aircraft unsteady aerodynamic model, (3) building a transfer relationship between plug-ins and inertial navigation, and (4) obtaining a primary-secondary inertial navigation error fitting empirical formula. The method has the advantages that speed errors and angular speed errors generated between the primary inertial navigation and the secondary inertial navigation of an aerial movable platform are analyzed through the built aircraft structure dynamical model, then the errors are eliminated through filtering, and in this way, the transfer alignment time of the primary inertial navigation and the secondary inertial navigation during guided missile launching can be shortened to a great degree.